Publication Abstract

Trace elements, particularly heavy metals like mercury, pose significant risks to marine ecosystems due to their toxic and bioaccumulative properties. Concentrations in some marine species show concerning temporal increases of some trace elements, yet spatiotemporal trends in UK marine mammals have not been comprehensively assessed for nearly two decades. Marine mammals serve as sentinel species for ocean health due to their long life span and high trophic level, which cause them to accumulate high levels of bioaccumulative pollutants. Monitoring trace elements, in highly exposed populations, is critical for assessing trends relevant to toxicological thresholds and indices of health, like infectious disease mortality. Using liver tissue samples of 739 UK-stranded harbour porpoises (Phocoena Phocoena) collected between 1990 and 2021, we show that concentrations of mercury and selenium have increased in contrast to declines in cadmium and lead. Spatial analyses revealed that mercury concentrations are highest at lower latitudes, while cadmium concentrations increase northward. We also demonstrate that Zn, Hg, Se and Cd are significantly associated with increased risk of infectious disease mortality. Our findings highlight the need for monitoring of trace elements in sentinel species to inform conservation efforts and evaluate the effectiveness of pollution mitigation policies such as the Minamata Convention on mercury. Increasing mercury levels, despite emission reductions, underscore the urgent need for improved regulatory measures to protect marine biodiversity and ecosystem health.

Rosie S. Williams, David J. Curnick, Andrew Baillie, Jonathan L. Barber*, James Barnett, Andrew Brownlow, Rob Deaville, Nicholas J. Davison, Mariel ten Doeschate, Rod Penrose, Matthew Perkins, Simon Spiro, Lee Warford*, Ruth Williams, Andrew A. Cunningham and Andrew C. Johnson.