Conversion of metham‐sodium to methyl isothiocyanate and basic data on the behaviour of methyl isothiocyanate in soil

Abstract

Data were collected that are needed to simulate soil fumigation with metham‐sodium with computation models. The rate of conversion of metham‐sodium into methyl isothiocyanate was dependent on temperature and soil type, and conversion was usually completed within a few hours. In comparison with dichloropropene, there was a higher water/gas distribution ratio and thus a slower vapour diffusion. Adsorption from the water phase onto the solid phase was weaker. The first‐order rate equation described the decomposition of methyl isothiocyanate and the half‐lives varied from a few days to a few weeks according to temperature and soil type.

Conversion of metam sodium and emission of fumigant from soil columns

“…The maximum amount of MITC was obtained in approximately 20 min in soil at 20% moisture. In the saturated soil (30%), metam sodium completely disappeared in about 0.5 h. In this study, the conversion of metam sodium to MITC was significantly faster than previously reported for high application rates of metam sodium (a few hours to a day) (Turner and Corden, 1963;Smelt and Leistra, 1974), but was similar to observations in which a concentration of metam sodium (48 mg g À1 soil) corresponding to a field application rate was used (Gerstl et al, 1977).…”

“…The rate of decomposition depends strongly on soil temperature, soil texture, and soil moisture. The efficiency of conversion in soil is reported to be very high, ranging from 87% to 95% (Turner and Corden, 1963;Smelt et al, 1989;Wales, 2000), but most of these studies investigated high metam sodium application rates (Turner and Corden, 1963;Smelt and Leistra, 1974;Gerstl et al, 1977). Less emphasis has been given to the conversion of metam sodium at application rates representative of typical contemporary fumigant usage in fields.…”

Incompatibility of metam sodium with halogenated fumigants

“…In moist soil, metam decomposes rapidly (half‐life 0.5–4 h) to methyl isothiocyanate (Fig 1),1 which is the primary biocidal agent. The major reaction can be described as:2 …”

Impact of fumigation with metam sodium upon soil microbial community structure in two Japanese soils

“…Metam sodium is rapidly hydrolysed in soils to methyl isothiocyanate (MITC), the active biocidal compound (Smelt and Leistra 1974). Whilst previous studies have revealed the fate of met am sodium and MITC in soil (Lloyd 1962;Smelt and Leistra 1974;Smelt et al 1989), little is known about the toxicity of MITC in the environment in terms of human health or natural resources (Taylor, Jr. et al 1996).…”