Levels of toxic PCB chemicals found at 30 times ‘safe’ limits in stranded whales

Almost half of the whales and dolphins found in British waters in the past five years contained harmful levels of toxic chemicals that were banned decades ago. research has found.

Among killer whales stranded in Britain, levels of PCBs, a group of highly dangerous and persistent chemicals that do not easily break down, were 30 times the concentration at which the animals would begin to suffer health effects, researchers said.

Scientists described the findings as a “huge wake-up call” that should ring alarm bells not only for the future of marine mammal health, but also for human health.

Dr. Rosie Williams, lead author and researcher from the Zoological Society of London (ZSL) Institute of Zoology, said: “It’s been more than two decades since several of these chemicals were banned worldwide, yet we still see worryingly high levels in wildlife .

“Although concentrations of the pollutants appear to be declining, our findings show that in many species they are still present at levels associated with negative effects on the immune and reproductive systems.”

High PCB concentrations are a major cause of the decline of European cetacean populations, research shows. One paper from 2018 suggests that killer whales near industrialized areas are at risk of population collapse as a result.

For the latest report, scientists examined post-mortem data and tissue samples from 1,000 marine mammals, comprising 11 different species stranded in Britain, using data collected over 30 years through a partnership including ZSL’s Cetacean Strandings Investigation Programme, a partnership established by the government-funded project, and the Center for Environment, Fisheries and Aquaculture Sciences.

They discovered that concentrations of PCBs, once widely used, but banned worldwide in 2004 according to the Stockholm Convention, were highest in long-lived species at the top of the food chain: killer whales, bottlenose dolphins and white-beaked dolphins.

Researchers said they took into account the bias introduced by examining stranded animals, whose deaths may have been hastened by chemicals, by including a high percentage of deaths due to trauma, such as boat strikes or entanglement with fishing lines.

Orcas follow a trawler off the Shetland Islands, Scotland. Strandings can be made worse by high levels of PCBs in their bodies. Photo: Nature Photo Library/Alamy

The toxins, which are initially absorbed by plankton at the bottom of the food chain and cannot be broken down, increase in concentration as they move up the chain, a process known as “biomagnification,” Williams said.

In 2017, Lulu, a killer whale from Britain’s last pod, was found dead on Tiree in Scotland. It was discovered to contain one of the highest levels of toxic pollutants ever found in a marine mammal. Some scientists believed that the extreme levels of PCBs in her blubber, at 950 mg/kg (0.033 oz/2.2 lb) – more than 100 times the limit of 9 mg/kg considered safe – contributed to her infertility .

“This is a huge wake-up call,” said Williams, calling for urgent action to protect the marine environment from historic and emerging contaminants. “We depend on the same ecosystem for some of our own food – so these findings not only raise alarm bells for the future of marine life, but also point to a risk to human health.”

The NHS advises pregnant women, breastfeeding women, women trying to conceive and girls eat no more than two portions of oily fish per weekbecause chemical pollutants can build up and affect a baby’s future development in the womb.