MP5 Agrochemicals and Pesticides
Monday, 14 November 2005: 8:00 AM - 5:30 PM in Exhibit Hall

(BON-1117-749339) Evaluation of K_d for Synthetic Pyrethroids Using Solid Phase Microextraction and Solvent Extraction.

Bondarenko, S¹, Qin, S¹, Gan, J¹, ¹ UC Riverside, Riverside, CA, USA

ABSTRACT- Sorption on sediment regulates the fate and bioavailability of contaminants in the aquatic environment. A common way to measure adsorption capacity of organic compounds in soil or sediment is to use the batch equilibration-solvent extraction method in which the solid and aqueous phases are separated by centrifugation and the aqueous phase concentration C_w is determined after exhaustive solvent extraction. However, this method may give artificially depressed K_d for strongly adsorbing compounds such as pyrethroids, as small colloidal particles and dissolved organic matter are not eliminated from the aqueous phase and may increase C_w. Solid phase microextraction (SPME) selectively detects the freely dissolved concentration and thus may be used to improve K_d measurement. K_d values for eight pyrethroid insecticides were determined using both solvent extraction (LLE) and SPME to measure C_w. K_d obtained with SPME was 2-100 times greater than that with the solvent extraction method. For instance, K_d values for cypermethrin measured by SPME and LLE were 1.16×10⁴ L/kg and 0.85×10³ L/kg, respectively. The difference was more significant for sediments with higher organic matter content. K_d measured with SPME is expected to be useful for predicting the bioavailability or toxicity of sediment-borne pyrethroids, as it correlates with the free or bioavailable concentration.

Key words: adsorption, synthetic pyrethroids, SPME