The Effects of Different Gold Mine Tailings on Growth, Reproduction and Avoidance-Behaviour of Earthworms

The mining industry plays a key role in the economic development of South Africa as one of the largest exporters of valuable resources, such as gold, platinum group metals and other metals and minerals. Unfortunately, mining produces large volumes of solid waste in the form of tailing disposal facilities (TDFs), which contain a variety of metals that are hazardous to the soil environment. The aim of this study was to use earthworm bioassays and avoidance-behaviour tests to assess the effects of gold mine tailings on soil organisms. Six random soil samples were taken from four different sites on a gold mine viz. two different TDFs and two grassy pasture sites. Earthworms (Eisenia andrei) were exposed for a period of 28 days to the soils from these different sites. Soil from the TDFs was also diluted to 25%, 50%, 75% and 100%, respectively. Soil chemical analysis showed that the TDFs had the lowest pH levels and that only Cr concentrations were higher than proposed benchmarks in two of the sites. Earthworms exposed to the TDF material showed significantly lower earthworm biomass, allied with a very low cocoon production. The avoidance-behaviour test showed similar results, where earthworms generally preferred natural and control soils over the TDF material. It can be concluded, that even though the gold mine was inactive for a long period of time, it still remains a highly contaminated area.