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
CARBON TETRACHLORIDE
This pesticide was previously evaluated at the Joint Meetings in 1965
(FAO/WHO 1965c) and was further considered in 1967 and 1968 (FAO/WHO
1968b, 1969b).
Reference should be made to Appendix IV. It includes Section 3 of the
report of the 1971 meeting (FAO/WHO 1972a); also information on some
commercially available fumigant mixtures.
RESIDUES IN FOOD AND THEIR EVALUATION
Use pattern
Post-harvest use on dry foodstuffs
Carbon tetrachloride is used in many countries as a fumigant either
alone, or, more usually, mixed with other more toxic fumigants
including 1,2-dibromoethane, carbon disulfide, 1,2-dichloroethane and
methyl bromide. The main use is in the disinfestation of bulks of
grain in bins or on floors and there is probably relatively little use
on other foodstuffs except for small-scale treatments. A recent
small-scale fumigation development in West Africa uses gelatine
capsules of carbon tetrachloride to treat individual bags of grain or
pulses, each enclosed in a bag made of polyethylene. The proportion of
carbon tetrachloride in commercially available mixtures varies between
5 and 80% by volume. The most widely used mixture is a 75:25% by
volume mixture of 1,2-dichloroethane and carbon tetrachloride
("3:1 mixture"). Other mixtures are listed in Appendix IV. The
toxicity of carbon tetrachloride to insects is low in comparison with
that of other fumigants and relatively long treatment periods such as
one or two weeks are required for effective disinfestation when it is
used alone. In mixtures it serves to reduce the fire and explosion
hazards from the use of fumigants such as carbon disulfide or ethyline
dichloride (i.e. 1,2-dichlorethane), or it is used to assist the
distribution of the more toxic ingredients of the mixture.
Residues resulting from supervised trials
Laboratory and larger scale supervised trials previously reported, in
which carbon tetrachloride was applied to raw cereal grains at normal
commercial dosages either alone or in mixtures containing a
substantial proportion of this fumigant, indicated that the amount of
unchanged compound to be found shortly after treatment is typically in
the range of 100 to 200 ppm. After storage without specifically airing
the grain, after a few months this usually falls to below 50 ppm. The
effect of processing to flour and bread has been studied in the
Netherlands by Wit et al. (1969). There were some discrepancies
between the results reported by the different participating
laboratories but the general picture emerged that, starting with grain
which had been aired for several weeks after fumigation and which then
contained 20 to 60 ppm of carbon tetrachloride, the amounts found in
white flour were usually between 2 and 10 ppm and in bread were
usually below 0.05 ppm and part of these small residues in bread may
have resulted from impurities in analytical reagents.
Scudamore and Heuser (1971) give some interim results from an
extensive investigation of the amounts of carbon tetrachloride in
wheat and maize after fumigation under controlled conditions. This
investigation was still in progress when the current review was
conducted but the results already demonstrate the persistent character
of the residue of carbon tetrachloride during storage after treatment.
On milling there was an immediate loss of residue with a further loss
during subsequent storage of the ground grains under freely exposed
conditions but a proportion of the residue (around 10%) was still very
firmly held. The initial loss of residual carbon tetrachloride was
more rapid from grain fumigated at 10° than from grain fumigated at
25° but in each case storage under freely exposed conditions at 25°
caused a more rapid loss than similar storage at 10°. These results
are at variance with those of Alumot and Bielorai (1971) who
unexpectedly reported that ventilation was more effective in removing
fumigant at lower than at higher temperatures.
Fate of residues
In the light of earlier work it was concluded (FAO/WHO 1965c) that
there was no evidence of chemical reaction with food constituents.
Evidence of residues in food in commerce or at consumption
In the period 1964 to 1966 a number of cereals imported into the
Netherlands were analysed and nearly half of the samples contained a
detectable amount of carbon tetrachloride (Wit 1968, summarized in
FAO/WHO 1968b). In about 20% of all samples the residue range was 0.1
to 0.5 ppm, in 5% the range was 0.5 to 1 ppm, and in 8% the range was
1 to 5 ppm. Three per cent. of the samples investigated exceeded the
5 ppm level. The maximum residue found was 58 ppm. Seven lots of grain
(wheat, corn and milo) commercially fumigated in the United States of
America with liquid fumigants containing either 70.5 or 82.2% by
weight of carbon tetrachloride were sampled after storage for one to
three months in bins and analysed (McMahon, 1971). Amounts of carbon
tetrachloride ranged from 2.9 to 20.4 ppm.
Analytical studies in Israel conducted on three commercial samples of
flour showed residues of 0.2 to 0.3 ppm. All eight samples of bread
tested were free from detectable carbon tetrachloride (less 0.005
ppm). Biscuits appeared to contain 0.004 ppm (Bondi et al., 1971 as
reported by Kenaga 1971).
Methods of residue analysis
Methods of determination based on gas liquid chromatography are now
preferred to earlier methods involving dry or wet aeration or
distillation, hydrolysis and determination of chloride (Winteringham,
1944, Mapes and Shrader, 1957, Conroy, Munsey and Ramsey, 1957) or
direct colorimetric determination of the carbon tetrachloride (Ramsey
1957). Four basic methods of extraction have been used in preparation
for determination by gas-chromatography.
(a) A steam distillation procedure adapted by Bielorai and Alumot
(1966) from the method of Kennet and Huelin (1957). This procedure was
used in later studies by Alumot and Bielorai (1969) and was also
followed by Wit et al. (1969).
(b) A sweep co-distillation method based on the procedures of Ragelis
et al. (1968) and Storherr et al. (1967).
(c) The acid reflux method of Ramsey (1957). Malone (1969) compared
these three methods and, whilst all were then considered suitable, the
acid reflux method was preferred and was further evaluated (Malone,
1970) and used in residue studies (McMahon 1971). The sensitivity of
the method for carbon tetrachloride in cereal grains using an electron
capture detector was 0.04 ppm. In the tests with all three of these
methods of extraction on grain fumigated with carbon tetrachloride
Malone (1970) reported finding chloroform. It would appear that this
was formed by conversion of carbon tetrachloride during the hot
extraction. This conversation was more severe when whole grains were
extracted. No chloroform was found when cold solvent extraction was
used.
(d) In the solvent extraction method of Heuser and Scudamore (1968)
the substrate is soaked in a 5:1 acetone water mixture at room
temperature and an aliquot of the supernatant liquid injected into the
gas-chromatograph. The method was later developed into a multi-residue
scheme (Heuser and Scudamore 1969) when drying and partial clean-up of
the extract was introduced as an additional step. Normally an
extraction period of 48 hours is allowed for whole cereal grains and
four hours for flour but recent studies (Scudamore and Heuser 1971)
have shown that a longer period may be required to extract the last
fraction of residual carbon tetrachloride in materials which have been
aired for some months after fumigation. Using an electron-capture
detector, a residue of 0.01 ppm can readily be detected.
It would appear that methods for extraction of carbon tetrachloride
from cereals which employ a heating step are less preferable than the
cold solvent extraction procedure because of the partial conversion to
chloroform caused by the former. Procedure (d) therefore is the
preferred method.
National tolerances (as reported to the meeting)
The following statements form the basis for regulatory action on
residues of carbon tetrachloride in the countries specified.
Australia Residues of the unchanged compound must not be
present in or upon foods ready for consumption.
Carbon tetrachloride is included in a group of
volatile, post-harvest fumigants which when used
as directed on stored products are held to meet
this requirement.
Canada When used according to recommendations for stored
food products, is held to disappear during the
subsequent processing and not to have harmful
residues.
United States For similar reasons, is exempted from the
of America requirements of a tolerance for the following
grains: barley, corn, oats, popcorn, rice sorghum
(milo), wheat.
Appraisal
The fumigant is quite widely used on stored cereal grains and to a
much smaller extent on other stored foods. It is frequently used in
mixtures with more insecticidally active fumigants.
There is no evidence of significant reaction with food constituents
but airing off of some of the residue may be slow. The residue is
greatly reduced on milling. The amount found in bread baked from flour
containing the residues persisting under commercial conditions after
milling of fumigated grain is below 0.05 ppm. Satisfactory analytical
methods are available, using gas-chromatography, capable of detecting
residues of 0.01 ppm.
From the available information on the occurrence of unchanged carbon
tetrachloride in or on raw 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 and before sampling 50 ppm
In milling cereal products which will be
subjected to baking or cooking 10 ppm
In bread and other cooked cereal products
(i.e. at or about the present limit of
determination) 0.05 ppm
Further work desirable
Further information from supervised trials and commercial treatments
on the amount of residues of unchanged carbon tetrachloride occurring
after fumigation of raw cereals showing the rate of disappearance
during subsequent storage or processing.
REFERENCES
Alumot, E. and Bielorai, R. (1969) Residues of fumigant mixture in
cereals fumigated and aired at two different temperatures. J. Agr.
Food Chem., 17: 869
Bielorai, B. and Alumot, E. (1966) Determination of residues of a
fumigant mixture in cereal grain by electron-capture gas
chromatography. J. Agr. Food Chem., 14: 622
Bondi, A. and Alumot, E. (1971) As reported by Kenaga, E. E., 1971,
IUPAC Meeting
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. Ass. Offic. Agr. Chem., 40: 185-189
Heuser, S. C. and Scudamore, K. A. (1967) Determination of ethylene
chlorohydrin, ethylene dibromide and other volatile fumigant residues
in flour and whole wheat. Chem. Ind., 16 September: 1557-1560
Heuser, S. G. and Scudamore, K. A. (1968b) Determination of residual
acrylonitrile, carbon disulfide, carbon tetrachloride and ethylene
dichloride after fumigation. Chem. Ind., 24 August: 1154-1157
Heuser, S. G. and Scudamore, K. A. (1969) Determination of fumigant
residues in cereals and other foodstuffs; a multi-detection scheme for
gas-chromatography of solvent extracts. J. Sci. Food Agric.,
20: 565-572
Kennet, B. H. and Huelin, F. E. (1957) Determination of
ethylenedibromide in fumigated fruit. J. Afr. Food Chem., 5: 201
Kolthoff, I. M. and Yutzy, M. (1937) Volumetric determination of
bromide 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 food resulting from post-harvest insecticidal
treatments. Residue Reviews, 21: 1-121
Lynn, G. E. and Vorhes, F. A. (1957) Symposium: Residues in food and
feeds resulting fumigation of grains with the commoner liquid
formulations of carbon disulfide, carbon tetrachloride, ethylene
dichloride and ethylene dibromide. J. Ass. Offic. Agr. Chem., 40:
163-209
Mapes, D. A. and Shrader, S. A. (1957) Determination of total and
inorganic bromide residues in fumigated products. J. Ass. Offic. Agr.
Chem., 40: 189-191
McMahon, B. Malone. (1971) Analysis of commercially fumigated grains
for residues of organic fumigants. J. Ass. Offic. Chem., 54: 964-965
Malone, B. (1969) Analysis of grains for multiple residues of organic
fumigants. J. Ass. Offic. Anal. Chem., 52: 800-805
Malone, B. (1970) Method for determining multiple residues of organic
fumigants in cereal grains. J. Ass. Offic. Anal. Chem., 53: 742-746
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
Ragelis, E. P. Fisher, B. S. and Klimeck, B. A. (1966) Note on
determination of chlorohydrins in foods fumigated with ethylene oxide
and with propylene oxide. J. Ass. Offic. Anal. Chem., 49: 963
Ramsey, L. L. (1957) Colorimetric determination of carbon
tetrachloride in fumigated cereal products. J. Ass. Offic. Agr. Chem.,
40: 175-180
Scudamore, K. A. and Heuser, S. G. (1971b) Progress report on an
investigation of the behaviour of residues of carbon tetrachloride in
cereals during storage. (Unpublished report to FAO)
Storrherr, R. W., Murray, E. J., Klein, I. and Rosenberg, L. A. (1967)
Sweep co-distillation clean-up of fortified edible oils for
determination of organophosphate and chlorinated hydrocarbon
pesticides. J. Ass. Offic. Anal. Chem., 50: 605-615
Winteringham, F. P. W. (1944) Determination of fumigants XI.
Determination of chlorohydrocarbons in air by reaction in
monoethanolamine. J. Sci. Chem. Ind., 61: 186-187
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