Persistent pollutants exceed toxic thresholds in a freshwater top predator decades after legislative control

Declining emissions of persistent organic pollutants (POPs), subject to international control under the Stockholm convention, are not consistently reflected in biotic samples. To assess spatial and temporal variation in organochlorine pesticides and PCBs in UK freshwaters, we analysed tissues of a sentinel predator, the Eurasian otter, Lutra lutra between 1992 and 2009. Past declines in otter populations have been linked to POPs and it is unclear whether otter recovery is hampered in any areas by their persistence. PCBs, DDT (and derivatives), dieldrin and HCB were detected in over 80% of 755 otter livers sampled. Concentrations of Sigma PCB, Sigma DDT and dieldrin in otter livers declined across the UK, but there was no significant time trend for Sigma PCB-TEQ (WHO toxic equivalency, Van den Berg et al., 2006) or HCB. In general, higher concentrations were found in the midlands and eastern regions, and lowest concentrations in western regions. Concentrations of PCBs and HCB in otters increased near the coast, potentially reflecting higher pollutant levels in estuarine systems. Decades after legislative controls, concentrations of these legacy pollutants still pose a risk to otters and other freshwater predators, with spatially widespread exceedance of thresholds above which reproduction or survival has been reduced in related species. (C) 2020 Published by Elsevier Ltd.

Automated summary

The study found that organochlorine pesticides and PCBs are still prevalent in Eurasian otters in UK freshwaters, despite a decline in concentrations over the years. Higher concentrations of pollutants were found in the Midlands and Eastern regions, as well as near the coast, which may pose a risk to otters and other freshwater predators. Despite legislative controls, these legacy pollutants continue to impact otters and exceed thresholds for reproduction and survival in related species.