Conclusions and Future Work

A mass balance model was developed to examine the transport, fate, and bioaccumulation of PCB homologues in the Lower Hudson River. A 15-year simulation period (1987-2002) was considered for model application and included the period of increased PCB loads from the Upper Hudson during the early 1990s. Results of the model provide a good description of observed PCB homologue concentrations in surface sediments and in fish.

A closer examination of model results indicated the following:

1. Sorptionof PCBs to phytoplanktonappears to control the partitioning of PCB homologues to suspended solids in the Lower Hudson River.

2. Organic carbon cycles, which are largely described by phytoplankton production and subsequent deposition and decompositionin sediments, act to scavenge PCBs from the water column and accumulate them in sediments.

3. During downstream transport, exchange of PCBs between the water column and sediments and the large capacity of sediments to store PCBs work together to dampen downstream responses to changes in Upper Hudson loads.

4. Differences in the hydrophobicity of di-through hexa-CBs (as expressed by a two order of magnitude variation in Kqw values) largely explain differences in PCB homologue accumulations in sediments and fish, in volatilization losses, and in temporal variations in white perch and striped bass.

5. Migration of striped bass plays a critical role in limiting their exposure to PCBs.

Although the current model provides a reasonable description for PCB transport, fate and bioaccumulation in the Lower Hudson, gaps remain in our understanding of several key processes. In particular, further studies are needed to address the partitioning of PCBs to different types of POC (for example, phytoplankton, fresh detritus, refractory organic material). In addition, our present understanding of sediment transport and how it affects the movement of POC (and POC-bound contaminants) in the Lower Hudson is limited and needs further evaluation. Finally, currentmodel descriptions for PCB bioaccumulation, provide useful information on the transfer of PCBs through the Lower Hudson food web. Continued investigations of bioaccumulation, however, are needed to provide us with a better understanding of PCB transfer pathways (including interactions with the benthic food web). Specific attention should also be given to differences inmigrationbehavior, feeding patterns, and other processes that may explain intraspecies variability of PCB accumulations in fish.

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