Selenium and Mercury in Pelagic Fish in the Central North Pacific Near Hawaii

Protective effects of selenium against mercury toxicity have been demonstrated in all animal models evaluated. As interactions between selenium and mercury and their molar ratios in seafood are essential factors in evaluating risks associated with dietary mercury exposure, considering mercury content alone is inadequate. In this study, the absolute and molar concentrations of mercury and selenium were determined in edible portions from 420 individual fish representing 15 species of pelagic fish collected from the central North Pacific Ocean near Hawaii. Selenium was in molar excess of mercury in almost all fish species evaluated. The rank order of mean Se/Hg molar ratios was striped marlin (17.6) > yellowfin tuna (14.1) > mahimahi (13.1) > skipjack tuna (12.8) > spearfish (11.4) > wahoo (10.8) > sickle pomfret (6.7) > albacore tuna (5.3) > bigeye tuna (5.2) > blue marlin (4.1) > escolar (2.4) > opah (2.3) > thresher shark (1.5) > swordfish (1.2) > mako shark (0.5). With a Se/Hg molar ratio of less than 1, mako shark was the only fish containing a net molar excess of mercury. A selenium health benefit value based on the absolute amounts and relative proportions of selenium and mercury in seafood is proposed as a more comprehensive seafood safety criterion.