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
See Also: Toxicological Abbreviations Hydrogen phosphide (FAO/PL:1967/M/11/1) Hydrogen Phosphide (FAO/PL:1969/M/17/1) Hydrogen phosphide (WHO Pesticide Residues Series 1)