The effects of banned chemicals on harbour porpoises in British waters are starting to become clearer, thanks to the Cetacean Strandings Investigation Programme (CSIP). The initiative has discovered that porpoises ingest so many of these chemicals that it makes the females’ milk toxic to their young.
Researchers from the Zoological Society of London (ZSL) and Brunel University London publish their latest findings in the Science of The Total Environment journal. By analysing post-mortem samples gathered from nearly 700 stranded porpoises between 1992 and 2015, the study has revealed that polychlorinated biphenyls (PCBs) linger and accumulate in the bodies of marine mammals, with some of the 209 variants more toxic than others.
“Our study has highlighted the need to change our approach to monitoring PCBs – to look at the composition of individual chemicals – so that we can get a better understanding of the risk posed by these chemicals to our marine wildlife,” says Rosie Williams, lead author and PhD Researcher at ZSL’s Institute of Zoology and Brunel University London.
A toxic legacy
PCBs are a group of over 200 toxic chemicals which were once commonly used as fluids in electrical equipment, surface coatings and paints. Despite being largely banned in the UK since 1981, these contaminants are an ongoing problem.
The latest UN Environmental Program assessment estimated that 14 million tonnes of PCB contaminated equipment and material still needs to be destroyed globally. These chemicals persist in soils and continue to be washed into rivers and seas where they pose a deadly threat to marine mammals.
The team’s most important finding was that harbour porpoise calves carry a more toxic cocktail of PCBs than their parents – transferred into their bodies from their mothers’ milk. Such dangerous levels prevent calves’ brains from developing normally.
“Juvenile porpoises are being exposed to a toxic cocktail of chemicals during feeding – when all they’re supposed to be getting are the vital nutrients they need for the crucial developmental stage of their life,” explains Williams.
By finding out more about PCB exposure in young animals, the team hope their research will, in the future, help protect marine life from the impact of these dangerous chemicals.
While porpoises remain abundant, other species, such as orcas, are at much higher risk of extinction in UK waters with only one pod of eight individuals still living off Scotland’s west coast. These whales accumulate the highest levels of PCBs due to their position at the top of the food chain. This new research could help predict how they are affected by such pollution.
The pollution fightback
First established almost two decades ago, scientists involved in the CSIP are continuing to monitor exposure to PCBs and other chemical pollutants by conducting post-mortems on animals washed up on British beaches.
“We’re using this data to determine the risk of chemical contamination to our cetaceans by investigating health effects such as immunosuppression and reproductive impairment,” says Williams.
“I think more action could be taken to identify the main sources of continuing PCB contamination so that action can be taken to prevent further contamination of the environment,” says Williams. “Despite this, environmental levels in many areas have decreased over time, so if PCBs continue to be eliminated, we expect this decrease to continue.”
Juvenile harbor porpoises in the UK are exposed to a more neurotoxic mixture of polychlorinated biphenyls than adults. Rosie S.Williams et al, Science of The Total Environment, Volume 708, 15 March 2020, 134835, https://doi.org/10.1016/j.scitotenv.2019.134835.
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