PESTICIDE RESIDUES IN FOOD - 1982 Sponsored jointly by FAO and WHO EVALUATIONS 1982 Data and recommendations of the joint meeting of the FAO Panel of Experts on Pesticide Residues in Food and the Environment and the WHO Expert Group on Pesticide Residues Rome, 23 November - 2 December 1982 Food and Agriculture Organization of the United Nations Rome 1983 PHOXIMIDENTITY Chemical Names OO-diethyl alpha-cyanobenzylidene-amino-oxyphosphonothioate alpha - (diethoxyphosphinothioyloxyimino) phenyl-acetonitrile alpha - / / (diethoxyphosphinothioyl)oxy/imino/benzeneacetonitrile O,O-diethyl phenylglyoxylonitrile oxime phosphorothioate Synonyms VolatonR BaythionR SRA 7502 BAYER 77488 Structural formula
Other Information on Identity and Properties Empirical formula C12H15N2O3PS Molecular weight: 298.3 Appearance light yellow oily liquid (pure active ingredient) Melting point 5-6°C (pure active ingredient) Specific gravity 1.176 at 20°/4°C (pure active ingredient) Vapour pressure approx. 10-4 mmHg at 20°C Solubility (in g/100 ml at 20°C) in water 0.7 in cyclohexane >60 in isopropyl alcohol >60 in methylene chloride >60 in toluene >60 Minimum degree of (pre-solution for reasons of stability in purity 9-11% butanol) 82.0% BIOCHEMICAL ASPECTS Absorption, Distribution, Excretion and Biotransformation Mouse Male Swiss mice were given a single oral dose of 32p-phoxim in olive oil at levels of 10.5, 114, and 955 mg/kg bw. At all three dosage levels, the recovery of administered radioactivity in urine and faeces was in the range of 73-82%, within 140 hours after dosing. However, the radioactivity appeared in the urine and faeces at a much lower than expected rate in the light of the low mammalian toxicity of phoxim. At the three dosage levels, respectively, only 43 22 and 15% of the administered radioactivity was excreted in the urine within 24 hours after treatment. An autopsy was performed on a mouse treated with 114 mg/kg bw after 48 hours to determine the internal fate of the administered dose. At this time, approximately 43% of the dose had been excreted in the urine. The results indicate that virtually all of the internal radioactivity was found in urinary bladder (88.4%), gut (8.8%) and liver (1.7%). The amounts of radioactivity found in other organs (brain, thymus gland, hind leg muscle, heart, kidney) and the amount of organic soluble material (which could include the strong anticholinesterase P=0 phoxim) were essentially insignificant. The autopsy data indicate that nearly all of the internal dose of phoxim remaining 48 hours after treatment was metabolized to water soluble compounds (97.6%), Five major metabolites were identified in the urine 0 to 24 hours after treatment with 114 mg/kg bw: (1) diethyl phosphoric acid, 58.9%; (2) phoxim, 1.1%; (3) phoxim carboxylic acid, 2.8%; (4) O,O-diethyl phosphorothioic acid, 20.0%; (5) either monodesethyl phoxim or monodesethyl P=O phoxim, 6.2%. The most relevant changes in the relative amounts of metabolites upon increasing the dose from 114 to 955 mg/kg bw occurred with phoxim carboxylic acid (2.8% to 23.6%) and diethyl phosphoric acid (58.9% to 43.1%) (Vinopal and Fukuto 1970). Fig. 1 presents the proposed metabolic pathway for phoxim in mice. Rat Male and female rats (Charles River CD strain) were intubated with 14C-phoxim (labelled in the benzene moiety) at a dose of 10 mg/kg bw. A group of male rats was also intubated at a dose of 1 mg/kg bw. The compound was readily absorbed from the gastrointestinal tract of male rats with average maximal plasma levels equivalent to 0.35 and 2.44 µg phoxim being reached within 30 minutes after dosing at 1 and 10 mg/kg respectively. A secondary peak, equivalent to 1.87 µg phoxim/ml, was observed at 4 hours in animals dosed at 10 mg/kg. A value of 0.04 µg phoxim/ml was measured at 24 hours in the plasma of rats receiving 10 mg/kg bw. There was a rapid uptake of radioactivity into the major organs and tissues following the administration of 10 mg/kg to male rats, the kinetics of which was similar to that for plasma. Slightly higher initial values were observed for kidney and liver, but levels of 0.06 to 0.6 µg equivalents of phoxim/g were reached in all tissues examined within 24 hours. Thus, there was no evidence for the selective retention of either phoxim or its presumed metabolites in any tissue and accumulation in the tissues is unlikely as a result of repeated administration.
In the 10 mg/kg treatment, male rats excreted an average of 92.9% of the radioactivity in the urine and 4.9% in the faeces in ten days, while females excreted 86.1% of the dose in the urine and 6.9% in the faeces in the same period. Male rats intubated at a dose of 1 mg/kg excreted 82% of the radioactivity in the urine and 7.9% in the faeces in ten days. However, most of the radioactivity (80-90%) was eliminated in 24 hours and excretion was virtually complete within 2 days. No evidence was obtained for the presence of 14CO2 in the expired air during the initial 24 hours. Radiochemical analysis 10 days after dosing of the major organs and tissues from animals dosed at both 1 and 10 mg/kg indicated the presence of only low levels of radioactivity, which corresponded to less than 0.1 µg phoxim/g tissue. An average of 0.80% and 3.3% of the radioactivity was excreted within 0-6 and 6-24 hours in the bile of cannulated male rats intubated at the 10 mg/kg dose level (Daniel et al 1978a). The biotransformation of phoxim was investigated in adult male rats (Charles River CD strain) following administration (by gavage) of a dose of 10 mg/kg bw. The major metabolites in the 24-hour urine was identified as hippuric acid (approx. 6%) and glucuronic and sulphuric acid conjugates (approx. 76%) of alpha-cianobenzaldoxime. Evidence was also obtained for the presence of both syn- and anti-forms of the oxime. Chromatographic analysis of the plasma obtained one hour after dosing revealed the presence of four radioactive components, two of which were characerized as mono-desethyl-phoxim (80%) and mono-desethyl PO-phoxim (12%). No evidence was obtained for the presence of PO-phoxim (Daniel et al 1978b). Effects on Enzymes and Other Biochemical Parameters In the rat, in vitro cholinesterase inhibition amounted to (I50) 4.19×10-4M for serum, 4.46×10-5M for erythrocytes and 2.51×10-6M for brain (Kimmerle 1968). The effect of the organophosphorus pesticide phoxim on the activity of liver succinate dehydrogenase (SDH) and cytochrome oxidase (CO) was studied in randomly bred albino rats. Animals received a single p.o. administration of phoxim at 0.5 LD50 (310 mg/kg) and were sacrificed 1 hour, 1 day and 5 days later. In chronic experiments, rats received phoxim at 31 mg/kg/day for 1, 3 and 6 months. Single administration of phoxim decreased CO activity in liver homogenate 1 hour after administration (5.3 IU, compared with 7.61 IU in controls), while the decrease in SDH activity was detected only on day 1 after administration (2.9 IU, compared with 7.55 IU in controls). In the supernatant, activities of CO and SDH showed an increase only on day 5 after administration (0.62 IU and 0.45 IU, respectively, compared with 0.42 IU and 0.086 IU in controls). Chronic exposure to phoxim did not change CO activity in the liver homogenate but resulted in an increase in CO activity in the supernatant (after 3 months exposure, CO activity was 0.80 IU compared with 0.42 IU in controls). Activity of SDH in the homogenate increased after exposure of 1 month (8.49 IU, compared with 7.55 IU in controls), while activity of SDH in the supernatant was increased only after 3 and 6 months of administration (0.35 IU and 0.59 IU, respectively, compared with 0.09 IU in controls) (Kuz'minskaia and Veremenko 1978). The effect of phoxim on the NADPH-dependent oxidation in the liver endoplasmic reticulum was studied in randomly bred albino rats, Phoxim was given p.o. for 3 days at 124 mg/kg/day (LD50 is 620 mg/kg). On days, 1, 5 and 15 after the last administration, animals were sacrificed and activity of liver demethylase (DM), hydroxylase (HL), uridine diphosphate glucuronyl transferase (UDPGT) and the level of ascorbic acid excretion were assessed. Phoxim administration was found to stimulate the process of demethylation. DM activity began increasing on day 5 after administration and remained at a high level up to day 15 (0.957 IU and 0.842 IU, respectively, compared with 0.602 IU in controls). HL activity was decreased on day 1 (0.714 IU, compared with 0.304 IU in controls), followed by a slight increase on day 5 (0.380 IU) and normalization on day 15. Activity of UDPGT was significantly increased only on day 1 after administration (5.48 IU, compared with 3.28 IU in controls). The level of urinary excretion of ascorbic acid showed a progressive increase up to 538 µg/ml on day 1, 194.8 µg/ml on day 5 and 174.8 µg/ml on day 15 (compared with 118.5 µg/ml in controls (Iakusko 1978). The effects of phoxim on the glucose-6-phosphatase (G6P), hexokinase (HK), total cholinesterase (ChE) and ChE isoenzyme activities were studied in the blood of male albino rats weighing 200-250 g. Group 1 served as a control, group 2 was treated (p.o.) with a single 310 mg/kg dose of phoxim (0.5 LD50), group 3 received 31 mg/kg/day for 1-6 months and treatment in group 4 was 3.1 mg/kg/day for 1-6 months. In group 4 the G6P and HK activities were increased and the ChE activity was reduced 1 hour after treatment. The HK activity became normal 1 hour later, the G6P activity remained elevated and the ChE activity declined further. All enzyme activities were normal 5 days after treatment. In group 3, the G6P and G6P dehydrogenase (G6PD) activities were increased by 45% and 70%, respectively, and the total ChE activity was decreased by 45% at the end of the first month. The ChE fractions 3, 4 and 5 were fully inhibited; fraction 2 was inhibited by 78%, and the activity of fraction 1 was increased by 61%. After treatment for 3 months the G6P activity was increased by 89%, the G6PD activity by 42% and the total ChE activity was inhibited by 26%, while the isoenzyme spectrum did not differ from that in the controls. After poisoning for 6 months, the G6P and G6PD activities were inhibited by 30%, and the total ChE by 24%. Fraction 1 was inhibited by 45% and the activity of fraction 2 increased by 35%, while the fractions 3, 4 and 5 remained normal. The changes seen in group 4 were similar to but less marked than those in group 3 (Kuz'minskaia et al 1979). TOXICOLOGICAL STUDIES Special Studies on Reproduction Groups of rats (10 male and 20 female, Long Evans FB30 strain/group) were fed diets containing phoxim (technical product, 85.7% a.i.) at concentrations of 0, 15, 75 and 375 ppm (calculated as pure a.i.) and subjected to a standard 2-litter per generation, 3-generation reproduction study. The rats were treated with the test compound throughout the study, including mating, gestation and lactation. At the start of the experiment, the rats were about 47 days old. The rats selected for the study were housed singly until they were sexually mature (up to an age of ca. 100 days). Then they were mated to initiate the study. During the mating period, two female rats were housed together with one male rat for 21 days. The male rats were rotated so that each female was paired with three different males for a period longer than one oestrous cycle. Immediately after the pups were delivered, their number and weights were recorded. Litters containing more than 10 pups were reduced on day 5 after delivery to 10 pups each, whereupon the weights of these litters were again measured. The pups were nourished for up to 4 weeks, weighed weekly, and then the offspring of each first mating (F1a, F2a, F3a) were sacrificed. The offspring of each second mating, as with those delivered after the first mating, were nourished for up to 4 weeks, then weaned and placed in separate sex groups. After week 8, 10 male and 20 female rats were again selected from each dose group for further matings. Upon reaching an average age of 100 days, the rats were mated as described above. After the dams of the F0, F1b and F2b generations had successfully nursed offspring twice, they were sacrificed. Necropsy was performed on rats that died during the study. Gross and histopathological examinations were performed on major organs and tissues of one male and one female 2-week old pup of the F3b generation from each of ten mothers in each group. There were no significant differences between the control and treated groups with respect to physical appearance, behavioural patterns, body weight curves of weaned males and females of the F0, F1b and F3b generations; some animals in both the control and treated groups died of pneumonitis. There were no significant differences between the control and treated groups with respect to pregnancy rate, litter size, 5-day survival rate (viability index), pups weights at birth and during lactation at all dose levels tested. Only the 375 ppm dietary concentration had a slight adverse effect on the lactation index in F3b. The inspections of the pups immediately after birth and during the lactation period did not reveal any signs of malformations. Gross and histopathological examinations did not provide any evidence of treatment-related alterations. The no-effect level in this multigeneration reproduction study was 75 ppm (Löser 1979). Special Studies on Mutagenicity The mutagenicity of phoxim (technical product, 83.8% a.i.) was studied by rec-assay and reversion test (Salmonella/microsome). The rec-assay was performed using two strains of Bacillus subtilis, H 17 and M 45. Volumes of 0.2 µl to 20 µ1 of phoxim per disc were tested. Kanamycin was used as a negative control and mitomycin C as a positive control. Phoxim did not inhibit the growth of H 17 and M 45 strains of B. subtilis at all the tested doses. On the other hand, with mitomycin C used as positive control more remarkable growth inhibition was identified in M 45 strain than in H 17 strain, and the growth of both strains was inhibited at the same degree with Kanamycin as the negative control. The reversion test was performed using two strains of Salmonella typhimurium TA 98 and TA 100, according to the Ames procedure, both with and without S-9 Mix derived from liver of SD strain rats treated with a single intraperitoneal injection of Arochlor 1254 (500 mg/kg bw). Concentrations of 10 - 5000 µg/plate were tested. 2-amino-anthracene (2-AA) and 2-(2-furyl)-3-(5-nitro-2- furyl) acrylamide (AF-2) were used as positive controls. A markedly increased number of revertant colonies was observed for AF-2 on the plates without S-9 Mix and for 2-AA on the plates with S-9 Mix. Phoxim did not increase the number of revertant colonies, either in the presence or absence of S-9 Mix. Under the conditions of the experiments, phoxim provided no evidence of mutagenic activity at concentrations up to 0.02 ml/disc of undiluted phoxim and 5 000 µg/plate, respectively, in a rec-assay and in a reversion test (Shirasu et al 1978). In another Ames test, phoxim (technical grade, a.i. 82.9% - 83.7%) was tested for mutagenicity with S. typhimurium TA 100, TA 1537 and TA 98 according to the Ames procedure, both in the presence and in the absence of S-9 Mix derived from male Sprague-Dawley rats treated with a single intraperitoneal injection of Arochlor 1254 (500 mg/kg bw). Seven concentrations (3.15-3150 nl/plate) were tested with S-9 Mix and five concentrations (31.5-3150 nl/plate) without it. At doses greater than 1 000 nl, however, part of the test compound separated as droplets from the top agar. In the experiments for direct mutagenicity N-methyl-N'-nitro-N-nitrosoguanidine and benzo(a)pyrene- 4,5-oxide were used as positive controls, whereas in the experiment with an activating system 3-methyl-cholantrene, benzo(a)pyrene and 2-amino-anthracene were used. Negative controls in the form of sterility controls and solvent blanks were run as well. For all three tested strains, there were no significant differences in the number of revertant colonies between the negative controls and the phoxim-treated plates, both with and without S-9 Mix. Positive controls displayed the expected increases, indicating the activity of the metabolizing system and the mutability of the bacteria. No bacteriotoxic effects were observed. Phoxim did not show a mutagenic effect in the Salmonella/ microsome test at concentrations as high as 3 150 nl/plate (Oesch 1977). Mouse - dominant lethal test on males Groups of mice (20 male NMRI mice/group) were given by gavage a single dose of phoxim (technical product stabilized with 10% n-butanol, 86.5% a.i.) corresponding to 0 and 500 mg/kg bw, the vehicle being a 0.5% Cremophor emulsion. The mouse strain used displayed a sensitive response to known chemical mutagens, such as cyclophosphamide. The dose was chosen on the basis of the results of a preliminary test conducted on male mice dosed orally with acute doses of 500, 750 and 1 000 mg/kg bw, respectively. At dose levels of 750 and 1 000 mg/kg bw the compound had a toxic effect and induced symptoms, but no mortalities occurred. Following dosing, each male mouse was caged with three untreated virgin female mice for 7 days. The procedure was repeated weekly with groups of three new untreated virgin females for a total of 8 weeks, in order to obtain and examine a complete sample of the successive germ cell stages of the males. The uteri of the females (466-480 per test group) were examined on gestation day 14. Counts were made of the corpora lutea, total implantations, viable implants and dead implants (sum of the deciduomata, resorptions and dead embryos and foetuses). There were no significant differences between the control and treated groups with respect to fertility quota, total implantations, viable implants, dead implants, ratio of dead implants to total implants and pre-implantation loss (estimated both directly from the difference between the number of corpora lutea and the number of implantations and indirectly through the comparison of the average number of implantations per fertilized female in the treated group with that in the control group). Thus, there was no indication for a mutagenic potential of phoxim in the dominant lethal test on the male mouse at an oral dose of 500 mg/kg bw (Machemer 1974). Micronucleus test Groups of mice (5 male and 5 female, NMRI (SPF) Han strain/group) were given (by gavage) two single doses of phoxim (technical product 84.3% a.i.) in aqueous 0.5% Cremophor emulsion at levels of 0, 250, 500 mg/kg bw. The interval between applications was 24 hours. Concurrently, a positive control group of mice received 2 × 100 mg/kg bw of cyclophosphamide. The doses were chosen on the basis of the results of a preliminary test in which groups of 5 mice were orally dosed with phoxim at 2 × 500 mg/kg bw and 2 × 1 000 mg/kg bw, respectively; in that test, the 2 × 500 mg/kg treatment was tolerated with induction of only weak symptoms. Six hours after the second application, the mice were sacrificed and femur bone marrow smears were prepared. Erythrocytes, 1 000 per mouse, were counted and the incidence of cells with a micronucleus was determined, as well as the ratio of polychromatic erythrocytes to normochromatic erythrocytes. The incidence of micronucleated polychromatic erythrocytes was 2.3/1 000 in the negative control group, and 1.8/1 000 and 1.0/1 000, respectively, in the phoxim-treated groups. There were no relevant differences between the negative control and phoxim-treated group with respect to the ratio of polychromatic to normochromatic erythrocytes. The incidence of micronucleated cells in cyclophosphamide-treated group was 68.2/1 000 and was thus biologically significantly higher than in the negative control group. Cyclophosphamide also exhibited a bone marrow depression, with the ratio of polychromatic to normochromatic erythrocytes showing a biologically relevant alteration (1 000 : 2 424.2 vs 1 000: 838.3 in the negative control group). The results provided no indication for a mutagenic potential of phoxim in the micronucleus test on mouse at the tested doses of 2 × 250 and 2 × 500 mg/kg bw per os. Treatments with phoxim also did not induce any depression of erythropoiesis (Herbold 1981). Special Studies on Embryotoxicity and Teratogenicity Groups of fertilized rats (20 Long Evans FB30 strain/group) received daily doses of phoxim (technical product stabilized with 10% n-butanol, 86.5% a.i.), administered by gavage in a 0.5% aqueous Cremophor emulsion, at levels of 0, 30, 100, 300 mg/kg bw from gestation day 6 through 15 (total of 10 doses). On gestation day 20, the dams were sacrificed and the foetuses removed by caesarean section. The foetuses were examined for external, internal and skeletal malformations. No dam died in any group and no adverse effects on behaviour patterns and general appearance were observed. The 300 mg/kg bw dose level had a maternal-toxic effect, resulting in significantly less weight gain during the treatment period as compared with the control animals. All animals in the test group showed comparable average weight gains throughout the period of gestation. There were no significant differences between the control and treated groups with respect to the measured parameters: fertilization quotas, pregnancy quotas, average numbers of implantations, foetuses and resorptions, average foetus weight, average placenta weight, average number of stunted foetuses (weighing less than 3 g) and type, frequency and localization of slight alterations in bone development. Sex distribution of foetuses was unaffected. Occasional malformations were seen, these being most frequent in the untreated control group. They were considered to be spontaneous malformations. The data provided no indication for embryotoxic or teratogenic activity in rats at an oral dose of 300 mg/kg bw and below (Machemer 1975). Special Studies on Carcinogenicity See under Long-Term Studies. Special Neurotoxicity Studies Hen Female White Leghorn hens, 2-5/group, about 14 to 18 months old, each received a single phoxim dose (without antidote) administered orally at levels of up to and including 50 mg/kg bw or intraperitoneally at levels of up to and including 37.5 mg/kg bw. The hens were kept under observations for 6 weeks. The determined LD50 was 37.5 mg/kg bw for both oral and intraperitoneal administration. In another study, hens 3-14/group, were each given as an antidote an intraperitoneal injection of 100 mg PAM/kg + 50 mg atropine sulphate/kg. They then received an oral or intraperitoneal application of phoxim at dose levels equal to the LD50 and higher. The survivors were kept under observation for 6 weeks. No histopathological examinations were carried out. The protection afforded by PAM + atropine to hens was more evident with intraperitoneal injection of phoxim than with the oral route. No positive controls were included. In both tests, without and with antidotal protection, no clinical signs of neurotoxic damage were seen (Kimmerle 1972). Groups of hens (10 White Leghorn, 12 to 14 months old/group) were fed diets containing phoxim from technical product stabilized with 10% n-butanol, 86.1% a.i. at concentrations of 0, 5 and 10 ppm for 28 days. During the feeding experiment, the behavioural pattern of all the hens was within the normal range. In particular, they did not display any symptoms of neurotoxicity. Treated and untreated controls hens were not significantly different with respect to food consumption and body weight gains. Blood acetylcholinesterase activity was not significantly depressed in the 5 ppm group. In the 10 ppm group, a marked (30%) depression of blood acetylcholinesterase activity was measured between day 14 and day 28 of the feeding experiment. The no-effect level was 5 ppm, equal to 0.32 mg/kg bw/day (Thyssen and Kimmerle 1973). Special Studies on Skin and Eye Irritation A dermal irritation study in rabbits of both sexes ("not of pure breed") showed that phoxim had only a very slight irritating effect on both intact and abraded skin (Kimmerle and Solmecke 1970). In an eye irritation test in rabbits, phoxim caused no eye irritation (Kimmerle and Solmecke 1970). Special Studies on Antidotes Male rats were given single oral doses of phoxim (technical product, 88.7% a.i.) to determine LD50 values with and without antidotes. Before the onset of severe poisoning symptoms (5 to 90 minutes), atropine sulphate (50 mg/kg bw), 2-PAM (50 mg/kg bw) or toxogonin (20) mg/kg bw) was given singly or in combination (atropine plus PAM-atropine plus toxogonin) by intraperitoneal injection. The results indicated that, among the tested antidotes, only combinations of 2-PAM or toxigonin with atropine sulphate had significant antidotal activity (Solmecke 1971). Special Studies on Potentiation Acute oral LD50 values in male Wistar II albino rats were determined experimentally for phoxim, phenamiphos and their equitoxic mixture. The observed LD50 value for the equitoxic mixture was compared with the expected value (calculated assuming an additive effect). The result was that simultaneous administration of phoxim and phenamiphos produced a less than additive effect (Thyssen 1976a). Special Studies on the Recovery of Cholinesterase Activity Groups of rats (15 male and 15 female, Wistar II, SBF albinos/group) were given daily doses of phoxim (technical product), administered by gavage in aqueous Cremophor EL emulsion, at levels of 0, 5, 50 mg/kg bw for 21 days. One-third of the rats were sacrificed upon termination of treatment, another third were kept under post- treatment observations for 14 days and then sacrificed and the remaining third were kept under post-treatment observation for 4 weeks. Determinations of acetylcholinesterase activities in erythrocytes and plasma were carried out before beginning treatment and thereafter at weekly intervals until 4 weeks after the end of administration. Brain acetylcholinesterase activity was measured at the end of treatment and 2 weeks after termination of treatment. During the 21-day treatment period and the 4-week post-treatment observation period, none of the treated rats in any dose group differed from the control rats with respect to behavioural patterns, physical appearance and body weight gain. No mortalities were observed. The following results were obtained in male rats: at 5 mg/kg bw, plasma and erythrocyte cholinesterase activities were not significantly different from the control group during both the treatment period and the post-treatment observation period; at 50 mg/kg, plasma and erythrocyte cholinesterase activities were about 65% and 56%, respectively, of the control after 1 week of treatment and remained similarly depressed during the treatment period; however, one week after the end of treatment, cholinesterase activity levels were again found not significantly different from the control. The following results were obtained in female rats; at 5 mg/kg bw, both plasma and erythrocyte cholinesterase activities were about 70% of the control after 1 week of treatment, but one week after the termination of treatment both were in the physiological range; at 50 mg/kg bw, both plasma and erythrocyte cholinesterase activities were about 37% of the control after 1 week of treatment; one week after termination of treatment plasma cholinesterase was again normal, while erythrocyte cholinesterase was 75% of the control and returned to normal at the end of the 4-week post-treatment observation period. Brain cholinesterase activity at the end of the treatment period was 82% and 67% of the control, respectively, for male and female rats of the 50 mg/kg bw group. However, the values measured 2 weeks after the end of treatment were not significantly different. Thus, female rats were more sensitive than males to the depression of plasma, erythrocyte and brain cholinesterase activities. The plasma, erythrocyte and brain cholinesterase activity depression was reversible; plasma cholinesterase returned to normal within 1 week, while erythrocyte and brain cholinesterase were normal in 2-4 weeks. The acute oral LD50 determinations prior to and after the 21-day treatment gave comparable values for both male and female rats (Thyssen 1976b). Special Studies on the Toxicity of Metabolites Acute toxicity studies were conducted with alpha- cyanobenzaldoxime (cyanoxime). The metabolite (and starting material in the synthesis of phoxim) has a very slight acute toxicity to rats: LD50 (mg/kg) Rat, male oral 4 520 Rat, female oral 4 063 Rat, male,female dermal (24 hours) >5 000 From the symptoms of poisoning observed (behavioural disorders, sedation, breathing disorders) cyanoxime seemingly acts on the central nervous system. In acute inhalational toxicity experiments, in which rats were exposed to dust for 1 hour and 4 hours, respectively, and rats and mice were exposed to vapour for 6 hours, no toxic effects were observed. In tests for skin and eye irritation, the metabolite did not cause any irritation to the skin of rabbits. In the eye of rabbits, however, it caused moderate to severe irritation on the conjunctiva and superficial corrosion on the cornea (Thyssen and Kimmerle 1976). The glucoside of alpha cyanobenzaldoxime did not cause any toxic effects when administered as an acute oral dose to female rats; a dose of 2 500 mg/kg bw was tolerated without inducing any symptoms (Mihail 1979). PO phoxim, formed as an intermediate product of metabolism, has an oral LD50 to the mouse of 1 000 mg/kg bw (Vinopal and Fukuto 1970). Special Studies on Cholinesterase Inhibition by P=O Phoxim The following 150 values were determined in vitro for the P=O analogue of phoxim: erythrocyte (bovine), 2.2 × 10-7M; brain (mouse), 6.0 × 10-8M (Vinopal and Fukuto 1970). Special Studies on Tolerability of Phoxim by Sheep Groups of sheep (25 freshly shorn Merinos/group) were given phoxim once, administered by intubation as an aqueous emulsion, at levels of 0, 25 and 50 mg/kg bw. Each of the treated groups was divided into two and one half was treated early in the morning and the other half late in the afternoon. This was done to vary the times of exposure to sunlight after treatment. The sheep were examined daily for 10 days after treatment and any abnormalities were recorded. The sheep treated in the morning remained exposed to strong sunlight for only 3 hours after treatment. Cloudy conditions prevailed for the remainder of the observation period, which reduced the possibility of determining any phototoxic effect. No signs of systemic toxicity or dermal inflammation were seen in any of the test animals up to day 10 after treatment (Baldock and Hopkins 1976). Acute Toxicity The results of acute toxicity studies are summarized in Table 1. Signs of poisoning in mammals after oral administration usually developed within 5 minutes to 2 hours after dosing in mice, rats, rabbits, cats and dogs and lasted for 1 to 7 days in survivors. Deaths occurred after 1 to 3 days. It was only at the highest dose levels that these symptoms took the form of acute cholinesterase depression (cramps, trembling, diarrhoea and red tears in rats). The only symptoms noted in the lower dose levels were lowering of the general condition and sedative effects. The toxicity signs did not differ in the tested species. The autopsies of the animals receiving high doses of the active ingredient showed no changes in the internal organs (Kimmerle and Solmecke 1970). Following intraperitoneal injection, the symptoms of poisoning did not appear more quickly than after oral application. As with oral treatment, the typical cholinergic symptoms were observed only at very high doses (Kimmerle 1968a). Hens are considerably more sensitive to phoxim than mammals (Kimmerle 1972; Thyssen and Kimmerle 1973). Table 1. Acute Toxicity of Phoxim Species Sex Route Vehicle LD50 Reference Mouse F oral none 2.53-3.38 Flucke 1978 a ml/kg b.w. F oral none 2.50-3.50 Flucke 1978 b ml/kg b.w. F oral none 2.62-2.77 Flucke 1979 a ml/kg b.w. F oral none 3.24-3.60 Flucke 1979 b ml/kg b.w. F oral none 2.50-3.18 Flucke 1980 ml/kg b.w. F oral none 2.96-3.40 Heinmann 1982 ml/kg b.w. M oral none 2 440 Kimmerle 1968 µl/kg b.w. F 3 240 µl/kg b.w. " M inhalation alcohol + >2.06 " (4-h exp.) Lutrol (1:1) mg/l air F i.v. none 950 µl/kg b.w. " M oral none 1 645 Kimmerle and µl/kg b.w. Solmecke 1970 Table 1. (con't) Species Sex Route Vehicle LD50 Reference Mouse F oral none 1 990 Kimmerle and µl/kg b.w. Solmecke 1970 M inhalation alcohol + >3.10 (4-h exp.) Lutrol (1:1) mg/l air " F i.v. physiological 481 solution & mg/kg b.w. " Cremophor EL F oral none 3.02-3.48 Mihail 1981 ml/kg b.w. F oral none 2.98-3.49 Mihail 1982 mg/kg b.w. Rat M oral none 7 060 Kimmerle 1968 µl/kg b.w. F 5 800 µl/kg b.w. M i.p. none 1 775 µl/kg b.w. " F 1 725 µl/kg b.w. Table 1. (con't) Species Sex Route Vehicle LD50 Reference Rat (con't) M dermal none > 1 000 (7-day exp.) µl/kg b.w. M inhalation alcohol + >1.99 (4-h exp) Lutrol (1:1) mg/l air M inhalation alcohol + >2.23 Kimmerle and (5x4-h exp.) Lutrol (1:1) mg/l air Solmecke 1968 F inhalation >2.22 (4-h, exp. ) mg/l air M dermal none >1 000 Kimmerle and (7-day exp.) µl/kg b.w. Solmecke 1970 M inhalation alcohol + >2.55 (4-h. exp.) Lutrol (1:1) mg/l air inhalation > 0.55 (5x4-h exp.) mg/l air F inhalation >2.78 (4-h exp.) mg/l air inhalation > 0. 55 (5x4-h exp.) mg/l air Table 1. (con't) Species Sex Route Vehicle LD50 Reference Rat (con't) M oral none 1 845 µl/kg b.w. F 1 680 µl/kg b.w. M i. p. none 1 645 µl/kg b.w. F 1 635 µl/kg b.w. M oral 2 650 mg/kg b.w Solmecke 1971 M oral water & Cremophor EL 2 825 Thyssen 1976 a mg/kg b.w. Guinea pig F oral none 350-500 Kimmerle, 1968 µl/kg b.w. F oral water & Cremophor EL 660 Kimmerle and mg/kg b.w. Solmecke 1970 Rabbit M&F oral none 250-500 Kimmerle 1968 µl/kg b .w. F oral water & Cremophor EL 250-375 Kimmerle and mg/kg b.w. Solmecke 1970 Table 1. (con't) Species Sex Route Vehicle LD50 Reference Cat M&F oral none > 1 000 Kimmerle - 1968 µl/kg b.w. F oral water & Cremophor EL 250-500 Kimmerle and mg/kg b.w. Solmecke 1970 Dog M&F oral none > 1 000 Kimmerle 1968 µl/kg b.w. F oral water & Cremophor EL 250-500 Kimmerle and mg/kg b.w. Solmecke 1970 oral] approx. 37.5 Kimmerle 1972 Chickens i.p.] mg/kg b.w. Hen oral water emulsion 19.6 Thyssen and mg/kg b.w. Kimmerle 1973 Short-Term Studies Rat - dietary Oral feeding tests were conducted to determine the safety of using Baythion (phoxim) in place of Cythion (malathion) in the treatment of stored grain to control insect pests. Baythion and Cythion were fed to rats at concentrations of 1, 2, 4, 6, 10 or 0 ppm in the diet. Adult rats and their offspring were fed for a period of up to 5 months. No adverse effects were noted as a result of these treatments. It is concluded that 4 ppm Baythion mixed with stored grains could be used as a substitute for Cythion, with no adverse effects expected in humans (Lin 1974). Groups of rats (15 male and 15 female, Wistar strain SPF/group) were fed diets containing phoxim (technical product stabilized with 10% n-butanol, 87.2% a.i.), at concentrations of 0, 5, 15, 50, 150 and 500 ppm for 3 months. The control group comprised 30 male and 30 female rats. Haematological, clinical chemical and urinalysis parameters were determined on 5 male and 5 female rats of each dose group after 4 weeks and 3 months of feeding. The cholinesterase activity in plasma and in erythrocytes was determined at 1, 4, 8 and 13 weeks after the start of the experiment in 5 male and 5 female rats of each group. The animals dying during the experiment were subjected to autopsy. At the end of the study, all the animals were sacrificed and gross and histopathological examinations were performed. There were no significant differences between control and treated animals with respect to behaviour, food and water consumption and body weight gain. Cholinergic symptoms were sometimes observed in the 500 ppm group only, particularly during the first half of the experiment. Only the male rats in the 500 ppm group showed significantly lower body weights. No compound-related mortality occurred. The treated animals of all dosage groups did not significantly differ from the control animals throughout the experiment with respect to haematological, clinical chemical and urinalysis parameters. There was an increasing dose-dependent inactivation of both plasma and erythrocyte cholinesterase in male rats at 50 ppm and above. In female rats, a dose-dependent depression was noted at 15 ppm and above in the plasma and at 50 ppm and above in the erythrocytes. The autopsy of all rats at the end of the feeding experiment showed no changes of the internal organs attributable to the inclusion of phoxim in the diet. Male rats in the 500 ppm group had significantly higher thyroid and liver weights, as compared to controls. There were no dose-related or significant differences between any of the dose groups up to 50 ppm and the control animals with respect to relative organ weights. Higher relative liver weights in males and females of the 150 ppm and 500 ppm groups were observed. These enlargements are indicative of an influence on the liver, although the liver function tests were all normal. Higher relative kidney weights were observed in the males of the 500 ppm groups and in the females of the 150 ppm and 500 ppm groups. Heart and adrenal in the males of the 500 ppm group and thyroid and lung in the females of 500 ppm group had significantly higher relative weights, as compared to the control animals. The no-effect level with respect to plasma and erythrocyte cholinesterase was 15 and 5 ppm, respectively, for male and female rats, equal to approximately 1.45 and 0.56 mg/kg bw/day (Löser 1970a). No histopathological change was seen in the tissues examined that was considered to be compound-related (Vince and Spicer 1971). Dog - dietary Groups of beagle dogs (2 males and 2 females/group) were fed diets containing phoxim (technical product stabilized with 10% n-butanol, 87.2% a.i.) at concentrations of 0, 2, 5 and 10 ppm for 3 months. The control group comprised 3 male and 3 female dogs. Inclusion of the active ingredient in the diet at dose levels up to 10 ppm did not affect the physical appearance, behaviour, food consumption, growth and mortality rate of male and female dogs. Cholinesterase activity in the plasma was depressed in both males and females at the dose level of 2 ppm after 1 month, but not at the end of the study. The results of the haematological, clinical chemical and urinalysis determinations showed no significant differences between the control and treated groups. The organ weights were unaffected by the administration of phoxim. Macroscopic examination of internal organs of the treated animals showed no pathological changes attributable to the inclusion of phoxim in the diet. A no-effect level was not observed (Löser 1970b). Groups of beagle dogs (2 males and 2 females/group) were fed diets containing phoxim (technical product stabilized with 10% n-butanol, 87.2% a.i.) at concentrations of 0, 50, 200 and 1 000 ppm for 3 months. The control group comprised 3 male and 3 female dogs. The dogs in the 1 000 ppm group showed cholinergic symptoms, but no dogs died in any of the dose groups during the experiment. The dose level of 1 000 ppm caused weight loss in the female dogs. Haematological determinations made after 6 weeks and at the end of the study did not reveal any pathological changes in the dogs of any groups. Clinical chemical parameters were normal in the 50 and 200 ppm groups. Increased activities of alkaline phosphatase (ALP) and lactate dehydrogenase (LDH) were determined in the animals of the 1 000 group. However, the activities of liver-specific enzymes ornithine carbamyl transferase (OCT), GPT and sorbitol dehydrogenase (SDH) did not change. Urine examinations and the kidney function test (urea and creatinine in serum) were normal in all groups, as were blood sugar and cholesterol levels. Plasma cholinesterase activity was depressed at 50 ppm and above, while erythrocyte cholinesterase was first affected at the 200 ppm level. The organ weights were unaffected by the administration of phoxim. Macroscopic examination of internal organs of the treated animals showed no pathological changes attributable to the inclusion of phoxim in the diet. A no-effect level was not observed (Löser 1971). Groups of beagle dogs (4 males and 4 females/group) were fed diets containing phoxim (91.1% a.i.) at concentrations of 0, 0.3, 1 and 2 ppm for 3 months. No deaths occurred during the study. There were no significant differences between the control and treated dogs with respect to behavioural pattern, physical appearance, food consumption, body weight gain, reflex, eye examinations, haematology, clinical chemistry, thromboplastin time and urinalysis, as determined at 0, 5 and 12 weeks. The no-effect level for plasma cholinesterase was 0.3 ppm for both males and females. Erythrocyte cholinesterase activity was not affected in any of the treated groups. Autopsy and histopathological examinations performed on all the animals provided no indication of treatment-related alterations (Mürmann and Luchaus 1973). Groups of beagle dogs (4 males and 4 females/group) were fed phoxim in the diet (technical product, stabilized with 10% n-butanol, 86.5 a.i.) at the following levels for 2 years: control group - 0 ppm; group I - males, 0.3 ppm and females 0.1 ppm from week 83; group II - 15 ppm; group III- 750 ppm. Daily examinations were made for physical appearance and behavioural pattern. Intake of food and water was also checked and noted daily. Body weights were recorded weekly in the first year and thereafter at 14-day intervals. At periodical intervals (14, 26, 39, 52, 64, 78, 92 and 104 weeks) reflex testing, ophthalmoscopy, haematology, clinical-chemistry and urinalyses were performed. Plasma and erythrocyte cholinesterase determinations at 4, 7, 10, 15, 27, 39, 51, 64, 77, 91 and 103 weeks and brain cholinesterase at the conclusion of the study were performed. At the end of the 104 weeks of dietary administration, all the dogs were sacrificed and gross and histopathological examinations of tissues and organs were performed. There was no mortality over the course of the study in any group. Treatment did not affect the behavioural patterns of any of the dogs. The female dogs of each treated group and the male dogs of group I did not differ in physical appearance from the controls. Male dogs in group II and group III had a poor state of nutrition. The male dogs of group III had a dull and ungroomed coat in the second treatment year. Food consumption levels were not affected by treatment. The time taken for the food ration to be consumed by the dogs was slightly longer in group II and considerably longer in group III. Average body weight curves, especially for the males, were lower than those for the control group and were dose related. However, only the body weights of group III rats were statistically significantly lower than those of control rats. A marked decrease of body weight was evident in male dogs of group III after 72 weeks. The reflexes were normal in all dogs at all times tested. The ophthalmoscopic examinations of the eyes provided no indication of any treatment-related variations from the physiological norm in either the transparent media or on the fundus oculi. The average total intake of phoxim per dog was 0.068 g, 3.60 g and 181.08 g, respectively for group I, group II and group III. Data from haematological tests and urinalyses were normal. Plasma and erythrocyte cholinesterase activities were not affected in males of group I, i.e. at 0.3 ppm. In females of group I, plasma cholinesterase activity was seen to be depressed to a level 26% below the control value in week 77. As this result was confirmed by repeated measurements, the concentration of phoxim administered to the female dogs of group I was reduced from 0.3 to 0.1 ppm from week 83. The later determinations in week 91 and 103 showed that plasma cholinesterase activities in group I females were again equal to the control values. At the 15 ppm level and above, plasma and erythrocyte cholinesterase activities were markedly depressed, and were dose related, from the first determinations and remained relatively constant over the entire study. Brain cholinesterase activity was not depressed at dietary concentrations of up to and including 15 ppm, being depressed 35-40% at 750 ppm level. Clinical chemistry values (glucose, urea, creatinine, total protein, GOT, bilirubin) showed no differences between treated dogs and controls. Statistically significant values, increasingly higher than controls, were observed for GPT (from week 52) and ALP (from week 14) in the dogs of group III (less marked in the females). In the group II dogs and in the males of group I, ALP activity values were statistically significantly higher than in the controls; they were at the same level throughout the second half of the experiment. In the controls, the physiological age-related reduction of ALP activity was observed during the course of the study. In the group III dogs the average serum cholesterol level was lower than that measured in the control dogs at every investigation time until the end of the feeding experiment. At gross pathological examination, the livers of 4 female dogs and one male dog of group III had a darker (dark brown to grey) colour than those of the control dogs and the dogs of the other two treated groups. Furthermore, the livers of some dogs in group III were seen to have a marked lobular pattern. There were no noteworthy differences between the treated dogs of all groups and the control dogs with respect to absolute and relative organ weights, with the exception of liver and thyroid. The absolute and relative weights of the liver in the male and female dogs of group III were statistically significantly higher than the weight of the liver in the control dogs. There was also a slight increase in the relative weight of the liver in the male dogs of group II, but this difference was not statistically significant. The absolute and relative weights of thyroid in the female dogs of group III were greater than those in the control dogs, but this difference was not statistically significant. Hepatocyte alterations were seen at histopathological examination in all the dogs of group III. The hepatocytes were dilated, the plasma had a light glassy appearance and was less structured than in the control dogs or the dogs of the other two dietary concentration groups. The increase in the absolute and relative thyroid weights in the female dogs of group III is not associated with histopathological alterations, so that it is doubtful whether this increase was compound related. Some other alterations of varying degree were observed in other tissues of both the control group and the treated groups, so they were not considered treatment related. The study indicated 0.3 ppm in the diet, equal to 0.068 mg/kg bw/day, and 0.1 ppm, respectively, for male and female dogs, as no- effect levels with respect to plasma and erythrocyte cholinesterase (Hoffmann and Gröning 1977). Monkey - dietary Rhesus monkeys (Macaca mulatta) (20 males and 20 females/group) were administered by gavage daily doses of phoxim (technical product stabilized with 10% n-butanol, 83.8% a.i.) dissolved in maize oil at levels of 0, 0.2, 0.65 and 2.00 mg/kg, 6 days per week for 6 months. Throughout the study the monkeys tolerated the administration of phoxim well and remained in good health. There was no evidence of any cholinergic effects despite the observed reduction of plasma cholinesterase activity. Average body weights and urinalyses were not significantly different between the control and treated groups, There were some differences between the control and treated groups with respect to some clinical chemistry values (blood urea nitrogen, glucose, total bilirubin, GOT, calcium) and some haematology values (packed cell volume, erythrocyte count). However, these fluctuations were, for the most part, within the normal limits for the colony of monkeys, and in no case were dose related. Erythrocyte cholinesterase activity was slightly reduced at 2.0 mg/kg, but plasma cholinesterase activity was reduced at all three dose levels tested. Expressed as percent of the control groups, the remaining activity after six months was, respectively, for each dosage level, 62%, 43% and 34%. A no-effect level was not determined. The microscopic examination of liver biopsy material obtained prior to the administration of phoxim and after six months of administration provided no evidence of an effect of phoxim on liver morphology (Coulston et al 1978). Rabbit - dermal Groups of 6 male and 6 female rabbits (3 males and 3 females/ group with intact skin and the remainder per group with abraded skin) were exposed dermally to phoxim (technical product stabilized with 101 n-butanol, 83.8% a.i.; as an emulsion in water and Cremophor EL) at dose levels of 0, 0.5 and 15 mg/kg bw/day, 7 hours per day, 5 days per week for a total of 15 applications in a 21-day period. The treated sites (5 × 5 cm) on the flank and back of the animals, not covered with bandages, were washed with water and soap at the end of each daily exposure period. Behaviour and general aspect were normal for all animals. No treatment-related deaths occurred. There were no adverse effects on the pre- and post-treatment values of body weight or on terminal haematological, clinical chemical and urinalysis parameters, Erythema was not observed in any animals with intact skin. A slight compound- related increase in time necessary for erythema to disappear was noted in treated animals with abraded skin. Skin-fold thickness was comparable between the control and treated groups. There were no significant differences between control and treated groups with respect to both absolute and relative weights of major organs. Histopathological examinations were performed on heart, lung, liver, spleen, kidney, adrenals, testis, epididymis, ovary, uterus and thyroid from control and 15 mg/kg bw groups. Some alterations occurred in both control and treated animals and were not considered compound related. Slight increases of degree of cell infiltrations and of incidence of epithelium thickening were observed on the treated skin of animals at 15 mg/kg bw with abraded skin, as compared to control animals. The same changes were not observed in animals with intact skin. These findings were considered the result of repeated mechanical stimuli. Plasma and erythrocyte cholinesterase activities measured after exposures 8 and 15 were significantly depressed (ca. 60%) at 15 mg/kg bw/day. Brain cholinesterase activity was slightly (23%) depressed only in male rabbits at 15 mg/kg bw/day (Flucke and Schilde 1978). Long-Term Studies Rat Groups of rats (50 males and 50 females, SPF Wistar strain/group) were fed a diet containing phoxim (technical product stabilized with 10% n-butanol, 85.7% a.i.) at concentrations of 0, 15, 75 and 375 ppm (calculated as pure active ingredient) for 24 months. The control group included 100 males and 100 females. In addition, 5 male and 5 female rats were used in each group for clinical laboratory examinations, which were carried out at 3, 6 and 12 months. At the end of the study, 10 males and 10 females were used for these examinations. There were no differences in appearance and behaviour between the treated and control animals during the study. In the 375 ppm group male rats had a lower mean daily food intake and females showed significantly less weight increase than control animals, mainly in the second half of the study. Mortality after 1 and 2 years was not increased in any treated groups. The overall mortality rate for treated and control groups at the end of the study was in the range of 24-26% for male rats and 14-21% for female rats. There were no significant differences between the control and treated groups with respect to haematological examinations at 3, 6, 12 and 24 months. There were no dose-related differences between control and treated groups with respect to alkaline phosphatase, GOT, GPT, glutamic dehydrogenase (GLDH, determined only at the end of the study), serum bilirubin and total serum protein, as determined at 3, 6, 12 and 24 months. Urinalyses, serum urea and creatinine, and urine protein showed no relevant differences between the control and treated groups after 3, 6, 12 and 24 months. Urine protein was sporadically increased in the 75 ppm group. Mean values for blood sugar and cholesterol showed some variations between the control and treated groups that were not dose related. Cholinesterase activity in erythrocytes and plasma was not significantly inhibited (less than 20%) in the male and female rats in the 15 ppm group. In the 75 ppm and 375 ppm groups, a marked and dose-related inhibition of the enzyme in plasma (16-42% in males, 41-64% in females) and in the erythrocytes (24-54% in males, 25-49% in females) throughout the study was observed. Brain cholinesterase activity (measured at the end of the trial) was slightly inhibited (18% in males, 23% in females) only in the 375 ppm group. The autopsies on rats dying during the study (106) and those sacrificed at the end of the treatment did not reveal any treatment- related damage. There was a significant, but not dose related, increase in the relative liver weight of male rats of all dose groups as compared to controls. There was also an increase in relative weights of spleen, lungs and heart of female rats of the 375 ppm group. Histopathological examinations performed on some 31 tissues of all the rats surviving the 2-year treatment did not reveal any treatment-related alterations. The differences in relative organ weights found were regarded as random, as they were not dose related, and there was no histopathological correlation. The analysis of tumour data according to the site, type and incidence of both benign and malignant tumours provided no indications suggestive of carcinogenic activity of phoxim in the rat. The no-effect level for both plasma and erythrocyte cholinesterase was 15 ppm (Bombhard and Löser 1977). COMMENTS Phoxim has been evaluated for the first time by the JMPR. It has a mild acute toxicity, as confirmed following the various routes of application. No sex-dependent differences were observed. In the longer-term experiments, however, females tended to display higher sensitivity. The acute experiments revealed a species-dependent toxicity. There was no available information on specification of the technical product. Phoxim is readily and almost completely absorbed. It is rapidly excreted in the rat, and there is no evidence of bio-accumulation. The metabolic pathway in mammals follows typical steps, such as hydrolysis, desulphuration and conjugation. Possible metabolites have a slight to moderate acute oral toxicity. A delayed neurotoxicity test was negative but the test was considered to be unacceptable. No-effect levels were determined with respect to reproduction and teratogenicity. Mutagenicity and carcinogenicity studies were negative. In a two-year dog study, plasma and erythrocyte cholinesterase were more sensitive than brain cholinesterase. A 90-day dog study provided a no-effect level bridging the large differences between effect and no-effect levels in the 2-year dog study. An increase in relative liver weight, not dose related, was also observed in the 2-year rat study at all dosage levels, without histopathological correlation. No observations in humans were available. The available data permitted the determination of no-effect levels in two mammalian species. Because of the unavailability of an acceptable delayed neurotoxicity study, only a temporary ADI was allocated. TOXICOLOGICAL EVALUATION Level Causing no Toxicological Effect Rat : 5 ppm in the diet, equivalent to 0.56 mg/kg bw Dog : 2 ppm in the diet, equivalent to 0.05 mg/kg bw. Estimate of Temporary Acceptable Daily Intake for Man 0 - 0.005 mg/kg bw FURTHER WORK OR INFORMATION Required (by 1984) An appropriate neurotoxicity study in hens. Desirable 1. Observations in humans (particularly effects on cholinesterases), 2. Type and content of impurities in the technical product. REFERENCES Baldock, C. and Hopkins, T. Bay 9053. Safety in sheep. Report from 1976 Bayer, Australia, submitted to the World Health Organization by Bayer, Australia, (Unpublished) Bombhard, E. and Loser, E. SRA 7502. Chronic toxicity studies in rats 1977 (feeding experiments over 2 years). Report (No. 7042) from Institut für toxicologie, Bayer, submitted to the World Health Organization by Bayer, F.R.G. (Unpublished) Coulston, F., Griffin, T., Talley, W. and Iatropoulos, M.J. A safety 1978 evaluation study of phoxim in Rhesus monkeys. Final Report from Institute of Comparative and Human Toxicology, Albany Medical College, Albany, New York, and International Center of Environmental Safety, Albany Medical College, Holloman, New Mexico, submitted to the World Health Organization by Bayer F.R.G. (Unpublished) Daniel, J.W., Swanson, S. and McLean, J. Phoxim: pharmacokinetics and 1978a biotransformation in the rat. Report (No. 78/BAG 5/194) from Life Science Research, Stock, Essex, England, submitted to the World Health Organization by Bayer, F.R.G.(Unpublished) Daniel, J.W., McLean, J. and Pringuer, M. Phoxim- biotransformation in 1978b the rat. 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See Also: Toxicological Abbreviations PHOXIM (JECFA Evaluation) Phoxim (Pesticide residues in food: 1983 evaluations) Phoxim (Pesticide residues in food: 1984 evaluations) Phoxim (Pesticide residues in food: 1984 evaluations)