Mobility and fate of contaminants in estuarine environments

Many estuaries are degraded to some extent by anthropogenic activities which have released pollutants into waters entering or residing in, these ecosystems. When contaminants enter the estuarine environment, they rapidly become incorporated into the sediment. A series of sediment cores were collected from along a transect in the Taunton River, a salt wedge estuary in Narragansett Bay. Cores were dated and analyzed for organic chemicals and heavy metals to reconstruct the spatial and temporal trends of contaminants in the river. Trends indicate that multiple sources of organic chemicals and heavy metals to the river existed. Heavy metals were the first contaminant to appear downcore, early in the nineteenth century, followed by PAHs. PCBs and pesticides appear at depths corresponding to their dates of introduction to the environment. A specific PCB Aroclor, 1268 was identified and measured in each of the sediment cores. Using sediment core data and public records, dates of Aroclor 1268 discharge to the Taunton River were reconstructed. The transport and burial of Aroclor 1268 was determined in each of the cores and from data compiled from other sources. Overall findings indicate that substantial levels of Aroclor 1268 are still present in surficial sediment more than fifty years after their discharge ceased. A series of laboratory experiments were conducted to evaluate and model metal mobility during sediment resuspension events. To accomplish this, formulated reference and field contaminated sediments were resuspended under controlled conditions. AVS was found to be the most effective sediment characteristic in controlling metals release during short term resuspension. Dissolved metals in AVS treatments were found to decline to trace levels when the AVS:metal molar ratio rose to, or exceeded one. Resuspension of field sediments resulted in little dissolved metal being released, regardless of AVS level, confirming the importance of other sediment binding phases in regulating metal release. Comparison of predicted versus measured metals in the field sediments yielded mixed results, further reinforcing the importance of non-AVS binding phases in controlling dissolved metal release during non-equilibrium conditions. In summary, results of these studies further the understanding of sediment-bound contaminants in dynamic environments such as estuaries