Polycyclic aromatic hydrocarbons (PAHs) in the aquatic ecosystems of Soweto and Lenasia

Abstract

In South Africa, our scarce water resources are fully utilised and its quality threatened by pollution and therefore must be protected. One of the pollutant classes of concern is the polycyclic aromatic hydrocarbons (PAHs). PAHs are widely distributed, constantly released into the environment making them persistently present. Sixteen priority congeners have been identified by the USEPA to be monitored and controlled based on their proven harmful effects on humans and wildlife.The main purpose of this thesis was to study the potential exposures of humans and wildlife to the 16 priority PAHs in Soweto and Lenasia—an area known to have high levels of these contaminants. The aims were: to determine the levels of the PAHs in the sediments, fish (Clarias gariepinus) and wetland bird eggs from the aquatic ecosystem of the Klip River in the densely populated study area; determine the origins of the PAHs (pyrogenic or petrogenic); finally, to determine the toxicity posed by these PAHs to wildlife and humans. The levels of the PAHs in the matrices were determined by instrumental analysis. The target compounds were extracted for quantification using specific methods for the abiotic matrix (sediment) and the biotic (fish muscle and bird eggs). Sediments were subjected to accelerated solvent extraction, size exclusion chromatography and solid phase clean-up techniques. The biotic samples followed the liquid-liquid extraction based method known as QuECHERS. Biliary metabolites in the fish were isolated by first deconjugation followed by liquid-liquid extraction. The native PAHs were quantified with gas chromatography and time-of-flight mass spectrometry (GC-TOFMS) and the metabolites with high pressure liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS). The pollutant profile was calculated by percentage congener contributions and potential origins were determined by diagnostic ratios. The toxicity assessment was a multi endpoint approach: Overall toxicity, sediment quality, and ecological risk were assessed by comparing concentrations to international sediment quality guidelines (SQGs) and calculating sediment quality indices. Investigating specific toxicity via the aryl-hydrocarbon receptor was measured using the H4IIE-luc reporter gene bio-assay and compared with toxic equivalence quotients (TEQs). The reaction of fish to environmental stressors was investigated on biochemical level with biomarker assays. These included biomarkers of exposure, oxidative stress, oxidative damage, and cellular energy allocation. Furthermore, individual and community fish health were assessed using various fish health indices. Finally, the potential health risk to the human population dependant on the water bodies was gauged by conducting a theoretical human health risk assessment. The levels of the ΣPAHs in the sediments for both sampling surveys ranged between 274–5 369 ng/g, which were dominated by 3-and 4-ring congeners, mainly from biomass combustion. Evidence of PAHs in the biotic matrices was seen in the form of low levels of low molecular mass PAHs in the eggs, and biliary metabolites (63–1 879 ng/mL) in the fish. Moderate to high toxicity was predicted for benthic organisms, fish, and mammalian systems, based on the instrumentally derived PAH sediment concentrations using international SQGs, sediment indices, and TEQs. These were comparable to the real biological responses of the H4IIE-luc reporter gene bioassay proving the usefulness of this bioassay. The clear responses of the biomarkers showed that the fish from the study area were exposed to xenobiotic stressors and there was strong evidence that these were responses to PAHs. The overall health of fish was visibly affected by environmental stressors (such as pollutant exposure, seasonal changes, and water parameters) and proven to be in poor health. Various routes of human exposure were investigated and the greatest cancer risk was from intentional ingestion and dermal exposure to the sediments. The greatest cancer risk was 227 in 10 000.