Biomagnification

The physical and chemical properties of PCBs has made them useful in the development of models for the environmental behavior and transport of chemicals, including models for bioconcentration, bioaccumulation, and risk assessment.

In aquatic organisms PCBs bioconcentrate strongly, as they are within the molecular size range and K0W range suited to efficient absorption through membranes. At higher trophic levels and in the terrestrial foodchain the diet is the most important source of PCBs, and PCBs strongly bioaccumulate. Absorption into an organism is controlled by the relationship between the amount of PCB present in the absorbing part(s) of the organism and the PCB concentrations encountered, which can be explained using the 'fugacity' concept. For example, an organism with large fat reserves will accumulate more PCBs in total from its environment or diet than an organism with smaller fat reserves because the fat reserves in the two organisms will reach equilibrium at the same concentration (or achieve steady state at similar concentrations). Efficient metabolism of particular PCB congeners has a strong effect on absorption (a positive effect) and biomagnification (a negative effect) because strongly metabolized PCBs are kept at lower concentrations within the organism. This is illustrated in Figure 2, where it can be seen that seal faecal concentrations are higher than the diet (fish) for the unmetabolized PCBs, because they are at relatively higher concentrations in the seals blood - they are absorbed less strongly than the metabolized PCBs, which are at relatively lower concentrations in the seals blood. Because of the role of K0W in the absorption of PCBs from either water or the diet, the more-chlorinated PCBs generally biomagnify more efficiently than the less-chlorinated PCBs.

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