The distinction made in the last slide further suggests that it is harder to provide estimates for a bioaccumulation factor (BAF) than for a bioconcentration factor (BCF), since the former involves the chemical uptake from all potential mechanisms. In fact, the methodology for deriving BAFs is far more complex than that for BCF. Procedures for calculating BAFs have been provided by U.S. EPA (Code of Federal Regulations, 2003).

In essence, four assessment methods are available for calculating the baseline BAFs for organic chemicals. These are: (1) the baseline BAFs measured from field studies; (2) the predicted baseline BAFs from using biota-sediment accumulation factors; (3) the predicted baseline BAFs each from multiplying a laboratory-measured BCF by a food-chain multiplier (FCM); and (4) the predicted baseline BAFs each from multiplying a predicted BCF by a FCM. FCM is defined as the ratio of a BAF to an appropriate BCF.

For inorganic chemicals, BAFs are derived from using either (1) field-measured BAFs or (2) by multiplying the BCFs by a FCM. For most inorganics, the FCM is assumed to be 1.

The terms baseline BAF and baseline BCF imply that the factors (ratios) are measured under certain standardized conditions for ease of comparison. For organic chemicals, the baseline BAF and the baseline BCF are each based on the concentration of freely dissolved chemical in the surrounding medium (e.g., water) and take into account the partitioning of the chemical within the organism. For inorganic chemicals, the baseline BAF and the baseline BCF are each based on the wet weight of the organism’s tissue (Code of Federal Regulations, 2003).