Discussion of Key Questions

KEY QUESTION 1. Are the current levels of PCBs in the upper Hudson River causing harm to the residents and environment of the upper and lower Hudson River?

Findings:

1. PCB levels in Hudson River fish far exceed those believed to impact the health of people who consume fish, based upon risk-based levels established by credible toxicological methods.

2. Concentrations of PCBs in fish and wildlife exceed levels believed to cause harm, based upon risk-based levels established by credible toxicological methods.

Effects of PCBs on people. The effects of PCBs on individual humans and on human populations have been studied extensively over the past thirty years (Agency for Toxic Substances and Disease Registry, 1999; Robertson and Hansen, 2001).

As a result of this research, PCBs have been labeled "probable human carcinogens" by the EPA, and are also suspected of inducing developmental and learning disorders, impairing human immune systems, andcausinglowbirth weights. Production of these chemicals hasbeenbannedinternationally under terms of the United Nations' recent treaty on Persistent Organic Pollutants (see http://www. chem.unep.ch/pops/POPs_Inc/dipcon/meeting-docs/conf_2/en/conf_2e.pdf).

It is very difficult to prove that exposure to an environmental contaminant harms people, as evidenced by debates over tobacco smoke and asbestos. Risks usually have to be judged in terms of probabilities. The science of risk assessment has matured considerably since the National Academy of Sciences endorsedit (National Research Council, 1983). Risk assessment has been widely adopted within the public health profession. The risk to people exposed to PCBs in the fish they eat depends upon the amount of fish they consume, the PCB

concentrations in those fish, and their vulnerability to PCB-induced diseases. Only the first two of these factors can be controlled.

To determine the "safe" level of PCB exposure for a human population, environmental epidemiologists first decide what level of risk is "acceptable." The U.S. Food and Drug Administration (FDA) has set the acceptable PCB level in fish sold for human consumption in interstate commerce at 2 parts per million (ppm, or milligram PCB per kilogram of edible fish tissue on a wet weight basis). This guidance, now seventeen years old, was based on the average amount of fish consumed by the American public and the known PCB effects on humans at the time. Since the FDA guidance level was set, the average U.S. diet has changed to include more fish (Reinert et al., 1991). Also, our understanding of the subtle impacts of PCBs on humans, including non-cancer effects such as developmental impairment has greatly improved (Agency for Toxic Substances and Disease Registry, 1999, Robertson and Hansen, 2001). More recent human health risk assessments of PCBs suggest that the FDA guidance level does not protect recreational fishers, certain ethnic groups, and coastal dwellers who consume more fish than the average U.S. resident. Non-cancer threats of PCBs, especially to children and women of child-bearing age, have led some coastal states to set more stringent PCB guidelines (see http://www.epa.gov/watescience/fish/ for most recent fish consumption advisories). Although the EPA provides some advice on how the states should evaluate PCB risks and set guidelines (see http://www.epa.gov/ost/sish/guidance.html for EPA's guidance to the states to set advisories), each individual state currently sets its own PCB advisory level. Many coastal states are following the Great Lakes Protocol, a risk-based approach (Table 24.1) for setting PCB advisory levels developed by a consortium of eight Great Lakes states (Great Lakes Sport Fish Advisory Task Force, 1993). While the public health advisories produced by individual states vary somewhat, in general they are very close to the Great Lakes Protocol.

In the Upper Hudson River, mean PCB levels in edible fillets of fish commonly caught in recre-ationalfisheriesrange (Table 24.2)from2to 41 ppm (U.S. Environmental Protection Agency, 2000c). These levels exceed by more then ten-fold the

Table 24.1. The Great Lakes Protocol

Risk-Based PCB Advisory

PCB concentration in

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