WHO Pesticide Residues Series, No. 1
1971 EVALUATIONS OF SOME PESTICIDE RESIDUES IN FOOD
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
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
This pesticide was evaluated in 1965 (FAO/WHO 1965c) and reviewed in
1968 (FAO/WHO 1969b), when a special evaluation was made of residues
of ethylene chlorohydrin formed by reaction between ethylene oxide and
inorganic chloride present in the food.
Section 3 of the report of the 1971 meeting (FAO/WHO 1972a), which
discusses general principles concerning residues of fumigants, is
reproduced in Appendix IV. This Appendix also contains information on
some commercially available mixtures.
RESIDUES IN FOOD AND THEIR EVALUATION
Post-harvest use on dry foodstuffs
Ethylene oxide has been used as an insecticide for about 40 years. Its
use for this purpose is now much diminished but it is still
occasionally used as an insecticide on a few commodities, mainly
flour, nuts, dried fruit and confectionery products in some European
countries, the United Kingdom, United States of America and Canada.
The compound is also used for sterilization, i.e. against moulds and
bacteria, of certain food materials, including spices, curry powder
and desiccated coconut. Sterilization requires higher dosages than
fumigation against insects. This has become an important process in
some food industries but the total tonnage so treated is small and
these materials do not constitute an important part of the diet.
Ethylene oxide is usually applied in admixture with carbon dioxide,
nitrogen or chlorofluorohydrocarbons, to provide non-explosive
conditions. Treatments for sterilization are usually undertaken in
specially designed vacuum fumigation installations.
In the appraisal of ethylene oxide agreed at the 1968 Joint Meeting
(FAO/WHO 1969b) it was concluded: "There is evidence that food treated
with ethylene oxide, either as a bacterial sterilant or to a lesser
extent as an insecticidal fumigant, may contain residues of unchanged
ethylene oxide unless there is an adequate subsequent holding period
or aeration treatment to allow this residue to volatilize. There is
also evidence of the formation, derived from inorganic chloride
present naturally in food, of residues of ethylene chlorohydrin; and
limited evidence that this does not disappear from the treated produce
in storage so readily as do residues of unchanged ethylene oxide". The
1968 Joint Meeting also indicated that data wore required on the
disappearance of residues during storage and processing following
bactericidal or insecticidal treatment.
Scudamore and Heuser (1971a) present information which partly meets
this requirement. They reviewed earlier published information on
residues following treatment with ethylene oxide and reported an
extensive investigation, under controlled laboratory conditions, on
the amount and persistence of these residues in a variety of foods.
Scudamore and Heuser used two levels of treatment representing insect
fumigation and sterilization dosages and samples of food were
subsequently kept either under sealed conditions or freely aerated on
trays. The effects of temperature during fumigation, temperature
during subsequent storage, and moisture content were investigated.
Each of these factors affected the amounts of ethylene oxide, ethylene
chlorohydrin and ethylene bromohydrin present at various intervals of
time after treatment as determined by solvent extraction of samples
followed by gas-liquid chromatography. The formation of the
halohydrins was dependent upon the presence of ionic chlorine or
bromine and when both these were available the bromohydrin was more
readily formed than the chlorohydrins. At the end of the experimental
storage period, determins were also made of the amounts of ethylene
glycol and diethylene glycol which had been formed by hydrolysis of
ethylene oxide or of the halohydrins.
When commodities were left at 25°C either under air-tight storage or
freely aired, residual ethylene oxide usually fell to below 1 ppm
within 14 days but in flour kept under air-tight conditions after
treatment at sterilization level, 50-100 ppm remained at this time and
at lower temperatures ethylene oxide disappeared more slowly. When
significant amounts of ethylene chlorohydrin were formed these were
much more persistent under air-tight conditions showing little loss
after a year. Residues of several thousand ppm occurred in sterilized
materials having a high content of chloride. Ethylene bromohydrin was
less persistent and decomposed slowly under sealed conditions.
When flour containing residual halohydrins was cooked, the loss of
these compounds was almost complete when the conditions were alkaline
but under more acid conditions up to 60 or 70% remained in the cooked
product. Scudamore and Heuser did not examine their samples for the
presence of alkylated and hydroxyethylated derivatives of food
constituents as found by Gordon et al., (1959) in dried prunes after
fumigation with 14C-labelled ethylene oxide.
Evidence of residues in commerce or at consumption
Scudamore and Heuser (1971a) examined a small number of samples of
flour after commercial fumigation with ethylene oxide. They found no
unchanged ethylene oxide but amounts of ethylene chlorohydrin ranging
from 10 to 70 ppm.
Methods of residue analysis
Scudamore and Heuser (1971a) determined ethylene oxide and also the
reaction products ethylene chlorohydrin, ethylene bromohydrin,
ethylene glycol and diethylene glycol in a range of commodities by
gas-liquid chromatography of extracts obtained by the use of a 5:1 by
volume acetone-water mixture at room temperature. Procedures were
based on a multi-detection scheme for volatile fumigant residues
(Heuser and Scudamore, 1969), but with some variation in the choice of
column and other operating conditions to obtain optimum performance
and sensitivity in the determination of certain compounds in
particular commodities. Ethylene oxide and the halohydrins were
separated on a polypropylene glycol column and determined by flame
ionization detector. The limit of detection was 5 × 10-11 g ethylene
oxide, 5 × 10-10 g chlorohydrin and 1 × 10-9 g bromohydrin,
equivalent, with 10 g commodity to 30 ml solvent and 1 µ 1 injection
volume, to 0.15, 1.5 and 3 ppm respectively.
Manchon and Buquet (1970) have determined residues of ethylene
chlorohydrin in bread treated with ethylene oxide. They extracted the
bread either with diethyl ether, according to Ragelis et al., (1966)
or with a mixture of acetone and water according to Heuser and
Scudamore (1967 and 1968) and determined the residues by GLC using
silicone oil on Diatoport S in the column and a hydrogen
Brown (1970) has determined ethylene oxide and ethylene chlorohydrin
in plastic and rubber surgical equipment sterilized with ethylene
oxide. A p-xylene extract of the sample is passed through three
chromatographic columns in series. The top column (I), which collects
the ethylene chlorohydrin, consists of Florisil. The second column
(II) mounted directly below the first column, consists of Celite mixed
with dilute Hcl and converts the extracted ethylene oxide to ethylene
chlorohydrin. The third column (III) placed directly below column II,
also contains Florisil and collects the ethylene chlorohydrin formed.
After removal of p-xylene the ethylene chlorohydrin collected on
columns I and III is eluted separately with ethyl ether and further
purified if necessary by sweep co-distillation before analysis by GLC.
A flame-ionization detector is used with a column packed with either
Carbowax 20M or Ucon 75-U-90 000 on a Gas Chrom Q support. A linear
response for ethylene chlorohydrin was obtained over the range 26 to
419 ng, the lower limit of detection being approximately 25 ng.
Weinberger (1971) describes a co-sweep distillation method for
removing and concentrating trace amounts of ethylene chlorohydrin from
a variety of materials including fabrics and cellulose-type materials
after sterilization with ethylene oxide. The chlorohydrin was
determined by gas-chromatography. Spitz and Weinberger (1971) extend
the method to determine ethylene oxide, ethylene chlorohydrin and
Stijve (1969) examined a variety of foods treated with ethylene oxide
for ethylene chlorohydrin and ethylene glycol by gas-chromatography of
aqueous distillates. He used thin layer chromatography to confirm the
presence of ethylene chlorohydrin in the distillates after its
conversion to ethanolamine by reaction with ammonia. However other
compounds, notably ethylene oxide and ethylene bromohydrin also
convert to ethanolamine by this treatment.
National tolerances (as reported to the meeting)
United States of America
A tolerance of 50 ppm is established for residues of the
anti-microbial agent and insecticide ethylene oxide when used as a
post-harvest fumigant in or on the following raw agricultural
commodities: black walnut meats, copra, whole spices. An extension to
the regulation also applies the tolerance to ground spices from both
post-harvest application to the raw whole spices and to the ground
No tolerances have been established.
1. The British Industrial Biological Research Association has
suggested a limit of 300 ppm ethylene chlorohydrin in spices.
2. The United States of America has restricted the use of ethylene
oxide for sterilizing foods containing large amounts of added
chloride. Also set limitations to residues from the use of propylene
oxide on certain foods, as follows:
cocoa, gums, processed nutmeats (except peanuts), spices
300 expressed as ppm of propylene oxide
glacé fruit, prunes (dried):
700 expressed as ppm of propylene glycol.
Ethylene oxide is still used, although only to a limited extent,
against insects and mites in a small range of dried foods. On a small
scale, but at higher dosage levels, it is also used against moulds and
bacteria on foods such as spices, curry powder and desiccated coconut.
Residues may include ethylene oxide itself and any of the following
derivatives: ethylene chlorohydrin, ethylene bromohydrin, ethylene
glycol, diethylene glycol and certain alkylated and hydroxyethylated
reaction products of food constituents. The amounts and persistence of
these residues depend upon the composition, especially the halide and
moisture content, of the food, the dose of ethylene oxide used, the
temperature during fumigation and the temperature and ventilation
during subsequent storage.
A selection of results is presented in the Table indicating the
amounts of these residues to be expected 7 and 28 days after treatment
at a fumigation dose. The full data available show that when fumigated
flour was freely ventilated at 25°C ethylene oxide was no longer
detected after 72 hours. In similar samples kept under sealed
conditions ethylene oxide typically persisted for more than a week and
ethylene chlorohydrin was, in some instances, present after one year
whilst the bromohydrin was less persistent than the chlorohydrin.
Little, if any chlorohydrin was found in cocoa beans or in groundnuts.
TABLE I. RESIDUES (IN PPM) 7 AND 28 DAYS AFTER TREATMENT AT FUMIGATION DOSES
Food Temperature Storage Residue at 7 days Residue at 28 days
°C EO ECH EBH EO ECH EBH
Wheat I 25 S 2.4 45 25 n.d. 25 10
F 0.8 20 10 n.d. 4 n.d.
Wheat II 25 S 4.3 50 3 n.d. 35 n.d.
Flour 25 S 0.2 100 - n.d. 100 -
F n.d. n.d. - n.d. n.d. -
Flour 15 S 13 85 85 n.d. 55 50
Sultanas 25 S n.d. 25 n.d. n.d. 20 n.d.
Sultanas 10 S 4.6 30 - n.d. 5 -
F 0.5 25 - n.d. n.d. -
Cocoa beans 10 S 8.7 n.d. - 0.1 n.d. -
F n.d. n.d. - n.d. n.d. -
Groundnuts 25 S 2.1 n.d. - n.d. n.d. -
F n.d. - - n.d. n.d. -
Wheat II contained 3 ppm inorganic bromide.
Wheat I contained 82 ppm inorganic bromide as a result of previous fumigation
with methyl bromide.
S = sealed in glass bottles.
F = freely exposed in a thin layer on a tray.
EO = ethylene oxide.
ECH = ethylene chlorohydrin.
EBH = ethylene bromohydrin.
n.d. = not detected.
In the same trials, after 6 to 12 months storage the amounts of
ethylene glycol present were determined. In samples treated at
insecticidal doses this amount was usually below 100 ppm but in
sterilized flour it could exceed 2000 ppm. Small amounts of diethylene
glycol (less than 100 ppm) were also found in sterilized samples of
flour. When flour containing residual halohydrins was cooked, the loss
of these compounds was almost complete when the conditions were
alkaline but under more acid conditions up to 60 or 70% remained in
the cooked product.
In curry powder containing 7% of chloride calculated as sodium
chloride, fumigated at a sterilization dose and then stored under
sealed conditions, the level of chlorohydrin residue was in excess of
4000 ppm for about 14 days and 350 ppm remained after one year. In a
similar sample freely aired, however, the chlorohydrin was no longer
detected after 72 hours.
Analytical methods are available for determining ethylene oxide,
chlorohydrin and bromohydrin in foods with a limit of detection of
0.15, 1.5 and 3 ppm respectively.
Although there are data on ethylene oxide residues in terms of
unreacted ethylene oxide, halohydrins and glycols, for a number of
products, there also is evidence of the possible occurrence of
unidentified residues and direct evidence of the formation of
alkylated and hydroxyethylated derivatives is available for prunes.
Therefore, it cannot at present be assured that the sum of residual
ethylene oxide, and halohydrins and glycols represent the total
significant residue. For the above reasons the meeting was unable to
propose tolerances or guideline levels for residues of ethylene oxide
and its main derivatives in food.
It has been shown that high levels of ethylene chlorohydrin result
from treatment at sterilization doses of foods containing high levels
of added inorganic chloride. Pending further clarification as to
whether these residues which may be several thousands of parts per
million, are toxicologically objectionable, it would seem desirable to
curtail the use of ethylene oxide for the sterilization of food
materials containing large amounts of added chloride. (This
restriction is imposed in the United States regulations).
Further work desirable
1. Data on the nature and amounts of alkylated and hydroxyethylated
derivatives of food constituents arising from the use of ethylene
2. Additional data on residues in food resulting from the use of
ethylene oxide in commercial practice.
Brown, D. J. (1970) Determination of ethylene oxide and ethylene
chlorohydrin in plastic and rubber surgical equipment sterilized with
ethylene oxide. J. Assoc. Offic. Anal. Chem., 53: 263-267
Gordon, H. T., Thornburg, W. W. and Werum, L. N. (1959) Fumigant
reactions with foods. Hydroxyethyl derivatives in prunes fumigated
with 14C-ethylene oxide. J. Agr. Food Chem., 7: 196-200
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. and Scudamore, K. A. (1968a) Fumigant residues in wheat
and flour: solvent extraction and gas-chromatographic determination of
free methyl bromide and ethylene oxide. Analyst, 93: 252-258
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 Agr.,
Lindgren, D. L., Gunther, F. A. and Vincent, L. E. (1968) Bromide
residues in wheat and milled wheat fractions fumigated with methyl
bromide. J. Econ. Entomol., 55: 773-776
Manchon, P. and Buquet, A. (1970) (Determination and levels of
ethylene oxide (oxirane) and its derivatives in bread with this
fumigant). Food Cos. Toxic., 8: 9-15
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. Assoc. Offic. Anal. Chem., 49: 963
Ragelis, E. P., Fisher, B. S., Klimeck, B. A. and Johnson, C. (1968)
Isolation and determination of chlorohydrins in foods fumigated with
ethylene oxide or with propylene oxide. J. Assoc. Offic. Anal. Chem.,
Scudamore, K. A. and Heuser, S. G. (1971a) Ethylene oxide and its
persistent reaction products in wheat flour and other commodities:
residues from fumigation or sterilization, and effects of processing.
Pesticide Sci., 2: 80-91
Spitz, H. D. and Weinberger, J. (1971) Determination of ethylene
oxide, ethylene chlorohydrin and ethylene glycol by
gas-chromatography. J. Pharmac. Sci., 60: 271-273
Stilve, T. (1969) (Analysis of residues formed during ethylene oxide
fumigation). Mitt. Geb. Lebensmittelunters. Hyg., 60: 373-379
Weinberger, J. (1971) GLC determination of ethylene chlorohydrin
following co-sweep extraction. J. Pharmac. Sci., 60: 545-547