Baby porpoises in Britain are being poisoned by their mother’s milk which has high levels of pollutants.
The chemicals are particularly toxic during brain development and are transferred by female harbour porpoises to their young through their milk.
Baby harbour porpoises around the UK are carrying a more toxic cocktail of Polychlorinated biphenyla known as PCBs than their mothers, according to the new study.
Figures show 209 variants of PCBs, used as a coolant for electrics, have varied levels of persistence in marine mammals.
But the most persistent toxins remain in a mother’s body until they are transferred to infants during lactation.
In the mid 80s, PCBs were used in electrical equipment, surface coatings and paints before being banned across Europe due to their toxic effects on both people and wildlife.
However, they continue to enter the marine environment through terrestrial runoff, dredging and atmospheric transport, resulting in a complex mixture of the chemicals entering the food chain.
Lead study author Rosie Williams, from 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 researchers predict their effects in more vulnerable species such as the UK’s native population of killer whale 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, the researchers said.
Ms Williams added: “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, said further research is “vital” to protecting marine mammals in UK waters.
She 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.”
In the study, scientists used the world’s largest cetacean toxicology dataset generated by the Centre for Environment Fisheries and Aquaculture Science.
The data is from samples collected from UK stranded cetaceans, with a total of almost 700 harbour porpoises stranded in the UK between 1992 and 2015 identified for the study.
Findings were published in the Science of the Total Environment journal today (Tues).
The study was led by Cetacean Strandings Investigation Programme (CSIP) scientists from international conservation charity Zoological Society of London and Brunel University London.