Nolde Natasa, Drobne Damjana, Horvat Milena, Jereb Vesna
Department of Environmental Sciences, Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia.
Environ Toxicol Chem. 2005 Jul;24(7):1697-704. doi: 10.1897/04-401r.1.
Reduction and methylation of inorganic mercury in Porcellio scaber (Isopoda, Crustacea) and its environment were studied, using a purpose-built experimental setup where Hg cycling was followed using 203Hg2+ tracer in experiments without and with isopods. In experiment without isopods, daily reduction of 203Hg2+ to 203Hg0 under sterile and nonsterile conditions was measured for three weeks to assess the contribution of bacteria to this process. In experiments with isopods, daily release of 203Hg0 was measured for two weeks. Total mercury (T203Hg) and monomethylmercury (Me203Hg) in whole animals, gut, digestive glands (hepatopancreas), food (hazelnut leaves), and feces were measured to obtain the assimilation and distribution of mercury in the animals, to investigate the origin and fate of Me203Hg, and, finally, to assess the mass balance of mercury in the experimental system. Experiment without isopods showed the important role of bacteria in reduction of 203Hg2+ to 203Hg0, especially in the first day of the experiment. Experiments with isopods showed that formation of 203Hg0 depended on the 203Hg2+ concentration in the food. The contribution of the isopod's digestive flora in reduction of 203Hg2+ to 203Hg0 was negligible. Approximately 3% of T203Hg and 2% of Me203Hg consumed was assimilated by the animals. Methylation of 203Hg2+ occurred already in the leaves before they were consumed by the isopods. Assimilation of Me203Hg from the food surprisingly was low. Also, a loss of Me203Hg was noticed when comparing assimilated and excreted Me203Hg versus consumed Me203Hg. This may be explained by the assumption that demethylation of MeHg prevailed over methylation of Hg2+ in the animal's digestive system, leading to excretion of ingested mercury as Hg2+.
利用专门构建的实验装置，研究了鼠妇（等足目，甲壳纲）及其环境中无机汞的还原和甲基化过程。在该实验装置中，使用²⁰³Hg²⁺示踪剂，分别在有无鼠妇参与的实验中追踪汞的循环。在无鼠妇参与的实验中，在无菌和非无菌条件下，持续三周测量²⁰³Hg²⁺每日还原为²⁰³Hg⁰的情况，以评估细菌在这一过程中的作用。在有鼠妇参与的实验中，持续两周测量²⁰³Hg⁰的每日释放量。测量了动物整体、肠道、消化腺（肝胰腺）、食物（榛树叶）和粪便中的总汞（T²⁰³Hg）和一甲基汞（Me²⁰³Hg），以了解汞在动物体内的同化和分布情况，探究Me²⁰³Hg的来源和去向，最终评估实验系统中汞的质量平衡。无鼠妇参与的实验表明细菌在将²⁰³Hg²⁺还原为²⁰³Hg⁰的过程中起着重要作用，尤其是在实验的第一天。有鼠妇参与的实验表明²⁰³Hg⁰的形成取决于食物中²⁰³Hg²⁺的浓度。鼠妇消化菌群在将²⁰³Hg²⁺还原为²⁰³Hg⁰过程中的作用可忽略不计。动物摄取的T²⁰³Hg中约3%以及Me²⁰³Hg中约2%被同化。²⁰³Hg²⁺在树叶被鼠妇食用之前就已发生甲基化。令人惊讶的是，动物从食物中同化Me²⁰³Hg的量很低。此外，在比较同化和排泄的Me²⁰³Hg与摄取的Me²⁰³Hg时，发现存在Me²⁰³Hg的损失。这可能是由于假设在动物消化系统中甲基汞的去甲基化作用强于汞离子的甲基化作用，导致摄入的汞以汞离子形式排泄。
