Strategies to suppress internal loads of metals in sediments

Mexican Institute of Water Technology, 62550 Jiutepec, Morelos, Mexico

^* Corresponding author: ahansen@tlaloc.imta.mx

Abstract

Sediments may act as secondary sources of pollutants, but no known criteria establish such relationship. This study aims at evaluating internal loads of Ni from sediments due to changing redox conditions caused by application of water treatment such as hypolimnetic oxygenation. Through hydrogeochemical modelling and experimental evaluation, the distribution of Ni was evaluated. Sediment and water samples from a reservoir located in central Mexico were located in a reactor and Eh was controlled in ±50 mV steps between +300 and -450 mV. The release of Ni was evaluated in each step and the results were construed to the reservoir, considering that water-sediment interaction occurs in a 5-cm sediment layer with known density. Under oxidized conditions, the metal was accumulated in the sediment. With the dissolution of Fe at lower Eh, dissolved concentrations of Ni increased. Under even lower Eh conditions, these concentrations decreased again. This was related to the formation of iron sulphide. Combining experimental evaluation with hydrogeochemical modelling, allowed evaluating different scenarios of distribution of Ni. The knowledge of reductive dissolution of metals is therefore essential for decision-making to mitigate health effects as result of water treatment strategies.