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

Cesário, Rute; Monteiro, Carlos Eduardo; Nogueira, Marta; O’Driscoll, Nelson J.; Caetano, Miguel; Hintelmann, Holger; Mota, Ana Maria; Canário, João

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

2016

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 μg g⁻¹ and 4.4 ng g⁻¹, respectively. While in summer organic matter and/or excess SO₄ ²⁻ 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.

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