SPECTRUM

Chemical Fact Sheet

Chemical Abstract Number (CAS #) 16752775
CASRN 16752-77-5
SynonymsMethomyl
Lannate
Ethanimidothioic acid, N-[[(methylamino)carbonyl]oxy]-, methyl ester
Acetamidic acid, thio-N-[(methyl-carbamoyl)oxy]-, methyl ester
Analytical Methods EPA Method 531.1
EPA Method 632
EPA Method 8318
Molecular FormulaC5H10N2O2S

Link to the National Library of Medicine's Hazardous Substances
Database for more details on this compound.

Use NEMATOCIDE INSECTICIDE ON VEGETABLES, TOBACCO, COTTON, ALFALFA, SOYBEANS, & CORN METHOMYL IS USED AS FOLIAR TREATMENT FOR CONTROL OF MANY INSECTS SUCH AS APHIDS, ARMYWORMS, CABBAGE LOOPER, TOBACCO BUDWORM, TOMATO FRUITWORM, COTTON LEAF PERFORATOR, COTTON BOLLWORM IS BROAD SPECTRUM INSECTICIDE REGISTERED ON SEVERAL AGRICULTURAL CROPS & COMMERCIALLY GROWN ORNAMENTAL PLANTS, PRIMARILY AGAINST LEPIDOPTEROUS INSECTS ON COLE CROPS, TOBACCO, LETTUCE, COTTON, & TOMATOES
Consumption Patterns ABOUT 50% AS AN INSECTICIDE ON VEGETABLES; ABOUT 50% AS AN INSECTICIDE ON ALFALFA, CORN, COTTON, SOYBEANS, & TOBACCO (1974) Alfalfa, 17.8%; Grapes, 9.8%; Lettuce, 26%; Sugarbeets, 6.1%; Tomatoes, 8.6%; Citrus, 3.9%; Other vegetables account for most of remainder, 18.1% (1984) California use, calculated from table 4.39X10 8 g Used in California
Apparent Color COLORLESS CRYSTALLINE SOLID; WHITE CRYSTALLINE SOLID
Odor SLIGHTLY SULFUROUS
Melting Point 78-79 DEG C
Molecular Weight 162.20
Density 1.2946 AT 24 DEG C/4 DEG C
Environmental Impact Methomyl is released into the environment primarily from its application to plants as an insecticide. If released to soil, methomyl will degrade primarily by microbial degradation with carbon dioxide as the principal end product; a lag period of one to two weeks may occur in unacclimated soils before biodegradation begins. A small degree of chemical hydrolysis may occur in moist soils. Methomyl may be susceptible to significant leaching. Field and greenhouse studies have shown that methomyl degrades rapidly in soil with half-lives of 14 days or less. If released to water, methomyl will hydrolyze at half-life rates of about 54, 38 and 20 weeks at pH's of 6.0, 7.0 and 8.0, respectively, at 25 deg C. Decomposition occurs more rapidly on aeration, in sunlight or with increased alkalinity. Methomyl may be susceptible to significant biodegradation in natural water as it has been shown to be readily biodegraded in soil. Aquatic volatilization, adsorption, and bioconcentration are not expected to be important. If released to the atmosphere, methomyl will react in the vapor-phase with photochemically produced hydroxyl radicals with an estimated half-life of 1.14 months. Direct photolysis may also contribute to its transformation in air. Methomyl adsorbed to particulates in air are subject to physical removal via wet and dry deposition. Major general population exposure to methomyl will occur through consumption of contaminated food. Occupational exposure by dermal and inhalation routes related to the use of methomyl as an insecticide may be significant.
Environmental Fate ONE DOES NOT EXPECT TO FIND RESIDUES OF METHOMYL IN SOIL BEYOND GROWING SEASON DURING WHICH IT WAS APPLIED. VERY LITTLE DATA ON BEHAVIOR OF ALDICARB & METHOMYL IN WATER ARE AVAILABLE. IN STUDY OF POND & LAKE WATER, HALF-LIFE OF 5 DAYS & 6 DAYS WERE DETERMINED FOR ALDICARB & METHOMYL, RESPECTIVELY. IN SOIL, LABELED METHOMYL WAS DEGRADED TO (14)CO2 & OTHER MATERIALS, SOME OF WHICH WERE REINCORPORATED INTO NORMAL COMPONENTS OF SOIL ORG MATTER. TERRESTRIAL FATE: Methomyl effectively controlled fall armyworm larvae in stands of Coastal Bermuda grass. Residues of methomyl declined rapidly with time after application, and by 7 days about 7% of the initial deposit remained regardless of the rate of application. Methomyl loss during dehydration in a natural gas dryer was approx 54%. The pelletizing process caused an additional loss of approx 14%. Thus, the total loss of methomyl during processing of green hay to pellets amounted to approx 68%. Losses of residues during air curing of hay in the field amounted to approx 37%. TERRESTRIAL FATE: The adsorption of methomyl onto 3 greenhouse soils was measured and found to be weak to moderate. The transformation rates in 3 greenhouse soils were reasonably high with half-lives from about 3 to 14 days. These data were introduced into 2 computational models of pesticide behavior in simplified greenhouse systems. The computed leaching of methomyl ranged from nil to very small (0.03% of the dose), depending on the transformation rate and the amt of irrigation water. The concn measured by high performance liquid chromatography in drainage water from 3 greenhouses were somewhat higher than computed, although they remained less than 1 ug/l. Various concn measured in water courses in an area with many greenhouses were distinctly higher than those measured in drainage water, which may be the result of discharge of surpluses of spray liq into the water courses. TERRESTRIAL FATE: Microbial degradation appears to be the major transformation process for methomyl in soil with carbon dioxide as the principal end product; a lag period of one to two weeks may occur in unacclimated soils before biodegradation begins. Some chemical hydrolysis of methomyl may also occur in moist soils. Methomyl may be susceptible to significant leaching; only slight leaching of methomyl was observed in a silt loam soil or sandy soil under field conditions but the degree of leaching may have been reduced by rapid degradation of the methomyl. Under field conditions, only 1.8% of applied methomyl remained in a Delaware soil after one month and no methomyl was detectable after 12 months; less than 0.005% of applied methomyl remained in a Florida field and in a North Carolina field after 3 and 5 months, respectively . In a soil treated with methomyl, only traces of parent compound, its oxime, and small polar fractions remained after one month . The half-life of methomyl in three greenhouse soils was found to range from 3 to 14 days . The half-life of methomyl on cotton plants has been found to range from 0.4 to 8.5 days; 0.8 to 1.2 days on mint plants, and approximately 2.5 days on Bermuda grass . AQUATIC FATE: The hydrolysis half-lives of methomyl in ethanol/water at pH's 6.0, 7.0 and 8.0 have been experimentally determined to be 54, 38 and 20 weeks, respectively, at 25 deg C. An experimental hydrolysis half-life of 262 days has been determined for methomyl in pure water at 25 deg C . Since methomyl absorbs UV light strongly at environmentally important wavelengths, direct photolysis is possible. Aqueous solutions of methomyl have been reported to decompose more rapidly on aeration, in sunlight or in alkaline media . Methomyl may be susceptible to significant biodegradation in natural water as it has been shown to be rapidly biodegraded in soil. Aquatic volatilization, adsorption and bioconcentration are not expected to be important . ATMOSPHERIC FATE: Methomyl present in the atmosphere in the vapor-phase will react with photochemically produced hydroxyl radicals with an estimated half-life of 1.14 months. Direct photolysis may contribute to its removal from the air. Due to its relatively low vapor pressure of 5X10-5 mm Hg at 25 deg C , a fraction of the methomyl present in the air in vapor-phase may become adsorbed to particulate matter which is subject to physical removal via wet and dry deposition. TERRESTRIAL FATE: Decomposes rapidly in soil.

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