Sorption and Degradation of Thiobencarb in Three Florida Soils

Abstract

Laboratory studies were conducted to characterize the adsorption-desorption and degradation of thiobencarb in soil. Thiobencarb adsorption on soil was correlated with soil organic carbon (r = 0.97) and values (ml g −1 ) for the following soils were: Pahokee muck 339, Everglades muck 169, and Immokalee sand 14. The adsorption values (ml g −1 ) per unit of organic carbon were Immokalee sand 1195, Pahokee muck 765, and Everglades muck 539. In desorption studies, thiobencarb K f values increased 80 ml g −1 from the first to the third desorption step in the muck soils, but were similar in three desorptions from the sand. The half-lives of thiobencarb averaged 16, 18, and 24 days on surface samples of Pahokee muck, Everglades muck, and Immokalee sand, respectively, across the range of 25 to 35 C and 10 to 100 kPa soil water tension. Half-lives were generally longer with water contents equivalent to 100 kPa than 10 kPa soil water tension and incubated at 25 than 35 C. The relative percentages of extractable 14 C, bound 14 C, and 14 CO 2 from 14 C-thiobencarb-treated soil were dependent on soil type, soil water content, incubation temperature, and time.