Persistent organic pollutants: assessing the threat to cetaceans

Abstract

Persistent organic pollutants (POPs) are a group of chemical compounds that are toxic to humans and wildlife. They are persistent in the global environment, can be transported over large distances and have the ability to biomagnify and bioaccumulate. Their extensive use in the 20th century led to widespread environmental contamination, causing harm to many wildlife populations. Despite their ban and restriction under the 2001 Stockholm Convention, one of the most critical international agreements administered by the UN Environment, pervasive and widespread contamination of the environment still occurs. As long-lived apex predators, cetaceans are known to be particularly vulnerable to accumulating high body burdens of POPs. To assess the effectiveness of pollution mitigation strategies and ensure cetaceans are adequately protected it is vital to determine the impacts of exposure to POPs in cetaceans. This thesis uses the world’s largest marine mammal strandings toxicology database, collected from stranded cetaceans between 1990 and 2018, to demonstrate that despite their ban under the Stockholm Convention in 2001, POPs are still a significant threat to cetaceans that inhabit the waters of the United Kingdom. I have demonstrated that although levels of POPs are declining, several species are still exposed to concentrations that are deemed to be a toxicological threat. Further, rates of decline vary between taxa and regions, hence some populations are more vulnerable than others. I have also demonstrated that, of the contaminants investigated, polychlorinated biphenyls (PCBs) are present at the highest concentrations, declining at the slowest rate and appear to be the greatest threat to cetacean health. Using harbour porpoises as a model species, this thesis has demonstrated that PCBs are significantly associated with increased disease prevalence and reduced testes weights, which suggests that male fertility may be impacted by exposure to POPs. This could have serious implications on the long-term population viability of harbour porpoises and similar species that are exposed to higher concentrations of PCBs. I also found age and sex related differences in the PCB congener profiles that harbour porpoises are exposed to, which suggests juveniles may be at a higher risk of experiencing neurotoxic effects than adults. Taken together, I believe these findings demonstrate that improved international POP elimination, mitigation and compliance strategies are required alongside conservation and management plans to adequately protect cetaceans from the deleterious effects of POPs.