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Banned Chemical Pollutant Threatens World's Killer Whale Populations

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It has been over 40 years since Polychlorinated Biphenyls (PCBs) were banned, but their harmful effects persist to this day. In fact, researchers of a new study find that the chemical pollutants may be slowly wiping out the killer whale population of the world, possibly wiping half of them out in heavily contaminated areas.

PCB Pollution Persists

Beginning in the 1930s, companies manufactured and mass produced over a million tons of PCBs to be used in various industrial and commercial purposes, the United States being a major user and producer. However, scientists linked the chemicals to cancer as well as health problems in the immune, endocrine, and reproductive systems in both animals and humans and eventually led to their banning in the United States in 1978 and worldwide in 2004. Unfortunately, these chemical pollutants do not break down easily, and they continue to persist even over 40 years after the initial banning.

Researchers of a new study published in the journal Science found that PCBs continue to threaten animal populations, particularly killer whales that are slowly being “wiped out” by the chemicals. In fact, they found that 10 out of the 19 killer whale populations they studied were already rapidly declining. Further, year-by-year models predicted that over half of the 19 populations studied will decline because of PCBs in the coming 30 to 50 years.

Disturbingly, researchers recorded PCB levels as high as 1,300 milligrams per kilo in the blubber of killer whales, when previous studies have shown signs of infertility and immune system impacts at 50 milligrams per kilo. The most threatened populations of killer whales are those in the heavily contaminated areas such as Brazil and the Strait of Gibraltar.

Predators’ Contamination

Killer whale diets include seals and big fish such as tuna. These animals are also contaminated with PCBs and accumulate the chemical pollutant as they move along the food chain. By the time that the food gets to the killer whales, they get to consume food with high levels of contamination. For comparison, the killer whales that tend to eat smaller fish such as mackerel face lower risks.

Other top predators are affected by PCBs as well. Sharks, seals, and even polar bears were found to have dangerously high levels of PCBs, and in fact, sea lions presented tumors and increased disease. Even the polar bears that are typically better than killer whales at expelling PCB in the food that they consume were found to have heavy exposures, particularly among those that consume hooded seals with higher PCB concentrations compared to ring seals.

“This suggests that the efforts have not been effective enough to avoid the accumulation of PCBs in high trophic level species that live as long as the killer whale does. There is therefore an urgent need for further initiatives than those under the Stockholm Convention,” said Paul D. Jepson of the Institute of Zoology, Zoological Society of London, England, killer whale expert and study co-author.

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