New report reveals toxic legacy of banned chemicals on marine populations

The team studied more than 800 of the small cetaceans and found that although toxicity was declining it was still present.

The new paper by Rosie Williams from Brunel University and the Zoological Society of London on the toxic legacy of PCBS was co-authored by members of the Scottish Marine Animal Strandings Scheme, including Dr Andrew Brownlow and Nick Davison.

“Polychlorinated biphenyls (PCBs) are toxic, persistent, and lipophilic chemical compounds that accumulate to high levels in harbour porpoises and other cetaceans,” said the report in Environmental, Science and Technology.

“It is important to monitor PCBs in wildlife, particularly in highly exposed populations to understand if concentrations are declining and how levels relate to toxicological thresholds and indices of health like infectious disease mortality.

“Here we show, using generalised additive models and tissue samples of 814 UK -stranded harbour porpoises collected between 1990 and 2017, that mean blubber PCB concentrations have fallen below the proposed thresholds for toxic effects.

“However, we found they are still associated with increased rates of infectious disease mortality such that an increase in PCB blubber concentrations of 1 mg kg-1 lipid corresponds with a 5% increase in risk of infectious disease mortality.

“Moreover, rates of decline and levels varied geographically, and the overall rate of decline is slow in comparison to other pollutants. We believe this is evidence of long-term preservation in the population and continued environmental contamination from diffuse sources.

“Our findings have serious implications for the management of PCB contamination in the UK and reinforce the need to prevent PCBs entering the marine environment to ensure that levels continue to decline.”

In 2017, it was revealed that one of the UK’s last killer whales was contaminated with “shocking” levels of a toxic chemical.

The animal, called Lulu, was found dead on the Isle of Tiree in Scotland in 2016 after becoming entangled in fishing lines.Tests revealed her body contained among the highest levels of PCBs ever recorded.

The chemicals – used as coolant fluids – were banned in the 1970s but are still in the environment.

Researchers fear that other animals in Lulu’s pod also have similarly high levels of contamination. The group, which is found off the west coast of Scotland, is thought to consist of just eight animals.

Scientists have not seen any calves born in over 25 years that they have been studying these animals, and it looks almost certain that they will eventually vanish.

Dr Brownlow, head of the Scottish Marine Animal Stranding Scheme and veterinary pathologist at Scotland’s Rural College (SRUC), said: “The levels of PCB contamination in Lulu were incredibly high, surprisingly so. They were 20 times higher than the safe level that we would expect for cetaceans to be able to manage.

“That puts her as one of the most contaminated animals on the planet in terms of PCB burden, and does raise serious questions for the long-term survivability of this group (of UK killer whales).”

PCBs were used widely in industry during the last century.

The manmade chemicals are extremely stable, resistant to extreme temperatures and pressures, and have insulating properties. Because of this they were used in everything from plastics to paints and electrical equipment.

But after concerns about the toxicity to humans and animals was raised, a series of bans were put in place around the world from the 1970s onwards.

However the chemicals take a long time to break down and have lingered in the environment, particularly in landfill sites where they can leach into waterways and on into the sea.

They then build up in the marine food chain, which means top predators such as killer whales are particularly affected. Dolphins, porpoises are also susceptible.