Mercury and Methylmercury Dynamics in Sediments on a Protected Area of Tagus Estuary (Portugal)

摘要

The Tagus Estuary is one of the most Hg-contaminated estuaries in SW Europe. Sediment cores were sampled at two low Hg-contaminated sites inside the natural park, Alcochete (ALC) and Vale Frades (VF), and analyzed for mercury and methylmercury. Concentrations of Hg and MeHg in sediments were below 1 mu g g(-1) and 4.4 ng g(-1), respectively. While in summer organic matter and/or excess SO42 promotes Hg methylation, in winter, Hg availability is the sole driver for methylation. Diffusive fluxes in the sediment/water interface show a sink of Hg species in the ALC site (ca. 170 mg year(-1) of Hg and 60 mg year(-1) of MeHg), while in the VF area, a sink of MeHg (ca. 1900 mg year(-1)) as well as a source of Hg (ca. 2000 mg year(-1)) is observed. The morphology and hydrodynamic regime of the Tagus Estuary seem to influence Hg dynamics even in areas with low levels of Hg contamination.