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 - DICHLOROETHANE
Explanation
This fumigant pesticide was evaluated at the meeting in 1965 (FAO/WHO
1965c) and reviewed in 1967 and 1971. Prior to the 1971 meeting, it
was listed as ethyclene dichloride. The report of the 1978 Meeting
made reference to problems caused in member countries of FAO and WHO
by the use of certain fumigants and recommended re-evaluation of
1,2-dichloroethane.
RESIDUES IN FOOD AND THEIR EVALUATION
The report of the 1971 Meeting to which reference should be made,
contained a statement of general principles relating to residues of
fumigants.
USE PATTERN
Post-Harvest Use
1,2-dichloroethane (Ethylene dichloride, EDC) has been widely used as
a grain fumigant in post-harvest storage. Because of its
flammability, it is always mixed with other less flammable liquids in
grain fumigant formulations, the most common being carbon
tetrachloride. The latter also acts as a fumigant and carrier to aid
downwards distribution of EDC which otherwise tends to adsorb heavily
in the upper grain layers. EDC has more effective insecticidal
properties than carbon tetrachloride and until recently it has also
been considered safer for semi-skilled or farmer application than the
more acutely toxic grain fumigants such as methyl bromide and
phosphine. There has therefore been considerable application of
liquid grain fumigants containing EDC by farmers and their employees
and by grain storage personnel.
Recent reports on tumour production in rats and mice (National Cancer
Inst. 1978) due to feeding EDC, albeit at high dosage levels, have led
to reconsideration of the use pattern of EDC in some countries, and
for example, in the UK a decision has been taken to withdraw grain
fumigant mixtures containing EDC from non-professional pest control
use. This decision is based on the promise that professional pest
control operators are in a better position to monitor and guard
against breathing the fumigant vapours during operations than
unskilled personnel. In fact the amount of vapour that could be
ingested say in the course of a day at the present Threshold Limit
Value (50 ppm) is considerably in excess of that which could
conceivably be consumed as a residue of the fumigant in food.
RESIDUES ARISING FROM SUPERVISED TRIALS
Post-harvest use
The 1971 Meeting noted results of work carried out in the Netherlands
(Wit et al. 1969) showing that wheat aired for several weeks after
fumigation with a mixture-of 1,2-dichloroethane, carbon tetrachloride,
1-2-dibromoethane contained 10-40 mg/kg EDC and that on milling the
amounts found in white flour ranged between 2 and 11 mg/kg with
residues in bread generally below 0.05 mg/kg.
Berck (1974) determined residual fumigants after treating a farm bin
containing 27 tons of wheat with a mixture of EDC, carbon
tetrachloride and 1,2-dibromoethane (30:63:7 w/w) at 0.661/tonne.
Although residues of carbon tetrachloride and 1,2-dibromoethane were
detected, Berck was unable to find any residual EDC in the wheat. It
is assumed that this was due to lack of analytical method sensitivity.
Cassells, Scudamore and Heuser (1975) found that after exposing wheat
and maize to EDC at a concentration-time product (cxt) of 1970 mg h/l
with carbon tetrachloride at a cxt of 1250 mg h/l by application of a
3:1 v/v EDC/carbon tetrachloride mixture, resulting EDG residue levels
immediately after removal of the cereal grains from the chamber were
about 450 mg/kg for wheat and 800 mg/kg for maize. These levels
greatly exceeded the residue levels of carbon tetrachloride found (40
and 170 mg/kg respectively) indicating heavier sorption of EDC than
carbon tetrachloride at equivalent dose levels. After 28 days airing
EDC residues were reduced to 70-150 mg/kg in wheat and 20-110 mg/kg in
maize, indicating a more rapid loss of residual fumigant from maize.
After 12 weeks airing, residue levels were 8-40 mg/kg for wheat and
4-10 mg/kg for maize. EDC aired from maize more rapidly at 25°C than
at 10°C but with wheat the effect of temperature was less marked.
FATE OF RESIDUES
As indicated by trials reported above, the major route of EDC residue
reduction in stored fumigated produce is by volatilization. No
reaction products in plant products have been reported so far as is
known.
In the rat EDC has been reported (Nachtomi et al., 1965) to react to
give mercapturic acid and S-(ß-hydroxythyl)N-acetyl cysteine. These
reaction products were also found when 1,2-dibromoethane was
administered. Alumot et al. (1975) in 2-year feeding studies in the
rat found only a slight increase in liver fat at very high doses and
proposed a no-effect level of 25 mg/kg (rat) and 250 mg/kg in the
diet. In 2-year tests on laying hens with EDC at 250 and 500 mg/kg in
the diet, Alumot et al (1975) reported a decrease in egg weight from
month 4, and egg production was affected at 500 mg/kg. A tolerance of
100 mg/kg in feed and ADI of 5 mg per kg body weight was suggested for
laying hens and a 250 mg/kg residue tolerance and an ADI of 25 mg per
kg body weight for growing chicks and cocks.
EVIDENCE OF RESIDUES IN FOOD IN COMMERCE OR AT CONSUMPTION
Selective monitoring of cargoes of wheat and other grains imported
into the U.K. during 1978-79 showed that all 267 wheat samples
contained less than 5.0 mg/kg of residual 1,2-dichloroethane. Of 323
samples of miscellaneous other grains, two samples of imported rice
alone contained residues between 5 and 10 mg/kg, and no samples of any
grain exceeded this level (Fishwick and Rutter 1979). Monitoring of
barley, rice, rye and wheat shipments imported into the Netherlands
(184 samples) revealed no residue levels exceeding 0.1 mg/kg (Admiral
et al., 1979).
METHODS OF RESIDUE ANALYSIS
Residual 1,2-dichloroethane in cereal grains and milled products and
other stored products can be determined by gas chromatography
following cold extraction (Heuser and Scudamore, 1969) or following
continuous solvent co-distillation from a suspension using toluene and
boiling water (Beilorai and Alumot, 1966) or by microdistillation
under vacuum (Page and Kennedy, 1975). For the method of Heuser and
Scudamore (1969) a limit of detection of 1-5 mg/kg was claimed and for
the method of Beilorai and Alumot (1966) 0.1-1.0 mg/kg. A head-space
analytical technique (Greve and Hogendoorn 1979) has claimed a
sensitivity of 0.1 mg/kg.
NATIONAL MRLs REPORTED TO THE MEETING
A number of countries including Australia, Canada and the United
States have taken the view that no residue will be present in foods
ready for consumption when 1,2-dichloroethane is applied to raw
commodities and require that residues must not be present (Australia)
or exempt foods from a tolerance (eg. USA). An EEC draft directive in
1976 proposed a limit of 10 mg/kg in cereals put into circulation for
human consumption. Netherlands' limits were reported to the meeting
as: cereals, 40 mg/kg; flour, 10 mg/kg.
APPRAISAL
1,2-dichloroethane (EDC) in used as a cereal grain fumigant in a
number of countries, generally in admixture with another liquid
fumigant used as a flame suppressant. It in generally most effective
in the control of insect pests in the upper 4-6 metres of grain bulks.
Because of its relative low acute toxicity, it has been used in
operations by farmers and unskilled persons as well as by pest control
operators in both technologically advanced and developing countries.
No breakdown products in grain have been identified, and the loss of
residue by volatilization follows a regular pattern depending on
amount of air movement, moisture content and temperature of the grain.
Very little if any of the residue persists through to bread baked from
fumigated wheat. As no ADI has been allocated, it was the opinion of
the meeting that existing guideline levels represent a realistic
appraisal of residue levels which need not be exceeded at the specific
stages of sampling if normal fumigation procedures are carried out.
There is a need for analytical methods with greater sensitivity which
are suitable for determining residue levels below 0.1 mg/kg. If the
compound is to continue in use as a fumigant, some consideration must
be given to the selection of substitute flame-suppressant additives,
since the most common one used today, carbon tetrachloride (q.v.) has
been the subject of many adverse toxicological findings.
EVALUATION
The following maximum residue levels may be found after good
fumigation practice. They are recorded as Guideline Levels:
Cereal grains 50a
Milled cereal products
(to be subjected to baking
or cooking) 10
Bread and other cereal products 0.1b*
FURTHER WORK OR INFORMATION
Desirable:
Development of residue analytical methods capable of determining <0.1
mg/kg in prepared foods.
REFERENCES
Admiral, P., de Bruin, A., Cat, H., Dornseiffen, J., Greve, P.A.,
Hogendoorn, E.A., and Mulders, E.J. - Rpt. No. 95/79, (1979) Rijts
Instituut voor de Volkagezondheid, Bilthoven, Netherlands.
Alumot, E., Meidler, M., Holstein, P. and Herzberg, M. - Tolerance and
acceptable daily intake of ethylene dichloride in the chicken diet.
Food Cosmet. Toxicol. 14, (2). 111-114.
Beilorai, R. and Alumot, E. - Determination of residues of a fumigant
mixture in cereal grain by electron capture GLC. J. Agric. Fd. Chem.
14, 622
a To apply at point of entry into a country, and in the case of
cereal grains for milling, if product has been freely exposed to air
for a period of at least 24 hours;
b To apply to commodity at point of retail sale or when offered for
consumption.
* At or about the limit of determination.
Berck, B. - Fumigant residues of carbon tetrachloride, ethylene
dichloride and ethylene dibromide in wheat flour bran, middlings and
bread. Agric. and Food Chem. 22, (6) 977.
Cassels, D.R., Scudamore, K.A. and Heuser, S.G. - Desorption of
1,2-dichloroethane and carbon tetrachloride from cereal grains after
fumigation. (1975) Unpublished report Pest Infestation Control Lab.,
U.K.
Fishwick, F.B. and Rutter, I.R. - U.K. Survey of pesticide residues in
cereals. (1979) Unpublished, MAFF Agric. Science, Slough Lab., U.K.
Heuser, S.G. and Scudamore K.A. - Determination of fumigant residues
in cereals and other foodstuffs: a multi-detection scheme for gas
chromatography of solvent extracts. J. Sci. Fd. Agric. 20, 566.
Nachtomi, E. Alumat, E. and Bounty, A. - The metabolism of ethylene
dibromide and related compounds in the rat. Israel J. Chem., 3, 119.
National Cancer Inst. - Report: Bioassay of 1,2-Dichloroethane for
possible carcinogenicity. Bull. Brit. Ind. Biol. Res. Assoc. 1978, 17
(8) 445.
Page, B.D. and Kennedy, M. - Determination of methylene chloride,
ethylene dichloride and trichloroethylene as solvent residues in spice
oleoresins using vacuum distillation and electron-capture gas
chromatography., J. Ass. Off. Agr. Chem. 58, 1062.
Wit, S.L Bessemer, A.F.H., Das, H.A., Goedkoop, W., Loosjes, F.E. and
Mappelink, E.R. - Results of an investigation of the regression of
three fumigants (carbon tetrachloride, ethylene dibromide and ethylene
dichloride) in wheat during processing to bread. Lab. Rept. 36/69.
National Inst. Publ. Health, Utrecht, Netherlands.