FAO/PL:1967/M/11/1
    WHO/Food Add./68.30

    1967 EVALUATIONS OF SOME PESTICIDE RESIDUES IN FOOD

    THE MONOGRAPHS

    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
    Committee on Pesticide Residues, which met in Rome, 4 - 11 December,
    1967. (FAO/WHO, 1968)

    FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
    WORLD HEALTH ORGANIZATION
    Rome, 1968

    METHYL BROMIDE

    This pesticide was evaluated by the 1966 Joint Meeting of the FAO
    Working Party and the WHO Expert Committee on Pesticide Residues
    (FAO/WHO, 1967). Since the previous publication, the results of
    additional experimental work have been reported. This new work is
    summarized and discussed in the following monograph addendum.

    EVALUATION FOR TOLERANCES

    USE PATTERN

    Pre-harvest treatments

    In addition to the previously described uses, methyl bromide may be
    used as a soil fumigant for nematode control.

    RESIDUES RESULTING FROM SUPERVISED TRIALS

    Bockman et al (1967) have reviewed the inorganic content of foodstuffs
    due to soil treatment with fumigants. Whilst they determined residues
    arising in this fashion in crops grown on experimental plots, some
    details of which are described in the accompanying supplementary
    monograph on ethylene dibromide, fumigation treatments did not include
    the use of methyl bromide. Getzandaner et al (1967) have shown that
    virtually no bromide residues occur in cane sugar, macaroni, margarine
    or butter following fumigation with methyl bromide and suggest that
    this indicates that methylation does not readily occur in these
    products.

    FATE OF RESIDUES

    General considerations

    The nature of terminal residues arising from the use of methyl bromide
    and other fumigants was reviewed by the IUPAC Commission on Terminal
    Residues (IUPAC, 1967b). The need to extend trace studies for methyl
    bromide residues from wheat to other commodities such as cocoa and
    rice was indicated; and for all of these it was desirable that the
    methyl as well as the bromide half of the molecule should be followed.
    The Commission also stressed the need for a method of analysis
    sensitive to 0.1 p.p.m. of unchanged methyl bromide in order further
    to evaluate the levels of this in food as consumed, especially insofar
    as this might indicate that no residues other than (a) unchanged
    methyl bromide and (b) inorganic bromide might be present as the
    result of methyl bromide treatment.

    The following note was prepared for the IUPAC meetings in August 1967
    in reply to the question: what are the methyl bromide residues in
    fumigated commodities (IUPAC, 1967b)?

    Methyl bromide undergoes the typical reactions of an alkyl halide.
    Inorganic bromides are formed by hydrolysis and are naturally present
    in many unfumigated foods where they are well tolerated by man.
    Methanol, the other product of hydrolysis, also occurs in small
    quantities. Typical reactivity includes methylation of OH, NH and SH
    bonds of amino acids and other proteins and SH groups of some enzymes.
    Among the alkylated derivates are N-methyl nicotinamide, methionine
    sulfonium methyl bromide, S-methyl-1-methyl histidine. Some
    esterification of carboxyl esters are also thought to occur. It
    appears that such methylations do not block essential metabolism and
    often are readily reversible. Lynn (1955) has summarized the
    literature up to 1955. Getzendaner, et al (1967) have shown that
    certain food materials such as cane sugar, macaroni, oleomargerine and
    butter pick up essentially no bromide residue following fumigation
    with methyl bromide, indicating no reaction with certain sugars,
    starches and fats, suggesting possibly that methylation is not readily
    accomplished in these commodities. These data also give support to the
    position that methyl bromide is rapidly and completely dissipated from
    fumigated commodities. Residues are modified by many physical and
    chemical factors related to the commodity such as exposure surface to
    volume ratio, solubility in the commodity, water content etc.
    Temperature, length of exposure, degree of aeration, variable
    analytical techniques, all make consistent correlation of bromide
    residues with given nutrient portions of food difficult to ascertain.
    Providing an analytical method is developed with sensitivity to 0.01
    to 0.1 ppm it is suggested that a working party be formed to further
    elucidate the methyl bromide residues in a select list of commodities
    representing the major classes of foodstuffs.

    METHODS OF RESIDUE ANALYSIS

    In reviewing methods of analysis for unchanged residues arising from
    the use of methyl bromide (and ethylene dibromide) earlier in 1967,
    the IUPAC Commission on Residue Analysis also drew attention to the
    possibility that small residues of modified (and possibly more toxic)
    compounds might not be detected by such methods (IUPAC, 1967a). The
    Commission recognized, however, the desirability of studies on the
    recovery of methyl bromide from treated products [using gas
    chromatographic techniques for the unchanged fumigant and by
    established methods for the increase in inorganic bromide arising from
    fumigation]. In its review the Commission also made special reference
    to the progress of work on multidetection systems for unchanged
    residues from mixed fumigants, including the work of Heuser and
    Scudamore (1967) on the extractions from flour and ground and whole
    wheat of mixtures containing methyl bromide with cold 5:1 v/v
    acetone-water.

    NATIONAL TOLERANCES

    While there are no tolerances for residues of unchanged methyl
    bromide, tolerances for inorganic bromide resulting from the use of
    methyl bromide (whether or not in conjunction with ethylene dibromide)
    have been published in the U.S. Federal Register (1966) as follows :

         dried egg, processed herbs, spices           400 ppm

         barley, corn, milo (sorghum)
         rice, rye, wheat flours                      125 ppm

    RECOMMENDATIONS FOR TOLERANCES

    No change from previous recommendations (FAO/WHO, 1967)

    FURTHER WORK

    Further work desirable

    Previous considerations have been on the basis of an acceptable daily
    intake of 1 mg/kg of inorganic bromide. Tolerances proposed at the
    previous meeting (FAO/WHO, 1967) have since been considered at the
    Second Session of the Codex Committee on Pesticide Residues (CCPR,
    1967).

    Almost all the measurements for methyl bromide residues in treated
    produce relate to inorganic bromide levels and not specifically to
    unchanged methyl bromide fumigant. The general significance of results
    obtained in this way summarized in the monograph published in 1965
    (FAO/WHO, 1965): residues, which are highest in oily or fatty
    materials, are relatively easily removed by aeration of the treated
    produce though some conversion to fixed inorganic bromide together
    with protein binding does occur. The application of gas chromatography
    to the determination of unchanged residues of methyl bromide in
    treated commercial produce is most desirable. Limited results for
    commercial shipments of wheat were reported in the monograph published
    in 1967 (FAO/WHO, 1967): no unchanged methyl bromide was detected in
    any of 227 shipments using a method of analysis sensitive to 0.1
    p.p.m. (A similar result was found for 99 other samples). No
    corresponding information appears to be available for commercial
    consignments of other produce such as rice, cocoa, spices and dried
    fruits.

    REFERENCES PERTINENT TO EVALUATION FOR TOLERANCES

    Beckman, H., Crosby, H.C., Allen, P.T. and Mourer, C. (1967) The
    inorganic bromide content of foodstuffs due to soil treatment with
    fumigants. J. Food Sci.32:138-140

    CCPR. (1967) Report of the Second Session of the Codex Committee on
    Pesticide Residues. SP 10/115

    FAO/WHO. (1965) Evaluation of the hazards to consumers resulting from
    the use of fumigants in the protection of food. FAO Meeting Rept.
    PL/1965/10/2;WHO/Food Add./28/65.

    FAO/WHO. (1967) Evaluation of some pesticide residues in food. FAO,
    PL: CP/15;WHO/Food Add./67.32

    Getzandaner, M.E., Doty, A.E., McLaughlin, E.L. and Lindgren, D.L.
    (1967)  Bromide residues from methyl bromide fumigation of food
    commodities. (Quoted in 1967 IUPAC Commission on Terminal Residues
    Proceedings, Appendix VIII).

    Heuser, S.G., and Scudamore, K.A., (1967) Determination of ethylene
    chlorohydrins, ethylene dibromide and other volatile fumigant residues
    in flour and whole wheat. Chem. Ind.: 1557 - 1560

    IUPAC. (1967a) Commission on Residue Analysis: Proceedings of the
    Meetings held in Vienna, Appendix XV

    IUPAC. (1967b) Commission on Terminal Residues: Proceedings of the
    Meetings held in Vienna, Appendix VIII

    Lynn, G.E. (1965) A review of methyl bromide fumigations with respect
    to methylation of naturally occurring compounds. The Dow Chemical
    Company, Midland, Michigan. Unpublished manuscript. June, 1955.

    U.S. Federal Register, (1966) 1 October 
    

    See Also:
       Toxicological Abbreviations
       Methyl Bromide (EHC 166, 1995)
       Methyl bromide (ICSC)
       Methyl bromide (PIM 340)
       Methyl bromide (FAO Meeting Report PL/1965/10/2)
       Methyl bromide (FAO/PL:CP/15)
       Methyl bromide (FAO/PL:1968/M/9/1)
       Methyl bromide (WHO Pesticide Residues Series 1)
       Methyl Bromide (IARC Summary & Evaluation, Volume 71, 1999)