One other factor affecting bioaccumulation, which has not been discussed thus far, is a chemical’s mobility in the environment. It was thought that persistent endocrine disruptors such as PCBs and DDT could reach remote regions of the earth typically via atmospheric, oceanic, or even terrestrial transport. Of the three, terrestrial transport appears less likely to be the major mode responsible for such a long-range mobility since soil, plants, runoffs, and the kind are stationary and not as migratory. Nonetheless, recently a fourth mode of transport has been identified or discussed more extensively (e.g., Ewald et al., 1998). This is animal migration or, more technically referred to as, biotransport.

In the study by Ewald et al., pacific salmon were noted to spawn in freshwater and then migrate downstream to the ocean to spend the majority of their lifecycle there. Prior to migration back upstream for spawning, they accumulate lipids for the energy required for migration and for gonadal development. The lipids that the salmon accumulated in their body were found to have been contaminated by lipophilic pollutants, such as PCBs and DDT.

The study concluded that biotransport of environmental pollutants is far more significant than other modes of transport, for at least two reasons. First, lakes that are within reach of salmon migration are quantitatively a larger contributor to local contaminant loads than the ocean is, since the former is a much smaller medium. Second, contaminants delivered via biotransport tend to be more biologically active and less vulnerable to environmental degradation than those arriving via other modes of transport, since they are within lipid stores and hence protected from various oxidation processes such as UV-radiation.