Ecological risk assessment of multimedia hazardous air pollutants: estimating exposure and effects

Hazardous air pollutants, some of which have the potential for multimedia distribution, raise several hurdles for ecological risk assessment including: (1) the development of an adequate transport, fate and exposure model; and (2) the selection of exposure-response models that can accommodate multiple exposure routes for ecological receptors. To address the first issue, the EPA Office of Air Quality Planning and Standards has developed TRIM.FaTE, a mass-balance, fate, transport, and ecological exposure model that is a component of the Total Risk Integrated Methodology (TRIM) for air pollutants. In addition to abiotic transfers and transformations, TRIM.FaTE estimates the uptake of a chemical by terrestrial and aquatic organisms with time. Measures of exposure that TRIM.FaTE can provide include: (1) body burdens or tissue concentrations; (2) doses averaged over any time period; or (3) concentrations of chemicals in abiotic media. The model provides the user with the flexibility to choose the exposure-response thresholds or dose-response relationships that are best suited to data availability, routes of exposure, and the mechanism of toxicity of the chemical to an ecological receptor. One of the challenges of incorporating TRIM.FaTE into a risk assessment methodology lies in defining a streamlined model simulation scenario for initial screening-level risk assessments. These assessments may encompass multiple facilities that emit a variety of pollutants near diverse ecosystems. The information on ecological risk assessment methodology that is described is applicable to the EPA Residual Risk Program with emphasis on multimedia pollutants and the role of TRIM.FaTE.