Anaerobic biochemical reactors (BCRs) are useful for removing metals from mining-impacted water at remote sites. Removal processes include sorption and precipitation of metal sulfides, carbonates, and hydroxides. A question of interest is whether BCRs remove aquatic toxicity. Influent and effluent samples from the Luttrell Repository and Peerless Jenny King, both in Montana, USA; Park City, Utah, USA; and Standard Mine, Colorado, USA, were examined and compared for removal of metals and aquatic toxicity. Effluent samples from Standard Mine included those having solely BCR treatment and those having BCR treatment followed by aeration in a polishing cell. Metal removal for all sites was >90%. All influent samples were acutely toxic to Ceriodaphnia dubia and Pimephales promelas; toxicity was removed following treatment, except in the Luttrell Repository and Standard Mine BCR samples. Laboratory aeration of undiluted samples eliminated (Standard Mine BCR) or significantly reduced (Luttrell Repository, 65% survival) acute toxicity, most likely through removal of hydrogen sulfide. A toxicity identification evaluation suggested that metals also might be contributing to toxicity in the Luttrell Repository effluent samples; metals other than Mn were either not detected or very low (Fe and Pb) in the Standard Mine BCR samples. Field-aerated samples were not acutely toxic, and only the Luttrell Repository and Standard Mine samples showed short-term subchronic toxicity. Overall, results indicated BCR treatment had high metal removal efficiency and that inclusion of in-field aeration was beneficial in removal of acute and short-term subchronic toxicity. Environ. Toxicol. Chem. 2011;30:385–392. © 2010 SETAC
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