In technical terms, the bioconcentration factor (BCF) is often measured as the ratio of the concentration of a chemical in all or part of an aquatic organism in milligrams per kilogram of wet tissue weight (mg/kg), to the chemical’s concentration in ambient water in milligrams per liter of water (mg/L). Many BCF assessments have been based on aquatic measurements because fish and shellfish provide a rich lipophilic microenvironment for bioaccumulation. However, BCFs can also be based on non-aquatic organisms (e.g., plants, cattle, earthworm) or on an environmental medium other than water (e.g., soil, sediment).

Bioaccumulation is a highly dynamic process as it is affected by many environmental factors. In general, site-specific data on tissue concentrations in the prey would best represent the actual chemical bioavailability at the site of concern (Bechtel Jacobs Co., 1998). Another approach is to conduct a bioaccumulation study in a laboratory setting. However, when neither field nor laboratory data are available, it may be necessary to use either a mechanistic or an empirical model to simulate the uptake and release of contaminants (Suter et al., 2000).

In general, the BCF may be calculated empirically using the following regression equation:

log BCF = A + B log K_ow,

where log K_ow is again (Slide 15) the octanol-water partition coefficient specific to the chemical of interest, and the constants A = - 0.23 and B = 0.76 are often used unless different values for these constants are warranted (Veith et al., 1980).