WORLD HEALTH ORGANIZATION FOOD AND AGRICULTURE
ORGANISATION MONDIALE DE LA SANTE ORGANISATION POUR L'ALIMENTATION
DATA SHEETS ON PESTICIDES No. 24
It must be noted that the issue of a Data Sheet for a
particular pesticide does not imply endorsement of the pesticide by
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Organization. la Santé.
Part 1 - General information
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:
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.
Practically insoluble in water and ethanol. Soluble in benzene and
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,
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
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
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
No information available.
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
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
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
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
No data available but presumably 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.
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
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
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
Minimum cautionary statement "POISON" (skull and crossbones
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
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
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
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
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.
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.
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.
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,
(b) Van Oettingen, E. W., The toxicity and potential dangers of zinc
phosphide and of hydrogen phosphide, Public Health Report 203,
(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.