ARSENIC MOBILIZATION IN A SOIL POLLUTED BY PYRITE CINDERS

Root and microbial mediated mobilization of As was studied in a soil polluted by pyrite cinders containing a large amount of Fe and other metals/metalloids (i.e. As, Cd, Cu). The soil contained As-tolerant heterotrophic bacteria. Microcosm and greenhouse experiments with Helianthus annuus L. were conducted on soil amended with glucose and manure. To understand the effects of microbial activity on the mobilization of As, the cycling of As was studied in microcosm under laboratory conditions. Slurry soils incubated aerobically showed negligible Fe and As solubilization. Under anaerobic conditions, relevant Fe reduction concomitant with As mobilization and increase of As(III)-tolerant bacteria resulted. In 'killed' samples no changes in As-speciation occurred, confirming that bacteria play a crucial role in catalysing the redox transformations that control the mobility of As. The results of the greenhouse experiment highlighted the beneficial effect of manure on plant biomass and the plant induced acidification of the rhizo-soil. No significant increase in plant As uptake and in As retention by soil were observed, except for a slight increase in As bound with crystalline Fe oxides.