"These chemicals enter the atmosphere at lower latitudes where they were used, and are then deposited down from the cold polar air, so Arctic animals are more highly exposed than animals in more temperate or equatorial regions," University of Florida researcher Margaret James (who wasn't involved in the study) told New Scientist.
Sure enough, the authors of the new study found a link between high levels of PCBs and low baculum density. The researchers can't be sure that PCBs are to blame, but this isn't the first indication that they could be causing serious trouble. In fact, the once-widely used chemicals were banned by the United Nations in 2011.
Used to create different kinds of plastics and rubbers during the 20th century, these compounds have proven difficult to remove from the environment since their ban. They remain stuck to sediments and are carried through waterways, building up in concentration (and toxicity) the higher up you go in the food chain. For top predators, such as humans and polar bears, the effects can be dire -- we consume all of the PCBs the animals we eat have stored in their body fat, and that adds up.
In humans, PCBs have been linked to all kinds of ailments. Increased risk of cancer is the largest concern, but studies have suggested that PCBs can cause developmental and behavioral problems as well.
And researchers worry that the effects of climate change and industrial pollution may be magnifying each other: Climate change leads to food scarcity, which makes polar bears skinnier. And if they've got less body mass, then smaller doses of environmental pollutants will be enough to cut off their reproductive chances.