PILOT-SCALE VALIDATION OF THE RIVER-FISH BIOACCUMULATION MODELING PROGRAM FOR NONPOLAR HYDROPHOBIC ORGANIC-COMPOUNDS USING THE MODEL COMPOUNDS 2,3,7,8-TCDD AND 2,3,7,8-TCDF

The interactive and user-friendly PC-computer-based RIVER/FISH mechani stic modeling procedure was evaluated and found to provide credible si mulations of aquatic organism bioaccumulation for nonpolar hydrophobic organic chemicals (NPHOCs) using a four-trophic-level food web calcul ation methodology. Model evaluation included calibration to observatio ns of tetrachlorinated dibenzodioxin and -furan (TCDD/F) bioaccumulati on in largemouth bass (Micropterus salmoides) and channel catfish (Ict alurus punctatus) that were exposed in pilot-scale experimental stream s receiving biologically treated pulp mill effluent and subsequent com parison of model predictions without bioaccumulation parameter adjustm ent (validation) to similar but independently obtained bioaccumulation observations. When calibrated with site-specific information on NPHOC loading rates and organism feeding habits, model prediction uncertain ty was within U.S. Environmental Protection Agency (EPA) established s tandards averaging 1.1 pg/g for the observations used for model valida tion, which all measured <20 pg/g. The procedure appears suitable for field-scale applications provided the site-specific feeding habits of each organism in the simulated food web can be estimated accurately, a ll significant chemical loadings are quantified, and the natural varia bility of bioaccumulation processes is considered when interpreting si mulation results.