TO METHYLATE OR NOT TO METHYLATE? STUDY OF MERCURY SPECIATION ALONG THE VENETIAN LITTORAL SYSTEM (Q-ALIVE PROJECT)

The biogeochemical cycle of mercury (Hg) is affected not only by the physical, chemical and hydrological characteristics of the environment, but also by changes in productivity and biodiversity. In waters the complexes of Hg are related to the salinity and to the load of dissolved organic carbon (DOC) in the dissolved and in the particulate phases. Surface and bottom seawater were sampled along the Venetian coast at ten sites with different characteristics. Samples were filtered, stored frozen (-20°C) till the analysis in amber bottles, previously cleaned to minimize any contamination. Samples were analyzed according to the method by Cairns et al. (2008), which employs hyphenated techniques (no derivatization steps are required). LOD (limit of detection) and LOQ (limit of quantification) were quantified. Although for some samples both the species were under the LOQ, the presence of CH3Hg+ and Hg2+ at the same time in surface and in bottom waters were observed. CH3Hg+ concentrations in bottom waters were an order of magnitude higher than those in surface waters. Besides the contribution of sedimentary methylation, that may also be due to the bottom bacterial community, variability in CH3Hg+ concentrations may be due to changes in the phytoplankton communities, which in turn may be affected by nutrient loads from the catchment area and port mouths of the Venice Lagoon. Thus, monitoring these nutrient loads may be essential for the health of the Venetian littoral system, since they may affect blooms, methylation and hyper-bioaccumulation along the trophic web, with effects on the environment and on human health.