E X T O X N E T
Extension Toxicology Network
A Pesticide Information Project of Cooperative Extension Offices of
Cornell University, Michigan State University, Oregon State University, and
University of California at Davis. Major support and funding was provided
by the USDA/Extension Service/National Agricultural Pesticide Impact
Publication Date: 9/93
TRADE OR OTHER NAMES
Trade names for products containing metalaxyl include Ridomil,
Apron, Delta-Coat AD, Subdue 2E.
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."
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.
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.
A three-generation rat study where animals were fed up to 62.5
mg/kg, showed no chemical related maternal toxicity or reproductive
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).
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
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).
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).
Metalaxyl is practically non-toxic to birds (8) and freshwater
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).
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).
|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)
|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
PO Box 18300
Greensboro, NC 27419
Review by Basic Manufacturer:
Comments solicited: January, 1992
Comments received: April, 1992
Hartley, D., and H. Kidd, Editors (1986). The Agrochemicals
Handbook. The Royal Society of Chemistry, The University, Nottingham,
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.
Worthing, Charles R., Editor (1983). The Pesticide Manual, A World
Compendium. The British Crop Protection Council, The Ravenham Press
Limited, Ravenham, Suffolk, England.
National Research Council (1987). Regulating Pesticides in Food,
The Delaney Paradox, National Academy Press, Washington, DC.
Food and Drug Administration (1986). The FDA Surveillance Index.
Bureau of Foods, Dept of Commerce, National Technical Information
Service, Springfield, VA.
Forest Service (1987). Pesticide Background Statements, Vol III
Nursery Pesticides, U. S. Dept of Agriculture, Agriculture Handbook No.
The Agrochemicals Handbook. 1991. The Royal Society of Chemistry.
Walker, Mary M. and Lawrence H. Keith. (1992). U.S. Environmental
Protection Agency's Pesticide Fact Sheet Database. Lewis Publishers,
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,