Arguments from a few scientists and many proponents of the seafood industry are suggesting that the high selenium in ocean fish like tuna is protective and counters the adverse health effects of the high mercury in the same fish. The stringest arument is that selenium and mercury bind in the test tube, and that one study in rats fed swordfish with and without selenium indicate that selenium is protective of the disease endpoints measured.

Although no human evidence has been produced, (and for ethical reasons it is unlikely that there will ever be a case control study in humans) the seafood industry has told us its OK to eat more fish, despite high mercury levels in many fish like swordfish and tuna, and the documented adverse effects of mercury on human health.

A new study published today in the journal of Biomedicine and Biotechnology
indicates that selenium may indeed not be protective if one uses rat physiology as a model for humans.
The study, titled Dietary Mercury Exposure Resulted in Behavioral Differences in Mice Contaminated with Fish-Associated Methylmercury Compared to Methylmercury Chloride Added to Diet also looked at mercury salts used as the mercury form in many toxicological mercury studies.


Abstract
Methylmercury (MeHg) is a potent neurotoxin, and humans are mainly exposed to this pollutant through fish consumption. However, in classical toxicological studies, pure methylmercury chloride (MeHgCl) is injected, given to drink or incorporated within feed assuming that its effects are identical to those of MeHg naturally associated to fish. In the present study, we wanted to address the question whether a diet containing MeHg associated to fish could result in observable adverse effects in mice as compared to a diet containing the same concentration of MeHg added pure to the diet and whether beneficial nutriments from fish were able to counterbalance the deleterious effects of fish-associated mercury, if any. After two months of feeding, the fish-containing diet resulted in significant observable effects as compared to the control and MeHg-containing diets, encompassing altered behavioral performances as monitored in a Y-shaped maze and an open field, and an increased dopamine metabolic turnover in hippocampus, despite the fact that the fish-containing diet was enriched in polyunsaturated fatty acids and selenium compared to the fish-devoid diets.

Read the full study here.
Volume 2012 (2012), Article ID 681016, 9 pages
doi:10.1155/2012/681016