Mercury and selenium status of bottlenose dolphins (Tursiops truncatus): A study in stranded animals on the Canary Islands

The mercury (Hg) level in the marine environment has tripled in recent decades, becoming a great concern because of its high toxic potential. This study reports Hg and selenium (Se) status, and the first Se/Hg molar ratio assessment in bottlenose dolphins (Tursiops truncatus) inhabiting the waters of the Canary Islands. Total Hg and Se concentrations were determined in the blubber and liver collected from 30 specimens stranded along the coasts of the archipelago from 1997 to 2013. The median values for total Hg in the blubber and liver were 80.83 and 223.77μgg-1 dry weight (dw), and the median levels for Se in both tissues were 7.29 and 68.63μgg-1dw, respectively. Hg concentrations in the liver were lower than 100μgg-1 wet weight (ww), comparable to those obtained in bottlenose dolphins from the North Sea, the Western Atlantic Ocean and several locations in the Pacific Ocean. The Mediterranean Sea and South of Australia are the most contaminated areas for both elements in this cetacean species. In addition, it must be stressed that the levels of Hg and Se in the liver showed an increasing trend with the age of the animals. As expected, a strong positive correlation between Hg and Se was observed (rs=0.960). Surprisingly, both younger and older specimens had a Se/Hg molar ratio different from 1, suggesting that these individuals may be at greater toxicological risk for high concentrations of both elements or a deficiency of Se without a protective action against Hg toxicity.