Impact/Purpose:

The primary goal of this project is to describe and demonstrate a framework for assessing ecological risks and developing risk-based water and sediment quality criteria for fish and wildlife populations exposed to PBTs. This framework will provide guidance for development and application of the criteria for protection of fish and wildlife populations on the basis of PBT residue-based toxicity data. It will allow presently available chemical mass balance models to link site-specific chemical loading, fate, and transport information to toxicity risks, including population level impacts. This, and the demonstration of capability for risk assessment of complex mixtures of PBTs having a common mechanism of toxicity, should allow EPA, the States, and Tribes to more effectively determine where and to what extent loadings of PBTs to aquatic ecosystems pose unacceptable ecological risks.

Description:

The fundamental purpose of this project is to insure that appropriate chemical residue-based toxicity data and models are effectively used, in conjunction with bioaccumulation and population dynamics models, to determine site-specific water and sediment quality conditions required to sustain populations of aquatic organisms and aquatic-dependent wildlife. This project will function as a framework for a continuing development and application of risk-based water and sediment quality criteria for PBTs. Three major groups of PBTs that must be addressed are halogenated organics, PAHs , and organometallic compounds such as methyl mercury. Initially, the conceptual model for risk assessments and criteria development involving determination of safe loadings of PBTs to aquatic systems will be applied to existing data and models for chlorinated aromatic chemicals that act through an AhR-mediated toxicity mechanism in vertebrates. This class of chemicals includes polychlorinated biphenyls (PCBs), polychlorinated dibenzo dioxins (PCDDs), and polychlorinated dibenzo furans (PCDFs), for which residue-based ELS toxicity data and a mixture toxicity model are available. Thus, ecological risk assessment tools and approaches will be described and demonstrated for risk-based criteria development and application, including use in TMDLs designed to protect populations of sensitive fish and wildlife species. The association of the historical lake trout population decline in Lake Ontario with exposure of embryos to AhR agonists (such as 2,3,7,8-TCDD) will be used as a device to examine the applicability of population models when used in tandem with residue-based toxicity data. The extent to which extrapolation of lake trout risks to other species involves more than species sensitivity to TCDD and degree of exposure/bioaccumulation will be examined in the context of toxicokinetic, toxicodynamic, biochemical, and life history factors. Data gaps and modeling limitations will be identified and further described as research needs for development of a general risk assessment capability for all PBTs. This analysis will include an initial conceptual evaluation of the degree to which similarities and differences in PBT properties and mechanisms of action will define a balance between generic and chemical specific PBT risk assessment approaches and models. Population matrix modeling will be a primary tool for evaluating vulnerability differences between species based on differences in life stage sensitivities, exposure profiles, and reproductive strategies.

Record Details: