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Metaldehyde

Publication Date: 9/93

TRADE OR OTHER NAMES

Some trade names include Antimilace, Antimitace, Ariotox, Cekumeta, Halizan, Limatox, Meta, Metason, Namekil, Ortho Metaldehyde 4% Bait, Slug Death, Slug Pellets, Slug-Tox, Slugit Pellets.

REGULATORY STATUS

Because of its potential short-term and long-term health effects on wildlife, is classified by the U.S. Environmental Protection Agency (EPA) as a Restricted Use Pesticide (RUP). Restricted Use materials may be purchased and used only by certified applicators. All product labels must include the following statement on the front panel, "This pesticide may be fatal to dogs or other pets if eaten. Keep pets out of treated areas" (18). Products containing metaldehyde must bear the signal word "Caution" or "Warning" (14). Check with specific state regulations for local restrictions which may apply.

INTRODUCTION

Metaldehyde is a molluscicide used to attract and kill slugs and snails (1, 4). It is used in a variety of vegetable and ornamental crops in the field or greenhouse, on fruit trees, small-fruit plants, or in avocado or citrus orchards, berry plants and banana plants. It is applied to the soil around plants (7). Care should be taken not to contaminate edible parts of the plant (1). It is used in the form of granules, sprays and dusts, or mixed with bran as a bait (8). It works primarily in the stomach by producing toxic effects after it is ingested by the pest (7). Metaldehyde is available in pelleted baits (14).

Tablets containing metaldehyde, or meta-fuel, are used in Europe as fuel for lamps and small stoves. Meta-fuel is not available in the United States (13).

TOXICOLOGICAL EFFECTS

ACUTE TOXICITY

Metaldehyde is highly toxic by inhalation, moderately toxic by ingestion and slightly toxic by dermal absorption (16). Skin and eye irritation may result from exposure to this material (11). Inhalation of vapors of metaldehyde may cause severe irritation of the mucous membranes lining the mouth, throat, sinuses and lungs (16). Ingestion of this molluscicide causes irritation of the stomach and intestines (7). Metaldehyde can also cause kidney and liver damage (11). One to three hours after ingestion, the following symptoms may appear: severe abdominal pain, nausea, vomiting, diarrhea, fever, convulsions, and coma. Other symptoms of acute exposure include increased heart rate, panting, asthma attack, depression, drowsiness, high blood pressure, inability to control the release of urine and feces, incoordination, muscle tremors, sweating, excessive salivation, tearing, cyanosis, acidosis, stupor, and unconsciousness (6, 13). Kidney injury and liver cell death ('necrosis') may also occur (4). Mental deficiencies and memory loss from ingestion poisoning may persist for one year or more (10, 13). Death may occur due to kidney or lung failure (6). Convulsions and eventual death within two hours of administration were seen in mice that were given an oral dose of 1,000 mg/kg of metaldehyde (12).

The amount of metaldehyde that is lethal to one-half (50%) of test animals when it is given orally is referred to as its oral lethal dose fifty, or LD50. The oral LD50 for metaldehyde in rats is 227 to 690 mg/kg, in cats is 207 mg/kg, in dogs is 100 to 1,000 mg/kg, in mice is 200 mg/kg, in guinea pigs is 175 to 700 mg/kg, and in rabbits is 290 to 1,250 mg/kg (1, 13). A child died after ingesting 3,000 mg of metaldehyde (4). The dermal LD50 for this molluscicide in rats is 2,275 mg/kg to greater than 5,000 mg/kg (1, 7, 16).

The lethal concentration fifty, or LC50, is that concentration of a chemical in air or water that kills half of the experimental animals exposed to it for a set time period. The 4-hour inhalation LC50 in rats is 203 mg/m3. The 2-hour inhalation LC50 in mice is 348 mg/m3 (16).

CHRONIC TOXICITY

Dosages which are not toxic when given singly do not cause illness when repeated (13).

Long-term, repeated skin exposure to metaldehyde can result in dermatitis, the inflammation of skin in humans (10). Prolonged eye exposure can cause conjunctivitis. Two-year toxicity studies and three generation reproductive studies in rats found liver enzyme activity and increased liver and ovary weight at 250 mg/kg in the diet (12, 13). Fifty percent of female rats given this dose showed paralysis (12).

Reproductive Effects

During a 3-generation study of rats exposed to chronic ingestion of metaldehyde, adverse effects were seen on reproduction and on the survival rate of offspring (10). Dietary levels of 1,000 and 5,000 ppm interfered with the reproduction of female rats in a 3-generation test (8).

Teratogenic Effects

Dietary doses of 10, 50, 250 mg/kg of metaldehyde were not teratogenic in three generations of experimental female rats (8).

Mutagenic Effects

Metaldehyde is suspected of causing mutagenic effects (6). There was no evidence of mutagenicity when metaldehyde was tested on five strains of bacteria (13).

Carcinogenic Effects

Dietary doses as high as 250 mg/kg over a two-year period did not increase the incidence of tumors in male and female rats (8).

Organ Toxicity

Metaldehyde or its breakdown byproducts, 'metabolites,' may cause problems in the central nervous system by some unknown mechanism. It may also cause lesions, inflammation of the gastrointestinal tract, liver damage, and brain damage (12). The autopsy of a 2-1/2-year-old boy, who lived only 33 hours after ingesting one tablet of metaldehyde, showed areas of collapse and congestion in the lungs, as well as cellular changes in the liver and kidney (8).

Fate in Humans and Animals

The central nervous system is either depressed or excited by metaldehyde or its metabolites. Metaldehyde is slowly decomposed in the body to a substance called acetaldehyde, a chemical that acts like a narcotic. Death from metaldehyde poisoning generally results from over depression of control centers in the brain that are responsible for the normal function of respiratory and vasomotor systems. Metaldehyde is readily absorbed into the bloodstream from the gastrointestinal tract. Its metabolites can cross the blood-brain barrier, as evidenced by their effect on the level of consciousness of animals (12). Autopsies of dogs poisoned with metaldehyde revealed congestion and hemorrhages in the liver, kidneys and heart (13).

ECOLOGICAL EFFECTS

Effects on Birds

Birds may be killed if they feed in metaldehyde-treated areas (2). Excitability, tremors, muscle spasms, diarrhea, and difficult or rapid breathing was observed in poultry that was exposed to metaldehyde (12).

Effects on Aquatic Organisms

Available data suggest that metaldehyde is practically non-toxic to aquatic organisms (17).

Effects on Other Animals (Nontarget species)

The 4% pelleted bait is toxic to wildlife (2). When used as directed, bait agents with 6% active ingredient are not toxic to bees (7). Bait pellets containing metaldehyde are attractive to dogs. Pets should be confined during application, and kept away from application and storage sites (17).

ENVIRONMENTAL FATE

Breakdown of Chemical in Soil

Metaldehyde has a low potential for groundwater contamination. While it does not adsorb strongly to soil particles, metaldehyde is insoluble in water and it has a short soil half-life (15).

Breakdown of Chemical in Water

This material should not be applied directly to water. Inappropriate storage or disposal, or cleaning of equipment can contaminate water (2).

Breakdown of Chemical in Vegetation

Metaldehyde must not be applied to edible parts of plants. Specific product labels should be referred to for particular crop guidelines (e.g., 4% baits should not be applied to strawberries within six days of harvest, nor to citrus within 14 days of harvest) (2). Many types of flowers lose their color when they come in contact with metaldehyde dust or spray (7).

PHYSICAL PROPERTIES AND GUIDELINES

Metaldehyde is a white or colorless crystalline solid with a mild characteristic odor and a powdery appearance (1, 9, 12). It may be formulated with or without calcium arsenate and is also available in a mixed formulation with thiram (1, 7). It is flammable and burns with a nonsmoking flame (8). It is dangerous when exposed to heat or flame and can react with oxidizing materials (11). Thermal decomposition of metaldehyde may release toxic oxides of carbon. Mixtures of metaldehyde dust and air may explode (16). It is compatible with other substances that are in neutral media. Metaldehyde is noncorrosive (7).

Metaldehyde should be used and stored under conditions that are not hazardous. All precautions should be taken to ensure that bait does not get mistaken for food or feed. As it is harmful if swallowed, it should be kept out of the reach of children and pets. Contamination of the edible parts of plants should be avoided when applying metaldehyde (1). Breathing of its dust, as well as skin, eye, or clothing contact should be avoided (2, 7). A respirator should be worn when using metaldehyde dust (7). After handling, a thorough washing is recommended (1). All unprotected persons should be kept out of the range of drift. Treated areas must not be entered without protective clothing until dusts settle. Metaldehyde is combustible and should be stored in its original container in a cool place, to minimize sublimation. Prolonged storage should be avoided (2).

Occupational Exposure Limits:

No occupational exposure limits have been established for metaldehyde by OSHA, NIOSH or ACGIH (16).

Physical Properties:

CAS #: 108-62-3 (13)
Specific gravity: 1.27 (16)
H20 solubility: insoluble in water (1); 23 mg/l (15)
Solubility in other solvents: insoluble in acetic acid; soluble in hot carbon disulfide (12)
soluble to 1.8 g/100 ml in ethyl alcohol at 70 degrees C (1)
fully soluble in benzene and chloroform, but only slightly soluble in ethanol and diethyl ether (8)
Melting point: 246 degrees C (475 degrees F) (sealed capillary) (9, 13); 234-239 degrees (10)
Boiling point: sublimes at 110-120 degrees C (13)
Flash point: 97 degrees F (36 degrees C) (16)
Vapor pressure: Low at room temperature; considerable at higher temperatures (7)
Chemical Class/Use: Aldehyde molluscicide
Koc: 240 g/ml (15)

BASIC MANUFACTURER

Chevron Chemical Company
Agricultural Chemicals Division
6001 Bollinger Canyon Rd.
San Ramon, CA 94583

Review by Basic Manufacturer:

Comments solicited: October, 1992
Comments received:

REFERENCES

  1. Berg, G. L., ed. 1986. Farm chemicals handbook. Willoughby, OH: Meister Publishing Company.
  2. Chemical & Pharmaceutical Press. 1987. Crop protection chemicals reference. Third edition. NY: John Wiley & Sons.
  3. Cornell University. 1986. 1987 New York State pesticide recommendations. Forty-eighth annual conference. Nov. 10, 11, 12. Ithaca, NY.
  4. Gosselin, R. E., et al. 1984. Clinical toxicology of commercial products. Fifth edition. Baltimore, MD: Williams and Wilkins.
  5. _____. 1976. Clinical toxicology of commercial products. Fourth edition. Baltimore, MD: Williams and Wilkins.
  6. Hallenbeck, W. H. and K. M. Cunningham-Burns. 1985. Pesticides and human health. NY: Springer-Verlag.
  7. Hartley, D. and H. Kidd, eds. 1983. The agrochemicals handbook. Nottingham, England: Royal Society of Chemistry.
  8. Hayes, W. J. 1982. Pesticides studied in man. Baltimore, MD: Williams and Wilkins.
  9. Melnikov, N.N. 1971. Chemistry of pesticides. NY: Springer- Verlag, Inc.
  10. Occupational Health Services, Inc. 1986. Material safety data sheet on metaldehyde. Secaucus, NJ: OHS, Inc.
  11. Sax, N.I. 1979. Dangerous properties of industrial materials. Fifth edition. NY: VanNostrand Reinhold Company.
  12. TOXNET. 1985. National library of medicine's toxicology data network. Hazardous Substances Databank. Public health Service. National Institute of Health. U.S. Department of Health and Human Services. Bethesda, MD: NLM.
  13. Hayes, W.J. and E.R. Laws (ed.). 1990. Handbook of Pesticide Toxicology, Vol. 3, Classes of Pesticides. Academic Press, Inc., NY.
  14. Meister, R.T. (ed.). 1992. Farm Chemicals Handbook '92. Meister Publishing Company, Willoughby, OH.
  15. U.S. Department of Agriculture, Soil Conservation Service. 1990 (Nov.). SCS/ARS/CES Pesticide Properties Database: Version 2.0 (Summary). USDA - Soil Conservation Service, Syracuse, NY.
  16. Occupational Health Services, Inc. 1992 (Feb. 25). MSDS for Metaldehyde. OHS Inc., Secaucus, NJ.
  17. US Environmental Protection Agency. 1988 (Dec. 23). Pesticide Fact Sheet Number 191: Metaldehyde. Office of pesticides and Toxic Substances, Office of Pesticide Programs, US EPA, Washington, DC.
  18. _____. 1990 (Feb.). Suspended, Cancelled, and Restricted Pesticides. Pesticides and Toxic Substances, US EPA, Washington, DC.