Characterisation of exposure and biological effects of contaminant of emerging concerns in Thukela and Mhlathuze River systems
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Date
2022-04
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Abstract
Rivers, estuaries, and oceans are exposed to a cocktail of pollutants, including contaminants of emerging concern (CECs). This study aimed to examine the extent of contamination and/or pollution of selected contaminants of emerging concern in the uMhlathuze and uThukela River-estuaries, following the source-to-sea approach. Microplastics, organic pollutants, engineered nanomaterials (ENMs) and metals were analysed in surface water samples, and accumulation of metals and biomarker response (acetylcholinesterase enzyme) were examined in the mud crabs Chiromantes eulimene. Thirty-eight organic compounds were detected in surface water samples from the uMhlathuze River-Estuary, which belonged to 14 classes of pharmaceuticals and lifestyle drugs, and 20 compounds were found in the uThukela River-Estuary, belonging to 13 therapeutic compound classes. The differences in detection frequency of compounds illustrated differences in pollution sources and consumption rates, due to differing land-use activities and disease burdens. Pesticides were also found in surface water samples, with a total of 13 herbicides, insecticides and fungicides in the uMhlathuze and 14 in the uThukela Estuary. Herbicides were the dominant pesticide class in both systems. The presence of pesticides was linked to agricultural activities in both catchments. Microplastic concentrations decreased towards the sea, and wastewater treatment works (WWTWs) did not appear to be a major source. Microplastics were detected in all surface water samples and were composed of fibres and films. Fibres were numerically dominant. Poly(propylene) (PP), polycarbonate (PC), nylons (NY), low density poly(ethylene) (LDPE), high-density poly(ethylene) (HDPE), poly (ethylene terephthalate) (PETE), poly (ethylene vinyl acetate) + poly (cyclohexanone) (EVA + poly(cyclohexanone)), poly (butyl acrylate) (PBA) were the dominant plastic polymers found in the uMhlathuze River-Estuary. In uThukela River-Estuary, PETE, NY, PP, PBA and low-density poly(ethylene) (LDPE) were dominant polymers. Engineered nanomaterials (ENMs) such as titanium dioxide (TiO2), silicon dioxide (SiO2), zinc oxide (ZnO), iron oxide (Fe2O3) and copper oxide (CuO) nanoparticles were also recovered from surface water samples. ENMs were irregular, sheet-like, spherical or hexagonal in morphology. The ENMs were possibly from the use of various domestic xvii nano-enabled products, for example, products manufactured for bathing, laundry washing and personal care products. The concentrations of zinc (Zn), chromium (Cr), aluminium (Al), lead (Pb), nickel (Ni), copper (Cu) and lead (Pb) detected in the studied systems exceeded the DWAF threshold values for freshwater and marine environments. High metal concentrations could be attributed to various industrial and agricultural activities dominating within these systems. Metals also accumulated in crabs, and accumulation varied between seasons. Chromium, Ni and Fe accumulation was also gender specific, with accumulation in females generally higher than in males in the uThukela Estuary. The effluent from domestic use, industries and other related activities are probable sources of metal contamination in these regions. Overall, AChE activity in the gills of C. eulimene was reduced in both systems, which was a negative effect deduced to be caused by contaminants. In conclusion, this study confirmed the occurrence of CECs in surface water samples, and contaminants such as metals were observed to bioaccumulate in crabs
Description
A dissertation submitted in fulfillment of the academic requirements for the degree of Master of Science in the Department of Geography and Environmental Studies in the Faculty of Science, Agriculture and Engineering, University of Zululand, 2022