The death of killer whales was feared due to chemicals banned in the 70s

An alarming study found that a group of industrial chemicals that humans began to ban several decades ago could cause the collapse of many global populations of orca whales in the next century.

Polychlorinated biphenyls, better known as PCBs, are synthetic compounds used once for a range of applications ranging from electrical appliances to household paints. They were widely banned in the 70s and 80s after significant contamination of humans and the environment. Research has since linked chemicals to endocrine and immune system disruption and reproductive failure in vertebrates – a legacy that continues to spread in the biosphere through the longevity of PCBs and their ability to accumulate the food chain.

This is nowhere more evident than in orcas, predators of the apex, which unfortunately have a tendency to accumulate industrial pollutants in their fat. Levels of PCBs greater than 50 milligrams per kilogram of tissue are a health problem for marine mammals, but in some killer populations, hundreds are more common. Whale mothers transmit chemicals to their babies in the placenta and in their milk, transferring the toxic inheritance from generation to generation. Despite all this, no one had systematically studied what PCBs could mean for the future of orcas.

The new study, published Thursday in Science, does exactly that and the results are not good: of the 19 populations examined, 10 appear to have a "high risk of collapse" over the next 100 years due to exposure to PCBs alone.

"It was really shocking for all of us," Earther told the senior author of the study, Jean-Pierre Desforges, a biologist at Aarhus University.

To arrive at a depressing conclusion, Desforges and his colleagues have established a global database of PCB concentrations in orca whale fat and have used previous studies a lack of data from orcas). All this has been introduced into the models to examine the accumulation and loss of PCBs in 19 populations over the next 100 years and to project trends at the population level.

Unsurprisingly, orcas living near highly industrialized areas where PCBs have been leached into soils and watercourses have tended to be the most contaminated and to have worse prospects for the future. However, diet also plays an important role, as shown by the fact that whale populations that eat mainly marine mammals tend to have a much higher exposure to PCBs than neighboring populations who prefer a diet based on of fish.

Five populations – the Bigg whales of the Northeast Pacific, the killer whales of the Strait of Gibraltar and those of Japan, Brazil and the United Kingdom – tend to[ed] to a complete collapse "in the models of the researchers. Five other groups are also expected to decline over the next century thanks to PCBs, not to mention other stressors, from noise pollution to overfishing.

Marine ecologist Olivia Lee, of the University of Alaska at Fairbanks, said the study's models offered "a disturbing case of potential disaster for orcas in a world of persistent PCBs." She pointed out, however, that the authors chose to maintain the effect of PCBs on calves in the same way from one generation to the next, which "really contributed to the decline in population trends. ".

"I do not think it's a bad approach, but it leaves no scenario for adaptation in the 100-year simulation," Lee said.

Desforges also said that the change in prey, which can occur when a food source becomes more or less abundant, could alter whale's exposure in the future. If the rapid warming of the Arctic leads to more whales heading north, for example, this could affect their diet with untold impacts on PCB exposure.

Nothing is frozen, but the results highlight the need to rid the world of these chemicals. The Stockholm Convention, an international treaty to reduce and eliminate persistent organic pollutants such as PCBs, entered into force in 2004. But the treaty does not oblige countries to stop using equipment. containing PCBs until 2025, and the old PCBs have not yet been destroyed by incineration, garbage ovens or one of the many chemical decontamination methods. The widespread use of these chemicals in paints and sealants in the 1950s and 1960s means that many old buildings also remain contaminated.

"In reality, countries are not really getting rid of equipment as quickly as they should be," Desforges said. "We are trying to make sure that people understand that this crisis is not over."