Polycyclic Aromatic Hydrocarbons in Kenyan Coral Reef Sediments: Distribution, Sources, and Equivalent Ecological Risks

Abstract

This study evaluated the spatial distribution, source apportionment, and equivalent ecological risk of polycyclic aromatic hydrocarbons (PAHs) in 18 surface sediments across four Kenyan coral reef ecosystems (Malindi, Watamu, Kilifi, and Mombasa-Nyali). Total PAH concentrations (∑PAHs) averaged 1.24 ng·g−1 (0.19–7.63 ng·g−1), with Kilifi recording the highest levels (mean: 3.45 ng·g−1) and Malindi showing baseline levels an order of magnitude lower (mean: 0.32 ng·g−1). Diagnostic ratios and principal component analysis (PCA) revealed a clear pollution gradient dominated by pyrolytic sources Phe/(Phe + Ant) > 0.6; Flu/(Flu + Pyr) = 0.52). Heavy PAH ratios indicated mixed gasoline vehicular exhausts and biomass burning BaA/(BaA + Chr): 0.37–0.42 and IP/(IP + BghiP) mean: 0.44), with PCA confirming a strong vehicular signature (F1, 73.61), notably in Kilifi stations and secondary biomass burning inputs (F2, 10.83%). In contrast, baseline sites of Malindi and Watamu Marine Park were influenced by localized petrogenic inputs from leisure boats and Sabaki riverine discharges. Sediment quality guidelines indicated below 0.1, corresponding to a <10% probability of adverse biological effects. Overall, these sedimentary environments present a negligible immediate threat to benthic communities, though potential long-term bioaccumulation highlights the need for monitoring.