E X T O X N E T

Extension Toxicology Network

Pesticide Information Profiles

A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Oregon State University, the University of Idaho, and the University of California at Davis and the Institute for Environmental Toxicology, Michigan State University. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program.

EXTOXNET primary files maintained and archived at Oregon State University

Revised June 1996

Metalaxyl

Trade and Other Names: Trade names for products containing metalaxyl include Apron, Delta-Coat AD, Ridomil, and Subdue.

Regulatory Status: Metalaxyl is a slightly toxic compound in EPA toxicity class III. It is a General Use Pesticide (GUP). Labels for products containing metalaxyl must bear the Signal Word CAUTION.

Chemical Class: benzenoid

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. Metalaxyl may be used on many different food crops, including tobacco, ornamentals, conifer, and turf applications.

Formulation: 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.

Toxicological Effects:

• Acute toxicity: The oral LD50 in rats is 669 mg/kg and the dermal LD50 is greater than 3100 mg/kg [8], indicating slight toxicity by ingestion and dermal application. Rabbits exhibited slight eye and skin irritation, but guinea pigs displayed no sensitization after metalaxyl exposure [1]. No information was available regarding the inhalation toxicity of metalaxyl.
• Chronic toxicity: A 90-day study of rats exposed to 0.1 to 2.5 mg/kg/day in diet, showed some cellular enlargement in the liver at the highest dose [19]. In a similar study with dogs fed diets of approximately 0.04 to 0.8 mg/kg/day for 6 months, the dogs were adversely affected by the highest dose. Manifestations included increased blood alkaline phosphatase and increased liver-to-brain weight ratio [19].
• Reproductive effects: A three-generation rat study where animals were fed up to 2.5 mg/kg/day showed no compound related maternal toxicity or reproductive effects [19]. These data suggest that metalaxyl is unlikely to cause reproductive effects.
• Teratogenic effects: Rats given a dosage of 120 mg/kg/day by stomach tube on days 6 to 15 of gestation exhibited no embryotoxicity or teratogenicity, nor did rabbits given a dosage of 20 mg/kg/day by the same route on days 6 to 18 [19]. These data suggest that metalaxyl is not teratogenic.
• Mutagenic effects: Studies including a dominant lethal assay in male mice indicate that metalaxyl has no mutagenic potential [19].
• Carcinogenic effects: Available studies of the carcinogenicity of metalaxyl are inconclusive [19].
• Organ toxicity: The liver is the primary target organ for metalaxyl in animal systems.

• Fate in humans and animals: Studies with rats and goats showed rapid metabolism and excretion via the urine and feces [19]. Metalaxyl is metabolized to a variety of products before excretion [19]. Forty-day feeding studies with dairy cattle at 15 ppm/day, showed less than 0.01 ppm was stored in the muscle and fat. The liver contained 0.13 to 0.20 ppm and the kidney 0.26 to 0.83 ppm [19]. Chickens fed for 28 days at 5 ppm in the diet had less than 0.05 ppm in the eggs, skin, fat, breast, and thigh, and less than 0.1 ppm in the liver [19].

Ecological Effects:

• Effects on birds: Metalaxyl is reported to be practically nontoxic to birds [46].
• Effects on aquatic organisms: Metalaxyl is practically nontoxic to freshwater fish. The 96-hour LC50 values in rainbow trout, carp, and bluegill are all above 100 mg/L [1]. 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 [46]. This indicates that metalaxyl is slightly toxic to this organism. There is little tendency for metalaxyl to accumulate in the edible portion of fish. Metalaxyl did not accumulate beyond seven times the background concentration and it was quickly eliminated after exposed fish were placed in fresh (metalaxyl-free) water [46].
• Effects on other organisms: Metalaxyl is nontoxic to bees [1].

Environmental Fate:

• Breakdown in soil and groundwater: Under field conditions, metalaxyl has a half-life of 7 to 170 days in the soil environment [11]. A representative half-life in moist soils is about 70 days [11]. Increased sunlight may increase the rate of breakdown in the soil. It is poorly sorbed by soils and highly soluble in water [11]; these properties in combination with its long persistence pose a threat of contamination to groundwater. It readily leaches in sandy soil, although increased organic matter may decrease the rate of leaching [47]. In a large-scale, national survey, metalaxyl was detected in the groundwater of several states at concentrations of 0.27 ug/L to 2.3 mg/L [48].
• Breakdown in water: At pH levels of 5 to 9 and temperatures of 20 to 30 C, the half-life in water was greater than 4 weeks [46]. However, exposure to sunlight reduced the half-life to 1 week [46].
• Breakdown in vegetation: 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 [7].

Physical Properties:

• Appearance: Metalaxyl is a colorless, odorless crystal [1].
• Chemical Name: methyl-N-(2,6-dimethylphenyl)-N-(2-xylyl)-DL-alaninate [1]
• CAS Number: 57837-19-1
• Molecular Weight: 279.34
• Water Solubility: 7100 mg/L @ 20 C [1]
• Solubility in Other Solvents: v.s. in methanol, benzene, and hexane [1]
• Melting Point: 71.8-72.3 C [1]
• Vapor Pressure: 0.293 mPa @ 20 C [1]
• Partition Coefficient: Not Available
• Adsorption Coefficient: 50 (estimated) [11]

Exposure Guidelines:

• ADI: 0.03 mg/kg/day [12]
• MCL: Not Available
• RfD: 0.06 mg/kg/day [13]
• PEL: Not Available
• HA: Not Available
• TLV: Not Available

Basic Manufacturer:

Ciba-Geigy Corporation
P.O. Box 18300
Greensboro, NC 27419-8300

• Phone: 800-334-9481
• Emergency: 800-888-8372
  

References:

References for the information in this PIP can be found in Reference List Number 10

DISCLAIMER: The information in this profile does not in any way replace or supersede the information on the pesticide product labeling or other regulatory requirements. Please refer to the pesticide product labeling.