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 (131°C) 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 37°C. 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 21°C. 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 43-48°C 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 46°C for 20 minutes, followed by vapour
fumigation with 1,2-dibromoethane at 8, 12 or 16 g per m3 for two
hours at 21°C. 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
20°C. 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 20°C 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(ß-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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See Also:
Toxicological Abbreviations