T11 PM Developments in Bioremediation of Acid Mine Drainage Wastes
Tuesday, 15 November 2005: 1:50 PM - 5:30 PM in 343-344

(SAN-1118-441262) Toxicity of lead on sulfate-reducing bacteria in the presence of goethite and quartz.

Sani, R¹, Peyton, B¹, Dohnalkova, A², ¹ Washington State University, Pullman, WA, USA² Pacific Northwest National Laboratory, Richland, WA, USA

ABSTRACT- Lead (Pb) and Pb-compounds are potentially mobile within ground waters and threaten down-gradient water resources at many US Department of Energy sites. The effective manipulation of indigenous bacterial communities to stimulate in situ activity in the presence of toxic heavy metals requires knowledge of the toxic effects of contaminants on subsurface bacteria. Goethite, quartz, and Pb were treated with the sulfate-reducing bacterium, Desulfovibrio desulfuricans G20, in a medium specifically designed in our laboratory to assess metal toxicity. Results showed that G20 first removed Pb from solutions, and then growth began resulting in visible black precipitates of Pb and iron sulfides. In the presence of goethite and quartz, Pb increased the lag time of G20 from two days in Pb-free treatments to five days in the presence of 26 M soluble Pb. In the absence of goethite and quartz, however, with 26 M soluble Pb, no measurable growth was observed. Analysis of thin sections of G20 treated with 10 M Pb using high resolution transmission electron microscopy showed cells with a heavy periplasmic precipitation of Pb-containing material. In fact, more than 50% cells had lead sulfide precipitates in the cytoplasmic space. Under the same conditions in the presence of goethite, however, no cells were detected that had lead sulfide precipitates in the cytoplasm. Selected area electron diffraction pattern and crystallographic analysis of transmission electron microscope lattice fringe images confirmed the structure of lead sulfide precipitates in the cytoplasmic spaces was identical to galena. Our results suggest that 1) at equivalent aqueous concentrations, the apparent Pb toxicity with and without goethite was not equivalent, i.e., addition of minerals in medium resulted in a decrease in Pb toxicity to G20; 2) once growth began, even after 5 days of lag period, cultures ultimately attained the same total cell protein yield as they did in Pb- and mineral-free treatments suggesting that observed toxic effects were reversible or non-permanent; and 3) the observed reduction in toxicity of Pb to G20 with and without minerals may reflect the differential bioavailability of Pb in the medium, since, in the presence of goethite, Pb did not enter to the cells i.e. Pb did not exert any toxicity.

Key words: SEAD, XRD, Bioavailability, Iron minerals