Striped dolphin detoxificates mercury as insoluble Hg(S, Se) in the liver

Sea mammals are known to contain high concentrations of mercury and selenium especially in the liver with no apparent symptoms of poisoning. We examined the chemical form of mercury and selenium in the liver of striped dolphin, Stenella coeruleoalba. Neither mercury not, selenium could be extracted with acetone, 80% ethanol or 0.2 M ammonium acetate. The residue after extraction was digested most effectively with alkaline protease, resulting in solubilization of almost all the material (99% by weight) but still leaving a small amount of insoluble material (1%), which contained 80% of mercury and 66% of selenium of the original amount. This insoluble material was subjected to transmission electron microscopic analysis, X-ray microanalysis, X-ray diffraction analysis and elemental analysis, which revealed that the material contained spherical crystals of Hg(S-0.34, Se-0.66) with 5-10 nm in diameter as a major component. These crystals may be the final detoxification product of mercury.