A comprehensive analysis of urban river pollution – the case of the Hennops river in Gauteng Province, South Africa
Date
2023
Authors
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Journal ISSN
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Publisher
University of the Witwatersrand, Johannesburg
Abstract
The water quality of rivers is declining at an alarming rate due to pollution from anthropogenic activities associated with urbanization. To ensure ecological restoration and management of rivers, engaging in pollutant source apportionment, evaluation, and monitoring of water quality is of great significance. The study delivers a comprehensive assessment of the state of pollution in the Hennops river catchment facing pollution threats from rapid urbanization. The water quality assessment of the Hennops river was performed through chemical, microbiological, microplastics analysis and ecotoxicological approaches, spanning from upstream region in Tembisa to the downstream Hartbeespoort Dam. Standard methods were employed to assess physiochemical properties of the river’s water. Electrical conductivity and pH fell within the accepted criteria based on the standard water quality guidelines. However dissolved oxygen (DO) levels were below acceptable limits, ranging from 1.53 mg L-1 to 6.47 mg L-1. This signifies a substantial demand for oxygen in the river, likely due to the discharge of sewage from leaking pipes and wastewater treatment plants. This sewage introduces a high volume of organic matter, leading to an increased oxygen demand in the water. Microbiological pollution
indicators were employed to assess the microbial water quality of the river. The study's findings revealed elevated bacterial counts, with Escherichia Coli (E. coli) reaching up to 2 250 cfu mL-1 upstream and decreasing to 30 cfu mL-1 downstream. These high counts suggest faecal contamination
in the river water. Similar trends were observed with total coliform counts, high coliform counts 170 000 cfu mL-1 in the upstream which remained detectable even downstream and beyond the Hartbeespoort Dam, despite the dilution effects within the dam. The dam was identified as the primary repository for pollution originating upstream. Grab sampling followed by solid phase extraction (SPE) and the passive sampling using a Polar Organic Integrative Sampler (POCIS), were employed as sample preparation methods for preconcentration of methocarbamol, etilefrine, nevirapine, carbamazepine and venlafaxine from river water with subsequent analysis on Liquid Chromatography coupled to quadrupole time of flight mass spectrometry. Both methods yielded good figures of merit with limits of quantification in the range of 0.57 to 2.12 ng mL-1
for POCIS and 0.19 to 1.82 ng mL-1 for SPE. The compounds were detected in the water but at low levels (µgL-1 ), with detected concentrations of carbamazepine in the range 0.62 ng mL-1 – 0.32 ng mL-1 , methocarbamol detected in the range 0.11 ng mL-1 - 0.14 ng mL-1 and venlafaxine 0.50 ng mL-1 – 0.44 ng mL-1 using POCIS. The detected concentrations using SPE were in the range 0.13 ng mL-1 – 0.19 ng mL-1 for carbamazepine, while nevirapine and venlafaxine were detected although below limit of quantification. This underscores the advantage of using passive samplers, which enable the detection of fluctuating contaminant concentrations over time, in contrast to the one-time measurements obtained through grab sampling. In the case of microplastics in the water and sediment samples, five polymer types were identified: polyethylene (PE), polypropylene
(PP), high density polyethylene, (HDPE), polyester and polystyrene. The predominant polymer type in surface water was PE (48.6 %), and that in sediment was PP (52.7 %). PE and PP were the most abundant polymer types in both phases, and as these also the leading polymers in plastics production. 80% of the identified microplastics were found to be fibre with most dominant sizes of 1-2 mm for sediments and 0.5-1 mm in water samples. The conducted tests deemed the river water not suitable for irrigation, drinking or recreational purposes and not capable to support aquatic life.
Description
A dissertation submitted in fulfilment of the requirements for the degree of Master of Science, to the Faculty of Science in the School of Chemistry, University of the Witwatersrand, Johannesburg, 2023
Keywords
River pollution, Water quality assessment, Passive sampling, Microplastics
Citation
Letseka, T.E. (2023). A comprehensive analysis of urban river pollution – the case of the Hennops river in Gauteng Province, South Africa [Masters dissertation, University of the Witwatersrand, Johannesburg