Sponsored jointly by FAO and WHO


    Data and recommendations of the joint meeting
    of the FAO Panel of Experts on Pesticide Residues
    in Food and the Environment and the
    WHO Expert Group on Pesticide Residues
    Geneva, 5 - 14 December 1983

    Food and Agriculture Organization of the United Nations
    Rome 1985




    Mecarbam was evaluated by the Meeting in 1980 (FAO/WHO 1981)1/ and a
    temporary acceptable daily intake (ADI) was allocated. Further studies
    were required by the previous Meeting which included complete
    metabolic studies in laboratory animals; a complete teratogenicity
    assay; studies to define the mutagenic potential, and studies in hens
    or other appropriate species to define the potential for delayed
    neurotoxicity. Some of the required studies have become available and
    are reviewed in this monograph addendum.

    A temporary maximum residue level for mecarbam in oranges was
    estimated by the 1980 Meeting. Several items of information on
    residues were required for 1983, including additional data for citrus
    and other fruit. Information on registered uses for citrus and residue
    data for citrus and grapes were provided and are reviewed herein. Also
    provided and evaluated are residue data from national monitoring for
    mecarbam in citrus and information on national tolerances.



    Absorption, Distribution, Elimination and Biotransformation


    Based on an interim report, male and female Sprague Dawley rats
    (fasted 16 hours) given a single oral dose of 10 mg 14C-mecarbam/kg
    b.w. excreted about 80, 2.8 and 0.2 percent of the administered dose
    in urine, faeces and expired air, respectively, within 48 hours of
    dosing. The radioactivity recovered in the urine was predominantly
    associated with seven major polar metabolites. There was little or no
    unchanged 14C-mecarbam or its potential metabolites, viz.
    mercarboxon, diethoate and diethoxon, in the non-hydrolysed urine. A
    significant sex difference in the metabolite profiles of 14C-mecarbam
    in urine was not observed (Ward 1983).


    1/ See Annex 2 for FAO and WHO documentation.


    Special Study on Teratogenicity


    Groups of 24 sexually mature (8-9 weeks old), time-mated rats (SPF,
    CrL:COBS CD (SD) BR strain) were intubated with mecarbam (97.5 percent
    pure) as a suspension in 0.2 percent Tween 80 and distilled water at
    0, 1 or 3 mg/kg b.w./day from days 6 through 19 inclusive (day 0 = day
    of positive vaginal smear) of pregnancy. The dosages selected were
    based on the results of a preliminary study in pregnant rats.
    The dams were sacrificed on day 20 of pregnancy and foetuses were
    removed by Caesarean section for examination of external, skeletal and
    visceral abnormalities. No mortality occurred. Dams at 3 mg/kg b.w.
    exhibited cholinergic signs (salivation and intermittent body tremors)
    and growth depression. Erythrocyte cholinesterase activity on day 20,
    prior to sacrifice, was inhibited in a dose-dependent pattern at both
    1 and 3 mg/kg b.w.

    Terminal necropsy of dams revealed no compound-related changes. There
    were no significant differences between control and treated groups in
    pregnancy rate, mean number of live births, corpora lutea,
    implantations, or embryonic deaths (early and late), post-implantation
    loss, sex ratio and mean foetal weight. Multiple defects characterized
    by for example facio-cranial schisis, ablepharia and domed palate were
    similarly observed in 4/17 foetuses from 1/24 litters at 3 mg/kg b.w.
    The fact that all four of the malformed foetuses were from a single
    litter tends to indicate that these abnormal findings are unlikely to
    be compound-related. Incidence of visceral and skeletal abnormalities
    were not significantly affected by treatment. Under the conditions of
    the experiment there were no indications of teratogenic activity of
    mecarbam (Bottomley et al 1983).

    Special Studies on Mutagenicity

    Mecarbam (purity not specified) was tested for its genetic activity in
    in vitro microbial systems (plate assay) in the presence or absence
    of a mammalian metabolic activation preparation (S-9 mix from the
    liver of rats induced with Aroclor 1254). Indicator organisms used
    were Salmonella typhimurium strains TA 1535, TA1537, TA 1538, TA 98
    and TA 100. Results indicated no evidence of mutagenicity of the
    compound to any of the tester strains at concentrations ranging from
    50 to 5 000 g/plate, with or without the addition of the S-9 mix
    (Richold et al 1982a).

    The ability of technical mecarbam to induce DNA repair was tested in
    cultured human epithelioid cells (HeLa). There was no indication of
    unscheduled DNA synthesis in this in vitro test system at
    concentrations up to 2 000 ug/ml, a level capable of causing some cell
    death, with or without metabolic activation employing S-9 mix from
    liver of rats induced with Aroclor 1254 (Richold et al. 1982c). 

    In a mouse lymphoma L5178Y cell TK locus mutation assay, technical
    mecarbam, at concentrations (100 - 160 ug/ml) resulting in cell
    survival of approximately 30 percent and above, induced no significant
    increase in mutation frequency, with or without the presence of a
    metabolic activation system (S-9 mix from liver of rats induced with
    Aroclor 1254). At the most toxic concentrations (180 ug/ml and above)
    when cell survival was only about 20 percent, a statistically
    significant increase in mutation rate was observed in duplicate
    experiments with the presence of S-9 mix and in one of the two
    experiments without metabolic activation. Since mecarbam only appeared
    to induce an increase in mutation frequency when present at highly
    toxic dose levels, the compound possessed no significantly relevant
    mutagenic potential (Richold et al. 1983a).

    In a micronucleus test, groups of five male and five female mice (SPF,
    CD-Swiss-derived strain) were intubated with technical mecarbam at a
    total dosage of 0, 45, 90 or 180 mg/kg b.w. given as two equal doses
    separated by an interval of 24 hours. The animals were sacrificed six
    hours after the second dose and the femurs were removed for the
    preparation of bone marrow smears. Four males and one female at 180
    mg/kg b.w. and one female at 90 mg/kg b.w. died. There was no
    significant treatment-related increase in the incidence of
    polychromatic erythrocytes containing micronuclei. The ratio of
    normochromatic to polychromatic erythrocytes was also unaffected
    (Richold et al. 1982b).

    Groups of five male and five female rats (SPF Sprague-Dawley CD
    strain) were intubated with mecarbam at a total dosage of 0, 12.5, 25
    or 50 mg/kg b.w. given as two equal doses separated by an interval of
    24 hours. In a preliminary toxicity study, 50 mg/kg b.w. was found to
    be a maximum tolerated dose in rats. Four hours after the second dose,
    the animals were given i.p. 4 mg/kg b.w. of colchicine and then
    sacrificed two hours later. Bone marrow cell preparations from the
    animals were evaluated for the presence of chromosome aberrations in
    50 metaphase figures per animal. Metaphase analysis showed no
    significant difference between treated and control groups in the
    incidence of aberrant cells, when gap damage was excluded, although a
    non-dose-related increase in the number of chromosomal aberrations was
    noted when gap damage was included. Examination of the data revealed a
    number of deficiencies in the study. For instance, considerably less
    than 50 metaphase figures per animal in the two high-dosage groups,
    particularly at the top-dosage level, were analysed, thus leaving a
    weak base of data to support any conclusion. In the top-dosage group,
    two animals died and a total of only 62 metaphases were found in four
    other animals. Notable also was the use of a single sacrifice time
    after dosing. It is known that chemicals have different times for the
    expression of a maximum effect in in vivo cytogenetic studies. The
    seemingly negative response obtained in the study could be due to an
    incorrect choice of time to terminate the experiment. Overall, the
    study failed to demonstrate conclusively that the compound was not
    mutagenic under the conditions of the experiment (Richold et al.

    Special Study on Neurotoxicity


    Six "young" hens of the Sterling Ranger hybrid (1.48 - 2.3 kg), after
    an acclimatization period of at least three weeks, were intubated with
    a single dose of technical mecarbam (92 percent w/w active) in maize
    oil at 200 mg/kg b.w. on day 1 and again on day 22. The birds were
    observed for a total period of up to 44 days. The acute oral LD50 of
    mecarbam in this strain of hens was determined to be 200 mg/kg b.w.
    prior to initiation of the neurotoxicity study. Hens showing overt
    cholinergic signs after each dose on the day of treatment were given
    intramuscularly 0.1 ml of atropine sulphate (8.909 percent w/v) and/or
    up to 0.98 ml of PAM (5 percent w/v). In spite of the administration
    of antidotes, one hen died during the first overnight period and
    another was sacrificed on day 7 due to "progressive loss of locomotor
    function such that on day 7 the legs were unable to support the body".
    A third hen died three hours after the second dose. Two replacement
    hens from the original acclimatized stock were similarly treated with
    mecarbam six days after the beginning of the study. With the exception
    of the bird sacrificed on day 7, all treated hens recovered from the
    toxic symptoms, including muscle tremors, salivation, lethargic 
    movements, hyper noea, ataxia or an inability to stand within 24 hours
    after each dose. Histopathological examination of brain (medulla,
    pons, cerebellar cortex, optic chiasma, basal ganglia,cerebral cortex
    and hippocampus), spinal cord and sciatic nerves from three surviving
    hens and three vehicle controls at the end of the observation period
    revealed no morphological changes characteristic of delayed neurotoxic
    effects.Concurrent positive control hens, treated with TOCP, displayed
    clinical signs and histopathological changes of the nervous system
    typical of delayed neurotoxicity (Buch et al.1983)

    Short-Term Studies


    Groups of five male and five female rats (COBS CD strain) were exposed
    dermally to technical mecarbam (undiluted) at 0, 250, 500 or 1000
    mg/kg b.w. under an occlusive patch for a period of 6 hours/day 7
    days/week for 21 days. There were no mortality and compound-related
    toxic signs. Growth depression and reduced food consumption were noted
    in males at 1000 mg/kg b.w. Terminal haematological and blood
    chemistry studies showed decreased haemoglobin concentration,
    erythrocyte counts, haematocrit values and erythrocyte cholinesterase
    activity in females at both 500 and 1000 mg/kg b.w. Females of the
    top-dosage group also had elevated blood urea nitrogen values.
    Absolute weight and organ/body weight ratio of the liver were
    increased in females at 500 mg/kg b.w. and above. Terminal necropsy of
    all animals in the study and histopathological examination of a number
    of selected tissues, including the skin at the application site, from
    animals of control and top-dosage groups revealed no significant
    findings that might be related to treatment (Woolley et al. 1983).


    The 1980 Meeting estimated a temporary ADI with a requirement for
    metabolic studies, a teratogenicity study, mutagenic studies and a
    delayed neurotoxicity study.

    An interim report of a study with 14C-labelled mecarbam indicated
    rapid absorption, complete metabolism and excretion mainly via urine.
    Over 80% excretion of the administered dose occurred within 48 hours,
    the major excretory products comprising seven polar metabolites.

    There was no evidence of teratogenic activity in rats dosed at 3
    mg/kg. Mutagenicity studies, including in vitro microbial assays,
    unscheduled DNA synthesis in cultured human epithelial cells and a
    micronucleus test in mice, were negative. However, a mouse lymphoma
    test, at highly toxic dose levels resulting in about 20 percent cell
    survival, seemed to elicit a positive mutagenic response. An in vivo
    cytogenic test in rats was inconclusive under the conditions of the
    experiment. A delayed neurotoxicity study in young adult hens was
    seemingly negative. However, histopathological examination of nerve
    tissue was confined to only three of the six surviving hens. Moreover,
    the dosage level used (equivalent to an oral LD50) is considered
    insufficient for a delayed neurotoxicity study.

    Since the only metabolic studies available (presented as an interim
    report) were carried out on the rat and the delayed neurotoxicity
    study was not acceptable, the Meeting could only extend the temporary
    ADI estimated in 1980.


    Level Causing no Toxicological Effect

    Rat: 5 ppm in the diet, equivalent to 0.21 mg/kg b.w. 

    Dog: 5 ppm in the diet, equivalent to 0.15 mg/kg b.w. 

    Estimate of Temporary Acceptable Daily Intake for Man

    0-0.001 mg/kg b.w.


    Required     (by 1985)

    1. An adequate delayed neurotoxicity study in hens.

    2. A full report of the metabolic studies in rats.

    3. Complete metabolic studies in laboratory animals other than the


    Observations in humans.


    Bottomley, A.M., Mayfield, R.      Effect of technical mecarbam &
    Clark, R.                          on pregnancy of the rat. Report
    1983                               from Huntingdon Research Centre
                                       submitted to WHO by Dow Chemical
                                       (Netherlands) B.V. (Unpublished)

    Buch, S.A., Gardner, J.R.,         Mecarbam: delayed neurotoxicity
    Whitney, J.C. &                    study in the hen. Report from Life
    Cavanagh, J.B.                     Science Research submitted to WHO
    1983                               by Dow Chemical (Netherlands) B.V.

    Richold, M., Jones, E. &           Ames metabolic activation test to
    Hales, J.F.                        assess the potential mutagenic
    1982a                              effect of mecarbam. Report from
                                       Huntingdon Research Centre
                                       submitted to WHO by Dow Chemical
                                       (Netherlands) B.V. (Unpublished)

    Richold, M., Richardson, J. C, &   Micronucleus test on mecarbam.
    Howell, A.                         Report from Huntingdon Research
    1982b                              Centre submitted to WHO by Dow
                                       Chemical (Netherlands) B.V.

    Richold, M., Allen, J.A. &         Autoradiographic assessment of DNA
    Proudlock, R.J.                    repair in mammalian cells after
                                       exposure to mecarbam. Report from
                                       Huntingdon Research Centre
                                       submitted to WHO by Dow Chemical
                                       (Netherlands) B.V. (Unpublished)

    Richold, M., Edgar, H.D.,          An assessment of the mutagenic
    Ramsome. S.J. & Banks, S.J.        potential of mecarbam using an
    1983a                              in vitro mammalian cell test
                                       system. Report from Huntingdon
                                       Research Centre submitted to WHO
                                       by Dow Chemical (Netherlands) B.V.

    Richold, M., Allen, J.A.,          Metaphase analysis on mecarbam.
    Richardson, J.C.,                  Report from Huntingdon Research
    Proudlock, R.J. & Morgan, N.       Centre submitted to WHO by Dow
                                       Chemical (Netherlands) B.V.

    Ward, C.                           (14C)-Mecarbam: metabolic fate in
    1983                               the rat. Interim report from
                                       Hazleton Laboratories Europe Ltd.
                                       submitted to WHO by Dow Chemical
                                       (Netherlands) B.V. (Unpublished)

    Woolley, A.P.A.H., Hill, R.E. &    Mecarbam. 21-day repeat dose
    Wood, C.M.                         dermal toxicity study in the rat.
    1983                               Report from Huntingdon Research
                                       Centre submitted to WHO by Dow
                                       Chemical (Netherlands) B.V.




    Information was provided (Ponena Chemicals 1983) on the registered use
    of mecarbam on citrus to control red scale in the Republic of South
    Africa. Even though mecarbam has been used for this purpose in South
    Africa for 10 years, it is said not to be a "popular" control measure.
    It is used as a 900 g/litre EC formulation at a rate of 55 ml/100 1.
    water (0.05 percent a.i.) during the period of 80-100 percent petal
    drop to eight weeks thereafter. A 100-litre spray mixture/tree and 200
    trees/ha equals approximately 10 kg a.i./ha. A 200 day 
    last-treatment-to-harvest interval is imposed. This use is comparable
    to high volume uses reviewed by the 1980 Meeting, although the
    estimate for maximum residue limit (MRL) is based on a 14-day 
    pre-harvest interval, which appears to be the most common one.


    Residue data were available from supervised trials in the Republic of
    South Africa for single mecarbam applications to citrus (Ponena
    Chemicals 1983) according to approved usage in that country and for
    three applications to grapes, for which it is not registered in that
    country (Murphy Chemicals 1983). Also available were residue trials
    data from Spain, but approved uses were not available (Dow Chemical
    1983a, Dow Chemical 1983b).


    From a total of 32 samples, residues in South Africa on two varieties
    of oranges ranged from 2.9-4.8 mg/kg in peel, <0.01-0.09 mg/kg in
    pulp and 0.9-1.4 mg/kg on the whole fruit at intervals ranging from 
    7-67 days after treatment to <0.01 mg/kg in peel, pulp or whole fruit
    220 days after treatment. Maximum residues in 16 grapefruit samples
    were 2.4, 0.15 and 0.8 mg/kg in peel, pulp and whole fruit,
    respectively, six days after the same 0.05 percent a.i. treatment and
    0.5,<0.01 and 0.16 mg/kg, respectively, after 34 days. Residues were

    less thereafter. Whole fruit residues in both cases were estimated by
    the Meeting from peel and pulp residue, assuming a 70:30 pulp:peel
    ratio. No information was provided on the analytical method used
    except that residue determination was by gas chromatography utilizing
    a flame photometric detector with a phosphorous filter. Residues are
    presumed to be for mecarbam alone.

    In residue field trials in Spain, conducted in 1981, both 50 percent
    EC and 25 percent WP formulations were applied at a concentration of
    0.1 percent a.i. to two varieties of lemons (Dow Chemical 1983a).
    Although no good agricultural practice information is available for
    Spain, the application rates are similar to those of North African and
    Mediterranean countries, where pre-harvest intervals for citrus are
    either unknown or typically 14 days. Whole fruit residues range from
    0.05-0.67 mg/kg (0.32  0.25 mg/kg mean) for the six samples 29-35
    days after treatment and 0.06-0.69 mg/kg (0.32  0.26 mg/kg mean) for
    another six samples after 45-51 days. The relatively large variability
    is due to 0.05 and 0.06 mg/kg residue levels from one of the four
    sites. The analytical method is said to be similar to that previously
    developed for oranges. Apparent residues in untreated controls are
    0.31 mg/kg in two of the 12 samples analysed and 0.01 mg/kg in the
    remainder. Both formulations resulted in similar residues at similar
    intervals and the data confirm the relative persistence of this

    When flesh and peel from the four trials in Spain were analysed for
    mecarbam and and its metabolites diethoxon, diethoate and mecarboxon
    29-30 days after treatment, no residues (<0.01 mg/kg were found in
    the flesh (Dow Chemical 1983b). Peel residues were 0.5-1.7 mg/kg
    mecarbam, <0.01 mg/kg diethoate and 0.1-0.22 mg/kg mecarboxon.
    Diethoxon could not be determined, owing to interference by co-eluting
    natural compounds. Calculations of whole fruit residues, based on
    those in peel and flesh, gave results comparable to whole fruit


    A 900 a.i./1 E.C. mecarbam formulation was applied in South Africa
    three times to grapes at a spray concentration of either 0.045 or
    0.068 percent. Residues (mg/kg) at the two application rates are shown
    in Table 1.

    No information was provided on the analytical procedure other than the
    fact that a gas chromatographic detector was utilised. Residues are
    presumed to be mecarbam alone and are obviously directly related to


    Information was available on mecarbam residues on citrus imported into
    Sweden for the period 1/1/81 to 4/30/83 (Sweden 1983) (Table 2)

    Table 1. Mecarbam residues in Grapes - South Africa


                              Interval after
    Application rate          last application         Residue
    (%)                       (days)                   (mg/kg)

    0.045                     19                       0.04
    0.068                                              0.3
    0.045                     26                       0.04
    0.068                                              0.14
    0.045                     33                       0.02
    0.068                                              0.04
    0.045                     40                       0.02
    0.068                                              0.04

        Table 2. Mecarbam Residues in Imported Citrus - Sweden


    Food           Origin      Number of    Number of samples with residues within     Maximum
                               samples      given ranges (mg/kg)                       residue
                               analysed     <0.41       0.41-1.03    1.03-2.05         (mg/kg)

    Grapefruit     Import      148          146         2                              0.42

    Lemon          Import      164          163         1                              0.55

    Mandarin       Import      292          290         1                              1.8



    The following maximum residue limits (MRLs) were reported from Sweden
    and South Africa.

                                 MRL (mg/kg)
    Commodity           Sweden         Republic of South Africa

    Citrus                 2                     0.5


    The Meeting reviewed additional good agricultural practice information
    for citrus from one country, additional residue data for citrus
    reflecting those practices, residue trials data for lemons from
    another country, residue data for grapes and citrus import monitoring
    data from another country. The good agricultural practice information
    for citrus is comparable to that previously reviewed by the Meeting,
    except that the pre-harvest interval is much longer.

    These citrus data generally support the 2 mg/kg limit previously
    estimated for oranges and, along with data previously reviewed,
    indicate that the limit should also be suitable for the food group
    "citrus". Swedish import monitoring data also give added assurance
    that the limit is adequate for oranges, grapefruit and lemons and
    demonstrates the need for a limit at that level for this relatively
    persistent pesticide in citrus. The data also confirm that citrus
    residues are mostly in the peel and demonstrate that up to 30 percent
    of the terminal residue in peel is mercarboxon.

    In the absence of information on approved or registered mecarbam uses
    on grapes, as well as the relatively limited amount of residue data or
    information on the analytical method used, the available data do not
    support a limit for grapes.

    The Meeting concluded that additional information is needed on the
    fate of residues in ruminants and that a ruminant metabolism study
    should be conducted. Depending on the results of that study, an
    additional ruminant feeding study may be required.


    The Meeting examined additional mecarbam residue data from supervised
    trials on citrus which reflect established good agricultural practice.
    From these data, the Meeting concluded that the previously estimated
    temporary limit for oranges is confirmed and can be extended to other
    citrus fruits when good agricultural practices and the reported
    intervals between last application and harvest are observed. The limit
    refers to mecarbam alone.

                                                      Interval between 
                             Estimated                last application
    Commodity                MRL (mg/kg)              and harvest (days)

    Citrus                       2                            14


    Required (by 1986)

    1. A ruminant metabolism study.

    2. If the metabolism study indicates any possibility of the presence
    of significant residues in animal tissues or milk, other than those
    identified in plants, data should be provided on such residues
    occurring in meat and milk from feeding ruminants with a diet
    containing residues found in treated citrus.


    Additional information on nationally registered or approved uses on
    other commodities (especially olives, olive oil, fruits and
    vegetables) and residue data from field trials that reflect those


    Dow Chemical.     Determination of mecarbam residues in lemon samples
    1983a     1981    from trials in Spain, Data submitted to FAO by Dow
                      Chemical Co. Ltd. (Unpublished)

    Dow Chemical.     Determination of mecarbam and related metabolite
    1983b             residues in lemons. Information provided to FAO by
                      Dow Chemical Co. Ltd.

    Murphy Chemicals. Data on mecarbam trials in grapes, Republic of
    1983              South Africa. Submitted to FAO by Murphy
                      Chemicals. (Unpublished)

    Ponena Chemicals. Data on mecarbam trials in citrus, Republic of
    1983              South Africa. Submitted to FAO by Ponena
                      Chemicals. (Unpublished)

    Sweden.           Mecarbam residues in imported citrus. Information
    1983              submitted to FAO by the Government of Sweden.

    See Also:
       Toxicological Abbreviations
       Mecarbam (ICSC)
       Mecarbam (Pesticide residues in food: 1980 evaluations)
       Mecarbam (Pesticide residues in food: 1986 evaluations Part II Toxicology)