Decomposition and stability studies of methylmercury in water

Long-term stability of Hg$^{+2}$ and MeHgCl, and decomposition of MeHgCl under different conditions are investigated. Studies were done with acids (HCl, HNO$_{3}$ , H$_{2}$SO$_{4}$, HClO$_{4}$) and sodium hydroxide with and without adding different reagents (NaCl, H$_{2}$O$_{2}$ , L-Cystein) at room and higher temperatures with and without UV-light. For the stability studies container materials used were of Boresilicate glass, polyethylene and PTFE. Measurements were done using mostly cold vapour AAS after preconcentration on gold wool, but also Gas-Liquid-Chromatography with Electron capture detector and $\gamma$-spectrometry were used to understand the decomposition and reaction mechanisms by labelling with $^{203}$Hg. The given detailed results show that in the absence of light MeHgCl does not decompose to Hg$^{+2}$ even in the presence of 25 % acids. MeHgCl is also not easily decomposed by heating in the presence of low acid concentrations. But with UV-light decomposition of MeHgCl to Hg$^{+2}$ takes place immediately depending upon the intensity of UV-light. In the presence of SH-groups (L-cystein) partial stability and complexation of mercury was observed. For long term storage of Hg and MeHgCl at low concentrations, in addition to certain reagents, the material of the container is also important. Glass and quartz containers are better as they minimize losses and contamination