Current Issues

Active sources of PCBs contribute to contamination of Delaware River fish  6/24/98

Active and historic sources of PCBs are contributing to the current fish contamination problem in the Delaware Estuary, according to a report released today by the Delaware River Basin Commission.

Concern regarding the levels of this class of pollutants in the tissues of recreationally caught fish has prompted the states of Delaware, New Jersey and Pennsylvania to issue fish consumption advisories. Lack of comprehensive and reliable information concerning the sources of PCBs to the estuary and the associated transport pathways has hindered mitigation of the problem. The Commission, state environmental agencies and federal agencies have documented elevated concentrations of PCBs in the river sediments over the last ten years. This study, which focused on wastewater treatment plants and tributaries, sought to develop solid information about these entities as conduits of PCB contamination.

The report indicates that the current fish contamination problem cannot be attributed solely or predominantly to "historic" sediment contamination already in the estuary, as many resource managers have believed. Indeed, the active loading entering the estuary from sewage treatment plants, combined sewage outflows (CSOs), and tributaries is sufficient, independent of the PCBs already in estuary sediments, to cause water quality criteria exceedances and associated fish contamination.

Water samples collected during both dry and wet weather revealed that wastewater treatment plants and tributaries discharging to the tidal Delaware River are active and significant sources of PCB. Wastewater treatment plants and overflows from their collection systems contributed 90% to 95% of the PCBs during both dry and wet weather sampling surveys. Significantly more PCBs (up to 60 times) entered the river during wet weather than during dry weather. Independent of weather conditions, most of the PCBs enter the river between the Tacony-Palmyra and Walt Whitman Bridges.

These findings suggest that rainfall significantly increases PCB mass loading to the estuary. The mechanisms presumably are increased resuspension, erosion, and transport of PCBs associated with contaminated upland sediments as well as PCBs associated with sewer systems.

The study also demonstrates that, independent of the PCB already present in estuary sediments, the active loading entering the estuary from sewage treatment plants, CSOs, and tributaries is indeed enough to degrade water quality and contaminate fish.

These sources are not themselves generators of PCBs. Rather, they are merely conduits for PCBs that have been inadvertently or deliberately introduced into sewage collection systems, eroded from contaminated upland sites, and transported via overland flow into the collection systems and down through tributary watersheds.

Sewage treatment plants, in fact, reduce significantly the amount of PCB entering the estuary, as evidenced by much lower concentrations of PCBs in the water discharged from the plants compared to that in the wastewater entering the plants. Presumably, much of the PCBs that enters the treatment plants is captured in sludge produced by the plants. That sludge in turn is then redistributed to the environment to an unknown extent.

The study results clearly show that additional steps need to be taken to mitigate the impact of PCBs on aquatic life and human health. Barriers to a comprehensive approach exist, however. These include the perception among both regulators and the public that PCBs are historical pollutants that are no longer manufactured and are therefore not currently entering the environment, the use of less sensitive analytical methods that often fail to detect individual PCBs, and the failure to consider some pathways by which PCBs enter the Delaware River.

The report also recommends systematic identification of significant upland sources of PCBs, enhancement of the Commission's mathematical model of the estuary, and implementation of effective sediment and erosion control practices.

In releasing this report, we hope to increase public awareness that PCBs are a current and not a historical threat to the health of the biota and to users of the estuary, and to encourage proper disposal of electrical equipment containing PCBs.

The study was jointly funded by the U.S. Environmental Protection Agency, Regions II & III, and the Delaware River Basin Commission.

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