Polychlorinated biphenyls (PCBs) are man-made chlorinated hydrocarbons that were largely manufactured in the 1920s and later banned in the 1970s. These chemical compounds were popular prior to the cessation of their production due to their low flammability attributes and versatility in a variety of industrial and consumer products. Products that formerly included PCBs were electrical wires, paints, plastics, rubber products and others.
Despite being banned in the late 1970s, PCBs are a pervasive chemical compound found in aquatic and marine environments. PCBs reach these watery environments through pollution, particularly ocean plastic pollution. This industrial chemical compound and other chemicals, such as organochlorine (OC) pesticides adhere to plastics afloat in aquatic and marine environments. These chemicals adhere to and leach from plastic particles in the water through chemical processes brought about by heating via solar radiation.
The particles can enter watery ecosystems through the lowest levels of the food web beginning with zooplankton. The zooplankton is then consumed by fish, which are in turn eaten by larger predators including seabirds and cetaceans. The plastic and the chemicals that adhere to it remain in the animals and are subsequently passed up through different food webs.
As the plastic sits in the gut of an animal it begins to leach chemicals that are stored in the fats and tissues of the animal that consumed it. With each successive transfer of the chemical laden animal through the food web, the concentration levels of the chemicals amplify in what is known as bioaccumulation. Bioaccumulation of PCBs was the focus of a recent study published in the scientific journal Nature.
Researchers in the study examined tissue samples of both beached and living cetaceans to determine the levels of PCBs in their bodies. Toxic chemicals such as PCBs have been proven to cause immunosuppression and reduced reproduction in mammals, including humans. The study included 1,081 samples from four different species of cetaceans including killer whales (Orcinus orca) and three other species of dolphins.
concentration levels are so high that the killer whales in hot spot areas face extinction.
According to BBC News, the study found that European cetaceans have the highest known concentrations of PCBs in their tissues. The article referred to PCB “hot spots” where concentration levels are so high that the killer whales in hot spot areas face extinction. A possible explanation offered by the article for these hot spots was that Europe banned PCBs much later than most countries. The amount of PCBs previously created in Europe accounts for nearly 15 percent of the world’s total production.
Also reported by BBC News, was that the transfer of these toxic chemicals can be passed from mother to calf via milk. The article pointed to declines in killer whales and poor reproduction rates, stating that there are currently only eight killer whales west of Scotland. In addition to the Scotland declines, a pod of 36 killer whales studied in southern Europe from 1999 to 2011 had just five calves survive. With low birth and high mortality rates these pods are at risk for extinction.