PESTICIDE RESIDUES IN FOOD - 1979 Sponsored jointly by FAO and WHO EVALUATIONS 1979 Joint meeting of the FAO Panel of Experts on Pesticide Residues in Food and the Environment and the WHO Expert Group on Pesticide Residues Geneva, 3-12 December 1979 CYPERMETHRIN IDENTITY Common Name: Cypermethrin (BSI). Chemical Name (IUPAC): [S,R]-alpha-cyano-3-phenoxybenzyl-2,2-dimethyl [1R,1S, cis, trans]-3-(2,2-dichlorovinyl) cyclopropanecarboxylate. Synonyms: WL 43467 (Shell), PP383 (ICI), CCN52(ICI), NRDG 149, RIPCORD(R) (Shell), CYMBUSH (R) (SHELL), CYMBUSH (R) (ICI) Empirical Formula: C22H19O3NCl2 Structural Formula:Molecular Weight: 416 Technical Material: Contains not less than 90% w/w cypermethrin which is a racemic mixture of the 8 isomeric forms with a cis: trans isomer ratio of approximately 40:60 Physical Form Technical material is a viscous yellow liquid. Density: 1.12 g/ml at 22°C. Thermal Stability: Thermal analysis has shown that at a temperature of 259°C slow weight losses occur accompanied by negligible heat of reaction indicating high thermal stability. Solubility: Water 0.009 mg/l. Hexane 103 g/l. Acetone, cyclohexanone, ethanol xylene and chloroform 450 g/l. Volatility: relatively non-volatile Vapour pressure: 5 × 10-6 N/m2 at 70°C Flash point: 80°C Formulations: Currently available in emulsifiable concentrates ranging from 25-400 a.i. g/l. Several formulations for ultra low volume applications containing 8-75 g/l are also available. EVALUATION FOR ACCEPTABLE DAILY INTAKE BIOCHEMICAL ASPECTS Absorption, Distribution and Excretion Studies were performed in vivo on a wide range of mammalian species and in vitro on isolated cell fractions to define the pharmacokinetics of cypermethrin. In general, a wide range of studies have shown that cypermethrin is rapidly absorbed, distributed to a variety of tissues and organs, metabolised and rapidly excreted from the body. Studies have been performed to evaluate the pharmacokinetics in mice, rats, dogs, sheep and cows. Mice Groups of male mice were orally administered the cis or trans isomers of cypermethrin dissolved in methoxytriglycol at dose levels of 7 mg/kg with the cyclopropyl-14C isomer and 8 mg/kg with the benzyl-14C isomer. Results suggest that the proportion of cypermethrin which was readily absorbed following oral dosing was rapidly eliminated in the urine of mice. Absorption from the gastrointestinal tract was more rapid with the trans isomer than with the cis as evidenced by high radioactivity levels of the cis isomers in the faeces within the first few days of the study. The rate of urinary excretion of cypermethrin isomers labelled in acid and alcohol portions of the molecule was very similar with the major quantity of radioactivity being eliminated from the body within three days. Tissue residues after three days were low. Adipose tissue was found to retain small quantities of the radioactivity in concentrations higher than that noted for most other tissues (Hutson, 1978a). To evaluate the elimination of cypermethrin and its metabolites from animal tissues following oral administration, groups of male mice were administered cypermethrin at dose levels approximating 9 mg/kg body weight (14C-benzyl, cypermethrin). In contrast to data from other tissues, the rate of elimination of cypermethrin from adipose tissue of mice was relatively slow with a half-life of approximately 10-20 days. Unchanged cis-cypermethrin was the only chemical residue identified in adipose tissue. There was little change in the residue during the last half of the 42-day trial following the relatively rapid elimination during the first three weeks suggesting possible long term storage and buildup of residue in adipose tissue (Crawford and Hutson, 1978a). Rat Groups of male and female Wistar rats were orally administered cypermethrin (14C benzyl, cis-isomer) at the dose level of 2.4 mg/kg for females and 1.8 mg/kg for males. Cypermethrin was administered in corn oil solution and animals and tissues were monitored over a period of eight days. Excretion was rapid with both sexes. There was a significant sex difference in the rate of excretion with male rats excreting a substantially larger portion of the radioactivity in urine than females over the first 24 hour interval. However, there were no substantial differences in the overall rate of elimination by both males and females when data were evaluated over the total 8-day period of the test. The residues of radioactivity in the tissue of animals of both males and females sacrificed at various periods over the 8-day interval showed a small residue in a variety of tissues. While the tissue residue in blood, liver, kidney, etc. was rapidly depleted over the test interval, concentrations of cypermethrin in adipose tissue were relatively stable over the 8-day trial (Crawford, 1976a). Groups of male and female rats were orally administered cypermethrin 14C-benzyl, trans-isomer) at dose rates of 2.4 mg/kg for males and 3.0 mg/kg for females. Again, excretion was rapid with both sexes with approximately 95% of the administered dose excreted within 48 hours. In contrast to that noted with the cis-isomer, there appeared to be no sex differences in the elimination of the trans-isomer. Residues in adipose tissue of females was somewhat higher than noted in adipose tissue of males. The observations are consistent with the suggestion that the trans-isomer is metabolised faster than the cis-isomer (Crawford, 1976b). Groups of rats were administered cypermethrin (1:1 cis: trans-isomer ratio, 14C-cyclopropyl) at dose rate of 1 mg/kg for males and 2 mg/kg for females. Rapid elimination of cypermethrin was observed with a substantial difference noted in the 24-hour urinary excretion in males and females. Females excreted considerably more radioactivity in urine over the first 24 hours. At the end of 72 hours urinary and faecal excretion in both sexes was approximately the same. Small quantities of radioactivity were expired as 14CO2 which suggested some metabolic breakdown of the cyclopropyl ring. At the end of three days, tissue concentrations in liver, kidney muscle, brain, blood, skin and remaining carcass were relatively low. Intestinal content was somewhat higher in males than in females ranging from 3 to 9% of the administered dose. Low residue concentrations, which never exceeded 1 ppm, were observed in fat (Crawford, 1977). The elimination pattern of cyclopropyl- and benzyl-labelled cypermethrin appears to be the owns in both males and females. Females absorb and metabolise the trans-isomer faster than males and males absorb and metabolise the cis-isomer faster than females (Crawford, 1976b). In a further study to resolve the residual nature of the residues of cypermethrin in adipose tissue of rat, Crawford and Hutson (1978b) again found that the cis-isomer was relatively stable in adipose tissue. Administration of 14C-benzyl cypermethrin (cis-isomer) at a dose of approximately 2 mg/kg to female rats resulted in a residue of approximately 0.3 ppm in the fat eight days after a single oral dose. Further studies through 42 days following dosing were performed to evaluate the half-life of the cis-isomer in fat and the total elimination pattern. At the end of 42 days, residues were observed in fat which were approximately 10% of those concentrations noted at eight days. There was a 90% loss of the material from fat over the 8-42 day interval during which time samples were taken. From these data with rats, a half-life of approximately 20-25 days was estimated with respect to removal of residues from fat following a single oral dose. These half-life values are somewhat longer than those noted with the mouse. Dogs Groups of male beagle dogs were administered 14C-benzyl cypermethrin and the individual 14C-benzyl labelled cis- and trans-isomers of cypermethrin, orally, at a dose of 2 mg/kg. Elimination of radioactivity from all animals was rapid although differences in data from individual dogs precluded a complete evaluation of the rate of elimination. Differences in the rates of elimination of the individual dogs in the study may have been due to differences in absorption as cypermethrin was given orally in a capsule with no solvent. Tissue residues observed 4 days after oral administration of cypermethrin were extremely low. The vast majority of the excreted material was observed in faeces (80%) with urine containing only 11% of the administered dose. As with other species, small residues of cypermethrin were observed in fat, approximating 2% of the administered dose (this residue was estimated to be 0.3 ppm based upon total adipose tissue of the dog) (Crawford, 1979b). Sheep Sheep were administered cypermethrin dermally (962 mg/animal administered in acetone) or orally (without solvent) in gelatin capsule at a dose of 4 mg/kg body weight. Following dermal administration, cypermethrin was not readily absorbed (less than 0.5% of the administered dose was observed in urine within 24 hours and 2% over the six day test interval). Little radioactivity was found in the liver and kidney of dermally-treated sheep. Tissue residues in renal and subcutaneous fat was found to be similar to those noted with other animal species and was qualitatively identified as cypermethrin. Elimination of cypermethrin from the orally-dosed sheep was rapid with 61% of the administered dose being eliminated within 48 hours (41% of the dose in urine and 20% of the dose in faeces). The tissue residue pattern in sheep following oral administration was similar to that noted with other mammalian species. Low levels of cypermethrin were noted in various tissues, including renal and subcutaneous fat (Crawford and Rutson, 1977a). Cows Cypermethrin (1:1, cis:trans-isomer, 14C-benzyl-label) was orally administered to lactating cows over a period of three weeks at a dietary dosage of 0.2 ppm. Urine, faeces and milk residues were examined over the course of the study and at the conclusion of the three week dietary interval, animals were sacrificed and tissue residues examined. Elimination of radioactivity in urine and faeces rapidly reached an equilibrium within 2-3 days. Radioactivity was eliminated in the urine and faeces predominantly and accounted for the major quantity of cypermethrin residues. Small quantities of radioactivity were noted in milk with a total radioactivity residue approximating 0.5% of the administered radioactive cypermethrin. Tissue residues were extremely low with notable residues in bile and fat as well as in the liver and kidney. There were no detectable residues in muscle, blood or brain. Analysis of the milk fat showed that a high percentage of the radioactivity was present in this portion of the milk. Residues in the milk fat or cream sample were reflective of the lipoidal nature of cypermethrin, with residues concentrating in fatty tissues (Hutson and Stoydin, 1976). In a further study to obtain information on the metabolic distribution of cypermethrin in cows, lactating cows were treated for 7 days at a dietary concentration of 5 ppm. Urine, faeces, and milk were analysed and at the conclusion of the feeding trial, all animals were sacrificed and tissue residues were determined. As in the previous study, elimination occurred rapidly after the onset of dosing with the major route of excretion being via urine and faeces. Tissue residues were extremely low with measurable amounts observed in blood, liver, kidney, bile and adipose tissue. Total milk residues amounted to approximately 0.2% of the applied cypermethrin, with the largest proportion of the residue again found in milk fat (Crawford, 1978). Metabolism The metabolic fate of cypermethrin was investigated in a variety of mammalian species and was determined to be relatively similar in the different species. The major metabolites are derived by cleavage of the ester linkage followed by subsequent metabolism of both the acid and alcohol fragments and conjugation and excretion of the fragments. Studies on the metabolic fate of both cis- and trans-cypermethrin administered orally to rats have shown that cypermethrin is rapidly cleaved at the ester bond to yield the cyclopropanecarboxylic acid and the 3-phenoxybenzyl alcohol moiety. The latter is rapidly oxidised to 3-phenoxybenzoic acid and conjugated prior to elimination. Major reactions occurring with the cyclopropanecarboxycyclic acid include, in part, oxidation at the methyl groups and apparent lactone rearrangement prior to conjugation and elimination. Hydroxylation of the phenoxybenzoyl moiety has been noted to occur in at least two positions prior to conjugation and elimination. Rats and mice metabolised cypermethrin in a similar fashion. In mice, a substantial portion of the phenoxybenzoic acid was conjugated with taurine as well as with glucuronic acid (Hutson, 1977). Oxidation has been noted to occur in the 4'- position of phenoxybenzoic acid. Following oxidation, the molecule is conjugated as a sulfate and excreted. A portion of unconjugated hydroxylated phenoxybenzoic acid was also excreted. Hydroxylated cypermethrin was observed in mouse faeces suggesting that hydroxylation may occur prior to ester cleavage (Hutson, 1978b). Shono, Ohsawa, and Casida (1978), using mouse liver microsomal preparations, showed that hydroxylation of the phenoxybenzyl moiety at positions other than the 4'- position can occur. Small amounts of the 5- and 6-hydroxy phenoxybenzyl derivatives were also observed. Both cis- and trans-isomers were rapidly metabolised by cleavage of the ester bond and aromatic hydroxylation at the 4'-position of the 3-phenoxybenzyl alcohol moiety. In rats, approximately half of the administered cypermethrin was excreted as sulfate conjugates of the hydroxylated phenoxybenzoic acid. Phenoxybenzoic acid was also excreted free and conjugated with glycine in contrast to the conjugate pattern noted in mice (Crawford and Hutson, 1977b, 1978c). In studies with cyclopropanecarboxylic acid-labelled cypermethrin, hydroxylation of the methyl groups on the cyclopropane ring occurred to a limited extent. Oxidation was believed to have occurred following ester cleavage. While most of the radioactive metabolites were found in the urinal a small quantity of hydroxylated metabolites were eliminated via the biliary-intestinal-faecal route suggesting absorption and re-distribution through the bile to the faeces. In both rats and mice as well as other species, ester cleavage is rapid. There is quantitative and qualitative evidence to suggest that the cis-isomer is more stable yielding a larger variety of hydroxylated products prior to ester cleavage while the trans-isomer yields a wider variety of hydrolytic products which in part are oxidised following the ester cleavage. The acid fragment is conjugated predominantly with glucuronic acid an a ß-glucuronide. Conjugated cyclopropanecarboxylic acid derivatives in urine were identified as glucuronides have a relative resistance to the action of ß-glucuronidase. ß-Glucuronides formed from these acids are generally of the ester type readily cleaved by mild acid hydrolysis. Thus, treatment of urine with methanol and sulfuric acid will convert both the free acid and the acid glucuronide into a methyl ester. The methyl ester of the carboxylic acid has been shown to be volatile and analytical losses may occur with this compound. The alcohol fragment, the alpha-cyano-3-phenoxybenzyl alcohol, is readily oxidised metabolically to the benzoic acid, conjugated and excreted. Alcohol conjugates with glucuronic acid are generally ether derivatives, stable to acid and enzymatically hydrolysable. The phenoxybenzyl moiety of cypermethrin has been found to form both ester and ether ß-glucuronides. Thus, the results of the studies with both rats and mice suggest that most of the excreted metabolites of cypermethrin are hydrolysis products, although hydroxylation of the intact ester has been reported. Hydroxylation of the methyl groups attached to the cyclopropane ring has also been reported. There was no evidence of metabolism at the 2,2-dichlorovinyl moiety. Evidence exists that the cis-isomer is somewhat more resistant than the trans-isomer to hydrolysis. In all cases, only small amounts of hydroxylated metabolites with the intact ester bond were observed with the cypermethrin. The metabolic fate of cypermethrin in dogs was qualitatively similar to that observed with other species with the exception being conjugation reactions of several metabolites. As with other species, cypermethrin is rapidly metabolised by cleavage of the ester bond and by hydroxylation of the phenoxybenzyl moiety at the 4' position. Sulfate conjugation of the hydroxylated benzoic acid was reported. Additionally, a major urinary metabolite was identified as the 3-phenoxybenzyl glycine. Studies on the metabolic fate of 3-phenoxybenzoic acid in dogs revealed a metabolic pattern of oxidation and conjugation similar to that noted with cypermethrin (Crawford, 1979a and 1979c). In cows, the major urinary metabolite of cypermethrin ( 14C-benzyl) was the glutamic acid conjugate of the 3-phenoxybenzoic acid (Crawford, 1978). The cyclopropanecarboxylic acid moiety was hydroxylated and/or conjugated with glucuronic acid prior to excretion. 3-Phenoxybenzoic acid has been observed as a major metabolite of cypermethrin in all species studied. Residues of cypermethrin in rat skin (<3% of the dose) were noted after oral administration. Further studies to define the skin residue were performed using 14C-3-phenoxybenzoic acid administered orally to rats as seven consecutive daily doses. The radioactive metabolites in skin were identified as predominately 3-phenoxybenzoic acid and a small quantity of glyceryl dipalmitate esters of 3-phenoxybenzoic acid (Crawford and Hutson, 1979). Further studies were performed in rats of the metabolism of 3-phenoxybenzoic acid and a glucoside conjugate isolated from plant tissue. 3-Phenoxybenzoic acid was oxidised at the 4' position of both aromatic moieties and to a minor extent at the 6' position of the benzoic acid moiety. Excretion occurred as conjugates, predominantly the 4-hydroxy-3-phenoxybenzoic acid-O-sulfate and 3-phenoxybenzoic acid. Additionally, other hydroxylated derivatives and conjugates of these oxidation products were observed. The excretion pattern of the glycoside conjugates of 3-phenoxybenzoic acid was qualitatively and quantitatively similar to that observed with 3-phenoxybenzoic acid suggesting rapid hydrolysis and availability of plant metabolites following oral administration (Crawford, 1978). Effects on Enzymes and Other Biochemical Parameters Preliminary evidence suggested that an increase in the activity of certain lysosomal enzymes in peripheral nerves and deficits in behavioural functioning tests could serve as indicators of peripheral nerve damage. During Wallerian degeneration, the activity of such enzymes as ß-glucuronidase and ß-galactosidase as well as other enzymes in nerve preparations were shown to be increased significantly (Dewar, 1977a). Cypermethrin (1:1 cis:trans) was administered to male and female rats at dose levels ranging from 25 to 200 mg/kg/day for five consecutive days by oral intubation as a 10% W/V solution in DMSO. A dose related functional deficit was observed when the mean slip angle test and the landing foot spread test were applied to the animals. The deficit was maximal from 6 to 14 days after the beginning of treatment and complete functional recovery occurred within four weeks. Substantial variation in data from the landing foot spread test was noted. Data were inconsistent over the course of the study. ß-glucuronidase activity was increased in a dose-dependent fashion in both males and females. The results suggest that cypermethrin produced a primary axonal degeneration, readily measurable 28 days after treatment as an increase in ß-glucuronidase activity and in deficits in specific behavioural-function testing of rats (Dewar, 1977b). When further studies were performed on the biochemical indices of nerve degeneration to compare results with known degenerating compounds (methyl mercury), it was observed that the changes in ß-glucuronidase and ß-glucuronidase activity were considerably smaller and less reproducible than those obtained following methyl mercury poisoning (7.5 mg/kg/day for 7 days). In comparison of central versus peripheral nerve damage, there was no evidence that the trigeminal nerve was more sensitive to the effects of cypermethrin than the sciatic and posterior tibial nerves. At near lethal doses of cypermethrin biochemical changes in the trigeminal nerve were consistent with those of Wallerian degeneration. The changes were similar qualitatively to those seen with methyl mercury, but were quantitatively much less intense (Dewar and Moffett 1978a). Electrophysiological studies were performed to determine whether acute or subacute intoxication with cypermethrin produced changes in the conduction velocity of slower fibres in peripheral nerves or alterations in the maximal motor conduction velocity. There was no evidence to suggest that cypermethrin, at doses that induced severe clinical signs of intoxication, including ataxia, had any effect on maximal motor conduction velocity or conduction velocity of the slower motor fibers in peripheral nerves. Doses used in the study ranged from a single dose of 200 mg/kg to 7 consecutive doses of 150 mg/kg followed by 2 doses of 400 mg/kg. At near-lethal doses there were no effects noted on conduction velocity in the slower motor fibers of the sciatic nerve and tail or on the maximal conduction velocity, even in the presence of clinical signs of acute intoxication and at dose levels where previous studies had shown functional degeneration. These electrophysiological findings are reflective of motor function which would suggest that the physiological and functional deficits observed as a result of acute intoxication may be primarily sensory in nature (Dewar and Deacon, 1977). SPECIAL STUDIES ON REPRODUCTION Dominant Lethal Studies Mice Groups of male mice (12 mice/group, 36 mice were used as controls) were administered a single dose of cypermethrin dissolved in dimethyl sulfoxide at dosage levels of 0, 6.25, 12.5 and 25 mg/kg body weight or 5 successive daily oral doses of 0, 2.5 and 5.0 mg/kg. Following dosing, each male was caged with 3 virgin females for 7 days. The mating procedure was repeated weekly over an interval of 8 weeks in a standard dominant lethal test. Females mated to males treated with 5 daily oral doses of 2.5 mg/kg and those mated to males receiving a single dose of 12.5 mg/kg showed a significant reduction in the incidence of pregnancy during the second and third week respectively of the onset of treatment. This did not occur with other either higher or lower dosed groups or at other intervals. In females, mated to males treated daily with doses of cypermethrin a significant reduction in foetal implants was observed during the second week of mating. Early foetal deaths were increased in the second week at 5 mg/kg. No such increases occurred in any other weekly interval or any other dosed group. Thus, multiple administration of cypermethrin on five successive days induced a significant reduction in foetal implants during the second week of mating and a marginal increase in early foetal deaths at the same time interval. To evaluate the potential (noted above) for a dominant lethal effect, a second experiment was performed. Groups of male mice (12 mice/group, a control group consisted of 36 mice) were administered five daily oral doses of cypermethrin at levels of 0, 2.5, 5.0, 7.5 and 10 mg/kg (in dimethyl sulfoxide). Following dosing each male was mated with three virgin females for four days and subsequently provided with virgin females every four days for a period of three weeks. Female mice were examined for evidence of dominant lethality 13 days after mating. In addition, 40 males of proven fertility were dosed for five successive days at the same dosage levels, 0, 2, 5, 5.0, 7.5 and 10 mg/kg. These animals were also mated with four virgin females on four successive days for a period of three weeks. Four animals from each group were sacrificed for histological examination of the testes and epididymis on days 1 and 7 after the final dosing. In contrast to the previous trial, no reduction in foetal implants was noted in any of the animals mated with cypermethrin-treated males. The number of early foetal deaths was marginally increased at the highest dose level in the 12-16 day interval after dosing and in the first 4 day period after treatment with 7.5 mg/kg males. In the groups of animals examined histologically, no abnormalities were detected in the testes and epididymis and there were no observable histological differences between any of the test groups and the controls (Dean et al., 1977). Rat Groups of rats (30 male and 30 female rats/group) were fed cypermethrin in the diet at concentrations of 0, 10, 100 and 500 ppm for five weeks after which they were mated to initiate a standard three generation, 2-litter per generation, reproduction study. After the selection of the second litter as parents for the following generation, the original parents were sacrificed and subjected to gross and microscopic examination. At the conclusion of the study, ten animals of each sex at the age of 21 days were also examined histologically. Calculations were made of the indices of fertility, gestation, viability and lactation. There was no mortality over the course of the study, and behaviour was not abnormal. Reduced body weight and food intake was seen at various intervals in both males and females fed 500 ppm in the diet. Reduced total weight was observed at 500 ppm in the F1A litters and reduced total weight and litter size were noted at 100 and 500 ppm in the F1B. No compound related gross or microscopic pathological findings were noted in any rats (Hend et al., 1978). SPECIAL STUDIES ON TERATOGENICITY Rat Groups of 25 pregnant rats were administered orally from day 6 to day 15 of gestation at dose levels of 0, 17.5, 35.0 and 70.0 mg/kg/day in a standard teratology bioassay. On day 21 of gestation, the animals were sacrificed and gross examination of foetuses were made, including skeletal and somatic examinations. Pre-implantation losses were evaluated based on corpora lutes, counts and implantation sites and post-implantation losses were evaluated based upon implantation sites and viable foetuses. Foetal somatic and skeletal examinations on day 21 of gestation showed no teratogenic changes that could be attributable to the treatment. There were no indications of embryotoxic or teratogenic events in the study (Tesh et al., 1978). Rabbit Groups of pregnant rabbits (20 rabbits/group, 30 rabbits were used as an additional control group) were administered cypermethrin dissolved in corn oil at dose levels of 0, 3, 10 and 30 mg/kg body weight orally from day 6 to day 18 of gestation. On day 28 of gestation the rabbits were sacrificed and examination made of live foetuses, dead foetuses, resorption sites and corpora lutea. Live foetuses were maintained for 24 hours to assess viability. Foetuses were also examined for gross somatic and skeletal deformities. There was no significant mortality or differences in weight gain during the period of gestation. There were no significant differences between control and test groups with respect to pregnancy, foetal death and survival. Although a wide range of skeletal and visceral abnormalities were found in the course of the study, there were no differences between control and test groups with respect to abnormalities. It was concluded that oral dosing at up to 30 mg/kg during the major period of organogenesis resulted in no teratogenic effects in the offspring (Dix, 1978). SPECIAL STUDIES FOR MUTAGENICITY Mice Host-Mediated Assay Groups of male mice (2-3 mice per group) were administered cypermethrin, orally, at dose levels of 0, 25 and 50 mg/kg in dimethylsulfoxide. The animals were immediately injected interperitoneally with a suspension of S. cerevisiae in a standard host mediated assay. After five hours, the mutagenic conversion rates in the yeast cells recovered from the treated animals were comparable with those of control animals suggesting that, under the terms of this assay, there was no evidence to suggest a mutagenic potential (Brooks, 1976). Microorganisms The mutagenic potential of cypermethrin on various microorganism species including: S. cerevisiae, E. coli WP2 uvr A, and S. typhimurium TA-1538 (with and without the use of a rat activation system) was examined. No increase in the mitotic gene conversion was recorded in S. cerevisiae, either in the presence or absence of microsomal oxidation. Cypermethrin, at concentrations up to 500 micrograms per plate, did not induce an increased mutation rate with E. coli or S. typhimurium TA-1538, in vitro either in the presence or in the absence of the microsomal oxidation system (Brooks, 1976). Cypermethrin did not increase the number of revertant colonies of S. typhymurium (TA-1535, TA-1537, TA-1538, TA-98 and TA-100) in the presence or absence of a mouse liver subcellular activation preparation obtained from 6 strains of PCB-treated mice. Cypermethrin was tested at dose levels up to 1 mg/plate (Suzuki, 1977). Hamster - Chromosomes Groups of Chinese Hamsters (12 males and 12 females/group) were administered orally on each of two successive days at a dose rate of 0, 20 or 40 mg/kg cypermethrin dissolved in dimethylsulfoxide. Positive and negative controls consisted of cyclophosphamide (100 mg/kg) and dimethylsulfoxide alone. In chromosome preparations of the control and cypermethrin-treated hamsters, there were no indications of abnormalities. The cylophosphamide treatment induced a significant degree of chromosomal damage (Dean, 1977). SPECIAL STUDIES ON NEUROTOXICITY Rats Cypermethrin, orally administered to rats at high acute dosage levels, produced severe clinical signs of poisoning which was accompanied by histological evidence of sciatic nerve damage. Within one day following the acute poisoning, neuropathy was evident as axonal breaks in the sciatic nerve (Carter and Butterworth, 1976). Groups of rats (10 males per group) were utilised in a paired feeding study to examine the neurotoxicological effects of high dietary levels. Rats were fed dietary levels of cypermethrin (45:55, cis:trans-isomer ratio) for 14 days at dosage levels of 0, 1250, 2500, and 5000 ppm. Growth was monitored and clinical evaluations for adverse behaviour were recorded during the course of the study. Gross pathology on tissues and organs and microscopic examination of the sciatic nerve were performed at the conclusion of the study. At 5000 ppm, mortality was observed with all rats either dying or sacrificed in a moribund condition within the first week. At 2500 ppm, 6 of 10 rats died before the conclusion of the study. There was no mortality in the low dose group. Clinical signs of neurotoxicity were characterised by an impaired ability to walk and splayed hind limbs. In extreme cases, clinical signs of ataxia and paralysis were reported. Other clinical signs included: hypersensitivity to external stimuli, gross disorientation and convulsions, the latter generally seen at high dose levels. The neurotoxic signs of poisoning observed in the 1250 ppm group after day three were spontaneously reversed by day nine when all surviving animals that were initially affected appeared to be normal. Remission of ataxia at the 2500 ppm group was also noted within 11 days of treatment. Growth reduction was observed in all animals in the study. At the lowest dose level, the rate of growth was delayed for the first few days after which time the rate was consistent with that of controls for the remainder of the study. The absolute body weight of the treated animals was, however, significantly lower than the controls at the conclusion of the two-week study. Reduction in body weight was consistent with reduction in food consumption. Ultrastructural changes in the sciatic nerve were observed in the two highest dose levels, although the number of animals examined was small. There was some evidence of axonal damage in the myelinated nerves primarily at the two highest dose groups. Changes in unmyelinated axons were not observed. In general, the histological and ultrastructural changes in the sciatic nerve, accompanied by clinical signs of poisoning, are not readily apparent at low doses. Thus, cypermethrin, at acutely toxic dietary levels,induces damage to sciatic nerves, the clinical signs of which may be reversible (Glaister et al., 1977a). Hamsters Groups of male and female Syrian hamsters were orally administered doses exceeding the LD50 in an attempt to define clinical signs of poisoning and to evaluate the histological damage to the sciatic nerve. At doses of 794 mg/kg and above, all animals showed clinical signs of poisoning including tremors, abnormal, irregular movements, and an unusual gait. As noted with rats, axon and myelin degeneration was noted in all groups treated. The lesions included swelling and breaks in the axons and clumping of myelin (Butterworth and Clark, 1977). A series of experiments were performed to further evaluate the neurotoxic potential following subacute, oral administration to Chinese hamsters. Clinical examination, functional testing and enzyme determinations using ß-galactosidase and ß-glucuronidase were performed. The functional test consists of measuring the mean slip angle where the animal is maintained on an inclined plane that steadily increases its angle until the animal can no longer maintain a stationary position. (The average angle of five replicate trials constituted the mean slip angle test.) Groups of 20 male and 20 female Chinese hamsters were orally administered at a dose of 40 mg/kg followed by a dose of 20 mg/kg for the following four days. Fifteen animals in each sex served as controls. There was extensive weight loss in all dosed groups and some mortality was observed primarily as a result of the initial administration of 40 mg/kg. There was a loss of fur and a dermal ulceration observed in the early parts of the study. This dermal occurrence was transient, disappearing rapidly after the treatments were concluded. There was significant weight loss in the initial phase of the study. However, after the last dose, the surviving animals rapidly gained weight at a rate consistent with the control animals. There were no effects noted on the mean slip angle experiment and a marginal increase in ß-galactosidase was observed in peripheral nerve. A further experiment utilising five male and five female Chinese hamsters administered cypermethrin daily for five days at dose levels of 0, 5, 10 and 20 mg/kg showed no mortality over the course of the study. There was a slower growth of the animals treated with 20 mg/kg which again was reversed at the conclusion of the treatment period. Hyperexcitability was noted in one female at the high dose level. There were no notable differences in behaviour in any of the animals. There was a significant deficit in the mean slip angle test with females showing an earlier dose-related deficit than noted in males. The females recovered from this deficit earlier than males who showed an erratic pattern of recovery. ß-galactosidase activity was increased at all dose levels three weeks after the onset of the experiment. This increase was statistically significant at the two highest dose levels. Dermal irritation and fur loss was not noted in this experiment. Sixteen male and sixteen female Chinese hamsters were administered five daily doses of 30 mg per kg of body weight or a control of dimethyl sulfoxide. Additionally eight animals of each sex were administered five daily doses of methyl mercury (7.5 mg/kg body weight) as a positive control. With cypermethrin, there was no mortality and the rate of weight gain was consistent with that of the controls. There was a transient dermal irritation in the majority of the animals accompanied by skin ulceration. This condition disappeared at the conclusion of the treatment interval. One male administered cypermethrin had an unusual gait. There was a slight deficit in the inclined plane test which was noted in the early parts of the experiment but was absent by the end of the third week. Increases in both ß-glucuronidase and ß-galactosidase were evident in peripheral nerve tissue. It was concluded that cypermethrin when administered at high subacute doses, produced changes in the sciatic nerve consistent with Wallerian degeneration. Biochemical changes were evident as increases in ß-glucuronidase and ß-galactosidase activity and clinically functional deficits were noted (Dewar and Moffett, 1978b). Hen Groups of adult hens were fed cypermethrin at a dosage rate of 1 mg/kg for five successive days. After 3 weeks, the dosing regimen was repeated. Positive (TOCP) and negative control groups were included in the study. There were no signs of delayed neurotoxicity (as generally noted with certain organophosphate esters) seen following cypermethrin treatment. TOCP induced the standard clinical and histological signs of axon and myelin disruption (Owen and Butterworth, 1977). Acute Toxicity Table 1 contains a summary of the findings of various studies on acute toxicities to a number of animals. Table 2 illustrates that the cis isomer is more toxic than the trans. Table 1. Acute Toxicity of Cypermethrin to Various Animals Species Sex Route Vehicle LD50 Reference (mg/kg) Mouse M,F Oral Corn oil 82 Coombes, Carter et al., 1976 Mouse M,F Oral Dimethylsulphoxide 138 Coombes, Carter et al., 1976 Mouse M,F Oral Aq.suspension 779b Jaggers, 1979 Mouse M,F I.P. corn oil 485 Combs, Carter et al., 1976 Rat M,F Oral Corn oil 251-992 Combs, Carter et al., 1976 Rat M,F Oral Dimethylsulphoxide 303 Combs, Carter et al., 1976 Rat M Oral Glycerol formal 200-400 Combs, Carter, et al.,1976 Rat F oral Glycerol formal app. 200 Combs, Carter et al., 1976 Rat M Oral Aq.suspension 400-800 Combs, Carter et al., 1976 Rat F Oral Aq.suspension app. 400 Combs, Carter et al., 1976 Rat F Oral Aq.suspension 4123b Jaggers, 1979 Rat M Oral Aq.suspension 3000c Jaggers, 1979 Rat (3wks) M,F Oral Dimethylsulphoxide 163 Rose and Dewar, 1978 (6wks) M,F Oral Dimethylsulphoxide 322 Rose and Dewar, 1978 (12 wks) M,F Oral Dimethylsulphoxide 526 Rose and Dewar, 1978 Rat F I.P. Aq.suspension >500b Jaggers, 1979 Rat M,F I.P. Propylene glycol 1000-2000b Jaggers, 1979 Rat F Dermal Undiluted >4800b Jaggers, 1979 Rat M,F Dermal Xylene >1600 Combs, Carter et al., 1976 Syrian hamster M,F Oral Corn oil >400 Combs, Carter et al., 1976 Chinese Hamster M,F Oral Corn oil 203 Combs, Carter et al., 1976 Guinea pig M Oral Corn oil app. 500 Combs, Carter et al., 1976 Guinea pig F Oral Corn oil >1000 Combs, Carter et al., 1976 Guinea pig M Oral Aq.suspension >4000b Jaggers, 1979 Table 1. Continued... Species Sex Route Vehicle LD50 Reference (mg/kg) Rabbit F Oral Undiluted >2400b Jaggers, 1979 Rabbit F Dermal Undiluted >2400b Jaggers, 1979 Dom. fowl M,F Oral Dimethylsulphoxide >2000 Combs, Carter et al., 1976 Partridge M,F Oral Dimethylsulphoxide >3000 Combs, Carter et al., 1976 a) Unless specified, all values refer to data generated using 50:50 cis:trans material. b) Data generated using 40:60 cis:trans material. c) Data generated using 53:46 cis:trans material. Table 2. Effect of Cis:Trans Ratio on Acute Toxicity of Cypermethrin LD50 Species Sex Vehicle Cis:trans ratio (mg/kg) Reference Rat M,F Dimethylsulphoxide cis only 160-300 Brown, 1979a M,F Dimethylsulphoxide trans only >2000 Brown, 1979b F Corn oil cis:trans 90:10 367 Jaggers, 1979 F Corn oil cis:trans 40:60 891 Jaggers, 1979 Cypermethrin was administered dermally to rats by a single application (5000 mg/kg) or 5 consecutive daily doses (2500 or 5000 mg/kg/day). Low mortality was observed in the multiple dose groups (20-30%). Toxic signs of poisoning were similar to those described below. Axonal lesions of the sciatic nerve were noted in microscopic examination (Okuno et al., 1976). The toxic signs noted following acute poisoning with cypermethrin were similar in most mammalian species. In rats this consisted of sedation, ataxia, a splayed or ataxic gait and occasional tremors or convulsions. The onset of toxic signs of poisoning were rapid and disappeared within several days in survivors. In dogs, signs of acute intoxication included nervousness, inappetance, diarrhea, vomiting, tremors and exaggerated ataxia while walking were noted at extremely high levels. A single application of undiluted cypermethrin to rabbit eyes produced a mild transient conjunctivitis lasting two days. Groups of ten male and ten female guinea pigs were used to assess the skin sensitizing potential of cypermethrin. Two guinea pigs out of the 20 exposed to cypermethrin showed a positive skin reaction indicating that cypermethrin may have a weak skin-sensitizing potential. Groups of four male and four female rabbits were administered cypermethrin dermally in a 24-hour skin test. A single application of cypermethrin was observed to be a moderate irritant to rabbit skin (Coombs et al., 1976). SHORT TERM STUDIES Rat Groups of rats (20 male and 20 female rats per group) were fed cypermethrin in the diet at concentrations of 0, 75, 150 and 1500 ppm for 90 days. Cypermethrin used in the study was a 44:56 (cis:trans-ratio) with a purity of 92%. Random samples were chemically analysed periodically during the course of the study. At the conclusion of the study, four animals of each sex were maintained on control diets for a one-week recovery period. There was no mortality over the course of the study although both males and females at 1500 ppm had reduced body weight and food consumption in the first month of the study. After the first month, the growth rate was similar to that of controls although the animals never achieved the weight noted in the other groups. At the conclusion of the study, hematology, clinical chemistry, urinalysis and histopathology were performed on all animals. With the exception of a slight increase in M/E ratio in the bone marrow of female rats fed 1500 ppm in the diet, there were no hematological or urinalysis effects. An increased microsomal (smooth endoplasmic reticulum) oxidative activity was noted as an increased hepatic aminopyrine demethylase activity in both males and females at 1500 ppm and in males at 150 ppm. These adaptive changes in the subcellular portions of the liver were substantially reversed within the four week recovery period. Increased liver weight was not noted on gross examination at the conclusion of the study. A slight reduction in pituitary weight of males, while statistically significant, was not dose-related. A slight decrease in female kidney weight was dose-dependent and significantly different from control values at the highest level. The decrease in kidney weight in males was slight and not significantly different from controls in any of the dietary levels. Gross and microscopic (including electron microscopic) examinations of tissues and organs showed no significant differences from the observations noted in controls. Examination of the sciatic nerve from animals in the control and 1500 ppm dietary group showed no changes which could be directly attributable to the presence of cypermethrin in the diet. Seven of the sixteen males fed 1500 ppm and two of twelve male controls showed slight changes in myelin which may or may not have been brought about by histological fixation of the material prior to examination. The condition of the sciatic nerve of females was similar to that noted in control females. There were no effects noted in unmyelinated axons in both males and females. Interim histological examination at 30 days, during which time clinical signs of poisoning were noted, was not performed in this study (Glaister et al., 1977b). Groups of rats (6 male and 6 female rats/group, 14 of each sex were used as controls) were fed trans-isomer for five weeks at dietary concentrations of 0, 30, 100, 300, 1000 and 3000 ppm. There was no mortality observed over the course of the study. Food intake and growth were reduced in the high dosage group. Alkaline phosphatase activity was increased at the two highest dose levels. Minimal changes were observed at the two highest dose levels including several hematological parameters (red blood cell count and hemoglobin concentration). Liver, spleen and kidney weights were increased at 1000 ppm and above with the spleen and at the 3000 ppm level with the kidney and liver. Gross and microscopic histopathologic examination of several tissues and organs revealed no cypermethrin-related injuries. Special reference was given to the examination of the sciatic nerve which showed no damage (Hend and Butterworth, 1977a). Groups of rats (6 male and 6 female rats/group, 10 of each sex were used as controls) were fed dietary concentrations of cis-isomer at concentrations of 0, 30, 100, 300, 750 and 1500 ppm for five weeks following a protocol similar to that described above. Mortality was observed at the 1500 ppm dose occurring at intervals from 4 to 17 days from the start of the experiment with all animals displaying neurotoxic signs of poisoning. At the next lower dose group (750 ppm) almost all of the animals showed gross neurotoxic signs of poisoning, abnormal sensitivity to sound and touch and slight cases of ataxia. There was no compound-related mortality at dose levels of 750 ppm or below. Growth was reduced at the 750 ppm over the course of the study. Significant reductions in food intake were also noted at 300 ppm and above at the initial phase of the study. Gross examination of tissues and organs again revealed a reduction in heart, liver, spleen and kidney weights. Adjustment of the data for terminal body weight revealed a statistically significant change in kidney weight at 300 ppm and above while liver weight was increased at 750 ppm. Plasma protein levels were decreased and urea and potassium concentrations were increased in male rats at 750 ppm. Gross and microscopic examinations of tissues and organs showed substantial degeneration at 1500 ppm and above in both the liver and sciatic nerve. Liver lesions consisted of a coagulative necrosis of hepatocytes occurring in both males and females. The sciatic nerve from both sexes showed swelling and breaks in axons with concomitant myelin degeneration and vacuolation. There were no lesions observed in the brain or the spinal cord (Hend and Butterworth, 1977b). Groups of rats (12 male and 12 female rats/group, 24 of each sex were controls) were fed cypermethrin in the diet at dosage levels of 0, 25, 100, 400, and 1600 ppm for 13 weeks. After two weeks exposure to 1600 ppm, both males and females exhibited hypersensitivity and varying signs of ataxia. Mortality was observed with male rats up to the fifth week of feeding after which the surviving animals improved clinically and appeared normal at the end of the study. Reductions in body weight, growth and food intake were also noted at the 1600 ppm dose level. At the conclusion of the study, small increases in plasma urea were noted in both sexes. Males had a slight increase in plasma potassium while females had a slight increase in alkaline phosphatase and plasma protein levels at the 1600 ppm dosage group. Hematological abnormalities noted at 1600 ppm at the end of 13 weeks included a reduction of hemoglobin, packed cell volume and red blood cell count in females and a reduction in kaolin-cephalin clotting time in males. There were no effects at dose levels below 1600 ppm. Gross and microscopic pathology performed at the conclusion of the study showed axonal breaks and vacuolation in the sciatic nerve of animals fed 1600 ppm in the diet. This was especially noted with those animals that showed clinical signs of ataxia and died during the course of the study. At the conclusion of the 13-week trial, sciatic nerve lesions were not noted in any surviving animals. An increased kidney weight in males fed 400 ppm was observed which was not associated with any clinical or pathological signs of abnormality (Hend and Butterworth, 1976). Dogs Groups of beagle dogs (4 male and 4 female dogs/group) were fed cypermethrin (1:1 cis:trans-isomeric mixture) in the diet at concentrations of 0, 5, 50, 500 and 1500 ppm for 13 weeks. There was no mortality over the course of the study. However, there were significant signs of poisoning observed at the 1500 ppm level which included diarrhea, anorexia and tremors as well as ataxia, incoordination and hyperesthesia. On account of these clinical signs, two male and two female dogs at the high dose level had to be sacrificed before the end of the experiment. Minor variations were observed at various hematological parameters with the kaolin-cephalin clotting time observed to be consistently lower throughout the study in female dogs at 500 ppm. There were no other significant differences with respect to standard hematological or clinical chemistry parameters. Gross examination of kidneys and organs showed no effect on organ weights attributable to the diet. Microscopic examination of tissues and organs revealed a nonspecific focal bronchopneumonia in the lungs of the animals surviving 1500 ppm. There were no compound-related changes and no histological abnormalities in other tissues examined with the exception of a variation in the intensity of the pink colour of the optic disc noted on ophthalmologic examination at the conclusion of the study. Because of the pink colouration observed in the optic disc, a further experiment was undertaken to determine the cause of this occurrence. Cypermethrin was fed to two groups of three male dogs at concentrations of 0 and 500 ppm for 13 weeks. Specific ophthalmologic examination was made to evaluate the degree of colouration of the optic disc. At the end of 13 weeks, there were no consistent differences between the colour of the optic discs of the treated dogs and controls. A no-effect level of 50 ppm was observed in this short-term study (Buckwell and Butterworth, 1977). LONG-TERM STUDIES Rat Groups of rats (48 male and 48 female rats/group, 96 of each sex were used as controls) were maintained under SPF conditions and fed 1:1 cis:trans in the diet for 2 years at dosage levels of 0, 1, 10, 100 and 1000 ppm. Chemical analyses were made confirming stability of cypermethrin in the diet over the test interval. There was no mortality over the course of the study attributable to cypermethrin in the diet. General health and behaviour of the cypermethrin-fed animals was not different from that of the control animals. Body weight and food consumption data showed a reduction in dietary intake and growth in both males and females in those groups fed 1000 ppm in the diet. Gross morphological changes were noted periodically over the course of the study. At six months, males fed 1000 ppm had a slightly reduced testes weight which was not seen thereafter. Slight changes in the gross kidney weight at periodic intervals in the study were not accompanied by notable changes in clinical measurements or on microscopic examinations. These changes in kidney weight were believed to be unrelated to the presence in the diet. Liver weight increases were noted at 18 months again in those animals maintained at the high dose level. The only clinical chemistry changes noted over the course of the study was a slight decrease in the activity level of alkaline phosphatase in males at the 2 year interval. The decrease in alkaline phosphatase activity was not dose-related and was not noted in females. Minor fluctuations were seen in various hematological parameters over the course of the study but these, too, were not compound related nor statistically significant. These changes are not believed to be related to the presence in the diet. Gross and microscopic examination of tissues and organs periodically over the course of the study did not suggest adverse somatic effects. The kidneys of most animals after 12 months showed chronic nephrosis, histologically characterized as tubular dilatations, interstitial chronic inflammatory infiltration and glomerular scarring. In the liver, varying degrees of chronic inflammatory infiltration, hepatocyte vacuolation and bile duct proliferation were observed. These changes were characteristic of ageing processes and were not attributable to cypermethrin. Dermal ulceration was present in a number of animals and over the course of the study. A portion of the sciatic nerve from 12 animals fed 1000 ppm for one year and 12 control animals was histologically examined for signs of neurotoxicity. There were no differences in the incidence of abnormal fibres in the control and animals fed for cypermethrin for 12 months (Trigg et al., 1977). Microscopic examination of the sciatic nerve from animals sacrificed at the conclusion of the study showed a small number of nerve fibers exhibiting slight Wallerian degeneration changes. These degenerative changes increased with age but did not appear to be dose-related with respect to severity. Thus, cypermethrin did not induce neuropathy clinically nor did it induce histological evidence of nerve degeneration. There did not appear to be a significant increase in the incidence of tumor formation in either males or females over the course of the study. A large number of pituitary adenomas were reported predominantly in females of all dose groups including controls. This occurrence did not appear to be dose-related as similar events were recorded in all dose levels. Based on the reduced body weight observed at 1000 ppm in the diet of both males and females, the no-effect level is 100 ppm (McAusland et al., 1978). Observations in Humans Urine obtained from operators spraying cypermethrin in experimental trials was analysed for the presence of the chlorinated cyclopropane carboxylic acid metabolite. Using standard gas liquid chromatography, the carboxylic acid metabolite was observed in urine of exposed workers at levels up to 0.4 µg/ml (the limit of detection was estimated to be 0.05 µg/ml) (Baldwin, 1978). Studies were carried out in the Ivory Coast, Africa where operators sprayed with a hand-held ULV apparatus either cypermethrin or a control UW formulation. The cypermethrin sprayers were found to have residues on the exposed parts of their bodies. Medical and electrophysiological examinations showed no adverse effects from the exposure. The rate of dermal exposure of the operators during spraying ranged from 1.5 to 46.1 mg/hour. There was a reasonable relationship between the total cypermethrin deposited dermally and the excretion in urine. The levels of the cyclopropane carboxylic and acid metabolite in the 24 hour urine were between <0.05 and 0.32 mg. This, together with the finding of 0.6 mg of this metabolite in 72 hour urine from one man led to the estimation that approximately 3% of the total dermal dose was absorbed and rapidly excreted by the operators (Prinsen and van Sittert, 1978). COMMENTS Cypermethrin is an insecticidally active synthetic pyrethroid currently being developed for use in agriculture. The acute toxicity has been studied in a variety of species and the toxic response in all species is very similar. Cypermethrin has a moderately acute oral toxicity. The acute signs of poisoning, in addition to a generalized nervous system response, include a neurological involvement in rodents where reversible clinical signs of ataxia was accompanied by histological and biochemical evidence of peripheral (and possibly central) nerve disruption. Myelin and axon degeneration in the rat sciatic nerve was noted following high dose level administration. There was no information on the relative sensitivity of humans to the nervous system disruption noted in rodent species (see Report Section 3.5). Cypermethrin is readily absorbed, distributed, and metabolised in mammals. Because of the chemical and especially the isomeric complexity of the molecule, the metabolic profile with respect to all of its isomers is extremely complex. Cypermethrin is readily cleaved at the ester linkage and subjected to oxidative degradation and conjugation of the metabolic products. Elimination from the body following acute and subacute administration is rapid. However, the clearance rate from adipose tissue is slow and a half-life in rats and mice may range from 10 to 30 days. The data suggested a potential for bioaccumulation in the body following continuous exposure. In a wide variety of studies, there was no carcinogenic or mutagenic potential as evidenced by short-term bioassays or a long-term chronic study. Reproduction was unaffected and no signs of teratogenic potential were noted in two species examined. Two dominant lethal tests were performed, and while data were basically negative, these studies did not give full assurance of the lack of a dominant lethal effect on male reproduction. In short-term tests, only younger animals were susceptible to the inductive effects of cypermethrin on liver metabolizing enzymes. The extensive toxicological data base already in existence lent assurance to the estimation of an ADI for man. The lack of data on tissue residue storage and release and on the limited human experience with cypermethrin were instrumental in making this temporary, pending further information. TOXICOLOGICAL EVALUATION Level causing no toxicological effect Rat: 100 ppm in the diet equivalent to 5.0 mg/kg body weight Dog: 50 ppm in the diet equivalent to 1.25 mg/kg body weight ESTIMATE OF TEMPORARY ACCEPTABLE DAILY INTAKE FOR MAN 0-0.006 mg/kg body weight RESIDUES IN FOOD AND THEIR EVALUATION USE PATTERN Cypermethrin is a recently introduced insecticide recommended as a foliar spray for the control of a wide range of insect pests. In line with other members of the pyrethroid group of compounds, it is used at lower rates than most other types of chemical insecticides. Application rates seldom exceed 250 g/ha. In most instances a considerably lower rate is required. Several applications, up to two per month and up to 7 days before harvesting, may be made during a growing season. Current recommendations for use on various food crops are summarised in Table 3. Table 3. Current dosage rates for use on various crops Recommendations Crop (in active ingredients) Alfalfa 25 g/ha Apples 0.003%-0.0125% Brassica leafy vegetables 30-200 g/ha Cereals (barley, wheat) 25-200 g/ha Cherries 0.0075%-0.0125% Citrus 0.0025%-0.01% Cotton 50 - 100 g/ha Grapes 30-50 g/ha Kiwifruit 0.01% Legume vegetables 25-200 g/ha Lettuce 50-150 g/ha Maize 25-200 g/ha Pasture 100 g/ha Peaches 0.002%-0.01% Pears 0.002%-0.0125% Plums 0.05%-0.0125% Potatoes 20-150 g/ha Rape 25-75 g/ha Raspberries 0.0075%-0.015% Soya 50-250 g/ha Strawberries 0.0075%-0.015% Sugar beet 25-125 g/ha Tomatoes 40-150 g/ha Post-harvest uses Although cypermethrin may be introduced to control pests of stored commodities and for animal health purposes, no data were available for evaluation at this meeting. RESIDUES RESULTING FROM SUPERVISED TRIALS Residue data have been obtained from numerous trials carried out on a world-wide basis and on the main crops treated. Some data from excessive treatments rates are included where they provide useful information, e.g. on the effect of processing. Treatments were generally made using E.C. formulations which are representative of current application practice. MAIN CROPS Apples Residue data have been obtained from trials in several countries. In these experiments, dosages covered recommended and higher rates and were in the range of 0.0025% - 0.02% (25-200 g/ha), based on a spray volume of 1000 l/ha. Treatments were made on up to 12 occasions. Results and details of the trials are summarised in Table 4. Residues in whole fruit one week after treatment at recommended rates up to 0.02% were usually below 1 mg/kg except when six or more applications were made. Apart from one instance, however, these were all less than 1.5 mg/kg. In the one case, where 2.7 mg/kg was reported, the result was considered to be atypical. Examination of fruit pulp and peel separately showed that residues were located mainly in the peel, the average weight of which was 10-18% of the whole fruit. After peeling, levels in 78 samples were generally less than 10% of those in whole fruit. Pears Samples of fruit were analyzed from trials carried out in Europe, Canada, Australia and South Africa. In these experiments, treatment rates were between 0.0008% and 0.04% (or 30-400 g/ha). Between one and six treatments were made and fruit harvested at various intervals after treatment. The results obtained were similar to those with apples. Residues in whole fruit, one week after treatment at rates up to 0.02% (slightly above the recommended rate of 0.015%), were all below 1 mg/kg. As with apples, analysis of peeled fruit showed that cypermethrin residues were mainly in the peel. In 32 samples, residues in the pulp did not exceed 30% of those in whole fruit. Table 4. Residues Following Supervised Trials with Apples (1976-1978) Application Interval between Ref. Varieties Country No. rate Appl.s Residues in mg/kg, at intervals (days) after application (Shell) kg a.i./ha (week) or % 0 7 12-17 21 28-30 35-42 56 Granny Smith Australia 3 0.02% (to run off) 382 0.95 0.45 0.45 1 MacIntosh Canada 3 0.18 2 0.57 0.38 2 Lobo 3 0.18 2 0.47 0.32 Northern spy 8 0.07 9-15 days 0.13-0.3 3 MacIntosh 8 0.07 9-15 days 0.1-0.251 Northern Spy 8 0.05 " 0.2-0.26 MacIntosh 8 0.15 " 0.2-2.25 Richared France 1 0.15 0.25 0.19 0.6 0.25 4 Golden Delicious 7 0.05 2-3 0.05 5 Golden Delicious FRG 6 0.2 2,3,2,3 3.1 1.0 0.6 0.3 0.5 6 and 1 3.2 2.7 1.9 1.7 0.81 James Grieve 6 0.02% 1,1,1´ 4 & 1´ 1.3 0.96 0.82 0.8 0.67 7 Table 4. Continued... Application Interval between Ref. Varieties Country No. rate Appl.s Residues in mg/kg, at intervals (days) after application (Shell) kg a.i./ha (week) or % 0 7 12-17 21 28-30 35-42 56 Cox's Orange 6 0.02% 1,3,4 4 & 2 0.97 0.75 0.6 0.84 0.31 Golden Delicious 6 0.02% 1,6,6, 2 & 2 1.7 1.3 0.93 0.9 0.9 6 0.1 1-3 1.2 1.1 1.0 0.9 0.8 8 6 0.1 1-3 0.8 0.7 0.7 0.95 0.5 Italy 1 0.037 - 0.3-0.5 11 Strumer N. Zealand 12 0.008% 2-3 1.1 0.6 0.7 0.53 12 Reinette Portugal 5 0.005% 3 0.19 0.2 0.14 13 5 0.0075% 3 0.32 0.1 5 0.01 3 0.6 0.35 0.45 Granny Smith S. Africa 1 0.005% - 0.42 0.36 0.28 0.25 14 Spain 1 0.024 - 0.06 0.05 0.04 10 1 0.048 - 0.1 0.1 0.05 0.06 10 U.K. 3 0.005% 1-2 0.29 0.45 0.27 3 0.01% 1-2 0.99 0.91 0.52 3 0.005% 1´ 0.6 0.81 0.64 3 0.01 1´ 1.1 0.98 0.82 1 0.01 - 1.3 1.2 0.83 Worcester Pearmain U.K. 2 0.015% 0.01 15 Table 4. Continued... Application Interval between Ref. Varieties Country No. rate Appl.s Residues in mg/kg, at intervals (days) after application (Shell) kg a.i./ha (week) or % 0 7 12-17 21 28-30 35-42 56 Chivers Delight 2 0.0025% 4´ 0.02 16 0.005% 4´ 0.05 2 0.01% 6´ 0.01 Laxton Superb 2 0.01% 6´ 0.01 Spartan 1 0.012% - 0.36 0.15 0.07 0.05 17 0.01 - 0.36 0.12 0.03 <0.01 Lobo Sweden 3 2´-4 0.1422 Sweden Ribston 3 2´-4 0.25 1 Minimum-maximum residues in three samples. 2 90 days after treatment. Peaches Residues in whole fruit, less stone, from trees sprayed with cypermethrin at recommended rate (0.005%-0.01%) and harvested one week after treatment were generally 1 mg/kg or less although in one trial in Germany a residue of 1.8 mg/kg was reported in fruit under these conditions. Analysing 43 samples of fruit after peeling and removal of the stone showed that levels in the pulp were less than 10% of levels found in whole fruit. Details of the trials are given in Table 5, which contains data relating to some treatments at rates higher than recommended. Citrus Experiments were carried out in South Africa (oranges), Spain (lemons) and Italy (oranges) in which applications of cypermethrin at recommended rates up to 200 g/ha were made on 1 or 2 occasions. Fruit was harvested 1 to 39 weeks after treatment, depending on the trial, and analysed for residues of cypermethrin. The results are shown in Table 6. Residues up to 1.3 mg/kg were found in whole fruit taken within six weeks of treatment. Analysis of peel and pulp showed that the residues were largely (90%) percent in the peel and that residues in the pulp were normally below the limit of determination, although in one series of experiments residue levels up to 0.16 mg/kg were reported (4 weeks after treatment at 0.02%). In some experiments samples of orange juice were obtained from treated fruit but residues were all less than 0.01 mg/kg. Cotton Samples of seed were obtained at harvest from trials in several countries in which up to 12 applications were made at recommended rates (up to 150 g/ha) and also at treatment rates up to 240 g/ha. The intervals between the last treatment and harvest varied between 1 day and 13 weeks. The data obtained are given in Table 7 which also summarises the trial details. The seed from these trials was ginned after harvest and was separated in the laboratory into kernels and hulls. The latter also contained adhering linters. In 8 samples no residue of cypermethrin was found in the kernels (limit of determination of 0.01 mg/kg). Analysis of hulls, which in most instances had adhering linters, showed that any residues present were located entirely on the seed surface and its associated fibre. Table 5. Residues Following Supervised Trials on Peaches (1976-1978) Application rate Intervals Residues in mg/kg, at intervals (days) after application1 (Shell) Country No. kg a.i./ha /week/ 0-1 6-7 12-14 18-21 28-30 40-43 54 Ref. or % Australia 3 0.02% 3 & 2 1.0 33 Canada 3 0.006% 4 & 5 0.07 34 3 0.006% 0.34 0.15 0.06 35 0.1 0.052 France 1 0.005% - <0.02 36 0.0075% <0.02 0.0125% - <0.01 0.0187% <0.01 0.015% 0.5 0.4 0.1 0.15 Federal Republic of Germany 4 0.02% 2 3.2 1.6 1.1 0.65 38 4 0.01% 3,3 & 2 0.85 0.7 0.5 0.18 39 4 0.01% 3,3 & 2 3.0 1.8 1.6 0.75 5 0.01% 2,3,3 & 2 2.0 1.0 0.85 0.3 Italy 1 0.01% - 0.1 40 1 0.02% 0.5 Portugal 1 0.005% 0.08 0.08 0.08 41 0.0075% 0.19 0.11 0.09 0.01% 0.32 0.21 0.14 Spain 1 0.15 0.15 42 2 0.195 3 0.03 2 0.195 1 0.04 1 Results refer to whole fruit without stone. 2 Average of ten samples taken from the same site (min.-.max. values: 0.02-0.11 mg/kg). Table 6. Residues of Cypermethrin in Citrus (1976 - 1977) Interval Cypermethrin Crop Dose Rate No. of between Residue (mg/kg) Ref. (Country) (a.i.) Applications applications Intervals WHOLE (Shell) (days) (days) PULP PEEL FRUIT LEMONS 150 g/ha 2 27 7 <0.01 2.1 1.1 43 Verna 14 <0.01 2.0 1.0 21 <0.01 2.1 1.1 (Spain) 58 <0.01 1.1 0.55 JUICE ORANGES 0.01% 1 - 60 <0.01 0.22 0.14 44 Moro 0.02% 1 - 60 <0.01 0.44 0.21 (Italy) PULP ORANGES Moro 0.005% 1 - 67 0.02 0.91 0.30 45 0.01% 1 - 67 0.02 1.2 0.39 0.005 1 - 91 0.01 0.69 0.19 0.01% 1 - 91 0.02 1.3 0.35 0.01% 1 - 27 0.06 1.0 0.36 46 43 0.05 1.5 0.48 56 0.05 1.3 0.40 0.02% 1 - 27 0.16 3.0 1.2 43 0.13 3.7 1.3 56 0.09 1.9 0.73 JUICE 0.005% 1 - 1 <0.01 0.50 0.13 47 4 <0.01 1.2 0.20 8 <0.01 1.0 0.16 18 <0.01 0.81 0.21 39 <0.01 1.1 0.28 68 <0.01 1.3 0.39 (S. Africa) 96 <0.01 1.3 0.38 Table 6. Continued... Interval Cypermethrin Crop Dose Rate No. of between Residue (mg/kg) Ref. (Country) (a.i.) Applications applications Intervals WHOLE (Shell) (days) (days) PULP PEEL FRUIT ORANGES 0.01% 1 - 1 <0.01 1.0 0.30 47 Moro 4 <0.01 0.55 0.22 8 <0.01 0.19 0.16 18 <0.01 0.83 0.25 39 <0.01 0.60 0.16 68 <0.01 0.45 0.13 96 <0.01 0.45 0.13 0.015% 1 - 1 <0.01 2.6 0.58 4 <0.01 1.2 0.30 8 <0.01 1.0 0.24 18 <0.01 1.3 0.25 39 <0.01 1.2 0.21 68 <0.01 1.8 0.40 96 <0.01 0.95 0.22 0.01% 1 - 0 <0.01 1.6 0.52 1 <0.01 2.9 0.85 2 <0.01 2.2 0.65 4 <0.01 2.8 0.55 9 <0.01 1.8 0.58 16 <0.01 1.9 0.72 0.005% 2 6-weeks 69 <0.01 <0.01 <0.01 114 <0.01 <0.01 <0.01 237 <0.01 <0.01 <0.01 0.01% 1 - 110 <0.01 <0.01 <0.01 155 <0.01 <0.01 <0.01 (S. Africa) 278 <0.01 <0.01 <0.01 Table 7. Residues Resulting from Supervised Trials in Cotton Seed (1975-1977) Application Residues in whole seed (mg/kg) at Intervals (days) after app. lication Ref. Country rate kg Intervals (Shell) No. a.i./ha or /Week) 1 7-8 13-15 19-20 28-37 44-55 70-91 Australia 1 0.0015% - 0.01 0.01 10 1 0.003% 0.05 0.01 Brazil 4 0.12 1 0.01 51 4 0.24 1 0.01 4 0.12 1 <0.01 52 0.24 1 0.01 Columbia 1 0.1 0.09 0.03 0.01 54 5 0.1 3 to 8 days <0.01 55 2 0.075 12 days <0.02 56 South Africa 12 0.2 1 to 2 0.01 58 11 0.2 1 to 2 0.02 1 0.1 - <0.01 10 0.2 <0.01 Spain 5 0.1 2,2, 1´ & 2´ 0.04 59 4 0.1 2,2 & 1´ 0.03 5 0.2 2,2, 1´ & 2´ 0.03 4 0.2 2,2,1´ 0.06 3 0.1 2 0.03 3 0.2 2 0.04 3 0.2 0.02 The presence of occasional small residues on the fibre and the outside of the seed case is to be expected, particularly where applications were made after the bolls had opened. However, the results indicate that migration through the seed case to the kernel did not occur even after treatment at excessive rates, and that measurable residues in kernels are unlikely to be found in practice. As a whole, the data suggest that, following treatment according to recommendations, seed taken 1 week after a series of applications is unlikely to contain more than 0.1 mg/kg cypermethrin on the whole seed. Leafy Vegetables (Brassicae) Trials have been carried out in a number of countries in order to obtain residue data on cabbages - including savoy, broccoli, Brussel sprouts, cauliflower and kale. These are described in Table 8. The treatments were made according to recommendations (up to 200 g a.i./ha or 0.02%) or at slightly higher dose rates. In most cabbage samples as expected, the residue was located mainly in the outer leaves, which are normally removed in the field, and the majority of the samples examined were received without the "discard" leaves. In one experiment however (New Zealand) whole unstripped cabbages were received. Residues in these samples reaches 3.2 mg/kg but were found to be reduced to below 0.1 mg/kg on removal of the outer leaves in the laboratory. With most of the other brassicae examined, including cauliflower heads, residue levels were similar to those in cabbage without discard leaves. But residues in kale from experiments in Germany tended to be somewhat higher. OTHER CROPS Supervised trials were carried out with a number of other crops in various locations. Residue data obtained in these experiments are summarized in Table 9 and the following comments. Alfalfa A single application at a rate equivalent to 0.1 kg a.i/ha was used to establish a residue decay curve. Beans Trials were carried out in South America on soya and on phaseolus bean. Residues in beans (soya and phaseolus) removed from their pods were below measurable levels (0.01 mg/kg) four weeks after treatment, even where excessive rates (up to 300 g/ha) were used. Table 8. Residues Resulting from Supervised Trials with Various Vegetables (1976/79) Crop Application Intervals (Country) rate between appl.s Residues in mg/kg, at intervals/days after application Ref. No. kg a.i./ha (week/ 0-1 3-4 7-8 10 14-16 21 28 (Shell) BROCCOLI 3 0.16 3 & 2 0.38 0.28 0.16 0.06 69 1 0.0015 - 0.11 0.03 <0.01 10 (Canada) 1 0.003% - 0.3 0.03 <0.01 BRUSSELS SPROUTS 3 0.15 1,5 0.55 0.25 0.25 70 7 0.07 3,3,2,2 0.14 0.1 71 2 & 3 0.12 0.09 0.23 0.13 0.18 0.18 6 0.07 3,3 & 2 0.06 0.09 0.1 (Canada) 0.08 CABBAGES 3 0.07 1,5 0.22 0.11 0.11 60 0.22 0.12 0.06 0.16 0.27 0.17 0.22 0.27 0.05 3 0.15 1,5 0.43 0.03 <0.01 61 (Canada) 3 0.16 2 0.15 0.1 0.02 <0.01 62 CABBAGES 4 0.06 2 1 0.4 0.11 <0.01 <0.01 63 (Germany) 4 0.06 2 0.1 0.02 <0.01 <0.01 <0.01 CABBAGES 1 0.25 0.161a Hungary 0.1 (Hungary) 0.2 0.2 Table 8. Continued... Crop Application Intervals (Country) rate between appl.s Residues in mg/kg, at intervals/days after application Ref. No. kg a.i./ha /week/ 0-1 3-4 7-8 10 14-16 21 28 (Shell) CABBAGES 5 0.002% 2 0.03 <0.01 0.01 5 0.006 2 0.05 0.02 0.02 66 1 0.002% - 0.07 0.02 0.02 (South Africa) 1 0.006% - 0.08 0.03 0.02 CABBAGES 6 0.14 2 2,11 1,71 1.41 67 0.061b 0.011b 0.011b 6 0.14 0.76 0.6 0.57 0.47 N.Z. (New Zealand) 6 0.28 1.13 0.82 0.68 0.42 CABBAGES 1 0.008% - 0.51 68 (U.K.) CABBAGES (Savoy) 4 0.06 1,1 & 2 0.55 0.4 0.35 0.15 <0.01 64 (Germany) 4 0.06 2 0.3 0.2 0.1 0.05 <0.01 1 0.005% 0.02 65 1 )0.015% 0.02 (Italy) 1 0.03% 0.02 CAULIFLOWERS 3 0.16 3 & 2 0.17 0.09 0.01 <0.01 72 3 0.07 1,5 0.23 0.21 <0.01 73 0.26 0.30 0.01 0.34 0.24 0.08 (Canada) 0.3 0.08 0.11 4 0.06 2 0.03 <0.01 <0.01 <0.01 (Germany) 3 0.06 2 0.05 <0.01 <0.01 <0.01 <0.01 KALE 4 0.06 2 1,6 0.85 0.4 0.3 0.25 75 (Germany) 4 0.06 2 1,4 0.9 0.7 0.5 2 0.075+0.04 6.5 1.1 0.76 0.47 0.13 76 (U.K.) 2 0.225+0.08 6.5 1.5 0.95 0.60 0.23 Table 8. Continued... Crop Application Intervals (Country) rate between appl.s Residues in mg/kg, at intervals/days after application Ref. No. kg a.i./ha /week/ 0-1 3-4 7-8 10 14-16 21 28 (Shell) KALE (China) 6 0.005% 4-5 days 0.85 (Thailand) NOTE: The cabbages were analysed without the outer leaves with some exceptions: 1 whole cabbage 1a whole cabbages as specified by CC/PR/153/ 1b heart only. Cherries and Plums Samples of plums and cherries have been obtained from field experiments in Germany in which cypermethrin was applied on several occasions (three in the case of cherries, five for plums) at approximately the recommended rate and double the recommended rate (0.01% and 0.02% respectively). Under similar conditions, residues in plums were found to be somewhat lower than in cherries. Grapes At recommended rates of up to 80 g/ha and treatments on up to 4 occasions, residues in grapes harvested one week after the last application were at or below 1 mg/kg (Table 9). In practice, the material is generally applied an a prophylactic treatment at 50 g/ha and harvest is likely to be more than one week after treatment. Lettuce Residue data are available from trials carried out in Canada, France and Germany at rates generally in the range of 50-70 g/ha (0.005% to 0.007%, based on 1000 l/ha spray volume). Residue levels were 1.6 mg/kg cypermethrin or less in lettuce taken one week after treatment. From the glasshouse data available, there was no evidence that levels in glasshouse lettuce were substantially different from levels in outdoor crops. Kiwi Fruit Supervised trials were carried out in New Zealand at the recommended dose rate and at double rate (Table 9). The pulp contained 5-10% of that which was found in whole fruit. Maize Residue experiments have been carried out in several countries in which cypermethrin has been applied to maize at recommended rates up to 150 g/ha. Green maize (whole plants) were sampled at intervals following treatment, and in some instances grain was also sampled at the sweet corn stage or when fully mature. In green maize following treatments at rates up to 150 g/ha, residues were below 1 mg/kg two weeks after treatment and below the limit of determination (0.01 mg/kg) after eight weeks. In grain, no residues were found in either sweet corn or mature grain, even in samples taken three days after treatment at this rate. Pasture Supervised trials were carried out in New Zealand in which cypermethrin was applied at several times higher than the recommended rate. The residues on the grass increased roughly in proportion to the increases in dosage (Table 8). Peas Trials were carried out on peas in the U.K., Hungary and South Africa. No residues were found at dose rates of 15 to 100 g/ha in the peas themselves which were sampled between one day and four weeks after treatment (limit of determination 0.01 mg/kg). However, an excessive dose rate of 200 g/ha resulted in residues between 0.04-0.07 mg/kg in the peas (Table 9). Potatoes Samples were obtained from residue trials carried out in Europe, Cyprus and Canada, with from 1-9 treatments at dosage rates in the range of 10 g/ha to 200 g/ha, and intervals between last treatment and harvest from 0-8 weeks. Detectable residues were absent from all samples of whole or peeled tubers, even 3-9 days after treatment. However, samples from one trial in Italy, obtained three weeks after treatment were peeled. Residues up to 0.05 mg/kg were found in the peel, but none was detectable in the peeled potatoes. Rape Data from supervised trials in Canada, Germany and the U.K. show that, where treatments at recommended rates were made more than six weeks before harvest, residues in the whole seed were below the limit of determination of 0.01 mg/kg. In one of the replicated Canadian experiments, however, residues were found in samples taken six weeks after treatment; residues between replicates varied from 0.01 mg/kg to 0.12 mg/kg. Raspberries and Strawberries Trials were carried out in Canada and the U.K. in which raspberry canes were treated with cypermethrin at rates between 0.005% and 0.015% (the maximum recommended rate). Residues in fruit taken 12 or more days after treatment were all below 0.5 mg/kg even where multiple applications were made. Residues in strawberries from Canadian experiments using cypermethrin at rates of 0.006% or 0.01% on two occasions at an interval of 8 or 9 days were also below 0.5 mg/kg when harvested three weeks after treatment (Table 9). Sugar Beet In experiments carried out in France, Germany and the U.K., 1 to 5 treatments were carried out at rates between 60 g/ha and 200 g/ha cypermethrin. Samples of both roots and tops were taken for analysis at intervals up to 17 weeks from the time of treatment. Apart from one sample taken two weeks after treatment at 60 g/ha, which contained a small residue of 0.02 mg/kg, no residues of cypermethrin were found in the root samples. In leaves, residues were between 6 and 13 mg/kg immediately after the last of 5 applications made at two weekly intervals. Subsequently these declined, reaching 0.02-0.13 mg/kg six weeks after treatment. After 11 weeks residues were 0.01 mg/kg or less (Table 9). Tomatoes In outdoor experiments carried out in Southern Europe, Australia, Canada, S. Africa, the Canary Islands and Mexico, tomatoes were given foliar treatments at rates between 50 g/ha and 300 g/ha. Applications were made on up to 9 occasions at intervals from 5 days to 3 weeks depending on the experiment. Samples were taken at intervals ranging from the day of treatment to six weeks later. Although some of the tomatoes received were green, they were close to ripening (approximately 5 cm diameter) and in the condition at which they would be picked for export. The residues (Table 9) did not exceed 0.5 mg/kg in any of the samples taken shortly after treatment at the recommended rates (up to 0.0% or 100 g/ha assuming use at 1000 l/ha). Wheat Residue trials have been carried out on wheat in Canada and Brazil, with application rates up to 150 g/ha. In the grain residues did not exceed 0.1 mg/kg at harvest two weeks after application. Residues in straw were higher, and the few data obtained suggest that under these conditions they may approach 10 mg/kg (Table 9). Table 9. Residues Resulting from Supervised Trials with Various Fruits and Other Crops (1974/79) Crop Country Application Interval (Variety) rate between Residues in mg/kg,at intervals (days) after application No. kg a.i./ha, appl.s Ref. or % (week) 0 2-3 6-7 13-17 21 28-30 (Shell) ALFALFA Cyprus 1 0.1 12 5.6 4.7 10 BEANS (Dried) Colombia 3 0.15 1 <0.011 87 CHERRIES Germany 3 0.02% 1-2 4.5 3.3 0.65 0.6 18 to run off 3 0.02% 1-2 2.7 1.6 1.0 0.39 to run off 3 0.02% to run off 1-2 7.4 5.4 1.5 1.2 3 0.01% 1.5-2 0.59 0.47 0.27 0.25 0.2 19 3 1.5-2 1.0 0.6 0.3 0.1 0.1 GRAPES Canada (Delaware) 1 0.08 - 0.7 0.32 20 21 (Elvira) 4 0.07 4,5 & 3 0.24 (0.1 to 0.37) (Friedamia) 1 0.006% to run off 0.75 0.41 0.25 (Sauvignon) France 4 0.075 1 0.08 0.03 0.02 <0.01 22 (Alicante) (Bouschet) 1 0.075 - 0.4 0.28 0.23 0.12 23 2 0.075 3 0.37 (Riesling) Germany 4 0.08 5,4 & 2 0.5 0.2 0.11 0.09 0.05 24 4 0.08 5,4 & 2 0.8 0.5 0.1 0.05 0.05 (Barbera) Italy 1 0.01% 0.1 25 S. Africa 1 0.0375 - 0.2 0.1 0.18 <0.05 <0.05 S. Africa Table 9. Continued... Crop Country Application Interval (Variety) rate between Residues in mg/kg,at intervals (days) after application No. kg a.i./ha, appl.s Ref. or % (week) 0 2-3 6-7 13-17 21 28-30 (Shell) GRAPES (Waltham Cross) 2 0.0375 2 0.24 0.2 0.19 0.07 <0.05 (Chemin Blane) 1 0.0375 - 0.1 0.12 <0.05 <0.05 2 0.0375 2 0.12 0.07 <0.05 <0.05 <0.05 KIWI FRUIT N. Zealand 6 0.01% 2.2 1.9 1.7 1.3 N.Zealand 6 0.02% 6.2 3.9 3.4 2.8 LETTUCE Canada 6 0.07 1 <0.012 78 0.02 France 1 0.15 0.52 79 0.3 1.1 France 1 0.05 1.2 0.27 0.123 80 1 0.05 1.1 0.3 0.06 81 1 0.05 2.2 1.6 0.35 1 0.05 1.8 0.5 0.02 1 0.054 2.4 1.0 0.85 82 Germany 3 0.06 2 4.0 0.25 0.04 0.02 <0.01 83 3 0.06 2 1.2 0.06 0.01 <0.01 Table 9. Continued... Crop Country Application Interval (Variety) rate between Residues in mg/kg,at intervals (days) after application No. kg a.i./ha, appl.s Ref. or % (week) 0 2-3 6-7 13-17 21 28-30 42-56 (Shell) MAIZE Cobs Australia 1 0.0015% <0.01 10 Cobs 0.003% <0.01 Sweet corn Canada 5 0.07 5 days <0.01 84 Sweet corn 3 0.075 1 <0.01 <0.01 Sweet corn 6 0.064 5 days <0.01 <0.01 <0.01 85 Germany 1 0.1 1.9 0.04 86 1 0.1 2.7 2.2 0.51 0.05 <0.015 1 0.1 2.9 1.1 0.15 0.05 0.025 <0.01 Leaves S. Africa 1 0.075 5.2 3.86 0.4 10 Leaves 1 0.15 17 106 2.6 Stalks 1 0.075 <0.01 0.086 <0.01 Stalks 1 0.15 0.05 0.02 0.06 PEAS U.K. 2 0.05 2 <0.01 88 w/o pods 1 0.025 - <0.01 89 Peas Hungary 1 0.1 - <0.017 pods (only) - 0.07 Peas 1 0.2 0.04 0.077 Sweden 2 0.08 2 <0.01 165 S. Africa 1 0.015 - <0.01 <0.016 <0.01 10 1 0.03 - <0.01 <0.016 <0.01 PLUMS Germany 5 0.02% 1-3 1.0 0.65 0.5 90 5 0.02% 1-3 0.9 0.75 0.4 0.25 5 0.02% 1-3 1.3 1.1 0.7 5 0.01% 3,2,3 & 1 0.3 0.29 0.29 0.25 0.11 91 5 0.01% 3,2,3 & 1 0.24 0.15 0.12 0.1 Table 9. Continued... Crop Country Application Interval (Variety) rate between Residues in mg/kg,at intervals (days) after application No. kg a.i./ha, appl.s Ref. or % (week) 0 2-3 6-7 13-17 21 28-30 42-56 (Shell) POTATOES Canada 4 0.075 2 <0.01 92 4 0.15 2 <0.01 9 0.072 1 <0.01 9 0.145 1 <0.01 4 0.150 2 <0.017 93 9 0.15 1 <0.01 94 Cyprus 1 0.1 <0.01 <0.01 10 France 1 0.15 <0.01 95 Germany 4 0.090 2 <0.01 <0.01 <0.01 96 4 0.2 2 <0.01 <0.01 <0.01 97 4 0.2 2 <0.01 <0.0l <0.01 4 0.2 2 <0.01 <0.01 <0.01 Italy 1 0.04 - 0.058 98 1 0.12 - 0.038 SOYA BEANS Brazil 2 0.24 2 <0.01 99 3 0.24 2 <0.01 dried Colombia 4 0.3 1,1 week & 4 days <0.01 100 SUGARBEET France 1 0.1 - <0.01 Leaves after 101 17 wks 1 0.15 <0.01 after 102 17 wks Germany 5 0.06 )2,2,2 1.3 0.52 0.07 0.05 103 5 0.06 )& 1 2.2 0.1 0.03 <0.01 5 0.2 2 12 4.0 2.3 0.02 104 Table 9. Continued... Crop Country Application Interval (Variety) rate between Residues in mg/kg,at intervals (days) after application No. kg a.i./ha, appl.s Ref. or % (week) 0 2-3 6-7 13-17 21 28-30 42-56 (Shell) SUGARBEET Germany 5 0.2 2 6.2 2.3 0.18 0.05 Leaves 5 0.2 2 13 0.73 0.23 0.13 U.K. 1 0.2 <0.01 after 15 weeks 105 RASPBERRIES Canada 1 0.225 - 0.2110 114 3 0.18 2 0.4510 115 3 0.135 2 0.410 116 U.K. 1 0.005% 1 0.1311 117 0.015% 1 0.2511 STRAWBERRIES Canada 2 0.23 9 days 0.07 118 2 0.18 90 0.04 119 2 0.18 8 days 0.45 120 TOMATOES Australia 9 O.01% 5-7 days 0.3 0.3 0.24 0.14 106 9 0.02% 5-7 days 0.57 0.57 0.44 0.53 1 0.0015% - 0.02 0.03 10 Canada 1 0.15 - 0.13 0.07 107 2 0.15 1 0.2 0.05 France 1 0.0075% - 0.09 0.06 0.04 108 Italy 1 0.005% - 0.02 109 0.015% 0.08 0.03 0.17 Mexico 1 0.0075 - 0.02 0.01 10 1 0.015 - 0.05 0.04 1 0.03 - 0.08 0.13 Portugal 3 0.075% 11 & 7 0.06 0.032 110 days Table 9. Continued... Crop Country Application Interval (Variety) rate between Residues in mg/kg,at intervals (days) after application No. kg a.i./ha, appl.s Ref. or % (week) 0 2-3 6-7 13-17 21 28-30 42-56 (Shell) TOMATOES S. Africa 4 0.0075% 3,2,2,2 0.17 0.1 0.05 111 4 0.01% 3,2,2,2 0.27 0.15 0.09 4 0 02% 312,2,2 0.27 0.14 0.08 4 0:03% 3,2,2,2 0.29 0.2 0.6 Spain 7 0.03% 3,2 & 2 0.08 112 1 0.075 - 0.16 0.07 0.14 10 0.16 0.06 0.10 2 0.2 1 0.1 0.09 0.06 113 3 0.2 1 0.25 0.2 0.05 Canary Is. 2 0.1 1 0.25 0.15 0.01 113 3 0.1 1 0.2 0.15 0.06 0.03 2 0.15 1 0.4 0.3 0.15 3 0.15 1 0.55 0.4 0.2 0.6 WHEAT Canada 1 0.14 - 0.1 0.07 0.05 121 1 0.15 - 0.08 0.08 0.08 0.04 122 0.07 0.05 0.06 0.03 0.07 0.05 0.05 0.04 0.09 0.09 0.06 0.04 Brazil 1 0.09 <0.01 <0.01 123 2 0.09 12 days 0.04 2 0.09 31 days 0.03 2 0.09 19 days 0.01 3 0.09 19 & 12 days 0.04 1 +4 week storage, beans were analysed without pods 2 In 3 samples 3 10 days after treatment 4 In glasshouse Table 9. Continued... 5 The grain contained <0.01 mg/kg 6 8 days after treatment 7 In 9 samples 8 In the peel 9 24 days after treatment 10 12-13 days after treatment 11 19 days after treatment FATE OF RESIDUES GENERAL OBSERVATIONS Following applications to crops cypermethrin may degrade to a variety of hydrolysis and oxidation products. The most likely degradation products present in crops at harvest following normal agricultural use of cypermethrin are the derived amide (compound B), 3-phenoxybenzoic acid and 2-(2',2'-dichloro vinyl)-3,3 dimethyl cyclopropane carboxylic acid (compound C), the structures of which are shown in Figure 1. The latter two compounds are found in the free state as well as in conjugated forms. However, the evidence indicates that the major component of any residue present at harvest will be cypermethrin itself. A number of crop samples obtained from supervised trials discussed previously were analysed also to determine compounds B, C and phenoxybenzoic acid. The results of these examinations involving some 20 crops showed no residues of Compound B, of Compound C or of 3-phenoxy benzoic acid in excess of 0.05 mg/kg. Following use on animal feed crops, residue may be present in feed at levels depending on the crop. However, since the product is readily metabolized by animals, these amounts are unlikely to give rise to more than traces of foods of animal origin. IN ANIMALS Cattle Feeding Studies Studies were undertaken to investigate the fate of cypermethrin in cattle and whether residues in meat or milk could arise from the use of cattle feed containing products made from treated crops. Two experiments were undertaken, both using radiolabelled cypermethrin. a. Low Dietary Intake (0.2 mg/kg) Two lactating cows were given feed concentrate containing radio-labelled cypermethrin twice daily for a three-week period with a feeding level equivalent to 0.2 mg/kg on total daily feed. The cows were milked twice daily and the amount of radioactivity determined at each milking. The total radioactivity present in whole milk was in the range of 0.0002 mg/1 to 0.0012 mg/1 in terms of cypermethrin equivalents and 60-70% of the amount of radioactivity in the milk was present in the cream fraction. The total radioactivity found in the milk amounted to only 0.5% of the radioactivity fed to the animals. The remainder of the radioactivity was excreted in the urine (54%) and faeces (43%). The elimination occurred rapidly after dosing and the rate of elimination of radioactivity reached its peak (near 100% of applied dose) after three days.
In the urine 3(4-hydroxyphenoxy) benzoic acid-O-sulphate and the glutamic acid conjugate of 3-phenoxybenzoic acid were detected in the ratio of 1:4. The free acids were not detectable. The faeces contained the parent compound amounting to approximately 85% of the faecal 14C, that is, about 36% of the amount ingested. At the end of the three-week feeding period the animals were slaughtered and samples of tissues examined for radioactivity. Levels were below 0.001 mg/kg, in cypermethrin equivalents, in blood, muscle and brain. In subcutaneous and renal fats, liver and kidney samples, residues were at or below the equivalent of 0.012 mg/kg cypermethrin (Shell R. 124). b. High Dietary Intake (5 mg/kg) Radiolabelled cypermethrin was fed in the feed concentrate twice daily and was given in amount equivalent to 4 mg/kg on total diet over a period of 7 days. The radioactivity in the milk, urine and faeces was monitored throughout the feeding period and showed that the major excretory route was via the kidneys. All the cows were found to be pregnant at necropsy and the milk yields throughout the experiment were poor. Equilibrium between intake and excretion was reached 3-4 days after commencement of feeding, after which levels in whole milk ranged between 0.009 mg/l and 0.013 mg/l cypermethrin equivalent to radioactivity present. The cream fraction of the milk contained 85-90% of the total radioactivity. Results of experiments carried out with 14C-benzyl and 14C-cyclopropyl labels indicate that the residue in milk is an ester and contains both the acidic and alcoholic functions of the parent compound. The major urinary metabolites in cows were identified as the glutamic acid conjugate of 3-phenoxybenzoic acid (68%), 3-phenoxybenzylglycine (16%), 3-phenoxybenzoic acid (9%). 3(4-hydroxy-phenoxy) enzoic-acid and its O-sulphate conjugate appeared to be present in only small amounts (1%). At the end of the test feeding period the animals were slaughtered and tissues were taken for measurement, with the following results, radioactivity being expressed as cypermethrin equivalents. Muscle 0.04 mg/kg Fat 0.01-0.10 mg/kg Liver and Kidney 0.05-0.13 mg/kg These results indicate that the cypermethrin does not accumulate in the tissues of the animals. Even at a high intake, residues are mostly in the fat, liver and kidney. Cereals and components of feed (e.g. cotton seed) treated with the highest recommended dose rates therefore, are unlikely to result in measurable residues in meat or milk of cattle (Shell R. 125). IN PLANTS Degradation on cotton, lettuce and apples has been studied using 14C-radiolabelled material with the label in various positions in the cypermethrin molecule. Structures of compounds mentioned are given in Figure 1. a. Cotton An experiment in which the cis- and trans-isomers of cypermethrin were applied in acetone/water solution to cotton leaves using a small syringe was carried out on plants grown in pots in the greenhouse. Each of the two isomers, which in themselves consisted of a racemic mixture of two enantiomeric pairs of stereo isomers, was labelled in the cyclopropyl and benzyl rings in separate experiments. In each experiment the rate of application was 10-20 µg/g of leaf. Leaf samples were taken for examination immediately after treatment and again 42 days later. The samples were extracted with acetone and the examined by chromatographic and radiochemical techniques. Forty-two days after treatment 75-85% of the original total applied radioactivity was still present in cotton leaves and 90% of this was acetone extractable. Thin-layer chromatography showed that at least six components were present in the extracts. Products identified and the approximate proportion present in the extracts were cypermethrin (40-50%), 4-hydroxy-cypermethrin (compound A/ 5-8%), 3-phenoxybenzoic acid (15%), and an amide (compound B/ 8-20%). In this preliminary study unidentified material accounted for the remaining 20-30% and was mainly polar material. No evidence of an appreciable difference in the rate of loss and breakdown of the two isomers was obtained. A second experiment was carried out on a larger scale, in which cypermethrin was 14C radio-labelled in the benzyl ring and applied at the rate of 4 µg/g leaf. Two applications were made 15 days apart and leaf samples were taken 5 weeks after the second treatment. Results were qualitatively similar to the first experiment, except that smaller amounts of metabolites were found and, in addition, some 3-(4-hydroxyphenoxy)-benzoic acid was also reported to be present. Due to the larger scale of the experiment it was possible to examine the polar fraction in more detail. This was found to consist of at least 8 compounds which were mainly conjugated forms of 3-phenoxybenzoic acids 3-(4-hydroxyphenoxy)-benzoic acid and 3-phenoxybenzyl alcohol. When the results from experiments using cypermethrin, separately labelled in the nitrile, cyclopropyl and benzyl groups, were compared, the properties of the polar products formed differed according to the label position. Thus it was again concluded that, following the primary step of hydrolysis of the ester link, further degradation of the component parts, including loss of nitrile, oxidation and conjugation, took place. In this work, the cyclopropane carboxylic acid (compound C) was identified as a metabolite. In a third experiment the cotton was grown in boxes outdoors in Seville, Spain. Cypermethrin, labelled either in the cyclopropane or benzyl rings, was applied to separate plants. The cis and trans isomers, in each case, were also applied in separate experiments. Three applications were made at rates equivalent to 300 g/ha and samples were taken at harvest 15 weeks after the final treatment. Seed, fibre, boll cases and leaves were examined separately. All the kernel samples separated from the seed cases contained small amounts of radioactivity equivalent to 0.07-0.24 mg/kg cypermethrin. Due to the oily nature of the extracts and the small size of the samples, it was not possible to fully identify the products present, although it was shown the radioactivity was not present in the form of cypermethrin itself. Seed cases freed from lint also contained radioactivity equivalent to up to 0.17 mg/kg cypermethrin, which again was shown not to be parent insecticide. The lint samples contained rather more variable amounts, between 0.08 and 0.62 mg/kg cypermethrin equivalents, probably depending on the degree of opening of the bolls at the time of spraying. Cypermethrin itself was the major compound present (between 50 and 90% of the total) but the remainder consisted of polar products. Foliage and boll cases were found to contain the same products as those reported from glasshouse experiments. These included cypermethrin, 3-phenoxybenzoic acid in free form, the cyclopropane carboxylic acid (free) and the amide, Compound A. The latter in particular was present, however, in considerably smaller amounts than found in the glasshouse experiment. Polar materials were also found in appreciable amounts. These could be hydrolysed by acid to give 3-phenoxybenzoic acid, 3-phenoxybenzyl alcohol and 3-phenoxybenzaldehyde. Unidentified materials in foliage amounted to only a small proportion of the total radio-label present. In another experiment, abscised cotton leaves were placed with their stems immersed in an aqueous solution containing ring 14C-radiolabelled Compound C for 72 hours. At the end of this period 90% of the radioactive material originally present in the solution had been taken up by the leaves. The major proportion (78%) of this material was found to be present as sugar conjugates of Compound C. Experiments have also been carried out with the degradation products 3-phenoxybenzoic acid (14C ring-labelled) and cis-2-(2',2'-dichlorovinyl)-3,3-dimethyl cyclopropane carboxylic acid (14C-C1-label). In some of these the stems of cotton leaves were immersed in aqueous solutions. There was a rapid uptake of both compounds and a rapid conversion to polar products. These products were subsequently shown to be derivatives with various mono- or di-saccharide sugar products in the case of the cyclopropane carboxylic acid and mainly glucose in the case of 3-phenoxybenzoic acid. Leaves to which 3-phenoxybenzoic acid was applied topically on the intact plant showed similar conversions to a mixture of sugar conjugates although at a much slower rate than in the case of petiole uptake. Similar experiments with 3-phenoxybenzoic acid have been undertaken on vine, tomato, soybeans, pea and broad bean leaves and with similar findings, (Shell R. 126, 127, 128, 158, 159 and 160) b. Lettuce Experiments were carried out on plants grown in pots in the glasshouse and treated with solutions of either the cis- or trans-isomer of cypermethrin. Each isomer was also labelled in either the benzyl or cyclopropyl rings. Details were similar to the first cotton experiment, described above, except that samples were taken immediately after treatment and 18 days later, and the results were qualitatively similar. Just over 70% of the original applied radioactivity was still present 18 days after application and 90% of this was extractable with acetone. But a higher proportion (50-70%) of the extracted radioactivity was present as cypermethrin than with cotton. The proportions of other products found were: compound A, 5-10%; 3-phenoxybenzoic acid, 10-15%; and compound B, 12-15%. An unidentified 11-15% consisted of several minor metabolites. An outdoor experiment was also performed on lettuce using cypermethrin labelled in the benzyl and cyclopropyl rings. The two labelled materials were applied to different plants as an overall foliar spray of a diluted E.C. formulation at a rate equivalent to 300 g/ha. Treatments were made on two occasions with an interval of about two weeks, and the plants were harvested approximately three weeks after the second treatment. The major part of the residue, which amounted to 0.8-1 mg/kg(radioactivity equivalent to cypermethrin) was located in the outer leaves and only 10-20% was present in the hearts. In the benzyl labelled experiment, 50% of the radioactivity was present as cypermethrin itself and most of the remainder as polar materials which individually were in too small amounts for detailed study. Only 4% was not extracted. In the cyclopropyl labelled experiment, 30% of the residue consisted of cypermethrin and 40% as conjugates of Compound C of which a glucose ester was identified (Shell R. 126, 129). c. Apples Apple trees growing in an outdoor wire-covered enclosure were treated with cis-cypermethrin, separately labelled in the benzyl or cyclopropyl rings, or with trans-cypermethrin, labelled in the benzyl ring. Leaves were treated on three occasions at intervals of 25 and 37 days, and harvested four weeks after the last treatment. Fruit was treated twice at a 24-day interval and harvested three weeks after the second application. Examination of the leaves showed that 32-46% of the residue consisted of the parent isomer applied. In addition, 7-15% of the radioactivity present was identifiable as compounds A and C, 3-phenoxybenzyl alcohol, 3-phenoxybenzaldehyde and 3-phenoxybenzoic acid. Polar compounds made up most of the remaining residue. Sugar conjugates of 3-phenoxybenzoic acid and the corresponding alcohol, as well as of 3-(4-hydroxyphenoxy)-benzoic acid, were identified. In fruit, results were similar although the quantities present were much lower. Examinations of peel and pulp separately showed that less than 2% of the total radioactivity in the fruit was present in the pulp. On the peel 50-77% was present in the form of the parent isomer applied. During the experiment 15% of the cis isomer was converted into the trans isomer. The amounts of metabolites were somewhat less than in leaves and accounted, as free compounds, for 3-7% of the radioactivity present. Polar materials from the fruit were present in much smaller amounts then in leaves and were not present in sufficient quantities to be studied in detail. In the experiments with the cis isomer some conversion (30%) into the trans isomer occurred, but the reverse change was not observed. In some routine examinations of field samples for residues of cypermethrin the glc analytical method used results in separation of the cis and trans isomers on the chromatograph trace. No change in the relative sizes of the two peaks with different treatment to harvest intervals, or between unresolved standard material and the test samples, has been observed. It would, therefore, seem that the conversion of cis isomer into trans compensates for the faster degradation of the trans isomer (Shell R. 130). IN SOIL Degradation on soils was studied by adding 14C-labelled cypermethrin to three different soils - a clay and a sandy clay from Spain, and a sandy loam from the U.K. Separate experiments were carried out with the molecule labelled in the benzyl or the cyclopropyl moiety. In addition, the cis and trans isomers were studied individually (Roberts and Standen, 1977). The cis isomer was found to degrade at an initial rate equivalent to a half life of between 2 and 4 weeks in sandy clay and sandy loam, and about 10 weeks in the clay soil. The trans isomer degraded more rapidly than the cis isomer in all three soils, with initial half-lives between about one and three weeks. Degradation was shown to proceed by hydrolysis of the ester link and cyano group with loss of carbon dioxide to give 3-phenoxybenzoic acid and Compound C, which were both present as free compounds. Subsequent degradation of both compounds was shown to occur, since 14 C-radiolabelled carbon dioxide was evolved over 22 weeks in amounts equivalent to 24% and 38%, respectively, of the total radioactivity initially present as ring label. As indicated by the presence of small amounts of Compounds A and 3-(4-hydroxyphenoxy)-benzoic acid, some hydroxylation of the aromatic rings also took place. Up to 36% of the original radioactivity was found to be difficult to extract 16 weeks after the commencement of the experiment. A study of this fraction showed it to be composed of several materials bound to soil components. Examination of the acid hydrolysed material showed that 30% or more of the radioactivity was in the form of Compound C. Smaller amounts of 3-phenoxybenzoic acid and 3-(4-hydroxyphenoxy)-benzoic acid were also found. After 52 weeks unchanged parent material accounts for 1.4-10.7% of the radioactivity originally applied to the soils. In one sample of a Spanish soil (Brenes) a trace amount of Compound B was also present and in the same soil 5.8% of the original radioactivity was present as a cyclopropane dicarboxylic acid, Compound D. In a separate experiment, this latter compound was also found, in amounts of 3-13% of the applied radioactivity, 8 weeks after application to soils stored in the laboratory. Under waterlogged and anaerobic conditions hydrolytic breakdown was found to be somewhat slower than under aeroboic conditions. Breakdown of 3-phenoxybenzoic acid was also slower. Compound C has also been shown to be formed from permethrin in soils and to be degraded by hydroxylation at the gem-dimethyl groups. Subsequent further breakdown has been shown in further studies, leading to extensive evolution of CO2 derived from ring and chloromethylene carbons (ICI, 132, 133, 134, 135). These data substantially confirm the results obtained with cypermethrin, showing that Compound C is unlikely to accumulate in soils following treatment with the pesticide. In addition to the degradation studies referred to above, studies have also been made to determine the rate of loss of cypermethrin from soils from field experiments in which very high rates of application had been made. The compound was applied as a diluted 40% EC and was partly incorporated to the soil (3-5 cm) after treatment. Samples were generally taken from 0-15 cm depth. The data obtained (Shell C and R. 136 to 140), show that for the same rate applied, the amount of residue initially present after treatment varied widely from one trial to the other, and that cypermethrin degrades fairly rapidly in soils. Only 1-5% of initial residue, if any, could be detected 4-8 months after treatment. The leaching studies with labelled cypermethrin in a column containing sandy loam soil show that less than 2% of applied radioactivity had been eluted with water at a rate of 2 ml/hr from the column over the 45-day period (Hungary, 1979), and that 90% of the initial activity was present in the top 2 cm of the soil. The findings from laboratory experiments are in agreement with the results of field trials. From the above findings, it may be concluded that, even when applications have been made to crops at recommended rates, residues of cypermethrin itself are unlikely to be present at detectable levels in soils at the beginning of the season following that in which treatments were made. It may also be concluded that crops grown in plots where treatments with cypermethrin have been made in a previous season are unlikely to contain detectable residues. IN PROCESSING Cypermethrin is a moderately stable and water-insoluble compound. Data relating to the effect on residue levels of various treatments given to harvested crops are as follows: a. Peeling Numerous data show that the residue present in a crop is largely on the surface. Analyses of pulp and peel after peeling apples, pears, peaches and citrus fruits (Table 6) show that levels in the pulp were below 30%, and in most instances below 10%, of those in whole fruit. b. Juice extraction - citrus Data for citrus have shown that residues of cypermethrin in juice extracted from treated fruits contained no measurable residues of the pesticide (see Table 6). C. Wine making Wine has been manufactured from grapes treated with cypermethrin and containing up to 0.15 mg/kg pesticide. No residues (limit of determination 0.01 mg/l) were found in the juice after fermentation (Shell C., 142). d. Cooking Studies were made on the effect of boiling on residue levels in plums, and cabbage. Levels were not substantially reduced by boiling plums for 30 minutes or cabbage for 45 minutes. Residues in the cooked commodities were 75-90% of the initial levels and only very small amounts were found in the cooking water (Shell C., 143). e. Oil seed processing An experiment was carried out with a cotton seed sample deliberately treated at the high rate of 300 g/ha and harvested one day after treatment. It contained 0.12 mg/kg cypermethrin on whole seed, with adhering linters. The sample was processed by simulating commercial practice in a laboratory specialising in the techniques. Residues were found to be transferred to kernels, which originally did not contain any detectable residue in the seed, during the commercial mechanical separation process (Shell R., 144). The residues of cypermethrin in the extracted oil at various stages were as follows: Crude oil 0.10 mg/l, neutralised oil 0.07 mg/l, bleached oil 0.08 mg/l and deodorised oil 0.05 mg/l. Both the alkali wash and deodorisation steps contribute to some losses. The results from this experiment suggest that the two processes together may be expected to remove about half of the residue. Hence, it is possible that residues may occasionally occur in oil obtained from seed, treated under practical conditions, at levels approaching those in whole seed. Photodecomposition The photodecomposition of cypermethrin was studied in methanol solution under UV light and in the solid phase (3 mg/cm2 on glass) under sunlight. 55% of cypermethrin was recovered from the methanol solution after two days. In sunlight there was no detectable loss of cypermethrin after 30 hrs. In both experiments cypermethrin proved to be more stable than decamethrin and its behaviour was comparable to permethrin (Ruzo et al, 1976, 1977). EVIDENCE OF RESIDUES IN FOOD IN COMMERCE OR AT CONSUMPTION At present no data deriving from national monitoring studies or market control are available. METHODS OF RESIDUES ANALYSIS Several methods have been developed for the analysis of agricultural commodities for residues. These are all based on gas-liquid chromatography procedures using equipment commonly found in modern analytical laboratories. Limits of determination of 0.01 mg/kg are usually attainable. The racemic cypermethrin contains eight possible steric and optical isomers which can be partially resolved in the GLC column depending on its polarity. On analysis of the mixture of isomers on OV-225 phase three partially resolved peaks with a characteristic pattern are obtained. However with apolar or moderately polar packings (OV-101 or OV-17) no resolution of isomers occurs which facilitates the quantitation of the residue. Four methods have been developed by Shell. For cotton and other oil-seed crops, the sample is extracted with an acetone/petroleum mixture and the extract subjected to clean-up by solvent partition followed by absorption chromatography on Florisil. The appropriate fractions of the eluate are then examined by gas-liquid chromatography using electron capture (63Ni) detection (Shell R. 147). For other crops the samples are ground with anhydrous sodium sulphate and cypermethrin extracted with acetone and petroleum spirit. The extract is washed with water and the resultant petroleum spirit layer separated and cleaned-up by chromatography on a Florisil column. Cypermethrin is eluted with ether/petrol and determined using gas-liquid chromatography and a (63Ni) electron-capture detector (Shell R. 148). Residues in animal tissues are determined by extracting the tissue with mixed acetone:hexane, and fat removed by partitioning between hexane and acetonitrile. The extract is cleaned-up by absorption chromatography on a column of Florisil and cypermethrin determined in the appropriate eluate fractions, by glc using electron-capture detection (Shell R. 149). Soil samples are mixed with anhydrous sodium sulphate and extracted with a mixture of acetone and petroleum spirit. The extract, which contains any cypermethrin present in the soil, is washed with water to remove acetone and cleaned up by adsorption chromatography on Florisil. Residues of cypermethrin are determined using GLC with an electron-capture detector (Shell R. 150). Confirmation of a residue in either soil or crop may be obtained by TLC (thin-layer chromatography) on Silica Gel plate eluted with toluene without previous saturation followed by further GLC. ICI have also developed basically similar analytical methods for application to crop samples. In their method the crop samples are extracted with 20% acetone in hexane and, where necessary, co-extractives removed by solvent partition. Further clean-up is carried out by adsorption column chromatography on Silica Gel or Florisil and cypermethrin determined by GLC in conjunction with an 63Ni E.C. detector (ICI 151). Recovery experiments have shown that all the methods cited are capable of measuring 80% or more of any cypermethrin residue present and that they are suitable for regulatory purposes. Chapman reported on the applicability of various adsorbent-solvent systems for the cleanup of some plant extracts containing cypermethrin, fenpropanate, permethrin, and fenvalerate. Analytical methods suitable for the determination of metabolites of cypermethrin in crop samples obtained following practical applications in the field have been developed using HPLC. Under normal circumstances the limit of determination is 0.05 mg/kg.(Shell R. 161) The amide, Compound B, is extracted with a mixture of water and acetonitrile from the sample of which the water content is known. Clean-up of the extract is performed by solvent partition and reversed-phase partition chromatography followed by reversed phase HPLC. Final analysis is carried out with normal HPLC using a UV detector (Shell R. 162). 3-phenoxybenzoic acid may be determined in a similar manner, although partition between dilute aqueous alkaline acetonitrile and hexane in used to remove parent cypermethrin from free 3-phenoxybenzoic acid. Conjugated material is hydrolysed by treatment of the concentrated aqueous extract with hydrochloric acid. The 3-phenoxybenzoic acid is converted into the methyl ester which may then be determined directly on HPLC. Alternatively, if further clean-up is required, HPLC may be used for this purpose and gas chromatography/mass spectrometry with multiple ion monitoring used for the determination (Shell R. 163). Compound C may also be extracted from crop samples with a mixture of water and acetonitrile and separated from unwanted material by solvent partition. Conjugated Compound C is however retained in the aqueous phase which may be concentrated and hydrolysed with hydrochloric acid. The liberated compound C may then be extracted with an ether/petroleum spirit mixture. Clean-up of the extracts is performed by reversed phase HPLC and Compound C determined by normal phase HPLC. If extracts are insufficiently clean for HPLC they may be treated with alpha-cyano-3-phenoxy-benzyl bromide, and the cypermethrin formed determined by gas chromatography with electron capture detection (Shell R. 164). Other experiments have shown that the great majority of samples may be stored for long periods in the deep freeze without appreciable loss of residues. Residue levels were determined in crop and soil samples at intervals following addition of known quantities of cypermethrin in the range of 0.2 mg/kg to 1 mg/kg. The samples were stored at -18°C between treatment and extraction for analysis, for periods between 1 and 54 weeks for crops and 4-49 weeks for soil. Recoveries of cypermethrin added to crops (21 samples) were 85-110%, apart from one sample of tobacco which yielded 45% after 6 months storage. In the case of soils (5 samples) recoveries were all between 90 and 110% (Shell R. 152). Studies have also been carried out on the stability in storage at -18°C of residues of 3-phenoxybenzoic acid and Compounds B and C. Over three months there was no evidence of loss of 3-phenoxybenzoic acid, since the total amounts recovered from the 6 crops used (lettuce, potatoes, cabbage, apples, pears and maize grain) were in the range of 75-100% and comparable to recovery values of the method itself. With Compound B experiments were carried over three months with sweet corn and over five months with apples and cabbage. Recoveries were 70%, 75% and 75% respectively. Cabbage and apples treated with Compound C were also stored at -18°C for five months. Recoveries were 90-95% respectively. These data, therefore, indicate that loss of any of the three degradation compounds mentioned were negligible over periods of 3-5 months at 18°C. NATIONAL MRLs REPORTED TO THE MEETING National MRLs and pre-harvest intervals have been established in several countries based on local requirements. The following were presented at the meeting: Country Commodity MRL Pre-harvest int. (days) Argentina Apples 21 Cotton 20 Peaches 25 Tomatoes 7 Soya, Sorghum 40 Sunflower 30 Colombia Cotton 35 Costa Rica Cotton, Vegetables 15 Country Commodity MRL Pre-harvest int. (days) Cyprus Vegetables 14 Top Fruit Fed. Rep. of Germany Leafy vegetables 14 Potatoes 14 Maize 49 France Apples 0.5 14 Peaches 0.5 14 Vines 0.5 14 New Zealand Kiwi fruit 2.0 14 Pome fruit 1.0 14 Brassicas 1.0 7 Peru Cotton 15 Tomatoes 15 Potatoes 15 Spain Cotton 21 Potatoes 21 Tomatoes 21 Citrus 21 South Africa Cotton 0.05 28 Grapes 0.05 28 Maise 1.5 28 Peas 0.1 7 Tomatoes 0.2 4 Syria Top fruit 7-10 Vegetables Experimental or wider use of cypermethrin in further 43 countries was reported where neither preharvest intervals nor MRL's have been yet established. APPRAISAL Cypermethrin is active against a wide range of insects which attack crops and can be used at a relatively low dose rate in the range of 0.02-0.25 kg a.i./ha. It is a moderately stable and water insoluble compound. The technical material contains not less than 90% w/w cypermethrin, which is a mixture of optical isomers, with a cis:trans isomer ratio of approximately 40:60. The maximum concentration of residues in/on the treated crops in the range of 0.05-2 mg/kg and decreases slowly. The majority of residues are in the peel or outer leaves, and in most instances the pulp or hearts contain below 10% of those in the whole crop. The trans isomers of cypermethrin degrades slightly faster than the cis, which is compensated by the conversion of cis isomer into trans during degradation, thus the isomers remain in a constant ratio at different times after application in plants. Degradation in crops occurs mainly by hydrolysis of the ester bond followed by further hydrolytic and oxidative processes to give a variety of products. Less rapid processes observed were hydrolysis of the nitrile group to amide and hydroxylation of the phenoxy ring. The compounds formed were, in turn, also hydrolysed at the ester link. However, metabolites have not been detected in crop commodities from supervised trials. At least 90% of the total residue present in plant material is extractable with acetone. Processing of treated crops after harvest usually reduces the residue significantly. Cattle consuming feed items treated with cypermethrin eliminate the residue rapidly. Equilibrium between intake and excretion is reached in 3-4 days. The total radioactivity found in the milk amounted to only 0.5% of the radioactivity fed to the animals and 60-90 of this residue was present in the cream fraction. The residues in the milk are esters and contain both acidic and alcoholic moieties of the parent compound. The vast majority of residue in the feed is excreted in the urine and faeces in roughly similar proportions. The main metabolite in urine is 3-phenoxybenzoic acid which is present as glutamic acid conjugate and glycine derivatives. The faeces mainly contain the intact molecule. Cypermethrin does not accumulate in the meat. Even when fed at a high dose rate residues are mostly in the fat, liver and kidney. The data indicate that the feeding of crops treated with cypermethrin following the recommended use patterns does not result in measurable residues in meat or milk of cattle. Since the compound may be used for direct treatment of animals and data deriving from the latter use are not available, recommendations of MRLs for animal products cannot be made at present. In soils, spray deposits remain in the surface layer. The rate of degradation is dependent on the type of soil and proceeds by hydrolysis of the ester link and cyano group finally resulting in acids from both parts of the parent compound. Some hydroxylation of the phenoxy aromatic ring occurs. Subsequent degradation also takes place with the breakdown of the carbon rings. The trans isomer degrades more rapidly than the cis. The results indicate that no detectable residue of cypermethrin itself will be present in soil 8-12 months after treatment and that crops grown in the next season will not contain measurable residues of cypermethrin. Analytical methods available for the determination of residues in various commodities are suitable for regulatory purposes. The limit of determination is typically 0.01-0.02 mg/kg. RECOMMENDATIONS The following temporary maximum residue limits are recommended based on the pre-harvest intervals indicated below. The limits refer to the sum of isomers of the parent compound in the portion of sample to be analysed as described by CC/PR. Pre-harvest interval on Commodity Temporary MRL mg/kg which recommendation is based (days) Citrus fruits 2 14 Peaches 2 7 Pome fruits 2 7 Cherries 1 7 Grapes 1 7 Brassica leafy vegetables 1 7 Lettuce 2 7 Plums 1 7 Raspberries 0.5 14 Strawberries 0.5 21 Tomatoes 0.5 3 Rapeseed 0.2 42 Wheat 0.2 14 Cottonseed 0.1 7 Cottonseed oil (finished) 0.2 Kidney beans, peas, soybeans (without pods) 0.05 7 Maize 0.05 7 Potatoes 0.05 7 Sugar beet (roots) 0.05 14 Sweet corn 0.05 7 FURTHER WORK OR INFORMATION Required by 1981: 1. Pharmacokinetic data on the potential bioaccumulation of cypermethrin and/or metabolites in adipose tissue. 2. Observations in man, especially those with high level of occupational exposure, to evaluate the potential susceptibility of man to the neurotoxic syndrome observed in rodents. Desirable 1. A dominant lethal bioassay. 2. Further residue data on kiwi fruit from supervised trials. 3. Selective surveys of residues in crops known to have been treated under practical circumstances. 4. Use patterns for animal health use and residues in animal products deriving from the recommended application. REFERENCES Baldwin, M.K. The analysis of a Metabolite of WL 43467 in Human Urine as an Index of Exposure to that Compound. (1978) Unpublished Report from Shell Research Ltd., submitted by Shell International Chemical Co. Brooks, T.M. Toxicity Studies with WL 43467. Mutagenicity Studies with WL43467 in the Host-Mediated Assay and in Micro-Organisms In Vitro. (1976) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. Brown, V.K. Toxicology of WL 43467 Isomers: Acute Toxicity of WL 43481 in DMSO to rats. (1979a) Unpublished report submitted by Shell International Chemical Company. Toxicology of WL43467 Isomers: Acute Toxicity of WL42641 in DMSO to Rats. (1979b) Unpublished report submitted by Shell International Chemical Company. Buckwell, A.C. and Butterworth, S.T.G. Toxicity Studies on the Pyrethroid Insecticide WL 43467. A 13-Week Feeding Study in Dogs. (1977) Unpublished Report from Shell Research Ltd., submitted by Shell International Chemical Company. Butterworth, S.T.G. and Clark, D.G. Toxicity Studies on the Insecticide WL43467: Acute Oral Toxicity and Neuropathological Effects in Syrian Hamsters. (1977) Unpublished report from Shell Research Ltd., Submitted by Shell International Chemical Company. Carter, B.I. and Butterworth, S.T.G. Toxicity of Insecticides. The Acute Oral Toxicity and Neuropathological Effects of WL 43467 to Rats. (1976) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. Chapman, R.A., and Harris, C.R. Extraction and Liquid-Solid Chromatography Cleanup Procedures for the Direct Analysis of 4 Pyrethroid insecticides in Crops by Gas Liquid Chromatography. J. of Chromatography 166. 513-518. Combs A.D., Carter, B.I. 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The Elimination and Retention of WL 43467 when administered Dermally or Orally to Sheep. (1977a) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. Crawford, M.J. and Hutson, D.R. The Metabolic Fate of the cis- and trans- isomers of WL 43467 (Cypermethrin). Metabolism and Elimination of 14C-labelled cis- and trans-isomers in Rats. (1977b) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. The Elimination of Residues from the Fat of Mice Following the Oral Administration of [14C-benzyl-] WL 43481 (cis-WL43467). (1978a) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. The Elimination of Residues from the Fat of Rats Following the Oral Administration of [14C-benzyl] WL 43481 (cis-WL 43467). (1978b) Unpublished Report from Shell Research Ltd., submitted by Shell International Chemical Company. The Metabolic Fate of the cis-and trans-isomers of Cypermethrin in the Rat. Metabolites Derived from the 14C-Labelled Cyclopropyl Ring. (1978c) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. Crawford, J.V. A Study of the Metabolism of 3-Phenoxybenzoic Acid and its Glucoside Conjugate in Rats. (1978) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. Crawford, J.V. and Hutson, D.H. The identification of Metabolites in the Tissues of Rats Treated Orally with 3-Phenoxybenzoic Acid. (1979) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. Dean, B.J. Toxicity Studies with WL 43467: Chromosome Studies on Bone Marrow Cells of Chinese Hamsters After Two Daily Oral Doses of WL 43467. (1977) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. Dean, B.J., van der Paux. C.L. and Butterworth S.T.G. Toxicity Studies with WL 43467: Dominant Lethal Assay in Male Mice After Single Oral Doses of WL 43467. (1977) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. Dewar, A.J. The Use of Lysosomal Enzyme Measurements as an Indicator of Chemically-Induced Peripheral Neuropathy. (1977a) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Co. Toxicity Studies on the Insecticide WL 43467: Biochemical and Functional Studies on the Neurotoxicity of WL 43467 to Rats. (1977b) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. Dewar, A.J. and Deacon, P.A. Toxicity Studies on the Insecticide WL 43467: Electrophysiological Studies on the Neurotoxicity of WL 43467 to Rats. I. - The Effect on Motor Conduction Velocity in the Sciatic and Tail Nerves. (1977) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. Dewar, A.J. and Moffett, B.J. Toxicity Studies on the insecticide WL 43467: Biochemical studies on the effect of WL 43467 on the rat trigeminal nerve and ganglion. (1978a) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. Toxicity Studies on the Insecticide WL 43467: Biochemical and Function Studies on the Neurotoxicity of WL 43467 to Chinese Hamsters. (1978b) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. Dix, K.M. Toxicity of WL 43467: Teratological Studies in Rabbits given WL 43467 Orally. (1978) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. Glaister, J.R., Pratt, I. and Richards, D. PP 383: Effects of High Dietary Levels on Clinical Behaviour and Structure of Sciatic Nerves in the Rat. (1977a) Unpublished report from ICI Central Toxicology Laboratory submitted by ICI Ltd. Glaister, J.R., Gare, C.W., Marsat, G.J., Phillips, C. and Pratt, I. PP 383: 90-Day Feeding Study in Rats. (1977b) Unpublished report from ICI Central Toxicology Laboratory submitted by ICI Ltd. Hend, R.W. and Butterworth, S.T.G. Toxicity Studies on the Insecticide WL 43467: A Three-month Feeding Study in Rats. (1976) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Co. Toxicity Studies on the Insecticide WL 42641: a Five-Week Feeding Study in Rats. (1977a) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. Toxicity Studies on the Insecticide WL 43481: A five-Week Feeding Study in Rats. (1977b) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. Hend, R.W., Hendy, R. and Fleming, D.J. Toxicity Studies on the Insecticide WL 43467: A Three-Generation Reproduction Study in Rats. (1978) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. Hungary. Information supplied by country delegation to Codex Committee on Pesticide Residues on compounds on priority list. (1979). Hutson, D.H. Taurine Conjugation in the Metabolism of 3-Phenoxybenzoic Acid and the Pyrethroid Insecticide Cypermethrin (WL 43467). (1977) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. (Published in Xenobiotica, 8 (1978) 565-571). The Elimination of Radioactivity by Mice Following Oral Dosing with 14C-cis and 14C-trans-WL 43467 (Cypermethrin). (1978a) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. The Metabolites of cis- and trans-Cypermethrin (WL 43467) in Mice. (1978b) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. Hutson, D.H. and Stoydin, G. The Excretion of Radioactivity from Cows fed with Radioactively Labelled WL 43467. (1976) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Co. ICI. (1979) Unpublished reports available to meeting (referred to in text by ICI and code numbers 10, 132 to 135 and 151). Jaggers, S. Cypermethrin: Summary and Review of Acute Toxicities in Laboratory Species. (1979) Unpublished report submitted by ICI, Ltd. McAusland, H.E., Butterworth, S.T.G. and Hunt, P.F. Toxicity Studies on the Insecticide WL 43467: A Two-year Feeding Study in Rats. (1978) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. New Zealand. Information supplied by CCPR country delegation on compounds on priority list. (1979) Okuno Y., Kohda, H. and Kadota, T. Neurotoxic Effects of S-5602 and NRDC 149 by Dermal Application in Rats. (1976) Unpublished report from Sumitomo Chemical Company submitted by Shell International Chemical Co. Owen, D.E. and Butterworth, S.T.G. Toxicity of Pyrethroid Insecticides: Investigation of the Neurotoxic Potential of WL 43467 to Adult Domestic Hens. (1977) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company. Prinsen, G.H. and Van Sittert, W.J. Exposure and Medical Monitoring Study of the Pyrethroid WL 43467 After Single Application on Cotton in Ivory Coast. (1978) Unpublished report from Shell International Research Maatschappij, B.V., submitted by Shell International Chemical Co. Roberts, T.R. and Stande, M.E. Degradation of the Pyrethroid Cypermethrin NRDC 149 (± alpha-cyano-3-phenoxybenzyl) ± (cis trans 3(2,2-dichlorovinyl) 2,2-dimethycyclopropane carboxylate and Respective cis (NRDC 160) and trans (NRDC 159) Isomers in Soils. Poetic. Sci. 8, 305-319 (1977). Rose, G.P. and Dewar, A.J. Toxicity Studies on the Insecticide WL 43467: The Effect of Age on the Neurotoxicity of WL 43467 to Rats. (1978) Unpublished report from Shell Research Ltd., Ruzo, L.O., Holmstead, R.L., Casida, J.E. Solution photochemistry of the potent pyrethroid insecticides alpha-cyano-3-phenoxybenzyl cis 2,2-dimethyl-3-(2,2dibromovinyl) cyclopropane carboxylate. Tetrahedron Letters 35, 3045/1976. Ruzo, L.O., Holmstead, R.L. and Casida, J.E. Pyrethroid Photochemistry: Decamethrin J. Agr. Food Chem 25, 1385 (1977). Shell Chemie. France. Unpublished Reports. Referred to by "Shell C" and numbers in the text: 2-9, 11, 12, 14, 17-25, 27-30, 34,40, 44, 47, 55, 56, 60-64, 67-75, 77-86, 90-97, 101-105, 107-109, 112, 114-116, 118-122 136, 137, 142, 143, 152, 154, 155. Shell Research Ltd., England - Unpublished reports referred to by "Shell R." and numbers in the text: 1, 13, 15, 16, 26, 31-33, 41-43, 45, 46, 48-54, 57-59, 65, 66, 76, 87-89, 98-100, 106, 110, 111, 113, 117 123-130, 138-140, 144, 147-150, 152, 156, 158-160, 162-164. Shono, T., Ohsawa, K. and Casida, J.E. Metabolism of trans- and cis-Cypermethrin, and Decamethrin by Microsomal Enzymes. J. Agric. Food Chem., 27 (2), 316-325. South Africa. Information on compounds on priority list. (1979) Sweden. Information on compounds on priority list. (1979) Suzuki, H. Studies on the Mutagenicity of Some Pyrethroids on Salmonella Strains in the Presence of Mouse Hepatic S9 Fraction. (1977) Unpublished report from Sumitomo Chemical Co., Ltd., submitted by Sumitomo Chemical Co., Ltd. Tesh, J.M., Tesh, S.A. and Davies, W. WL 43467: Effects Upon the Progress and Outcome of Pregnancy in Rat. (1978) Unpublished report from Life Science submitted by Shell International Chemical Company. Trigg, C.E., Butterworth, S. and Hunt, P.F. Neurotoxicity of Pyrethroids: A Study of Teased Nerves from Rats Fed WL 43467 for 12 Months. (1977) Unpublished report from Shell Research Ltd., submitted by Shell International Chemical Company.
See Also: Toxicological Abbreviations