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    WHO Pesticide Residues Series, No. 1

    1971 EVALUATIONS OF SOME PESTICIDE RESIDUES IN FOOD

    THE MONOGRAPHS

    The evaluations contained in these monographs were prepared by the
    Joint Meeting of the FAO Working Party of Experts on Pesticide
    Residues and the WHO Expert Committee on Pesticide Residues that met
    in Geneva from 22 to 29 November 1971.1

    World Health Organization

    Geneva

    1972

                     
    1 Pesticide Residues in Food: Report of the 1971 Joint Meeting of
    the FAO Working Party of Experts on Pesticide Residues and the WHO
    Expert Committee on Pesticide Residues, Wld Hlth Org. techn. Rep.
    Ser., No. 502; FAO Agricultural Studies, 1972, No. 88.

    These monographs are also issued by the Food and Agriculture
    Organization of the United Nations, Rome, as document AGP-1971/M/9/1.

    FAO and WHO 1972


    1,2-DIBROMOETHANE

    This pesticide was evaluated at the Joint Meeting in 1965 (FAO/WHO
    1965c) and it was reviewed in 1966, 1967 and 1968 (FAO/WHO 1967b,
    1968b, 1969b). Previously it has been referred to as ethylene
    dibromide.

    Reference should be made to Appendix IV which includes Section 3 of
    the report on the 1971 Meeting (FAO/WHO 1972a), where general
    principles concerning the occurrence of residues of fumigants are
    discussed.

    RESIDUES IN FOOD AND THEIR EVALUATION

    Use pattern

    Post-harvest use on dry foodstuffs

    1,2-dibromoethane is rarely used alone except in certain small-scale
    treatments. Thus, in West Africa, gelatine capsules have been used to
    deliver small doses of 1,2-dibromoethane (5 ml, 10.8 g) in the
    treatment of individual bags of cereal or cereal products, each
    enclosed in a polythene bag.

    More commonly it is used in mixtures with other "liquid fumigants",
    such as 1,2-dichloroethane and carbon tetrachloride, for treating
    cereals in bins or in bulks on floors. Mixtures with methyl bromide
    are also used for this purpose, particularly in parts of India, where
    these mixtures may also be applied on products other than cereals.
    They are also used as "spot" fumigants for the treatment of individual
    items of machinery in milling plants.

    Other uses

    As indicated in previous monographs, the compound is also used for the
    treatment of soil before planting; also of certain fruits for
    quarantine purposes.

    Residues resulting from supervised trials

    The fumigant is sorbed strongly by cereal grains, cereal products or
    other produce during the exposure period and, even when normal airing
    procedures are followed, the residue of fumigant is dispersed very
    slowly. Nearly all the fumigant taken up is physically sorbed and at
    normal temperatures there appears to be only a very small reaction
    leading to the formation of inorganic bromide. On occasion, however,
    in produce at higher temperatures and moisture contents a rapid
    breakdown to inorganic bromide has been noted (Heuser et al., 1969).

    Interpretation of some of the early work is uncertain because the
    analytical procedures adopted did not effectively differentiate
    between inorganic and organic bromide. Heuser (1961) examined the
    conditions for recovery of unchanged 1,2-dibromethane from wheat and
    milled products and followed the slow diminution of residual fumigant
    during laboratory and field trials. When wheat containing 80 ppm of
    total bromide was removed from the upper layers of a bin 49 days after
    fumigation a large proportion of the residual bromide was in the form
    of unchanged fumigant and most of this was retained in the fractions
    on milling, particularly in the bran. Other workers confirm the
    concentration of the sorbed fumigant in the seed coat.

    The effect of processing of wheat treated with a fumigant mixture
    containing 3.5% by volume of 1,2-dibromoethane was studied in the
    Netherlands by Wit et al., (1969). Discrepancies between the results
    obtained by two participating laboratories using the same analytical
    procedure, involving steam distillation followed by
    gas-chromatography, make it difficult to summarize the results. After
    storage with some ventilation for six or more weeks the two
    laboratories reported amounts of ethylene dibromide in the wheat and
    processed products as follows.

                                                                

                             Laboratory A           Laboratory B
                                                                

    Wheat                       10-20                   5-13
    Flour                         4                      2
    Coarse and fine offals      18-23                    2
    White bread              0.002-0.003            0.018-0.040
    Wholemeal bread             0.006                0.12-0.16
                                                                

    In a subsequent collaborative study by these two laboratories flour
    was treated directly with 1,2-dibromoethane, aired thoroughly and
    baked into loaves. Good agreement was obtained in results showing
    residues of 20 to 24 ppm in the flour which were reduced to 0.33 to
    0.47 in the bread. In tests of a method of treating 200 lb lots of
    white maize with 5 ml of 1,2-dibromoethane applied from a gelatine
    capsule Heuser et al., (1969) found up to 50 ppm of unreacted fumigant
    in samples taken shortly after a seven-day exposure to the fumigant.
    This was reduced to approximately 15 ppm after free exposure to air
    for one week, but a sample in a sealed tin retained the original
    amount of 1,2-dibromoethane. The amount retained in the original bag,
    kept closed between samplings, fell progressively over a period of
    three months. Similar samples of maize containing around 30 ppm of
    unreacted 1,2-dibromoethane were prepared and cooked according to
    Ghanaian custom. In dough the amount of unreacted fumigant was reduced
    to 3 ppm and the amount in the cooked foods was less than 0.5 ppm.

    Fate of residues

    Using 1,2-dibromoethane labelled with bromine-82, Bridges (1956)
    showed that in spite of the high physical sorption of the fumigant by
    wheat and its slow rate of airing, the amount of chemical reaction
    between it and the wheat is very small at room temperature. The
    precise nature of the reaction was not determined but it appeared to
    occur mainly with the wheat protein. On heating wheat containing
    sorbed 1,2-dibromoethane for 30 minutes at 180C about one third or
    one half of this residue broke down to ethylene glycol and inorganic
    bromide and the remainder volatilized.

    Sorption of 1,2-dibromoethane by and reaction with various cereals and
    cereal constituents has been extensively investigated in Israel
    (Olomuchi and Bondi 1955, Bondi and Alumot 1966). It was shown that
    the presence of fat increased the sorption of 1,2-dibromoethane but
    not its reaction with the grains. The reaction was mainly with the
    protein fraction. From tests with different proteins it was concluded
    that the amount of reaction was little affected by their chemical
    composition but was in accordance with the extent of the initial
    sorption which depended upon the physical structure and condition of
    the protein.

    The biochemical effects of ingestion of 1,2-dibromoethane in chicks
    and rats has also been extensively investigated in Israel (Nachtomi,
    Alumot and Bondi, 1965, 1966, 1968). Nachtomi (1970) has recently
    studied the reaction with glutathione in vitro and in vivo.

    Methods for residue analysis

    Since unchanged 1,2-dibromoethane residues are of much greater
    toxicological significance than is ionic (inorganic) bromide, it is
    important that the two forms are distinguished by the analytical
    methods employed. Many methods hitherto employed for determining
    bromide residues arising from treatments with 1,2-dibromoethane have
    included both unchanged fumigant and the ionized bromide fraction in a
    total bromide figure. Such methods include those which employ a
    preliminary alkaline hydrolysis step followed by an ashing procedure,
    e.g. Sinclair and Crandall (1952) and also methods based on
    neutron-activation (Guinn and Polter, 1962) and X-ray fluorescence
    (Getzendaner, 1961).

    If dilute (2-5%) alcoholic potash is employed for hydrolysis, the
    1,2-dibromoethane molecule is split with volatilisation and loss of
    50% of the bromine as vinyl bromide, enabling some differentiation to
    be made if an alternative total hydrolysis step is also employed
    (Olomuchi and Bondi, 1955).

    Heuser (1961) found that the ionic bromide could be separated from the
    unchanged 1,2-dibromoethane in cereals by extraction with water after
    preliminary aeration. However, methods which rely on subtraction of
    one component from a total bromine figure to obtain the value for the
    second component are necessarily limited in sensitivity and accuracy.

    Bridges (1956) and Heuser (1961) found that adsorbed 1,2-dibromoethane
    could not be successfully removed from cereals, even when finely
    divided, with organic solvents such as ether, chloroform or methylene
    chloride, to allow differentiation from the insoluble ionic bromide,
    though Shrader et al., (1942) and Heuser and Scudamore (1970)
    successfully separated adsorbed methyl bromide from ionic bromide in
    this manner. This means that the total bromide methods mentioned above
    cannot be used with any confidence to determine the ionic bromide
    after attempting removal of the 1,2-dibromoethane in this way.

    Before the development of gas-chromatography techniques, methods for
    removal of residual 1,2-dibromoethane from citrus fruits and cereals
    were published (e.g. Kennet and Huelin, 1957; Mapes and Shrader, 1957)
    which included a steam distillation stop, after which the volatile
    organic bromide was decomposed by alkaline hydrolysis or by a
    catalytic method, and then determined as bromine. These and similar
    methods, whilst giving good recoveries of 1,2-dibromoethane added to
    substrates, failed to characterize the fumigant and would have
    included other volatile bromine compounds such as
    1-bromo-2-chloroethane or 1,2-dibromo-3-chloropropane in samples of
    unknown history.

    One early attempt at separation and characterization of the two forms
    of bromine was the method of Tanada, Matsumoto and Scheuer (1953) who
    distilled 1,2-dibromoethane from fresh fruits in a benzene extract,
    reacting the 1,2-dibromoethane in the distillate with potassium iodide
    and acetic acid to give potassium tri-iodide in quantitative amount,
    and also determined ionized bromide in the distillation residue.

    Gas-chromatographic methods

    In recent years gas-chromatographic methods have been developed which
    are capable of identifying fairly conclusively and determining with
    accuracy and high sensitivity amounts of 1,2-dibromoethane in solution
    (e.g. Bielorai and Alumot, 1966; Heuser and Scudamore, 1967, 1969).
    The choice of a method of extraction which will allow the removal of
    1-2-dibromoethane from the substrate efficiently and without chemical
    breakdown is therefore the major consideration in the application of
    this technique to the analysis of the residual fumigant.

    Heuser (1961) showed that even moderate heating of a dry cereal
    substrate containing adsorbed 1-2-dibromoethane rapidly caused its
    decomposition to water-soluble ionic-bromide; which suggested that
    methods for recovery of the unchanged fumigant involving heating
    should be avoided. Nevertheless, Bielorai and Alumot (1965)

    successfully adapted Kennet and Huelin's (1957) steam-distillation
    apparatus for the recovery of 1,2-dibromoethane to allow determination
    in the distillate by gas-chromatography. Malone (1969) compared this
    method and two other methods involving removal of 1,2-dibromoethane by
    heating, namely acid-reflux distillation (after Mapes and Shrader,
    1957) and sweep-codistillation using gas-chromatography with
    electron-capture detection as the determinative step. With spiked
    substrates, Malone found that sweep-codistillation was only partially
    effective in recovery of 1,2-dibromoethane and that the acid-reflux
    method gave slightly lower results than the Kennet-Ruelin technique.
    Percentage recovery figures were not obtained for any of these methods
    using previously fumigated samples.

    Heuser and Scudamore (1967, 1969) with a solvent extraction method at
    room temperature employing a 5:1 by volume mixtures of acetone and
    water or acetonitrile and water, obtained 98-100% recovery of known
    amounts of 1,2-dibromoethane from fumigated cereals, determined by
    gas-chromatography using flame-ionization and electron-capture
    detectors. These authors used a total recovery technique involving
    partial aeration to establish the amount of 1,2-dibromoethane
    remaining to be determined in the substrate, and also established the
    rate at which the fumigant residue was removed from it.

    Heuser and Scudamore (1970) later extended their method for the
    determination of residual 1,2-dibromoethane to the selective
    determination of ionic bromide by gas-chromatography. The ionic
    bromide was reacted with ethylene oxide in a specified solvent mixture
    to give ethylene bromohydrin in quantitative yield. 1,2-dibromoethane
    and methyl bromide were shown to remain intact under these conditions.
    The bromohydrin was determined by gas-chromatography with
    electron-capture detection, enabling the two forms of bromide residue
    to be determined in one operation, the ionic bromide with a limit of
    detection of 0.5 ppm and 1,2-dibromoethane with a limit of detection
    of 0.02 ppm. The procedures of Heuser and Scudamore therefore are
    preferred for residue analysis at this time.

    National tolerances (As reported to meeting)

    Residues of unreacted ethylene dibromide

    In the United States of America the following grains: barley, corn,
    oats, popcorn, rice, rye, sorghum (milo), wheat, are exempted from
    requirements. Canada and Australia similarly consider that there is no
    necessity for a tolerance on the grounds that the residue of the
    unchanged compound will disappear before the food reaches the
    consumer. Australia requires that residues of the unchanged compound
    must not be present in or upon foods as consumed.

    Residues of inorganic bromide

    Many countries have adopted tolerances for bromide in specified foods
    arising from a particular source, or from all sources. Some are
    defined in terms of inorganic bromide only, others as total bromide.
    The lists are too extensive to reproduce here. (But see Appendix IV
    for a discussion of the general significance of such residues).

    Appraisal

    Is used for the treatment of cereals in bins or in bulks on floors
    commonly in admixture with other "liquid fumigants" such as
    1,2-dichloroethane and carbon tetrachloride. The total post-harvest
    use outside the United States of America and India is probably small.
    Used in the treatment of fresh fruits and vegetables for quarantine or
    other purposes; also as a soil fumigant against nematodes and
    soil-borne insects.

    There is ample evidence, from supervised trials, that
    1,2-dibromoethane is strongly sorbed on foods. The residues of
    unchanged fumigant are only very slowly lost by aeration and under
    normal storage conditions the rate of loss by breakdown or reaction
    with food constituents is low so that the residues of unchanged
    fumigant persist for long periods and are not readily eliminated by
    processing, although they are normally destroyed by cooking or baking.
    At normal temperatures there is a small amount of reaction on wheat
    which appears to be with the proteins, with formation of inorganic
    bromide, but this reaction is much smaller than that of methyl bromide
    with wheat and, for this reason, the nature of the reaction appears
    not to have been studied. On heating, any residual unreacted fumigant
    breaks down to ethylene glycol and bromide ion.

    The residue of unchanged 1,2-dibromoethane is of more importance and
    concern than the residue of inorganic bromide. There is little
    information on the residues of unreacted fumigant occurring in
    commerce and most of the data on bromides refer to determinations of
    total bromine. Sometimes these determinations were made after
    extraction of the sample with non-aqueous solvent but it has been
    shown that this removes only part of the organic bromide.

    In the collection of residue data or in obtaining evidence for any
    regulatory action it is desirable to determine amounts of unreacted
    1,2-dibromoethane and of bromide ion separately and specifically.
    Analytical procedures are now available for both these determinations
    using gas-chromatography, enabling bromide ion to be determined with a
    limit of detection of 0.5 ppm and 1,2-dibromoethane with a limit of
    detection of 0.02 ppm and with 0.1 ppm as a reliable limit of
    determination for regulatory purposes.

    From the available information on the occurrence of unreacted
    1,2-dibromoethane in or on raw cereals or cereal products after
    fumigation in accordance with good practice it appears that the
    following amounts need not be exceeded and it is recommended that
    these residue levels be used as guidelines.

         In raw cereals at point of entry into a country
         or when supplied for milling, provided that the
         commodity is freely exposed to air for a period
         of at least 24 hours after fumigation before
         sampling                                              20 ppm

         In milled cereal products which will be
         subjected to baking or cooking                         5 ppm

         In bread and other cooked cereal products
         (i.e. at or about the present limit of
         determination)                                       0.1 ppm

    Insufficient information is available on the residues of unchanged
    1,2-dibromoethane occurring in fresh fruits and vegetables fumigated
    with this compound for quarantine or other purposes to permit similar
    practical limits for these foods to be proposed.

    Even though the content of bromide ion per se resulting from
    fumigation of food with 1,2-dibromoethane may be small and may be
    considered of minor importance, nevertheless, in order to guard
    against the excessive use of this or other brominated fumigants it is
    recommended that the previously recommended tolerance of 50 ppm of
    bromide ion in raw cereals should stand.

    It is recommended that temporary tolerances previously recommended for
    residues of bromide ion in other foods should be suspended (see
    Report).

    Further work desirable

    1.   Further data on residues of unchanged 1,2-dibromoethane occurring
         in foods in commercial practice including data for fresh fruits
         and vegetables.

    2.   Further information on the nature and amount of the reaction
         products of 1,2-dibromoethane in cereals and in a selection of
         other foods.

    REFERENCES

    Alumot, E. and Bielorai, R. (1969) Residues of fumigant mixture in
    cereals fumigated and aired at two different temperatures. J. Agric.
    Food Chem., 17: 869

    Bielorai, R. and Alumot, E. (1965) Determination of ethylene dibromide
    in fumigated feeds and foods by gas-liquid chromatography. J. Sci.
    Food Agric., 16: 594-596

    Bielorai, B. and Alumot, E. (1966) Determination of residues of a
    fumigant mixture in cereal grain by electron-capture
    gas-chromatography. J. Agric. Food Chem., 14: 622

    Bondi, A. and Alumot, E. (1966) Effect of ethylene dibromide fumigated
    feed on animals. Final report of research conducted under grant
    authorized by United States Public Law 480

    Bondi, A. and Alumot, E. (1971) As reported by Kenaga, E. E., 1971,
    IUPAC Meeting

    Bridges, R. G. (1956) The fate of labelled insecticide residues in
    food products. V. The nature and significance of ethylene dibromide
    residues in fumigated wheat. J. Sci. Food Agric., 7: 505-313

    Conroy, M. W., Munsey, V. E. and Ramsey, L. L. (1957) Total volatile
    organic halide determination of aggregate residue of carbon
    tetrachloride, ethylene dichloride, and ethylene dibromide in
    fumigated cereal products. 2. Ethanolamine-sodium reduction procedure.
    J. Assoc. Offic. Agric. Chem., 40: 185-189

    Getzendaner, M. E. (1961) Bromide residues in cereal products
    resulting from experimental fumigations with methyl bromide. Cereal
    Sci. Today, 6: 268-270

    Heuser, S. G. (1961) Residues in wheat and wheat products after
    fumigation with ethylene dibromide. J. Sci. Food Agric., 12: 103-115

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

    Heuser, S. G., Goodship, G. and Duffin, P. (1968) Residues of ethylene
    dibromide on samples of maize and prepared foods. Pest Infestation
    Research, 1968. Agricultural Research Council, London

    Heuser, S. G. and Scudamore, K. A. (1969) Determination of fumigant
    residues in cereals and other foodstuffs: a multidetection scheme for
    gas-chromatography of solvent extracts. J. Sci. Food Agric.,
    20: 565-572

    Heuser, S. G. and Scudamore, K. A. (1970) Selective determination of
    ionized bromide and organic bromides in foodstuffs by gas-liquid
    chromatography with special reference to fumigant-residues. Pesticide
    Sci., 1: 244-249

    Kennet, B. H. and Huelin, F. E. (1957) Determination of ethylene
    dibromide in fumigated fruit. J. Agric. Food Chem., 5: 201

    Kolthoff, I. M. and Yutzy, M. (1937) Volumetric determination of
    bromide after oxidation to bromate in the presence of much chloride.
    Ind. Eng. Chem. (Anal. Edn.), 9: 75

    Lindgren, D. L., Sinclair, W. B. and Vincent, L. E. (1968) Residues in
    raw and processed foods resulting from post-harvest insecticidal
    treatments. Residue Review, 21: 1-121

    Lynn, G. E. and Vorkes, F. A. (1957) Symposium: Residues in foods and
    feeds resulting from fumigation of grains with the commoner liquid
    formulations of carbon disulfide carbon tetrachloride, ethylene
    dichloride, and ethylene dibromide. J. Assoc. Offic. Agric. Chem.,
    40: 163-209

    McMahon, B. Malone. (1971) Analysis of commercially fumigated grains
    for residues of organic fumigants. J. Assoc. Offic. Agric. Chem.,
    54: 964-965

    Malone, B. (1969) Analysis of grains for multiple residues of organic
    fumigants. J. Assoc. Offic. Analyt. Chem., 52: 800-805

    Malone, B. (1970) Method for determining multiple residues of organic
    fumigants in cereal grains. J. Assoc. Offic. Analyt. Chem.,
    53: 742-746

    Mapes, D. A. and Shrader, S. A. (1957) Determination of total and
    inorganic bromide residues in fumigated products. J. Assoc. Offic.
    Agric. Chem., 40: 189-191

    Nachtomi, E. (1971) The metabolism of ethylene dibromide in the rat.
    The enzymic reaction with glutathion in vitro and in vivo.
    Biochem. Pharmac., 19: 2853-2860

    Nachtomi, E., Alumot, E. and Bondi, A. (1965) The metabolism of
    ethylene dibromide and related compounds in the rat. Israel J. Chem.,
    3: 119

    Nachtomi, E., Alumot, E. and Bondi, A. (1966) The metabolism of
    ethylene dibromide in the rat. Identification of detoxification
    products in urine. Israel J. Chem., 4: 239-246

    Nachtomi, E., Alumot, E. and Bondi, A. (1968) Biochemical changes in
    organs of chicks and rats poisoned with ethylene dibromide and carbon
    tetrachloride. Israel J. Chem., 6: 803-811

    Olomucki, E. and Bondi, A. (1955) Problems connected with ethylene
    dibromide fumigation of cereals. 1. Sorption of ethylene dibromide by
    grain. J. Sci. Food Agric., 6: 592-600

    Shrader, S. A., Beshgetoor, A. W. and Stenger, U. A. (1942)
    Determination of total and inorganic bromide in goods fumigated with
    methyl bromide. Ind. Eng. Chem. (Anal. Edn.), 14: 1-4

    Sinclair, W. B. and Crandall, P. R. (1952) Determination of ethylene
    dibromide in liquid and gas phases by the use of monoethanolamine.
    J. Econ. Ent., 45: 80

    Tanada, A. F., Matsumoto, H. and Scheuer, P. J. (1953) J. Agric. Food
    Chem., 1: 452

    Wit, S. L. (1968) Residues of insecticides in cereals and related
    products incorporated in the Netherlands, 1964/66. Report No. 17/68
    Tox. (CCPR 68/2 Report)

    Wit, S. L., Besemer, A. F. H., Das, H. A., Goedkoop, W., Loosjes, F.
    E., and Meppelink, E. R. (1969) Results of an investigation on the
    regression of three fumigants (carbon tetrachlorine, ethylene
    dibromide and ethylene dichloride) in wheat during processing to
    bread. Report No. 36/69
    


    See Also:
       Toxicological Abbreviations
       Dibromoethane, 1,2- (EHC 177, 1996)