Polycyclic aromatic hydrocarbons loads and potential risks in freshwater ecosystem of the Ikpa River Basin, Niger Delta-Nigeria

In this study, the levels of 16 USEPA-prioritized polycyclic aromatic hydrocarbons (PAHs) were quantified in various environmental matrices in Ikpa River Basin and nearby dumpsites using gas chromatography- mass spectrometry (GC-MS). The levels of the contaminants were further subjected to models to estimate possible sources and potential risks. The results obtained revealed that nearby dumpsites could be the major source of contamination of the Ikpa River Basin. The total sum of PAHs in water and sediment samples gave 926.6 mu g/l and 1099.7 mu g/kg, respectively. Higher concentrations, 3025.8 mu g/kg, 3645.7 mu g/kg, and 2457.2 mu g/l, were recorded for nearby municipal dumpsite soil, hospital dumpsite soil, and landfill leachates, respectively. Hierarchical cluster analysis (HCA) and PAH molecular diagnostic ratios (MDRs) suggest that PAH loading in the river basin were mostly of pyrogenic origin. The risk assessment indicated that exposure to PAHs through dermal contact with sediments was most significant than oral ingestion of water and children were the most vulnerable group. Noncancer (toxic) risks due to exposure to PAHs by oral ingestion of water from Ikpa River were within acceptable limits as the calculated hazard quotients (HQs) and hazard indexes (HIs) were below unity, suggesting negligible or no toxic risk. However, toxic risks through dermal contact with sediments reached unacceptable limits as HI values exceeded unity for all sample stations. Estimated cancer risks due to oral ingestion of water reached the USEPA minimum risk level (3.14x 10(-5)) requiring public notification while risks due to dermal adsorption of PAHs from the sediments reached levels (2.10x10(-1)) requiring remediation actions.