Reduction of perchlorate in river sediment

Abstract

The transformation of perchlorate was investigated in river sediment during laboratory batch and column studies to determine if reduction of perchlorate is a viable pathway in natural sediment without previous exposure to perchlorate. Perchlorate at an initial concentration of 10 microM was reduced quantitatively to chloride in 3 d after a lag phase of 2 d in sediment slurries amended with lactate. Raising the initial concentration of perchlorate to 1,000 microM increased the lag phase to 20 d before reduction occurred. At perchlorate concentrations greater than 1,000 microM, the reduction of perchlorate was not observed within 40 d. We speculate that the high concentration of perchlorate specifically was problematic to the microbes mediating the reduction of perchlorate. High levels of nitrate inhibited the reduction of perchlorate as well. In sediment slurries amended with 870 microM sodium nitrate, the reduction of perchlorate at an initial concentration of 100 microM did not occur before day 15 of the experiment, but complete removal of nitrate had occurred by day four. Sediment column studies further demonstrated the dependence of perchlorate reduction on endogenous nitrate levels.