Persistent Hg contamination and occurrence of Hg-methylating transcript (hgcA) downstream of a chlor-alkali plant in the Olt River (Romania)
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Chlor-alkali plants using mercury (Hg) cell technology are acute point sources of Hg pollution in the aquatic environment. While there have been recent efforts to reduce the use of Hg cells, some of the emitted Hg can be transformed to neurotoxic methylmercury (MeHg). Here, we aimed (i) to study the dispersion of Hg in four reservoirs located downstream of a chlor-alkali plant along the Olt River (Romania) and (ii) to track the activity of bacterial functional genes involved in Hg methylation. Total Hg (THg) concentrations in water and sediments decreased successively from the initial reservoir to downstream reservoirs. Suspended fine size particles and seston appeared to be responsible for the transport of THg into downstream reservoirs, while macrophytes reflected the local bioavailability of Hg. The concentration and proportion of MeHg were correlated with THg, but were not correlated with bacterial activity in sediments, while the abundance of hgcA transcript correlated with organic matter and Cl− concentration, indicating the importance of Hg bioavailability in sediments for Hg methylation. Our data clearly highlights the importance of considering Hg contamination as a legacy pollutant since there is a high risk of continued Hg accumulation in food webs long after Hg-cell phase out.
KeywordsBacterial activity Biota Dispersion Methylmercury Reservoir Sediments Water
This work is part of the Romanian–Swiss Research Program with the project number IZERZO-142228, funded by the Swiss National Science Foundation (SNF) and Romanian Executive Agency for Higher Education, Research, Development and Innovation Funding (UEFISCDI). The work was also partially supported by the SNF (project 205321_138254) and Swedish Research Council (project 623-2011-7191). We thank the National Administration Apele Romane Olt for permission to work in their laboratory, GeoEcoMar for providing the boat, Aline Freiburghaus and Dany Dumitru Grosu for support and help during the sampling, Dolly Kothawala for English editing and improvement.
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