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Zinc phosphide

Publication Date: 9/93

TRADE OR OTHER NAMES

Trade names for commercial products containing zinc phosphide include Arrex, Denkarin Grains, Gopha-Rid, Phosvin, Pollux, Ridall, Ratol, Rodenticide AG, Zinc-Tox and ZP.

INTRODUCTION

Zinc Phosphide is an inorganic chemical that is used to control rats, mice, voles, ground squirrels, prairie dogs, nutria, muskrats, feral rabbits and gophers. It is also uses as a tracking powder for the control of house mice. It is used on crop areas and on non-crop areas including lawns, golf courses, highway medians, and areas adjacent to wetlands (2). It may be formulated as a grain based bait, as scrap bait or as a paste. Rodenticide baits usually contain 2.0 percent of zinc phosphide.

Zinc Phosphide is a Restricted Use Pesticide (RUP). RUPs may be purchased and used only by certified applicators.

TOXICOLOGICAL EFFECTS

ACUTE TOXICITY

Some formulations of this rodenticide are classified as highly toxic and require the signal word DANGER-POISON on the label. Others are either moderately toxic or only slightly toxic and thus require the signal words WARNING or CAUTION respectively. Zinc phosphide reacts with water and acid in the stomach and causes severe irritation (7). Symptoms of acute zinc phosphide poisoning include nausea, shock, weak heart beat and low blood pressure, loss of consciousness (3). Other symptoms include vomiting, diarrhea, cyanosis, rales, restlessness and fever. There are documented cases of adults dying from massive doses of the pesticide (4,000 to 5,000 mg) although others have survived acute exposure of as high as 25,000 mg to 100,000 mg of zinc phosphide if vomiting occurred early and absorption was limited (4).

The LD50 for the technical product (80-90% pure) is 45.7 mg/kg while the LD50 values for lower concentration formulations are slightly higher (i.e. less toxic). In sheep the LD50 ranges from 60 to 70 mg/kg (6).

The inhalation of zinc phosphide or its breakdown product phosphine gas may result in acute toxicity (7). No specific doses were mentioned in the reference. The compound is non-irritating to the skin and eyes (5).

CHRONIC TOXICITY

Rats fed zinc phosphide over a wide range of doses experienced toxic effects at the lowest dose tested. Increased liver, brain and kidney weights were noted in rats exposed to around 10 mg/kg. Body hair loss, reduction in body weight, and reduction of food intake were all noted at 3.5 mg/kg. The study was conducted over thirteen weeks (7).

There have been no observed symptoms of chronic poisoning due to zinc phosphide exposure in humans (5). However another reference noted that chronic exposure to sublethal concentrations for extended periods of time may produce toxic symptoms (7). No specific note was made of the toxic symptoms or the doses required to produce them. In that the available information is inconclusive or undocumented, no definitive conclusions can be drawn to the chronic toxic potential of zinc phosphide.

Reproductive Effects

No information currently available.

Teratogenic Effects

No information currently available.

Carcinogenic Effects

No information currently available.

Mutagenic Effects

No information currently available.

Organ Toxicity

Damage to the kidneys, to the liver and the stomach have been noted in humans but only at high acute doses of the rodenticide. Zinc phosphide reacts with water and stomach juices to release phosphine gas which can enter the blood stream and adversely affect the lungs, liver, kidneys, heart and central nervous system (7).

There is little tendency for the compound to concentrate in living tissue.

Fate in Humans and Animals

Zinc phosphide reacts in the stomach and intestines with water and hydrochloric acid to liberate phosphine gas. Small amounts of the rodenticide fed to experimental animals may have produced an eighty percent absorption of zinc as well.

ECOLOGICAL EFFECTS

Zinc Phosphide is highly toxic to wild birds and freshwater fish. It is also toxic to non-target mammals. Nearly sixty studies have been conducted on the toxicity of this rodenticide to wild animals. The most sensitive bird species which have been evaluated are geese (LD50 of 7.5 mg/kg for the White- fronted Goose). Pheasants, morning doves, quail, mallard ducks and the horned lark are also very susceptible to this compound. Blackbirds are less sensitive (2).

The fish species which have been evaluated include bluegill sunfish (LC50 = 0.8 mg/l) and rainbow trout (0.5 mg/l) (5). Carp were also found to be susceptible to zinc phosphide, especially in weakly acidic water.

Secondary toxicity to mammalian predators from zinc phosphide is rather low (2) primarily because the compound does not significantly accumulate in the muscles of target species. Some of the toxic effects to predators have been due to the ingestion of zinc phosphide that was in the digestive tract of the target organism (the prey). However, most predators will not eat the digestive tract. Studies on secondary organisms have focused on coyotes, fox, mink, weasels and birds of prey. Under field conditions most of the toxic effects to non-target wildlife are due to misuse or misapplication of this rodenticide (2).

ENVIRONMENTAL FATE

Zinc phosphide may be applied as an active ingredient in either bait or a dust. Soil acidity tends to break the compound down liberating phosphine a highly toxic gas. There is a potential for movement of this compound into adjacent, slightly acidic waters, where it can endanger fish populations (7).

PHYSICAL PROPERTIES AND GUIDELINES

Exposure Guidelines:

TLV: 0.3 ppm (7)
RfD: 0.0003 mg/kg

Physical Properties:

CAS #: 1314-84-7
Chemical name: Zinc phosphide
Chemical class/use: inorganic rodenticide
Solubility in water: practically insoluble
Solubility in other solvents: practically insoluble in alcohol; slightly soluble in benzene
Melting Point: >420 degrees C
Vapor Pressure: Negligible in the dry state

BASIC MANUFACTURER

Bell Laboratories, Inc.
3699 Kinsman Blvd.
Madison, WI 53704

Review by Basic Manufacturer:

Comments solicited: December, 1992
Comments received:

HACCO, Inc.
537 Atlas Ave.
Madison, WI 53714

Review by Basic Manufacturer:

Comments solicited: December, 1992
Comments received:

REFERENCES

  1. Briggs, S.A. 1992. Basic Guide to Pesticides: Their Characteristics and Hazards. Hemisphere Publishing Corp., WA.
  2. Johnson, G.D. and K.A. Fagerstone. 1992. Primary and Secondary Hazards of Zinc Phosphide to Nontarget Wildlife: A Review of the Literature. Denver Wildlife Research Center, USDA/APHIS, Denver, CO.
  3. Clarkson, T.W. 1991. Inorganic and Organometal Pesticides. In Handbook of Pesticide Toxicology, Volume 2, Classes of Pesticides. W.J. Hayes and E.R. Laws (eds.). Academic Press, NY.
  4. Ecobichon, D.J. 1991. Toxic Effects of Pesticides. In Casarett and Doull's Toxicology: The Basic Science of Pesticides, Fourth Edition. M.O. Amdur, J. Doull and C.D. Klassen (eds.). Pergamon Press, NY.
  5. The Agrochemicals Handbook. 1991. The Royal Society of Chemistry. Cambridge, England.
  6. Worthing, C.R. (ed.). 1991. The Pesticide Manual: A World Compendium. The British Crop Protection Council.
  7. TOXNET. 1992. Hazardous Substance Database. Zinc Phosphide. National Library of Medicine. Hazardous Substance Data Base.