Laboratory Assessment of Bioavailability Reduction of DDx by Sorbent Amendments to Sediment.

摘要

Past research has shown that amendment of activated carbon and other sorbents can be a viable option for reducing the contaminant bioavailability in sediments. In situ remediation can serve as an alternative or additional solution to the traditional approach of dredging and capping. The research documented in this thesis evaluates the effectiveness of different types and doses of sorbents in reducing bio uptake of DDx (DDT, DDD, DDE) from an industrially impacted sediment.;Bioaccumulation studies were performed in laboratory microcosms to understand the impact of sorbent amendments on DDx bioavailability. Sediment amended with a coal based and coconut shell based activated carbon applied in a pelletized form at 0.5 times of sediment organic carbon reduced bioaccumulation of three DDT compounds (4,4-DDD, 2,4-DDD, 4,4-DDE) by 70-90% in L. Variegatus. Direct addition of coconut shell based activated carbon was less effective in the reduction of DDx bioaccumulation compared to SediMite(TM). The amendment of sediment with AmbersorbRTM was not effective in reducing bioaccumulation compared to activated carbon. Freely dissolved concentration of contaminants in sediment porewater constitutes an important route of exposure to benthic organisms. Polyoxymethylene (POM) was used as a passive sampler to measure aqueous concentrations of DDx from sediment porewater. The reductions in aqueous equilibrium concentration from sediment amended with three different sorbents correlate well with the reductions observed in biouptake studies.;Desorption tests showed a strong correlation between carbon dose and reductions in an easily desorbed fraction of three DDT compounds (4,4-DDD, 2,4-DDD, 4,4-DDE) in sediment. Compounds desorbed in 6 hr from sediment may provide a good surrogate for bioavailability of the sediment sorbed contaminants. Desorption kinetic studies support the findings from both bioaccumulation and aqueous equilibrium studies, and demonstrate that DDx bioavailability in sediments is reduced greatly by activated carbon applied in a pelletized form. The promising results with activated carbon applied as SediMite(TM) illustrate the potential for delivering in situ treatment material to DDx contaminated sites.