Mercury and its relation with selenium in the liver of Dallʹs porpoises (Phocoenoides dalli) off the Sanriku coast of Japan

Liver samples of 22 Dallʹs porpoises (Phocoenoides dalli) collected off the Sanriku coast of Japan were analyzed for investigation on bioaccumulation of total mercury (ΣHg), organic mercury (OrgHg), inorganic mercury (InHg) and selenium (Se). In the liver, detoxification of Hg was evident by transformation of OrgHg. Se showed different Hg detoxification patterns in the liver with a threshold range of hepatic ΣHg concentration of about 20–30 μg/g dry weight. The molar ratios of Se/InHg or Se/ΣHg were obviously higher than 1 when hepatic ΣHg levels were less than the range, while both ratios were close to 1 when ΣHg levels were higher than the threshold, suggesting a mechanism by detoxification of OrgHg into less toxic mercuric selenide (HgSe) forms in the latter.