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