W8 AM Agrochemicals and Pesticides
Wednesday, 16 November 2005: 8:00 AM - 11:40 AM in 337-338

(GUN-1115-081350) The microbial dechlorination of thiobencarb in rice field soils.

Gunasekara, A¹, Tjeerdema, R¹, ¹ University of California, Davis

ABSTRACT- Thiobencarb is a common chlorinated herbicide that is effective in controlling annual grasses and broadleaf weeds in rice fields. The microbial dechlorination of thiobencarb in saturated anaerobic rice field soils was examined in laboratory microcosm experiments. In this study, thiobencarb was effectively dechlorinated in anoxic laboratory microcosms in two Sacramento valley rice field soils to its dechlorinated species, deschlorothiobencarb, within 30 days. Logistic regression analysis found that the half-life (t_0.5) for thiobencarb in the non-sterile soils ranged from 10 to 15 days. Similar t_0.5 values were observed when the microcosms were amended with low concentrations of copper (Cu²⁺). Microcosms were also amended with phosphate (PO₄^2-), a nutrient applied to anaerobic rice field soils. Results showed the dechlorination of thiobencarb was inhibited at high PO₄^2- and Cu²⁺ concentrations. The low copper-amended soils closely resembled the non-sterile experiments while the high copper-amended microcosms were similar to the sterile experiment, over 30 days.

Key words: thiobencarb, dechlorination, half-life, copper