EVIDENCE FOR MICROBIAL IRON REDUCTION IN A LANDFILL LEACHATE-POLLUTEDAQUIFER (VEJEN, DENMARK)

Aquifer sediment samples obtained from the anaerobic part of a landfil l leachate plume in Vejen, Denmark, were suspended in groundwater or i n an artificial medium and incubated. The strictly anaerobic suspensio ns were tested for reduction of ferric iron [Fe(III)] oxides, which wa s measured as an increase in the concentration of dissolved Fe(II). Ir on reduction did not occur when the medium was inoculated with inactiv e sediment and when the organisms in the inoculated medium were killed by formaldehyde, by chloroform, or by pasteurization, whereas the lev el of iron reduction was significant when living bacteria were present . Mixed cultures were obtained from the sediment samples, and differen ces in apparent iron reduction rates among the different cultures were maintained during several transfers. In addition, iron reduction was observed in unamended incubation mixtures containing whole sediment an d groundwater. Synthetic amorphous Fe(III) oxides, as well as naturall y occurring sediment-bound Fe(III) oxides, could be reduced by the cul tures. Together, our results provide evidence that iron-reducing bacte ria are present and microbial iron reduction occurs in the polluted aq uifer sediments which we studied.