Validation of Ambient Water Quality Criteria (AWQC) Bioaccumulation Methodology Using Green Bay Mass Balance and Hudson River Datasets
(U.S. Environmental Protection Agency Office of Science and Technology Health and Ecological Criteria Division)

In July 1998, EPA published its draft revision to the methodology for deriving ambient water quality criteria to protect human health (U.S. EPA, 1998). Included in the draft Technical Support Document (TSD) are various approaches to determining bioaccumulation factors (BAFs) for nonpolar organic chemicals. These approaches included: (1) use of field-measured BAFs; (2) use of BAFs predicted from biota sediment accumulation factors (BSAFs); (3) use of laboratory-measured bioconcentration factors (BCFs) with food chain multipliers based upon a food web bioaccumulation model; and (4) use of Kow-predicted BCFs and the same FCMs. Under a Work Assignment with EPA's Health and Ecological Criteria Division, GLEC tested and evaluated the accuracy in predicted BAFs (Methods 2 and 4) using high quality field data from the Green Bay Mass Balance project and the Hudson River PCB data set. The validation exercise included:

• Database retrieval of PCB congener concentrations from complex relational databases;
• Calculation of maximum likelihood estimate (MLE) unbiased mean concentrations using Dolan and El-Shaarawi's (1991) algorithm, which estimated unbiased mean concentrations in samples containing data censored at multiple detection limits;
• Calculation of baseline (lipid- and organic carbon-normalized) and total bioaccumulation factors (BAFs);
• Calculation of predicted BAFs using AWQC draft methods 2 and 4;
• Comparison of predicted and measured BAFs, and analysis of factors contributing to prediction errors;
• Evaluation of baseline normalization BAF variability reduction