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Toxicity Of Metal-Mine Drainage Before And After Biochemical Reactor Treatment: National Tunnel In The Clear Creek Watershed, Colorado, USA
Citation:
BUTLER, B., M. E. Smith, J. M. LAZORCHAK, AND D. J. REISMAN. Toxicity Of Metal-Mine Drainage Before And After Biochemical Reactor Treatment: National Tunnel In The Clear Creek Watershed, Colorado, USA. Presented at SETAC North America 30th Annual Meeting, New Orleans, LA, November 19 - 23, 2009.
Impact/Purpose:
To evaluate the reduction in acute toxicity to Ceriodaphnia dubia and Pimephales promelas through BCR treatment of drainage from the National Tunnel, a primary point source of metals to the North Fork of Clear Creek, Colorado.
Description:
Many miles of streams in the US (and worldwide) are contaminated by metals originating from both active and abandoned mine-sites. Streams affected by mine drainage are often toxic to aquatic life. Thus, it is desirable to remediate these sites through treatment of the source(s). Passive-treatment biochemical reactor (BCR) systems have been shown to be effective at removing metals contamination from these systems. An issue that is of recent interest is whether the toxicity of these waters is reduced and/or eliminated by the BCR treatment. BCRs generally facilitate sequestration of metals as sulfides within the reactor, but sorption of metals onto mineral or organic surfaces may occur also. In most cases, the concentration of metals in BCR effluent is greatly reduced compared to the influent. This study evaluated the reduction in acute toxicity to Ceriodaphnia dubia and Pimephales promelas through BCR treatment of drainage from the National Tunnel, a primary point source of metals to the North Fork of Clear Creek, Colorado. The BCRs being evaluated for efficiency of metals removal at the site contain four different substrates: ethanol, hay/wood, corn stover/wood, and chitin [crab shells] and are being operated in duplicate. BCR effluent was less toxic than the influent, except from the BCR containing chitin, which also was the only effluent to have substantial concentrations of un-ionized ammonia (0.25 mg/l and 0.41 mg/l for the replicates). Toxicological response varied between the substrate types, with the BCRs having ethanol and one of the replicates having corn stover/wood providing the least toxic effluent. There also was a substantial difference in effluent toxicity observed between the replicates having the hay/wood and the corn stover/wood substrates. A correlation analysis suggests toxicity may be related to NH3, S (presumably as sulfide), Al, Cd, Ni, alkalinity, and/or conductivity. Because this study indicated toxicity form the BCR effluents, studies are underway to evaluate further these types of effluents at several other abandoned mine-sites having different substrate types, as well as testing to evaluate which of the water chemistry parameters is causing any observed toxicity.