It has been shown that POPs can evaporate at their release point in the environment and condense again at a point sometimes many hundreds of kilometres away. Once there, the Arctic acts as a kind of cold trap. Evaporation, if it occurs at all, does so much more slowly. The substance is then taken up into the ecosystem. In the Great Lakes, local sources of POPs are certainly a greater concern, thanks to the preponderance of industrial activity.
Distant sources can also have an effect, however.
DDT levels in Great Lakes sediments, for example, decreased slowly, if at all, after it was banned in Canada and the United States. It has been determined that DDT still in use in countries like Mexico is making its way north on air currents to the Great Lakes basin. The Great Lakes region is one of the best-documented regions in the world regarding the effects of POPs. Wildlife have been impacted tremendously by POPs-herring gulls, cormorants, bald eagles, mink, otter and even humans have showed effects associated with the presence of DDT, PCBs, mirex and other POPs. In humans the effects include decreased attention span in children whose mothers eat Great Lakes fish.