WORLD HEALTH ORGANIZATION FOOD AND AGRICULTURE ORGANIZATION ORGANISATION MONDIALE DE LA SANTE ORGANISATION POUR L'ALIMENTATION ET L'AGRICULTURE VBC/DS/77.24 ORIGINAL: ENGLISH DATA SHEETS ON PESTICIDES No. 24 December 1976 ZINC PHOSPHIDE It must be noted that the issue of a Data Sheet for a particular pesticide does not imply endorsement of the pesticide by WHO or FAO for any particular use, or exclude its use for other purposes not stated. While the information provided is believed to be accurate according to data available at the time when the sheet was compiled, neither WHO nor FAO are responsible for any errors or omissions, or any consequences therefrom. The issue of this document does Ce document ne constitue pas une not constitute formal publication. Il ne doit faire publication. It should not be l'objet d'aucun compte rendu ou reviewed, abstracted or quoted résumé ni d'aucune citation sans without the agreement of the l'autorisation de l'Organisation Food and Agriculture des Nations Unies pour Organization of the United l'Alimentation et l'Agriculture Nations or of the World Health ou de l'Organisation Mondiale de Organization. la Santé. Part 1 - General information CLASSIFICATION: Primary use: Rodenticide Secondary uses: None Chemical group: Inorganic phosphide Data sheet No.: 24 Date issued: December 1976 1.1 COMMON NAME - ZINC PHOSPHIDE Identity: Zn3 P2 Synonyms: Local synonyms: 1.2 SYNOPSIS A rodenticide of high mammalian toxicity which in the presence of dilute acid will decompose to liberate phosphine. It is not cumulative in body tissues. 1.3 SELECTED PROPERTIES 1.3.1 Physical characteristics A grey powder of high melting point which sublimes when heated in the absence of oxygen. 1.3.2 Solubility Practically insoluble in water and ethanol. Soluble in benzene and carbon disulfide. 1.3.3 Stability Stable when dry but decomposes slowly in moist air. It reacts violently with acids with decomposition to the spontaneously inflammable phosphine gas. 1.3.4 Vapour pressure Very low. Phosphine odour detectable at 1.5-3.0 ml/m3 of air, depending on its purity. 1.4 AGRICULTURE, HORTICULTURE AND FORESTRY 1.4.1 Common formulations 2.5% and 5% pastes for bait preparations. These are diluted with 10 times their own weight of bait. 1.4.2 Pests mainly controlled Mice, common rat, ship's rat, field mice, gophers, ground squirrels, prairie dogs. 1.4.3 Use pattern Confined in most countries to trained personnel. 1.4.4 Unintended effects Under exposed conditions toxicity is lost in about two weeks. 1.5 PUBLIC HEALTH PROGRAMME Rodent control - see HOUSEHOLD USE 1.6 HOUSEHOLD USE Rodent control. Under some circumstances secondary poisoning can result to cats eating freshly poisoned rodents. Part 2 - Toxicology and risks 2.1 TOXICOLOGY - MAMMALS 2.1.1 Absorption route: Absorbed by inhalation and from the gastrointestinal tract. 2.1.2 Mode of action: Probably decomposes to phosphine in the stomach and is absorbed both as phosphine and as the phosphide. It has a toxic action on the heart, liver and kidneys. Death occurs from heart and kidney failure. 2.1.3 Excretion products: Excreted in urine either as a hypophosphite or as dissolved phosphine. The presence of strong reducing substances in the urine is a common feature of poisoning with this material. Also, exhaled as phosphine from the lungs. Other metabolites include phosphoric acid and phosphate. 2.1.4 Toxicity, single dose Oral: LD50 Rat(M)41 mg/kg. After a massive dose, death may occur in 70 minutes; with smaller doses, death may be delayed from 24 hours up to 2-3 days. Symptoms appear after 20-25 minutes. Animals become prostrate with deep slow respiration, finally terminating in convulsions. Posture at death is characteristic: animals are found on their bellies with legs and tail spread out. Dermal: No information. 2.1.5 Toxicity, repeated doses Oral: After repeated doses, kidney damage and hyaline degeneration of the myocardium was observed. Livers showed cloudy swelling, hyaline degeneration and necrosis usually located in the centre of the lobules. Inhalation No information. However, inhalation of phosphine gas or dust would be hazardous. See 2.2.2 below for relevant human data. Cumulation of compound: Zinc phosphide is not cumulative in any body tissues. Cumulation of effect: In case of repeated exposure, there is cumulation of effect resulting in liver, kidney and lung damage. 2.1.6 Dietary studies Short-term: Six rats were fed a diet containing 300 ppm zinc phosphide. During the first week weight gains were markedly reduced and all six died during the second week of feeding. A further group of six rats were fed zinc phosphide 200 ppm for one month. Two deaths were recorded in the second week and weight gains were half that of the controls over the feeding period. Histopathology revealed liver damage in the peripheral and central lobular areas. The lungs showed evidence of congestion with haemorrhage or exudate in the alveolar spaces. Long-term: No information. 2.1.7 Supplementary studies of toxicity Carcinogenicity No information available. Teratogenicity No information available. 2.1.8 Modifications of toxicity Experiments in dogs have shown that zinc phosphide has a low toxicity on these animals unless it is combined with a dilute acid or following the stimulation of normal gastric secretion. Under these circumstances phosphine is liberated in the stomach. 2.2 TOXICOLOGY - MAN 2.2.1 Absorption Absorbed from the gastrointestinal tract. It can also be absorbed by inhalation of dust or of liberated phosphine gas. Does not appear to be absorbed through the intact skin, but can be absorbed through abrasions in the skin. 2.2.2 Dangerous doses Single: A dose of 5 g has caused death. However a 50 g dose has been survived. Toxicity is lessened if vomiting occurs soon after ingestion. Phosphine gas can be hazardous to rodent control officers. 2.8 mg/litre of air is rapidly fatal in less than 30 minutes, but levels of 0.14-0.26 can be withstood for 30-60 minutes without consequences. Repeated: Doses in the region of 100 mg daily appear to be harmless, though 30 mg has been stated to cause nausea. 2.2.3 Observations of occupationally exposed workers The safety record of this compound has been good; one industrial accident has been reported involving three cases. 2.2.4 Observations on exposure of the general population Cases of poisoning, both accidental and intentional have resulted from ingestion of zinc phosphide, see 2.2.6 below. 2.2.5 Observations on volunteers Volunteers who ate three geese poisoned with zinc phosphide over a period of two days were unaffected on the first day. However, on the second day two of the three volunteers suffered from stomach pains and diarrhoea. 2.2.6 Reported mishaps Twelve children were poisoned by eating contaminated barley. Several cases of poisoning have occurred as domestic accidents. Between 1917 and 1965, 26 fatalities have been reported from zinc phosphide poisoning, of which 18 were suicides. 2.3 TOXICITY TO NON-MAMMALIAN SPECIES 2.3.1 Fish No data available but presumably toxic. 2.3.2 Birds Very toxic. 2.3.3 Other species Very toxic to cows, goats, sheep, pigs, wild rabbits. Part 3 - For regulatory authorities RECOMMENDATIONS ON REGULATION OF COMPOUND 3.1 RECOMMENDED RESTRICTIONS ON AVAILABILITY (For definition of categories, see introduction.) All formulations, category 2 3.2 TRANSPORTATION AND STORAGE All formulations: United Nations Classification 6.1 for all formulations. Should be stored in clearly labelled, hermetically sealed impermeable containers away from oxidizing agents, acids and living quarters, under lock and key, secure from access by unauthorized persons and children. They must not be stored in damp conditions or be allowed to become damp, as in these circumstances there is both a toxic and fire hazard. No food or drink should be stored in the same compartment. 3.3 HANDLING All formulations: Full protective clothing should be used by all those handling the compound. Adequate washing facilities should be available at all times during handling and should be close to the site of handling. Eating, drinking and smoking should be prohibited during handling and before washing after handling. Baits of zinc phosphide should be removed and the area thoroughly cleaned up after the necessary purpose has been fulfilled. 3.4 DISPOSAL AND/OR DECONTAMINATION OF CONTAINER All formulations: Containers must either be crushed and buried below the topsoil or burned. Care must be taken to avoid subsequent contamination of water sources. Decontamination of containers in order to use them for other purposes should not be permitted. 3.5 SELECTION, TRAINING AND MEDICAL SUPERVISION OF WORKERS All formulations: Pre-employment and periodic medical examination of workers desirable. Workers suffering from active hepatic or renal disease should be excluded from contact. Special account should be taken of the workers' mental ability to comprehend and follow instructions. Training of workers in techniques to avoid contact essential. 3.6 ADDITIONAL REGULATIONS RECOMMENDED IF DISTRIBUTED BY AIRCRAFT All formulations Not applicable. 3.7 LABELLING All formulations Minimum cautionary statement "POISON" (skull and crossbones insignia). Zinc phosphide is a very toxic substance. Do not inhale dust or fumes. Keep this material or baits containing it, out of reach of children and domestic animals and well away from foodstuffs, animal feed and their containers. Keep dry and away from acids of all kinds. 3.8 RESIDUES IN FOOD If used correctly as a bit, residues of zinc phosphide will not appear in human food. 3.8.1 Maximum residue levels Levels for zinc phosphide have not been recommended by the joint FAO/WHO meeting on Pesticide Residues. Part 4 - Prevention of poisoning in man and emergency aid 4.1 PRECAUTIONS IN USE 4.1.1 General Zinc phosphide is a rodenticide of high toxicity. It is readily absorbed from the gastrointestinal tract and dusts may be absorbed by inhalation. In addition it may decompose to liberate phosphine gas which is extremely hazardous. It is not readily absorbed through the intact skin. 4.1.2 Manufacture and formulation T.L.V. For phosphine gas, PH3 (AGGIH) 0.4 mg/m3 (USSR) 0.1 mg/m3. Closed system and forced ventilation may be required to reduce as much as possible the exposure of workers to the chemical. 4.1.3 Mixers and applicators Particularly when opening container and when mixing, protective impermeable boots, clean overalls, gloves and a face mask should be worn. Mixing, if not mechanical, should always be carried out with a paddle of appropriate length. The applicator should avoid inhaling dust particles and avoid contact with the mouth. Particular care is needed when the equipment is being washed after use. All protective clothing should be washed immediately after use including the insides of gloves. Splashes must be washed immediately from the skin or eyes with large quantities of water. Before eating, drinking or smoking, hands and other exposed skin should be washed. Zinc phosphide baits should not be used where there is a risk of contaminating food, animal feeding stuffs or drinking or washing water. Exposed baits should be laid in containers clearly marked "Poison". Baits should not be laid unless all access by children and animals other than rats and mice can be prevented. Except in locked unoccupied premises, baits should not remain down for more than 24 hours. All exposed baits and their containers should be removed after treatment and burned. Rodent bodies should be searched for and destroyed by burning. 4.1.4 Other associated workers (including flagmen in aerial operations) Not applicable. 4.1.5 Other populations likely to be affected With correct use as described under mixers and applicators (4.1.3 above) other populations should not be exposed to hazardous amounts of zinc phosphide. 4.2 ENTRY OF PERSONS INTO TREATED AREAS The general public should be excluded from all access to premises while baits are exposed. 4.3 SAFE DISPOSAL OF CONTAINERS AND SPILLAGE Residues in containers should be emptied in a diluted form into a deep pit, taking care to avoid contamination of ground waters. Decontamination of containers in order to use them for other purposes should not be permitted. Spillage should be removed as much as possible into a deep dry pit and the remainder washed away with large quantities of water. It should be borne in mind during these operations that in the presence of water, phosphine gas will be liberated and therefore a respirator may be advisable. 4.4 EMERGENCY AID 4.4.1 Early symptoms of poisoning After ingestion there is a latent period of approximately one hour. Earliest symptoms are usually nausea, abdominal pain, chest tightness, excitement, and agitation and a feeling of chilliness and of being "cold all over". Vomiting is constant. Shock, early dyspnoea, thirst, oliguria, convulsions or coma have been observed. 4.4.2 Treatment before person is seen by a physician if these symptoms appear following exposure If swallowed, vomiting should be induced if the person is conscious. Complete rest and quiet are indicated. Part 5 - For medical and laboratory personnel 5.1 MEDICAL DIAGNOSIS AND TREATMENT OF CASES OF POISONING 5.1.1 General information Zinc phosphide is a compound of high toxicity normally used in bait form as a rodenticide. It is readily absorbed by the gastrointestinal tract and may be absorbed by inhalation in dust form or as phosphine gas. Although it is not absorbed through the unbroken skin, it may be absorbed through cuts or abrasions. Its toxicity is related to its liberation of phosphine on decomposition, following absorption. Organs that may be affected include the heart, lung, liver and kidney. 5.1.2 Symptoms and signs There is a latent period of about 60 minutes following ingestion and the appearance of symptoms. Earliest symptoms are usually nausea, abdominal pain, chest tightness, excitement and agitation and a feeling of chilliness, of being "cold all over". Vomiting is constant. Later symptoms may include shock, dyspnoea, thirst, oliguria and kidney failure, convulsions and coma. Purpura and asymptomatic thrombocytopenia have been observed. Early deaths may occur from pulmonary oedema. The majority of fatal cases die after 30 hours as a result of cardiac damage. 5.1.3 Laboratory There are no simple tests to confirm exposure. However, the patient's breath may smell of phosphine (garlic odour). Serum zinc levels will be raised and the urine will contain reducing substances, which may be hypophosphite, dissolved phosphine or due to zinc glycosuria. If stomach aspiration is performed a black fluid with a pungent smell of phosphine is typical of ingestion of this compound. Circulating methemalbumin has also been observed. 5.1.4 Treatment Treatment is mainly symptomatic. Vomiting should be induced immediately followed by gastric lavage with 2-4 litres of water. It is important to clear zinc phosphide from the gastrointestinal tract, with non-oily purgatives if absorption of zinc phosphide particles is to be avoided. Correction of fluid loss and electrolyte disturbances is important. Two suggested treatments are the use of 0.5 gm of copper sulfate (as a 1% aqueous solution) which has the additional theoretical benefit of forming insoluble copper phosphide, or gastric lavage with a 1 in 1000 potassium permanganate solution, which has been suggested as a means of oxidizing the phosphide. 5.1.5 Prognosis Early vomiting improves the prognosis. If the patient survives for three days the further outlook is good. However, no patient who has experienced shock has yet survived. 5.1.6 References of previously reported cases The following review covers poisoning cases with zinc phosphide reported in Europe and gives a detailed case history. (a) Stephenson, J. B. (1967) Archives of Environmental Health, 15, 83-88 (b) Van Oettingen, E. W., The toxicity and potential dangers of zinc phosphide and of hydrogen phosphide, Public Health Report 203, 1.1947 (c) Frketic, J., Magdic, A. & Stajduhor-Djuric, Z., Otravanja cinkovrim fosfidom Arh. Hig. Rada., 8.15.1957 5.2 SURVEILLANCE METHODS There are no readily available surveillance procedures. 5.3 LABORATORY METHODS References only are given. 5.3.1 Detection and analysis Microdistillation of liver and reaction of the phosphorous with silver nitrate to form silver phosphide using paper electrophoresis. Curry, A. S. et al., J. Pharm. Pharmacol., 10:635, 1958. A sophisticated method involving neutron activation analysis for the determination of phosphides and white phosphorous in biological materials has been published. Krishnan, S.S. et al., Anal. Chem., 42(6), 557-560, 1970. A method involving gas chromatography is reported by Robinson, W. H. et al., J. Ag. Food Chem., 19(5), 875-8, 1971. 5.3.2 Other tests in cases of poisoning These include measurement of serum zinc levels, estimation of urine reducing substances, and estimation of methaemoglobin.