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(W/MF179) Heavy metal resistance of soil bacterial populations in restored soils after Aznalcollar accident. de Vicente, Antonio 1, Olea, Francisco1, Arrebola, Eva1, Codina, Juan 1, Pérez-García, Alejandro1, 1 ABSTRACT- The crack of the mining waste pond of Aznalcollar mines (Spain) in April 1998 caused the disposal of 6 Hm3 of acid waters and pyritic sludges, and the basin of Guadiamar river was flooded, accumulating sediments highly contaminated with heavy metals. Following the accident, it was stablished a cleaning and restoration programme of the contaminated area that is being currently evaluated. The ability of bacteria to adapt to the presence of toxic substances, such as metals, and then, the resistant bacteria proportions can be used to indicate whether certain metals are present or have been present in the recent past in this environment. In this work, the impact of heavy metal contamination after the Aznalcollar accident on soil bacterial communities and the efectiveness of the restoration programme have been studied, using the levels of total (plate counts on Tris-lactate and MGY) and heavy metal resistant bacteria (plate counts on media amended with metals) as indicators of recovery of bacterial populations by comparing of soil samples from non-contaminated, restored and contaminated non-cleaned areas. Determinations of total heterotrophic bacterial populations showed that, two years after the accident, in the cleaned and restored soils there were bacterial levels close to non-contaminated soils, whereas in sediments of non-cleaned areas bacterial population levels were very low. Relatively high levels of bacteria resistant to arsenic, nickel and zinc were observed, and also low frequencies of copper and cadmium resistance were detected. The Microtox Solid Phase assay was used to estimate the remaining toxicity in soil samples. This work has been supported by a grant from Consejeria de Educacion y Ciencia, Junta de Andalucia. Key words: Metal, Bacteria, Resistance, Toxicity |
