Gaseous methyl isothiocyanate (MITC), the principal breakdown product of the soil fumigant metam sodium (sodium methyl-dithiocarbamate), is an inhalation exposure concern to bystanders, especially in residential communities near large production acreages. Inhalation exposure might not be limited to MITC but might also include methyl isocyanate (MIC), a tropospheric oxidative transformation product of MITC. Under controlled laboratory conditions, the gas-phase reaction of hydroxyl (OH) radicals with MITC was examined using static relative-rate techniques in 10 L Tedlar air sampling bags over a 1 hr period. Gas phase MITC, MIC, and OH reference compounds were quantified by solid phase microextraction-GC/MS. In this work an MITC OH rate constant of 25 x 10-12 cm3 molecule-1 s-1 was estimated. The MITC atmospheric lifetime would be ca. 0.6 days under tropospheric OH radical concentrations of 8.0 x 105 molecules cm-3 over a period of 24 hrs. MIC was observed to be the primary transformation product in the gas phase.

Gas-phase reaction of methyl isothiocyanate with hydroxyl radicals under static relative-rate conditions

244th National Meeting (2012)

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