No description available.

Frankfurt (Main), Universiẗat, Diss., 2008.

No description available.

No description available.

No description available.

none

Giessen, Universiẗat, Diss., 2004.

Frankfurt (Main), Universiẗat, Diss., 2003.

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.

In natural systems, the solution concentration and hence, potential bioavailability of trace metals is primarily controlled by adsorption-desorption reactions at the mineral-water interface. While many studies have been conducted to understand the adsorption of trace metals to soil minerals, less is known about long-term adsorption/desorption processes. In this study, we examined the influence of mixing and sorption period on the desorption of lead from goethite. Lead sorption was rapid and essentially complete in 1 h, with no change in the quantity of lead adsorbed over the 6 month sorption period. Desorption of lead was slower than the adsorption reaction and was best modeled by two first order equations. At all sorption densities, the desorption of lead followed the order Short-term (24 h) > Long-term non-stirred (6 months) > Long-term stirred (6 months). However, statistical analysis indicated that these differences were not statistically significant. Furthermore, the desorption rate coefficients were very similar for all the experiments indicating that there was no significant residence time effect in this study. However, a sample from a previous study that was allowed to age 5 years and then analyzed by the desorption procedure did have statistically significant differences between the long-term (5 years) and the short-term (5 months). These results suggest that longer adsorption periods, perhaps a number of years, may be necessary to determine if residence time effects are an artifact of the experimental conditions or truly the length of the adsorption period. / Master of Science