MALEIC HYDRAZIDE First draft prepared by I.C. Dewhurst and M. Watson Pesticides Safety Directorate, Ministry of Agriculture, Fisheries and Food, Mallard House, Kings Pool, York, United Kingdom Explanation Evaluation for acceptable daily intake Biochemical aspects Absorption, distribution, and excretion Biotransformation Toxicological studies Acute toxicity Short-term toxicity Long-term toxicity and carcinogenicity Reproductive toxicity Developmental toxicity Genotoxicity Special studies: Dermal and ocular irritation and dermal sensitization Comments Toxicological evaluation References Explanation Maleic hydrazide was previously evaluated for toxicological effects by the Joint Meeting in 1976, 1980, and 1984 (Annex 1, references 26, 34, and 42). In 1984, an ADI of 0-5 mg/kg bw was established for maleic hydrazide of 99.9% purity, containing < 1 ppm hydrazine. The compound was reviewed by the present Meeting within the CCPR periodic review programme. This monograph summarizes new data not previously reviewed on maleic hydrazide and relevant data from the previous monographs on this pesticide (Annex 1, references 27, 35, and 43). Evaluation for acceptable daily intake 1. Biochemical aspects (a) Absorption, distribution, and excretion The absorption, distribution, and excretion of orally administered 3,6-dione-labelled 14C-maleic hydrazide was investigated in groups of five male and five female Sprague-Dawley rats given single doses of 2 or 100 mg/kg bw or 14 unlabelled daily doses followed by a labelled dose of 2 mg/kg bw by gavage in water. More than 90% was recovered. No marked differences in results were seen by sex, dose, or whether the animals were pretreated. Less than 1% of the administered dose was present in exhaled air. Absorption was rapid and extensive, with about half the dose present in the 0-4-h urine sample. During the first 24 h after dosing, about 85% of the dose was excreted in the urine and 9-13% in the faeces, and there was little further excretion over the following six days. The results of intravenous dosing indicate that half the faecal residue may be associated with biliary excretion. Tissue and carcass residues represented < 1% of the administered dose after seven days, all tissue levels being equivalent to < 0.01 µg/g at the low dose and < 0.15 µg/g at the high dose, with peak levels in fat, bone, and lung. Blood levels were not given (Caley & Cameron, 1989). These findings are consistent with those reported by Mays et al. (1968), reviewed by the 1976 JMPR (Annex 1, reference 26), which showed that low doses (< 10 mg/kg bw) of maleic hydrazide are rapidly excreted, unmetabolized, in urine. Another study reviewed by the 1976 JMPR indicates that at very high doses (4000 mg/kg bw) absorption and excretory mechanisms may become saturated, particularly in females (Food & Drug Research Laboratory, Inc., 1955). A group of laying hens received seven doses of 15 mg/kg bw per day 3,6-dione-labelled 14C-maleic hydrazide, equivalent to about 200 ppm on a dietary basis, over 3.5 days by gavage and were killed 24 h after the last dose. Egg white and yolk, major organs, muscle, blood, and excreta were analysed for total radiolabel by liquid scintillation counting and extracted to permit identification of metabolites by thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC). About 98% of the administered dose was present in the excreta and cage washes collected up to termination, with approximately 96% of the daily dose excreted within each 24-h period. The residues in eggs represented < 0.01% of the administered dose; the concentration in egg white rose from an equivalent of 0.02 µg/g on day 1 to 0.33 µg/g on day 4 and then fell to 0.20 µg/g on day 5; in the yolk, the peak value, 0.23 µg/g, was reached on day 5. The equivalent tissue levels at termination were generally lower than those in plasma (0.13 µg/g), except in liver (0.13 µg/g) and kidney (0.20 µg/g) (Johnston et al., 1993). A single, non-pregnant, lactating, British Saanen goat received seven doses of 15 mg/kg bw per day 3,6-dione-labelled 14C-maleic hydrazide, equivalent to 441 ppm on a dietary basis, over 3.5 days by gavage after the morning and afternoon milkings. The animal was killed 24 h after the final dose, and edible tissues, bile, and blood were analysed; milk, urine, and faecal samples were taken throughout the study. More than 86% of the radiolabel was recovered within 24 h after the last dose, except from the carcass and gastrointestinal tract, which were not analysed; 63% was found in urine, 23% in faeces, and 0.13% in milk. Faecal excretion after an initial 24-h lag phase and urinary excretion were consistent for each 24-h period. The residues in milk increased with each dose and then fell when dosing stopped, reaching a peak of 0.88 ppm with limited evidence for a plateau at around 1 ppm. Levels in excess of those in plasma (0.7 µg/g equivalent) were found only in liver (1.2 µg/g) and kidney (3.3 µg/g); the concentration in muscle was 0.44 µg/g (Cameron et al., 1992). The distribution and excretion of 3,6-dione-labelled 14C-maleic hydrazide was investigated in groups of five male and five female Sprague-Dawley rats given a single intravenous dose of 2 mg/kg bw in water. More than 90% was recovered. There were no marked sex differences in distribution or excretion patterns. Less than 1% of the dose was present in exhaled air. Excretion via the urine was rapid, with about 60% of the dose present in the 0-4-h sample and > 80% in the 0-24-h sample; about 5% of the administered dose was excreted in the faeces within 24 h, with little additional excretion over the next six days. Total tissue and carcass residues represented < 1% of the administered dose at termination on day 7, with a peak residue of < 0.01 µg/g (Caley & Cameron, 1989). (b) Biotransformation Samples obtained from rats, hens, and goats in the studies described above (Caley & Cameron, 1989; Cameron et al., 1992; Johnston et al., 1993) were investigated to determine the levels of maleic hydrazide and metabolites. The results for the three species were generally consistent, showing that maleic hydrazide undergoes only limited metabolism; the predominant residue in tissues is an acid-labile conjugate. In rats, the urine and faeces samples contained two peaks. Poor chromatographic separation and low levels of radiolabel in the faecal samples precluded reliable identification, but the peaks appeared to represent maleic hydrazide and possibly fumaric acid. The major peak in urine, representing 60% of the urinary radiolabel in males and 80% in females, co-chromatographed with maleic hydrazide. The minor urinary peak was initially found to co-chromatograph with maleimide, fumaric acid, or maleic diamide, depending on the solvent system, but subsequent investigation (Caley et al., 1990) with deconjugation with a ß-glucuronidase containing sulfatase activity and HPLC showed this peak to be a maleic acid conjugate, probably a sulfate. In hens, samples of breast muscle, egg white and yolk, kidney, liver, and excreta were analysed by TLC and HPLC. In excreta, which contained 98% of the administered dose, two major peaks were seen: one representing about 80% of the urinary radiolabel co-chromatographed with maleic hydrazide; the second peak did not coincide with any of the standards used, but subsequent investigations indicated that it was probably N-acetylmaleic hydrazide. In tissue and egg samples, up to three clear peaks were detected (Table 1), the most polar of which was an acid-labile maleic acid derivative the structure of which was not characterized. Investigations of the structure of 'metabolite 1' by preparative HPLC and mass spectrometry indicated it to be an O-methyl conjugate of maleic hydrazide. Only in egg yolk was unconjugated maleic hydrazide present as a significant proportion of the residue. The residue profiles did not alter significantly during storage for up to 20 months at -20°C (Johnston et al., 1993). Table 1. Metabolites of maleic hydrazide in samples from hens (as percentage of sample radiolabel) Tissue 'Metabolite 2' Maleic 'Metabolite 1' (polar) hydrazide (non-polar) Liver 4.8 ND 50.9 With acid hydrolysis 1.5 7.0 44.0 Kidney 30.8 2.3 28.1 With acid hydrolysis 2.9 26.9 31.7 Breast muscle 8.5 4.0 60.1 With acid hydrolysis ND 9.0 48.9 Egg white 30.9 ND 31.8 With acid hydrolysis ND 31.1 33.7 Egg yolk 12.0 68.6 7.3 With acid hydrolysis ND 71.0 17.7 12-33% of total residue was unextractable. ND, no detectable peak Samples of fat, kidney, muscle, liver, and milk from goats were investigated by HPLC and TLC to determine the metabolite profile; the urine and faeces, which contained > 86% of the administered radiolabel (equivalent to about 99% of the recovered radiolabel), were not analysed. In liver samples, > 40% of the residue was bound after extraction and acid hydrolysis and required pepsin treatment for release. Up to four clear peaks were noted (Table 2) and determined to be (i) maleic hydrazide; (ii) the major residue component, a partly acid-labile sulfate conjugate of maleic hydrazide; (iii) a non-polar metabolite which appears to be closely related to maleic hydrazide as it is produced by both acid and enzymic hydrolysis of the maleic hydrazide conjugate but did not correlate with any of the standards used and was not present in hens; and (iv) a peak with elution properties similar to those of fumaric acid (Cameron et al., 1992). Table 2. Metabolites of maleic hydrazide in samples from goats (as percentage of sample radiolabel) Tissue Conjugate Maleic Fumaric Non-polar hydrazide acid? metabolite Liver 39.4 ND ND 2.9 With acid hydrolysis 12.1 12.0 7.4 10.3 Liver with pepsin 32.7 19.5 ND 6.7 With pepsin and acid hydrolysis 21.5 23.3 ND 21.0 Kidney 83.4 ND ND ND With acid hydrolysis 53.8 28.8 ND 3.8 Muscle 60.7 5.8 ND 11.3 With acid hydrolysis 12.5 34.6 10.5 35.1 Fat 83.2 ND ND 5.7 With acid hydrolysis 35.8 25.6 6.3 14.5 Milk 45.4 12.9 6.8 16.6 With glucuronidase 6.0 44.8 6.4 29.1 Bound residue represented < 4% ,except in liver where it represented < 43%. ND, no detectable peak Owing to the very limited information available on metabolism, no metabolic pathway was prepared. 2. Toxicological studies The 1976 JMPR (Annex 1, reference 26) reviewed a number of studies in which repeated doses of the sodium or diethanolamine salts of maleic hydrazide were administered. Some of the studies on the sodium salt are summarized below. The diethanolamine component was found to exert marked toxicological effects, indicating that the results of studies on the diethanolamine salt are not applicable to consideration of the simple metal salts of maleic hydrazide. (a) Acute toxicity The results of studies on the acute toxicity of maleic hydrazide are summarized in Table 3. The studies of oral and dermal toxicity (Shapiro, 1977a,b) contained minimal details about clinical signs or gross or histopathological findings, but both show that technical- grade maleic hydrazide (purity unspecified) has little toxicity. Application to abraded skin did not cause more deaths than application to unabraded skin (Shapiro, 1977b). In Sprague-Dawley rats of each sex, exposure by snout-only to potassium maleic hydrazide (purity, 96.5%; maximal mean aerodynamic diameter, < 6.6 µm) for 4 h in atmospheres of up to 4 mg/litre (maximum achievable) did not induce death or other notable adverse effects (McDonald & Oshodi, 1989). These findings are consistent with those of an earlier study indicating an LC50 of > 20 mg/litre for a 1-h exposure (Shapiro, 1977c). Studies reviewed by the 1976 JMPR (Annex 1, reference 26) identified oral LD50 values in rats of 1180 mg/kg bw for the diethanolamine salt and 5800 mg/kg bw for the sodium salt of maleic hydrazide (Food & Drug Research Laboratory, Inc., 1955) (b) Short-term toxicity Rats In a 13-week study used as a range-finding investigation for a long-term study of toxicity, groups of 10 male and 10 female Sprague-Dawley rats received potassium maleic hydrazide (purity, 97.8%) in the diet at levels varied weekly to give intakes of 0, 30, 100, 300, or 1000 mg/kg bw per day. Histological examinations were limited to a maximum of seven major tissues and gross abnormalities. Blood and urine were not analysed. There were no effects on mortality, clinical signs, body-weight gain, water consumption, or gross pathological appearance. A slight increase in food consumption was seen in animals at the highest dose. Reduced spleen weights in females at 30 or 1000 mg/kg bw per day and increased incidences of basophilic renal tubules in all treated males were small effects and showed no dose-response relationship; these effects are therefore considered to be of minimal biological significance. Although no adverse effects were recorded, the limited evaluations performed in this study preclude identification of a reliable NOAEL (Perry et al., 1990). Table 3. Acute toxicity of maleic hydrazide (purity unspecified) Compound Species Route LD50 (mg/kg bw) Reference or LC50 (mg/litre) Maleic hydrazide, technical-grade Rat Oral > 5 000 Shapiro (1977a) Maleic hydrazide, technical-grade Rabbit Dermal > 20 000 Shapiro (1977b) Maleic hydrazide, technical-grade Rat Inhalation > 20 (1 h) Shapiro (1977c) Potassium maleic hydrazide Rat Inhalation > 4 (4 h) McDonald & Oshodi (1989) The 1976 JMPR (Annex 1, reference 26) reviewed a 12-week study in which sodium maleic hydrazide (purity unspecified) was administered in the diet to rats at concentrations of 0, 0.5, 1, 2, or 5%. Reduced blood sugar and increased non-protein nitrogen were seen at the highest dose. No significant effects were reported on haematological or urinary parameters, food use, or on the limited gross and histopathological examinations. The NOAEL was 2%, equivalent to 1000 mg/kg bw per day, but the limited extent of pathological examination (two animals of each sex per group) indicate this may not be valid (Food & Drug Research Laboratory, Inc., 1955). Groups of five male and five female Sprague-Dawley rats were exposed dermally to potassium maleic hydrazide (purity, 97.8%) in water for 6 h per day under a non-occlusive dressing at levels of 0, 100, 500, or 1000 mg/kg bw per day. All animals were observed for changes in clinical signs, body weight, organ weights (not brain), and clinical chemical, haematological, and gross pathological parameters; major organs (excluding brain) from controls and animals at the highest dose were examined histologically. Some local dryness or scabbing was seen at the application sites in both treated and control females. Males receiving 500 or 1000 mg/kg bw per day had lymphocyte counts increased by 21 and 39%, respectively, but similar changes were not seen in females and are considered to be of questionable biological significance. Increases in erythrocyte parameters in females at the low and intermediate doses are not considered to be treatment-related as such findings were not present in animals at the highest dose. Increased absolute liver weights seen in males at 500 or 1000 mg/kg bw per day were due in part to the increased body weights and were not associated with any histological change. No significant findings were noted at gross or histopathological examination. The NOAEL was 1000 mg/kg bw per day, on the basis of the absence of clearly adverse findings (Perry et al., 1989). Dogs In a 13-week range-finding study, beagle dogs received a diet containing potassium maleic hydrazide (purity, 97.8%) at concentrations providing doses of 0, 750, 2500, or 25 000 ppm, equivalent to 18, 63, or 620 mg/kg bw per day. All values covering a range of end-points were reported to be within the expected values, but as only single animals were used for each dose no reliable conclusions can be drawn (Goburdhun, 1990). In a one-year study, groups of six male and six female beagle dogs received a diet containing potassium maleic hydrazide (purity, 99.8%; 0.04 ppm hydrazine) at concentrations of 0, 750, 2500, or 25 000 ppm, equal to 29, 87, or 970 mg/kg bw per day. The animals were examined for changes in clinical signs, body weight, food consumption, haematological, clinical chemical, urinalytical, and ophthalmological parameters, organ weights, and gross and microscopic pathological appearance. One male at the highest dose was killed in extremis in week 28; the findings at necropsy included a distended, fluid-filled abdomen, calculi in the urinary bladder, increased lobation of the pancreas, and enlarged liver and kidneys. Body-weight gain was reduced by > 20% in animals of each sex at 2500 ppm and by > 35% in those at 25 000 ppm, with no effects on food consumption. Increased serum enzyme activities and reduced albumin levels consistent with pathological effects in the liver were seen in animals at the high dose; the reduced serum chloride levels seen in animals at 2500 or 25 000 ppm may be secondary to the high potassium content of the diet. The urinary pH was increased consistently in dogs at 25 000 ppm. Decreased absolute and relative heart weights were seen in males at 2500 ppm and in males and females at 25 000 ppm but were not associated with adverse histological findings. Increased absolute and relative thyroid weights seen in males and females at the highest dose were consistent with the findings of foci of epithelial hypertrophy in some animals in these groups. Increased frequencies of inflammatory lesions of the liver and oesophagus were seen in dogs at 25 000 ppm. The NOAEL was 750 ppm, equal to 29 mg/kg bw per day, on the basis of marked reductions in body-weight gain at 2500 ppm and effects on body weight, liver, thyroid, and urine at 25 000 ppm (Anderson & McDonald, 1991). Two studies in dogs given repeated doses of sodium maleic hydrazide were reviewed by the 1976 JMPR (Annex 1, reference 26). Neither study was conducted to current standards, but no marked effects were reported at 1000 mg/kg bw per day over five weeks or at < 20 000 ppm in the diet, equivalent to 500 mg/kg bw per day (Food & Drug Research Laboratory, Inc., 1955). (c) Long-term toxicity and carcinogenicity Mice The long-term toxicity and carcinogenicity of potassium maleic hydrazide (purity, 97.6%; 1.63 ppm hydrazine) was investigated in groups of 50 male and 50 female CD-1 mice which received diets containing 0, 1000, 3200, or 10 000 ppm maleic hydrazide for 23 months. Dietary incorporation was 82-129% of the nominal value, with means over the entire study of 95-102%, providing doses equal to 160, 510, and 1500 mg/kg bw per day in males and 190, 600, and 1800 mg/kg bw per day in females. Survival was 60-78% at week 82; clinical signs, body-weight gain, and food consumption were unaffected by administration of maleic hydrazide. Blood samples taken at 6, 12, 18, and 23 months showed no effects of treatment. Gross pathological examination indicated an increased frequency of lung lesions in mice at 10 000 ppm, congestion, redness, nodules, and masses in males, and congestion and redness in females; the finding in females was confirmed by the histopathological results. Amyloidosis was increased in various organs (particularly the jejunum, kidney, and liver), in a dose-related manner in males in all treated groups that died or were sacrificed during the study and at terminal sacrifice, and at termination in females at the highest dose. In females at 3200 or 10 000 ppm, a dose-related decrease in adrenal hyperplasia was seen. The incidence of carditis and myocarditis was increased in females at 3200 or 10 000 ppm, and the incidences of lung congestion and ovarian cysts were increased females at the highest dose. Slightly increased incidences of alveolar adenomas and uterine haemangiomas were identified in females at the highest dose (7/50 and 2/50, respectively, in comparison with 3/50 and 0/50 in concurrent controls and a background rate of 3-30% and 0-2% in historical controls at the test facility), which were found to be statistically significant by the author. These tumour incidences are not significant by Fisher's exact test (one-tailed, p > 0.05) and were considered not to indicate clear carcinogenic potential. Amyloidosis is a common finding, of uncertain biological significance, in CD-1 mice. Therefore, the lowest dose, equal to 160 mg/kg bw per day, was the NOAEL, despite the increased amyloidosis of the jejunum and kidney at this dose, on the basis of altered pathological appearance of the heart and adrenals at higher doses (Jessup, 1981). The 1984 JMPR (Annex I, reference 42) reviewed a study in which maleic hydrazide (purity, 98.5% as free acid, containing 0.6 ppm hydrazine) was administered orally or by subcutaneous injection to C57B1/B6 mice. Groups of 40 male and 42 female mice were given 510 mg/kg bw per week of maleic hydrazide orally in olive oil from weaning at four weeks for life. A group of 13 male and 13 female mice received olive oil only, and 51 males and 49 females formed an untreated control group. Groups of mice, which were not defined precisely, received maleic hydrazide suspended in tricaprylin subcutaneously four times on days 1, 7, 14, and 21 after birth at doses of 5, 10, 20, or 30 mg per mouse. The equivalent amount of solvent was given to a control group of 61 newborn mice. At the time the first tumour was detected, 36 females and 41 males given maleic hydrazide and 22 females and 23 males in the control group were still alive. At 120 weeks, all of the surviving mice were autopsied, and the major organs and those showing gross abnormalities were examined histologically. Oral treatment had no effect on growth or survival, and there were no differences in the numbers of tumour-bearing animals. The number of tumours found in the mice treated subcutaneously was not significantly different from that in the solvent control group, but the corresponding comparison between the treated and untreated control groups demonstrated a significant increase in the incidence of liver-cell tumours in the animals at the high dose. The incidences of other types of tumours were similar in treated, vehicle control, and untreated control groups (Cabral & Ponomarkov, 1982). Rats The long-term toxicity and carcinogenicity of potassium maleic hydrazide (purity, > 97.8%; < 0.05 ppm hydrazine) was investigated in groups of 50 male and 50 female Sprague-Dawley rats, with 20 of each sex per group taken for interim sacrifice at week 52. The animals received diets providing doses of 0, 25, 500, or 1000 mg/kg bw per day. The dietary levels were varied to account for body-weight gain and food consumption and ranged between 262 and 1023 ppm, 5144 and 16 700 ppm, and 10 214 and 31 325 ppm for the low, intermediate, and high doses, respectively. As animals were housed in groups of five, the achieved doses in individual animals varied around the cage means, which were within 10% of the nominal value over the whole study. Owing to an error, five females in the control, low-, and middle-dose groups were mis-dosed for 38 weeks; these animals were excluded from the overall results. Survival to termination was > 38% in all groups and > 50% in the animals at the highest dose, with no treatment- related effects. Clinical signs (examined in all groups) and ophthalmoscopic results (only in the controls and animals at the high dose) appeared to be unaffected by treatment. Food consumption was increased by approximately 10% in animals at 500 or 1000 mg/kg bw per day, contrasting with a decrease (> 10%) in body-weight gain from week 10 in these groups; similar effects were seen at the interim kill, but these did not achieved statistical significance. A dose-related decrease in leukocyte count seen at week 51 in males was reversed by week 104, when dose-related increases were seen in animals of each sex. These changes were not statistically significant individually but were all associated with an increase in the neutrophil:lymphocyte ratios; the biological implications to humans of such changes in the leukocyte picture in rats are unclear. Decreased blood urea nitrogen was seen in males at the highest dose in weeks 25 and 51 and in males at the middle dose in week 51; there was evidence of a similar slight effect in females at week 51. Serum phosphate levels were increased in males at the highest dose in week 25 and in males at the intermediate and highest doses in week 51; serum calcium was also increased in males at the middle and highest doses at week 51. Females at 500 mg/kg bw per day had increased alanine aminotransferase and lactic dehydrogenase activities at week 25 and decreased serum chloride levels, but similar changes were not recorded subsequently. Evidence of decreased urinary pH in animals at the highest dose was seen in week 51. Statistically significant reductions (about 20%) in absolute liver weights in males at the highest dose at interim sacrifice and in males and females at the highest dose and females at the intermediate dose at termination were related, at least in part, to the reduced body weights in these groups. Although the relative liver weights were reduced in these groups, the reductions were not statistically significant and were without obvious pathological sequelae. No treatment-related effects were seen at interim sacrifice, during the study or at the terminal gross pathological examinations. Extensive microscopic pathological examinations were performed on all controls, animals at the highest dose, and animals that died during the study. Only the liver, kidney, lung, and heart (at week 104 only) from animals at the low and intermediate doses were examined at interim and terminal sacrifice. The incidence of myocarditis of the ventricle, described as fibrous or chronic, was increased in males at the highest dose at interim sacrifice and throughout the study, but as there was no dose-response relationship this may be a chance finding. The incidence of periacinar vacuolation of the liver was increased in males at the highest dose at interim sacrifice and throughout the study. A change in the pattern of renal lesions was seen in females at week 104, with a non-dose-related increase in the incidence of progressive nephropathy in all groups and a decrease in that of pelvic epithelial hyperplasia at the highest dose. The incidences of hydronephrosis and proteinaceous plugs in the urinary bladder were increased in males at the highest dose. Adrenal medullary hyperplasia and cystic degeneration were increased in incidence in males at the highest dose, with a non-significant increase in adrenal cortical hyperplasia and a decrease in cystic degeneration in females at the highest dose in week 104. The frequencies of cholesterol clefts in the pituitary and parafollicular-cell hyperplasia of the thyroid were increased in males at the highest dose. None of the incidences of alterations was consistent between the sexes, although there is some evidence that the kidney may be a target organ. It is therefore uncertain whether the lesions were due to maleic hydrazide. Occasional increases in tumour incidences were seen, but as these were not consistent between the two sexes and did not achieve statistical significance they are considered not to be directly attributable to maleic hydrazide. The NOAEL was 25 mg/kg bw per day on the basis of the marked effects on body-weight gain in the presence of increased food consumption, together with alterations in clinical chemical parameters at higher doses (Perry et al., 1991). The 1980 JMPR (Annex 1, reference 34) reviewed a study in which 55 rats of each sex were given diets containing 0 or 1% maleic hydrazide (containing < 1.5 ppm hydrazine) and 65 male and 65 female rats were given a diet containing 2% maleic hydrazide. The rats were kept on their respective diets for 28 months after weaning. No clear differences between the control and test groups were seen in respect of mortality, food consumption, haematological parameters, or organ weights. The body-weight gain of treated females was decreased, especially during the first half of the experiment. The males at 2% showed a tendency to a lower growth rate. All animals at this dose had a significant increase in water consumption, measured during weeks 18 and 25; those at 1% had a tendency to increased water consumption. Urinalysis revealed that doses of 1 and 2% maleic hydrazide caused proteinuria and increased the protein:creatinine ratios in both males and females after 6 and 12 months; however, no histopathological lesions in the kidneys or other tissues were observed. There was no treatment-related change in tumour incidence (van der Heijden et al., 1979). The 1980 JMPR concluded that 2%, equivalent to 1000 mg/kg bw per day, was the NOAEL. The 1976 JMPR (Annex 1, reference 26) reviewed a study in which maleic hydrazide was given in the diet at concentrations of 0, 0.5, 1, 2, or 5% to groups of 10 male and 10 female rats, with a continuous breeding protocol covering eight matings. The group size was small by current standards. No marked effects were reported on parental animals in any treated group (Food & Drug Research Laboratory, Inc., 1955). The NOAEL for chronic toxicity and carcinogenicity, within the limitations of the study, was thus 5% in the diet, equivalent to 2500 mg/kg bw per day. (d) Reproductive toxicity Rats The potential reproductive effects of maleic hydrazide were investigated in rats in a two-generation study with two litters per generation. Groups of 30 female and 15 male CD(SD)BR rats received diets containing 0, 1000, 10 000, 30 000, or 50 000 ppm maleic hydrazide (purity, 99%; < 2 ppm hydrazine) for 105 days before mating for the F1a generation until weaning of the F1b litter. The F1b litter received treated diet from weaning through mating to provide the second generation until termination after weaning of the F2b generation. These dietary levels resulted in achieved doses of 0, 80, 770, 2350, and 3940 mg/kg bw per day. Litters were culled on day 4 of lactation to a maximum of 10 pups, and the culled pups were subjected to a gross external examination. All parental animals and selected F1b and F2b pups underwent gross necropsy, and selected tissues were examined histologically. Dietary incorporation and stability were acceptable, with mean values within 5% of the nominal value throughout the study. Owing to significant deficits in body weight in parental animals (F0) and pups (F1a and F1b) receiving 50 000 ppm (by about 20% in pups at day 21), this dose was not fed to the F1b generation. No adverse effects on reproductive outcome or on the measured parameters were seen at any dose or mating. F0 females receiving 30 000 ppm had reduced body-weight gain from week 8 onwards; in F1b females fed this level of maleic hydrazide, a slight reduction in body-weight gain was seen which never achieved statistical significance. At 30 000 ppm, deficits in F1b, F2a, and F2b pup weights occurred at various times, but pup weight at birth was not affected. No adverse effects on pup behaviour or development were seen. A number of changes in organ weights were noted during the study, primarily associated with changes in body weight; only the increased absolute and relative kidney weights of F1b females receiving 30 000 ppm are considered to be biologically significant. In conjunction with the slight increase in the incidence of dilated renal pelves (5/28 versus 2/29 in controls), the increased kidney weights may indicate an adverse effect on the kidney. Urinalysis showed considerable variability and no clear effects. Macroscopic and microscopic examinations showed no significant alterations in the incidence of lesions. No reproductive toxicity was recorded. The NOAEL was 10 000 ppm, equal to 770 mg/kg bw per day, on the basis of reduced body weight in female parents and pups at doses > 30 000 ppm (Mackenzie, 1983). A multigeneration study reviewed by the JMPR in 1976 (Annex 1, reference 26) showed reduced F3b litter size in animals at 5% maleic hydrazide in the diet, with no effects at 2% (Food & Drug Research Laboratory, Inc., 1955). (e) Developmental toxicity Rats Groups of 23-25 mated female Sprague-Dawley rats were given solutions of potassium maleic hydrazide (purity, 97.8%; 0.048 ppm hydrazine) in distilled water, prepared to give doses of 0, 30, 300, or 1000 mg/kg bw maleic hydrazide per day, by gavage on days 6-16 of gestation. The highest dose was the limit for such studies performed to OECD guideline 414. All dams were killed on day 20, their reproductive tracts examined, and the fetuses removed. All fetuses were examined for external malformations; half were then investigated by Wilson sectioning, and the remainder were dissected to examine visceral abnormalities before staining with alizarin red S for skeletal examination. Doses of maleic hydrazide < 1000 mg/kg bw per day had no adverse effects on maternal body weight, clinical signs, food consumption, pregnancy rate, implantation rate, or fetal weight. In comparison with concurrent controls, animals at the highest dose had increased incidences of testes displaced over the bladder, vestigial 14th ribs, and retarded ossification of the pelvis, with evidence of a dose-response relationship; however, the incidences were reported to be within the rates in historical controls at the test facility. Four fetuses from different litters in the group at the highest dose had major malformations, with none in concurrent controls. Micrognathia and cleft palate were seen in three fetuses from the same dam treated at 300 mg/kg bw per day, one fetus at the highest dose had cleft palate, and one fetus at 30 mg/kg bw per day had a misshapen palatal arch; neither micrognathia nor cleft palate was seen in fetuses of the concurrent controls. None of the findings achieved statistically significance (by Fisher's exact test). The NOAEL for both maternal and fetal effects was 1000 mg/kg bw per day (Wilson & Hazelden, 1989). Rabbits Groups of 16 artificially inseminated belted Dutch rabbits were dosed by gavage with potassium maleic hydrazide (purity, 99.8%; 1 ppm hydrazine) in deionized water at levels of 0, 100, 300, or 1000 mg/kg bw maleic hydrazide per day on days 7-27 of gestation. The doses were chosen on the basis of the results of a range-finding study in which there was total mortality at 2500 mg/kg bw per day. The dams were killed on day 28, their reproductive tracts examined, and the fetuses removed. All fetuses were examined for viability, sex, and external malformations and variations, and were then dissected for investigation of visceral abnormalities before staining with alizarin red S for skeletal examination. An increased incidence of alopecia in animals at the highest dose was the only clinical sign associated with treatment. Maternal body-weight gain was reduced at 1000 mg/kg bw per day on days 7-13 of gestation. A single death occurred during the treatment period, in a dam at 300 mg/kg bw per day, probably as a result of an accident during gavage. Treatment had no significant effects on the number of abortions, implantation rate, pregnancy rate, fetal weight, litter size, or fetal viability. Eight late resorptions from five litters occurred in the group at the highest dose, with 0, 1, and 2 in the controls and in the groups at the low and intermediate doses, respectively. The only malformation or anomaly clearly related to treatment was scapular defects, which were seen in four fetuses (three forked scapulae, one bent; 4%) at the intermediate dose and in two (two forked scapulae; 2%) at the highest dose, with none in controls or animals at the low dose. The incidence of such anomalies in historical control animals at the test facility was 1 in 1536 (0.065%). As these anomalies were not identical, however, they should not have been combined; the ranges were thus within those seen in rabbits at other test facilities. Given the low incidences and the lack of a clear dose-response relationship for the fetal effects, the NOAEL was 1000 mg/kg bw per day for embryotoxicity and teratogenicity and 300 mg/kg bw per day for maternal toxicity on the basis of increased absorptions and decreased body-weight gain at the beginning of treatment (Miller, 1983). Table 2. Results of tests for the genotoxicity of maleic hydrazide End-point Test system Concentration Purity Results Reference (%) In vitro Reverse mutation S. typhimurium 625, 1250, 2500, 5000, 88.7a + Negative +/- S9 Foyster (1988) TA98, TA100, 10 000 µg/plate 10.5% TA1535, TA1537, (distilled water) water TA1538 DNA repair B. subtilis H17, 1, 10, 100, 500, 1000, 97 Negative -S9; Hoorn (1988) M45 (rec+/-) 2500, 5000, 10 000 positive at 10 000 µg/plate (DMSO) µg/plate +S9 DNA repair E. coli polA+/- 0.01, 0.1, 1, 5, 10, 25, NR Negative +/- S9 Jagannath (1981) 50 µl/plate (water) Forward mutation Mouse lymphoma 0.625, 1.25, 2.5, 5, 10 NR Negative +/- S9; Cifone (1981) L5178Y tk+/- cells µl/ml (water) assay not repeated Chromosomal Chinese hamster 1000, 2150, 4640 µg/ml 88.7a Weakly positive at Mosesso (1988) aberration ovary cells - S9 + 10.5% 4640 µg/ml 2150, 4640, 10 000 µg/ml water Positive at 10 000 + S9 (Hams F10) µg/ml Sister chromatid Chinese hamster 100, 1000, 10 000 µg/ml 88.7a Weakly positive at Mosesso (1989) exchange ovary cells - S9 (Hams F10) + 10.5% 10 000 µg/ml 32, 320, 3200, 10 000 water Positive at 3200, µg/ml + S9 10 000 µg/ml Table 2. (Cont'd) End-point Test system Concentration Purity Results Reference (%) In vivo Sister chromatid B6C3F1 mice 110, 551, 1100 mg/kg bw approx. 96b Negative; 80% Putman (1990) exchange (males and i.p. each sex; 800 mg/kg mortality in males females) bw i.p. males only (water) at 1100 mg/kg bw Chromosomal Male CD1 mice, 500, 1000, 5000 mg/kg bw 99 Negative for structural Matheson (1978) aberrations tibial bone marrow; single or 5 daily oral aberrations; hyperdiploid 6-, 24-, 48-h doses (water) cells increased at 500 sampling mg/kg bw and repeat 1000 mg/kg bw per day Micronucleus CD1 mice, males 2500, 5000 mg/kg bw, approx. 96b Negative in each sex Putman & Morris formation and females, 72-h gavage (water) (1990) femur samples Recessive lethal Drosophila 0.4, 1% w/v (water) NR Negative; toxicity Jagannath (1978) mutation melanogaster at 1% Basc Spot test Drosophila 1, 2, 5, 10 mmol/litre 100 Positive at > 2 Torres et al. melanogaster (1% Tween 80/5% mmol/litre; (1992) ethanol) concentration-related Recessive lethal Drosophila 820, 2500 µg/ml (water) 99 Positive Zimmering et al. mutation melanogaster (1989) larvae DMSO, dimethyl sulfoxide; - S9, no metabolic activation; + S9, in the presence of metabolic activation; i.p., intraperitoneally a 0.31 ppm hydrazine b 0.041 ppm hydrazine (f) Genotoxicity The genotoxic potential of maleic hydrazide has been investigated in a range of test systems in vitro and in vivo, the results of which are summarized in Table 4. A number of studies in which unusual test systems (e.g. allium root cells) or maleic hydrazide of unspecified hydrazine content were used were not included, as the existing database covered an extensive range of end-points. Some positive results were reported in tests in vitro at high concentrations in both the presence and absence of metabolic activation systems. The studies performed in vivo, which were of adequate standard, gave negative results, although a non-dose-related increase in the occurrence of hyperdiploid cells in mouse bone marrow indicates that maleic hydrazide may affect cell division under certain conditions. The biological significance of the positive results obtained in mammalian cells in vitro is questionable, as the osmotic potential in the culture media containing the maleic hydrazide was within the range reported to interfere with chromosomal structure. It was considered that the results of the studies in mammals in vivo show that maleic hydrazide does not present a genotoxic hazard to humans. (g) Special studies: Dermal and ocular irritation and dermal sensitization The dermal irritancy of 0.5 ml technical-grade maleic hydrazide (purity unspecified) was investigated under occlusive conditions in three male and three female New Zealand white rabbits. Slight oedema was seen in one male, and slight erythema was present at intact sites in all males at 24 h, with complete regression within 72 h. Abraded sites had a longer erythematous response, again limited to males. Maleic hydrazide was thus slightly irritating to rabbit skin (Shapiro, 1977d). A study reviewed by the 1976 JMPR (Annex 1, reference 26) showed that a 20% solution of maleic hydrazide was not irritating to rabbit skin (Food & Drug Research Laboratory, Inc., 1955). The ocular irritancy of 0.1 g technical-grade maleic hydrazide (purity unspecified) was investigated in three male and three female New Zealand white rabbits. Slight, transient conjunctival reactions were recorded in some animals, with complete regression within 72 h. Maleic hydrazide is thus slightly irritating to rabbit eyes (Shapiro, 1977e). A study reviewed by the 1976 JMPR (Annex 1, reference 26) showed that a 5% solution of maleic hydrazide was not irritating to rabbit eyes (Food & Drug Research Laboratory, Inc., 1955). A group of 20 female Dunkin-Hartley albino guinea-pigs were treated with a 25% w/v solution of potassium maleic hydrazide (purity, 97.8%) in water in a Buehler epicutaneous test for dermal sensitization. No skin reactions were recorded after induction or challenge. The maximal non-irritating concentration of potassium maleic hydrazide (25%) thus had no skin sensitizing potential in guinea-pigs (Cuthbert & Jackson, 1989). A study reviewed by the 1976 JMPR (Annex 1, reference 26) showed that a 0.1% solution of maleic hydrazide was not sensitizing in guinea-pigs (Food & Drug Research Laboratory, Inc., 1955). Comments Maleic hydrazide is rapidly and extensively absorbed after oral administration of single doses of 2 or 100 mg/kg bw or 2 mg/kg bw per day for 15 days. Excretion is rapid (> 80% in 24 h) after either oral or intravenous administration, with urinary excretion predominating (> 80%). Metabolism of maleic hydrazide is minimal, the parent compound representing over 60% in males and 80% in females of the urinary radiolabel; conjugation to sulfate is the only significant reaction. There was no evidence that absorption or metabolism was affected by dose or by repeated administration in rats. The total tissue residues in rats represented < 1% of the administered dose after seven days. The acute toxicity of maleic hydrazide after administration by the oral, dermal, or inhalation route is low, with LD50 and LC50 values greater than the limit doses (5 g/kg bw orally, 20 g/kg bw dermally, and 20 mg/litre by inhalation). No target organs were identified. Maleic hydrazide was only slightly irritating to the skin and eyes and is not a skin sensitizer. The compound has been classified by WHO as unlikely to present an acute hazard in normal use (WHO, 1996). After administration of repeated oral doses of maleic hydrazide to rats (0, 30, 100, 300, or 1000 mg/kg bw per day or 0, 0.5, 1, 2 or 5% in the diet) and dogs (0, 750, 2500, or 25 000 ppm) for 12-13 weeks, no marked adverse effects were seen at doses < 1000 mg/kg bw per day; however, the extent of the examinations performed in these studies was inadequate to permit a reliable NOAEL to be determined. In rats treated dermally for three weeks, no significant effects were seen on gross or histopathological examination of animals at doses < 1000 mg/kg bw per day. An increased lymphocyte count in males at 500 or 1000 mg/kg bw per day was considered to be of questionable biological significance in the absence of similar findings in other studies. The NOAEL was 1000 mg/kg bw per day. In a one-year study in dogs treated in the diet at levels of 0, 750, 2500, or 25 000 ppm, reduced body-weight gain, thyroid hypertrophy, and inflammatory lesions of the liver were seen at 25 000 ppm (equal to 970 mg/kg bw per day), with changes in urinary pH, serum enzyme activities, and albumin level. As significant reductions in body-weight gain were seen at 25 000 ppm (35%) and 2500 ppm (20%), the NOAEL was 750 ppm, equal to 29 mg/kg bw per day. Earlier studies with limited protocols were inadequate for deriving reliable NOAELs for dogs but showed no marked effects at doses < 500 mg/kg bw per day over two years. In a 23-month study in mice fed diets containing 0, 1000, 3200 or 10 000 ppm, there was a dose-related increase in the prevalence of amyloidosis in males, which also occurred in females at the highest dose. The frequencies of adrenal hyperplasia and carditis or myocarditis were increased in females at the two higher doses. Increases in the frequencies of alveolar adenomas and uterine haemangiomas in females at the highest dose were not statistically significant and do not represent clear evidence of carcinogenic potential. The NOAEL was 1000 ppm (equal to 160 mg/kg bw per day) on the basis of cardiac and adrenal changes in females at doses > 3200 ppm. A small increases in the frequency of amyloidosis was observed in males at 1000 ppm, which was considered not to be significant. An earlier long-term study in mice treated by oral or subcutaneous administration provided no evidence of carcinogenicity. In a two-year study of toxicity and carcinogenicity in rats in which the levels incorporated in the diet were varied to give 0, 25, 500 or 1000 mg/kg bw per day, there was no evidence of an increase in tumour incidence. Reductions in body-weight gain, despite increased food consumption, were noted at 500 and 1000 mg/kg bw per day. An altered pattern of renal lesions, myocarditis, adrenal hyperplasia, and thyroid hyperplasia was seen at 1000 mg/kg bw per day. The NOAEL was 25 mg/kg bw per day on the basis of clear effects on weight gain at doses > 500 mg/kg bw per day. Earlier long-term studies in rats provided no evidence of carcinogenicity at doses < 2% in the diet (equivalent to 1000 mg/kg bw per day). In a two-generation study of reproductive toxicity in rats given 0, 1000, 10 000, 30 000, or 50 000 ppm in the diet, significant effects on the body-weight gain of parents and pups were evident at the two highest doses, to such an extent that the dose of 50 000 ppm was discontinued after the first generation. There were no adverse effects on reproductive parameters. Increases in organ weight and histological findings indicated a slight effect on the kidney at 30 000 ppm. The NOAEL was 10 000 ppm (equal to 770 mg/kg bw per day). In a study of developmental toxicity, rats were given 0, 30, 300, or 1000 mg/kg bw per day maleic hydrazide by gavage on days 6-16 of gestation. There was no clear evidence of effects on the fetus or of mammal toxicity, even at the highest dose tested. In a similar study in rabbits treated with 0, 100, 300, or 1000 mg/kg bw per day by gavage on days 7-27 of gestation, there was no clear evidence of fetotoxicity or teratogenicity. Reduced maternal body-weight gain and an increased frequency of late resorptions were seen at 1000 mg/kg bw per day. The NOAEL was 300 mg/kg bw per day. A wide range of tests for genotoxicity in vitro with high concentrations of maleic hydrazide resulted in several positive findings. No positive effects were recorded in four studies in vivo. The Meeting concluded that maleic hydrazide is not genotoxic. An ADI of 0-0.3 mg/kg bw was established on the basis of the NOAEL of 25 mg/kg bw per day in the two-year study of toxicity and carcinogenicity in rats and the one-year study of toxicity in dogs, using a 100-fold safety factor. Toxicological evaluation Levels that cause no toxicological effect Mouse: 1000 ppm, equal to 160 mg/kg bw per day (toxicity in a 23-month study of toxicity and carcinogenicity) Rat: 25 mg/kg bw per day (toxicity in a two-year study of toxicity and carcinogenicity) 1000 mg/kg bw per day (highest dose tested in a study of developmental toxicity) 10 000 ppm, equal to 770 mg/kg bw per day (toxicity in a two-generation study of reproductive toxicity) Rabbit: 300 mg/kg bw per day (maternal toxicity in a study of developmental toxicity) Dog: 750 ppm, equal to 29 mg/kg bw per day (one-year study of toxicity) Estimate of acceptable daily intake for humans 0-0.3 mg/kg bw Toxicological criteria for estimating guidance values for dietary and non-dietary exposure to maleic hydrazide Exposure Relevant route, study type, species Results, remarks Short-term (1-7 days) Oral, toxicity, rat LD50 > 5000 mg/kg bw Skin, toxicity, rabbit LD50 > 20 000 mg/kg bw Inhalation, 1 h toxicity, rat LC50 > 20 mg/litre Dermal, irritation, rabbit Slightly irritating Ocular, irritation, rabbit Slightly irritating Dermal, sensitization, guinea-pig Not sensitizing Medium-term (1-26 weeks) Repeated dermal, 21 days, toxicity, rat NOAEL = 1000 mg/kg bw per day (highest dose tested) Repeated oral, reproductive toxicity, rat NOAEL = 750 mg/kg bw per day, reduced weight gain; no effects on reproduction Repeated oral, developmental toxicity, rat NOAEL = 1000 mg/kg bw per day (highest dose tested) Repeated oral, developmental toxicity, NOAEL = 1000 mg/kg bw per day (highest dose tested), rabbit embrotoxicity and teratogenicity NOAEL = 300 mg/kg bw per day, maternal toxicity (increased resorptions and decreased weight gain) Long-term (> 1 year) Repeated oral, 2 years, toxicity and NOAEL = 25 mg/kg bw per day, decreased weight carcinogenicity, rat gain, increased food intake, and clinical chemical changes Repeated oral, 1 year, toxicity, dog NOAEL = 25 mg/kg bw per day, reduced body-weight gain References Anderson, B.T. & McDonald, P. (1991) Maleic hydrazide. Fifty-two week dietary toxicity study in dogs. Unpublished report from Inveresk Research International, Tranent, Scotland, Report No. 7709. Submitted to WHO by Uniroyal Chemical Co., Bethany, CT, USA. Cabral, J.R.P. & Ponomarkov, V. (1982) Carcinogenicity study of the pesticide maleic hydrazide. Toxicology, 24, 169-173. Caley, C.Y. & Cameron, B.D (1989) Metabolism of [14C]-maleic hydrazide in the rat. Unpublished report from Inveresk Research International, Tranent, Scotland, IRI Project No. 140024. Submitted to WHO by Uniroyal Chemical Co., Bethany, CT, USA. Caley, C.Y., Cameron, B.D. & Martin, W.S. (1990) Identification of metabolites of [14C]-maleic hydrazide in rat urine. Unpublished report from Inveresk Research International, Tranent, Scotland, IRI Project No. 380060. Submitted to WHO by Uniroyal Chemical Co., Bethany, CT, USA. Cameron, S.A., Haycox, G.R. & Johnston, A.M. (1992) [14C]-Maleic hydrazide: Absorption, distribution, metabolism and excretion in the lactating goat. Unpublished report from Inveresk Research International, Tranent, Scotland, IRI Project No. 151921. Submitted to WHO by Uniroyal Chemical Co., Bethany, CT, USA. Cifone, M.A. (1981) Mutagenicity evaluation of KMH solution in the mouse lymphoma forward mutation assay. Unpublished report from Litton Bionetics, Inc., Kensington, MD, USA, Project No. 20989. Submitted to WHO by Uniroyal Chemical Co., Bethany, CT, USA. Cuthbert, J.A. & Jackson D. (1989) Maleic hydrazide: Buehler sensitization test in guinea pigs. Unpublished report from Inveresk Research International, Tranent, Scotland, Report No. 5807. Submitted to WHO by Uniroyal Chemical Co., Bethany, CT, USA. Food & Drug Research Laboratory, Inc. (1955) Reports on toxicology studies of chemical additives; 3. Maleic hydrazide (1,2-dihydro- pyridazone 3,6 dione). Unpublished report. Submitted to WHO by Uniroyal Chemical Co., Bethany, CT, USA. Foyster, R. (1988) Reverse mutation in Salmonella typhimurium. Unpublished report from Life Science Research, Rome, Italy, Report No. 131004-M-02988. Submitted to WHO by Uniroyal Chemical Co., Bethany, CT, USA. Goburdhun, R. (1990) Maleic hydrazide. Thirteen week dose range finding study in dogs. Unpublished report from Inveresk Research International, Tranent, Scotland, Report No. 5924. Submitted to WHO by Uniroyal Chemical Co., Bethany, CT, USA. van der Heijden, C.A., Berkvens, J.M., den Tonkelaar, E.M., Droes, R., Nesselrooy, J.H.J., Vries, T. & van Esch, G.J. (1979) Maleic hydrazide: An oral carcinogenicity study in rats. Unpublished report No. 7/79 Tox/path from the National Institute of Public Health, Netherlands. Hoorn, A.J.W. (1988) Mutagenicity test on maleic hydrazide potassium salt (KMH) in the REC-assay with Bacillus subtilis (preincubation and suspension methods). 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See Also: Toxicological Abbreviations Maleic hydrazide (Pesticide residues in food: 1976 evaluations) Maleic hydrazide (Pesticide residues in food: 1977 evaluations) Maleic hydrazide (Pesticide residues in food: 1980 evaluations) Maleic hydrazide (Pesticide residues in food: 1984 evaluations) Maleic hydrazide (Pesticide residues in food: 1984 evaluations) Maleic Hydrazide (IARC Summary & Evaluation, Volume 4, 1974)