Adsorption and Analysis of the Insecticides Thiamethoxam and Indoxacarb in Hawaiian Soils

Abstract

A method was developed for the simultaneous extraction and analysis of the insecticides indoxacarb and thiamethoxam from five Hawaiian soils. Using pressurized fluid extraction followed by liquid chromatography, optimized recoveries from the five soils were obtained ranging from 80% +/- 5 to 101% +/- 10 for thiamethoxam, and 83% +/- 6 to 106% +/- 7 for indoxacarb. Aging studies also showed strong binding of indoxacarb to all soils tested after 30 days, while thiamethoxam remained quite available for extraction during the length of the study (90 days). Freundlich constant (K(f)) and empirical value (n) for thiamethoxam sorption on Lihue soil were 0.007391 mmol((1-1/)(n)).L(1/)(n).g(-1) and 1.1377, respectively; K(f) and n were 0.007844 mmol((1-1/)(n)).L(1/)(n).g(-1) and 0.8473, respectively, on Wahiawa soil. The organic carbon adsorption constant (Koc) of thiamethoxam was 0.53 in Lihue soil and 0.23 in Wahiawa soil.