Dietary selenomethionine influences the accumulation and depuration of dietary methylmercury in zebrafish (Danio rerio)

Abstract

Methylmercury (MeHg) is a toxicant of concern for aquatic food chains. In the present study, the assimilation and depuration of dietary MeHg and the influence of dietary selenium on MeHg toxicokinetics was characterised in zebrafish (Danio rerio).In a triplicate tank experimental design (n=3 tanks per treatment group), adult zebrafish were exposed to dietary MeHg (as methylmercury-cysteine) at 5 and 10μg/g and with or without selenium (as selenomethionine) supplemented to the diets at a concentration of 5μg/g for 8 weeks followed by a 4-week depuration period.Methylmercury accumulated in muscle, liver and brain of zebrafish; with higher mercury concentrations in liver and brain than in muscle following 8 weeks of exposure. In muscle, the mercury concentrations were 3.4±0.2 and 6.4±0.1μg/g ww (n=3) in zebrafish fed the 5 and 10μg Hg/g diets, respectively. During the depuration period, mercury concentrations were significantly reduced in muscle in both the 5 and 10μg Hg/g diet groups with a greater reduction in the high dose group. After depuration, the mercury concentrations were 2.4±0.1 and 4.0±0.3μg/g ww (n=3) for zebrafish fed the 5 and 10μg Hg/g diets, respectively.Data also indicated that supplemented dietary selenium reduced accumulation of MeHg and enhanced the elimination of MeHg. Lower levels of mercury were found in muscle of zebrafish fed MeHg and SeMet compared with fish fed only MeHg after 8 weeks exposure; the mercury concentrations in muscle were 5.8±0.2 and 6.4±0.1μg/g ww (n=3) for zebrafish fed the 10μg Hg/g+5μg Se/g diet and the 10μg Hg/g diet, respectively. Furthermore, the elimination of MeHg from muscle during the 4-week depuration period was significantly greater in the fish fed the diet containing SeMet compared to a control diet; the mercury concentrations were 3.3±0.1 and 4.0±0.3μg/g ww (n=3) for zebrafish fed the 5μg Se/g and the control diets, respectively. In summary, dietary SeMet reduces the accumulation and enhances the elimination of dietary MeHg in muscle of zebrafish.