The Eurasian otter: an at risk species and indicator of chemical contamination of freshwaters

Student Spotlight - Emily O'Rourke

PhD Research at Cardiff University

Email: ORourkeEB@cardiff.ac.uk   Twitter: @otter_em

A History of Otters in Britain

Have you ever seen an otter in Britain? Unless you have sat on a riverbank at dawn or dusk with a lot of patience, or have had a very lucky encounter, the answer is probably no. These elusive top predators live a mostly solitary life in and near our waterways. Although, if you want to have that magical moment of seeing an otter in the wild, you do have a much better chance now than you did in the 1970s.

During the 1950s to 1970s Eurasian otters (Lutra lutra) went through a dramatic population decline across Britain and western Europe, due to the introduction of industrial chemicals called PCBs, and organochlorine pesticides called DDT and dieldrin. These chemicals reached the environment, got into wildlife, moved up through the food chain, and caused death and reproductive failure in top predators such as otters and birds of prey. The chemicals were banned in the 1970s, and the otters were given legal protection, and subsequently, otter populations have been recovering. The National Otter Surveys which have been undertaken five times in England, Wales and Scotland, between 1977 and 2010 have shown a clear increase in the occurrence of otter signs (mainly their ‘spraint’ - faecal deposits) and for a long time, otters have been hailed as a conservation success story. However, the most recent Otter Survey of Wales (2015-18) has revealed a down-turn in Welsh otter populations, with Wales-wide totals of 70% of sites showing signs of otter presence recently, compared with 90% in the 2009-10 survey (Kean and Chadwick, 2021). While this is not close to the 1977 low (when only 20% of sites had signs of otters), it is concerning. The decline is widespread across Wales, and potential reasons are complex - changing diet (e.g. Moorhouse-Gann et al., 2020), loss and fragmentation of habitat, road traffic collisions (e.g. Raymond et al., 2021) and pollution all potentially play a part. Further investigation is needed to identify the key causes. In response to these findings, a survey of England is being organised by the Mammal Society and Environment Agency, and there have been calls for surveys of Scotland and Northern Ireland.

My Research

I am undertaking my PhD with the Cardiff University Otter Project. The project is a national research and monitoring programme, which collects otters found dead in order to study environmental health and otter ecology. My research focuses on chemical pollution of otters and our waterways. Chemical use is essential for modern life, however, through manufacture, use and disposal these chemicals are inevitably entering our environment, and some have toxic effects on wildlife and humans. As top predators, otters are vulnerable to persistent, bioaccumulative and toxic (PBT) chemicals, therefore it is important to monitor chemicals in our wildlife so we know which chemicals are bioavailable (getting in) to wildlife, and can identify threats to wildlife health. But additionally, otters can act as effective ‘sentinels’ telling us what chemicals are present in the environment that may also be available to other species, including humans: the rivers where otters feed provide the water for our reservoirs. Due to dilution, chemicals in water samples are often at concentrations below the limit of detection (i.e. below a level that can be picked up by the analytical methods used). Due to bioaccumulation, concentrations in otters can be at a level which are detectable, and, due to otters being non-migratory, concentrations found in their bodies after death are reflective of the area where they lived and fed. Consequently, we can use otters to compare concentrations between different areas, and to make comparisons between years (e.g. Kean et al., 2021).

Excitingly, some of my research has recently been the focus of national media attention (e.g. in the BBC and i News). I have co-authored two papers focused on a large family of synthetic chemicals called per- and polyfluoroalkyl substances (PFASs). They provide excellent oil and water repelling properties and have been used in many products such as firefighting foam, food packaging, non-stick cookware, waterproof clothing, stain resistant products and paints. PFASs are often referred to as ‘forever chemicals’ due to their extreme environmental persistence, they can bioaccumulate (build up) in wildlife and humans, potentially having a range of toxic effects.

In the first paper (Androulakakis et al., 2021) which was part of a European project called LIFE Apex, PFAS concentrations in top predators from four countries (UK, Sweden, Netherlands and Germany) were quantified. Results showed Eurasian otters were more contaminated with PFASs than buzzards (Buteo buteo), which typically feed on terrestrial prey, and marine apex mammals (harbour seals [Phoca vitulina], and harbour porpoises [Phocoena phocoena]). Differences in top predator accumulation of PFASs between freshwater, terrestrial and marine systems are likely to reflect a complex suite of factors, including proximity to sources, differing food webs, and species specific differences in bioaccumulation and metabolism. Our research supports evidence that, due to the high solubility of PFASs, the predominant exposure pathway to the environment is via water, with freshwater wildlife having the highest concentrations due to their proximity to anthropogenic sources of the chemicals.

The second paper (O’Rourke et al., 2022) was my first as lead author, and forms a key part of my PhD thesis. In this study we analysed the livers of 50 otters from across England and Wales. All otters in the study had detectable concentrations of PFASs in their livers, with 80% of otters having 12 or more of the 15 compounds that we looked for. As has been seen in other studies on wildlife, perfluorooctane sulfonic acid (PFOS), a type of PFAS which was used extensively prior to being restricted under the Stockholm Convention in 2009, was detected at the highest concentrations. We analysed the data to determine associations between the PFAS concentrations in the otters and anthropogenic sources of PFASs. We found a significant negative correlation between perfluorooctanoic acid (PFOA, a type of PFAS) concentrations in otters and the location of a factory which used PFOA at the time of the study. Our results support evidence that industry is a key source of PFAS pollution, and the distance from the factory at which elevated PFOA was found, suggests air dispersal is an important pathway for PFOA contamination of the environment.

Results also suggest that wastewater is a key source of PFASs to the environment. Higher concentrations of PFASs were found in areas which had high load (i.e. more waste water, from domestic and other sources) entering wastewater treatment works and/or a high proportion of arable land. Wastewater treatment works are not equipped to breakdown PFASs so they pass through the process and are released to waterways in effluent. PFASs are also retained in the sewage sludge (solid waste) produced at treatment works, which is spread on arable land as a fertiliser. The PFASs can then leach from the land and enter waterways. Our research supports calls for an evaluation of the chemicals retained in sewage sludge in order to protect human health and the environment (e.g a recommendation by the House of Commons EAC, 2022), and calls for a class-based approach to regulating PFASs in order to reduce the introduction of PFASs to the environment (e.g. CHEM Trust, 2021).

Looking to Future Research

This study used otters which died between 2007 and 2009, a time point where legislation and usage of certain PFASs was changing. More recently, funding made available by the Environment Agency has enabled me to analyse samples from otters which have died since these changes occurred. I will be looking at how concentrations have changed over time, since usage of some compounds (e.g. PFOA and PFOS) was restricted, and other, replacement compounds have increased. I am also using the data to examine the magnification of PFASs through the food chain, using the Environment Agency’s water and fish data which are collected annually from monitoring sites. The Otter Project is providing samples for the ‘Managing exposure to chemicals’ target of the 25 Year Environment Plan (25-YEP; GOV.UK, 2021), thanks to funding from the Environment Agency to support the ongoing collection and post mortem of otter carcasses, and annual chemical analysis of otter liver samples. Data will feed into the H4 (exposure and adverse effects of chemicals on wildlife in the environment) indicator of the 25-YEP. Additionally, in collaboration with Natural Resources Wales I am examining time trends in some other industrial chemicals, PCBs and PBDEs, to look at the effect of legislation on environmental levels.

The condition of our rivers has received a lot of media attention recently, and globally, chemical pollution is said to have crossed a ‘planetary boundary’, a threshold beyond which there is a threat to Earth’s system processes (Persson et al., 2022). Government agencies have responded by providing funding for research and mitigation, and I hope our collaborations and the wider research around chemical contamination will help show the respective UK governments where further funding and policy action are needed.  

Acknowledgements

Thank you to my PhD funder, the Waterloo Foundation, and to my supervisors; Dr Liz Chadwick and Dr Frank Hailer of Cardiff University, Dr M Glόria Pereira of UK CEH, Graham Scholey of the Environment Agency and Dr Marc Naura of the River Restoration Centre. Thank you also to the funders (LIFE and Esmée Fairbairn Foundation) and co-authors of the published PFAS papers, and the Environment Agency and Natural Resources Wales for enabling further analysis. Our research at the Otter Project relies on the collection of otters found dead from across Britain, thank you to everyone who has supported the project by reporting, collecting and delivering otters to us, and to the many students and volunteers who have assisted in the running of the Otter Project since it began in 1994.  If you find a dead otter, please report it so it can be used in valuable research, information is on our website.

References

Androulakakis A, Alygizakis N, Gkotsis G, Nika M-C, Nikolopoulou V, Bizani E, Chadwick E, Cincinelli A, Claßen D, Danielsson S, Dekker RWRJ, Duke G, Glowacka N, Jansman HAH, Krone O, Martellini T, Movalli P, Persson S, Roos A, O’Rourke E, Siebert U, True G, van den Brink NW, Walker LA, Deaville R, Slobodnik J and Thomaidis NS (2021) Determination of 56 per- and polyfluoroalkyl substances in top predators and their prey from Northern Europe by LC-MS/MS. Chemosphere. 287(2). DOI: 10.1016/j.chemosphere.2021.131775

CHEM Trust (2021, May 13) UK NGOs outline 12 key asks for the UK chemicals strategy.  Available at: https://chemtrust.org/news/ngos-12-key-asks/ Date Accessed: 3/2/2022

GOV.UK (2021, October 22) Policy paper at a glance: summary of targets in our 25 year environment plan. Available at: https://www.gov.uk/government/publications/25-year-environment-plan/25-year-environment-plan-our-targets-at-a-glance Date accessed: 3/2/2022

House of Commons Environmental Audit Committee (EAC) (2022) Water quality in rivers. Report ordered by the House of Commons.

Kean EF, and Chadwick EA (2021) Otter Survey of Wales 2015-2018. NRW Report No: 519, NRW: https://cdn.cyfoethnaturiol.cymru/media/694539/osw-6th-report-final.pdf

Kean EF, Shore RF, Scholey G, Strachan R and Chadwick EA (2021) Persistent pollutants exceed toxic thresholds in a freshwater top predator decades after legislative control. Environmental Pollution. 272, DOI: 10.1016/j.envpol.2020.116415

Moorhouse-Gann RJ, Kean EF, Parry G, Valladares S, Chadwick EA (2020) Dietary complexity and hidden costs of prey switching in a generalist top predator. Ecology and Evolution. 10:6395–6408. DOI: 10.1002/ece3.6375

O'Rourke E, Hynes J, Losada S, Barber J, Pereira MG, Kean EF, Hailer F and Chadwick EA (2022) Anthropogenic drivers of variation in concentrations of perfluoroalkyl substances in otters (Lutra lutra) from England and Wales. Environmental Science and Technology. 56 (3): 1675–1687. DOI: https://doi.org/10.1021/acs.est.1c05410

Persson L, Carney Almroth BM, Collins CD, Cornell S, de Wit CA, Diamond ML, Fantke P, Hassellöv M, MacLeod M, Ryberg MW, Søgaard Jørgensen P, Villarrubia-Gómez P, Wang Z and Zwicky Hauschild M (2022) Outside the Safe Operating Space of the Planetary Boundary for Novel Entities. Environmental Science and Technology. 56 (3), 1510-1521. DOI: https://doi.org/10.1021/acs.est.1c04158 

Raymond S, Schwartz ALW, Thomas RJ, Chadwick E, Perkins SE (2021) Temporal patterns of wildlife roadkill in the UK. PLoS ONE. 16(10): e0258083. DOI: 10.1371/journal.pone.0258083