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Abstract Title: Mercury Contamination in the Tagus Estuary: An Overview of the Major Findings in the Last Decade
Presenter Name: Rute Ces rio
Company/Institution: CQE-IST
Session: Mercury in Contaminated Sites
Day and Session: Thursday 28th July - Session Two
Start Time: 10:00 UTC
Co-Authors: Rute Ces rio

Abstract Information :

The Minamata Convention recognized mercury (Hg) as a chemical of global concern. Research in this Tagus Estuary started in the late 70?s; however, knowledge on Hg contamination in this system has greatly improved in the last decade.
Results showed two highly contaminated zones, whereas, in areas far from the sources, Hg and monomethylmercury (MMHg) were also detected, indicating that estuarine hydrodynamic contributes to Hg contamination spreading.
The data from the last decade showed a seasonal variation effect in MMHg levels with increasing Hg methylation during summer. Additionally, methylation rates measured in saltmarsh sediments, mainly vegetated, reflected the optimal environmental conditions for MMHg production. This, coupled with the ability of plants to accumulate Hg through roots, translocate it to aerial parts and volatilize it to Hg0 point the Tagus estuary in terms of a highly dynamic Hg system, mostly due to their saltmarshes.
In the water column, the transport of Hg and MMHg in the Tagus estuary, due to the tidal oscillation, was shown to be mainly associated with dissolved organic carbon and SPM, with the advective transport at the interface sediment-water much higher than predicted diffusive fluxes. Tides also induced increments of Hg and MMHg in surface waters coupled with a decrease in the pore waters due to tidal flushing. Due to this process, dissolved Hg species were found to be easily reduced to Hg0 (dissolved gaseous mercury-DGM) in the water-air interface, rapidly escaping to the atmosphere.
In summary, all data sets obtained in the last decade point to the persistence of Hg contamination in the Tagus estuary more than 30 years after its substitution in industrial processes. The ?hotspots? identified around the 1980?s remain important sources of Hg and MMHg to the estuary, directly impacting ecosystem services, which further require urgent measures to mitigate and remediate Hg contaminated areas.

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