Mercury stable isotopes for monitoring the effectiveness of the Minamata Convention on Mercury

The Minamata Convention on Mercury (MC) includes provisions for a global monitoring program (GMP) and effectiveness evaluation (EE) to provide information on changes in mercury sources in various environmental media. While conventional measurement and modeling techniques have limitations in explaining the changes in mercury concentrations, the measurements of natural abundances of mercury stable isotopes have become powerful tracers for distinguishing between mercury sources and for understanding biogeochemical processes in the environment. Unfortunately, it is uncertain whether mercury isotope ratios can provide globally comparable results on specific mercury sources for the GMP and trend analyses for the EE. We have compiled a dataset from the literature to evaluate large-scale patterns of mercury isotope ratios in various environmental samples and to summarize sample types that can be used for the GMP. Total gaseous mercury, precipitation, foliage, and litter can provide comparable source information regarding atmospheric mercury across a large spatial scale. Interpretation of spatially relevant information using sediment and fish mercury isotope ratios are challenging because they represent multiple mercury sources and contain mercury that has been subject to biogeochemical transformation leading to isotope fractionation. In regards to the EE, data that provides evidence of changes due to source regulation needs to be gathered from local point source regions to assess health impacts. We recommend that the measurements of particulate-bound mercury in the atmosphere and sediment mercury isotope ratios near mercury hotspots and in fish, are needed to identify ecosystems sensitive to atmospheric deposition and to evaluate the effectiveness of the MC.