Metam sodium

Metam sodium is an organosulfur compound with the formula. The compound is a sodium salt of a dithiocarbamate. The compound exists as a colorless dihydrate, but most commonly it is encountered as an aqueous solution. It is used as a soil fumigant, pesticide, herbicide, and fungicide. It is one of the most widely used pesticides in the United States, with approximately 60 million pounds used in 2001.
Metam-sodium belongs to two HRAC groups, so it is designated Group A/C, Group A/C1 and Group 1/5.

Preparation and properties

Metam sodium is prepared by combining methylamine, carbon disulfide, and sodium hydroxide:
It also arises from the reaction of methyl isothiocyanate and sodium thiolate.
Upon exposure to the environment, metam sodium decomposes to methyl isothiocyanate and other sulfur compounds.

Safety and environmental considerations

Metam sodium is nonpersistent in the environment since it decomposes rather quickly to toxic methyl isothiocyanate and carbon disulfide. In 1991 a tank car with 19,000 gallons of a metam sodium based pesticide spilled into Sacramento River above Lake Shasta. This killed all fish in a 41-mile stretch of the river. 20 years later the rainbow trout population had recovered.