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    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 g/g at the low dose and < 0.15 g/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 g/g on day 1 to 0.33 g/g on day 4 and then fell to 0.20 g/g on
    day 5; in the yolk, the peak value, 0.23 g/g, was reached on day 5.
    The equivalent tissue levels at termination were generally lower than
    those in plasma (0.13 g/g), except in liver (0.13 g/g) and kidney
    (0.20 g/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 g/g
    equivalent) were found only in liver (1.2 g/g) and kidney (3.3 g/g);
    the concentration in muscle was 0.44 g/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 g/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 -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 -20C (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 m) 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 g/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
                                             g/plate (DMSO)                            g/plate +S9
    DNA repair         E. coli polA+/-       0.01, 0.1, 1, 5, 10, 25,     NR            Negative +/- S9             Jagannath (1981)
                                             50 l/plate (water)
    Forward mutation   Mouse lymphoma        0.625, 1.25, 2.5, 5, 10      NR            Negative +/- S9;            Cifone (1981)
                       L5178Y tk+/- cells    l/ml (water)                              assay not repeated
    Chromosomal        Chinese hamster       1000, 2150, 4640 g/ml       88.7a         Weakly positive at          Mosesso (1988)
    aberration         ovary cells           - S9                         + 10.5%       4640 g/ml
                                             2150, 4640, 10 000 g/ml     water         Positive at 10 000
                                             + S9 (Hams F10)                            g/ml
    Sister chromatid   Chinese hamster       100, 1000, 10 000 g/ml      88.7a         Weakly positive at          Mosesso (1989)
    exchange           ovary cells           - S9 (Hams F10)              + 10.5%       10 000 g/ml
                                             32, 320, 3200, 10 000        water         Positive at 3200,
                                             g/ml + S9                                 10 000 g/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 g/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
                                                                                                                                      
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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)