Interspecific Variations in the Internal Mercury Isotope Dynamics of Antarctic Penguins: Implications for Biomonitoring

Abstract

Mercury (Hg) biomonitoring requires a precise understanding of the internal processes contributing to disparities between the Hg sources in the environment and the Hg measured in the biota. In this study, we investigated the use of Hg stable isotopes to trace Hg accumulation in Ad & eacute;lie and emperor penguin chicks from four breeding colonies in Antarctica. Interspecific variation of Delta Hg-199 in penguin chicks reflects the distinct foraging habitats and Hg exposures in adults. Chicks at breeding sites where adult penguins predominantly consumed mesopelagic prey showed relatively lower Delta Hg-199 values than chicks that were primarily fed epipelagic krill. Substantial delta Hg-202 variations in chick tissues were observed in both species (Ad & eacute;lie: -0.11 to 1.13 parts per thousand, emperor: -0.27 to 1.15 parts per thousand), whereas only emperor penguins exhibited the lowest delta Hg-202 in the liver and the highest in the feathers. Our results indicate that tissue-specific delta Hg-202 variations and their positive correlations with % MeHg resulted from MeHg demethylation in the liver and kidneys of emperor penguin chicks, whereas Ad & eacute;lie penguin chicks showed different internal responses depending on their exposure to dietary MeHg. This study highlights the importance of considering intra- and interspecific variations in adult foraging ecology and MeHg demethylation when selecting penguin chicks for Hg biomonitoring.