What is the best explanation for the high concentrations of PCBs in polar bears?

The high concentrations of PCBs (polychlorinated biphenyls) in polar bears can best be attributed to the phenomenon known as global distillation, which is the process where volatile organic compounds evaporate in warmer locations and then are transported to cooler areas, like the poles, where they condense and accumulate in the environment.

As PCBs are carried by atmospheric currents from industrialized regions, they travel long distances from their original sources. Upon reaching the Arctic, these compounds do not readily break down due to cold temperatures, allowing them to persist long-term in the environment. Over time, PCBs accumulate in the food web, particularly in fatty tissues. Polar bears, being apex predators within their icy habitat, consume a significant quantity of high-fat prey such as seals. As a result, they ingest and accumulate higher levels of PCBs than animals lower in the food chain, leading to the observed high concentrations of these pollutants in their bodies.

This situation highlights how pollutants released in one part of the world can affect ecosystems far removed from the source of pollution, due to the global transport of these chemicals and their tendency to accumulate in organisms at higher trophic levels.