Toxic banned chemicals exceed safe thresholds in UK orcas

Published: 30 November 2023

Levels of banned chemicals in UK-stranded orcas are 30 times over the toxic threshold, uncovers new research.

Levels of banned chemicals in UK-stranded orcas are 30 times over the toxic threshold, uncovers new research. The finding is just one alarming discovery from the investigation into the scale at which chemical pollution threatens the future of marine mammals.   

A dolphin in the sea

This first-of-its-kind study, which was led by ZSL (the Zoological Society of London) in collaboration with researchers at the University of Glasgow and others, reveals that levels of six chemical pollutants remain at highly toxic levels within UK marine mammals – exceeding the safe limits in half of animals investigated – more than two decades after the use of many of them was restricted or banned.   

Collected over 30 years, the data behind the shocking findings comes from one of the world’s largest marine mammal toxicology datasets, created by partners across the UK - including the Centre for Environment, Fisheries and Aquaculture Science (Cefas) and ZSL’s Cetacean Stranding Investigation Programme (CSIP), a Defra-funded programme which investigates strandings of marine mammals, marine turtles and sharks around the English and Welsh coast to understand the threats they face.  

By analysing post-mortem records and associated tissue samples from over 1000 animals spanning 11 species of whales, dolphins and seals stranded in the UK, the research uncovered how concentrations of these dangerous chemicals were highest in long-lived species at the top of the food chain - orcas, bottlenose dolphins and white-beaked dolphins. The scientists behind the research call for urgent action to protect marine wildlife from the lethal impacts of chemical pollution. 

The team identified that in recent years, the average concentrations of banned toxic chemicals known as polychlorinated biphenyls (PCBs) in orcas were thirty times the amount at which marine mammals would start to face negative health effects. Once used widely - including in paints, adhesives and motor oil - PCB’s were internationally banned in 2004. However, the report highlights how many of these chemicals continue to impact the natural world.

The work looks at UK-wide contaminant data based on stranded marine animals, including in Scotland where marine mammals have some of the highest levels of these industrial pollutants seen globally.  

Dr Andrew Brownlow, co-author from the University of Glasgow, said: “Despite production of these pollutants being banned decades ago, and indication that levels are decreasing over time, several species of marine mammals in UK waters have some of the  highest pollution burdens seen globally. Nearly half of the cases examined over the most recent five years (88/184) had concentrations exceeding known toxic thresholds and therefore likely suffered impacts to their health and reproductive fitness. These pollutants pose an ongoing, critical threat to biodiversity and planetary ocean health, and, despite bans on production and guidelines for containment and disposal, this work shows that strategies aiming to control and mitigate the release of these pollutants into the marine environment are still highly inadequate. 

The research was made possible by lab analysis from Cefas, along with partners from Brunel University London, The University of Glasgow/Scottish Marine Animal Strandings Scheme, the Natural History Museum, Cornwall Wildlife Trust, Cornwall Marine Pathology Team, Marine Environmental Monitoring and Galway-Mayo Institute of Technology. 

Dr Rosie Williams, lead author and postdoctoral researcher at ZSL’s Institute of Zoology explained: “It’s been over 20 years since several of these chemicals were banned globally, yet we still see concerningly high concentrations in wildlife. Chemical pollutants such as PCB’s pose one of the biggest threats to marine mammal health. Although concentrations of the pollutants appear to be declining, our findings reveal that, in many species, they are still present at levels associated with negative effects on the immune and reproductive systems.”  

The research identified that in the most recent five years of the study (2014-2018), almost half of the animals studied had pollutant levels exceeding toxic thresholds. In bottlenose dolphins, the concentrations of polybrominated diphenyl ethers (PBDEs) – a chemical used as a flame retardant in several products including electronics and soft furnishings– was on average 200 per cent above the threshold for the onset of negative health effects. Like PCBs, PBDEs are known to weaken the immune system, increasing disease susceptibility.  

Rosie explained why pollutant levels are so high: “These toxins are initially taken up by plankton at the bottom of the food chain. Unable to be broken down or excreted, these persistent chemicals increase in concentration the further up the food chain they go, in a process known as ‘biomagnification’. As apex predators, many marine mammal species consume large amounts of toxins every time they feed, making them some of the most contaminated wildlife species.”  

The study identified the rates of decline of most pollutants has slowed – indicating that concentrations are approaching a constant level and raising concern about the potential for ongoing pollution. The situation threatens to worsen further with climate change, as around 10,000 landfills in Europe are situated on coasts at risk of climate change, sea-level rise, flooding or erosion with the potential to release their contaminant load directly to the marine environment. 

The scientists behind the alarming discovery are calling for urgent action to protect the marine environment from both historic and emerging pollutants - by improving current pollution control measures and encouraging governments to take a more proactive approach to regulation – such as phasing out all non-essential use of hazardous chemicals and preventing one harmful chemical from being replaced by a closely-related and equally damaging substitution.  

Rosie added: “This isn’t just a UK problem and chemical pollution is just one of multiple threats facing marine ecosystems worldwide. We are putting our ocean under an ever-increasing amount of stress as climate change, overfishing and plastic pollution all continue to worsen. As our understanding of these interconnected issues grows, world decision makers must act now to protect our oceans from further harm.” 

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First published: 30 November 2023