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Integrated modeling systems to assess exposure and toxicity of chemicals in support of aquatic ecological risk assessment of methodologically challenging chemicals
Citation:
Barber, Craig, Kate Sullivan, AND C. Stevens. Integrated modeling systems to assess exposure and toxicity of chemicals in support of aquatic ecological risk assessment of methodologically challenging chemicals. Presented at International Society of Exposure Science 24th Annual Meeting, Cincinnai, OH, October 12 - 16, 2014.
Impact/Purpose:
Presented at the International Society of Exposure Science 24th Annual Meeting.
Description:
From an exposure assessment perspective, persistent, bioaccumulative and toxic chemicals (PBTs) are some of the most challenging chemicals facing environmental decision makers today. Due to their general physico-chemical properties [e.g., high octanol-water partition coefficients (Kow), low aqueous solubilities, and slow abiotic and biotic transformation rates], exposure assessment of these chemicals is methodologically challenging either because reliable empirical data concerning their environmental fate, transport, and bioaccumulation is unavailable, or because the available data is so limited that extrapolations to unmeasured environments and release scenarios cannot be made confidently. In either case, integrated environmental modeling (IEM) offers decision makers an objective and scientifically defensible approach to assessing such chemicals. Importantly, such IEM approaches should be tiered in ways that allow decision makers to evaluate expected environmental exposures and hazards posed by the chemicals of concern with a realistic understanding of environmental and biological variability. Each tier should enable users to predict expected environmental concentrations (EECs) that in turn are used to predict expected biological concentrations (EBCs) in exposed biota. Resulting EBCs can then be compared to appropriate residue-based toxicity benchmarks to assess the condition of exposed biota or be inputted to dietary exposure calculators/models for humans and wildlife species of concern. In this presentation, we present a two-tier integrated modeling system for assessing the fate, transport, and bioaccumulation of PBTs discharged into wadeable and large rivers. Whereas the Tier I system links a steady-state fate and transport model to a steady-state bioaccumulation model, the Tier II system links a dynamic fate and transport model to a dynamic bioaccumulation model. For this demonstration, we used the USEPA's EXAMS, KABAM, and BASS models which are both peer reviewed and used routinely by the Agency to assess ecological and human health exposures in and from aquatic ecosystems. Nine EXAMS environments were constructed to simulate the steady-state and dynamic fate and transport of PBTs in rivers of different sizes and physiographic provinces. Hydrological data for these sites were obtained from USGS sources, and required climatic data were obtained from NOAA's National Climatic Data Center. Seventy-four PBT and endocrine disrupting chemicals having Kow > 1 000 were chosen for analysis, and their physico-chemical properties were estimated using both observed data and values predicted by a variety of chemical property calculators. Finally, we forecast regional trends for these chemicals' EECs and EBCs and enumerate the parameter sensitivity and variability of these forecasts.
