Abstract
Whales accumulate mercury (Hg), but do not seem to show immediate evidence of toxic effects. 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. Isotopic analysis revealed remarkable differences between juvenile and adult whales. During the first period of life, Hg in the liver became isotopically lighter (δ202Hg decreased) with a strongly decreasing methylmercury (MeHg) fraction. 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. Also changes in diet, with high MeHg intake in utero and during lactation, followed by increasing consumption of solid food contribute to this behavior. Interestingly, this trend in δ202Hg is reversed for livers of adult whales (increasing δ202Hg value), accompanied by a progressive decrease of δ202Hg in muscle at older ages. 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.
Highlights
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]
In vivo mass-independent isotope fractionation (MIF) is not observed for these processes, suggesting that the MIF signature of Hg – Δ199Hg, Δ201Hg and Δ199Hg/Δ201Hg – in aquatic animals is typically more useful for provenance determination of the accumulated Hg than the mass-dependent isotope fractionation (MDF) signature[36,38,39,40,41]
Based on the assumption that the Hg is mainly taken in by marine mammals from the diet[43], the relatively low MeHg fraction observed in liver and kidney suggests that the MeHg ingested is slowly demethylated in vivo and converted into inorganic Hg forms
Summary
On the 12th of September 2012, 31 long-finned pilot whales (Globicephala melas) stranded on a beach between Ansturther and Pittenween in Scotland, United Kingdom. Based on the assumption that the Hg is mainly taken in by marine mammals from the diet (including transport across the placenta before birth and via milk though lactating)[43], the relatively low MeHg fraction observed in liver and kidney suggests that the MeHg ingested is slowly demethylated in vivo and converted into inorganic Hg (iHg) forms. The THg concentration increases as a function of age, while the MeHg fraction decreases (Fig. 1) This suggests that the Hg metabolism changes over the lifespan of the whales, most likely inducing a higher extent of MeHg demethylation and/or a greater accumulation of iHg, e.g., under the form of less toxic HgSe particles[10,11]. Different tissues most likely result from in vivo demethylation of MeHg46, and the MDF of Hg accompanying this process (the lighter Hg isotopes are preferentially demethylated), resulting in higher δ202Hg values in the remaining MeHg fraction (muscle) and in lower δ202Hg values in the iHg produced (liver, kidney)[47]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
