FAO, PL:CP/15
WHO/Food Add./67.32
EVALUATION OF SOME PESTICIDE RESIDUES IN FOOD
The content of this document is the result of the deliberations of the
Joint Meeting of the FAO Working Party and the WHO Expert Committee on
Pesticide Residues, which met in Geneva, 14-21 November 1966.1
1 Report of a Joint Meeting of the FAO Working Party and the WHO
Expert Committee on Pesticide Residues, FAO Agricultural Studies, in
press; Wld Hlth Org. techn. Rep. Ser., 1967, in press
HYDROGEN PHOSPHIDE
IDENTITY
Synonyms
phosphine
Formula
H3P
Note
The data here considered refer to hydrogen phosphide from tablets or
similar formulations based upon aluminium phosphide from which the gas
is released on exposure to moist atmosphere.
BIOLOGICAL DATA AND TOXICOLOGICAL EVALUATION
Acute toxicity
Animal Route Concentration Death occurred after the References
following time of exposure
Rat inhal. 0.68 mg/l 65-75 min. Neubert &
Hoffmeister,
1960
Rat inhal. 1.47 mg/l 35-50 min. Neubert &
Hoffmeister,
1960
Rat, rabbit inhal. 0.2-1% 30 min. Laue, 1954
Rabbit inhal. 10 ppm 120 min. daily, during 2 Harger &
days Spolyar, 1958
Guinea-pig inhal. 25 ppm 4 hr daily, during 2 days Harger &
Spolyar, 1958
Mouse inhal. 50 ppm 2 hr daily, during 1 day Harger &
Spolyar, 1958
Cat inhal. 25 ppm 2, 3 to 4 hr daily, during Harger &
3 days Spolyar, 1958
Hydrogen phosphide is a very toxic gas with a cumulative effect. There
are no data available on the acute LD50 of phosphide. The LD50 for
rats of the related compound zinc phosphide is 40.5 + 2.9 mg/kg
(Johnson & Voss, 1952).
Man. 2.8 mg hydrogen phosphide/l of air are lethal for man in a
short time (Flury & Zernik, 1931).
The threshold limit for hydrogen phosphide is set at 0.4 mg/m3
(Anon., 1964).
Short-term and long-term studies
It is reported that rats, fed with grain which had been fumigated at
excessive dosages, showed no ill effects, even when the grain was not
cleaned before consumption (Schulemann, 1953).
Comments
If this fumigant is proposed for use on foods other than cereals,
further work is required to establish that no residues left. If,
however, residues are left and cannot be removed, adequate
toxicological studies should be performed.
TOXICOLOGICAL EVALUATION
Cereals treated with aluminium phosphide must be properly cleaned and
washed before being processed for food, so that no residue of powder
derived from the fumigant material reaches the consumer.
RESIDUES IN FOOD AND THEIR EVALUATION
Use pattern
(a) Pre-harvest treatments
Hydrogen phosphide in not used on living plants.
(b) Post-harvest treatments
Hydrogen phosphide is used for controlling insects mainly in grain and
other cereals; but also in legumes and many other dry stored foods.
The tablets are applied as the grain or other foodstuff is being
loaded into bins or box cars, or by insertion whilst the foodstuff is
standing in bins or warehouses. Treatments must be undertaken in grain
bins, or some other kind of enclosure. Gas-proof sheets are sometimes
used to cover stacks of bagged foodstuffs in warehouses. Comparatively
recently the use of hydrogen phosphide has been extended to animal
feeds and processed food for human consumption, subject to
recommendations that no unreacted aluminium phosphide will come into
contact with such food and that none of the food be offered to the
consumer before 48 hours airing has taken place. These foods include
certain items (e.g. dried fruits, nuts) which might be eaten without
cooking.
(c) Other uses
Phosphine as an insecticide is only used as in (b).
(d) Extent of use
Phosphine tablets are registered and used in very many countries, but
fairly extensively in Argentine, Australia, Eastern Europe, India,
Japan, South Africa and Turkey. The manufacturers of the principal
proprietary product ("Phostoxin") estimate that 15 to 20 million
metric tons of grain were treated in 1964.
Tolerances (established or considered)
Comeco (i.e. Bulgaria, - Cereals 0.1 ppm
Roumania, USSR, German
Democratic Republic and
Poland)
Czechoslovakia - Cereals 0.1 ppm
- Wheat 0.01 ppm
Netherlands - Grain 0.1 ppm
Canada - Grain 0.1 ppm
USA - Grain 0.1 ppm
In the USA and Canada petitions have been made to establish a
tolerance of 0.1 ppm of hydrogen phosphide in various processed
foodstuffs including flour and other cereal products, dried fruits
and dried milk.
Residues resulting from supervised trials
In the Netherlands wheat was fumigated in a dose of three, four,
five and six tablets PHOSTOXIN per m3 grain. After this fumigation
the grain was aerated during 48 hours. Analysis after 12 days showed
residues which were under the 0.005 ppm level. Similar results were
obtained in Germany after the exposure over a period, from 48 hours up
to 30 days, of wheat, wheat flour, oats and rice (Unpublished
communication).
Wheat, corn and milo were fumigated in the USA at the maximum
recommended rate and with four times this rate of application.
Experiments were also made to determine the effects of high and low
temperatures, aeration, fumigation of cracked grain, fumigation in
sealed containers and re-fumigation of previously treated grain. The
results showed that the residues almost completely disappeared, within
12 days after the application. Only in sealed containers were high
residues (up to 3 ppm) obtained. After exposure to air the residues
disappeared within 12 days. (Cogburn & Tilton, 1963; Lindgren, Vincent
& Strong, 1958; McGregor, 1961; Strong & Lindgren, 1960.)
Wheat fumigated under practical conditions revealed a maximum residue
of 0.016 ppm just after turning but not aerating. After aerating the
residue dropped to 0.006 ppm. Analyses were made one to 14 days after
treatment of the grain (Bruce, Robbins & Tuft, 1962).
Residues in food moving in commerce
In 99 samples taken at time of import from cargoes shipped from all
over the world to Rotterdam and Amsterdam the amount of insecticide
was determined. One sample showed a residue of 0.3 ppm. The rest of
the investigated samples showed a maximum residue of 0.04 ppm, using a
method with a limit of sensitivity of 0.01 ppm (Phytopharmacy
Committee, Netherlands, 1966).
Investigations carried out on arrival of treated grain in the United
Kingdom showed residues below 0.1 ppm on grain treated with phosphine.
Residues at time of consumption
Various workers have shown that most of the phosphine present in
foodstuffs at the termination of the period of exposure to the
fumigant is very loosely held. For example, flour which at the
termination of an experimental fumigation at a high dosage contained
nearly 700 parts per million, gave less than 0.1 ppm after 24 hours
free exposure to the air (Degesch, Unpublished report).
The rate of evolution of phosphine from aluminum phosphide is
dependant on atmospheric moisture. After short periods of exposure
(e.g. 72 hours or less) at very low moisture contents (e.g. grain of
below nine per cent water content) it is possible for residues of
aluminium phosphide to be present. However such residues readily
disappear during the airing turning and cleaning to which grain is
normally submitted prior to milling (Heseltine & Thompson, 1957;
Feursinger, 1960).
In studies of the effects of baking no significant residues could be
found in bread baked from grain or flour which had been treated
(Bruce, Robbins & Tuft, 1962). The vitamin A and B2 contents of
wheat germ and whole meal flour were not affected by fumigation with
hydrogen phosphide. The differences between untreated and treated were
within the limit of the natural variation. Extension of the exposure
time up to five days did not affect this result (Unpublished report
from Degesch).
Methods of residue analysis
Residues of phosphine may be removed from cereals and similar
foodstuffs for analysis with a stream of nitrogen or other inert gas,
as described by White & Bushey (1949) or Diemair (1954). The method of
Bruce, Robbins & Tuft (1962) in which phosphine is oxidized to
phosphate with bromine and then determined colorimetrically with
ammonium molybdate is suggested. The method is sensitive to 0.01 ppm
of phosphine.
RECOMMENDATIONS FOR TOLERANCES
Phosphine aerates rapidly from treated foodstuffs and a residue of 0.1
ppm in a raw cereal would yield a residue in bread or other food ready
for consumption which is at or below the level of detection by current
methods of analysis (i.e. about 0.01 ppm). Therefore, there is no
necessity for an acceptable daily intake figure. For cereals in
international trade, a tolerance of 0.1 ppm expressed as PH3 is
recommended.
Data exist for the residues likely to result after the treatment of
certain other foods with phosphine. These include some processed
foods. If there should be a need for tolerances for foods other than
cereals therefore the data in respect to each should be reviewed at
subsequent meetings with a view to determining the residue limits in
the foods acceptable to international commerce.
Further work
Further information is desirable on the levels of Phosphine occurring
in foodstuffs which have been treated in the course of commerce.
REFERENCES PERTINENT TO BIOLOGICAL DATA
Anon. (1964) Threshold limit values for 1964, Arch. environm.
Hlth, 9, 545
Flury, F. & Zernik, F. (1931) Schädliche Gase, Berlin, Springer
Harger, R. N. & Spolyar, L. W. (1958) Arch. industr. Hlth, 18, 497
Johnson, H. D. & Voss, E. (1952) J. Amer. pharm. Ass., 41, 468
Laue, V. G. (1954) Nachrichtenblatt für den deutschen
Pflanzenschutzdienst., 8, 13
Neubert, D. & Hoffmeister, I. (1960) Arch. exp. Path. u. Pharmak.,
239, 219
Schulemann (1953) Unpublished report from Degesch, Frankfurt-am-Main.
REFERENCES PERTINENT TO AGRICULTURAL DATA
Bruce, R. B., Robbins, A. J. & Tuft, T. O. (1962) Phosphine residues
from Phostoxin treated grain, Agric. and Food Chem., 10 (1962):
18-21
Cogburn, R. E. & Tilton, E. W. (1963) Studies of phosphine as a
fumigant for sacked rice under gas-tight tarpaulins. J. of Econ.
Entom., 56, pp. 706-708
Degesch. (1965) Deutsche Gesellschaft für Schädlingsbekämpfung,
Frankfurt-am-Main, Report on Phostoxin
Diemair, W. (1954) "Bericht über die Unterschung von mit Phostoxin
begasten Getreide." Thesis University of Frankfurt-am-Main
Feuersenger, M. (1960) Über die Bestimmung von
Schädlingsbekämpfungsmitteln in Lebensmitteln. Bundesgesundheitsblatt
(10) pp. 149-152
Heseltine, H. & Thompson, B. H. (1957) The use of aluminium phosphide
tablets for the fumigation of grain. Milling 28: XII
Lindgren, D. L., Vincent, L. E. & Strong, R. G. (1958) Studies on
hydrogen phosphide as a fumigant. J. of Econ. Entom., 51, PP.
900-903
McGregor, H. E. (1961) Evaluation of phosphine gas as a fumigant. The
Northwestern Miller 265, (13)
Phyto-pharmacy Committee (Netherlands). (1966) Residues of
insecticides in cereals, imported in the Netherlands 1964/65. Second
report, Jan. 1966
Strong, R. G. & Lindgren, D. L. (1960) Germination of cereal, sorghum,
and small legume seeds after fumigation with hydrogen phosphide. J. of
Econ. Entom., 53, (1) pp. 1-4
White, W. E. & Bushey, A. H. (1949) Aluminium phosphide preparation
and composition. J. Am. Chem. Soc., 66: 1666