Assessment of persistent organic pollutant accumulation in sediments of Klip river Wetland,Johannesburg

Olasupo, Ayo
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The Klip River wetland located south of Johannesburg is economically significant and serves as an important source of water and purifier of pollutants originating from mining and industrial activities occurring within the Witwatersrand Basin. Importantly, the Klip River is also a source of water to the Vaal Dam, which serves Johannesburg with portable water. Previous investigations have revealed that the upper reaches of the Klip River wetland sequester high levels of inorganic pollutants associated with mining activities. This study was initiated to investigate the accumulation and potential source of Polyaromatic Hydrocarbons (PAHs) and Polychlorinated Biphenyls (PCBs) in sediments from the Klip River wetland. PAHs and PCBs were found to be widely distributed in the surface sediments of two main tributaries entering the wetland. Total PAH concentrations were in the range of 44 – 95 mg/kg, while total PCB concentrations ranged from 0.2 – 5.3 mg/kg. The spatial distribution of PAHs showed that upstream sites were more polluted, which was attributed to the proximity of these sites to heavy traffic and industrial complexes. Conversely, the spatial distribution of PCBs showed increasing contamination downstream, which was ascribed to anthropogenic activities from the residential settlements of Soweto and Lenasia. A sediment core from the wetland revealed lower levels of contamination, with total PAH and PCB concentrations in the range of 2.4 – 6.3 mg/kg and 0.17- 0.80 mg/kg, respectively. PAH and PCB concentrations increased with depth, indicating a potential groundwater source of pollution. Potential source identification using a combination of different PAH isomeric ratios, indicated a mix petrogenic and pyrogenic sources of contamination, with petrogenic sources having a stronger influence. PCB congeners indicated a potential source of contamination originating from dielectric fluids in electric transformers and industrial capacitors. Ecological risk assessments conducted using National Oceanic and Atmospheric Administration’s (NOAA) sediment quality guidelines indicated a probable adverse effect to aquatic life and possibly human health for most of the PAH and PCB congeners investigated. A further risk characterisation of the sites indicated that about 60% of the investigated sites could be classified as moderately to highly polluted sites with potential ecological risk. A further and more in-depth investigation is therefore needed to assess the bioaccumulation and biomagnification of contaminants within the Klip River system and determine the ecotoxicological impact this has on both aquatic health and humans who rely on resources from the Klip River wetland.
A dissertation submitted to the Faculty of Science, University of the Witwatersrand in fulfillment of the requirements for the degree of Master of Science , University of the Witwatersrand, Johannesburg, July 2018
Olasupo, Ayo (2018) Assessment of persistent organic pollutant accumulation in sediments of the Klip River Wetland, Johannesburg, University of the Witwatersrand, Johannesburg,