Sponsored jointly by FAO and WHO


    The monographs

    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
    Rome, 24 September - 3 October 1984

    Food and Agriculture Organization of the United Nations
    Rome 1985



         Methamidophos was first evaluated by the 1976 JMPR 1/ at which
    limits were established for a number of commodities. Additional or
    revised limits were estimated in 1979 and 1981. On several occasions
    the CCPR has requested that methamidophos should be considered
    together with acephate, of which it is a metabolite. To date
    information has not been sufficient to do that fully, although the
    JMPR has taken their relationship into account as far as possible.

         This meeting received additional residue data on methamidophos in
    egg plants, which are reviewed below. This addendum should be read in
    conjunction with that on acephate elsewhere in these evaluations.




         The meeting was informed by one manufacturer that Mexican uses on
    egg plants call for a 0-day pre-harvest interval instead of the 14
    days on which the current 0.1 mg/kg limit (1979 JMPR) is based. The
    original 1 mg/kg estimated by the 1976 JMPR was based on a 7-day
    pre-harvest interval. Other information on Mexican uses available to
    the meeting indicates a 1-day interval for a 50% LM formulation and 14
    days for a 50% EC formulation (Manual de Plaguicidas, 1981).


         Geographically restricted uses in the U.S.A. permit
    1.1 kg a.i./ha (1 lb a.i./A) 0.75%SP with a 7-day pre-harvest
    interval. The U.S. tolerance of 1 mg/kg is also designed to
    accommodate Mexican uses of 150-600 g a.i. EC/ha (5.4 kg a.i./ha


         The manufacturers have submitted additional residue data on egg
    plants (Table 1) not previously reviewed by the JMPR (Chevron, 1984;
    Bayer, 1984).


    1/  See Annex 2 for FAO/WHO documentation

        Table 1.  Methamidophos residues on egg plants resulting from supervised field trials.

                                    Application                                            Residues,mg/kg
    Country        Year                rate
                             no     kg a.i./ha   formulation    0         1         3       5        7        14       21        Reference

                                                                                                                                 Mobay Repts.

    Mexico         1972-     15     8x0.4-0.6    2% D           0.15      0.13      0.08    0.08     0.07                        37305
                   73               2% dust
                                    +            EC
                                    1X 0.6EC

                   1972-     13     9x0.3-0.5    2% D           0.37      0.17              0.19     0.12     0.13     0.05
                   73               (includes    +              (0.68) 1  (0.31)    -       (0.35)   (0.22)   (0.24)   (0.09)    37306
                                    6 appl of    EC
                                    2% dust
                                    + 2
                                    4x0.6EC                                                                                      Chevron

    U.S.A.3        1978      3      1.1          4 spray                                                                         4769
                                    (4 lb.                                                           0.29
                                    a.i./Gal)                                                        0.30

                   1979      14     1.1          4 spray                            1.9              0.04     0.05     0.03      4770
                                                                                    0.0              0.03     0.07     0.02

                   1980      10     1.1          4 spray                            0.49             0.65     0.15               5142
                                                                                    1.1     0.45     0.12

                   1979      17     1.1          4 spray                            0.23    0.11     0.02
                                                                                    0.38             0.11     0.04               4768

    1  Values in parentheses are adjusted to maximum U.S. approved 1.1 kg a.i./ha rate.
    2  Last 4 applications were EC
    3  Residue data corrected for recovery.
         The Mexican data do not strictly represent approved uses, since
    dust applications are included with EC applications. In practice,
    however, the data are indicative of likely residues from approved uses
    since all of the last applications were with approved EC formulations.
    At approved application rates up to 1.1 kg a.i./ha, maximum residues
    were 0.65 and 0.15 mg/kg at 7- an 14-day intervals respectively,
    1.9 mg/kg at 3 days and 0.37 mg/kg (0.68 mg/kg adjusted to maximum
    U.S. application rates) on the day of last application.

         Maximum residues of methamidophos in or on kiwi fruit resulting
    from the use of acephate were 0.012 mg/kg.


         The meeting had information that one 1979 shipment of egg plant
    of 38 sampled exported to the U.S.A. had over-tolerance residues of
    1.9 mg/kg (FDA Surveillance, 1980).


         The meeting reviewed additional residue and good agricultural
    practice information for the use of methamidophos on egg plant and
    responded to requests of the CCPR to consider acephate and
    methamidophos together. The meeting reaffirmed its approach to setting
    separate limits for acephate and methamidophos and concluded that
    current good agricultural practice information and residue data were
    still insufficient to permit an effective reassessment of most
    previously estimated limits.

         It is noted in the review of acephate elsewhere in these
    evaluations that methamidophos limits have been estimated for all
    crops for which there are acceptable limits. In the case of animals,
    levels of 0.01 mg/kg (limit of determination) were estimated for the
    carcase meat and fat of cattle, goats and sheep, and for milk. These
    were apparently based on the studies of methamidophos in the goat
    reviewed by the 1976 JMPR. Data were also available to that meeting on
    acephate and methamidophos residues from the simultaneous feeding of
    acephate and methamidophos to goats and pigs. The 0.01 mg/kg limit for
    methamidophos in cattle, goats, sheep and milk is probably adequate
    for residues resulting from the use of acephate or methamidophos on
    feed items for which there are proposed Codex TMRLs.

         Studies are not adequate to support methamidophos limits in
    poultry or eggs, although trace levels have been observed in the
    muscle and eggs of poultry from high dose levels of acephate (1976

         Residues data and good agricultural practice information on egg
    plants provided to the present meeting indicate that the current
    0.1 mg/kg limit would not be adequate to accommodate good agricultural
    practices which include 7-day (and possibly shorter) pre-harvest
    intervals instead of the 14 days on which the 0.1 mg/kg limit is
    based. The 1976 evaluations show that even average residues on peppers

    and tomatoes at a 7-day interval from similar application rates to
    those approved on egg plant are 0.2 - 1.0 mg/kg and maxima are twice
    as high. Even after two weeks, maximum tomato and pepper residues
    exceed 1 mg/kg. These data can reasonably be used to supplement egg
    plant data.

         It is also noteworthy that residues found in commerce have
    exceeded 1 mg/kg, although it is not known whether they resulted from
    good agricultural practice.

         Additional data on methamidophos residues resulting from the use
    of acephate do not indicate any need to revise current methamidophos
    limits on the commodities concerned. Acephate limits have been
    estimated for tree tomatoes (tamarillos). Data were also available for
    methamidophos residues resulting from the use of acephate on tree
    tomatoes, and these allowed the meeting to estimate a maximum residue
    level for methamidophos on this commodity.


         The meeting examined residue data from supervised trials
    reflecting established good agricultural practice and was able to
    estimate residue levels likely to occur when methamidophos is used in
    practice and when the reported interval between the last application
    and harvest is observed. These estimates are recommended as TMRLs.
    They refer only to methamidophos.

                                            Interval between last
                                            application and harvest
    Commodity         TMRL (mg/kg)          (days) on which
                                            recommendations are based

    Egg plant         1 (previously 0.1)    7 (previously 14)

    Tree tomato
    (Tamarillos)      * 0.01                14


    Bayer,              Unpublished Reports made available to the
    1984                1984 JMPR by Bayer AG

    Chevron,            Unpublished Reports made available to the 1984
    1984                JMPR by Bayer AG

    FDA Surveillance,   Results of FDA Surveillance of Mexican Produce for
    1980                Pesticide Residues (Compliance Programs 7305. 008
                        - Fiscal Year 1979), Bureau of Foods and Office of
                        the Associate Commissioner for Regulatory Affairs,
                        Food and Drug Administration, April 23, 1980.

    Manual de Plaguicidas Autorizados En 1981 Cultros de Hortalizas Para

    See Also:
       Toxicological Abbreviations
       Methamidophos (HSG 79, 1993)
       Methamidophos (ICSC)
       Methamidophos (JMPR Evaluations 2002 Part II Toxicological)
       Methamidophos (Pesticide residues in food: 1976 evaluations)
       Methamidophos (Pesticide residues in food: 1979 evaluations)
       Methamidophos (Pesticide residues in food: 1981 evaluations)
       Methamidophos (Pesticide residues in food: 1982 evaluations)
       Methamidophos (Pesticide residues in food: 1985 evaluations Part II Toxicology)
       Methamidophos (Pesticide residues in food: 1990 evaluations Toxicology)