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    PESTICIDE RESIDUES IN FOOD - 1981


    Sponsored jointly by FAO and WHO






    EVALUATIONS 1981







    Food and Agriculture Organization of the United Nations
    Rome

    FAO PLANT PRODUCTION AND PROTECTION PAPER 42

    pesticide residues in food:
    1981 evaluations

     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

    Geneva, 23 November-2 December 1981

    FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
    Rome 1982

    METHAMIDOPHOS

    Explanation

         Because of the special relation of methamidophos and acephate,
    the Thirteenth Session of the Codex Committee on Pesticide Residues
    requested the Joint Meeting to re-examine the limits for both
    compounds to determine if they are still adequate. Governments were
    requested to provide good agricultural practice information to
    facilitate this review.

         Methamidophos was previously reviewed in 1976 when maximum
    residue levels were estimated for a variety of commodities. In 1979,
    some levels were revised and new ones estimated, partly to allow for
    residues resulting from the use of acephate.*

         Some additional residue data, good agricultural practice
    information, and information on the fate of residues have been
    received and are reviewed in this addendum. However, the limited
    amount of information that has been provided to this Meeting is not
    adequate to fully address the issues that have been raised by the
    Codex Committee. To the extent new data are available, residues
    resulting from the use of acephate are considered, and this addendum
    should be read in conjunction with the one on acephate elsewhere in
    these evaluations.

    RESIDUES IN FOOD

    USE PATTERN

         Some good agricultural practice information has been provided to
    this Meeting and are summarized below:

              

    *  See Annex II for FAO and WHO documentation.

                                                                                                   

    Country        Formulation         Commodity           Application         Pre-harvest
                                                           Rate (kg a.i./ha)   Interval (days)
                                                                                               

    Australia      -                   tomato              -                   4
    US             Monitor 4 spray,    cabbage             0.56-1.12           35
                   Monitor 4 liquid,   broccoli            0.56                14
                   and                                     1.12                21
                   Monitor 6 spray     Brussels                                14
                                       sprouts
                                       cauliflower                             28
                                       potato                                  14

    New Zealand    60% E.C.            Brussels            1.1-1.5 l/ha        -
                                       sprouts
                                       broccoli            1.5 l/ha            -
                                       potato              0.8 l/ha            -

    Germany        600 g a.i./ha       cauliflower         0.36 kg/ha          21
                                       red and white
                                       and savoy cabbage,
                                       kohlrabi
                                                                                               
    
    RESIDUES RESULTING FROM SUPERVISED TRIALS

         Additional residue data were available from six countries on a
    total of 12 commodities. However, little information was provided as
    to whether there are approved good agricultural practices for the
    formulations used in the residue trials or what rates and pre-harvest
    intervals are recommended. Results of the field trials are summarized
    in Table 1.

    Brussels sprouts

         Minimal data were available from one country, with maximum
    residues of 0.04 mg/kg at application rates and pre-harvest interval
    (7 to 8 days) approximating that used as a basis for the current
    1 mg/kg Codex limit. There is no need to change the previous estimate,
    which should be adequate to cover residues resulting from the use of
    methamidophos or acephate on the same crop, but not necessarily both.

        TABLE 1.  Residues of methamidophos from supervised trials
                                                                                                                                               

                                    Application                      Residues (mg/kg) at intervals (days) after application2
                   Country                                                                                                                     
    Crop           (Year)             Rate
                                 No.  (kg a.i./ha)     Formulation   0       1       3       5-6     7-8     10      14-15   21     Control
                                                                                                                                               

    Brussels
    sprouts        New Zealand   4    1.1 l/ha1        60% E.C.              0.78    0.17    0.09    0.02   <0.007                  <0.007
                   (1977)             broadcast
                                      (proposed use)

                   New Zealand   4    1.3 l/ha.1       60% E.C.              1.7             0.1     0.04    0.01   <0.007          <0.007
                   (1977)

                   (1973)        4    1.5 l/ha.1       60% E.C.      no residues (<0.007 mg/kg) 6 week post-treatm.                 <0.007

    Broccoli       New Zealand   4    1.5 l/ha1        60% E.C.                                                             <0.007  <0.007
                   (1973)

    Broccoli       USA           5    0.28             6E3           4.8             2.1             0.64            0.11
    (head)         (1968)                                            4.2             2.5             0.77            0.11
                   CA            7                                                                   1.7
                                                                                                     1.4
                                 8                                                                   1.3
                                                                                                     1.4
                                                                                     5.0             2.7
                                 9                                                   5.7             1.1

                   (1967-        5    0.56             6E            6.7             5.2             1.5             0.27
                   1968)                                             7.3             5.1             1.3             0.23
                   CA            7                                                                   3.1
                                                                                                     2.8
                                 8                                                                   4.0
                                                                                                     2.7
                                 9                                                   1.3             5.3
                                                                                    11.0             5.3
                                                                                                                                               

    TABLE 1.  (con't)
                                                                                                                                               

                                    Application                      Residues (mg/kg) at intervals (days) after application
                   Country                                                                                                                     
    Crop           (Year)             Rate
                                 No.  (kg a.i./ha)     Formulation   0       1       3     5-6     7-8      10   14-15
                                                                                                                                               

    Broccoli       USA
    (head)         (1967-        4-5  1.1              6E3           3.1             1.4
                   1968)                                             3.4             1.4
                   (CA, NY,                                          6.4             1.6
                   FL,NJ)                                            5.4             1.3
                                                                    17               2.1
                                                                    15               2.1
                                                                     5.3             2.1
                                                                     2.8             2.5
                                                                                     8.7
                                                                                    12
                                                                                     1.6
                                                                                     1.2
                                 7-9

                                                                                     8.8             7.0
                                                                                     4.7             3.0
                                                                                                     9.1
                                                                                                     1.1
                                                                                                     8.8
                                                                                                     9.9
                                 14                                  3.0             2.1             1.3             0.27
                                                                     3.3             2.4             1.3             0.17

                   CA
                   (1969)        4    2.24             6S                                            0.28    0.21    0.03
                                                                                                     0.65    0.36    0.01
                                                                                                                                               

    TABLE 1.  (con't)
                                                                                                                                               

                                    Application                      Residues (mg/kg) at intervals (days) after application
                   Country                                                                                                                     
    Crop           (Year)             Rate
                                 No.  (kg a.i./ha)     Formulation      0               1               3              7         14
                                                                                                                                               

    Potato         New Zealand   1    1.54/ha1         Tamaron       0.13,0.08       0.35,0.26       0.13,0.44       0.07    0.005,0.03
                   (1972)                              600g/L                                                        0.19

                                                                                                                                               
                                                                                                                                    No. of
                                                                     0      1      2-3    6-7    9-10   13-14  15      20-21   24   Samples
                                                                                                                                               

    Cabbage        Australia
                   * (1976)      (2-  0.24% to run     580 g/l                     0.61          0.18   0.07           0.02         1 each
                                 4)5  off                                                                                           interval

                   * (1976)      (2-  0.12% to run     580 g/l                     0.43          0.12   0.03          <0.01
                                 4)5  off                                                                                           1

                   * (1976)      (2-  0.06%            580 g/l                     0.19          0.08   0.02          <0.01
                                 4)5

                   * (1976)      6    0.036%           580 g/l                     0.16   0.11   0.04          0.04    0.02
                                      a.i. or
                                      163-509 g/ha

                   (1973)        4    1.5 l/ha         6E                          0.05   0.002                0.0007
                                                                                   (3     (6
                                                                                   day)   day)
                                                                                                                                               

    TABLE 1.  (con't)
                                                                                                                                               

                                    Application                      Residues (mg/kg) at intervals (days) after application2
                   Country                                                                                                                     
    Crop           (Year)             Rate                                                                                         No. of
                                 No.  (kg a.i./ha)     Formulation  0      1      2-3    6-7    9-10   13-14  15      20-21   24   Samples
                                                                                                                                               

    Cauliflower    Australia     1    1.3              580 g/l      11.1                  4-7           3              2            Duplicate
    leaves         * (1970)                                                                                                         analysis

    head                                                                                  0.2           0.12           0.06

    Cauliflower    * (1977)      4    58 g/100 l       58% E.C.                                                        0.34
                                      (0.06%)                                                                          (38
                                                                                                                       days)

                                                                                                                                               
                                                                                                                                     No. of
                                                                             0       1       3       7       14      21      28      samples
                                                                                                                                               

    Cauliflower    Germany    1976     3           0.36       0.1%           0.55                    0.02   <0.01   <0.01    N.D.7

                              1976     3           0.36       0.1%           0.7                     0.1     0.04    0.01   <0.01

                              1976     3           0.36       0.1%           0.55                    0.07    0.01   <0.01   <0.01

                              1978     2           0.36       600g/L

    flower                                                                   2.0             0.9     0.55    0.34    0.04    N.D.7

                                                                             2.3             1.2     0.56    0.27

    leaf                                                                                     1.62

                                                                                             1.62
                                                                                                                                               

    TABLE 1.  (con't)
                                                                                                                                               

                                    Application                              Residues (mg/kg) at intervals (days) after application2
                   Country                                                                                                                     
    Crop           (Year)             Rate                                                                                           No. of
                                 No.  (kg a.i./ha)     Formulation           0       1       3       7       14      21      28      samples
                                                                                                                                               

                              1978     2           0.36       600 g/L
    flower                                                                   0.37            0.17    0.07    0.02    0.01    N.D.7

                                                                             0.36            0.32    0.07    0.02    0.01

                                                                                             1.3

                                                                                             1.3

                              1978     2           0.36       600g/L         0.53                    0.01    N.D.7   N.D.7   N.D.7

                                                                             0.56

                                                                                                                                               
    Crop           Country      No.    Rate            Formulation           Days after               Residues (mg/kg)    
                   (year)                                                 last application   fruit       peel        whole6
                                                                                                                                               
    Citrus         Egypt
                   (1970-        2     0.15%
    Tangerine      1971)               (10.6g/tree)     5546                     0            0.02        4           1.2
    (Clementine)                                                               111            0.01        0.02

    Lemon          Egypt         6     0.2%             600 g/L
    (Italian       (1971)              (12g/tree)                               18            0.13        1.7
    seedless)

                                                                                32            0.01        0.35
                                                                                47            0.01        0.09
                                                                                62            N.D.7       0.05
                                                                             76-90            N.D.       <0.01
                                                                                                                                               

    TABLE 1.  (con't)
                                                                                                                                               

                                    Application                                                       Residues (mg/kg)
                   Country                                                                                                                     
    Crop           (Year)             Rate                                Days after last
                                 No.  (kg a.i./ha)     Formulation          application       fruit       peel        whole6
                                                                                                                                               

    Lemon          Egypt         2     0.15%            5546                     0            0.2         8.6         2.7
    (Italian       (1970-              (196g/tree)
    seedless)      1971)                                                       111            0.02        0.2         0.07

    Lemon          Egypt         7     0.2%             600g/L                   1            0.17        5.2         1.7
    (Eureka)       (1971)              (12g/tree)                               18            0.1         2.0         0.7

                                                                                32            0.01        0.6

                                                                                47            ND7         0.09
                                                                                62            ND          0.05

                                                                                76            ND          0.01

                                                                                90            ND          -

                                                                                                                                               
                                                                                              pulp        peel        whole6
                                                                                                                                               

    Lemon          U.S.A.        2     1.1              4WM                      0            0.0         3.2         1

      FL           (1974)                               foliar                   7            0.06        0.9         0.3

                                                        spray                   14            0.15        0.8         0.3

                                                                                22            0.08        0.14        0.1
                                                                                                                                               

    TABLE 1.  (con't)
                                                                                                                                               

                                    Application                                                       Residues (mg/kg)
                   Country                                                                                                                     
    Crop           (Year)             Rate                                Days after last
                                 No.  (kg a.i./ha)     Formulation          application       pulp        peel        whole6
                                                                                                                                               

                                                                                38            0.05        0.03        0.04

                                                                                58            0.1         0.0
                                                                              control         0.0         0.0

      FL           (1974)        2     1.1              4WM                      0            0.04        2.1

                                                        foliar                   7            0.06        0.38

                                                        spray                   14            0.03        0.13

                                                                                30           <0.01        0.01

                                                                                60            0.0         0.01

                                                                                90            0.0        <0.01
                                                                              control        <0.01        0.0

      CA           (1974)        2     1.1              4WM                      0            0.08       12.5         3.8

                                                        foliar                   7            0.17       11.3         3.5

                                                        spray                   14            0.06        5.5         1.7

                                                                                28            0.19        3.2         1.2

                                                                                60            0.03        0.7         0.23
                                                                                                                                               

    TABLE 1.  (con't)
                                                                                                                                               

                                    Application                                                       Residues (mg/kg)
                   Country                                                                                                                     
    Crop           (Year)             Rate                                Days after last
                                 No.  (kg a.i./ha)     Formulation          application       pulp        peel        whole6
                                                                                                                                               

    Lime           U. S .A.      2     1.1              4WM                      0            0.03        2.9

      FL           (1974)                               foliar                   7            0.0         0.13

                                                        spray                   14            0.01        0.03

                                                                                30            0.0         0.01

                                                                                60            0.0         0.1

                                                                                90            0.0         0.0

                                                                              control                     0.00

    Oranges        U.S.A.        2     1.1              4WM                      0            0.21       14.9         4.6
                   (FL)                                 foliar                   7            0.14        4.8         1.5
                   (1974)                               spray                   14            0.12        2.2         0.74
                                                                                30            0.08        0.43        0.19
                                                                                60            0.03        0.04        0.03
                                                                                91            0.02        0.03        0.02
                                                                              control         0.00        0.00

    Lettuce        U.S.A.
    (head)         (NJ, CA)      7     1.1              6S                       7            0.08-0.5
                   (1969)                                                                    (0.25)

                                                                                10            0.03-0.14
                                                                                             (0.1)
                                                                                                                                               

    TABLE 1.  (con't)
                                                                                                                                               

                                    Application                                                       Residues (mg/kg)
                   Country                                                                                                                     
    Crop           (Year)             Rate                                Days after last
                                 No.  (kg a.i./ha)     Formulation          application       pulp        peel        whole6
                                                                                                                                               

                                                                                14            0.01-0.13
                                                                                             (0.08)

                   N.J.          7     2.2              6S                       7            0.5,0.4
                   (1969)                                                       10            0.4,0.4

                                                                                14            0.3,0.3

                   U.S.A.              0.5              6E                       0            0.4-5
                   (NJ, CA)      4-8                                                         (1.4)
                   (1968-
                   1969)                                                         3            0.1-0.4
                                                                                             (1.1)

                                                                                 7            0.06-4.5
                                                                                             (0.93)

                                                                                14            0.01-0.7
                                                                                             (0.3)
                                                                                                                                               

    TABLE 1.  (con't)
                                                                                                                                               

                                    Application                                                       Residues (mg/kg)
                   Country                                                                                                                     
    Crop           (Year)             Rate                                Days after last     Threshed      Dry         Control
                                 No.  (kg a.i./ha)     Formulation          application        beans       vines    beans     vines
                                                                                                                                               

    Soybean        U.S.A.
                   All           2     1.1              aerial            57                 <0.01        <0.01     <0.01     <0.01
                   (1978)                               spray
                                                        4
                   TX            2     1.1              foliar            66                 <0.01        <0.01     <0.01     <0.01
                   (1977)                               spray
                                                        4

                   TX                  1.1              foliar            66                 <0.01        <0.01     <0.01     <0.01
                   (1977)                               spray
                                                        4

                   NC            2     1.1              foliar            77                 <0.01        <0.01     <0.01     <0.01
                   (1977)                               spray
                                                        4
                   GA                  1.1              foliar            161-162             0.02        <0.01     <0.01     <0.01
                   (1977)                               spray
                                                        4

    Tomato         New Zealand   1     1.5 l/ha1                          1                   0.13
                   (1974)                               600 g/L           4                   0.02
                                                                          7                   0.005
                                                                          14                  Nil
                   New Zealand         1.5 l/ha1        600 g/L           1                   0.13
                                 1                                        3                   0.05
                                                                          7                   0.004
                   (1974-                                                 10                  0.002
                   1975)
                                                                                                                                               

    TABLE 1.  (con't)
                                                                                                                                               

                   Country       Application                              Residues (mg/kg) at intervals (days) after application
                                                                                                                                               
    Crop           (Year)              Rate
                                 No.   (kg a.i./ha)     Formulation       4h        3         7         10        14
                                                                                                                                               

    Tomato         South Africa  7     0.6                                0.53      0.45      0.3       0.14      0.25
                   (1978)
                                                                                                                                               

    Notes:  Data in Table are based on reports submitted to the 1981 JMPR by Bayer, including reports from Mobay and Chevron.
            Data provided by the Australian Government indicated by *

    1  Litres of product (proposed use);
    2  Mean in parentheses;
    3  E = emulsion;
    4  Proposed label rate is 0.56-1.1 kg a.i./ha;
    5  2 applications at 20 days preharvest test, 3 applications at 13 days preharvest test, 4 applications at 2 and 0 days
       preharvest tests;
    6  Based on assumption of 70:30 pulp: peel weight ratio.;
    7  Limit of sensitivity: 0.01 mg/kg;
    8  Average of two analyses where single values are given.
        Broccoli

         Several delegations to the Codex Committee on Pesticide Residues
    (CCPR) at the 12th and 13th sessions expressed concern that limits for
    methamidophos on some commodities are too high and specifically (at
    the 12th session) that the 2 mg/kg limit on broccoli was too high.
    Additional residue data have been provided.

         The current 2 mg/kg limit is based on 3 to 5 applications at
    0.56 - 1.12 kg a.i./ha and a seven-day pre-harvest interval. Most of
    the data submitted to this Meeting do not fall into those constraints.
    Those that do confirm the need for the current 2 mg/kg limit are based
    on the above criteria for the formulations used. No information was
    provided as to whether the formulations used in the trials are
    approved for use on broccoli and, if they are, what rates or pre-
    harvest intervals are considered good agricultural practice. The
    application rates are consistent with those used as the basis for the
    existing limit.

         The new data do suggest that a 1.0 mg/kg limit would be supported
    if no more than five applications are made at the 0.56 - 1.12 kg
    a.i./ha application rate and a pre-harvest interval of 14 days is
    observed. However, data previously reviewed (1976) indicate that a
    21-day pre-harvest interval would be required. A 1.0 mg/kg limit would
    also be consistent with methamidophos data on other brassica,
    methamidophos residues on broccoli resulting from uses of acephate
    (assuming both methamidophos and acephate are not used on the same
    crop) and national tolerances reported to the Meeting.

    Cabbage

         The new residue data are within the current 1.0 mg/kg limit.
    Furthermore, if residues of methamidophos on cabbage resulting from
    the use of acephate (see acephate addendum) are assumed to be
    approximately 15% of total acephate + methamidophos residues, the
    1.0 mg/kg limit is sufficient to cover methamidophos residues in
    cabbage resulting from the use of acephate, if the 5 mg/kg acephate
    limit is not exceeded. It would not necessarily be adequate if both
    acephate and methamidophos were used on the same crop.

    Cauliflower

         The new residue data are consistent with the 1.0 mg/kg level
    estimated by the 1979 JMPR. No additional data have been provided on
    which to base estimates of residues of methamidophos in cauliflower
    resulting from the use of acephate. However, based on the same
    assumptions and data for cabbage, the 1.0 mg/kg limit would probably
    suffice for the use of methamidophos or acephate on cauliflower, but
    not necessarily both.

    Citrus

         The current 0.5 mg/kg residue level for methamidophos on citrus
    was estimated by the 1979 Meeting to allow for residues of
    methamidophos resulting from the use of acephate, for which a maximum
    level of 5 mg/kg was estimated. Residue data reflecting the use of
    methamidophos on citrus in two countries were submitted to this
    Meeting, although no information on national use patterns was
    provided.

         The data indicate that residues in the pulp would be well under
    the current 1.0 mg/kg limit, even at day of application. Peel
    residues, however, were as high at 15 mg/kg at day of application. If
    a pulp:peel ratio of 70:30 is assumed, it can be estimated that a
    pre-harvest interval of approximately 35 days would be required to
    assure whole-fruit residues no greater than 1.0 mg/kg, and
    approximately 50 days to assure residues less than the current
    0.5 mg/kg level estimate. In the absence of information on approved
    national use patterns for methamidophos on citrus, there is no basis
    to change the current 0.5 mg/kg limit, which covers residues of
    methamidophos resulting from the use of acephate.

    Lettuce

         Lettuce, with a current limit of 2 mg/kg, is one commodity for
    which concern has been expressed that the limit is higher than
    necessary. It is not clear what pre-harvest interval the 1976 Meeting
    used for the 2 mg/kg limit, but it was presumably two weeks, based on
    the data. However, based on the 'recommended' uses (1976 Evaluations)
    a 21-day interval could be used, and based on the 1976 summary data
    (head + wrapper leaves <0.4 mg/kg at 21 days) a lowering of the limit
    to 1.0 mg/kg could be supported if a 21-day interval were observed.

         Additional data from residue trials in one country were submitted
    to this Meeting, although it could not be confirmed that the trials
    represent approved good agricultural practices in that country. The
    application rates are similar to the rates 'recommended' in the 1976
    Evaluations. At 14 days from application and with rates approximately
    0.5 × the maximum 'recommended' rate, maximum residues are 0.7 mg/kg.
    These data are consistent with a 1.0 mg/kg limit based on a 21-day
    pre-harvest interval.

         No additional data were provided to this Meeting to permit
    estimation of methamidophos residue levels in lettuce resulting from
    the use of acephate. Based on results in other brassica, a 1.0 mg/kg
    methamidophos limit would probably be adequate to include residues of
    methamidophos resulting from the use of acephate, but probably not for
    the use of acephate and methamidophos on the same crop.

         On the basis of data and uses previously reviewed and data
    submitted to this Meeting, a 1.0 mg/kg limit after a 21-day pre-
    harvest interval, could be supported.

    Potato

         Residue data from trials reflecting two times the recommended
    national application rate were available from one country. Although
    the pre-harvest interval basis for the current 0.1 mg/kg limit for
    methamidophos on potatoes was not specified, it was probably 2 to 3
    weeks. If the uses utilized in the trials submitted to this Meeting
    become nationally approved uses, a 14-day pre-harvest interval would
    be required to assure that residues would not exceed the current
    0.1 mg/kg limit.

         No data were available to estimate possible methamidophos
    residues resulting from the use of acephate (1.0 mg/kg limit) on
    potatoes. In the absence of such data, the current 0.1 mg/kg limit for
    methamidophos should also apply to residues resulting from the use of
    acephate. It may not be adequate to cover residues of methamidophos
    resulting from the use of methamidophos and acephate on the same crop.
    There is insufficient information to warrant a revision of the current
    0.1 mg/kg limit.

    Soybean

         The 1979 Meeting estimated the current 0.05 mg/kg level for
    methamidophos residues on soybeans to include residues resulting from
    the use of acephate, for which residues were estimated at 0.5 mg/kg
    with a 14 day pre-harvest interval.

         Residue data reflecting experimental trials of a foliar spray 4
    formulation were available to this Meeting from one country. As
    residues in beans at 57 to 162 days after treatment were below the
    current 0.05 mg/kg limit, there is no basis for revising the current
    limit even if the uses were approved ones.

    Tomato

         Tomato is a commodity for which concern has been expressed at the
    CCPR as having a limit higher than necessary. It is currently 2 mg/kg
    as estimated by the 1976 Meeting, which apparently used a one-week
    pre-harvest interval as a basis. One government has informed this
    Meeting that their good agricultural practice requires a four-day pre-
    harvest interval, presumably at application rates comparable to those
    submitted to the 1976 Meeting.

         Additional residue data were available to this Meeting resulting
    from residue trials in two countries. It could not be determined
    whether the trials represent nationally approved good agricultural
    practices. However, all residues were <1.0 mg/kg, even after a four-
    hour pre-harvest interval.

         No additional data were provided to the Meeting for use in
    estimating methamidophos residues in tomatoes resulting from the use
    of acephate. However, based on data provided to the 1976 Meeting, the
    current 2 mg/kg methamidophos limit should be more than adequate for
    such use, if both acephate and methamidophos are not used on the same
    crop.

         On the basis of the new data, summary data in the 1976 Evaluation
    (residues up to 1.8 mg/kg at one week), and a national good
    agricultural practice allowing a four-day pre-harvest interval, a
    lowering of the 2 mg/kg limit on tomatoes cannot be justified with
    current uses.

    FATE OF RESIDUES

    In animals

         Sixteen hens were given a single dose of methyl-carbon C-14
    labelled methamidophos at 1 mg (14.15 µCi/mg) per kilogram body weight
    and the tissues, eggs and faecal matter analysed at different
    intervals up to 96 hours (Bayer 1975). Results for methanol
    extractable and unextracted (bound) residues in individual tissues and
    eggs are given in Table 2. It can be seen that more of the residue
    becomes bound at the longer interval and that the binding at six hours
    was more rapid in the enzymatically active liver and kidney than in
    other tissues.

         Faeces were analysed in a similar 3, 24 and 96 hours post-
    treatment. Bound and methanol extractable methamidophos were as
    follows:

    Hours               Extractable (%)     Bound (%)

     3                      36.5               53
    24                      18.2               69
    96                      30.2               66

         Investigations were made into the nature of the residues in the
    liver and in the breast and thigh muscle, with only limited success.
    The residues in all cases were found to be very polar and could not be
    separated from impurities, although a number of purification and
    separative techniques were used. In muscle tissue, approximately 80%

        TABLE 2.  Methanol extraction of Carbon-14 labelled residues of methamidophos from the organs
              and tissues of hens sacrificed at 6 and 96 hours and eggs at 72 hours post-treatment.1
                                                                                                      

                        Extractable                     Bound                 Recovery from Extration
    Sample             Residue (TER)                 Residue (TBR)                 (sum TER and TBR)
                   6 h.           96 h           6 h            96 h           6 h            96 h
                                                                                                      

    Liver          66.22          25.83          36.42          72.13         102.6           97.9
    Kidney         60.6           46.4           31.0           50.1           91.6           96.5
    Gizzard        84.2           66.4           17.7           27.2          101.5           93.6
    Heart          78.7           48.1           21.7           40.4          100.4           88.5
    Skin           85.2           23.7           16.3           57.8          101.5           81.5
    Fat            81.2           11.7           16.8            7.0           98.0           18.74
    Thigh          82.2           33.3           11.6           58.1           93.8           91.4
    Breast         81.5           37.9           14.3           52.6           95.8           90.5

                                  72 h                          72 h                          72 h
                                                                                                      

    Eggs                          50.45          44.35          94.7
                                                                                                      

    1  All figures are percent of total residues;
    2  Average of three samples;
    3  Average of 4 samples;
    4  Remainder of residue was in methanol insoluble liquid fat;
    5  Average residue of eggs collected from two hens.
    
    of the residue was found to be in the polar lipid fractions where
    methamidophos, O, S-dimethyl-phosphorothioate and some methyl
    dihydrogen phosphate would be found, if present. However, the residues
    could not be identified because of impurities.

         In a poultry feeding study, three groups of eight hens were fed
    respectively,  ad libitum, rations containing approximately 2, 6 and
    20 mg/kg methamidophos for 28 consecutive days (Bayer 1975a). Eggs
    were collected daily. After 28 days the animals were sacrificed and
    samples of heart, gizzard (emptied and stripped of lining), liver,
    kidneys, muscle, subcutaneous and visceral fat and skin were sampled
    for analysis by a gas chromatographic procedure (Stanley 1971), which
    was modified to use pentane extraction, a carbowax 20 M liquid phase
    and a flame photometric detector. Other slight modifications were made
    for eggs, and in both cases analytical standards were prepared in
    extracts of control samples.

         At the 20 mg/kg feeding level composites of like tissues
    (including heart and gizzard) were analysed after 28 days. Four-egg
    composites were analysed at 3, 7, 14 and 28 days at the 20 mg/kg
    feeding level and at the 2 and 6 mg/kg level at 28 days. As tissue
    residues were low at the 20 mg/kg feeding level, tissues were not
    analysed at the lower feeding levels. Residues in tissues and eggs
    corrected for average overall recoveries of 86% and 60% respectively
    are summarized in Table 3, which also gives a relative comparison of
    results from the feeding study with total residues from the metabolism
    study.

         It can be seen in Table 3 that residues in eggs had reached
    equilibrium by the third day. Although not shown in Table 3, residues
    in eggs at 28 days at the 2 and 6 mg/kg feeding levels were 0.008 and
    0.032 mg/kg respectively (corrected for 64% recovery).

         In the feeding study, liver and kidney contained the lowest
    residues of methamidophos and muscle and eggs the highest. This
    contrasts to local residues in the metabolism study, which indicates
    the highest total radioactive tissue residues in kidney and liver.
    This comparison suggests that residues are distributed to the
    respective tissues before substantial metabolism occurs, resulting in
    greater metabolism and bound residues in the enzymatically active
    tissues and more unmetabolized residue in tissues of less enzymatic
    activity.

        TABLE 3.  Residues in tissues and eggs of hens fed methamidophos
              at 20 ppm in the diet for 28 days compared with total
              carbon-14 methamidophos residues from the metabolism study.
                                                                                     

                                 Methamidophos (mg/kg)       Total Carbon-14
    Tissue                       from feed study             residue(mg/kg)at 6 hours
                                 corrected for recovery      from metabolism study
                                                                                     

    Liver                               0.003                       1.070
    Kidney                              0.005                       0.700
    Skin                                0.022                       0.146
    Fat                                 0.003                       0.024
    Heart and gizzard                   0.026                       0.2341
    Muscle                              0.033                       0.1842

    Eggs

    28(day of collection)               0.198                       -
    14                                  0.178                       -
     7                                  0.142                       -
     3                                  0.181                       0.3213
                                                                                     

    1  Average of values for breast and thigh muscles;
    2  Average of values for heart and gizzard;
    3  Average of four separate determinations.
    
    In plants (rotational crops)

         Wheat, soybeans, turnips and cauliflower were grown in plastic
    containers containing 800 g of soil previously treated 11 times with
    [S.methyl-14C] methamidophos at a rate equivalent to 227 g a.i./a
    (McNamara 1976). The soil was previously used to grow cabbage plants
    for three weeks. Mature soybeans, wheat, turnips and cauliflower were
    harvested after 124, 124, 201 and 275 days respectively.

         Except for 0.31 mg/kg methamidophos equivalent residues in
    immature whole turnip plants, residues in turnips and all parts of
    cauliflower were < 0.08 mg/kg and were not further characterized.
    Residues in all immature and mature wheat and soybeans (whole or
    parts) were > 0.1 mg/kg, with maximum methamidophos equivalents of
    1.3 and 1.1 mg/kg in wheat stems and soybean leaves respectively.
    Residues in wheat heads and soybean pods were 0.27 and 0.14 mg/kg
    respectively. Further characterization of the radioactive residues in
    parts of wheat and soybeans indicated that residues of intact
    methamidophos was < 0.08 mg/kg.

         Another rotational crop residue study was carried out by applying
    methamidophos to soil plots in Kansas and Florida (US) at rates of
    1.7, 3.4 (normal seasonal rate), 6.8 and 13.6 kg a.i./A and planting
    sorghum, wheat, snapbeans, peas, carrots, radishes, maize black-eyed
    peas and turnips at 30, 60, 90, 120 and 365 days post-treatment
    (Murphy and Morris 1979).

         In all mature crops (or parts), except maize green forage at 365
    days post soil treatment, residues were < 0.03 mg/kg. At 365 days
    at the 60-240 oz./A rates on green maize forage residues were
    0.09-0.15 mg/kg. These values are inconsistent with the < 0.03 mg/kg
    residue in an earlier post soil treatment.

         Apparent residues in green maize forage controls were < 0.01 and
    0.06 mg/kg. Therefore, there is reason to suspect that the high values
    in green maize may be aberrant. Even at the 0.1 mg/kg level, residues
    of methamidophos would not be expected in animal products as a result
    of residues in rotational crops from normal usage.

    In soils

         Sandy loam soil (2.8% organic matter and pH 5.1) was fortified at
    10 mg/kg with [S-methyl-14C] methamidophos, aged at room temperature
    for 30 days, then packed and eluted from 4.8 cm i.d.x30 cm long
    columns with oxygen-saturated water at a rate of 1.25 cm/day for 45
    days (Obrist 1979). Approximately 80% of the radioactivity was lost
    during the ageing process, presumably due to volatilization. Over 80%
    of the aged residue was found in the upper 1.25 cm, approximately 5%
    in the leachate and an additional 11% was lost during the leaching
    period, presumably due to volatilization. None of the residue in the
    leachate or organosoluble soil fractions was intact methamidophos.
    Residues were unidentified.

         Methamidophos adsorption experiments were carried out on three
    soil types (Shaw 1979). One-gram soil samples were added to 10-ml
    solutions of [S-methyl-14C] methamidophos at concentrations of 0.5
    to 10 µg/ml and equilibrated for three hours at 15 and 30°C. The
    highest adsorption was 5% on high organic silty clay loam at 15°C.
    Freundlich adsorption constants were 1.28 (l/n) and 0.12 (ka).
    Essentially no adsorption occurred on any soil at 30°C.

    In storage and processing

         An 11.34 kg samples of shelled peanuts was fortified with
    345 mg/kg methamidophos by dipping (473 ml Monitor 4 in 38 litres of
    water) then processed into meal, crude oil, refined oil, refined
    deodorized oil and soapstock (Morris  et al 1981). Concentration
    factors were shelled peanuts (1.0), pressed and extracted peanut meal
    (0.59), crude peanut oil (0.07 screw pressed; 0.2 solvent extract),

    and < 0.01 in all other fractions. Controls were < 0.01 mg/kg except
    for 0.03 mg/kg in the meal and recoveries in all fraction > 73% at
    the 0.1 mg/kg fortification level.

         Tomatoes and savoy cabbage, previously sprayed with a
    600 g a.i./l formulation, were cooked in open and closed vessels with
    an equal amount of water for 20 minutes (Möllhoff 1978). Residues in
    uncooked cabbages were 0.77 and 0.57 mg/kg and in tomatoes 0.067 and
    0.055 mg/kg. Recoveries of methamidophos were 84% and 86% in the
    cabbage cooked in open and closed vessels respectively and 100 and 87%
    in tomatoes cooked in open and closed vessels respectively.

    NATIONAL MAXIMUM RESIDUE LIMITS REPORTED TO THE MEETING
                                                                        

                                             MRL    Pre-harvest interval
    Country        Crop                    (mg/kg)         (days)
                                                                        

    Australia      tomato                    2      4

    USA1           broccoli, Brussels        1      (see use patterns)
                   sprouts, cabbage
                   cauliflower, cucumber,
                   eggplant, lettuce,
                   pepper and tomato
                   melon                     0.5

                   cottonseed and potato     0.1
                                                                        

    1  These tolerances replace those reported to the 1976 Meeting.

    EVALUATION

    APPRAISAL

         The Meeting took note of the request of the Thirteenth Session of
    the Codex Committee on Pesticide Residues (CCPR) to re-examine maximum
    residue limits (MRLs) for methamidophos and acephate, taking into
    account their relationship. The Committee requested governments to
    provide good agricultural practice information to facilitate this
    review.

         The Meeting has not received sufficient information to address
    fully the questions raised by the CCPR. It did receive a very limited
    amount of good agricultural practice information and was informed that
    at least two countries were planning to provide additional
    information. The Meeting also received additional residue data on
    several crops and information on the fate of methamidophos residues.

    On the basis of these new data, the Meeting was able to confirm the
    1 mg/kg limit for Brussels sprouts, cabbage and cauliflower; 0.5 mg/kg
    for citrus; 0.1 mg/kg for potato; 0.05 mg/kg for soybean and 2 mg/kg
    limit for tomato. New good agricultural practice information and
    residue data for broccoli (head) and residue data for lettuce indicate
    that the current 2 mg/kg limits could be lowered if longer pre-harvest
    intervals were observed.

         Although the Thirteenth Session of the CCPR also discussed limits
    for eggplant and cucumber, no additional information was available for
    these crops.

         Metabolism and feeding studies in poultry supplement that
    previously reviewed for rats and lactating goats. In the poultry
    metabolism study, binding of radioactive residues increased with time
    from dosing and was more predominant in enzymatically active tissues.
    Analytical difficulties prevented identification of the metabolites,
    although the majority of the radioactivity was found in polar lipid
    fractions, as was the case for one rat study previously examined by
    the Meeting.

         Comparison of methamidophos residues from the poultry feeding
    study with total active residues from the metabolism study suggests
    that residues are rapidly distributed to the various tissues, where
    they are metabolized. Metabolism is more rapid, with more rapid
    conjugation in enzymatically active tissues and conversely, more
    methamidophos is found in less enzymatically active tissues.

         Radioactive rotational crop studies in containers indicate
    considerable uptake of residues in a variety of crops. This was not
    confirmed from field tests with unlabelled material applied at
    exaggerated rates.

         In leaching studies, most of the residue was found in the upper
    1.3 cm of soil, although laboratory adsorption studies indicate very
    low adsorption of methamidophos from aqueous solutions by soil.

         Residues were found not to concentrate in processed fractions of
    peanuts fortified with methamidophos. Residue losses of 0-16% were
    observed when methamidophos fortified cabbage or tomatoes were cooked
    in open or covered vessels.

    RECOMMENDATIONS OF RESIDUE LIMITS

         The Meeting examined residue data from supervised trials on a
    number of crops. From these data, the Meeting was able to confirm or
    estimate revised MRLs that are likely to occur when methamidophos (or
    acephate) are used in practice and when the reported intervals are
    observed. These levels refer to methamidophos alone and are intended
    to cover residues of methamidophos resulting from the use of either

    acephate or methamidophos on a crop (but not both), except where
    indicated otherwise. The Meeting concluded that the revised maximum
    residue levels given below are suitable for establishing MRLs.

                                                                                      
                                                      Pre-harvest interval on
              Previous residue    Revised             which the revised estimates
    Crop      estimate (mg/kg)    estimate(mg/kg)     are based (days)
                                                                                  

    Broccoli         2                  1                        21

    Lettuce          2                  1                        21
    
    REFERENCES

    Bayer AG  An investigation of the extractable residues of Carbon-14
    1975      labeled Monitor in tissues, organs, eggs and faeces
              following oral administration of the pesticide to laying
              hens. Report No. 44069 and No. 3 of ADC Project No. 124.
              2 April 1975. Submitted by Bayer. (Unpublished)

    Bayer AG. Residues of Monitor in tissues and eggs and the effect upon
    1975a     serum acetylcholinesterase activity following oral
              administration of the pesticide to poultry for twenty-eight
              consecutive days. Bayer Report No. 43737 (Report No. 2 of
              ADC Project No. 124), 11 February 1975. (Unpublished)

    McNamara, F.T. Radioactive residues of [14C] - Monitor in rotational
    1976      crops. Mobay Report No. 49656. 1 September 1976.
              (Unpublished)

    Morris, R.A., Delphia, L.M. and Murphy, J.J. The effect of processing
    1981      on residues of Monitor in peanuts.  Mobay Report No. 68649,
              2 March 1981. (Unpublished)

    Möllhof, Dr., Kochversuche mit Tameron-behandeten Wirsing and Tomaten;
    1978      Leverkusen, Bayerwerk, Dr. Mö/Kuj., RA-857, Bayer Ag
              Pflanzenschultz-Anwendungstechnik, Biologische Forschung,
              Institut Für Ruckstandsanalytik, 12 December 1978.
              (Unpublished)

    Murphy, J.J. and Morris, R.A. Residues of Monitor in rotational crops.
    1979      Mobay Report No. 68476, 3 August 1979. (Unpublished)

    Obrist, J.J. Leaching characteristics of aged monitor soil residues.
    1979      Mobay Report No. 68005, 5 July 1979. (Unpublished)

    Shaw II, H.R. Adsorption of Monitor by soils. Mobay Report No. 6849,
    1979      31 July 1981. (Unpublished)

    Stanley, C.W. A gas chromatographic method for the determination of
    1971      residues of Monitor in animal tissues and milk. Chemagro
              Report No. 31093. (Unpublished)


    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: 1982 evaluations)
       Methamidophos (Pesticide residues in food: 1984 evaluations)
       Methamidophos (Pesticide residues in food: 1985 evaluations Part II Toxicology)
       Methamidophos (Pesticide residues in food: 1990 evaluations Toxicology)