Banned Pollutants Threaten Orca Population
A class of banned chemical pollutants known as polychlorinated biphenyls (PCBs) may end up wiping out over half of the world’s populations of killer whales in a few decades, according to a study recently published in the journal Science.
PCBs were used widely in a variety of commercial products before they were discovered to be highly toxic and carcinogenic. Production of PCBs was banned in the United States in 1978 and the 2001 Stockholm Convention ended production worldwide. However, they are still used in several parts of the world and are not due to be completely phased out until 2025.
According to Jean-Pierre Desforges, researcher at the Aarhus University in Denmark and coauthor of the published report, “there’s a good chance that anything built in the ’60s and ’70s contain PCBs, and if they’re improperly disposed in a landfill, those PCBs have a chance of entering the environment… once there, [PCBs] are extremely hard to get rid of.”
Once PCBs enter the ocean, they are consumed by marine organisms until they reach the top of the food chain, where marine mammals like orcas are located. The chemicals pose a unique risk because they are not readily metabolized, resulting in a build up of PCBs concentrated in the blubber of orcas as they consume more and more fish. The effects of PCB are intergenerational- passed from mother to offspring through milk.
Research has shown that PCBs are the highest chemical contaminant in the blubber of killer whales, causing damage to their reproductive system, immune system, brain function and endocrine system. PCBs are also a known carcinogen.
Based on the calculations made by Dr. Desforges and his colleagues, an estimated half of the killer whale populations in the world will stop expanding and subsequently shrink in the coming decades. According to the report, although much remains uncertain, the impact of contamination on these populations is estimated to take over a century. PCB exposure levels reached their peak 40 years ago, and while legislation has decreased PCB exposure, the levels of PCB in marine predators like orcas have stopped falling.
Steven Bursian, an environmental toxicologist at Michigan State University stated that “it’s sobering to be made aware of the potential long-term effects of chemicals that were introduced into the environment over 80 years ago… It’s a wake-up call that similar predictions could be made about several other species.”
Desforges also recognizes the severity of the study’s results, stating that "a group of chemicals we thought was no longer a threat is still present at concentrations that will continue to pose significant risk.” He added that the results are concerning in part because PCBs are only one of several dangers to the orca population, and not even the foremost one.