Forty years after they were banned, the threat from pollutants called PCBs, or polychlorinated biphenyl, are still painting a gloomy picture for the future of the orca population.
A Danish report in the journal Science found that PCBs could lead to the disappearance of half of the world’s orcas from the most heavily contaminated areas in the next 30 to 50 years.
“This class of chemical is, in my view, the No. 1 threat at the top of the food chain,” Peter Ross, vice-president of research at Ocean Wise Conservation, told Global News. “In this case, our study was able to show PCBs are not only a significant health threat to killer whales but a number of populations around the world.”
Overfishing and man-made noise may also affect the health of the southern resident in B.C. but PCBs particularly can have a dramatic effect on their reproduction and immune system.
“Two hundred times the level in the average Canadian and that is astounding. It is way above the threshold where the immune system won’t work as well as they are more susceptible to infections.”
The orcas’ diet includes, among other items, seals and large fish such as tuna and sharks, which accumulate PCBs and other pollutants stored at successive levels of the food chain. It is these populations of whales that have the highest PCB concentrations and it is these populations that are at the highest risk of population collapse.
“PCBs are likely to create a threat that will linger for the entire 21st century and in the case of some populations, could contribute to their extinction,” Ross said.
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Through the 1970s and 1980s, PCBs were banned in several countries and in 2004, through the Stockholm Convention, more than 90 countries have committed themselves to phase out and dispose of the large stocks of PCBs.
PCBs are only slowly decomposed in the environment. Moreover, PCBs are passed down from the mother orca to its offspring through the mother’s fat-rich milk, as reported in the study.
Marie Noel, a marine mammal toxicologist with the Ocean Wise Pollution Research program, did not work on the study but does look at contaminants in marine life.
“There are thousands of new chemicals coming on the market every year and getting into the ocean,” she said.
She said PCB is a very old chemical.
“It was heavily used after the Second World War. But those chemicals are so persistent, you still find them today in marine environments and even in the Arctic, you still find them,” Noel said.
“Now we have some of the highest PCB levels in marine mammals.”