Biomobilization of Heavy Metals from the Sediments Affect the Bacterial Population of Al-Ghadir River (Lebanon)

Abstract

Although there is no doubt about the importance of the bacterial activity on the solubilisation and the distribution of heavy metals in aquatic sediments, hydromorphic soils and ground waters; little is known about the involvement of bacterial dissolution in periodically anaerobic environments like that found in dredged sediments and little is known about the processes and the environmental factors controlling this process.The aim of this paper was to study the effect of the autochthonous bacterial activity on the biodegradation of organic matter and the mobilization of heavy metals in the sediments of Al-Ghadir river (Mount Lebanon). Sediments were incubated under standard anaerobic conditions and enriched with glucose to stimulate and accelerate microbial metabolism. The evolution of carbon metabolism (Organic matter evolved, carbon consumed and organic acids produced) and metals released in batch reactors were followed over time. Under the adopted conditions, analysis of the chemical parameters indicated that the incubated sediments showed a significant release of organic carbon corresponding to bacterial development. Mineral analysis showed an important solubilisation of Fe 2+ and Mn 2+ indicating the presence of Fe-and Mn-reducing bacteria in sediments. Pb, Cd and Cr solubilisation profiles were observed and appeared concomitant to the solubilisation profiles of Fe and Mn indicating that the redox cycle has been well installed and that Pb, Cd and Cr were associated to Fe and Mn oxides. The production of Cu appeared in parallel to the mineralization of the organic matter in the sediment indicating that Cu was associated to this fraction. Zn appeared associated to the sulphide fraction than to the Fe and Mn oxides fraction. Microbiological and genetic analysis showed a decrease and the disappearance of some bacterial strains due to the shift in the culture conditions and the toxicity of the released heavy metals but at the same time the development and the growth of many other populations which showed to be tolerant to the same conditions.

Metal Pollution Assessment of Sediment and Water in Al-Ghadir River: Role of Continuously Released Organic Matter and Carbonate and Their Purification Capacity

“…What happens is that when wastewaters are released, for example between the source (point A) and point B, we remark that the sequence of reduction in the sediments is similar to that reported by [47]. At point B, when a new quantity of organic matter is released, this release may affect the sequence of reduction [47] and can poise the soil Eh for several days where autochthonous bacteria consume the newly released organic matter as a source of carbon [48] and release another type of organic matters (organic acids). The increase in the specific area of the degraded organic matter may explain the raise of absorption or adsorption of the heavy metals to the newly released organic matter.…”

Effects of Extracellular Electron Shuttles on Microbial Iron Reduction and Heavy Metals Release from Contaminated Soils

“…These results suggest that microbial iron reduction and EES-mediated iron reduction may not release heavy metals from contaminated soils. Previous studies reported that microbial iron reduction of heavy metal contaminated soil and sediments can release heavy metals into porewater and groundwater under anaerobic conditions (Cummings et al, 1999;Gounou et al, 2010;Mcheik et al, 2013). However, the reductive transformation of iron (hydr)oxides can result in the formation of secondary iron minerals such as magnetite, siderite, vivianite, and mackinawite depending on surrounding geochemical conditions (Bae and Lee, 2013;Zachara et al, 2002).…”