News Release

Harbor porpoise calves exposed to neurotoxic PCBs in mothers' milk

New ZSL study reveals mothers detoxify themselves by passing on most neurotoxic PCBs through lactation

Peer-Reviewed Publication

Zoological Society of London

Harbour Porpoise at Seaford

image: This is a harbor porpoise at Seaford. view more 

Credit: Rob Deaville_CSIP-ZSL

Harbour porpoise calves around the UK are carrying a more neurotoxic cocktail of PCBs than their mothers, as females unknowingly detoxify themselves by transferring the chemicals while feeding their young, new research reveals today.

Published in the Science of the Total Environment today (Tuesday 3 December 2019) and led by Cetacean Strandings Investigation Programme (CSIP) scientists from international conservation charity ZSL (Zoological Society of London) and Brunel University London, the study shows that the 209 variants of PCBs have varied levels of persistence in marine mammals, with some types of the chemicals proving less toxic and more efficiently metabolised than others throughout an animal's lifetime.

Critically however, the most persistent toxins remain in a mother's body until they are transferred to infants during lactation - exposing their young to dangerous doses of the chemical pollutants, that are particularly toxic during brain development.

PCBs were once used in the likes of electrical equipment, surface coatings and paints back in the mid-1980s, before being banned across Europe due to their toxic effects on both people and wildlife. However, the group of persistent toxic chemicals continues to enter the marine environment through terrestrial run off, dredging and atmospheric transport, resulting in a complex mixture of the chemicals entering the food chain.

The highest levels are often found in odontocetes (toothed whales) that are high up in the food chain, where they can cause suppression of the immune and reproductive systems and have contributed to population declines of several species in some regions.

Rosie Williams, lead author and PhD Researcher at ZSL's Institute of Zoology and Brunel University London said: "It's a tragic irony that 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.

"Previously, scientists tended to monitor PCB concentrations by grouping them together and treating them as one chemical, but as we know, they're a group of chemicals with different toxicity levels so it was a bit like trying to measure how much caffeine someone's had - without knowing whether they drank three cans of red bull or three cups of tea. 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.

"Studying PCB exposure in more abundant species like porpoises, helps us to predict their effects in more vulnerable species already low in numbers; such as our native population of orcas in the UK that are facing extinction because of PCBs, with only eight remaining. As top predators, killer whales are exposed to some of the highest levels of PCBs, because there is an accumulative effect of PCBs as you go up the food chain.

"It's obvious that marine mammals are still experiencing the lingering impacts of PCBs, so identifying the sources and pathways they're entering our oceans is a vital next step to preventing further pollution."

Professor Susan Jobling, co-author at Brunel University London's, Institute of Environment, Health and Societies said: "This research helps further our understanding of these legacy industrial chemical pollutants and the effects that different levels of exposure, in complex mixtures, may have. Learning more about PCB exposure in juvenile animals is vital, so that we can try to mitigate the impact of these dangerous chemicals on populations and help protect the future status of marine mammals in UK waters."

The team of scientists used the world's largest cetacean toxicology dataset generated by the Centre for Environment Fisheries and Aquaculture Science from samples collected by the CSIP from UK stranded cetaceans, with a total of 696 harbour porpoises stranded in the UK between 1992 and 2015 identified for the study.


R. S. Williams, D. J. Curnick, J. L. Barber, A. Brownlow, N. J, Davidson, R. Deaville. M. Perkins, S. Jobling, P. D. Jepson (2019) Juvenile harbor porpoises in the UK are exposed to a more neurotoxic mixture of polychlorinated biphenyls than adults. Science of the Total Environment.

Notes to editors

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The study

The ZSL study also found that animals were exposed to a different cocktail of PCBs dependent on where they were found stranded - with higher amounts of persistent PCBs found in the areas they were historically produced, such as the West coast of England.

The differences found could be evidence of the transport of PCBs, via various process such as wind and precipitation, whereby PCBs are being transported from where they were traditionally produced, to areas with higher latitudes and lower concentrations. For example, there is a strong body of existing evidence to suggest that PCBs have reached the Arctic because of long range transport from industrialised Europe.

CSIP (Cetacean Strandings Investigation Programme)

The UK Cetacean Strandings Investigation Programme (CSIP) was established in 1990 to coordinate the investigation of all whales, dolphins and porpoises that strand around the UK coastline, in addition to any stranded marine turtles and basking sharks. Data collected by the CSIP feed into reporting and assessment of status, which influences policy decisions and conservation efforts. CSIP partner organisations are ZSL (Zoological Society of London), Scotland's Rural College, Inverness, the Natural History Museum, Marine Environmental Monitoring and Cornwall Wildlife Trust Marine Strandings Network/University of Exeter. The Programme is funded by Defra and the Devolved Governments of Scotland and Wales. The Joint Nature Conservation Committee act as contract managers on behalf of funders. For more information on the CSIP, please visit:

ZSL (Zoological Society of London)

Founded in 1826, ZSL (Zoological Society of London) is an international scientific, conservation and educational charity whose mission is to promote and achieve the worldwide conservation of animals and their habitats. Our mission is realised through our ground-breaking science, our active conservation projects in more than 50 countries and our two Zoos, ZSL London Zoo and ZSL Whipsnade Zoo. For more information visit

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