Seasonal variations, source apportionment, and risk assessment of polycyclic aromatic hydrocarbons (PAHs) in sediments from Klip River, Johannesburg, South Africa

The widespread occurrence of polycyclic aromatic hydrocarbons (PAHs) in water bodies is a significant cause of concern due to their persistence and toxicity. This study aimed at assessing the qualitative and quantitative profile of 16 EPA PAHs present in sediment collected from nine sites along the Klip River, Johannesburg, South Africa. The target compounds were extracted from sediment by microwave-assisted extraction (MAE). The extraction method accuracy was evaluated by analyzing certified reference material of sediment (CRM-104). The total concentration of PAHs detected in sediment samples ranged from 1.46 to 7.41 mg/kg. High molecular weight (HMW) PAHs were found to be in higher concentrations for both low flow (24.5 mg/kg) and high flow (19.4 mg/kg) seasons compared to the lower molecular weight (LMW) PAHs, which had 11.1 mg/kg for low flow and 5.63 mg/kg for high flow seasons. For identification of source of PAHs in sediments, the diagnostic ratio was employed, which revealed the PAHs were from petrogenic and pyrogenic sources. Toxicity test using zebrafish embryo development test (ZFET) resulted in high mortality, low hatch rate, and high malformations, which indicated the contamination of sediments from the Klip River. These findings suggest that exposure to this water system poses risks to the environment, aquatic life, and humans who depend on it.