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Methomyl Structural Formula
Methomyl Structural Formula1990
CAS Number: 16752-77-5
Synonyms: Lannate, Lanox, Methavin, Metofan, Nudrin
Contaminant Type: Chemical

Methomyl is an oxime carbamate insecticide. Its IUPAC name is S-methyl (EZ)-N-(methylcarbamoyloxy) thioacetimidate.  It is a broad spectrum insecticide used in a wide variety of treatment applications, including field, vegetable, and orchard crops, sod farms, livestock quarters, and commercial ornamentals. It is also used as an acaricide.  Methomyl was first registered in the United States in 1968, and is not registered for residential use [2000].  It is registered for use as an aerial dispersant.

Methomyl is highly soluble in water and is moderately persistent. It does not readily adsorb to soil and is considered highly mobile [495, 2000]. In water, it is stable under neutral to acidic pH ranges, but degrades in alkaline conditions. Methomyl can contaminate surface waters from spray drift during application or by runoff from treated sites. It has been detected in frequently in ground water and in surface water in monitoring studies at concentrations typically below 1 ug/L [2000]. Methomyl is not likely to persist in soil, as it has been found to degrade relatively rapidly by microbes [495].

Its principal hydrolysis and microbial degradates are S-methyl-N-hydroxythioacetimidate and methomyl oxime.  These may be further degraded to acetonitrile and carbon dioxide [2000] [2005].   It photodegrades in water with th eprincipal degadant as acetonitrile [2000].  It can slowly volatilize with acetonitrile and carbon dioxide as products [2000].

Methomyl is not regulated by USEPA in drinking water. Based on the results of several studies, it has been classified as a Group E carcinogen, meaning it is not likely to be carcinogenic. However, in acute toxicity testing for ingestion methomyl is classified as a Toxic Category I chemical (the highest toxicity category) [2000]. This is because methomyl inhibits cholinesterase, an enzyme that is essential to the nervous system.  It has no demonstrated reproductive, teratogenic, mutagenic or carcinogenic effects.

Methomyl is a degradate of thiodicarb, another registered insecticide, as thiodicarb is two methomyl molecules connected at nitrogen sites by a sulfur atom.  Thus, methomyl may be present in field and drinking waters resulting from the application of either thiodicarb or methomyl.

Date of Literature Search: October 2010

495 Extoxnet; 1996; Extoxnet pesticide information profiles; http://extoxnet.orst.edu/; As posted on July 26, 2007. Extoxnet is a cooperative effort of University of California-Davis, Oregon State University, Michigan State University, Cornell University, and the University of Idaho.
1990 Tamimi, M., Qourzal, S., Barka, N., Assabbane, A. and Ait-Ichou, Y.; 2008; Methomyl degradation in aqueous solutions by Fenton's reagent and the photo-Fenton system; Separation and Purification Technology; 61:103-108
2000 USEPA; 1998; R.E.D. Facts - Methomyl; R.E.D. Facts - Methomyl; EPA Report 738-F-98-019. Prevention, Pesticides And Toxic Substances.