[ad_1]
Most people thought that the problem of polychlorinated biphenyls – known as PCBs – had been solved. Some countries started to ban toxic chemicals in the 1970s and 1980s, and global production ended with the 2001 Stockholm Convention.
But a new study based on modeling shows that they are found in the fat of killer whales – and that they could end up destroying half of the world's population of killer whales in the coming decades.
"It's certainly alarming," said Jean-Pierre Desforges, a post-doctoral researcher at the University of Aarhus in Denmark and senior author of the new study published Thursday in the journal Science.
Whales are at the top of their food chain. Chemicals such as PCBs are absorbed by the plankton at the base of the food chain, then eaten by herring and other small fish, which are themselves eaten by larger fish, and so on. At each stage of this chain, PCBs are becoming more and more concentrated. The killer whales most at risk are those who eat seals and other animals that are themselves high enough in the food chain and are highly contaminated, said Dr. Desforges.
The study reveals that killer whale populations in Alaska, Norway, Antarctica and the Arctic, among others, where chemical levels are lower, will likely continue to grow and thrive. . But animals living in more industrialized areas, off the coasts of the United Kingdom, Brazil, Hawaii and Japan, and in the Strait of Gibraltar are likely to collapse because of PCBs alone , not counting the other threats.
Dave Duffus, who heads the whale research laboratory at the University of Victoria in Canada and did not participate in the new research, said his findings were "shocking, but I have no doubt".
Whales close to him in the Pacific Northwest are surrounded by contaminants, are undergoing changes in their diet and are continuously bombarded with noise. "You can see the downward trend of their population, "said Dr. Duffus.
[[[[Like the Science Times page on Facebook. | Register for the Science Times Bulletin.]
The researchers used fat samples to estimate the amount of PCB contamination in killer whales around the world. They have also developed a model for predicting the amount of PCBs transmitted to calves by placenta and breast milk, as well as prey consumption. The researchers then compared these concentrations to the known damages that can come from different amounts of PCBs.
According to their calculations, about half of the world's killer whale populations will stop growing and then decline in the decades to come. Dr. Desforges said he was not sure how long it would take for these populations to collapse, but his team estimated the impact of contamination over a century – and the clock began almost 40 years ago. he said. Exposures to PCBs have decreased with bans, but levels have stopped falling in long-lived marine predators such as killer whales, he added. According to Dr. Desforges, whales metabolize PCBs very slowly over a lifetime of 50 to 80 years.
PCBs remain the largest chemical contaminant in whale fat and are known to disrupt the reproductive, endocrine, thyroid and immune systems of whales, harm their brains and trigger cancer. Other chemicals are also present, but in lower concentrations and with much less knowledge about their potential hazards, he said.
"We're looking at one contaminant, and that's one of many risk factors," said Dr. Desforges.
Despite the depressing results, Dr. Desforges said that he remained optimistic about the future of killer whales.
"It's not a story without a way out. Much remains to be done about this, "said Dr. Desforges. Many countries are not meeting their commitments to dispose of old PCB-contaminated equipment by 2028, he said.
He said he hoped policymakers would do more to protect them, the study helping to convince them, as well as the substantial appeal that the Orcas have had with the public.
"If the killer whales can not do it in the water, like the pandas on the land sites, I do not know who will do it," he said.
Source link
