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| - Arsenic Mobilization throughMicrobially Mediated Deflocculationof Ferrihydrite
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| - This study examined the potential impact of microbiallymediated reduction of Fe in the Fe(III)−(hydr)oxide mineralferrihydrite on the mobility of As in natural waters. Inmicrocosm experiments, the obligately anaerobic bacteriumGeobacter metallireducens reduced on average 10% ofthe Fe(III) in ferrihydrite with varying sorbed As(V) surfacecoverages, which resulted in deflocculation of initiallymicron-sized As-bearing ferrihydrite aggregates to nanometer-sized colloids. No reduction of As(V) to As(III) wasobserved in microcosm samples. Measurement of Fe andAs within operationally defined particulate, colloidal,and dissolved fractions of microcosm slurry samplesrevealed that little Fe or As was released from ferrihydriteas dissolved species. Microbially induced deflocculationof ferrihydrite in the presence of G. metallireducens wascorrelated with more negative zeta potential of ferrihydritenanoparticles suggesting that G. metallireducens mediatedAs mobilization through alteration of ferrihydrite surfacecharge. TEM analysis and solution chemistry conditionssuggested formation of a magnetite surface layer throughtopotactic recrystallization of ferrihydrite (2LFH) drivenby sorbed Fe(II). The formation of nanometer-sizedAs-bearing colloids through microbially mediated reductionof Fe−(hydr)oxides has the potential to increase humanAs exposure by enhancing As mobility in natural waters andhindering As removal during subsequent drinking watertreatment.
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