Introduction. The objective was to evaluate the toxicity of
poisoning by
metam sodium, a dithiocarbamate fumigant, the breakdown products of which are
methyl isothiocyanate (MITC),
carbon disulphide (CS2), and dihydrogen sulphide (H2S). Methods. This is a retrospective, observational case series of
metam sodium exposure cases reported to the Angers
Poison and Toxicovigilance Centre from 1992 through 2009. Results. A total of 106 cases of
metam sodium exposure were recorded and 102 cases were included in this study. All cases of exposure were unintentional. Occupational
poisoning occurred in eight cases. The most common route of exposure was inhalation (n = 96). In 79 cases, the patients were people living near fields where
metam sodium had recently been applied. Most of the reported symptoms involved irritation of the eyes (n = 76), throat and nose (n = 65), attributable to MITC.
Cough and dyspnoea occurred in four cases but no persistent,
irritant-induced
asthma or persistent exacerbation of
asthma was observed. Sixteen patients at two different sites of pollution were exposed to emanations from the drainage system in their homes following the illicit discharge of
metam sodium into the sewers. Most presented with
nausea and
headaches, but only four experienced eye or throat irritation. A breakdown product other than MITC was involved: air analysis at one site revealed the presence of CS2 (337 mg/m(3)) and no H2S. Two of these patients, who had consumed some alcohol, experienced
dysgeusia but no
disulfiram-like reaction. The only lethal case recorded was a truck driver who was found dead of
acute lung injury after falling into a tank that had previously contained
metam sodium. Two patients who ingested a dilute
solution, presented with mild epigastric
pain. Four skin exposures caused
erythema (n = 2), moderate
burns (n = 1), and
urticaria (n = 1). According to the
poisoning severity score, their symptoms were minor in 99% of cases. Conclusion. Acute
metam sodium exposure usually causes minor symptoms. They vary as a function of the circumstances of exposure, which determine the degradation product that forms. On contact with moist soil,
metam sodium decomposes into MITC and causes
irritant symptoms. Under specific conditions, such as a spillage in the drainage system,
metam sodium can degrade into CS2 and cause neurological signs.