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Metalaxyl

Publication Date: 9/93

TRADE OR OTHER NAMES

Trade names for products containing metalaxyl include Ridomil, Apron, Delta-Coat AD, Subdue 2E.

INTRODUCTION

Metalaxyl is a systemic, benzenoid fungicide used in mixtures as a foliar spray for tropical and subtropical crops, as a soil treatment for control of soil-borne pathogens, and as a seed treatment to control downy mildews (2). Experimental-use permits are in effect authorizing the application of metalaxyl on some food crops, although tobacco, ornamentals, conifer, and turf applications are the major uses. Smokers could be exposed through inhalation (5). Products containing metalaxyl must bear the signal word "Caution."

TOXICOLOGICAL EFFECTS

ACUTE TOXICITY

The oral LD50 in rats is 669 mg/kg and the dermal LD50 is >3,100 mg/kg. Rabbits exhibited slight eye and skin irritation, but guinea pigs displayed no sensitization.

CHRONIC TOXICITY

A 90-day rat study at levels in the diet of 2.5 to 62.5 mg/kg, showed some cellular enlargement in the liver at the highest dose. The NOEL was determined to be 12.5 mg/kg/day (5).

In a similar study with dogs fed diets of approximately 1.25 to 25 mg/kg for six months, the dogs were adversely effected by the highest dose. Manifestations included increased alkaline phosphatase and increased liver-to-brain weight ratio.

Reproductive Effects

A three-generation rat study where animals were fed up to 62.5 mg/kg, showed no chemical related maternal toxicity or reproductive effects (5).

Teratogenic Effects

Rats and rabbits have been treated by intubation during gestation. Rats given a dosage of 120 mg/kg on days 6 to 15 exhibited no embryotoxicity or teratogenicity, nor did rabbits given a dosage of 20 mg/kg on days 6 to 18 (5).

Mutagenic Effects

In vitro rat liver preparations did not produce any detectable aniline or nitroso compounds from metalaxyl which could be mutagenic (2). Dominant lethal studies in male mice also indicated no mutagenic potential (5).

Carcinogenic Effects

The EPA Cancer Assessment Group decided that metalaxyl should not be classified as an oncogen because even though a study showed significant parafollicular adenomas of the thyroid in female rats at low and middle doses, this did not occur at the higher dose (4).

Organ Toxicity

In a long term feeding study with mice at low levels of exposure, the animals' livers were the primary target for metalaxyl-related effects (8). No specifics about the changes in the liver or the doses administered were given in the reference.

Fate in Humans and Animals

Studies with rats and goats showed rapid metabolism and excretion via urine and feces. Glucuronic acid conjugates of the metabolites were the main rat excretion products (5). There is hydrolysis and oxidative cleavage in warm-blooded animals (1).

Forty-day feed studies with dairy cattle at 15 ppm, resulted in <0.01 ppm in the muscle and fat. The liver contained 0.13 to 0.20 ppm and the kidney 0.26 to 0.83 ppm (5).

Chickens fed for 28 days at 5 ppm in the diet had <0.05 ppm in the eggs, skin, fat, breast and thigh and <0.1 ppm in the liver (5).

ECOLOGICAL EFFECTS

Metalaxyl is practically non-toxic to birds (8) and freshwater fish.

The 96-hour LC50 for rainbow trout, carp, and bluegill is > 100 mg/l (3). Freshwater aquatic invertebrates are slightly more susceptible to metalaxyl. Daphnia magna, a small freshwater crustacean, has an LC50 of 12.5 to 28 mg/l, depending on the product formulation. This indicates that metalaxyl is slightly toxic to this organism (8). Currently the toxicity of the product is undocumented for marine organisms. The EPA has requested that these studies be done (8).

There is little tendency for metalaxyl to accumulate in the edible portion of fish. Metalaxyl did not accumulate beyond 7 times the background concentration. It was quickly eliminated after exposed fish were placed in fresh (metalaxyl free) water (8).

Metalaxyl is non-toxic to honeybees (3, 7). The EPA has indicated that metalaxyl poses little threat to aquatic or terrestrial endangered species, whether plant or animal (8).

ENVIRONMENTAL FATE

Under field conditions, metalaxyl has a half-life of one to eight weeks in soil. Its average half-life in soil is about 70 days. The major breakdown product is from the hydrolysis of the methyl ester. Although it readily leaches in sandy soil, increased organic matter decreases leaching (2). In a large scale, national survey, metalaxyl was detected in the groundwater of several states at concentrations of 0.27 ppb to 2.3 ppb (9).

At pH's of 5 to 9 and temperatures of 20 to 30 degrees C, the half- life in water was greater than four weeks. Water exposed to sunlight, however, had a residue half-life of one week. In water, metalaxyl is not readily degraded by sunlight. In soil, it has a half-life of about 2 weeks when exposed to sunlight.

Plants absorb foliar applications through the leaves and stems, and can translocate the compound throughout the plant. Metalaxyl is not absorbed directly from the soil by plants.

The parent compound is the major residue in potato tubers and grapes, but in potato leaves and on lettuce, metabolites are the major product (5). Metalaxyl acts by inhibiting protein synthesis in fungi. It has a calculated three-week duration of activity (1).

Exposure Guidelines:

NOEL: rat: 12.5 mg/kg/day, based on chronic effects; dog: 6.25 mg/kg/day, based on chronic effects
ADI: 0.03 mg/kg/day
RfD: 0.06 mg/kg/day (EPA)
LEL: 25 mg/kg/day (dog)

Physical Properties:

CAS #: 57837-19-1
Chemical name: methyl-N-(2,6-dimethylphenyl)-N-(2-methoxyacetyl)-DL-alaninate
Chemical class/use: benzenoid fungicide
Solubility in water: 8,400 mg/l
Solubility in other solvents: methanol 65 g/100 g; benzene 55 g/100 g; hexane 0.91 g/100 g
Melting Point: 71-72 degrees C
Vapor Pressure: 5.6 x 10 to the minus 6 power mm Hg

BASIC MANUFACTURER

Ciba-Geigy Corporation
PO Box 18300
Greensboro, NC 27419
Telephone: 919/292-7100

Review by Basic Manufacturer:

Comments solicited: January, 1992
Comments received: April, 1992

REFERENCES

  1. Hartley, D., and H. Kidd, Editors (1986). The Agrochemicals Handbook. The Royal Society of Chemistry, The University, Nottingham, England.
  2. Kimmel, E.C., J.E. Casida, and L.O. Ruzo (1986). Formamidine Insecticides and Chloroacetanilide Herbicides: Disubstituted Anilines and Nitrobenzenes as Mammalian Metabolites and Bacterial Mutagents, J. Agri Food Chem 34:157-161.
  3. Worthing, Charles R., Editor (1983). The Pesticide Manual, A World Compendium. The British Crop Protection Council, The Ravenham Press Limited, Ravenham, Suffolk, England.
  4. National Research Council (1987). Regulating Pesticides in Food, The Delaney Paradox, National Academy Press, Washington, DC.
  5. Food and Drug Administration (1986). The FDA Surveillance Index. Bureau of Foods, Dept of Commerce, National Technical Information Service, Springfield, VA.
  6. Forest Service (1987). Pesticide Background Statements, Vol III Nursery Pesticides, U. S. Dept of Agriculture, Agriculture Handbook No. 670.
  7. The Agrochemicals Handbook. 1991. The Royal Society of Chemistry. Cambridge, England.
  8. Walker, Mary M. and Lawrence H. Keith. (1992). U.S. Environmental Protection Agency's Pesticide Fact Sheet Database. Lewis Publishers, Chelsea, MI.
  9. Williams, W.M., P.W. Holden, D.W. Parsons and M.N. Lorber. 1988. Pesticides in Groundwater Database: 1988 Interim Report. U.S. Environmental Protection Agency. Office of Pesticide Programs, USEPA, Washington, DC.