Sponsored jointly by FAO and WHO


    Joint meeting of the
    FAO Panel of Experts on Pesticide Residues
    in Food and the Environment
    and the
    WHO Expert Group on Pesticide Residues
    Rome, 6-15 October 1980



    Carbofuran was evaluated for an acceptable daily intake in 1978 and
    1979 and a temporary ADI for man was estimated to be 0-0.003 mg/kg
    body weight (FAO/WHO 1977; FAO 1980).  The available data reflected
    that carbofuran is a highly toxic carbamate ester whose metabolic
    profile has been well defined.  Carbofuran is a potent, reversible
    cholinesterase inhibitor.  Cholinesterase inhibition and acute toxic
    signs of poisoning are subject to rapid spontaneous reversal and
    recovery.  The measurement and evaluation of cholinesterase depression
    induced by carbofuran, because of the rapid reversibility, is
    difficult and requires substantial care.

    In a variety of short-term and long-term studies, in several animal
    species, cholinesterase depression was the principal effect noted. 
    The 1976 Meeting expressed concern over the lack of appropriate data
    evaluating the reversible cholinesterase depression in dietary studies
    and on the apparent sensitivity of brain rather than erythrocyte or
    plasma cholinesterase.  No-effect levels were based on data from a rat
    reproduction study (short-term) and a short-term dietary study in

    Further studies on cholinesterase depression, induced by dietary
    administration of carbofuran, were requested.  It was suggested that a
    definition be made of the sensitivity of juveniles, when compared with
    adults on acute toxicity and cholinesterase depression levels, as
    observed in preliminary studies and that an additional reproduction
    study define the highest no-effect level.

    Additional data were received with respect to all of the requested
    information.  In addition, further long-term studies in several rodent
    species were made available.  These new data are reviewed in this
    monograph addendum.



    Effects on enzymes and other biochemical parameters

    An evaluation was made on the possible differences in brain and
    erythrocyte cholinesterase activity in adult and juvenile rats of both
    sexes following acute exposure to carbofuran.

    Groups of rate (five rats per sex, using either juvenile or adult
    animals) were sacrificed and cholinesterase activity measured by a
    colorimetric procedure suitable for evaluating a rapidly reversible,
    carbamate-induced inhibition.  These animals were untreated and served

    as baseline values of cholinesterase activity.  A further group of
    eight animals per sex, both juvenile and adult, were treated with
    carbofuran and sacrificed at various times up to 24 hours after
    treatment to evaluate the optimal time for depression of both brain
    and erythrocyte cholinesterase.  In all cases, sample preparation was
    rapid following sacrifice and dilution of tissues was kept to a
    minimum.  Baseline cholinesterase data in brains of juveniles were
    slightly higher than those noted for adults in both males and females.
    With erythrocyte cholinesterase, adult values were found to be higher
    than juvenile values in both males and females.  Examination of the
    optimal sampling time for evaluating maximum erythrocyte
    cholinesterase depression showed that approximately 30 minutes
    following acute administration was the optimal in both sexes in adults
    and juveniles.  The optimal sampling time for brain cholinesterase
    depression was approximately one hour following acute poisoning.  The
    data showed recovery was almost complete four hours following acute
    carbofuran treatment.  Complete recovery was noted at the 24-hour
    interval.  While the cholinesterase depression and recovery studies
    were difficult to fully evaluate because of large standard deviations
    of the mean cholinesterase activities, it was quite evident that
    complete recovery of all enzyme depression was attained within one
    day. There were no significant differences in juvenile and adult
    recovery studies in either brain or erythrocyte cholinesterase.
    Further, the data did not suggest significant differences in
    sensitivity to carbofuran-induced inhibition in either adult or
    juvenile rats (Case, 1980).

    Toxicological studies

    Special studies on reproduction

    Groups of rats (10 male and 20 female rats per group, 12 male and 24
    females per group were used in the third generation) were fed
    carbofuran in the diet at dosage levels of 0, 20, or 100 mg/kg and
    subjected to a standard 2-litter per generation, 3-generation
    reproduction study.

    Growth, as evidenced by differences in body weight and food
    consumption, was reduced in parental rats administered 100 mg/kg in
    the diet.  This was consistent throughout three generations at the 100
    mg/kg dosage level.  No treatment-related growth or food consumption
    depression was noted with any of the animals administered 20 mg/kg in
    the diet.

    There was no effect associated with carbofuran with respect to the
    standard reproduction parameters (fertility, gestation, lactation, and
    viability) with the exception of a slight reduction in viability at
    day 4 at 100 mg/kg.  This was observed in the first litter of all
    generations.  These differences were not noted in the second litters
    of the 100 mg/kg group and the significance of this reduction is
    questionable.  Mean pup body weights in the 100 mg/kg group were
    consistently lower than control values.  This growth reduction, noted

    at day 21, was statistically significant in both males and females at
    the 100 mg/kg dosage level throughout the study.

    At the conclusion of the study, parental animals and pups from the
    second litters of the second and third generations were sacrificed and
    subjected to gross examination.  No pathological lesions or
    abnormalities, which were considered to be compound-related, were
    noted at the time of gross examination.  Statistically significant
    mean weight variations occurred in various organs among the F2 and
    F3b weanling rats.  The significance of these weight variations,
    which appear to occur frequently in toxicity studies, is questionable
    in light of the microscopic examination of tissues and organs which
    did not appear to show substantial effects attributable to the
    presence in the diet of carbofuran.  Microscopic examination of
    tissues and organs of the parental F2b and F3b showed a variety of
    morphologic changes, none of which were considered to be related to
    the presence of carbofuran.  All histologic lesions were considered to
    represent spontaneous occurrences.  Based upon the slight, but
    significant, growth reduction at 100 mg/kg, it may be concluded that
    20 mg/kg represents a dietary level that would induce no effect on
    reproduction (Goldenthal, 1979b; 1980b).

    Special studies on teratogenicity

    Groups of rate (24 mated females per group) were administered
    carbofuran (suspended in 0.25% methylcellulose) at dosage levels of 0,
    0.1, 0.3, or 1.0 mg/kg body weight/day throughout gestation (days 6-15
    of pregnancy).  On day 20 of gestation, animals were sacrificed and
    parents and foetuses were subject to complete internal and external
    examination to evaluate effects indicative of a teratogenic response
    of carbofuran.

    Toxicological signs of poisoning were evidenced in females at the two
    higher dose levels.  There was one death at the highest dose level.
    The signs of poisonings were of the typical cholinergic response
    associated with carbofuran.  There were no differences in growth
    within any treatment group over the 20-day gestation period.  At the
    conclusion of the study, examination of all animals showed a larger
    number of resorptions in the control group than in any of the
    treatment groups.  There were no differences within the groups
    administered carbofuran and the high incidence of resorptions in the
    control group could not be explained.  Somatic and skeletal
    examinations failed to show teratogenic effects of the administration
    of carbofuran.  Carbofuran, while inducing toxicological signs of
    poisoning in maternal rats, induced no teratogenic response in rats
    (Barron, et al., 1978).

    Groups of pregnant rabbits (17 rabbits/group) were administered
    carbofuran ( in 0.25% methylcellulose) at dosage levels of 01 0.21
    0.6l or 2.6 mg/kg body weight daily from day 6-18 of gestation.

    On day 30, all animals were sacrificed and, following laparotomy, an
    examination of the parents and foetuses was performed to evaluate a
    potential teratogenic effect.  For the parents, this included an
    examination for early and late resorptions, implantation sites,
    abnormal placental sites, and for any other abnormalities.  Corpora
    lutea were counted and the placenta was weighed.  Gross examinations
    were made of the parents and somatic and skeletal examinations of
    foetuses were performed.

    Toxic signs of poisoning were observed in rabbits administered the
    high dose level of carbofuran.  Toxic cholinergic signs of poisoning
    were evident and several animals died during the course of the study.
    There ware no toxicological signs of poisoning evident at the lower
    dose levels.  Growth, over the period of gestation, did not appear to
    be affected by the administration of carbofuran.  There were no
    significant gross somatic effects observed in either parents or
    foetuses at any dose level in the study.  Pregnancy and viability was
    unaffected by carbofuran.  Foetal body weights, placental weights, and
    development of foetuses were not affected.  Soft tissue and skeletal
    examinations showed no adverse effect as a result of carbofuran
    treatment.  Under the conditions of this bioassay, carbofuran did not
    induce a teratogenic effect in rabbits at dose levels up to and
    including that which induced maternal toxicity (Felton, et al.,

    Long-term studies


    Groups of mice (100 male and 100 female, Charles River CD-1
    mice/group) were fed carbofuran in the diet at dosage levels of 0, 20,
    125 or 500 mg/kg for two years in an effort to evaluate the
    carcinogenic potential of carbofuran.  Groups of animals were examined
    at periodic intervals (6, 12, 18, and 24 months) for haematologic
    parameters, biochemical studies, and urinalyses.  At similar intervals
    over the course of the study, groups of animals were sacrificed and
    subjected to gross and microscopic examination of tissues and organs
    for abnormalities, particularly to assess the carcinogenic potential.

    There was no mortality in the course of the study that could be
    attributed to the presence of carbofuran.  Additionally, no changes in
    appearance or behaviour were noted.  A localized hair loss and
    reddening of the ear(s) frequently followed by scabbing or sloughing
    of portions of the ears was noted with greater frequency in the
    treated mice.  There was no mortality attributable to carbofuran.  A
    slight decrease in body weight was evidenced through the first year of
    the study predominantly at the high dose level.  During this period
    where growth reduction was noted, food consumption was also reduced
    slightly at the high dose level.  With the exception of brain
    cholinesterase depression, there were no specific differences with
    respect to haematological parameters, clinical chemistry parameters,
    and urinalysis determinations that could be attributable to
    carbofuran.  Brain cholinesterase was depressed in both males and

    females at the two highest dose levels and all time intervals

    At the conclusion of the study, gross and microscopic examination of
    tissues and organs showed several statistically significant weight
    variations occurring periodically throughout the study.  These changes
    in organ weights were not accompanied by changes observed
    microscopically which would be indicative of significant morphologic
    effects.  There were no differences with respect to the occurrence of
    neoplastic or non-neoplastic changes in any of the carbofuran-treated
    mice.  It was concluded that carbofuran was not tumorigenic nor
    carcinogenic in this strain of mice (Goldenthal, 1980; Brown, 1980).


    Groups of rats (90 male and 90 female/group) were fed carbofuran in
    the diet at dosage levels of O, 10, 20, or 100 mg/kg for 2 years.
    Carbofuran was dissolved in acetone and mixed with a small amount of
    laboratory diet to provide a premix, which was then diluted to provide
    larger quantities of the appropriate concentration for the test diet.
    Analytical evaluations of the test diets at periodic intervals
    verified the presence and concentration of carbofuran.

    Rats were observed daily for overt toxicity, mortality, and general
    behaviour and appearance.  Body weights were measured weekly, as was
    food consumption.  At 6, 12, 18 and 24 months, groups of animals were
    sacrificed for a variety of clinical chemistry studies, haematologic
    examinations, and urinalysis.  Ophthalmologic examinations were
    performed at 0, 12, and 24 months.  Groups of 10 animals of each sex
    were sacrificed at 6, 12, and 18 months and a final sacrifice of all
    survivors was made at the conclusion of the study.  Gross and
    microscopic examinations of tissues and organs were performed on all
    animals that died during the study or were sacrificed at periodic

    There was no excessive mortality over the course of the study that
    could be attributed to the presence of carbofuran.  Growth, as
    evidenced by body weight, was depressed significantly at the high dose
    level, although food consumption was unaffected.

    With the exception of cholinesterase activity depression, there were
    no significant findings in any of the clinical chemistry, haematology,
    urinalysis, or ophthalmological examinations.  At 100 mg/kg
    cholinesterase depression was observed in plasma, red blood cell, and
    brain of both male and female rats.  There was no significant
    cholinesterase depression observed at 20 mg/kg. (Cholinesterase
    depression was evaluated in the study using specific techniques and
    procedures that would be applicable for assessing the reversible
    nature of the inhibition.)

    Analysis of the gross and microscopic pathology data did not suggest a
    compound-related pattern in any of the lesions observed.  While there
    were sporadic lesions observed in a variety of tissues at various

    sacrifice times with respect to gross changes in weight, these were
    not accompanied by histological evidence of adverse morphologic
    effects.  It was considered that both neoplastic and non-neoplastic
    histologic changes represented spontaneous lesions and were unrelated
    to the presence of carbofuran in the diet.  Gross lesions without
    definitive morphologic change were assumed to have represented
    physiological variations, artifacts, or other causes that did not
    induce detectable morphologic alterations on histological

    A no-effect level in this study is 20 mg/kg in the diet equivalent to
    1.0 mg/kg body weight.  This is based on changes in growth and on
    depression of cholinesterase activity level observed at the highest
    dose level (Goldenthal, 1979a; Rapp, 1980a).



    Carbofuran, an anticholinesterase carbamate ester currently in
    extensive use as an insecticide, has been reviewed at two previous
    meetings.  Additional studies made available to this meeting were

    There were no differences between juvenile and adult rats with respect
    to cholinesterase inhibition.  Studies on reproduction, including an
    evaluation of the teratogenic potential of carbofuran, showed that
    carbofuran was not teratogenic and did not affect reproduction in

    Long-term dietary studies on both rat and mouse failed to demonstrate
    a carcinogenic potential for carbofuran.  In two new long-term
    studies, a dietary no-effect level was observed.  Cholinesterase
    depression was the most sensitive effect noted in these studies.

    The data reviewed met the requirements of previous meetings and
    allowed the estimation of no-effect levels in two mammalian species
    (mouse and rat).  The rat and the mouse were used in an evaluation of
    the no-effect levels.  Data with the dog (1976 report) showing a
    no-effect level of 50 mg/kg were based on clinical signs of poisoning
    where cholinesterase assays were not performed.  The available studies
    with the dog are of limited value in the toxicological evaluation as
    cholinesterase data were not included.

    Level causing no toxicological effect

    Rat:    20 mg/kg in the diet equivalent to 1.0 mg/kg bw/day.

    Mouse:  20 mg/kg in the diet equivalent to 2.5 mg/kg bw/day.

    Estimate of acceptable daily intake for man

    0-0.01 mg/kg bw/day.


    Barron, P,. Giesler P., and Rao, G.N. Teratogenicity of Carbofuran in
    Rats. (1978) Unpublished report from WARF Institute submitted by the
    FMC Corporation to the World Health Organization.

    Brown, W.R. 2-Year Dietary Toxicity and Carcinogenicity Study in Mice.
    Technical Carbofuran Histopathology. (1980) Unpublished report from
    Research Pathology Services, Inc. submitted by the FMC Corporation to
    the World Health Organization.

    Case, R.S. A Comparative Evaluation of Cholinesterase Activity of
    Juvenile and Adult Rats Treated with Carbofuran. (1980) Unpublished
    report from the FMC Corporation submitted by the FMC Corporation to
    the World Health Organization.

    Felton, S., Gielsler, P., and Rao, G.M. Teratology Study of Carbofuran
    in Rabbits. (1978) Unpublished report from WARF Institute submitted by
    the FMC Corporation to the World Health Organization.

    Goldenthal, E.I. A Two-year Dietary Toxicity and Carcinogenicity Study
    in Rats. (1979a) Unpublished report from International Research and
    Development Corporation submitted by the FMC Corporation to the World
    Health Organization.

    Goldenthal, E.I. Three-generation Reproduction Study in Rats. (1979b)
    Unpublished report from International Research and Development
    Corporation submitted by the FMC Corporation to the World Health

    Goldenthal, E.I. Two-year Dietary Toxicity and Carcinogenicity Study
    in Mice. (1980) Unpublished report from International Research and
    Development Corporation submitted by the FMC Corporation to the World
    Health Organization.

    Rapp, W.R. A 24-month Dietary Toxicity/Carcinogenicity Study of
    Carbofuran in Rats - Pathology report (terminal phase). (1980a)
    Unpublished report from Wm. R. Rapp and Company submitted by the FMC
    Corporation to the World Health Organization.

    Rapp, W.R. A Three-generation Reproduction Study of Carbofuran in
    Rats. Pathology report. (1980b) Unpublished report from Wm R. Rapp.
    and Company submitted by the FMC Corporation to the World Health


    See Also:
       Toxicological Abbreviations
       Carbofuran (ICSC)
       Carbofuran (Pesticide residues in food: 1979 evaluations)
       Carbofuran (Pesticide residues in food: 1996 evaluations Part II Toxicological)
       Carbofuran (JMPR Evaluations 2002 Part II Toxicological)