Methylmercury determination in sub-ppb level by cold vapor analysis: facts, mechanisms and optimization

Recent reports, according to international organizations, on the highly toxic presence of methylmercury (MeHg) in the environment, classify it among the other high priority pollutants. Mercury mainly released in its inorganic or elemental form through anthropogenic emissions. MeHg is formed through biotic and abiotic mechanisms when inorganic or elemental Hg enters water resources and seawater. Understanding the need to find new, but also safe, sources of usable water and to monitor the current ones, aim of this study is to investigate the determination of MeHg by cold vapor analysis, providing useful facts regarding methods optimization, in order to be adopted from other researchers. Since Hg regulation limit in drinking water is 1 μg/L, experimental pollutant’s concentration was in the range 0-10 μg/L, while as matrix was applied natural-like water, according to National Sanitation Foundation. During cold vapor analysis organic or/and inorganic mercury atomization takes place chemically by a reducing agent. The most known agent is SnCl₂, which however reduces only the inorganic Hg. Instead, NaBH₄ is capable to reduce both Hg modes but a pretreatment of the sample is required before the measurement, namely the addition of KMnO₄. So, in this work, reagents’ concentration was studied, and their role was clarified in every step of the proposed method analysis. According to the results, the addition of at least 0.005% w/v KMnO₄ and 0.05% w/v NaBH₄ is needed in the aquatic sample for a reliable MeHg measurement. Even if the KMnO₄ addition intended to transform organic mercury to inorganic, it was proved that this is only partially true. In fact, the formed MnO₂, that produced by the reduction of the residual KMnO₄ from NaBH₄, catalyzes the MeHg atomization reaction.

Acknowledgments: This research is co-financed by Greece and the European Union (European Social Fund- ESF) through the Operational Programme «Human Resources Development, Education and Lifelong Learning» in the context of the project “Reinforcement of Postdoctoral Researchers - 2nd Cycle” (MIS-5033021), implemented by the State Scholarships Foundation (ΙΚΥ).