Date of Award
Master of Science
The current study assessed the bioavailability of slower desorbing sediment-associated permethrin by manipulating the desorption properties of two sediments with an absorbent, Amberlite XAD-4. The two sediments differed in OC content and the size of the rapidly desorbing pool and rate constants were smaller in the higher OC sediment. Manipulation decreased desorption rate constants in the treated sediments compared to the untreated sediments. Greater activity of permethrin in the pore water was observed in the lower OC sediment compared to the higher OC sediment, and in the untreated sediment compared to the treated sediment. The higher occurrence of permethrin in the pore water was attributable to the larger pool of rapidly desorbing compound. Based on BAF calculations, bioaccumulation of permethrin by all three species was lower in the higher OC sediment compared to the lower OC sediment, and bioaccumulation was also lower in the treated sediments compared to the untreated sediments for Lumbriculus variegatus and Hexagenia sp., suggesting that bioavailability was reduced for those organisms. Desorption rate constants suggest that a reduction in desorption was the cause. However, bioaccumulation was not reduced for Hyalella azteca whose body residues were not significantly different between the two treatments and so BAF values did not reflect a reduction in bioavailability. The results for H. azteca do not match with typical observations, where bioaccumulation decreases with decreased desorption; suggesting that an important exposure pathway for those organisms was not influenced heavily by the sediment desorption properties. Therefore, the role of ingestion was investigated as a route of uptake. Synthetic digestive fluid extractions increased desorption compared to water; indicating that ingestion increased desorption, and thus bioavailability of sediment-associated permethrin. Estimated pore water and feeding contributions suggested that more than one route of exposure contributed to the uptake of permethrin, and that neither exposure route was responsible for uptake alone. The contribution from feeding was estimated to be greater than the contribution from pore water for WBS sediment for all three species, and for the treated sediments compared to the untreated sediments; indicating that as desorption decreases, the role of ingestion in uptake increases. Therefore, pore water may be more important to the contribution of uptake for faster desorbing compound, and ingestion may be more important to the contribution of uptake for slower desorbing compound.
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