DIAMOND STATE SALVAGE
WILMINGTON, NEW CASTLE COUNTY, DELAWARE
Polychlorinated biphenyls are a group of man-made chemicals that are widely distributed as environmental pollutants. They are considered to be probable human carcinogens by EPA. Their persistence in the environment and bioaccumulation potential in fish and animal tissue are major contributing factors for levels of PCBs commonly found in the blood and fat tissue of the general population . Polychlorinated biphenyls have a low solubility in water, but have a high affinity for adsorption onto organic particulates. These particulates settle onto existing sediments in areas of slower current, that are referred to as deposition areas.
Polychlorinated biphenyls were detected in sediment samples collected from Brandywine Creek at concentrations below levels of concern for direct exposure (i.e., through ingestion or dermal contact). Various metals were also detected in these samples below their respective background levels for natural soils. Generally, the impetus for PCBs clean-up is the impact on aquatic life and human consumption of aquatic life . Therefore, EPA has developed interim sediment quality criteria for several organic chemicals such as PCBs. Briefly, these interim sediment quality criteria are based on assumptions that address equilibrium partitioning, toxicity to aquatic life, and bioaccumulation of the chemicals by benthic organisms .
Using assumptions for biota sediment accumulation factor (1.85) and tissue lipid content (3%) in EPA's National Sediment Quality Survey and site specific considerations for sediment organic carbon content (2.5%), a mean sediment concentration of 0.081 ppm would not present a health hazard. A mean sediment concentration of 0.213 ppm may present a health hazard, if fish consumption rates of trophic level 4 fish from Brandywine Creek were consumed more than approximately once a month.
Given the large uncertainty associated with biota sediment accumulation factor analysis, in the event that 0.213 ppm is accepted as the true mean it would be prudent to sample fish tissue from the creek before significant actions are taken based on current sediment levels and the fish consumption exposure pathway alone.
At this site (Brandywine Creek), there was no information provided to indicate that recreational activities occur, except for recreational fishing. There were data provided to suggest that PCBs are bioaccumulating in fish to unacceptable levels. However, there were no data indicating high fish consumption rates. Most of the PAHs analyzed was not detected, and the ones reported were expressed as estimated values, because the results were below the instrumentation detection limits.
Creek sediment PCBs and other contaminants are generally unavailable for direct human exposure, unless the sediments are disturbed and ingested while engaging in recreational activities at the creek, such as swimming. Exposures resulting from these activities would not present a health hazard. Additionally, metals detected in samples from this site are not elevated in comparison to natural soils.
The closest residential well is about 2 miles from the creek. It is believed that most of the residents who live nearby are using the municipal water system for potable purposes.