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Aluminum Phosphide

TRADE OR OTHER NAMES

Current trade or other names include Fastphos, Fumitoxin, Gastoxin, Max- Kill, Phosfume, Phostoxin and Weevilcide (1, 4). Al-phos, Celphide, Celphine, Celphos, Detia-Gas-Ex, and Quick Tox may have been used in previous formulations (1, 3).

REGULATORY STATUS

Aluminum Phosphide is a Restricted Use Pesticide so may be purchased and used only by certified applicators (2). It is in EPA Toxicity Class I and products containing it must bear the signal word DANGER (1, 2). Aluminum Phosphide was first registered for use in the United States in the late 1950s (4).

INTRODUCTION

Aluminum phosphide is an inorganic phosphide used to control insects and rodents in a variety of settings. It is mainly used as an indoor fumigant at crop transport, storage or processing facilities (or in shipholds, railcars, etc.) for both food and non-food crops (1, 3). It may also be used as an outdoor fumigant for burrowing rodent and mole control, or in baits for rodent control in crops (3).

Aluminum Phosphide is available in pellet and tablet form, and is also available in porous blister packs, sachets or as dusts (3, 4). As in the case of Phostoxin, it may be formulated as 55% active ingredient along with ammonium carbamate and inert ingredients (3, 5).

TOXICOLOGICAL EFFECTS

ACUTE TOXICITY

Phostoxin and aluminum phosphide are not absorbed dermally; main routes of exposure are through ingestion and inhalation (5). They are highly toxic via both these routes. The reported rodent oral LD50 is 11.5 mg/kg for Phostoxin, with that for the technical compound presumably lower (4, 5). Aluminum phosphide ingested orally reacts with water and stomach acids to produce phosphine gas, which may account in a large part for observed toxicity (6, 7). Phosphine generated in the gastrointestinal tract is readily absorbed into the bloodstream, and it is readily absorbed through the lung epithelium (6). Phosphine may cause denaturing of oxyhemeglobin (the carrier for systemic distribution of oxygen) as well as enzymes important for respiration and metabolism, and may also have effects on cellular membranes (9). Inhaled aluminum phosphide dust undergoes the same reaction in the moist air sacs of the lung, although at a lower rate, resulting in similar local and systemic effects (6, 7).

The rodent 4-hour inhalation LC50 for phosphine gas (the product of phosphide reaction with water) is widely reported as 15 mg/meters cubed (15 ug/L, or approximately 10.7 ppm) (6,7). Recent study indicates that the rodent 4-hour inhalation LC50 may exceed 15 mg/meters cubed (8). In this study, male and female rats experienced no mortality at one-time 6-hour exposure levels of 15 mg/meters cubed (8). Red mucous discharge from the nostrils ceased during a 14-day recovery period; postmortem examination revealed no gross or microscopic treatment-related effects (8).

Symptoms of mild to moderate acute aluminum phosphide toxicity include nausea, abdominal pain, tightness in chest, excitement, restlessness, agitation and chills (5, 6). Symptoms of more severe toxicity include, diarrhea, cyanosis, difficulty breathing, pulmonary edema, respiratory failure, tachycardia (rapid pulse) and hypotension (low blood pressure), dizziness and/or death (6, 7). Convulsions have been reported in lab animals exposed to high concentrations of phosphine (6). Severe exposure may also result in proteinuria or glucosuria (low molecular weight proteins or glucose in the urine) indicating kidney damage (7).

Pathological examination of exposed laboratory animal tissue and results of post-mortem examinations of phosphine poisoning victims generally indicate hypoxia, with evidence of local trauma in the gastrointestinal tract or lungs, liver, kidneys and central nervous system (6).

Data from a cohort of occupationally-exposed Indian agricultural fumigation workers undergoing single exposures of approximately 1-3 mg/meters cubed (0.71 - 2.22 ppm) revealed reversible (within 2 weeks) symptoms of mild acute exposure (of the types noted above) (7).

CHRONIC TOXICITY

Rats fed aluminum phosphide-fumigated chow averaging 0.51 ppm phosphine residues (approximately 0.43 mg/kg/day) showed no differences from the control animals with respect to blood or urine chemistry and no observable differences in tissue structure (7). It was reported that workers had probably encountered similar exposures on an intermittent basis (in some cases over as long as a 20 year period) and had yet to show signs of toxicity (7), which suggests that chronic effects may be minor or have a very long latency period.

Inhalation studies were conducted on the effects of phosphine gas on male and female rats exposed at levels of 0.5, 1.5, and 4.5 mg/meters cubed for six hours per day over a 13 week period (8). Higher exposure groups (7.5 and 15 mg/meters cubed) were added following preliminary acute test results (8). Results indicated that 15 mg/meters cubed was lethal to 4 out of ten female rats following three days of exposure (8). Significant treatment-related effects on body weight and decreased food consumption were seen across all treatment groups and sexes, but were reversible (8). Decreases in red-blood cell counts, hemoglobin, hematocrit and increased platelet counts were seen in male rats of the 4.5 mg/meters cubed group (8). Dose-related changes in blood urea nitrogen and other clinical parameters were also seen across exposure groups (8). Post-mortem examination of test animals revealed microscopic lesions in the outer cortex of the kidneys of rats exposed to 15 mg/meters cubed, but not at lower exposure levels (8). All of these effects were apparently reversible following a four-week recovery period (8).

Reproductive Effects

Post-mortem examination of test animals revealed apparently reversible damage to seminal vesicles in male rats exposed to 1.5 mg/meters cubed phosphine (8). Pregnancy rates for female rats exposed to 4.5 mg/meters cubed on days 6-10 of gestation were comparable to those in the unexposed group (8). No adverse effects on uterine implantation were seen in the 0.3, 3 and 4.5 mg/meters cubed exposure groups, although a statistically significant elevation in resorptions was seen in the 0.015 mg/meters cubed exposure group (8). Thus, this effect may not be dose-related as it there was not increased effect with increased dose. The available evidence for reproductive effects in animals suggest that reproductive effects are not likely in humans under normal conditions.

Teratogenic Effects

No effects on fetal birthweights or sex ratios were seen in offspring of rats exposed to up to 4.5 mg/meters cubed for six hours a day on days 6-10 of gestation (8). No statistically significant differences in development or morphology were seen in the offspring of rats in the exposed groups versus unexposed groups upon external, visceral or skeletal evaluation (8). The available evidence for teratogenic effects in animals suggests that such effects are not likely in humans under normal conditions.

Mutagenic Effects

No evidence was available regarding the ability of aluminum phosphide or phosphine to cause mutations or increase the mutation rate. Studies of human lymphocyte cultures exposed under laboratory conditions showed significant increases in phosphine-induced total chromosomal aberrations (e.g. gaps, deletions, breaks or exchanges) with increasing phosphine concentrations (9). In the same study, analysis of lymphocyte cultures drawn from fumigators (using phosphine exclusively) exposed to phosphine showed significant increases in the same types of chromosomal aberrations.

Carcinogenic Effects

No data are currently available; it is possible that some testing on the oncogenicity may be initiated in the near future (4).

Organ Toxicity

Acute toxicity resulting from aluminum phosphide exposure is apparent most immediately in the heart and lungs; it may also affect the central nervous system, liver and kidneys (6).

Fate in Humans & Animals

As stated above, aluminum phosphide rapidly reacts with water to form highly toxic phosphine gas. It has been reported that aluminum phosphide may be absorbed directly into the bloodstream, although this is probably a very minor route of entry (10). That phosphine which is not expired through the lungs may be metabolized to phosphates, hypophosphite and phosphite (1, 10).

ECOLOGICAL EFFECTS

Effects on Birds

The precise oral or inhalation median lethal doses for aluminum phosphide or phosphine in birds are not known. It is reported that exposure of turkeys and hens to 211 and 224 mg/meters cubed for 74 and 59 minutes respectively resulted in labored breathing, swelling of organs, tonic-clonic convulsions and death (11). Due to the mechanism of action it is likely that it could similarly affect other bird species at similar levels of exposure. Fortunately, such exposure is not very likely, as phosphine is rapidly dissipated in open air.

Effects on Aquatic Species

The reported acute LC50 is 4.1 ug/L in rainbow trout, indicating very high toxicity (12). No data were available regarding the specific toxicity of aluminum phosphide or of phosphine to other fish or aquatic species (e.g. LC50 or EC50 values), but due to the mechanism of action it is likely that it will be very highly toxic to them as well. Such exposure is unlikely; aluminum phosphide will rapidly react to form phosphine gas, which is somewhat soluble in water, but will mainly bubble up into the air (2).

Effects on Other Animals (Non target species)

No data were available.

ENVIRONMENTAL FATE

Breakdown of Chemical in Soil and Groundwater

Aluminum phosphide will breakdown spontaneously in the presence of water to form a gaseous product, and so it is non-persistent and non-mobile in the soil environment, and poses no risk to groundwater.

Breakdown of Chemical in Surface Water

It is highly unlikely that aluminum phosphide or phosphine will be found in surface waters.

Breakdown of Chemical in Vegetation

No data were available.

PHYSICAL PROPERTIES AND GUIDELINES

Aluminum phosphide is a greenish gray solid at room temperature. Hydrogen phosphide (phosphine) gas, produced by reaction with aluminum phosphide in contact with water (even at ambient humidity), has an odor similar to garlic or decaying fish (2, 5).

Exposure Guidelines:

ADI: NA
HA: NA
RfD: 0.004 mg/kg/day (13)
PEL/TLV: For phosphine 0.42 mg/meters cubed (0.3 ppm) (14)

Physical Properties:

Chemical Name: aluminum phosphide
CAS: 20859-73-8
Molecular Weight: 57.95 (3)
Water solubility: Insoluble; reactive with water to form hydrogen phosphide (phosphine), H3P (3)
Solvent solubility: Not Available
Melting Point: 1,000 degrees C (5)
Vapor Pressure: negligible @ 25 degrees C (5)
Partition Coefficient (octanol/water): Not Available
Adsorption Coefficient: Not Available

BASIC MANUFACTURER

Degesch America, Inc.
275 Triangle Dr.
P. O. Box 116
Weyers Cave, VA 24486 USA
Telephone: 740-234-9281

Review by Basic Manufacturer:

Comments solicited: June, 1995
Comments received: January, 1996

REFERENCES

  1. Royal Society of Chemistry. 1991 (as updated). The Agrochemicals Handbook, Royal Society of Chemistry Information Services, Cambridge, UK.
  2. Meister, R.T. (ed.). 1992. Farm Chemicals Handbook '92, Meister Publishing Co., Willoughby, OH.
  3. US Environmental Protection Agency. 1992. Office of Pesticides and Toxic Substances, Fact Sheet Number 118: Aluminum Phosphide/Magnesium Phosphide. Washington, DC.
  4. Shaheen, D. 1996. Technical Vice President, Degesch America, Inc., Weyers cave, VA, Personal Communication.
  5. Degesch America, Inc. 1988. Material Safety Data Sheet: Aluminum Phosphide, Phostoxin, Degesch America, Weyers Cave, VA.
  6. Gehring, P.J., Nolan, R.J., Watanabe, P.G. and Schumann, A.M. 1991. Chapter 14: Solvent, Fumigants and Related Compounds, In Hayes, W.J. and Laws, E.R., Jr. (Eds.) Handbook of Pesticide Toxicology, Academic Press, New York, NY.
  7. U.S. Department of Health and Human Services. 1994. File: Aluminum Phosphide Hazardous Substance Data Base (HSDB). HHS. Washington, DC.
  8. Newton, P.E., Shroeder, R. E., Sullivan, J. B., Busey. W.M. and Banas, D.A. 1993. Inhalation toxicity of Phosphine in the rat: acute, subchronic and developmental Inhal Toxicol 5(2):223-239.
  9. Garry, V.F., Griffith, J., Danzl, T. J., Nelson, R. J., Whorton, E. B., Krueger, L. A. and Cervenka, J., Human Genotoxicity: Pesticide Applicators and Phosphine. Science 246 (35) pp. 251-254.
  10. World Health Organization (WHO). 1988. Environmental Health Criteria 73, Phosphine and Selected Metal Phosphides. World Health Organization, Geneva.
  11. Klimmer, O.R. 1969. Contribution to the study of action of phosphine. Archiv fur Toxikologie, 24(23):164-187.
  12. Leuschner, F. 1984. Evaluation of the acute toxicity of Phostoxin (active ingredient: aluminum phosphide) to rainbow trout. Laboratory for Pharmacology and Toxicology. Hamburg, German Federal Republic.
  13. U.S. Environmental Protection Agency. 1994. File: Aluminum Phosphide Integrated Risk Information System (IRIS). US EPA, Washington, DC.
  14. Sullivan, J.B. and Krieger, G.R. 1992. Hazardous Materials Toxicology, Clinical Principles of Environmental Health. Williams & Wilkins, Baltimore, MD.