Levels of toxic chemicals found in the blubber of seal pups from the North Sea have shown little or no change in 15 years - despite an international ban.
New research led by Abertay University, in partnership with the University of St Andrews Sea Mammal Research Unit and the University of Liege in Belgium, has revealed persistent organic pollutants (POPs) are falling very slowly in Scottish waters, despite the UK and many other countries not using or producing them for decades.
POPs include PCBs - which were widely used as stabilisers in paints, sealants and in electrical transformers - as well as the pesticide, DDT.
Known as legacy pollutants, POPs are no longer manufactured or used but don’t break down easily in the environment and are toxic to humans and wildlife.
They reach the sea through incineration, water run-off or careless disposal in landfill, and are able to travel a long way from where they were released because they are so stable.
Mother seals ingest POPs through the fish they eat, and the contaminants are then passed on to their pups through milk.
The study compared POP levels present in Scottish grey seal pups today to concentrations measured in 2002.
It showed that while some POPs, including many of the PCBs, had fallen by around a quarter during that time, other pollutants, like DDT and its breakdown products, had not changed.
Dr Kimberley Bennett, who led the project and is a lecturer in Biomedical and Environmental Science at Abertay, said: “Environmental POPs fell dramatically in the environment immediately following the 2001 Stockholm Convention ban, but our research shows that this fall has slowed dramatically in recent years.
“In previous studies we’ve already shown that even low POP concentrations can alter fat tissue function in seal pups, and it now seems likely that these negative biological effects will continue well into the future.
“We need additional measures to clean up POPs that go beyond the ban, but because they are effectively locked into the food chain, that’s going to be very difficult to achieve.”
The Stockholm Convention is a UN treaty which was brought forward with the aim of “eliminating or restricting” the production and use of POPs.
Despite being exposed to these toxic chemicals, grey seal numbers in the North Sea have not been affected.
The new research appears in a Special Issue of Aquatic Conservation: Marine and Freshwater Ecosystems.
To read the full study visit: https://onlinelibrary.wiley.com/doi/10.1002/aqc.3137