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    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 m in size, and the remainder from 5 to 10 m.  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 g/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 g/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 g/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 g/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.

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    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)