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Thiodicarb Structural Formula
Thiodicarb Structural Formula
CAS Number: 59669-26-0
Synonyms: Dicarbasulf, Judge, Larvin, Lepicron, Toro
Contaminant Type: Chemical

Thiodicarb [CAS name dimethyl-N,N'-thiobis(methylimino)carbonyloxy-bis-ethanimidothioate] is an N-methyl carbamate insecticide of the carbamate class of pesticides. It is primarily used for control of a number of insect pests on cotton, sweet corn, and soybeans, although it is also used to a lesser extent on leafy vegetables, cole crops, and ornamentals. It is also a mulluscicide.  Thiodicarb was first registered in the United States in 1984, and approximately 113,000 pounds are used on agricultural use sites per year [1949]. Thiodicarb is not registered for residential use.  It is registered for application via aerosal dispersal [1950].

Thiodicarb is two methomyl molecules connected by a sulfur atom.  Methomyl results from cleavage of the -N-S-N- bond.

In the environment, thiodicarb rapidly degrades to methomyl, which is also registered for use as an insecticide. Studies show that thiodicarb degrades within several hours to a few days with the primary degradation mechanisms thought to be biodegradation, hydrolysis, and photolysis [1950, 1951]. While thiodicarb does not appear to be very persistent or highly mobile, its metabolite, methomyl, is more persistent, more mobile, and more toxic [1950]. Thiodicarb is not expected to have a high potential to contaminate groundwater, however, methomyl has been detected infrequently in groundwater due to its moderate persistence and high mobility [1950]. 

Thiodicarb is not regulated by USEPA in drinking water, but is an unregulated contaminant listed on the USEPA's Contaminant Candidate List 3 [620]. Thiodicarb is classified as a Group B2 agent, meaning it is a probable human carcinogen [1950].  It is also a blood toxicant, neurotoxicant and an acetylcholinesterase inhibitor.

Because of its instabilty (principally by hydrolysis) thiodicarb is not expected to be present in ground water, or in surface water unless in close time and proximity to aerial application.  Thus it is not expected to be present in drinking water.  Methomyl, however, mey be present in field waters and in drinking waters as a degradate.  For treatment of methomyl, go to List of Contaminants.  

Date of Literature Search: September 2010


620 USEPA Office of Ground Water and Drinking Water; 2008; Contaminant Candidate List 3 (CCL3); USEPA Office of Ground Water and Drinking Water; http://www/epa.gov/OGWDW/ccl/ccl3.html
1949 USEPA; 2009; Thiodicarb Summary Document Registration Review: Initial Docket; Thiodicarb Summary Document Registration Review: Initial Docket; Agency Docket I.D. EPA-HQ-OPP-2009-0432
1950 USEPA; 1998; R.E.D. Facts - Thiodicarb; R.E.D. Facts - Thiodicarb; EPA Report 738-F-98-020. Prevention, Pesticides And Toxic Substances.
1951 Jones, R., Hunt, T., Norris, F. and Harden, C.; 1989; Field research studies on the movement and degradation of thiodicarb and its metabolite methomyl; Journal of Contaminant Hydrology; 4:359