Abstract
In coastal marine systems at high level of anthropization and socio-economic exploitation, like harbours, sediment represents a sink and a source for contaminants. Indeed, organic and inorganic pollutants coming from the water column are adsorbed and accumulated by sediment, as a consequence of natural processes occurring in all the aquatic systems. Unlike organic contaminants, metals cannot be degraded. Metal contamination in marine sediment is an environmental problem of high magnitude and, as a consequence, there is a need for environmentally friendly strategies. In this contest, biologically mediated leaching (bioleaching) may offer a solution. In the present work, bioleaching is applied on metal contaminated sediment coming from a marine harbour. Laboratory scale experiments were performed, at 10 g/L sediment content, in order to deepen the mutualistic interaction between chemolithotrophic Fe/S oxidizing bacteria, commonly applied in bioleaching strategies, and acidophilic heterotrophic Fe-reducing bacteria. Indeed, previous papers have partially investigated this aspect and offer some interesting insights. Here, the mutualism eventually occurring is better investigated, in view of the understanding of the processes involved during bioleaching, where the interaction metal-bacteria-sediment appears to be of central importance. Target metals were those mainly relevant in the sediment sample: arsenic (48 ± 2 ppm), chromium (140 ± 50 ppm), cadmium (1.8 ± 0.5 ppm) and zinc (1030 ± 70 ppm). During the experiment, other investigated responses were pH, microbial abundances and iron speciation. At the end of the experiment, Zn and Cd were the main solubilized metals, while Cr and As were scarcely removed from the sediment. Data about iron speciation also suggested that mutualism between chemolithotrophs and heterotrophs occurred, despite the presence of a complex environmental matrix such as marine sediment.
