Uptake and elimination routes of inorganic mercury and methylmercury in Daphnia magna.
Uptake and elimination routes of inorganic mercury and methylmercury in Daphnia magna.
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DOI：
10.1021/es034638x
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发表时间：
2004-02
影响因子：
11.4
通讯作者：
M. Tsui;Wen-Xiong Wang
中科院分区：
文献类型：
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作者：
M. Tsui;Wen-Xiong Wang
汞(Hg)具有剧毒性质，广泛存在于水生环境中，是一种重要的环境污染物。在以往的研究中，浮游动物体内汞的生物动力学在很大程度上被忽略了。本研究研究了淡水枝角类大型水蚤对无机汞[Hg(II)]和甲基汞(MeHg)的同化、溶解吸收和外排，并模拟了汞(II)和甲基汞(MeHg)在水蚤中的暴露途径。两种汞的同化效率(AEs)均随藻类碳浓度的增加而显著降低。汞和甲基汞的溶解吸收与环境浓度成正比(在3-4个数量级的变化范围内，从环境现实浓度到高浓度)，而甲基汞的吸收速率常数(0.46 L g(-1)h(-1))略高于汞(II)(0.35 L g(-1)h(-1))。令人惊讶的是，汞(11)和甲基汞的外流速率常数相当接近(0.041-0.063天(-1))。进一步研究了不同食物浓度下汞(II)和甲基汞通过不同途径(排泄、排出、蜕皮和新生儿产生)的释放。研究发现，进入溶解阶段的再生对于消除这两种汞很重要，但母体向新生儿转移汞(11-15%)和甲基汞(32-41%)是从母亲体内消除汞(II)和甲基汞的另一条重要途径。模拟结果表明，食物是甲基汞暴露的重要来源(47%-98%)，但水暴露占大型沼虾汞(II)累积的31%-96%，这取决于摄入食物中汞的生物浓缩系数的变化。此外，尽管甲基汞只占水中总汞的一小部分，但甲基汞在大型金枪鱼体内的生物积累中占主导地位。这一结果有力地表明，淡水浮游动物体内汞(II)和甲基汞的母体转移应被考虑在水生食物链的许多毒性测试和风险评估中。
Mercury (Hg) is an important environmental pollutant due to its highly toxic nature and widespread occurrence in aquatic systems. The biokinetics of Hg in zooplankton have been largely ignored in previous studies. This study examines the assimilation, dissolved uptake, and efflux of inorganic mercury [Hg(II)] and methylmercury (MeHg) in a freshwater cladoceran, Daphnia magna, and models the exposure pathways of Hg(II) and MeHg in the daphnids. The assimilation efficiencies (AEs) of both Hg species decreased significantly with increasing algal carbon concentrations. The dissolved uptake of Hg(II) and MeHg was proportional to the ambient concentration (ranging from environmentally realistic to high concentration over a 3-4 orders of magnitude variation), whereas MeHg had a slightly higher uptake rate constant (0.46 L g(-1) h(-1)) than Hg(II) (0.35 L g(-1) h(-1)). Surprisingly, the efflux rate constants of Hg(ll) and MeHg were rather comparable (0.041 -0.063 day(-1)). The release of both Hg(II) and MeHg via different routes (excretion, egestion, molting, and neonate production) was further examined at different food concentrations. It was found that regeneration into the dissolved phase was important for D. magna to eliminate both Hg species, but maternal transfer of Hg(II) (11-15%) and MeHg (32-41%) to neonates represented another important pathway for the elimination of Hg(II) and MeHg from the mothers. Modeling results suggest that food is an important source for MeHg exposure (47-98%), but water exposure represents 31-96% of Hg(II) accumulation in D. magna, depending on the variation of Hg bioconcentration factor in ingested food. Furthermore, MeHg predominates the bioaccumulation of Hg in D. magna even though MeHg constitutes only a small percentage of the total Hg in the water. The results strongly indicate that maternal transfer of Hg(II) and MeHg in freshwater zooplankton should be considered in manytoxicity testings and risk assessment in aquatic food chains.