Atmospheric Hg is predominantly deposited in oceans, one of the major reservoirs of Hg on Earth 3. Mercury (Hg) is a toxic heavy metal that is globally distributed through the atmosphere, in which Hg has a residence time of up to 1 year 1, 2. These total Hg (THg) isotopic trends suggest changes in the Hg metabolism of the long-finned pilot whales, development of (a) detoxification mechanism(s) ( e.g., though the formation of HgSe particles), and Hg redistribution across the different organs. Interestingly, this trend in δ 202Hg is reversed for livers of adult whales (increasing δ 202Hg value), accompanied by a progressive decrease of δ 202Hg in muscle at older ages. Also changes in diet, with high MeHg intake in utero and during lactation, followed by increasing consumption of solid food contribute to this behavior. We suggest this is due to preferential demethylation of MeHg with the lighter Hg isotopes and transport of MeHg to less sensitive organs, such as the muscles. During the first period of life, Hg in the liver became isotopically lighter (δ 202Hg decreased) with a strongly decreasing methylmercury (MeHg) fraction.

Isotopic analysis revealed remarkable differences between juvenile and adult whales. Analysis of different tissues (liver, kidney, muscle) and biofluids (blood, milk) from a pod of stranded long-finned pilot whales ( Globicephala melas) showed accumulation of Hg as a function of age, with a significant decrease in the MeHg fraction. Whales accumulate mercury (Hg), but do not seem to show immediate evidence of toxic effects.

Spacechem postmortem