Polycyclic aromatic hydrocarbons (PAHs) in the river Rwizi watershed in Uganda: Occurrence, sources, ecological and human health risk assessment

Sixteen (16) priority polycyclic aromatic hydrocarbons (PAHs) were determined in the River Rwizi water and sediment in order to evaluate the sources, extent of pollution, and potential risk posed to ecological and human health. The PAHs were quantified using gas chromatography with a mass spectrometer detector (GC-MS). The sources were identified using diagnostic ratios, and ecological risk was assessed using the Mean Effect Range Median Quotient (M-ERM-Q). Human health risk was evaluated using Incremental Lifetime Cancer Risk (ILCR). Analytical method performance was assessed based on recovery, limits of detection and quantitation, and linearity. All the16 PAHs were detected in surface water, sediment and wastewater released from stabilization ponds in Mbarara City, in the ranges of ND-87.722 µg/L, ND-389.110 µg/kg, ND-142.196 µg/L respectively. PAH sources were pyrogenic and the upper reaches of the River Rwizi were more impacted. Ecological risk was low to medium, while human health risk from drinking untreated river water was high for both children and adults. Risk associated with accidental drinking of water during swimming was negligible to acceptable. The occurrence of PAHs at concentrations higher than the World Health Organization guidelines threatens ecological and human health; therefore, mitigation efforts are urgently required.