Risk Assessment

Ecological

Ecological risks (e.g., potential risks to birds, mammals, fish, etc. that inhabit the Grasse River) were also evaluated in EPA's 1993 baseline risk assessment. The 1993 document identified potential ecological risks to the sediment dwelling organisms of the lower Grasse River, birds foraging in the Grasse River, bats foraging above the lower Grasse River, and mink. PCBs are the primary chemical of concern with respect to ecological risks. The potential risk to higher level organisms such as birds and mink is associated with the consumption of prey that accumulate PCBs in their tissue (e.g., fish). As is the case with human health risks, the principal concern with respect to ecological risks involves consumption of fish containing PCBs. EPA revisited the ecological baseline risk assessment in 2010 to incorporate the additional Grasse River data along with the most current scientific and regulatory policy on risk evaluation.

The 2010 update was developed using EPA's prescribed methodology for ecological risk assessments that calculated risk to aquatic organisms from exposure to chemical compounds in sediment and surface water. EPA performed this evaluation by determining the following:

  • Risk to aquatic organisms was estimated by comparing maximum and mean sediment and surface water exposure concentrations with benchmark values to calculate hazard quotients.
  • Risk to fish was evaluated by comparing measured concentrations of chemicals in fish tissue with concentrations cited in published studies that identified adverse effects in fish and concentrations at which adverse effects were observed.
  • Food chain models were used to calculate risk to upper trophic level fish-eating birds and mammals and insect-eating mammals from consumption of fish and aquatic invertebrates.
  • Risk was estimated by comparing maximum and mean calculated dietary PCB intake with toxicity reference values for birds and mammals.

The 2010 update concludes there is potential risk to fish-eating birds and mammals and insect-eating mammals. The potential risk to higher level organisms such as birds and mink is associated with the consumption of prey that accumulate PCBs in their tissue (e.g., fish). As is the case with human health risks, the principal concern with respect to ecological risks involves consumption of fish containing PCBs.

Arconic (formerly Alcoa) provided comments to EPA expressing concern that a number of the assumptions adopted in the analysis are overly conservative and that the most recent data available should be used as the basis for the assessment. Based on these considerations, the company believes that the analysis provides an overstatement of the current potential ecological risk associated with the Grasse River site.

Summary

Because fish are the main driver of potential human health and ecological risks in the lower Grasse River, reducing PCBs in fish is a primary goal of remediation within the lower Grasse River. The source of PCBs to the fish is the PCBs contained in the surface sediments of the lower Grasse River. As such, reducing PCBs in lower Grasse River fish is directly related to reducing the PCBs levels in the surface sediments of the river, which is where they can enter the food chain and ultimately be taken up by the fish.