Utilizing earthworm and microbial assays to assess the environmental effects of different mining activities
Van Coller, Charné
MetadataShow full item record
Mining has negative impacts on the environment, and is one of the main contributors to environmental pollution. This holds a potential hazard for ecosystems surrounding mining areas and also for public health in the surrounding communities. There is therefore a need for ecotoxicological research in order to assess these possible risks and find ways to minimize the harmful effects. One way in which to assess soil vitality are soil enzymes which are produced by plants and microorganisms and will therefore be more abundant in healthy soils. Earthworms have been proven to be useful bioindicators for metal contamination of soil, as they are able to accumulate metals from their environment into their body tissue. The aim of this study was to use earthworm bioassays, neutral red retention time analysis (NRRt), enzymatic analysis and RAPD-PCR to determine the effect of mining activity on the environment. This was done by assessing the ecotoxicity of tailings collected from three different mines, viz. gold-, opencast chrome- and coal mines. The metals chosen for analyses included four (Cr, Co, Ni and Pb) of the seven (Cd, Cr, Ni, Pb, Zn, Cu, Co) environmentally important trace elements as described for South African soils. Arsenic was also chosen since it is associated with gold mine tailings. Tailings and soil were collected from three sites at each of the mines which included unrehabilitated (TDF-U) and rehabilitated (TDF-R) substrates from tailings disposal facilities (TDFs) and reference soils (RS) in close proximity to TDFs. The physical and chemical properties of these different substrates were determined in terms of pH, particle size as well as metal contents. In addition to this, they were analysed for microbial community function by means of enzymatic activity, which has been proven to be useful in evaluating contamination of soil. The enzymes analysed in this study included dehydrogenase, ß-glucosidase, acid phosphatase, alkaline phosphatase and urease. Earthworms (Eisenia andrei) were exposed to different material for 28 days during which their biomass, reproduction, mortality and lysosomal membrane stability were monitored weekly. Hereafter, they were removed from the material while the cocoons were left behind for a further 56 days. The hatched and unhatched cocoons as well as the juvenile worms were then counted to determine reproduction patterns in the materials. Metal concentrations in the substrates and earthworm body tissues were compared to selected benchmarks. Results indicated that when comparing the different materials from each mine, enzymatic activity proved to be a very sensitive parameter. Enzymatic activity showed significant differences (p < 0.05) between RS, TDF-R and TDF-U materials. Biomass was not a sensitive parameter (p > 0.05) for the worms exposed to the gold and chrome mine tailings, but it was a sensitive parameter (p < 0.05) for the coal mine exposed earthworms, showing early differences between the worms from the different sites (RS, TDF-R and TDF-U). The NRR-t assay was very sensitive (p < 0.05), indicating clear differences between the worms from each investigated site. In terms of reproduction, the production of cocoons showed clear differences (p < 0.05) between the different sites and could therefore be considered a sensitive parameter. Hatching success however, was not a sensitive parameter. The reason being that there were so little cocoons produced that it is not possible to determine the correct percentage of juvenile worms hatching from, for example, only one or two cocoons. Mortality was also not a sensitive endpoint as it was only observed in the coal mine material. RAPD - PCR results indicated genetic differences between earthworms exposed to the control- and the tailings materials, indicating either DNA alterations due to possible genotoxic effects, or genetic variation between individuals of the same species. Since mine waste materials often contain complex mixtures of metals that might be toxic on their own or in combination with other factors, it is difficult to attribute any observed genotoxic effect to any of the specific metals.