The persistence of chemicals banned back in the 1980s alongside rising ocean temperatures are putting the UK’s population of short-beaked common dolphin under increased pressure from the spread of infectious diseases and, ultimately, the risk of death. 

These are the findings from new research – led by the Cetacean Strandings Investigation Programme (CSIP) at the Zoological Society of London and the Scottish Marine Animal Strandings Scheme at the University of Glasgow – into the effect that environment stressors (themselves, two of what is regarded as the triple planetary threat in pollution, biodiversity loss, and climate change) has on mammals in the marine environment.

Separately linking rising rates of infectious disease threatening biodiversity in marine ecosystems with both chemical pollutants found in the waters around the UK and the stress being suffered by marine life under rising ocean temperatures, the study is the first time the impact of such individual stressors have been analysed together, outside of their siloes.

The study – titled “Sea temperature and pollution are associated with infectious disease mortality in short-beaked common dolphins” – has been published this week in the scientific journal, Communications Biology.

 It details the findings of an epidemiological study of some 836 short-beaked dolphins stranded across UK coastlines over the 30 years between 1990 and 2020 as well as a subset of 153 dolphins used for toxicological analysis of blubber to assess the concentrations of the chemical polychlorinated biphenyls (PCBs) – a substance that was banned by the UK and Europe four decades back, in the mid 1980s.

Forty years on from that ban and the findings indicate that the fallout from the use of these chemicals is still being felt today. No more so than in the population of beak-nosed common dolphins making the coastal waters around the UK their home.

PCBs are, afterall, toxic. They also accumulate in the fatty tissues of marine mammals – like dolphins – to impair immune function and reproduction. While they were banned both in the UK and Europe in the mid-1980s, legacy chemicals continue to enter marine systems through runoff, inadequate disposal, dredging, and atmospheric fallout.

“What the study teaches us is that there’s still a huge amount of work to be done to make sure we’re protecting our environment from these chemicals,” said Dr Rosie Williams, a postdoctoral research assistant at the Institute of Zoology at the Zoological Society of London and lead author on the study.

According to Dr Williams, the study directs attention towards the lessons that still need to be learned today, and the haste with which they need to be addressed.

“Even now, we have lots of chemicals that show similar profiles in terms of toxicity, persistence, and the ability to transport – such as PFAS at the moment, but we haven’t yet banned them or regulated them properly. It’s crucial that we learn from the mistakes of the past to be more reactive of regulation in the chemical space.”

But chemicals are just one part of the problem. Increasing sea surface temperatures are now altering species distributions, disrupting food webs, and changing how pathogens move through marine systems. These warmer waters have, too, been associated with higher disease rates across multiple marine species. 

The results of the study showed a statistically significant association between both sea surface temperature and PCB concentration with infectious disease mortality. In fact, for each 1mg per kilogramme of lipid increase in PCB blubber concentration, risk of infectious disease mortality in the beak-nosed common dolphin population increased by 1.6%. 

Meanwhile, and just as shockingly, for each 1°C rise in sea surface temperature corresponded to a 14% increase in mortality risk.

“We have traditionally looked at these threats in isolation. We have a bunch of people looking at the impacts of bycatch, people looking at pollution, and people looking at climate change, but it’s really important to account for the interconnected nature of these threats,” said Dr Williams. 

“This study is the first time that we have tried to do this, and there is a lot more that can be done to bring data of other threats into the same conversation, so this study is really highlighting that we just can’t regulate and think about these things in isolation because they often have this synergy that we can see here.”

Armed with such findings, researchers at the Zoological Society of London are clear on the next steps they would like to see implemented – and that’s in the swift strengthening of regulations on the kind of chemicals – those with similar traits to the PCBs banned in the 1980s – currently used across all manner of consumer products.

“Countries like France have already agreed to ban the use of PFAs chemicals in non-essential products by 2026, but the UK is severely falling behind on making a move on this issue,” said Dr Williams. “We’ve been promised a new chemical strategy since 2020 and we’re yet to see it. We are falling behind, and we need to make sure this isn’t the case because these chemicals are so costly and damaging to clean up.

“When it comes to the climate piece, this study also illustrates just how little we know about what some of the impacts might be on some of these animals. It’s not intuitive that a sea temperature rise would have an adverse effect on a warm water species, so this highlights that we just need to know a lot more about the impact of climate change and until we do, minimize the impacts of it.”

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