Arctic animals are at risk from black soot from the combustion of fuels and biomass burning, additional soot from forest fires, and chemical fumes from industries around the globe. Why? Because they rise in the sky, travel around the world, and settle on arctic snow and ice.
Likewise, contaminants from agricultural run-off, untreated sewage, and chemical-laden discharge from ships and factories flow into ocean currents and eventually pollute places far from their source—places like the Arctic.
Modern synthetic chemicals are especially threatening. The best-studied example is PCB, or Polychlorinated Biphenyl. Manufacture of PCB was finally banned when scientists learned that it persists in the environment and injures wildlife.
- Trace amounts of PCB make their way to the Arctic and concentrate as they rise up the food chain. Polar bears ingest these higher levels when they eat seals.
- PCB in the fat of polar bears appears to weaken their immune systems leading to greater threat from parasites and disease. PCB has also been linked to reproductive failure and malformed organs.
Studies show that all polar bears carry significant pollution loads, but we don't know at what levels they cause biological problems. What's more, multiple pollutants sometimes have synergistic effects.
On 2004, major industrial nations signed the Stockholm Convention on Persistent Organic Pollutants (or POPs) treaty. It calls for increased efforts to reduce, contain, and eliminate POPs.