WHO/FOOD ADD/71.42



    Issued jointly by FAO and WHO

    The content of this document is the result of the deliberations of the
    Joint Meeting of the FAO Working Party of Experts and the WHO Expert
    Group on Pesticide Residues, which met in Rome, 9-16 November, 1970.



    Rome, 1971



    This pesticide was evaluated by joint meetings in 1965, 1966 and 1967
    (FAO/WHO 1966b, 1967b and 1968b).

    On the latter occasion temporary tolerances for three classes of
    fruits and vegetables were recommended, the latter being for a
    combination of dimethoate and its oxygen analog, now known as
    omethoate. Further work was required before 30 June 1970 on the fate
    of the compound during processing and preparation for consumption and
    on residues appearing in total diet studies.


    Analysis of fresh fruit and vegetables, obtained from field trials in
    northern Italy and flown with due precautions to Helsinki, were made
    at the Institute of Food Chemistry and Technology (Koivistoinen,
    1970). Information concerning rates and dates of application of
    dimethoate, and of harvest dates, is given in Table 1. The samples
    were stored at -20°C and analysed within five days by a method
    employing gas chromatography with a phosphorous sensitive detector.
    The lowest level detectable (LLD) was 0.02 ppm for either dimethoate
    or omethoate, recovery at such levels being 90 percent. Other samples
    taken at harvest were processed in Italy by normal commercial
    procedures, and later analysed in a similar way. The processing
    treatment(s), and the residues of dimethoate and omethoate found both
    for the fresh and the processed commodities, are given in Table II.

    All forms of processing reduce the level of dimethoate and omethoate;
    the latter is always present at a much lower level than the parent

    It is worth noting that Lee (1968) has published data showing that
    residues of dimethoate on commercially sprayed green peas and lettuce
    did not exceed 0.24 and 0.8 ppm at 2 and 9 days harvest intervals,

    Total diet samples, each consisting of 7 sub-samples (cereals, meat
    and fish, fats, fruit and preserves, root vegetables, green
    vegetables, milk), were collected over a 12 month period in England
    and Wales, and analysed for organophosphorous pesticide residues by a
    gas chromatographic procedure using a phosphous-sensitive detector
    (Abbott et al., 1970). Neither dimethoate nor omethoate was detected
    in any sample. Duggan and Lipscomb (1969) did not find dimethoate or
    omethoate in any class of food during four years' studies of total
    diets in the U.S.A.

        TABLE I

    Data on dimethoate application

                                                          Interval between
                        Concn.a.i.      No. of times      final application
    Crop                %               sprayed           and harvest (days)

    Tomatoes            0.04                2                      7

    Peas, garden        0.04                2                      6

    Beans, green        0.04                2                      6

    Carrots             0.04                2                      7

    Peppers             0.04                2                      7

    Cherries            0.02                1                      10

    Oranges             0.05                3                      10

    Pears               0.04                3                      10

    Peaches             0.04                2                      10

    Spinach             0.04                2                      6

    Cabbage, Savoy      0.05                2                      7

    Artichokes          0.04                2                      7


    Dimethoate and omethoate residues in fresh and processed commodities

    Commodity                     Dimethoate      Omethoate        Total
                                  (ppm)           (ppm)            (ppm)

    Tomatoes, fresh
    washed 2 min.                 <LLD            <LLD             <LLD
    (egg-shaped) peeled

    Peas, fresh                   <LLD-0.1        <LLD             <LLD-0.1
       canned                     <LLD            <LLD             <LLD

    TABLE II (cont'd)

    Dimethoate and omethoate residues in fresh and processed commodities

    Commodity                     Dimethoate      Omethoate        Total
                                  (ppm)           (ppm)            (ppm)

    Beans, fresh                  0.2-0.3         0.04-0.1         0.24-0.4
       canned                     <LLD            <LLD             <LLD

    Carrots, fresh                <LLD            <LLD             <LLD
       canned                     <LLD            <LLD             <LLD

    Peppers, fresh                0.38-0.58       0.16-0.26        0.58-0.84
       canned                     <LLD-0.04       <LLD             <LLD-0.06

    Cherries, fresh               0.55-0.85       0.2              0.8-1
       canned (with syrup)        0.36-0.5        0.07-0.13        0.45-0.63

    Oranges, fresh(unpeeled)      1.2-1.5         <LLD             1.2-1.5
       canned juice               0.24-0.32       <LLD             0.24-0.32
       marmalade                  0.02-0.04       <LLD             0.02-0.04

    Pears, fresh                  0.44-0.70       0.1-0.2          0.55-0.9
       canned                     0.17-0.23       0.02-0.04        0.2-0.24

    Peaches, fresh                0.23-0.4        <LLD             0.23-0.4
       canned halves(in syrup)    0.07-0.33       <LLD             0.08-0.33
       jam                        0.05-0.06       <LLD             0.05-0.06

    Spinach, fresh                2.24-3.08       0.1-0.16         2.34-3.24

    Cabbage (savoy), fresh        0.57-0.84       <LLD             0.57-0.84

    Artichoke, fresh              0.48-1.05       0.1-0.3          0.62-1.36

    NOTE:  Lowest level detectable (LLD) was 0.02 ppm.
    The report from Storherr and Watts (1969) that the initial ratio of
    1:20 for dimethoate and omethoate, following the spraying of
    dimethoate on kale, changed after fourteen days to 4:1 must be taken
    to indicate a different pattern of metabolism in this crop from that
    leading to the results quoted above for other vegetables and for

    Beck et al. (1968) fed silage made from dimethoate-treated corn to
    cows and found no trace of dimethoate or omethoate in the milk. But
    when capsules containing 1 mg/kg dimethoate and 0.1 mg/kg omethoate
    were fed to three cows for fourteen days, the level of omethoate in
    the milk varied from 0.004 to 0.125 ppm, although no dimethoate was


    Among new methods of residue analysis using gas chromatography, that
    described by Abbott et al. (1970) should be adequate for regulatory
    purposes for the tolerances recommended.


    Analyses of vegetables and fruits treated with dimethoate according to
    recommended practice in northern Italy have shown that fresh tomatoes
    and tomato products and fresh or canned carrots contained no
    detectable residues of dimethoate or its oxygen analogue, omethoate.
    Residues of dimethoate present at harvest in garden peas, green beans,
    peppers, spinach, cabbage, artichokes, cherries, pears, peaches and
    oranges were reduced by processing to levels well below those
    recommended in the '1967 Evaluations of some pesticide residues in

    Total diet studies in the U.S.A. and in England and Wales have shown
    that neither dimethoate nor omethoate were detected. The two items of
    further work required by 1970 have therefore been adequately met.

    As the A.D.I. set in 1967 (FAO/WHO, 1968) was not temporary, and as
    the total diet studies show that this A.D.I. is not being exceeded,
    the tolerances recommended in 1967 on a temporary basis can now be
    regarded as acceptable tolerances for dimethoate and omethoate
    combined. The tolerances are:

                      Tree fruits (including citrus)          2 ppm
                      Tomatoes and peppers                    1 ppm
                      Other vegetables                        2 ppm

    The only commodity with a significantly higher residue than that
    reported in the earlier monograph (FAO/WHO, 1968b) is spinach, and in
    this case the harvest interval was much shorter than before.

    Other samples of the spinach, savoy cabbage, and artichokes were
    subjected to cooking in salt water for suitable periods and analysed
    for dimethoate only (Table III).


    Dimethoate residues in cooked vegetables

                        Dimethoate                         Dimethoate
    Vegetable           (ppm)          Vegetable           (ppm)

    Spinach, fresh      = 2.23-2.92    cooked 10 min.      = 0.52-0.70

    Savoy cabbage,      = 0.23-0.31    cooked 30 min.      = 0.11-0.14

    Artichokes, fresh   = 0.3-0.48     cooked 30 min.      = 0.27-0.32


    Abbott, D.C., Crisp, S., Tarrant, K.R. and Tatton, J.O'G. (1970)
    Pesticide residues in the total diet in England and Wales, 1966-1967.
    III. Organophosphorous pesticide residues in the total diet. Pestic.
    Sci., 1: 10-13

    Beck, E.W., Johnson, J.C., Jnr., Getz, M.E., Skinner, F.B., Dawsey,
    L.H., Woodham, D.W., and Derbyshire, J.C. (1968) Effects of feeding
    dimethoate, its oxygen analog, and dimethoate treated silage to
    cattle. J. econ. Ent., 61: 605-610

    Duggan, R.E., and Lipscomb, G.Q. (1969) Dietary intake of pesticide
    chemicals in the United States (II), June 1966 - April 1968.
    Pesticides Monit. J., 2 (4): 153-162

    Koivistoinen, P. (1970) Report on dimethoate and dimethoxon residues
    in fresh and processed fruits and vegetables. Institute of Food
    Chemistry and Technology, Helsinki, Finland. 15 p.

    Lee, D.F. (1968) Pesticide residues in foodstuffs in Great Britain.
    VII. Demeton-methyl and dimethoate residues in Brussels sprouts,
    lettuce, green peas and French beans, potatoes and strawberries. J.
    Sci. Fd Agric., 19: 451-453

    Storherr, R.W., and Watts, R.R. (1969) Gas chromatographic
    determination of residues of dimethoate and its oxygen analog in
    field-sprayed kale. J.A.O.A.C., 52: 511-513

    See Also:
       Toxicological Abbreviations
       Dimethoate (EHC 90, 1989)
       Dimethoate (HSG 20, 1988)
       Dimethoate (ICSC)
       Dimethoate (FAO Meeting Report PL/1965/10/1)
       Dimethoate (FAO/PL:CP/15)
       Dimethoate (FAO/PL:1967/M/11/1)
       Dimethoate (JMPR Evaluations 2003 Part II Toxicological)
       Dimethoate (Pesticide residues in food: 1983 evaluations)
       Dimethoate (Pesticide residues in food: 1984 evaluations)
       Dimethoate (Pesticide residues in food: 1984 evaluations)
       Dimethoate (Pesticide residues in food: 1987 evaluations Part II Toxicology)
       Dimethoate (Pesticide residues in food: 1996 evaluations Part II Toxicological)