Water quality implications of pyrethroid insecticide sorption and desorption processes.

摘要

Pyrethroid insecticides are hydrophobic organic compounds that have been widely detected in sediments at concentrations that cause toxicity to aquatic organisms. The main hypothesis of this dissertation is that the fate and transport of pyrethroid insecticides in the environment will be dominated by sorption to and desorption from sediments and soils. The goal of this research was to better characterize these processes by performing sorption and desorption rate studies, as well as sorption equilibrium experiments. This information is essential to reliably predicting ecotoxicity and downstream transport of these compounds.;Batch reactor isotherm experiments were performed with two pyrethroids using suspended material and bed sediment from the Sacramento River, CA. The Freundlich isotherm model was fit to the data and Freundlich exponents indicated sorption nonlinearity for some experimental conditions. Calculated organic carbon normalized distribution coefficients were larger than those previously reported in the literature by approximately an order of magnitude. Higher than expected sorption to these materials was explained by adsorption to mineral surfaces and black carbon, with the mineral surface accounting for the largest portion. Sorption to mineral phases may be more important than previously thought for pyrethroids, especially for sediments with low organic carbon contents.;Isomerization of lambda-cyhalothrin was observed in batch reactor sorption rate studies and a combined model incorporating a two site sorption term and a linear isomerization term was fit to the data. It appeared that isomerization occurred more rapidly or exclusively in the aqueous phase. The stereoisomers range in biological activity, thus isomerization could potentially increase or decrease toxicity.;Desorption experiments were performed with three sorbents, three aging times, and four pyrethroids; a biphasic rate model was fit to these data. Suspended solids from irrigation runoff water collected from a field sprayed with permethrin one day prior were used to compare the rates of desorption of field-applied pyrethroids to those of laboratory spikes. Rapid desorption of field-applied permethrin was not statistically different than laboratory spiked permethrin. The sorbent had the greatest effect on desorption rate parameters, while significant differences in desorption were not observed among several pyrethroids, nor for aging times of 1-28 d.