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    PESTICIDE RESIDUES IN FOOD - 1979


    Sponsored jointly by FAO and WHO






    EVALUATIONS 1979





    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, 3-12 December 1979



    1,2-DIBROMOETHANE

    Explanation

    This fumigant pesticide was evaluated in 1965 and reviewed in 1966,
    1967 and 1968.  It was re-evaluated in 1971.  Prior to 1971 it was
    listed as ethylene dibromide.

    The report of the 1978 Meeting made reference to problems caused in
    member countries of FAO and WHO and recommended re-evaluation of
    1,2-dibromoethane.

    RESIDUES IN FOOD AND THEIR EVALUATION

    The report of the 1971 Meeting contained a statement of general
    principles relating to residues of fumigants, to which reference
    should be made.

    USE PATTERN

    1,2-dibromoethane is used extensively as a pre-planting soil fumigant
    and also as a post-harvest fruit and stored product fumigant.  It has
    been estimated that some five million pounds of the fumigant was used
    in US agriculture in 1976 (Great Lakes Chemical Corp. 1977).  Of this
    about one third was employed in non-food crop culture, the remainder
    predominantly in soil nematode control in food crop culture, with a
    relatively small proportion used in post harvest bulk cereal and fruit
    fumigation.

    A small use has been in the dosing of individual sacks of grain in
    developing countries for stored product pest control.  Because of its
    persistence in cereal grains, its use has been discouraged for cereal
    fumigation in some countries.  A rebuttable presumption against
    re-registration of pest control products containing 1,2-dibromoethane
    was issued in the United States in 1977.

    Pre-harvest Use

    1,2-dibromoethane is widely applied as a soil fumigant for nematode
    control on plots used in fruit tree culture e.g. pineapples (Milne,
    1973, Webster and Keetch, 1975) and for a variety of other crops such
    as groundnuts, sorghum, millet, tomatoes and potatoes (Newton and Toth
    1952).

    Post-harvest Use

    1,2-dibromoethane is used as a stored bulk-grain fumigant, mainly as a
    component of mixtures containing carbon tetrachloride and ethylene
    dichloride or carbon disulphide.  In India and Africa, where high
    ambient temperatures render its high boiling point (131C) less of a
    disadvantage, it has been used alone for treating small quantities of
    commodities and in India mixed with methyl bromide as a bulk grain

    fumigant.  There is also a minor use of liquid fumigants containing
    1,2-dibromoethane in `spot' fumigation of foci of infestation in
    milling machinery.

    A further considerable use of the fumigant is in treating harvested
    fruit and vegetables e.g. citrus, mangoes, papaw, passion fruit
    against fruit fly larvae (Hargreaves et al., 1978; Singh et al,
    1979; Alumot et al., 1965).  It may be applied as a vapour or by
    dipping fruit in dilute solutions of 1,2-dibromoethane.

    RESIDUES RESULTING FROM SUPERVISED TRIALS

    Pre-harvest Use

    When 1,2-dibromoethane is applied to soil by injection or spraying,
    the fumigant not lost by vaporisation gradually hydrolyses to yield
    inorganic bromide (bromide ion).  However, even when plants have been
    grown in soil still containing free 1,2-dibromoethane, no unchanged
    fumigant was detected in 15 different types of crop using an
    analytical method capable of detecting 0.01 mg/kg (Great Lakes
    Chemical Corp., 1977).

    On the other hand, a correlation between the amount of bromide ion in
    the soil arising from 1,2-dibromoethane application and the bromide
    content of crops has been observed as with bromomethane usage as a
    soil fumigant (Brown and Jurinak, 1958).  Similar considerations
    therefore apply on the amounts of bromide ion in food plants arising
    from soil fumigation with either of these fumigants (see also
    Monograph on Bromomethane, loc. cit.).

    Post-Harvest Use - Cereals

    Studies on the retention of 1,2-dibromoethane by wheat after
    fumigation and the subsequent fate of residues on milling and baking
    and on preparation of African fermented food products, were reviewed
    by the meeting in 1971.  Further studies have since been completed.

    Berck (1974) reported on residue levels of 1,2-dibromoethane in wheat
    fumigated in a 27 ton bin with a 63:30:7 w/w mixture of carbon
    tetrachloride, 1,2-dichloroethane and 1,2-dibromoethane (Dowfume EB5)
    at 4 gals/1000 bu. (0.661/tonne).  Residues of 1,2-dibromoethane in
    flour, bran, middlings and bread were also determined.  Wheat was
    taken from the bin for these determinations at intervals of 3 days to
    7 weeks after fumigant application.  Residues reported ranged from
    0.05 to 3.3 mg/kg in the wheat, from 0.01 to 0.29 mg/kg in the flour,
    from 0-0.4 mg/kg in bran and from 0-0.30 mg/kg in middlings.  No
    residual fumigant was found in bread baked from composite flour
    samples prepared from wheat drawn from the bin over the period of the
    experiment.  The maximum amounts found by Berck in the wheat only
    three days after application are however only of the order of 1/10th
    to 1/100th of the levels found by other workers at similar dosage
    levels (Jagielski et al., 1978; Beilorai and Alumot 1975; Wit et

    al., 1969; Heuser 1961).  Since the rate of application of
    1,2-dibromoethane in the mixture used by Berck was equivalent to about
    100 mg/kg, these residue figures may be questioned.

    Jagielski et al (1978) determined residual 1,2-dibromoethane in
    wheat and maize in chamber and model silo treatments, which were
    followed by controlled aeration of cereal samples.  In the silo
    experiments, in which the liquid 1,2-dibromoethane was applied to the
    grain surface at 0.041/tonne in admixture with carbon tetrachloride to
    simulate commercial practice, 1,2-dibromoethane residues in maize
    ranged from 450 mg/kg at the surface one day after application to 0.5
    mg/kg after 90 days airing of samples from the base of the silo.
    Corresponding residue figures for wheat treated at the same dosage
    level ranged between 270 and 0.01 mg/kg.  6.7 mg/kg was found in
    wholemeal bread baked from wheat containing 419 mg/kg
    1,2-dibromoethane after a particularly heavy fumigant exposure, but
    only 0.08 mg/kg was found in white bread baked from wheat containing
    33 mg/kg (flour 10 mg/kg).  Amounts of bromide ion in bread made from
    the fumigated wheat exceeded that in controls by 5-14 mg/kg,
    suggesting almost complete chemical breakdown of residual
    1,2-dibromoethane during the white bread-making process.  Jagielski
    et al. (1978) concluded that, provided that residue levels of
    1,2-dibromoethane in wheat were below the then current FAO/WHO
    guideline level of 20 mg/kg at the time of processing into bread, the
    final residue in white bread would not exceed 0.1 mg/kg or 0.5 mg/kg
    in wholemeal bread.  This latter level corresponds closely to that
    found in the African fermented maize products aflata and kenkey by
    Heuser et al. (1969) after individual maize bag treatments with 1,2-
    dibromoethane.  Jagielski et al. (1978) considered that after normal
    fumigation procedures, about 7-14 days free airing of raw cereals
    would be required to reduce residual 1,2-dibromoethane to below the
    guideline level.  Sidhu et al. (1975) determined 1,2-dibromoethane
    residues in whole and milled wheat fractions after fumigating wheat at
    65 or 325 mg per litre (applied) for 23 days at 37C.  After these
    very heavy dosages they found 1,2-dibromoethane residues ranging from
    84-270 mg/kg in whole wheat immediately after fumigation to 25-105
    mg/kg after 8 days free aeration.  On milling the aerated wheat, the
    milled fractions were found to contain: flour 10-40; shorts 33-96;
    bran 51-153 mg/kg and it was estimated that losses from the wheat on
    milling were from 18-38%.

    Amuh (1975) determined free and bound 1,2-dibromoethane in maize after
    laboratory exposure to 14C-labelled fumigant.  He found that about
    six weeks was required to remove volatilizable 1,2-dibromoethane from
    the maize but that the unchanged fumigant content continued to reduce
    up to 14 weeks after application and about 40% remained chemically
    bound to the grain after this period.

    Post-Harvest Use - Fruit and Vegetables

    Hargreaves et al. (1978) fumigated capsicum, cucumber, mangoes,
    papaw, passion fruit, pumpkin and zucchini at vapour concentrations
    ranging from 16-48g per m3.  They both found inorganic bromide and

    free 1,2-dibromoethane in the edible portion of the commodities.
    192-dibromoethane residues averaging 10-20 mg/kg immediately after
    fumigation were reduced to below 0.5 mg/kg within seven days at the
    commercially recommended dosage level.  Bromide ion (inorganic
    bromide) levels due to the treatments did not exceed 12 mg/kg.

    Alumot et al. (1965) determined free and bound 1,2-dibromoethane in
    grapefruit and oranges, and in peaches, raisins, dates and figs at
    intervals up to 14 days after fumigation.  In treatments at commercial
    levels, increases in bound bromine did not exceed 4 mg/kg, levels
    remaining stable on airing.  No free, 1,2-dibromoethane was found in
    the pulp of oranges or grapefruit seven days after fumigation at 17 g
    per m3 for three hours.  Free fumigant was not separately determined
    in the other fumigated fruits but total bromine residues did not
    exceed 15 mg/kg.  The wet chemical methods used in this work may not
    have been sensitive enough to determine amounts of free fumigant below
    2 mg/kg.  Seo et al. (1970) determined 1,2-dibromoethane and
    inorganic bromide in lychees, papaya, cayenne pineapples and bell
    peppers after vapour fumigation at doses ranging from 8-32 g per m3
    and also oranges at 24 and 48 g per m3, at 21C.  Inorganic bromide
    residues produced did not exceed 8 mg/kg.  Maximum 1,2-dibromoethane
    residues were, at one and three days after fumigation respectively:
    lychees 3.5 and 1 mg/kg, papayas 20 and 7; pineapples 6 and 2; peppers
    45 and 24 and oranges 32 and 42.  1,2-dibromoethane residues
    determined in oranges two days after treatment were reduced a further
    75% six days after fumigation.  Storage at low temperatures lessened
    the rate of loss of residual free fumigant.  Seo et al (1970) also
    treated papayas by dipping them in a 1,2-dibromoethane/hot water
    solution (max. 144 mg fumigant per litre of water at 43-48C for 20
    minutes).  1,2-dibromoethane residues were less than 0.1 mg/kg three
    days after dipping.

    In later work Seo et al. (1972) treated mangoes by preliminary
    immersion in hot water at 46C for 20 minutes, followed by vapour
    fumigation with 1,2-dibromoethane at 8, 12 or 16 g per m3 for two
    hours at 21C.  Residues in mango peel ranged from 2.6-3.0 mg/kg at
    one day and 0.3-0.4 mg/kg at three days after fumigation; in the pulp,
    residues ranged from 2.9-3.4 mg/kg at one day and 0.2-0.3 at three
    days.  Residual inorganic bromide did not exceed 2 mg/kg.

    Singh et al. (1979) determined 1,2-dibromoethane and bromide ion
    residues in oranges after fumigation at 24 g per m3 for two hours at
    20C.  They determined loss of 1,2-dibromoethane at intervals up to or
    exceeding 28 days.  They concluded that a 14 day withholding period
    was necessary to reduce levels of 1,2-dibromoethane below 0.5 mg/kg.
    Inorganic bromide levels, based on whole fruit determinations did not
    exceed 12 mg/kg.

    Melksham and Munro (1979) found that in mango, capsicum, passion fruit
    and papaw fumigated for two hours at 20C at dose levels of 16-36 g
    per m3, 1,2-dibromoethane residues in the commodities other than
    passion fruit were reduced to below 0.1 mg/kg within 3-7 days.  With

    passion fruit the rate of residue loss was much slower and about 2
    mg/kg was still present 7 days after fumigation.

    FATE OF RESIDUES

    In Plant Materials

    Apart from slow description and volatilization of unchanged fumigant,
    a proportion of the residue remaining associated with cereals and with
    fresh fruits has been shown to give rise to bromide ion (inorganic
    bromide) either by hydrolysis or by reaction with food constituents
    (Bridges 1956, Heuser 1961, Hargreaves et al, 1978).

    Amuh (1975) using 14C-labelled 1,2 dibromoethane, found that 61% of
    the original residue in fumigated maize was lost by volatilisation and
    the remaining 39% by chemical reaction.  The non-volatile 14C was
    found associated with an unspecified protein fraction.

    In animals

    Nachtomi (1970) found that a stoichiometric reaction of
    1,2-dibromoethane with glutathione in rat liver in vitro and in
    vivo, catalysed by glutathione-5-alkyl transferase produced bromide
    ion and S,S-1-ethylene bis-glutathione.  Nachtomi et al. (1965) had
    earlier reported the presence of mercapturic acid and
    5(-hydroxyethyl) N-acetyl cysteine and bromide ion in rat urine after
    dosing with 1,2-dibromoethane.  These reaction products were later
    confirmed in studies by Edwards et al. (1970).

    In Storage and Processing

    Very little chemical breakdown of 1,2-dibromoethane appears to occur
    in dry stored materials.  The residual fumigant airs off from cereal
    grains only slowly under bulk storage conditions with little air
    movement and may persist for some months (Jagielski et al 1978,
    Heuser, 1961).  Upon milling of raw cereals some reduction in residue
    levels takes place, but higher levels occur in bran and offals than in
    the flour.  On baking, most of the free 1,2-dibromoethane in the flour
    disappears, but small amounts can be detected in bread using sensitive
    analytical methods.  (Jagielski et al, 1978).  Small amounts of
    residual 1,2-dibromoethane remaining in fruit and vegetables are
    reduced generally to below 1 mg/kg by 7 days after fumigation (Seo et
    al., 1970, 1972; Hargreaves et al., 1978).

    Levels of inorganic bromide either increase slightly due to breakdown
    of 1,2-dibromoethane during storage or remain constant.

    EVIDENCE OF RESIDUES IN FOOD IN COMMERCE OR AT CONSUMPTION

    Cereals

    Selective monitoring of cargoes of wheat and other grains imported
    into the United Kingdom during 1978-79 showed only three wheat samples
    (out of a total of 854 samples of all grains) to contain
    1,2-dibromoethane residues, all falling in the range of 0.1-1.0 mg/kg
    (Fishwick and Rutters 1979).  In a survey of 189 samples of barley,
    rice, rye and wheat entering the Netherlands, no 1,2-dibromoethane was
    detected at a method-sensitivity of 0.01 mg/kg (Admiraal et al.,
    1979).

    Fruit and Vegetables

    Studies by Hargreaves et al. (1978) showed that 1,2-dibromoethane
    residues up to 4 mg/kg could occur in fruit and vegetables (e.g.
    capsicum, mango, papaw, passion fruit, pumpkin and zucchini) during
    the period after fumigation of which these items could reach the
    market and they suggested that the withholding period should be
    increased to 5 days after fumigation, with a tolerance of 0.5 mg/kg.

    METHODS OF RESIDUE ANALYSIS

    a)  Residual 1,2-dibromoethane

    Residual 1,2-dibromoethane can be determined in a range of commodities
    by gas chromatography either after cold extraction (Heuser and
    Scudamore 1969) or after continuous hot solvent co-distillation with
    boiling water and collection in toluene (Beilorai and Alumot, 1966)
    with a limit of determination of 0.01 mg/kg.  It has also been
    determined in whole and milled wheat by extraction with benzene
    followed by azeotropic distillation of the extract with water, with
    iodometric estimation as bromide ion, after breakdown by alcoholic
    potash  (Sidhu et al., 1975).  The cold acetone/water solvent
    extraction method has been collaboratively tested on grain samples
    (Panel on Fumigants Residues in Grain, 1974).  If 1,2-dibromoethane is
    first distilled from the commodity, it can also be determined by X-ray
    fluorescence (Hargreaves et al, 1974, 1978).  Greve and Hogendoorn
    (1979) claim a sensitivity of 0.01 mg/kg for 1,2-dibromoethane in
    grain using a head-space analytical technique.

    b)  Bromide ion

    Methods available for determining bromide ion (inorganic bromide)
    resulting from any source, including breakdown of 1,2-dibromoethane,
    are the same as those described under bromoethane in the present (i.e.
    1979) volume of monographs.  The same limitations regarding prior
    removal of free fumigant apply to certain of the methods available
    which do not differentiate between organo-bromine and bromide ion.
    This should be accomplished by non-aqueous solvent extraction and not

    by heating the sample as described for example, by Hargreaves et al.
    (1978), since this can result in breakdown of 1,2-dibromoethane
    (Bridges 1955, Heuser, 1961).

    NATIONAL LIMITS REPORTED TO THE MEETING

    a)  Residues of 1,2-dibromoethane

    The United States of America exempts barley, corn, oats, popcorn,
    rice, sorghum and wheat from a tolerance requirement on the grounds
    that residues of the unchanged compound should have disappeared before
    food reaches the consumer.  Canada and Australia do not enforce a
    tolerance level, but Australia requires that no residues of the
    unchanged fumigant must be present in food as consumed.  An EEC draft
    directive in 1976 proposed a limit of 5 mg/kg in cereals put into
    circulation for human consumption.

    An Australian Department of Agriculture publication (quoted by
    Hargreaves et al., 1978) states that an MRL of 0.1 mg/kg
    1,2-dibromoethane in fruit and vegetables is recommended by the
    Australian National Health and Medical Research Council, to apply
    after a withholding period of two days, with the exception of citrus
    fruit, for which an MRL of 0.5 mg/kg is stipulated.  Netherlands'
    limits were reported to the meeting as: cereals, 30 mg/kg; flour 4
    mg/kg; and fruit and vegetables 0.01 mg/kg.

    b)  Residues of Bromide ion (inorganic bromide)

    Many countries have adopted limits for bromide ion in specified foods,
    but there is no way of determining the source of the residue, which
    could, for example, also be present in plant-derived foods an a result
    of up-take from soil.  It is therefore realistic to regulate residues
    of bromide ion arising from the use of a specific fumigant.

    APPRAISAL

    The use of 1,2-dibromoethane either alone or in admixture with other
    halogenated hydrocarbons, or other volatile chemical compounds, an a
    cereal grain fumigant, has decreased significantly in many countries
    as a result of recognition of the persistence of the residues in
    stored produce and of its adverse toxicological properties.  However,
    it is known that 1,2-dibromoethane is being used on an increasing
    scale in other countries where insect pest damage to stored grain is
    particularly severe and alternative pest control methods are not
    currently practicable.  Sensitive analytical methods now available
    have shown that a minute part of the residue present in raw wheat
    grains can reach the baked loaf, although residues in bread made from
    wheat treated at normal field levels would not be expected to exceed
    0.5 mg/kg.

    The occurrence of significant unchanged fumigant residues in wheatmeal
    and bran products which might receive little further processing before

    consumption (Jagielski et al., 1978), was however noted with
    concern.  The meeting recognised that in setting a new guideline level
    for residues in cereal products to be offered for consumption without
    cooking was in line with its concern about the toxicological
    properties of 1,2-dibromoethane.  There was the likelihood that such a
    level could be exceeded if cereal grains destined for processing into
    such products were fumigated with 1,2-dibromoethane and the object of
    proposing such levels was to restrict the use of the fumigant on
    cereal grains to be used for such purpose.

    The use of the compound for fumigating fruit and vegetables, in some
    cases shortly before reaching the point of retail sale, continues in a
    number of countries.  The meeting concluded that guideline levels
    should be set for residues of 1,2-dibromoethane in fruit and
    vegetables, in line with residue levels know to occur at the end of
    suitable withholding periods after treatment.

    In products which have been exposed to 1,2-dibromoethane some limited
    breakdown of the fumigant takes place especially at elevated
    temperatures releasing bromide ion.  It is therefore necessary to
    determine separately residues of the unchanged fumigant and of bromide
    ion, which have widely differing toxicological effects.  Analytical
    methods are available for these purposes, but it is not possible to
    ascribe any bromide ion content to specific pesticide use, since it
    can occur from uptake by plants of soil bromide which may or may not
    be of natural origin.

    The meeting concluded that the levels of residues to be expected in
    some stored products fumigated with 1,2-dibromoethane or its mixtures
    with other fumigants according to present agricultural practice did
    not accord with its assessments of the possible toxicological effects
    of such residues, and it therefore felt that the use of the fumigant
    in these circumstances was inadvisable.

    When used as a soil fumigant, 1,2-dibromoethane may increase the
    bromide ion content of soil and hence the inorganic bromide content of
    plant leaf and/or fruit.  There is, so far as is known, no published
    evidence of residues of the unchanged fumigant reaching edible plant
    parts in this way.  Again however, as with stored product fumigation,
    the bromide ion content in plant material samples in commerce cannot
    be ascribed with any certainty to specific pesticide usage.

    EVALUATION

    The following maximum residue levels may be found after fumigation
    practices currently acceptable in some countries:

    Cereal grains                  20 mg/kg a
    (to be subjected to
    baking or cooking)

    Milled cereal products         0.01 mg/kg b *
    intended for consumption
    without cooking

    Bread and other cooked
    cereal products                0.01 mg/kg c *

    Passion fruit                  0.5 mg/kg e

    Citrus fruits                  0.5 mg/kg e

    Fruit and vegetables
    (except citrus fruits          0.1 mg/kg d
    and passion fruit)

    The meeting concluded that these levels are suitable for use as
    Guideline Levels and should not be exceeded if good fumigation
    practices including adequate aeration, are followed.

                   

    a)  At point of entry into a country, and in the case of cereal grain
    for milling, if product has been freely exposed to air for a period of
    at least 24 hours;

    b)  To comply with the guideline level proposed for milling cereal
    products intended for consumption without cooking, the cereal grain
    must be selected from lots which have not been treated with ethylene
    dibromide;

    c)  To apply to a commodity at point of retail sale or when offered
    for consumption;

    d)  To apply after a withholding period of not less than three days;

    e)  To apply after a withholding period of not less than five days.
    Where the withholding period is impracticable, the use of the fumigant
    is contra-indicated.

    *   At or about the limit of determination.

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    ethylene dibromide methyl bromide and ethylene chlorobromide resulting
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    Seo, S.T., Chambers, D.L., Akamine, E.K., Komura, M. and Lee, C.Y.L.
    Hot water ethylene dibromide treatment - refrigeration treatment for
    mangoes infested with oriental and Mediterranean fruit flies. J. Econ.
    Ent. 65, 1372.

    Sidhu, V.S., Muthu, M. and Bains, G.S. - A study of 1,2-dibromoethane
    residues in wheat and milled products. Pestic. Sci. 6, 451.

    Singh G. Rigney, C.J. and Gilbert, W.S. - Ethylene dibromide and
    inorganic bromide residues in oranges after fumigation and storage.
    Aust. J. Exp. Agric. Animal Husb. 19, 377.

    Webster, G. and Keetch, D.P. - The effect of EDB, potassium and
    nitrogen on the yield of smooth cayenne pineapple plants in the
    Eastern Cape. Citrus and Subtropical fruit Journal 1975, p. 15.

    Wit, S.L., Bessemer, A.F.H., Das, H.A., Goedkoop, W., Loosles F.E. and
    Meppalink, E.A.  Results of an investigation on the regression of
    three fumigants (carbon tetrachloride, ethylene dibromide and ethylene
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    (1969). Natl Inst. for Public Health, Utrecht, Netherlands.
    


    See Also:
       Toxicological Abbreviations