ZINEB
First draft prepared by
M. Caris
Health Canada, Ottawa, Canada
EXPLANATION
Zineb was previously evaluated by the Joint Meeting in 1963,
1965, 1967, 1970, 1974, 1977 and 1980 (Annex I, references 2, 4, 8,
14, 22, 28, 34). An ADI of 0-0.05 mg/kg bw, of which not more than
0.002 mg/kg bw may be present as ETU, was allocated at the 1980
Meeting for zineb or the sum of maneb, mancozeb, and zineb. Little
new information on zineb has become available since the previous
evaluation. This monograph summarizes the data that were reviewed
at the present meeting, which consisted primarily of data that were
summarized in previous monographs and monograph addenda.
EVALUATION FOR ACCEPTABLE DAILY INTAKE
BIOLOGICAL DATA
Biochemical aspects
Absorption, distribution and excretion
Mice
Groups of three adult male ND/4(S)BR mice received a single
oral dose of radiolabelled ethylenethiourea (ETU, 0.05 or 0.25
mmol/kg bw), ethylene bis(isothiocyanate) sulfide (EBIS, 0.05 or
0.25 mmol/kg bw), maneb (0.05 or 0.25 mmol/kg bw) or zineb (0.25
mmol/kg bw). Urine, faeces, and CO2 were collected and analyzed.
Total recovery of radiolabel with EBIS (54%) and zineb (65%) was
less than with ETU (72-100%) and maneb (81-91%). The percentage of
the recovered radioactivity excreted in the urine following
treatment with ETU (47-48%) and EBIS (40-74%) was greater than with
maneb (7-9%) and zineb (10%). The majority of the radioactivity in
the urine was excreted during the first 24-hour period following
dosing. Elimination via the faeces represented the greatest
percentage of the recovered radiolabel with ETU (52-53%), maneb (91-
93%) and zineb (91%). Treatment with EBIS at 0.25 mmol/kg bw
resulted in a higher percentage of radioactivity recovered in the
urine (74%) when compared to the lower EBIS dose (40%). None of the
14C-ETU, EBIS, maneb or zineb was excreted as 14C-CO2.
Characterization of the radioactivity in the urine revealed that the
principal components following treatment with ETU, EBIS, maneb and
zineb were ETU, ethylene urea (EU), and polar products (more polar
than EU). The majority of the radioactivity in the urine was
present as polar components following dosing with EBIS (77-100%),
maneb (78-82%) and zineb (81%). Approximately half of the
radioactivity in the urine after dosing with 14C-ETU was unchanged
compound. The presence of ETU in the urine following treatment with
14C-EBIS, maneb and zineb represented 0-11%, 8-16% and 15% of the
radioactive components, respectively (Jordan & Neal, 1979).
Rats
The capacity of the human gut to absorb zineb is not known,
though in the rat, 11-17% is taken up after ingestion. It is
believed that thiocarbamates may act as inhibitors of certain -SH
enzymes in the body (Annex I, reference 2).
Biotransformation
The dithiocarbamate compounds are thought to break down to
alkyl-thioureas, carbon disulfide and hydrogen sulfide. Breakdown
of nabam, as well as zineb and maneb, in aqueous systems has been
demonstrated to produce ethylene thiourea and ethylene thiuram
monosulfide (Falk et al., 1965; Vonk & Kaars Sijpesteijn, 1970;
Annex I, reference 15).
With maneb, zineb and nabam, ETU and ethylenediamine were found
in all cases, often as the end products of breakdown. Levels of the
intermediates, such as ethylene-bis thiuram monosulfide and
ethylene-diisothiocyanate, varied according to the compound studied
(Engst & Schnaak, 1970a,b; Annex I, reference 15).
Groups of Charles River CD rats and purpose-bred marmosets
(2/sex/species) received a single oral dose of 50 mg 14C-zineb/kg
bw. The majority of the radiolabel was excreted within the first 24
hours post-dosing. Excretion of radiolabel over a 96-hour period
revealed similar patterns of elimination in the marmoset and rat,
with highest levels present in the urine (53% and 68%) and lesser
amounts in the faeces (38% and 34% in the marmoset and rat,
respectively). Only minimal amounts of radioactivity were detected
in the carcass or expired CO2. In both the marmoset and rat, the
total amount of extractable material represented only about half of
the measurable radioactivity. Characterization of excreted
metabolites revealed the presence of ethylene thiourea, polar
products and ethyleneurea (Searle et al., 1987).
Effects on enzymes and other biochemical parameters
The effect of inhalation of maneb and zineb on five isoenzymes
of lactic dehydrogenase in rat testes was studied. With maneb-
poisoned animals, an increase in the isoenzyme related to aerobic
metabolism and a decrease in that related to anaerobic metabolism
was observed. There was no effect on these isoenzymes in the case
of animals exposed to zineb (Izmirova et al., 1969; Annex I,
reference 15).
Zineb, ziram, maneb or urethane were administered orally once a
week during six weeks to mice (A and C57) and to rats (SPF). The
total dose of single substances administered to the rats was 120 mg
(ca. 600 mg/kg bw/6 weeks) and to mice 60 mg (ca. 3000 mg/kg bw/6
weeks), with the exception of ziram, where the total dose
represented only half this amount i.e. 30 mg (ca. 1500 mg/kg bw/6
weeks). Comparison was made between the activity of glucose-6-
phosphate dehydrogenase in liver and deoxyribonuclease in serum
under development of proliferative changes in the lungs. With
regard to zineb, ziram and urethane, the correlation was ascertained
in rats only between the early blastogenic changes in lungs and the
deoxyribonuclease activity in the serum. In the case of the weak
blastogens, zineb and ziram, maximum increase of ferment activity
was apparent at 9 months and lung changes at 12 months after
exposure. With urethane, these reactions in rats were observed
earlier (6 months and 9 months, respectively). Neither the activity
of glucose-6-phosphate dehydrogenase in the liver of mice and rats
nor that of deoxyribonuclease in serum changed, and there was no
correlation with proliferative changes in the lungs (Chepinoga et
al., 1969; Annex I, reference 15).
A study was conducted to determine the potential effects of
zineb on the hepatic microsomal systems. Groups of 8 adult male
Swiss albino mice and 8 Wistar rats were treated orally by gavage
with zineb (89.5% purity, containing 0.07% ETU) at a single dose of
0 (vehicle control, arachid oil), 50, 100, 200 or 400 mg/kg bw, and
ETU (98% purity) at 0 (vehicle control, water), 100 or 200 mg/kg bw.
Liver enzymatic assays performed 24 hours following treatment with
zineb revealed depressed aminopyrine-N-demethylase levels in rats at
> 200 mg/kg bw and in mice at > 100 mg/kg bw. Aniline
hydroxylase levels were decreased in rats at > 200 mg/kg bw and
increased in mice at 400 mg/kg bw. There were no significant
differences in cytochrome P-450 or in the microsomal protein
concentration. To examine the effects of treatment on microsomal
systems over time, additional groups of 8 rats and mice were treated
with a single oral dose of zineb at 200 mg/kg bw with scheduled
sacrifices after 2, 18, 24 or 48 hours following dosing. The data
confirmed maximum effects on liver microsomal enzymes at
approximately 24 hours post-treatment. Treatment with ETU at 100
mg/kg bw and higher increased aniline hydroxylase levels in mice and
decreased aminopyrine-N-demethylase levels in rats (Meneguz &
Michalek, 1987).
Toxicological studies
Acute toxicity studies
The results of acute toxicity studies on zineb are summarized
in Table 1. Zineb was practically non-toxic when administered
orally to rats and guinea-pigs, when given subcutaneously to rats,
or when given by intraperitoneal injection to mice. WHO has
classified zineb as unlikely to present acute hazard in normal use
(WHO, 1992).
Short-term toxicity studies
Rats
Groups of weanling rats (20/sex/dose) were given diets
containing 500, 1000, 2500, 5000 or 10 000 ppm of zineb for 30 days.
Thyroid enlargement was seen at all dose levels, but unequivocal
histopathological changes were observed only at 10 000 ppm
(Blackwell-Smith et al., 1953; Kampmeier & Haag, 1954; Annex I,
reference 2).
Table 1. Acute toxicity of technical zineb
Species Sex Route LD50 Purity Reference
(mg/kg bw)
Rat ? oral > 5200 ? Annex I, reference 2
Guinea-pig F oral > 4800 ? Annex I, reference 15
Mouse M intraperitoneal 2400 ? Annex I, reference 15
Rat M subcutaneous > 5600 ? Annex I, reference 15
Groups of newly-weaned rats (10/sex/dose) were given 0, 15, 60,
250 or 1000 mg/kg bw/day of zineb by gavage, five days a week for
four weeks. Blood samples were taken during the final week. Some
of the animals were sacrificed for autopsy immediately upon
termination of the period of administration of zineb; others were
kept for two weeks without receiving zineb prior to sacrifice. No
effects attributable to zineb were detected at levels of 250 mg/kg
bw/day or lower. At 1000 mg/kg bw/day, the kidneys were enlarged in
the animals of both sexes, but no histological changes were apparent
in that organ. The thyroids were not enlarged, although
histological examination indicated a slight hyperplasia in the
females given 1000 mg/kg bw/day. Weight gain was normal, as was the
blood picture. There were no histological changes in any tissue
other than in the thyroid. One female given 1000 mg/kg bw/day died
of an unknown cause. Withdrawal of zineb appeared to result in a
reversal of the effect on the kidney and thyroid, as evidenced by
examination of the animals sacrificed two weeks after discontinuing
treatment. The NOAEL was 250 mg/kg bw/day (Lessel & Cliffe, 1961;
Annex I, reference 15).
In a study in rats, zineb (490 or 2450 mg/kg bw), maneb (350 or
1750 mg/kg bw), and mancozeb (700 or 3500 mg/kg bw) were
administered orally twice a week for 4 months. Mortality was high,
and paresis of the hind limbs appeared in the third month of the
study and progressed to complete paralysis (Ivanova-Chemishanska,
1969; IPCS, 1988).
Male rats were maintained for six weeks on diets containing 0,
500 or 5000 ppm of either maneb or zineb. Gross and
histopathological changes in the thyroid gland, reduced assimilation
of 124I and slightly reduced respiratory activity of the liver
mitochondria were observed at 5000 ppm. No significant alterations
were observed with respect to the following parameters:
mitochondrial cytochrome oxidase; glucose-6-phosphate dehydrogenase
in the erythrocyte and liver homogenates; contents of cytochromes
a3, b and c; content of flavoproteides in the mitochondria and
content of oxidized and reduced nicotineamidoadenine in liver and
kidney homogenates. The NOAEL was 500 ppm (equivalent to 25 mg/kg
bw/day) based on morphological changes of the thyroid gland and
reduced uptake of 124I at 5000 ppm (Bankowska et al., 1970; Annex
I, reference 15).
Female Wistar rats were fed a diet containing 1300 ppm zineb or
1875 ppm maneb for 7 months. Significant increases in the weight of
the thyroid gland and decreases in the weight of the kidneys,
adrenal glands and ovaries were observed (Przezdziecki et al.,
1969; IPCS, 1988).
Inhalation toxicity was studied in rats with zineb (70%
purity), maneb (80% purity), and mancozeb (80% purity), applied 6
days per week over a period of 4´ months, at concentrations of 2,
10, 50, 100 or 135 mg/m3. The pesticides were given in the form of
dispersed aerosols, with 95% of the dust particles ranging from 1 to
5 µm in size, and the remainder from 5 to 10 µm. Local irritation
of the mucosa of the upper respiratory tract was noted and
concentration-related non-specific changes in the liver and kidneys
were evident. However, only slight changes were found at
concentrations of 2 mg/m3 (Ivanova-Chemishanska et al., 1972;
IPCS, 1988).
Dogs
Groups of 3 mongrel dogs (3/dose) were fed diets containing 20,
2000 or 10 000 ppm of zineb for 1 year. All the animals survived
and no persistent change in growth rate was seen in any of the
groups; there were no histopathological changes in the tissues,
except in the thyroid gland, and haematological findings were
normal. At 10 000 ppm, thyroid hyperplasia was found. The NOAEL
was 2000 ppm, equivalent to 50 mg/kg bw/day (Blackwell-Smith et
al., 1953; Kampmeier & Haag, 1954; Annex I, reference 2).
Long-term toxicity/carcinogenicity studies
Mice
Groups of 18 mice of each sex from two hybrid strains were
given various dithiocarbamate fungicides from 7 days of age up to 18
months. The compounds were given daily, by gavage, from 7 days to
weanling and thereafter were added to the diet. The compounds and
the respective amounts administered were: ferbam, 10 mg/kg bw/day,
then 32 ppm in the diet; maneb, 46.4 mg/kg bw/day, then 158 ppm;
nabam 21.5 mg/kg bw/day, then 73 ppm; thiram, 10 mg/kg bw/day, then
26 ppm and zineb, 460 mg/kg bw/day, then 1300 ppm. No significant
increase in tumours was found. However, when ethylene thiourea (a
metabolite of some dithiocarbamates) was administered at 215 mg/kg
bw/day and then after weaning incorporated into the diet at 646 ppm,
the total incidence of tumours was 14 out of 16 for males and 18 out
of 18 for females in one strain; and 18 out of 18 and 12 out of 16,
respectively, for males and females in the other strain (Innes et
al., 1969; Annex I, reference 15).
Rats
Groups of rats (10/sex/group) were fed diets containing 500,
1000, 2500, 5000 or 10 000 ppm of zineb for 2 years. At the two
highest dose levels, there was an increase in mortality rate in
females and, at 10 000 ppm, there was a diminished growth rate in
both sexes. Haematological studies were all normal. Goitrogenic
effects (thyroid hyperplasia) were seen at all dose levels. Kidney
damage (renal congestion, nephritis and nephrosis) was seen in 6
animals at the 10 000 ppm dose level, and in one animal in each of
the groups receiving 1000, 2500 or 5000 ppm, but not in any of those
given 500 ppm. The tumour incidence was not significantly greater
among any of the treated animals than it was in the controls
(Blackwell-Smith et al., 1953; Kampmeier & Haag, 1954; Annex I,
reference 2).
Reproduction studies
Rats
In a reproduction study, rats were given ziram at doses of 10
or 50 mg/kg bw/day and zineb at doses of 50 or 100 mg/kg bw/day
orally for 2-6 months. Sterility, resorption of fetuses and
anomalous tails in newborn rats were observed at the high levels.
The lower doses did not cause any significant changes, compared with
a control group (Rjazanova, 1967; Annex I, reference 9).
Maneb, zineb and mancozeb exerted dose-dependant damaging
effects on the gonads of rats of both sexes. The dose levels were
96-960 mg zineb/kg bw, 140-1400 mg mancozeb/kg bw, and 14-700 mg
maneb/kg bw, given twice a week for 4.5 months. Both reproductive
and endocrine structures were affected at all dose levels, leading
to decreased fertility (Ivanova-Chemishanska et al., 1973, 1975;
IPCS, 1988).
Special studies on teratogenicity
Mice
Groups of mice (CD-1) were administered zineb (85.5% purity) at
dose levels of 0, 200, 630 or 2000 mg/kg bw/day for 11 days from day
6 of gestation and sacrificed on day 18. Gross examination for
maternal well-being and fetal anomalies, both somatic and skeletal,
failed to show any maternal or teratogenic effects (Short et al.,
1980; Annex I, reference 35).
Rats
Groups of rats (26-27 pregnant CD-1 rats/group) were
administered zineb (purity 85.5% containing 0.35% ETU) at doses of
0, 200, 630, or 2000 mg/kg bw/day on days 6-19 of gestation. The
equivalent dose levels were 0, 170, 540, or 1710 mg/kg bw/day for
zineb and 0, 0.7, 2.2, or 7.0 mg/kg bw/day for ETU.
Maternal body weight and food consumption data were recorded.
Pregnant rats were sacrificed at day 20 and a laparotomy was
performed. Fetal data included live, dead and resorbed fetuses as
well as somatic and skeletal abnormalities. There was no maternal
mortality, but a substantial weight loss was seen at the highest
dose level. Fetuses from mothers administered 2000 mg/kg bw/day
also showed a reduced body weight. Fetal mortality was not
observed, and there were no significant anomalies noted on gross
external examination. A higher incidence of abnormalities of the
tail were noted at the highest dose level (short or kinky tails).
Teratogenic effects were noted in fetuses at the highest dose level.
A significant increase in lateral hydrocephalus and hydrocephalus of
the third ventricle was noted at 2000 mg/kg bw/day. In addition,
there was an increased incidence of skeletal anomalies (enlarged
frontal and occipital fontanelle, split centra and incomplete
ossification of the supraoccipital). The abnormalities were not
noted at 630 mg/kg bw/day and were suspected of being due to the
presence of ETU, which occurred both in the formulation (up to 7
mg/kg bw/day was directly administered) and as a result of
metabolism of zineb. It was concluded that teratogenic anomalies
were produced in rats by zineb at doses that were extraordinarily
high and were maternally toxic. The abnormalities may have been
due, in part, to ETU known to be present in the formulation (Short
et al., 1980; Annex I, reference 35).
Special studies on genotoxicity
The results of mutagenicity assays with zineb, are presented in
Table 2. Zineb has been adequately tested in a series of in vivo
genotoxicity assays. Positive responses were obtained in a
Drosophila study and in a study for chromosomal aberrations in
cultured mammalian cells. Other assays were negative. The Meeting
concluded that zineb was not likely to be a significant genotoxic
hazard.
Special studies on thyroid function
Rats
Groups of 10 rats of unspecified sex received orally 0 or 3500
mg/kg bw/day of maneb or 2400 mg/kg bw/day of zineb, presumably as a
single dose. After 24 hours the animals were injected
intraperitoneally with 1 mCi of 131I. Animals receiving zineb
accumulated nine times less, and those given maneb 4.5 times less
131I than the control group. The goitrogenic effect of these
dithiocarbamates was considered to be related to their metabolites
which are derivatives of thiourea (Ivanova-Chemishanska et al.,
1967; Annex I, reference 15).
Zineb was given orally to white rats at dose levels of 96 or
960 mg/kg bw for 4.5 months. Compared with that of untreated
animals, the thyroid was enlarged with microfollicles and columnar
cells. Succinic dehydrogenase and cytochrome oxidase activities
were raised in these cells, while the colloid in the follicles
showed reduced PAS-positive granules. These changes were consistent
with an increase in TSH. An increased number of basophilic cells
containing PAS-positive granules was observed in the adenohypophysis
(anterior pituitary). These effects were seen only at the highest
dose level. The uptake of 131I was also increased at the highest
dose level, and a high plasma TSH level was recorded in treated
animals. The changes observed in both thyroid and pituitary were
probably a compensatory response to the antithyroid effect of the
dithiocarbamate (Ivanova-Chemishanska et al., 1975; IPCS, 1988).
After oral administration of zineb to rats at dose levels of
9.6 or 960 mg/kg bw, twice a week for 4.5 months, the gonadotropic
and thyroid-stimulating functions of the adenohypophysis were
significantly increased compared with those of control values, more
markedly in those receiving the higher dose (Ivanova-Chemishanska
et al., 1974; IPCS, 1988).
The condition of the thyroid gland was studied in male albino
rats which were administered 700 mg maneb/kg bw, 960 mg zineb/kg bw,
or 1400 mg mancozeb/kg bw. After 30 days, the distinct
morphological changes observed indicated stimulation of the thyroid
by TSH. Hypophyseal stimulation is the consequence of release from
negative feedback by thyroxine, the plasma level of which is
depressed by the action of EBDCs (Ivanova-Chemishanska et al.,
1971, 1974; IPCS, 1988).
Table 2. Results of genotoxicity assays on zineb
Test Test system Concentration Purity Results Reference
Reverse mutation S. typhimurium 0, 1, 3.3, 10, 33, unknown negative 1., 2. Zeiger et al., 1988
(in vitro) TA97, 98, 100, 1535 100, 333, 1000, 3333, (rat & hamster)
6666 µg/plate
S. typhimurium not specified unknown negative* Moriya et al., 1983
TA98, 100, 1535, 1537, 1538
E. coli (WP2 hcr)
S. typhimurium unknown unknown negative 1.,2. Enninga, 1986a
strains unknown
S. typhimurium 15-5000 µg/plate 91.5% megative 1.,2. HRC, 1985a
TA1535, 1537, 1538, 98, 100 (rat)
Gene mutation Mouse lymphoma L5178Y cells unknown unknown negative 1., 2. Enninga, 1987
(in vitro)
Mouse lymphoma 0.313-8.0 µg/ml 91.5% negative 1., 2. HRC, 1985c
(rat)
Chromosome aberration Chinese hamster ovary unknown unknown positive 1., 2. Enninga, 1986b
(in vitro) (CHO) cells
Micronucleus (in vivo) Mouse (male & female) 10 g/kg 91.5% negative HRC, 1985b
strain unknown
(bone marrow)
Sex-linked recessive Drosophila melanogaster unknown unknown negative* Annex I, reference
lethal 15
Table 2 (contd)
Test Test system Concentration Purity Results Reference
Sex-linked recessive Drosophila melanogaster 0, 0.0005, 0.001, 75% active positive Tripathy et al.,
lethal: somatic and (adult eyes and wings: 0.0025, 0.0035, ingredient 1988
germ-line mosaic assays screened for induction of 0.005, 0.007
mosaic spots / eggs laid in the feed
by females: induction of
germ-line mosaicism)
Spot test for DNA damage S. typhimurium 5-300 µg/plate unknown positive* 1., 2. Shiau et al., 1980
and mutation TA98, 100, 1535, 1536, for S. typhimurium
1537, 1538 TA1535 and
B. subtilis TKJ 6321
Bacillus subtilis
TKJ5211, TKJ6321
1. = in the presence of metabolic activation
2. = in the absence of metabolic activation
* = insufficient detail provided for adequate review
Special studies on irritation
Nabam (19% solution) and zineb (65% wettable powder) were each
applied to the right eye of 10 rabbits, the left eye being used as a
control. Nabam did not produce signs of irritation, while zineb
produced mild irritation (erythema), which subsided within 6-8
hours. No edema was seen. The mild irritation may have been caused
by the non-specific foreign body reaction to the dry, insoluble
powder. When this procedure was repeated with both compounds
diluted and suspended for agricultural use (for nabam, 0.5% of the
commercial 19% solution plus zinc sulfate, 0.125% in water; for
zineb, a 0.188% suspension of the commercial 65% wettable powder in
water), no irritation was seen (Blackwell-Smith et al., 1953;
IPCS, 1988).
Observations in humans
A person suffering from hypocatalasaemia developed
sulfhaemoglobinaemia, haemolytic anaemia and Heinz body formation
after contact with zineb (Pinkhas et al., 1963; Annex I, reference
2).
The irritant and allergic potential of most dithiocarbamates is
evident in occupational exposure. Skin irritation and sensitization
were studied in man using a conventional patch test. A cotton
square was dipped in zineb 65% wettable powder and placed on the
inner surface of the forearm, and, 14 days later, this procedure was
repeated on the opposite forearm. The patches were left in place
for 48 hours. Of the 50 subjects used, no reaction at all was seen
in 49 of them. One reacted in such a way that it indicated primary
irritation rather than sensitization (Blackwell-Smith et al.,
1953; IPCS, 1988).
An epidemiological study was carried out on 137 workers engaged
in zineb manufacturing (51 men and 86 women). The duration of
exposure to zineb for 52 workers was between 1 and 3 years, and for
85 workers between 4 and 5 years. Control groups in this study
consisted of 193 persons, not exposed to chemicals and matched for
age, period of employment rate, and sex. The concentrations in the
air of the working area never exceeded 1 mg/m3. Among workers
occupationally exposed to zineb, the following changes were found:
hepatocholecystitis (28.4% of workers, versus 13.5% in controls);
vegetovascular dystonia connected with disorders in the central
nervous system (34.9%, versus 22.3% in controls); chronic bronchitis
(4.4%, versus 0.5% in controls); contact dermatitis (11.9%, versus
0.1% in controls); and disorders in the menstrual cycle (16.91%,
versus 4.3% in controls). These studies indicated a change in
catecholamine metabolism (Kaskevich et al., 1981; IPCS, 1988).
In a study with cultured lymphocytes from 15 workers working in
different stages of zineb manufacture, the mean incidence of
aberrant metaphases was 6% greater than that in controls (Antonovich
et al., 1972; IPCS, 1988).
A case of acute intoxication was reported in a 42-year old man,
who sprayed a cucumber plantation twice during a week with a
combined maneb and zineb solution. The first exposure occurred on
the day following treatment of the plantation with 250 grams of the
compound dissolved in 100 litres of water. Although protective
clothing had been worn on the day of spraying, the man walked in the
field a day later without taking any protective measures. On the
same day, he experienced behavioural changes and complained of
tiredness, dizziness and weakness. The symptoms subsided within
three days. Six days following the first field application, the man
used a ten times stronger solution of the compound and sprayed
again. He took the same precautionary measures while spraying, but
again walked through the field the following morning without any
protective clothing. The man was admitted that same day to
emergency in an unconscious state with occasional tonic and clonic
convulsions and signs of right hemiparesis with diffuse slow rhythm
in the electroencephalogram. The symptomatology disappeared
spontaneously after a few days, and an electroencephalogram was
normal two weeks later (Israeli et al., 1983).
COMMENTS
Zineb was poorly absorbed when administered orally to mice.
The extent to which enterohepatic circulation may have been involved
in the species studied, the mouse, rat and marmoset, has not been
investigated. Absorption, based on urinary excretion in the rat,
was highly variable and factors potentially contributing to the
differences observed have not been ascertained. The elimination
pattern in the marmoset revealed that the majority of the
administered dose was excreted in the urine, with lesser amounts in
the faeces. The principal routes of excretion were via the faeces
and urine, with negligible amounts in expired CO2.
The metabolic pathway of zineb has not been clearly delineated.
Characterization of urinary components in the mouse, rat and
marmoset have revealed the presence of ethylenethiourea, ethylene
urea and polar components.
Zineb was practically non-toxic upon acute oral administration
to rats and guinea-pigs, when given subcutaneously to rats or when
given by intraperitoneal injection to mice. WHO has classified
zineb as unlikely to present acute hazard in normal use.
Dietary administration of zineb to rats for six weeks at 0, 500
or 5000 ppm indicated a NOAEL of 500 ppm (equivalent to 25 mg/kg
bw/day) based on morphological changes of the thyroid gland and
reduced uptake of 124I at 5000 ppm. Rats treated with zineb orally
by gavage for four weeks (5 days/week) at 0, 15, 60, 250 or 1000
mg/kg bw/day exhibited slight hyperplasia of the thyroid at a dose
level of 1000 mg/kg bw/day resulting in a NOAEL of 250 mg/kg bw/day.
There were no significant changes in the thyroid noted in rats
previously treated at 1000 mg/kg bw/day following a two-week
recovery period. Rats administered zineb at doses of 490 or 2450
mg/kg bw, twice weekly for four months, developed paresis of the
hind limbs, which progressed to complete paralysis. Similar
treatment-related effects on the hind limbs were not confirmed in a
two-year study in rats (see below) at the highest dietary level of
10 000 ppm, equivalent to 500 mg/kg bw/day.
In a limited one-year study, dogs treated with zineb at dietary
levels of 20, 2000 or 10 000 ppm revealed thyroid hyperplasia at 10
000 ppm, resulting in a NOAEL of 2000 ppm (equivalent to 50 mg/kg
bw/day).
Zineb was not carcinogenic when given to mice at 460 mg/kg
bw/day from postnatal day 7 until weaning followed thereafter with
dietary administration of 1300 ppm until 18 months of age. A two-
year study in which rats (10/sex/group) were fed zineb at dietary
levels of 500, 1000, 2500, 5000 or 10 000 ppm revealed goitrogenic
effects at all doses. Treatment-related effects were manifest at or
above 1000 ppm as renal congestion, nephritis and nephrosis
increased mortality and diminished growth rate. There was no
evidence of carcinogenic potential. It should be recognized,
however, that neither of these long-term studies were judged to have
adequately studied the carcinogenic potential of zineb.
Treatment of rats with zineb at doses of 50 to 960 mg/kg bw/day
suggested adverse effects on reproduction, depicted as sterility,
decreased fertility and resorption of fetuses. From the limited
data available, a dose level of 50 mg/kg bw/day appeared to be
without significant adverse reproductive effect.
Treatment of mice with zineb at dose levels of 0, 200, 630 or
2000 mg/kg bw/day during critical periods of organogenesis did not
induce any maternal or embryo/fetotoxicity or teratogenicity at any
of the dose levels studied.
An oral teratogenicity study in rats at doses of 0, 200, 630 or
2000 mg/kg bw/day revealed that zineb was teratogenic at the
maternally toxic dose level of 2000 mg/kg bw/day. Treatment with
zineb resulted in a significant increase in hydrocephalus, skeletal
anomalies (enlarged frontal and occipital fontanelle, split centra,
incomplete ossification of the supraoccipital) and a higher
incidence of abnormalities of the tail.
Zineb has been adequately tested in a series of in vivo
genotoxicity assays. Positive responses were obtained in a
Drosophila study and in a study for chromosomal aberrations in
cultured mammalian cells. Other assays were negative. The Meeting
concluded that zineb was not likely to be a significant genotoxic
hazard.
The Meeting concluded that the toxicological data specifically
generated for zineb were inadequate to estimate an ADI. However,
because of the similarity of the chemical structure of zineb with
the other EBDCs, the comparable toxicological profile of the EBDCs
based on the toxic effects of ETU, and the fact that no
differentiation can be made among the parent EBDC residues using
presently-available regulatory methods, zineb was included in the
group ADI of 0-0.03 mg/kg bw for the EBDC group evaluated at this
Meeting (mancozeb, maneb, metiram).
TOXICOLOGICAL EVALUATION
Level causing no toxicological effect
Mouse: 460 mg/kg bw/day (18-month study: did not adequately
study long-term toxicity or carcinogenic potential)
2000 mg/kg bw/day (teratogenicity study)
Rat: 500 ppm, equivalent to 25 mg/kg bw/day
(six-week study)
< 500 ppm, equivalent to < 25 mg/kg bw/day
(two-year study: did not adequately study
long-term toxicity or carcinogenic potential)
50 mg/kg bw/day (reproduction study: did not
adequately study potential for adverse effects on
reproduction)
630 mg/kg bw/day (teratogenicity study)
Dog: 2000 ppm, equivalent to 50 mg/kg bw/day (one-year
study: did not adequately study potential for
toxicity in a non-rodent species)
Estimate of acceptable daily intake for humans
0-0.03 mg/kg bw (group ADI with mancozeb, maneb, and metiram)
Studies which will provide information valuable in the continued
evaluation of the compound
Further elucidation of absorption/distribution/excretion
patterns and metabolic pathways.
Reproduction study.
Long-term toxicity/carcinogenicity studies in two appropriate
species.
Short-term repeated exposure studies in a rodent and non-rodent
species to determine NOAELs with respect to effects on the
thyroid and potential for neurotoxicity.
Observations in humans.
REFERENCES
Antonovich, E.A., Chernov, O.V., Samosh, L.V., Martson, L.V.,
Pilinskaya, M.A. Kurinny, L.I., Vekshtein, M.S., Martson, V.S.,
Balin, P.N. & Khitsenko I.I. (1972). A comparative toxicological
assessment of dithiocarbamates. Gig. i. Sanit., 37: 25-30 (in
Russian).
Bankowska, J., Bojanowska, A., Komorowska-Malewska, W., Krawczynski,
K., Majle, T., Syrowatka, T. & Wiadrowska, B. (1970). The studies on
the influence of zineb and maneb on the functional state of the
thyroid gland and some related enzymatic systems (in Polish).
Boczn. Zak. Hig. (Warsz.), 21(2): 117-127.
Blackwell-Smith, R., Jr., Finnegan, J.K., Larson, P.S., Sahyoun,
P.F., Dreyfuss, M.L. & Haag, H.B. (1953). Toxicologic studies on
zinc and disodium-ethylenebisdithiocarbamates. J. Pharmacol. exp.
Therap., 109: 159-166.
Chepinoga, O.P., Zastavnyuk, N.P. & Zadorozhnaya, N.A. (1969).
Blastogenic hazard of some derivatives of the dithiocarbamic acid
and approaches to the detection (in Russian). Gigiyena primeneniya,
toksikologiya pesticidov i klinika otravleniy (Kiev), 7: 153-166.
Engst, R. & Schnaak, W. (1970a). Studies on the metabolism of the
ethylenebisdithiocarbamate fungicides maneb and zineb. Z. Lebensm.
Unters. Forsch., 143: 99-103 (in German).
Engst, R. & Schnaak, W. (1970b). Studies on the metabolism of the
ethylenebisdithiocarbamate fungicides maneb and zineb. Z. Lebensm.
Unters. Forsch., 144(2): 81-85 (in German).
Enninga, I.C. (1986a) Evaluation of the mutagenic activity of zineb
in the Ames Salmonella/microsome test. Unpublished report dated
December 29, 1986 from Pennwalt Holland B.V.
Enninga, I.C. (1986b) Evaluation of the ability of zineb to induce
chromosome aberrations in cultured Chinese hamster ovary (CHO)
cells. Unpublished report dated December 29, 1986 from Pennwalt
Holland B.V.
Enninga, I.C. (1987) Evaluation of the mutagenic activity of zineb
in an in vitro mammalian cell gene mutation test with L5178Y mouse
lymphoma cells. Unpublished report dated January 23, 1987 from
Pennwalt Holland B.V.
Falk, H.L., Thompson, S.J. & Kotin, P. (1965). Carcinogenic
potential of pesticides. Arch. environm. Hlth., 10: 847-858.
Huntington Research Centre (1985a) Reverse mutation/ Salmonella
typhimurium. Report No. FMT4/85394. Unpublished report dated
August 23, 1985 from Huntingdon Research Centre, England.
Huntington Research Centre (1985b) Micronucleus assay in [the]
mouse. Report No. FMT4/85394. Unpublished report dated August 23,
1985 from Huntingdon Research Centre, England.
Huntington Research Centre (1985c) Lymphoma mutation. Report No.
FMT6/85539. Unpublished report dated July 23, 1985 from Huntingdon
Research Centre, England.
IPCS (1988) International Programme on Chemical Safety.
Environmental Health Criteria 78. Dithiocarbamate pesticides,
ethylenethiourea, and propylenethiourea: A general introduction.
World Health Organization, Geneva.
Israeli, R., Sculsky, M., Tiberin, P. (1983) Acute intoxication due
to exposure to maneb and zineb. Scandinavian Journal of Work,
Environment and Health, 9: 47-51.
Ivanova-Chemishanska, L. (1969). Toxicological characteristics of
dithiocarbamates, zineb, maneb, and mancozeb. Sofia (dissertation).
Ivanova-Chemishanska, L., Sheytanov, M. & Moscheva-Izmirova, N.
(1967). Changes in the functional state of the thyroid gland upon
acute intoxication with certain dithiocarbamates: zineb and maneb.
Med. Toxicol., 20(9): 1011-1013.
Ivanova-Chemishanska, L., Markov, D.V. & Dashev, G. (1971). Light
and electron microscopic observation on rat thyroid after
administration of some dithiocarbamates. Environ. Res., 4: 201-
212.
Ivanova-Chemishanska, L., Kaloyanova, F., Izmirova, N., Zlateva, M.
& Valcheva, V. (1972). Experimental inhalatory toxicity and
substantiation of the maximum allowable concentration for some
dithiocarbamates in the air of the working area. Truh. Dzihot.,
23: 55-64 (in Russian).
Ivanova-Chemishanska, L., Valcheva, V. & Takeva, T.Z. (1973).
Effect of chronic peroral poisoning with perozine (zineb) on the
reproduction of white rats. Acta med. soc., 1: 107-108.
Ivanova-Chemishanska, L., Milanov, S.T., Chemishanski, G. & Dashev,
G. (1974). Attempt of biological dose of some hypophyseal hormones
in white rats after experimental oral administration of zineb.
Environ. Res., 8: 160-165.
Ivanova-Chemishanska, L., Petrova-Vergieva, T. & Mirkova, E. (1975).
Embryotoxic and teratogenic action of some pesticides. Eksp. Med.
Morfol., 14(1): 29-33 (in Russian).
Izmirova, N., Izmirova, I. & Ivanova, L.(1969). The effect of zineb
and maneb on the isoenzymes of lactate dehydrogenase in the testes
of rats. C.R. Acad. Bulg. Sci., 22(2): 225-227.
Jordan, L.W. & Neal, R.A. (1979) Examination of the in vivo
metabolism of maneb and zineb to ethylenethiourea (ETU) in mice.
Bull. Environ. Contam. Toxicol. 22(1-2): 271-277.
Kampmeier, C. & Haag, H.B. (1954). Toxicological considerations in
use of dithiocarbamates. Agric. Chem., April: 49-50, 133.
Kaskevich, L.M., Komarova, L.I., Ilina, V.I., Ivanicki, V.A. &
Shilina, V.F. (1981). [Clinical-functional changes due to exposure
to zineb], pp. 109-111 (in Russian).
Lessel, B. & Cliffe, E.E. (1961). The mammalian toxicity of metiram.
Short-term (4-week) oral toxicity. Unpublished report, submitted by
Boots Pure Drug Co. Ltd.
Meneguz, A. & Michalek, H. (1987) Effect of zineb and its
metabolite, ethylenethiourea, on hepatic microsomal systems in rats
and mice. Bull. Environ. Contam. Toxicol. 38: 862-867.
Moriya, M., Ohta, T., Watanabe, K., Miyazawa, T., Kato, K., Shirasu,
Y. (1983) Further mutagenicity studies on pesticides in bacterial
reversion assay systems. Mutation Research, 116: 185-216.
Pinkas, J., Djaldetti, J., Joshua, H., Reswick, C. & de Vries, A.
(1963). Blood, 21: 484.
Przedziecki, Z., Bankowska, J., Komorowska-Malewska, W. & Janicka,
T. (1969). Studies of the chronic short-term toxicity of zineb,
maneb and kaptan. Rocz. Panstw. Zakl. Hlg., 20: 133-140.
Rjazanova, R.A. (1967). The effects of the fungicides ziram and
zineb on the generative function of test animals. Gig. i. Sanit.,
2: 26-30 (in Russian).
Searle, A.J., Stewart, A.C. & Paul, M. (1987) The measurement of
ethylenethiourea and ethyleneurea in the rat and common marmoset
Callithrix jacchus after zineb (zinc ethylenebisdithiocarbamate)
dosing. Xenobiotica, 17(6): 733-740.
Shiau, S.Y., Huff, R.A., Wells, B.C. & Felkner, I.C. (1980)
Mutagenicity and DNA-damaging activity for several pesticides tested
with Bacillus subtilis mutants. Mutation Research, 71: 169-179.
Short, R.D., Minor, J.L., Unger, T.M., Breeden, B., van Goethem, D.
& Lee, C.C. (1980). Teratology of a zineb formulation. (Results of
a study performed at Midwest Research Institute for the US
Environmental Protection Agency submitted to the World Health
Organization) (EPA-600/1-80-017).
Tripathy, N.K., Dey, L., Majhi, B. & Das, C.C. (1988) Genotoxicity
of zineb detected through the somatic and germ-line mosaic assays
and the sex-linked recessive-lethal test in Drosophila
melanogaster. Mutation Research, 206: 25-31.
Vonk, J.W. & Kaars Sijpesteijn, A. (1970). Studies on the fate in
plants of ethylene bisthiocarbamate fungicides and their
decomposition products. Ann. appl. Biol., 65: 489-496.
WHO (1992). The WHO recommended classification of pesticides by
hazard and guidelines to classification 1992-1993 (WHO/PCS/92.14).
Available from the International Programme on Chemical Safety, World
Health Organization, Geneva, Switzerland.
Zeiger, E., Anderson, B., Haworth, S., Lawlor, T. & Mortelmans, K.
(1988) Salmonella mutagenicity tests: IV. Results from the
testing of 300 chemicals. Environmental and Molecular Mutagenesis,
11(12): 1-158.
See Also:
Toxicological Abbreviations
Zineb (ICSC)
Zineb (FAO Meeting Report PL/1965/10/1)
Zineb (FAO/PL:1967/M/11/1)
Zineb (IARC Summary & Evaluation, Volume 12, 1976)