Bioconcentration and Bioaccumulation in Aquatic Organisms

In surface waters, the bioconcentration factor (BCF) is the ratio of a chemical s concentration in an organism to the chemical s aqueous concentration. BCF is often expressed in units of liter per kilogram (i.e., the ratio of mg of chemical per kg of organism to mg of chemical per liter of water). The BCF 

FIGURE 2-28 Correlation of the measured, lipid-normalized bioconcentration factor (BCF) with the triolene-water partition coefficient (Ktw) for a suite of 16 nonpolar compounds. (The partition coefficient Ktw is similar to Kow.) Note that the overall correlation is very strong, but any single prediction of BCF from Ktw may be in error by half a log unit (a factor of three) [Smith et al. (1988). Reproduced with permission of Springer-Verlag New York, Inc.]. 

It is important to note that partitioning models do not imply that an increase in chemical concentration occurs as one moves up a food chain in fact, partitioning models predict that the concentration of a chemical in an organism is not dependent on what the organism eats. Partitioning models are not appropriate for terrestrial ecosystems for those ecosystems, models for chemical accumulation must be based on the food chain (i.e., bioaccumulation). 

Bioaccumulation can be estimated by a kinetic model. In kinetic models (sometimes called physiological models or physiologically based pharmacokinetic models), consideration is given to the dynamics of ingestion, internal transport, storage, metabolic transformation, and excretion processes that occur in each type of organism for each type of chemical. In kinetic models, 

FIGURE 2-29 Schematic representation of a physiologically based kinetic model for bioaccumulation of a chemical that is absorbed through the gills, transported by blood flow, stored in various body tissues, and metabolized by the liver. Such a model requires much more detailed information on the fish than does a partitioning model however, it may be necessary to use this more complex approach for chemicals that are metabolized or excreted by the fish more rapidly than they are exchanged with the water [adapted from Barron (1990). Reprinted with permission. 1990 American Chemical Society]. 

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