GAS-PHASE PHOTOLYSIS OF METHYL ISOTHIOCYANATE

Methyl isothiocyanate (MITC) is the major volatile transformation product of the fumigant metam sodium. The objectives of these studies were to determine both the products and the kinetics of photolysis of MITC in the gas phase in order to better understand its transformation in the atmosphere. The gas phase photolysis of MITC was examined using Tedlar, borosilicate, and quartz chambers. Since sorption of MITC on the walls of the reactors is potentially important, these studies used a ratioing technique that relates sorption of MITC to two other photostable compounds of similar vapor pressure. These experiments showed that MITC undergoes photolysis in the gas phase with a half-life of 10 +/- 3 h under xenon are irradiation and slightly greater than 1 day of late summer sunlight. Photolysis products were determined using GC-NPD/FPD and GC/MS. Products observed include methyl isocyanate, methyl isocyanide, sulfur dioxide, hydrogen sulfide, carbonyl sulfide, N-methylformamide, and methylamine. These data have implications on the risk assessment of metam sodium on human health and environmental receptors.