CHLORMEQUAT JMPR 1972 Explanation The data relative to identity and residues in food and their evaluation were reviewed at the 1970 Joint FAO/WHO Meeting on Pesticide Residues (FAO/WHO, 1971). At that time the original reports of most of the biochemical and toxicological studies conducted with chlormequat were not available. Many of these data are now reviewed. EVALUATION FOR ACCEPTABLE DAILY INTAKE BIOCHEMICAL ASPECTS Absorption, distribution and excretion An oral dose of chlormequat (chlorocholine chloride) labelled with 14C was administered to male rats. The bulk (60.6%) was excreted in the urine in four hours and 96% was eliminated within 46.5 hours. Faecal excretion accounted for 2.3% and <1% was expired as 14CO2. The remaining 0.5% was found in the tissues, the largest amount being in the carcass (0.25%), intestines (0.11%) and liver (0.08%). Chromatography indicated that the radioactivity was all in the form of chlormequat (Blinn, 1967). In an earlier study 330 mg were administered to male and female rats. The compound was detected in the urine after 30 min. and reached a peak at 1-8 hours. It could no longer be detected after 56 hours (Shaffer, 1970). In an analysis of the urine of rats that had received 200 mg/kg of chlormequat orally, only chlormequat and two other compounds, which may have been other salts of chlorocholine, were found. Choline itself was not identified (Bronisz und Romanowski, 1968). Rats were administered orally a single (60 mg) dose of 15N-labelled chlormequat or they received 2 mg of the labelled compound daily for 100 days. After the single dose the amount of compound in the brain decreased rather quickly, but there was considerable accumulation in the kidneys over the 20 days of the investigation. After the continuous administration, chlormequat was noted particularly in active muscles such as the heart and diaphragm (Bier and Ackermann, 1970). When a lactating cow received a single oral dose of 1 000 mg of 15N-labelled chlormequat, the compound was demonstrated in the milk and urine three hours after administration. The main excretion of chlormequat was 15-39 hours after administration, the total during that time being 489 mg. Only 22 mg was excreted in the milk and the concentration in the milk never exceeded 1 ppm, the peak concentrations being 12-60 hours after administration (Lampeter and Bier, 1970). Effect on enzymes and other biochemical parameters Suggestions that chlormequat may inhibit acetylcholinesterase and microsomal oxidation are not based on substantial evidence. A study in which rats were fed diets containing 500 - 3 000 ppm chlorocholine and/or chlormequat, with or without cysteine, produced no evidence to suggest that chlormequat has a lipotropic effect on the formation of fatty liver produced by choline deficiency (Proll et al., 1970). Groups of 4 male and 4 female rats were fed a diet containing 0 or 2 000 ppm of chlormequat for 21 days. The animals were then sacrificed for cholinesterase determinations. There was no difference between test animals and controls with respect to plasma, RBC or brain cholinesterase (Levinskas, 1965). TOXICOLOGICAL STUDIES Special studies on reproduction Groups of 20 male and 20 female rats received diets containing 0, 100, 300 or 900 ppm of chlormequat in a standard three-generation study. Chlormequat produced no abnormalities in the appearance, behaviour, food intake, weight gain, fertility, gestation, lactation or viability of offspring. No foetal malformations or macro- or micro-histopathological abnormalities could be attributed to chlormequat (Leuschner et al., 1967). In a long-term feeding study in which rats received a diet containing 10 to 1 000 ppm chlormequat, there was no evidence of effect on fertility, development of young or of teratogenicity (Ackermann et al., 1970). Special studies on teratogenicity Groups of pregnant mice received an i.p. injection (30 mg/kg) of chlormequat either on days 14 and 15 or on days 11 to 15 inclusive, of gestation. Another group of mice received 200 mg/kg by gavage daily on days 11 to 15. On day 19 all mice were sacrificed. The mean number of foetuses per mother, foetal size, frequency of resorption and incidence of malformation did not vary between test and control animals (Shaffer, 1970). Pregnant mice were fed dietary levels of 0, 1 000 or 10 000 ppm of chlormequat from days 1 to 15 of gestation or 25 000 ppm from days 11 to 15 inclusive. All animals were sacrificed on day 19. The average number of foetuses per mother, size of foetuses and number of resorption sites did not vary between test and control groups. The number of malformations among foetuses of mothers fed 1.0% or 2.5% of chlormequat was slightly higher than that of the controls (Shaffer, 1970). Groups of mature male and female mice were fed dietary levels of 0, 1 000 or 5 000 ppm of chlormequat for ten weeks. Matings were conducted after 1, 3, 4 and 10 weeks between the controls and animals on the various dose levels. Upon sacrifice on day 19 of gestation, the feeding of chlormequat was found to have no effect on the fertility of the mice and produced no terata among the offspring (Shaffer, 1970). Groups of rats were fed dietary levels of 0, 1 000 and 5 000 ppm of chlormequat from days 1 to 21 of gestation. The animals were sacrificed the day before parturition and no teratogenic effect was observed (Shaffer, 1970). Groups of pregnant golden hamsters (treatment groups of 8 animals and 15 controls) were given chlormequat by gavage at levels of 0, 25, 50, 100, 200, 300 or 400 mg/kg body-weight once on day 8 of gestation. Another group received 100 mg/kg daily on days 7, 8 and 9 of gestation. Signs of toxicity were evident in the higher dosed groups. All surviving animals were sacrificed on day 14 of gestation. The number of foetuses produced was less than in the controls and an increase in foetal resorption was observed at 100 mg/kg and above. Foetal size and weight was significantly reduced at 200 mg/kg and above. No abnormalities were encountered in the foetuses from the groups given 0, 25 or 50 mg/kg nor in the group given one dose of 100 mg/kg. Malformed or underdeveloped foetuses occurred in the groups given three doses of 100 mg/kg and above. Malformations consisted of anophthalamus, microphthalamus, encephaloceles, head deformation, harelip, polydactylism, subcutaneous effusion of blood and body oedema (Juszkiewicz et al., 1970). Pregnant rabbits were fed 1 000 ppm chlormequat from day 1 to 28 of pregnancy. Two days before parturition the animals were sacrificed. No evidence of teratogenicity was observed (Shaffer, 1970). Acute toxicity Acute toxicity to chlormequat has been studied in several animal species, and findings are summarized in Table 1. Short-term studies Rat Rats exposed to chlormequat at doses equal to or greater than 18 mg/kg showed slight traces of damage to the internal organs. At high doses (162 mg/kg) changes in the liver and lungs appeared in the form of diffuse fatty degeneration and hemorrhagic inflammation, respectively. Necrotic changes in the testicles were observed in one animal being treated with a dose of 18 mg/kg body-weight. No effects were noted at 6 mg/kg or below in this study, the results of which have not been confirmed (Niepolomski et al., 1970). TABLE 1 Acute toxicity of chlormequat in different animal species LD50 Species Route mg/kg Reference bodyweight Mouse oral 215 - 1 020 Oettel, 1965; Levinskas and Shaffer, 1966, Ignatiev, 1967. Mouse ip 60 Shaffer, 1970 Hamster oral 1 070 Levinskas and Shaffer, 1966 Rat oral 330-750 Oettel, 1965; Levinskas and Shaffer, 1966; Ignatiev, 1967; Anonymous, 1969; Stefaniak, 1969 Guinea oral 215 Oettel, 1965 pig Guinea oral 620 Levinskas and Shaffer, pig 1966 Rabbit oral 60-81 Oettel, 1965; Levinskas and Shaffer, 1966; Anonymous, 1969 Cat oral 7-50 Oettel, 1965; Levinskas and Shaffer, 1966; Anonymous, 1969 Dog oral 100 Anonymous, 1969 Dog oral <50 Levinskas and Shaffer, 1966 Monkey oral >800 Costs et al., 1967 Sheep oral >150-<200 Schulz et al., 1970 Groups of ten male rats were fed dietary levels of chlormequat of 0, 500, 1 000 or 2 000 ppm for 29 days. There were no deaths nor were there any signs of abnormal behaviour. Mean body-weight gain and mean food intake did not differ between test animals and controls. At sacrifice, after completion of the study, no gross pathological abnormalities were observed (Levinskas and Shaffer, 1962). Rats fed the equivalent of 600 mg/kg body-weight of chlormequat in their diet for three months showed no adverse effect other than reduced weight gain. When the daily dietary dosage was increased to 1 200 mg/kg the only abnormality was a more pronounced reduction in growth rate. No gross or histopathological abnormalities were observed (Shaffer, 1970). Groups each containing 20 male and 20 female rats were fed dietary levels of 0, 200, 600 or 1 800 ppm of chlormequat for 90 days. There were no deaths and there was no difference in behaviour, blood chemistry or appearance between test and control. The mean weight gain in the males (but not the females) was significantly less in the group fed 1 800 ppm compared to the controls and other test groups. A trend was observed toward increased kidney to body-weight ratios in females, and liver to body-weight ratios in males with increasing doses. These increases appeared to be significant only at the 1 800 ppm level. Histological examination of all major organs from animals fed 1 800 ppm were normal (Levinskas, 1965). Addition of 10 or 1 000 ppm of chlormequat to a suboptimal, protein-deficient, diet in rats resulted in significant reduction in relative liver weights (Ackermann et al., 1970). Cat Two castrated male and two female cats received 1 mg/kg body-weight per day of chlormequat five days a week for six months without any harmful effects as evidenced by behaviour, weight gain and absence of toxic signs and abnormal results of blood analyses (Shaffer, 1970). Dog Groups of dogs (2 males and 2 females/group) received dietary levels of 0, 20, 60 or 180 ppm of chlormequat for 106-108 days. Food intake, weight gain, behaviour, appearance, clinical and chemical tests were unaffected by chlormequat. At the end of the test period, gross histopathological examination of all main organs revealed no lesions that could be related to feeding chlormequat. Organ to body-weight ratios showed no marked changes (Levinskas, 1965). Groups of dogs (10 males and 10 females in the control and 3 males and 3 females in the test groups) were fed dietary levels of 0, 100, 300 or 1 000 ppm chlormequat for two years. Some animals on 1000 ppm exhibited excessive salivation and weakness of the hindquarters. This problem was reduced or overcome by feeding the dogs a daily ration in two stages rather than all at once. One male and one female on 1 000 ppm died at 22 and 38 days. At 300 ppm and below there were no overt signs of toxicity. Food intake was unaffected at all levels. Extensive blood and urine analysis revealed no abnormalities except the presence of chlormequat in the urine of the test animals. At sacrifice, organ to body-weight ratios were not significantly different between test and control groups. Extensive gross and histopathological examination of all major organs revealed no changes attributable to feeding chlormequat (BASF, 1967b). Monkey One of four rhesus monkeys receiving an oral dose of 500 mg/kg body-weight of chlormequat died. At this high dose level heavy salivation and emesis were noted, but the survivors appeared normal after administration and remained so during the 7 day follow-up period. Gross pathology revealed little change that could be related to chlormequat (Costa et al., 1967). Sheep Sheep administered a single dose of 200 mg/kg body-weight of chlormequat died in 5-20 hours. Serum cholinesterase, total bilirubin and direct bilirubin were decreased. Acute liver damage was found in three and massive excretion of protein in the proximal segment of the renal tubules was described (Schulz et al., 1970). Signs of intoxication after a single dose in all species studied appear characteristic of cholinergic agents and most deaths occur between 6 and 24 hours after administration of the dose. The variation in species susceptibility is reported to be typical of ganglionic blocking agents of the decamethonium type (Shaffer, 1970). Daily administration of 1, 2, 5 or 10 mg/kg body-weight of chlormequat to sheep was not lethal. There were no important changes in the clinical status or in the results of laboratory tests and there was no evidence of injury to the parenchyma of internal organs. The feeding of meat from these sheep to cats and dogs had no adverse effect (Schulz et al., 1970). Long-term studies Mouse Groups of 52 male and 52 female CFLP mice were fed dietary levels of 0 or 1 000 ppm of chlormequat for up to 78 weeks. Survival was not adversely affected. The rate of gain in body-weight began to be reduced in the test group after 24 weeks and was about 6% lower in the surviving animals during the final weeks of the study. No overt signs due to treatment were seen. The incidence of benign lung tumours was higher (20 out of 52) in the males fed 1 000 ppm of chlormequat than in the controls (10 out of 51). It was considered that this incidence in the treated mice fell within the normal range under the conditions studied. Incidence of lung tumours in the males and incidence of tumours in all other organs examined in both species was not significantly higher in the test group than in the controls (Weldon et al., 1971). Two hybrid strains of mice (18 males and 18 females of each strain/group) were given chlormequat by gavage at a dose of 21.5 mg/kg from 7 to 28 days and then fed a diet containing 65 ppm for 18 months. Based upon the number of hepatomas encountered in test and control groups the authors considered that the evidence was inconclusive to categorize chlormequat as being tumorigenic and stated that further studies were required (Innes et al., 1969). Hepatomas were found in five males of each strain (5 out of 18) compared to the control values of 6 out of 257 for one strain and 7 out of 240 for the other strain (Shaffer, 1970). Rat Groups each of 50 male and 50 female rats were fed diets containing 0, 500 or 1 000 ppm of chlormequat for two years. There were no signs of abnormal behaviour or appearance or other signs of toxicity. Food intake and body-weight gain were comparable in test and control groups. Haematological and blood chemical determinations were normal, as were urinalysis and microscopic examination of urine sediment. Gross and histopathological examination of organs revealed no abnormalities attributable to chlormequat (BASF, 1967a). COMMENTS Chlormequat is a stable quaternary compound that appears to act by depolarizing the post-junctional membrane, and although the signs of toxicity from high dosages in mammals resemble those of anticholinesterase agents, it does not inhibit cholinesterase. Chlormequat is rapidly absorbed and excreted mainly unchanged in the urine of mammals. A three-generation study in rats did not reveal adverse effects on reproduction. Teratogenic studies in several species indicate effects only at dose levels exceeding 50 mg/kg/day. Long-term studies in mice and rats indicate no effects at 1 000 ppm. However, in the rat, reproduction study levels of 300 ppm may have caused delayed maturation of stages of spermatogenesis in 9-week-old offspring whilst 100 ppm caused no effect. A two-year study in dogs demonstrated a no-effect level at 300 ppm; at 1 000 ppm some signs of cholinergic effect were noted. TOXICOLOGICAL EVALUATION Level causing no toxicological effect Mouse: 1 000 ppm in the diet equivalent to 150 mg/kg body-weight/day. Rat: 100 ppm in the diet equivalent to 5.0 mg/kg body-weight/day. Dog: 300 ppm in the diet equivalent to 7.5 mg/kg body-weight/day. ESTIMATE OF ACCEPTABLE DAILY INTAKE FOR MAN 0 - 0.05 mg/kg body-weight RESIDUES IN FOOD AND THEIR EVALUATION In addition to those uses referred to in the 1970 evaluations (FAO/WHO, 1971) information was received on the use of chlormequat on pears for promoting fruit bud formation and reducing excessive vegetative growth. The major use, however, remains on cereal crops, especially wheat, to reduce straw length, strengthen straw and prevent lodging. Pears are treated about 14 days after full flowering with chlormequat solutions at 0.1 - 0.2%. Treatment may be repeated once 14 days later. Split applications at low concentrations are more effective than a single treatment at higher concentrations. RESIDUES RESULTING FROM SUPERVISED TRIALS Wheat One application with 4.5 kg a.i./ha when wheat was 10-20 cm in height and one spraying with 3 kg a.i./ha at a height of 30-35 cm gave residues of 0.5-1 ppm in wheat grain (Jung and Henjes, 1964a). In experiments on winter wheat with applications of from 1.2 - 6 kg a.i./ha, the residues summarized in Table 2 were found in wheat grain and straw. Winter wheat treated with 1.25 to 10 kg a.i./ha 3-4 months before harvest was found to have residues in grain ranging from 0.02 - 2.36 ppm. Spring varieties treated with 1.2 - 10 kg a.i./ha 2-3 months before harvest had residues ranging from 0 - 2.5 ppm in the grain at harvest. In a variety of soft wheat grown in Italy and treated at various stages of growth with 2 and 4 kg a.i./ha the following residues were detected in the grain: 1.36 - 2.18 ppm when treated 2 weeks after initiation of stem elongation; 2.24 - 6.78 ppm, when treated at the boot stage (Cyanamid International 1966). TABLE 2 Chlormequat residues in wheat Residues (ppm) Chlormequat Grain Straw (kg a.i./ha) Average Range Average Range 1.2 0.5 2.4 0.8 N.D.1 - 2.0 15.8 N.D. - 40 3.0 - N.D. - 0.5 20 10 - 40 6.0 0.5 1 N.D. = not detectable (<0.5 ppm). In dry years when the dose is high or the application is made late, higher chlormequat residues can be found in the grain of treated wheat plants. It seems that high rainfall can reduce or eliminate chlormequat residues resulting from high or late application of the growth regulator. After the wet summer of 1965 analysis of wheat grain from a crop which had been treated with 12 kg a.i. chlormequat/ha, showed no trace of any chlormequat (Jung and El-Fouly, 1966). It is interesting to observe that residues decrease with increasing storage time. This is obviously connected with the enzymatic transformation of chlormequat in the plant. Jung and El-Fouly (1966) found only 0.5 ppm or less in 12 samples of wheat grain, which originally contained 1.0 - 2.5 ppm chlormequat, after they had been stored for 12 months. Rye For short-straw winter ryes, chlormequat is applied at the rate of 1.5 kg a.i./ha at a growth height of 20-30 cm. Analysis of rye grain from the 1966 harvest after 1.8 kg a.i./ha had been applied, showed 1.0-1.3 ppm chlormequat in the dry grain, average of four locations (Jung, 1968a). Oats The question of chlormequat residues in oats is of special interest, as the most effective time of chlormequat application is when growth height is 40-50 cm. Harvest samples from field trials in various parts of West Germany in 1967 showed a definite dependency on the time of treatment (Jung, 1968b). Early sprayed plants, when treated at a height of 20-30 cm with 1.5 - 3 kg a.i./ha, generally showed not more than 1.0 to 1.4 ppm chlormequat in the dry grain. The values for late treated (at a growth height of 40-50 cm) were 3.8 and 6.1 ppm, respectively. Straw residues averaged 1.2 - 1.7 ppm (early) and 9.5 - 14.1 ppm (late) from the two different times of application. Analysis of oat grain and straw of the 1968 harvest, based on an average of 11 field trials in all parts of West Germany (Jung, 1969), are given in Table 3. TABLE 3 Chlormequat residues in grain and straw of oats from field trials1 Treatment2 Chlormequat in the dry grain (l/ha Cycocel) (ppm) Grain Straw Untreated 0.4 0.7 2 1.7 5.9 4 2.3 9.9 6 3.5 16.2 1 Average of 11 field trials at each treatment rate. 2 At growth height of 40-50 cm. Analysis of samples harvested from trials at the same location near Cologne showed an average residue in grain of 0.9 - 1.5 ppm chlormequat (dry basis), after treatment with 1 and 1.5 kg a.i./ha at a growth height of 20 cm, and of 2.3 - 3.5 ppm chlormequat after treatment with the same quantity at a growth height of 40 cm. The straw of early treated plants was found to have an average of 0.7 - 1.1 and later treated plants 4.2 - 11.4 ppm (Jung, 1969a). Results are shown in Table 4. Apples and pears In 1967 after treatment of eight varieties of apples with 0.3% chlormequat solution, residue levels were found to range between 0.95 and 1.6 ppm in the fresh fruit. Repeated treatments led to residue levels up to 3 ppm. The method used was capable of determining 0.2 ppm chlormequat in apples (Jung, 1969b). In 1968, five apple varieties were sprayed with 0.2% chlormequat solution. The residue in the fresh fruit was between 0.2 and 1.4 ppm. In the year following a single treatment with 0.2% chlormequat, no residue was traceable in the apples. After two sprays, about 0.4 ppm could be traced in the fruit the following year. Apples from trees which had been treated with chlormequat in both 1967 and 1968 contained residues of 0.4 - 1.4 ppm when harvested in 1969. The analyses of treated pears showed a distinct dependence on the date of treatment. After a normal treatment with 0.2% solution, the average of four varieties was 0.2 to 1 ppm chlormequat in the fresh fruit. An extreme four-time spraying with 0.25% chlormequat solution led to residue of 6 ppm. Fruit from the succeeding year did not contain any residue (Jung, 1969b). Vegetables Analysis of several types of vegetables in 1967 and 1968 (Jung, 1969b) led to the following results: cucumbers in the pot, which had been treated with 0.25% solution, contained 1.6 ppm chlormequat. After treating the soil with 0.15% and 0.5% solution and comparative spray treatment with 0.25% solution, the residue fluctuated between 0.2 and 1.1 ppm chlormequat. Capsicum, after spraying with 0.15 - 1.0% solution, contained 5.8 - 8.9 ppm chlormequat. In tomatoes which were cultivated under greenhouse conditions no residue was found after soil treatment with 10 and 30 mg chlormequat per pot, and 0.5 - 1.4 ppm chlormequat was found after spraying with 0.1 - 0.25% solution. Tomatoes raised in the field showed 0.6 ppm chlormequat in the fruit after soil treatment with 50 cc 0.5% solution. No residue could be traced in radish after soil and spray treatment with 0.15 - 0.25% solutions. TABLE 4 Chlormequat residues in grain and straw of oats Treatment Nitrogen Growth Chlormequat, dry basis (kg a.i./ha) fertilizer stage (ppm) (kg/ha) Grain Straw Untreated 60 0.37 0.34 Untreated 80 0.41 0.24 1.0 60 0.89 0.93 1.5 1.25 0.72 1.0 80 at 20 cm 1.16 1.11 1.5 1.47 0.77 1.0 60 2.42 4.16 1.5 3.23 6.61 1.0 80 at 40 cm 2.18 5.23 1.5 3.52 11.45 FATE OF RESIDUES In animals Orloski (1970) reported experiments designed to determine chlormequat residues in the milk of dairy cows receiving 10 ppm chlormequat in the ration for 14 consecutive days. Each animal received 128 mg chlormequat daily via oral dose syringe. The results show trace residues of chlormequat ranging from 0.024 to 0.034 ppm at each of milk samplings 1, 4, 7 and 14 days during feeding. When the chlormequat was removed from the ration no residues above the limit of detection (0.01 ppm) were found in the milk. In plants The chlormequat level in vegetative parts of plants declines quickly after treatment. Residue analyses based on the half-quantitative method, in 1963 showed 2200 and 3600 ppm for winter wheat ("Werla") and 1200 and 2400 ppm for summer wheat ("Koga") after treatment with 2 and 4 kg chlormequat/ha. After five weeks the residue in the complete plant was reduced to 7 and 25 ppm, respectively, in winter wheat and 17 and 47 ppm, respectively, in summer wheat. No chlormequat could be traced in the ears. The ripe wheat grains were also free of traceable residue; 5 and 7 ppm chlormequat were found in the ripe straw of winter wheat and 6 and 11 ppm chlormequat in the straw of summer wheat (Jung and Henjes, 1964a). Analysis of summer wheat in the year 1965, after treatment with up to 12 kg chlormequat/ha, showed the same tendency (Jung and El-Fouly, 1966). A similar rapid reduction of residues was also found by Mooney and Pasarela (1967) in wheat plants of the "Redcoat" type. The residue level was reduced from 218 ppm on the day of the treatment to 125 ppm after 21 days, 20 ppm after 42 days and 5 ppm (straw) after 64 days. After 91 days, the average residue content in six samples was 1.4 ppm and in the straw 2.8 ppm. The untreated grain sample contained 0.15 ppm chlormequat. The plants had been treated with 4.5 kg a.i/ha at a growth height of 20 cm, the precipitation during the vegetation period being 344.5 mm. The biological half-life for chlormequat determined by this study was 13 days. High chlormequat applications frequently increase the content of choline chloride (CC) shortly after treatment, and it therefore is possible that chlormequat is transformed into CC and possibly betain. Consequently, Jung and El-Fouly (1966) carried out tests in vivo and in vitro to determine whether chlormequat is transformed into betain and/or choline chloride. Their results are shown in Table 5. It is not fully understood whether chlormequat, which is closely related to the choline and betain contained in plants, is already acting in the plant as a "natural" growth regulator. On the other hand, the quarternary ammonium combinations choline and betain, chemically closely related to chlormequat, can be traced in the plant in relatively large quantities (Jung and El-Fouly, 1966; Jung and Henjes, 1964b; Paxton and Mayr, 1962). In the process of decomposition in vitro, transformation evidently starts a few minutes after chlormequat solution has been added to the plant extract. In each case, choline chloride could be traced as the decomposition product. It is noticeable that chlormequat decomposes differently in leaf extracts of different plants. Plants sensitive to chlormequat seem to decompose the growth regulator more slowly than plants which are less sensitive. Perhaps the explanation for the different effect of chlormequat on different plants and/or plant types can be found here. If the speed of decomposition of chlormequat in wheat is 100, the relative values in maize and rice would be 180, in beetroot and apples 130, in rapeseed 120, in poinsettia and cotton 100, in tomatoes 70, in beans 40 and in grapes and chrysanthemums 20 (Jung and El-Fouly, 1966). TABLE 5 Choline chloride and betain content in wheat plants after treatment with high rates of chlormequat Treatment 3 days after treatment 24 days after treatment (kg a.i./ ha) Chlormequat CC betain Chlormequat CC betain (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) Untreated - 3 100 3 500 - 900 1 000 6 1 400 3 900 4 300 100 900 1 200 12 2 800 3 800 4 200 200 1 000 1 300 These authors have established the following scheme (figure 1) for the decomposition of chlorine choline chloride.(chlorine choline chloride)-> (choline chloride)-> (betain) Figure 1 - Decomposition of chlorine choline chloride As choline occupies a central position in plant metabolism and can be oxidized to betain, the increase of betain content after chlormequat treatment could thus be explained. Paxton and Mayr (1962) have shown the transformation of choline and betain in a further scheme. According to the latest research, the enzymatic system controlling the decomposition of chlormequat into CC, is pH-dependent and thermostable (Jung and El-Fouly 1969). On the whole, the decomposition of chlormequat increases with the increasing pH value of the plant extract and reached a maximum at pH6. Above this value the rate of decomposition decreases since chlormequat is decomposed in alkaline medium. Heading (40-90°C) the plant extracts and subsequent cooling to room temperature did not affect the rate of decomposition of chlormequat which was added later. Only by cooking the extracts for several hours could inactivation be obtained. Temperatures which increase from 10-40°C, however, accelerate the decomposition of chlormequat into CC, if the chlormequat is already present in the extract. The enzymatic system only becomes active in the presence of at least two components (one precipitated with ZnCl2 and one dialysable). Schneider (1967) demonstrated chromatographically that radio-labelled chlormequat was transformed into a substance identical to choline in barley and chrysanthemum sprouts. He was able to isolate radioactive choline or radioactive choline metabolites from plant tissue, which had been standing in chlormequat-containing solutions for some time. During decomposition the carbohydrate skeleton of chlormequat seems, therefore to remain intact. The unknown metabolites were identical to the metabolites isolated from plants after a choline or choline plus chlormequat treatment. An additional combination, which only appeared after chlormequat treatment, is taken as an intermediate of the decomposition processes. On the whole, 50-80% of the added radioactivity was found unchanged in the chlormequat solution, 15-40% in the residue solutions and 35-40% in the methanol extracts. At least 10-15% of the added radioactivity had been transformed in metabolic products of chlormequat. Schneider (1967) sees a contradiction in the relatively fast decomposition of chlormequat and its long lasting effect on plant growth. Since choline also, though at ten times higher concentrations than chlormequat, delayed the growth of barley roots and sprouts in such tests, this author believes that the effect normally assigned to chlormequat alone could result from chlormequat choline and further unknown metabolites of these combinations. The contradiction between chlormequat decomposition and lasting effect could be explained if the metabolism of chlormequat only takes place in one part of the plant tissue, whilst other parts store unchanged chlormequat. This explanation would comply with observations of Sachs and Kofranek (1963), who have noted that chlormequat activities mainly take place in the subapical meristem. In soil Chlormequat decomposition in soil takes place relatively fast. Cathey and Stuart (1961) assess the persistency of choline chloride in soil as only three weeks. The opinion that the soil does not provide the plant with a continuous subsequent supply of chlormequat is also shared by Schneider (1967). Trials were carried out by Jung (1965) in which four different soils were treated with 5 mg chlormequat 0-6 weeks before sowing wheat seeds in all pots. After 4-6 weeks there was almost complete inactivation. In further tests it was established that chlormequat in quantities of 3, 30 and 300 kg/ha did not exert a definable influence on the microbic activity of five different soils. CO2 production and nitrification were taken as the basis for these observations (Jung, 1964). In storage and processing Jung and El-Fouly (1966) found that chlormequat residues in wheat decline significantly in storage. Twelve samples of wheat which originally contained 1.0 - 2.5 ppm chlormequat were found to have less than 0.5 ppm after being stored for 12 months. Cyanamid International (1971) reports trials to determine the level of chlormequat residues in milling products processed from wheat treated with chlormequat at the rate of 1.2 kg per ha by aircraft and harvested 95 days later. The wheat was milled five months after harvest and the bran and flour collected. The flour was made into bread. The treated grain was found to contain 0.26 ppm chlormequat. The bran contained 0.8 ppm, the flour 0.32 ppm and the bread 0.06 ppm chlormequat. It is apparent that milling does not substantially reduce the level of chlormequat residues in wheat but that baking of the flour in the production of bread largely eliminates the residue. The analytical method used had a limit of determination of 0.05 ppm. The work of Tafuri et al. (1970) indicates that wine made from grapes grown under chlormequat treatment will contain residues substantially similar to those in the fresh grapes (up to 1 ppm). APPRAISAL Chlormequat is used as a growth regulator in cereals, grapes and pears. Residues in wheat grain which mostly lie below 1 ppm, may range up to 2 ppm. When such wheat is milled, the flour will contain substantially similar levels but these are largely destroyed in the baking of bread. Cows fed on the straw of chlormequat-treated cereals excrete small traces of chlormequat in milk during the period of feeding, but residues disappear as soon as the treated feed is withdrawn. The treatment of pear trees at flowering in order to prevent vegetative growth and encourage fruit bud formation for the next season gives rise to residues ranging up to 2.6 ppm in fruit at harvest. Residues are not found in the succeeding crop. The gas chromatographic method of Tafuri et al. (1970) is recommended as suitable for regulatory purposes. It is suitable for use with the commodities included in the list of recommended tolerances having a limit of determination of 0.05 ppm. RECOMMENDATIONS TOLERANCES The following tolerances are for residues likely to be found at harvest. Due to the stability of chlormequat residues, it is not anticipated that residue levels will change significantly in storage, although they will be largely destroyed by cooking. ppm Oats and rye 5 Wheat 3 Pears 3 Grapes, raisins and other dried vine fruits 1 Milk and milk products 0.1* * at or about the limit of determination FURTHER WORK OR INFORMATION DESIRABLE 1. Information on other registered uses for chlormequat. 2. Further information on residues of chlormequat in raw agricultural commodities from a number of different countries. 3. Information on chlormequat residues in commodities moving in international trade. REFERENCES Ackermann, H. and Kretzschmann, F. (1970) Einfluss von Chlorcholinchlorid auf die Toxizität von Cholinesterase-Inhibitoren. Arch. exp. Vet.-Med., 24 (4): 1045-1047. Ackermann, H., Proll, J. and Lüder, W. 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(1970) Effet embryopathique du chlorure de chlorocholine (CCC) chez le hamster doré. Europ. J. Toxicol., 3(5): 265-270. Lampeter, W. and Bier, H. (1970) Ausscheidung von chlorcholinchlorid über Milch und Harn nach oraler Applikation von 1g15N-markiertem Chlorcholinchlorid an eine laktierende Kuh. Arch. exp. Vet. Med., 24(4): 1027-1031. Leuschner, F., Leuschner, A. and Schwerdtfeger, W. (1967) Uber die chronische Verträglichkeit von CCC. Chronischer Reproduktionsversuch uber 3 Generationen an Wistar-Ratten. Report from Laboratory for Pharmacology and Toxicology, Hamburg, Germany submitted by Cyanamid GMBH. (unpublished) Levinskas, G.J. (1965) Cyclocel(R), growth regulator; 2-chlorethyl-trimethylammonium chloride. Report on 90-day feeding trials on dogs and rats conducted at the Central Medical Department, American Cyanamid Company. (unpublished) Levinskas, G.J. and Shaffer, C.B. (1962) 2-chloroethyl-trimethylammonium chloride; CL 38,555; limited release toxicity studies. 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CCC-Symposium der BASF 14 Dezember 1965 (cited in Schulz and Lampeter, 1970). Orloski, E.J. (1970) Cycocel residues in milk. Report No. C225 American Cyanamid. (unpublished) Paxton, R.C. and Mayr, H.H. (1962) "Untersuchungen über das natürliche Vorkommen quaternärer Ammoniumbasen in Lycopersicum esculentum" (Examinations on the natural presence of quaternary ammonium bases in Lycopersicum esculentum). Planta, 59: 165. Proll, J., Ackermann, H. and Lüder, W. (1970) Untersuchungen zur toxikologischen Beurteilung von Chlorcholinchlorid. 3. Mitteilung: zur lipotropen Wirkung von Chlorcholinchlorid. Arch. exp. Vet. Med., 24(4): 1065-1068. Sachs, R.M. and Kofranek, A.M. (1963) Comparative cytohistological studies on inhibition and promotion of stem growth in Chrysanthemum morifolium. Am. J. Botany, 50: 772. Schneider, E.F. (1967) Conversion of the plant growth retardant (2-chlor-ethyl)-trimethyl-ammoniumchloride to choline in shoots of chrysanthemum and barley. Can. J. Biochem., 45: 395. Schulz, J.A., Eichelberger, P., Schäppel, K.F. and Johannsen, U. (1970) Untersuchungen zur Verträglichkeit das Chlorcholinchlorids nach oraler Verabreichung an Schafe. Arch exp. Vet. Med., 24(4): 1033-1044. Schulz, J.A. and Lampeter, W., (1970) Vorwortzuden Untersuchungen über Chlorcholinchlorid-Rückstände im Pflanzenmaterial die Wirkung des Chlorcholinchlorids auf Warmblüter und über den Verbleib des Chlorcholinchlorids bei Verfütterung an Ratten und an die Kuh. Arch. exp. Vet. Med., 24(4): 1013-1018. Shaffer, C.B. (1970) Chlormequat. "Monograph" from Central Medical Department, American Cyanamid Co. submitted to Joint FAO/WHO Meeting on Pesticide Residues. Stefaniak, B. (1969) Severe toxicity of chlorocholine chloride (CCC) to rats (in Polish). Med. weteryn, 25(5): 285-286. Tafari, F., Businelli, M., Scarponi, L. and Giusquiani, P.L. (1970) Chlorocholine chloride residues in grapes and their fate in winemaking. J. Agr. Fd. Chem., 18: 869-871. Weldon, G.H., Hunter, B., Hague, P.H. and Spicer E.J.F. (1971) Long-term feeding study of Cycocel in the mouse. Report No. 4059/71/217 from Huntingdon Research Centre submitted to American Cyanamid Company and to Cyanamid of Great Britain Ltd. (unpublished)
See Also: Toxicological Abbreviations Chlormequat (AGP:1970/M/12/1) Chlormequat (Pesticide residues in food: 1976 evaluations) Chlormequat (Pesticide residues in food: 1994 evaluations Part II Toxicology) Chlormequat (Pesticide residues in food: 1997 evaluations Part II Toxicological & Environmental) Chlormequat (JMPR Evaluations 1999 Part II Toxicological)