Measurement and Modeling of Polychlorinated Biphenyl Availability from Contaminated Sediment and Evaluation of Ecosystem Recovery

Download or read book Measurement and Modeling of Polychlorinated Biphenyl Availability from Contaminated Sediment and Evaluation of Ecosystem Recovery written by Elisabeth Marie-Louise Janssen and published by Stanford University. This book was released on 2010 with total page 163 pages. Available in PDF, EPUB and Kindle. Book excerpt: This research comprises measurement and modeling of polychlorinated biphenyl (PCB) bioaccumulation from contaminated sediments and the evaluation of an in-situ sorbent amendment with activated carbon (AC) to allow ecosystem recovery. Laboratory bioassays with the deposit feeding polychaete Neanthes arenaceodentata, showed that PCB uptake from the aqueous phase accounted for less than three percent of the total uptake. High sediment ingestion rates and fast bioaccumulation of PCBs exceeding sediment concentration within 14 days of exposure suggest that deposit feeders are promising test organisms to evaluate local sediment conditions. A biodynamic model that described bioaccumulation by a mass balance approach of contaminant influx and efflux was parameterized for this polychaete. The model allows the prediction of tissue concentrations and facilitates the understanding of exposure pathways. Subsequently, the effects of an AC-amendment to sediment from a PCB-contaminated site at Hunters Point within the San Francisco Bay, California, were evaluated by employing caged deposit-feeders, along with polyoxymethylene (POM) samplers using parallel in situ and ex situ bioassays with homogenized untreated or AC-amended sediment. The AC-amendment reduced bioaccumulation by 90% in the laboratory and by 44% in parallel field tests with treated and untreated sediment. In-situ measurements with passive pore water samplers showed that PCB uptake was greater for samplers placed in the surface sediment compared to the underlying AC-amendment. The tests revealed three factors that influenced the in-situ bioassays: 1. AC-amendment significantly reduces bioavailability under laboratory and field conditions; 2. Deposit-feeding organisms exhibit less PCB uptake from untreated sediment when feeding is reduced; and 3. Sediment deposition within test cages in the field partially masks the benefit of underlying AC-amended sediment and emphasizes the need of area-wide considerations when assessing contaminated sediment management and remediation strategies. Parallel ex-situ and in-situ bioassays in combination with passive sampler measurements can tease apart field influences on PCB exposure. These tests should accompany each other to evaluate in-situ exposure and the effectiveness of remediation alternatives. This research further focused on pollution-induced changes of the benthic community at Hunters Point and the evaluation of the expected recovery potential after an AC-amendment for in-situ sediment remediation. The benthic community composition was compared for the PCB-contaminated site at Hunters Point and 30 reference sites in the San Francisco Bay to evaluate pollution-induced changes. Given the similar number of species, total abundance, and diversity indices between the reference sites and Hunters Point, it could be concluded that the benthic communities did not differ greatly. However, further analysis based on functional traits of the benthic community shows that the community at Hunters Point is deprived of species that may be stressed by the contaminated sediment due to their feeding mode, reproductive mode, or position in the sediment. The benthic community in comparison to reference sites lacks deposit feeders, subsurface carnivores, egg laying species, and species with no/weak protective barrier. Sediment chemistry analysis shows that PCBs are the major risk drivers at Hunters Point and that the reference sites show only ambient levels of PCB contamination. Biodynamic modeling demonstrates how varying exposure and functional feeding strategies affect PCB bioaccumulation, with a deposit feeder accumulating two orders of magnitude more PCBs in its lipids than a facultative deposit feeder and up to three orders of magnitude more than a filter feeder. Modeling scenarios also show that PCB tissue concentrations at Hunters Point are two orders of magnitude higher than at the reference sites. Sediment remediation with a sorbent (activated carbon) amendment at Hunters Point can reduce PCB availability by 85 to 90% under favorable field and treatment conditions. The expected remedial success corresponds to exposure conditions within sediment quality guidelines and the cleanup goal but remains slightly higher than at the reference sites.