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
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