Metam sodium

Metam sodium is an organosulfur compound (formally a dithiocarbamate), which 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 can be prepared from methylamine, carbon disulfide, and sodium hydroxide; or from methyl isothiocyanate and sodium thiolate.
Upon exposure to the environment, metam sodium decomposes to form methyl isothiocyanate.
Metam sodium is a documented cause of reactive airways dysfunction syndrome.
In 1991 a tank car with 19,000 gallons of metam sodium spilled into Sacramento River above Lake Shasta. This killed all fish in a 41-mile stretch of the river. By 20 years later the rainbow trout population had recovered.