Product: VAPAM
Active ingredient: METAM SODIUM 32.7%
Active ingredient: Sodium methyldithiocarbamate (MITC)
Other ingredients :67.3% Identity withheld as trade secret by manufacturer
Type: biocide/soil fumigant Dithiocarbamate
Mode of Action: Methyldithiocarbamate (MITC) binds to oxygen carrying molecules and prevents tissues from using oxygen.
Metam Sodium is a biocide which is used to sterilize soil prior to planting. Once applied, metam sodium decomposes into MITC, which is the actual pesticidal compound. Metam sodium was spilled into the Sacramento River in Dunsmuir during a train accident in 1991, killing all aquatic life for 20 miles and injuring hundreds of nearby residents. MITC and metam sodium are restricted use chemicals and can only be applied by licensed professionals.
TOXICOLOGY
Metam sodium is considered a possible carcinogen by the U.S. EPA (OPP 1997).
Metam sodium is acutely toxic (Gossilin 1984). Its breakdown product and the actual pesticidal compound, MITC, is a potent mucus membrane irritant (DHS 1991). For their claims of industrial asthma induced by airborne exposure to MITC, scores of plaintiffs in a lawsuit concerning a Sacramento River metam sodium spill in 1991 won settlements fof over $7 million (S.F. Chronicle 1993).
Metam sodium caused severe spinal and brain birth defects and early pregnancy loss in test animals. Neural tube defects were observed in the offspring of exposed animals (DHS 1991). This information was available to state and federal authorities since 1987, but was not reviewed until after the 1991 spill (ibid.; N.Y. Times 1991).
Metam sodium is a mutagen. In cultures of human cells it caused increased chromosomal aberrations (CDFA 1989).
Metam sodium is a Category I for skin irritation, Category II for acute dermal toxicity and Category III/IV for eye irritation (CDPR 1994).
Skin exposure tests demonstrated signifigant adverse effects to the immune system of laboratory animals (Pruett 1991).
Metam sodium breaks down into several other toxic chemicals. These include two highly flammable and toxic compounds, monomethylamine and carbon disulfide. Carbon disulfide is listed by the Office of Environmental Health Hazards under California's Proposition 65 as a female and male reproductive toxicant, and as a developmental toxicant. It can be inhaled or absorbed through the skin, and rapidly enters the bloodstream through the lungs. It interferes with alcohol metabolism, which can result in alcohol poisoning if an exposed person ingests alcohol. Carbon disulfide causes direct injury to the cells lining the blood vessels and changes the body's metabolism of fats (ATSDR 1994). Hydrogen sulfide is another highly toxic decomposition product of metam sodium.
ENVIRONMENTAL FATE AND EFFECTS
Cal EPA characterizes both metam sodium and MITC as high priority pesticides for evaluation as toxic air contaminants. MITC and hydrogen sulfide, are highly volatile and smell like horseradish and rotten eggs.
MITC is considered a potential groundwater contaminant (Pease 1995). |
