Acid Mine Drainage Impacts on Hydrochemistry
Besides altering surface and groundwater flow directions and water balances, AMD also has adverse impacts on surface and groundwater hydrochemistry. Several studies drawn from various countries have reported the impacts of AMD on hydrochemistry, including extremely acidic conditions and high concentrations of dissolved contaminants (Grande et al., 2018; Gwenzi et al., 2017; Xia et al., 2017; Wen et al., 2018; Mungazi and Gwenzi,
- 2019). For example, extremely high concentrations of metals, sulphates and acidity were reported at Iron Duke Mine in Mazowe, Zimbabwe (Gwenzi et al., 2017; Mungazi and Gwenzi, 2019). According to Williams and Smith (2000), AMD at Iron Duke Mine has some of the highest values ever reported in the world as evidenced by extremely low pH (0.52-0.82), and very high concentrations of both sulphates (S042-) (220 853-355 425 mg/L) and iron (Fe) (85 672-132 929 mg/L. High concentrations of other anions such as chloride and fluoride have also been reported (Alsaiari and Tang, 2018; Li et al.,
- 2019), while other studies detected high concentrations of toxic metalloids (e.g., arsenic) and radionuclides (Galhardi and Bonotto, 2017; flay et al., 2019; Manjon et al., 2019). Recent studies also reported the enrichment of rare earth elements (REEs) in AMD and receiving waters (Migaszewski et al., 2019; Soyol-Erdene et al., 2018). For example, a study conducted in Poland detected extreme enrichment of arsenic and REEs in AMD with concentrations of up to 1548 mg L 1 for arsenic and up to 24.84 mg L 1 for REEs (Migaszewski et al., 2019).
The changes in hydrochemistry induced by AMD have potential ecological and human health risks (Ochieng et al., 2017). For example, metals, metalloids, and radionuclides are well-known toxins that have adverse impacts on human and ecological health (Martinez-Alcala and Bernal, 2020; Iryna, 2017). The REEs pose several human health risks, including genotoxicity, teratogenicity, and carcinogenicity (Gwenzi et al., 2018a; Squadrone et al., 2019). Gwenzi et al. (2018b) discussed the contribution of mining and mineral processing including AMD to REEs detected in aquatic systems and the associated health risks.