Banned chemicals ‘reducing weight of porpoise’ testes’ and could affect human fertility too, study warns

Male porpoises living around the UK coast may be experiencing significant fertility reductions due to the presence of banned industrial chemicals, new research indicates.

Use of toxic polychlorinated byphenyls (PCBs) was made illegal in the UK in the 1980s, but their widespread use means they are still entering waters where they can build up in whales, dolphins and porpoises, and are known to affect population rates.

Scientists examining their presence in cetaceans have found they can have a “substantial impact on the reproductive health” of species including porpoises.

While previous studies have focussed on the reproductive impacts on female porpoises, the new research examines male reproductive biology.

The research team, which was made up of the Cetacean Strandings Investigations Programme (coordinated by ZSL), Brunel University, the Centre for Environment, Fisheries and Aquaculture Science, the University of Exeter and the Scottish Marine Animal Stranding Scheme, found that PCBs are associated with reduced testes weights in otherwise healthy porpoises.

“The population studied have pregnancy rates that are less than half of those observed in other less contaminated populations and we believe the impacts of PCB exposure on male fertility offer a partial explanation as to why rates in this population are so low,” the researchers said.

They said the confirmation of the role of PCBs had grave implications for other species which live or spend time in UK waters.

“The findings are particularly important in the context of other cetacean species, such as killer whales,” the authors said.

Killer whales “accumulate the highest concentrations of PCBs and therefore, face the greatest threat. The impacts of PCB exposure in killer whales are compounded by their low birth rates.”

“Consequently, several populations that live close to industrialised areas face an immediate threat from exposure to PCBs.”

In 2016, a killer whale named Lulu was found dead after becoming entangled in netting, but a post-mortem revealed she was contaminated with “shocking levels of PCBs”, with one of the highest readings of any animal ever tested.

Killer whales, whose diet includes seals, tuna and sharks, exhibit the highest PCB concentrations and it is these populations that are at the highest risk of population collapse, while other populations which feed on smaller fish are at less risk.

However, the threat from PCBs doesn’t necessarily end when a whale dies, but can be passed down the generations as PCBs contaminate the whales’ milk which they feed to their young.

The new study is the first study to investigate the relationship between PCB burdens and testes weights in cetaceans. The authors said they “believe it represents a substantial advance in our understanding of the relationship between PCB exposures and male reproductive biology in cetaceans.”

They have called for further regulation on PCBs’ impact on the marine environment.

“The results suggest that more effective PCB controls could have a substantial impact on the reproductive health of coastal cetacean species and that management actions may need to be escalated to ensure adequate protection of the most vulnerable cetacean populations,” they said.

The scientists warned it was not only cetaceans which are at risk from the long-term damage caused by PCBs and humans are also at risk of contamination and subsequent reproductive issues.

“The results are in agreement with studies on other mammals that have shown that PCB exposure inhibits the male reproductive system. For example, human epidemiological studies have found negative associations between PCB exposure, sperm motility and circulating testosterone levels in men,” the authors said.

“There is a growing consensus that exposure to contaminants that disrupt hormonal systems may be partially responsible for the global decline in male fertility rates that has occurred over the last 50 years. Therefore, it is imperative that more is done to protect humans and our environment from exposure to these dangerous chemicals.”

The study follows alarming research from Germany which indicates porpoise populations in the North Sea have been declining in recent decades.

The study is published in the journal Environment International.