Abstract:
The success and long term effectiveness of extensive and expensive engineering solutions to restore streams
impacted by Acid Mine Drainage (AMD) is rarely tested. Concentrations of pollutants were measured in water
along a longitudinal gradient from a stretch of the Tweelopie stream, South Africa, that receives pH-treated acid
mine drainage (AMD) from an abandoned gold mine. The biotoxic effects of treated AMD were determined
through macroinvertebrate biotic indices (SASS5) and a battery of toxicity bioassays. These included the L.
sativa, A. cepa, D. magna toxicity and Ames mutagenicity tests, as well as an in vitro human liver cancer cell line
HepG2. Even though the Tweelopie stream was moderately to severely degraded by multiple anthropogenic
stressors, the impact of the treated AMD was masked by the improvement in the system downstream after mixing
with the domestic wastewater effluent receiving stream, and subsequent further dilution as a result of the karst
springs downstream. The general improvement of the system downstream was clearly shown by the decrease in
the ecotoxicity and mutagenicity in relation to the in-stream macroinvertebrates. PCA multivariate analysis
successfully displayed associations between the different environmental variables and the decrease in toxicity
and subsequent ecosystem improvement downstream. This study indicated that environmental management of
AMD remediation should consider long term assessment strategies, including multiple factors, to promote biological
ecosystem recovery.
