Selenium Health Benefit Values as Seafood Safety Criteria

Abstract

Selenium (Se) is absolutely required for activity of 25-30 genetically unique enzymes (selenoenzymes). All forms of life that have nervous systems possess selenoenzymes to protect their brains from oxidative damage. Homeostatic mechanisms normally maintain optimal selenoenzyme activities in brain tissues, but high methylmercury (MeHg) exposures sequester Se and irreversibly inhibit selenoenzyme activities. However, nutritionally relevant amounts of Se can replace the Se sequestered by MeHg and maintain normal selenoenzyme activities, thus preventing oxidative brain damage and other adverse consequences of MeHg toxicity. Findings of studies that seem contradictory from MeHg exposure perspectives are entirely consistent from MeHg:Se molar ratio perspectives. Studies that have reported dose-dependent consequences of maternal MeHg exposures on child development uniformly involved seafoods that contained much more Hg than Se. Meanwhile more typical varieties of ocean fish contain much more Se than Hg. This may explain why maternal MeHg exposure from eating ocean fish is associated with major IQ benefits in children instead of harm. Therefore, instead of being avoided, ocean fish consumption should be encouraged during pregnancy. However, the safety of freshwater fish consumption is less certain. In freshwater fish, MeHg bioaccumulation and toxicity are both inversely related to Se bioavailability. Their Se can be far lower than their MeHg contents, potentially making them more dangerous than pilot whale meats. Therefore, to provide accurate and appropriate regulatory advice regarding maternal consumption of seafoods and freshwater fish, Hg:Se molar ratios need to be incorporated in food safety criteria.

Total mercury and selenium concentrations in Sarpa salpa and Balistes capriscus and in their respective Digenean endoparasites Robphildollfusium fractum and Neoapocreadium chabaudi from Tunisia

“…On the other hand, selenium is though to have a protective effect against mercury toxicity (Kaneko and Ralston 2007;Ralston 2008Ralston , 2009Ralston et al 2008;Burger and Gochfeld 2012) mainly because of the high affinity of selenium to mercury. In fact, selenium is thought to sequester methylmercury and reduce its bioavailability in organisms (Sørmo et al 2011).…”

“…Several authors have argued that higher Se:Hg molar ratios indicate a more protective effect of selenium against mercury toxicity (Ralston 2008;Peterson et al 2009a, b), even though contradictory results indicate that the effect of selenium on mercury bioaccumulation is an extremely complex process (Dang and Wang 2011). There has been a growing concern about the evaluation of Se:Hg molar ratios in fish muscle with focus on the methylmercury toxicity for humans as consumers of fish (Kaneko and Ralston 2007;Ralston 2008Ralston , 2009Ralston et al 2008;Burger and Gochfeld 2012). In the present study, the muscular Se:Hg molar ratio in S. salpa from Mahdia was significantly higher than in S. salpa from Sfax.…”

Selenium:Mercury Molar Ratios in Freshwater Fish from Tennessee: Individual, Species, and Geographical Variations have Implications for Management

“…Selenium–mercury interaction may reduce the bioavailability or toxicity of methylmercury, and conversely some mercury toxicity may be due to impaired selenium-dependent enzyme synthesis or activity (Watanabe et al 1999; Ralston 2008; Ralston et al 2008). Cell culture studies and animal experiments show adverse impacts of high methylmercury exposure on selenoenzymes (Beyrouty and Chan 2006; Cabanero et al 2007; Pinheiro et al 2009).…”

“…Ralston and colleagues (Raymond and Ralston 2004; Ralston et al 2007; Kaneko and Ralston 2007; Peterson et al 2009a; Ralston 2008) have argued strongly that a molar excess of selenium in salt water fish, offers protection against mercury. They indicates that Se:Hg molar ratio are important considerations for risk assessment and management.…”

“…The question then becomes—what levels of selenium are necessary to protect against mercury? Ralston and colleagues (Ralston 2008; Peterson et al 2009a) suggested that selenium:mercury molar ratios above 1 are probably protective for adverse mercury affects. But this assumes that the selenium and mercury are completely mutually bioavailable and do not interact with other substances.…”