FAO/PL:1967/M/11/1
WHO/Food Add./68.30
1967 EVALUATIONS OF SOME PESTICIDE RESIDUES IN FOOD
THE MONOGRAPHS
The content of this document is the result of the deliberations of the
Joint Meeting of the FAO Working Party of Experts and the WHO Expert
Committee on Pesticide Residues, which met in Rome, 4 - 11 December,
1967. (FAO/WHO, 1968)
FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
WORLD HEALTH ORGANIZATION
Rome, 1968
HYDROGEN PHOSPHIDE
This pesticide was evaluated by the 1966 Joint Meeting of the FAO
Working Party and the WHO Expert Committee on Pesticide Residues
(FAO/WHO, 1967). Since the previous publication, additional
information pertinent to evaluations for tolerances has become
available and is summarized and discussed in the following monograph
addendum.
IDENTITY
Other relevant chemical properties
For use against insects in foods, phosphine is generated in situ from
aluminum phosphide formulated with ammonium carbamate into tablets,
pellets and granules. The release of phosphine is due to reaction
between aluminum phosphide and moisture in the atmosphere. The rate of
release of phosphine gas depends upon the formulation and physical
condition of the aluminum phosphide, and on the temperature and
moisture of the ambient air and the commodity being fumigated.
Aluminum phosphide tablets generally used weigh 3 g each, and produce
about 1 g of phosphine. The pellets weigh 0.6 g each and yield about
0.2 g of the gas.
Registered in 70 countries (Dieterich et al, 1967) and used fairly
extensively in Argentina, Australia, Eastern Europe, India, Japan,
Turkey and the United States. Manufacturers of principal product
("Phostoxin"(R)) estimate that 15 to 20 million metric tons of grain
were treated in 1964.
EVALUATION FOR TOLERANCES
USE PATTERN
Pre-harvest treatments
Not used on living plants.
Post-harvest treatments
Phosphine derived from aluminum phosphide has been used for the
control of stored-product insects in many countries all over the world
for the fumigation of raw cereal and processed cereal products, beans,
peas, cottonseed meal, spices, dried vegetables and other foods and
animal foods. The recommended dosage to 45 to 60 tablets or 165 to 200
pellets/1,000 cu ft (28.3/m3) of space or 3 to 6 tablets/ton or 1,000
kg of rain. The fumigation period varies with the temperature; 5 days
at 54° - 59°F (12° - 15°C), 4 days at 60° - 68° (16° - 20°C), and 3
days at 69°F (20°C) and above. Fumigation with aluminum phosphide is
not recommended at temperatures below 40°F (5°C). For treating bulk
grain and other raw commodities, the phosphine tablets or pellets are
introduced into the stream of the commodity as it is being loaded into
bins or freight cars, or the fumigant tablets or pellets are inserted
into the commodity by a special probe. Bagged or packaged foods and
feeds are fumigated either in some kind of an enclosure or under a
gasproof sheet. The phosphine tablets or pellets are placed in trays
located on, under, or in the stack of food; or the tablets can be
pulverized and blown on the stack of packaged food which has been
covered with paper. Sometimes the ground pellets are placed in
moisture-permeable envelopes, and the envelopes are located on top of
the stacked food or stapled to the sides of the enclosure. Aluminum
phosphide must not come in contact with processed foods or feeds, and
must not be placed in or attached to packages intended for consumers.
All processed foods should be aerated for 48 hours before they are
offered to the consumer.
RESIDUES RESULTING FROM SUPERVISED TRIALS
Milo fumigated with aluminum phosphide at the rate of 10 tablets/ton
of grain had phosphine residues in one sample 11 and 16 days after
treatment of 0.436 ppm and 0.209 ppm, respectively. In the second
sample, the residues were 0.286 ppm and 0.085 ppm 7 and 11 days after
treatment, respectively (Bruce, 1958 (unpublished)). Wagner and
Fogleman (1962) reported no detectable phosphine residues in flour 24
hours after treatment with aluminum phosphide.
When fumigating processed foods, the aluminum phosphide or its
decomposition products must not come in direct contact with the food.
Any phosphine residue present in the food must, therefore, come from
sorption of the phosphine gas. Using an indirect method for the
analysis of phosphine residues, Mayr and Hild (unpublished) showed
there was no evidence of phosphine absorption by or adsorption on any
of the following foods after fumigation with aluminum phosphide at the
recommended dosage rate : Barley, wheat, flour, oat flakes, noodles,
rice, wheat bran, semolina, macaroni, dried apples, dried apricots,
raisins, prunes, cottonseed cake, a variety of dog foods, peas,
spinach, almonds, hazelnuts, peanuts, walnuts, coffee, tea, sugar
lumps, chives, beans, lettuce, lentils, ground red and black pepper,
curry powder, tumeric, marjoram, and potato flour. Although fresh
vegetables are not customarily fumigated, these items were included to
study any possible effects of the fumigation (Dieterich et al., 1967).
Green coffee beans, cocoa powder, nonfat instant dry milk powder,
malted barley flour, institutional doughnut mix, pie crust mix, oat
flour, gluten concentrate, high fat soy flour, rice flour, gluten
flour, bran buds, primary yeast, beet pulp, cornstarch, deer pellets,
mink conditioner, raisins, dried apples and apricots, pecan pieces,
corn flakes, rice breakfast food, and shredded wheat were fumigated at
the recommended level and then aerated for 48 hours. The highest level
of phosphine found in any product was 0.017 ppm (Dieterich et al,
1967).
When phosphine was applied in a closed container to wheat, oats,
barley, flax, and milled grain at concentrations of 0.15 - 0.60 mg/l,
no detectable free PH3 was found even after accelerated aeration with
nitrogen. However, there wereindications that under ideal laboratory
conditions irreversible sorption may take place since chemisorbed PH3
equivalent to 2.16 ppm was detected (Berck (unpublished)).
FATE OF RESIDUES
In storage and processing
The rate of evolution of phosphine from aluminum phosphide is
dependent on atmospheric moisture. After short exposure periods (72
hours or less), it is possible for residues of aluminum phosphide to
be present in grain with a 9 per cent moisture content or below.
However, such residues readily disappear during airing, turning and
cleaning to which grain is normally submitted prior to milling
(Heseltine and Thompson, 1957; Feuersenger, 1960; Liscombe, 1963).
During studies of the affects of baking, no significant residues could
be found in baked bread made of treated flour or flour from treated
grain (Liscombe, 1963).
METHODS OF RESIDUE ANALYSIS
The method developed by Bruce, Robbins, and Tuft (1962) hydrolyzes
aluminum phosphide in the presence of dilute sulfuric acid to form
phosphine. The liberated phosphine is driven out by nitrogen gas into
scrubbers, and then the contents of the scrubbers are analyzed. This
method is sensitive to less than 0.001 ppm [although previously stated
to have a sensitivity of 0.01 ppm (FAO/WHO, 1967)].
The method by Heseltine (1963) is based in part on the above method
and depends upon reaction with acid potassium permanganate and a
colorimetric determination of the phosphate as the blue reduction
product of the phosphomolybdate. Accuracy for phosphine residues in
grain is 0.01 ppm.
NATIONAL TOLERANCES
Country Tolerance, ppm Crop
Bulgaria 0 Cereals
Canada Negligible Cereals and
processed foods
CoMECo (i.e. Bulgaria,
Roumania, U.S.S.R.,
German Democratic
Republic and Poland) 0.01 Corn
Country Tolerance, ppm Crop
Czechoslovakia 0 Cereals
0.01 Wheat
Netherlands 0.1 Grain
United States 0.1 Grain
0.01 Processed foods
RECOMMENDATIONS FOR TOLERANCES
Tolerances
The 1966 Joint Meeting (FAO/WHO, 1967) concluded that phosphine
aerates rapidly from treated foodstuff and a residue of 0.1 ppm in a
raw cereal would yield a residue in bread and other food ready for
consumption of a level at or below that which can be detected by
current methods of analysis (0.01 ppm). Therefore, there was no
necessity for an ADI figure. A tolerance of 0.1 ppm as PH3 on cereals
was recommended.
Considerable data are now available that show processed foods
fumigated with aluminum phosphide according to good agricultural
practice will have phosphine residues close to or below the
sensitivity of the analytical methods presently used (0.01 to 0.001
ppm). According to good agricultural practice the treated processed
food shall be aerated for a minimum of 48 hours before it is offered
to the public. Furthermore, under no condition shall the aluminum
phosphide or its unreacted residues come in contact with the processed
food.
When used according to the above good agricultural practices, the
following tolerances are recommended :
Cereal products (only items to be cooked)
vegetables, dried spices 0.01 ppm
Raw cereals 0.1 ppm
FURTHER WORK
Further work desirable
It is desirable to have more data on the residues likely to result
from the fumigation of cereal products, dried fruit, tree nuts, and
other processed food that may be eaten without cooking. If there
should be a need for a tolerance on any of these foods, the additional
data will be used in subsequent meetings for determining the residue
limits.
More data are also desirable on the phosphine residues in various food
moving in commerce and on the amount of phosphine in total diet
studies.
REFERENCES PERTINENT TO EVALUATION FOR TOLERANCES
Bruce, R.B., Robbins, A.J., Tuft, T.O. (1962) Phosphine residues from
Phostoxin treated grain. J. Agric. Food Chem., 10 : 18-21.
Dieterich, W.H., Mayr, G., Hild, K., Sullivan, J.B., Murphy, J. (1967)
Hydrogen phosphide as a fumigant for foods, feeds, and processed food
products. In Gunther, F.A., ed. Residue Reviews, 19 : 135-149.
FAO/WHO. (1967) Evaluation of Some Pesticide Residues in Food. FAO
Mtg. Rept. No. PL: CP/15; WHO/Food Add./67.32
Feuersenger, M. (1960) Uber die Bestimmung von
Schädlingsbekampfungsmitteln in Lebensmitteln. Bundesgesundheitsblatt
(10): 149-1952.
Heseltine, H.K. (1963) Detection and estimation of fumigants in
air-determination of phosphine. In Pest Infestation Research,
p. 40-41.
Heseltine, H., Thompson, R.H. (1957) The use of aluminum phosphide
tablets for the fumigation of grain. Milling, Part 1 CXXIX (24): 676;
Part 2 CXXIX (25): 730; Part 3 CXXIX (26) : 774.
Liscombe, E.A.R. (1963) Hydrogen phosphide in tablet form as a grain
fumigant. Research for Farmers, Can. Dept. Agric. (Summer 1963).
Wagner, R.M., Fogleman, R.W. (1962) Determination of phosphine
residues in commercial wheat flour. Unpublished report from
Hazleton-Nuclear Science Corporation to Hollywood Termite Control Co.,
Inc. (Jan. 9, 1962).