Resumo

HANSEN, Anne M.; MAHE, Florence  e  CORZO-JUAREZ, Carlos E.. Methodology to determine the liberation of metals from sediments to water in lakes and reservoirs. Rev. Int. Contam. Ambient [online]. 2013, vol.29, n.3, pp.179-190. ISSN 0188-4999.

Although the sediment in water bodies may act as a secondary source of aqueous contaminants, no criteria are known that establish such relation. The present study proposes a methodology to determine risks of water pollution by release of metals accumulated in the sediment. The liberation of metals was evaluated in environments ranging from oxidized to reduced. A combined sediment sample from a reservoir in a tropical area was suspended with magnetic stirring and control of redox potentials (Eh) between -450 and +300 mV. We calculated the metals release per mass unit of sediment, considering that this occurs in a 5-cm sediment layer of 0.34 kg/L density. Likewise, distributions of metals among dissolved and solid phases were evaluated by hydrogeochemical modeling with PHREEQC v. 2. Three scenarios of water depth were evaluated and results were compared with the Mexican Ecological Water Quality Criteria for water supply sources (CECA). It was found that metals are adsorbed on solid iron oxides of the sediment in oxidized water-sediment systems. As solid iron phases dissolve at negative Eh, aqueous concentrations of most metals increased. At even more reduced conditions, Eh < -214 mV, the dissolved concentrations of metals decreased, probably due to coprecipitation with and/or adsorption on iron sulfide. The methodology presented here allows estimating future water pollution by metals contained in sediment. Understanding the reductive dissolution of metals is essential to mitigate health effects and for decision-making regarding water treatment.

Palavras-chave : water-sediment interaction; redox potential; reductive dissolution; hydrogeochemical modeling; adsorption; coprecipitation; iron sulfide; iron and manganese oxides.

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