Abstract
The freshwater environment globally is faced with a drastic deterioration of the water quality, and a decline in biodiversity. An increase in anthropogenic activities associated with the freshwater environment has resulted in a decrease in water quality due to the release of toxic effluent and various other pollutants into this environment. The Tweelopiespruit in the Krugersdorp area is one such system being impacted by mining activities, effluent from wastewater treatment works, and farming activities. The last two decades have seen a drastic decrease in the water quality of the Tweelopiespruit. Of late, concerns focused on the sediment environment. Sediment plays an important ecological role in an aquatic environment. It provides nesting grounds and acts as a source of food for various organisms. Therefore, contaminated sediment poses a threat to aquatic community structures. Sediment can act as both a sink and a secondary source of pollution. Disturbed sediment would result in the remobilisation of contaminants. The use of an integrated approach to assess sediment toxicity in different sites and seasons was therefore vital for identifying and monitoring water and sediment quality.
The focus of the study was the Tweelopiespruit located in Krugersdorp, a mining city in the West Rand, Gauteng Province. This study area was chosen due to its proximity to an important ecological area, the Krugersdorp Game Reserve, and to areas of intense anthropogenic activities. The aim of this study was to assess sediment toxicity using an integrated approach focusing on the chemical and physical analysis of water and sediment, use of the Phytotoxkit-F bioassay, and multivariate statistical analysis. Site 1 was associated with a high fraction of fine (<212 μm) sediment particles and moisture content, while both Site 2 and Site 3 were associated with an increase in Total Organic Carbon (TOC) and fine sediment particles. Metals of concern were Copper (Site 2), Arsenic (Sites 1 and 2), Chromium, Nickel, and Zinc (all sites). These metals all exceeded the ANZECC/ARMCANZ SQG values. Bioassay analysis revealed stimulated growth of the roots of the different plant seeds during the wet season and inhibited growth during the dry season. Sinapis alba and Sorghum saccharatum were identified as the most sensitive plant species, respectively. The use of an integrated approach to assess sediment toxicity was successful and revealed that sites 2 and 3 presented the highest toxicity during the wet and dry seasons, respectively. The aim and the objectives of this study were met, and the findings of this study revealed that there is an introduction of contaminants and sediment deposits from upstream in the Tweelopiespruit, posing a long-term threat to the downstream sites.