R7 PM Uncertainty Analysis in Risk Assessment: Influences on Decision-making
Thursday, 17 November 2005: 1:50 PM - 5:30 PM in 327-329

(TOL-1117-851660) Deriving Localized Bioaccumulation Models for Setting Site-Specific Water Selenium Concentration Benchmarks for Pollution Control Decisions.

Toll, John¹, Brix, K.², DeForest, D.³, Tear, L.⁴, Adams, W.⁵, ¹ Toll Environmental, Seattle, WA, USA² EcoTox, Coral Gables, FL, USA³ Parametrix, Bellevue, WA, USA⁴ , Seattle, WA, USA⁵ Rio Tinto, Murray, UT, USA

ABSTRACT- We have developed a procedure for determining site-specific water quality benchmarks for substances regulated based on tissue residues. The method uses a multi-site regression model to solve for the conditional prior probability density function on water concentration, given that tissue concentration equals a tissue-based water quality criterion. It then uses site-specific water and tissue concentration data to calibrate the probabilistic model and identify the water concentration that, if met at the site, would provide a desired level of confidence of meeting the tissue-based criterion. This allows for derivation of a site-specific water quality benchmark. The procedure is fully reproducible, statistically rigorous and easily implemented. We have applied it to selenium. The current draft aquatic life criteria for selenium would set the freshwater chronic criterion based on a whole body fish tissue concentration. If the measured tissue concentration data indicate that the use is not protected, back-calculation of a water concentration benchmark could be triggered to support pollution control decisions. Our procedure provides a way to do that.

Key words: bioaccumulation modeling, uncertainty analysis, water quality criteria, risk assessment