Microbial ecology, toxicology and chemical fate of methyl isothiocyanate in riparian soils from the upper Sacramento river

Abstract

Abstract-On July 14, 1991, 72,000 L of the pesticide Metam (active ingredient, methyl isothiocyanate) was accidentally released into the Upper Sacramento River. We hypothesized that the spill affected streamside microbial communities and that the effects were persistent. To address this hypothesis, we sampled river soils a year later from sites above and below the spill as well as from an agricultural area and determined soil carbon dioxide efflux (as a measure of soil respiration) in response to methyl isothiocyanate in controlled-environment microcosms, resulting in estimates of the EC50 and soil degradation rates of methyl isothiocyanate. The soil respiration EC50s for the river soils ranged from 13.2 to 51.4 g/g methyl isothiocyanate, whereas that of the agricultural soil was 72.2 g/g. Thus, the soils from the Upper Sacramento River were more sensitive to the toxicologic effects of methyl isothiocyanate than was the agricultural soil. Soils from below the spill site also showed higher (factor two or more) EC50s than soils from reference locations above the spill site. The half-life of methyl isothiocyanate in soils ranged from 2.7 to 6.9 days and was longer by a factor of two in the river soils. These degradation rates are controlled by both biotic (microbial) and abiotic processes. The presence of a microbial community accelerated the degradation rate by a factor of two. The pattern of EC50 data demonstrates that changes in the microbial community in the river soils were persistent a full year after the spill and that the stress elicited responses that were indicative of physiologic accommodation or selection for resistance at the population, species, and/or community level.

Investigation of effects of trifluoroacetate on vernal pool ecosystems

“…The CO 2 concentrations were measured in mV and converted to μmol CO 2 per mol air (μmol/mol) using a linear regression equation. Methods and procedures for this study are similar to those described by Walton et al [28] and Taylor et al [29]. After headspace sampling, the microcosms were opened for 30 min and allowed to degas.…”

Litter quality is in the eye of the beholder: initial decomposition rates as a function of inoculum characteristics

“…One possible reason that functional dissimilarity may arise is due to a microbial community's past exposure to litters of differing chemistry (Hunt et al 1988; Gholz et al 2000). Implicit evidence of this phenomenon has been shown for both the degradation of subsequent applications of pesticides and litter residues (Taylor et al 1996; Laha & Petrova 1997; Cookson et al 1998) as well as in reciprocal litter transplant experiments (Hunt et al 1988; Gholz et al 2000; Castanho & de Oliveira 2008; Vivanco & Austin 2008). However, it is unknown whether or not the past exposure of a microbial community to litter inputs of differing chemistry also relates to that community's ability to decompose novel litters which themselves differ chemically.…”

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). In addition, there are few reports on the effects of metam sodium fumigation on soil microorganisms.…”