Abstract
Reactive oxygen species (ROS) production and resultant oxidative stress (OS) has been implicated as a pathway of toxicity in animal species exposed to pollutants. The gills of aquatic animals and the liver and kidneys of mammalian species are specific cellular sites of toxicity. Oxidative effects of acid mine drainage effluent (following passive and active treatment) impacting a natural stream were assessed using selected cell lines. Levels of pollutants such as heavy metals in acid mine drainage (AMD) effluent can be quantified following treatment, but it is unknown whether this is associated with equivalent reduction in toxicity. ROS production by AMD untreated (U) and after treatment (T) was quantified in a fish gill cell line (RTgill-W1) and in two mammalian cell lines (C3A human liver and Vero monkey kidney). ROS production was determined using the oxidant sensitive fluorogenic probe, 2′, 7′-dichlorofluorescein diacetate (DCFH-DA) following exposure to U and T, AMD water. Treatment of AMD water caused reduction in levels of Al, Zn, Fe, Si and Mn while levels of Cr, Cu, Ar and Hg remained unchanged. A dose-dependent increase in ROS production was observed for U and T. ROS formation decreased from 14% to 4.5%, 16.4% to 7.2% and 25.3% to 17.7% in the RTgill-W1, C3A, and Vero cell lines exposed to 100% AMD water, U and T. The presence of Mn and/or other ions in treated water and subsequent ROS formation indicates that water could still be toxic to cells and requires further processing. The DCFH-DA assay in several cell lines can be used to rapidly bio-monitor quality of AMD water related to formation of ROS and subsequent cellular effects. However, cut-off levels for cellular toxicity must be established to ensure safety of this water for aquatic animals and for animal and human consumption.
Highlights
Coal mining is a major industry in South Africa, as coal is the principal energy source for the country (Mangena and Brent, 2006)
EC values obtained for U and T (320 and 326 mS/m) water samples were higher than the recommended guidelines stipulated for industrial and domestic use (250 mS/m, 70 mS/m)
This study showed that the water quality parameters of the receiving stream were adversely impacted by acid mine drainage (AMD) discharge and the presence of metals at environmentally-relevant concentrations may have contributed to observed increased reactive oxygen species (ROS) formation in cell lines exposed to U and T
Summary
Coal mining is a major industry in South Africa, as coal is the principal energy source for the country (Mangena and Brent, 2006). A number of coal mines are located in the Mpumalanga Province, where over 10 000 km of hydraulically interlinked mines host 8 of the country’s 10 operational coalfired power stations (Heath et al, 2010). Most rivers have been negatively impacted by extensive industrial and mining activities in the Mpumalanga Province, threatening aquatic ecosystems (De Villiers and Mkwelo, 2009). Coal mining is the most important source of acid mine drainage (AMD) contamination affecting streams and rivers in the upper catchment of the Olifants River (Adler et al, 2007; Driescher, 2008). AMD effluent contains substances that contaminate aquatic ecosystems with effects ranging from chemical (bioavailable metal concentration), biological (acute and chronic toxicity) and ecological (loss of habitat and elimination of sensitive species) to others (Gray, 1997). Human exposure occurs by ingestion of contaminated water through drinking, preparation of food or irrigation of crops (Awofolu et al, 2005), and causes multiple organ toxicity in the brain, liver and kidneys (André et al, 1991; Bouquegneau and Joiris, 1992; Dietz et al, 1998)
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