Distribution, source identification and eco-toxicological risks of PAHs in sediments of Aba River at Ogbor-Hill region, Nigeria

Augustine Avwerosuo Chokor and Chimezie Nathaniel Achugwo

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The distribution, identification of potential sources, and eco-toxicological risks assessment of polycyclic aromatic hydrocarbons (PAHs) in the sediments of Aba River at Ogbor Hill segment in Aba, South-Eastern Nigeria was investigated. Composites samples were collected from sediments at five (5) different locations (LT-A, LT-B, LT-C, LT-D & LT-E), and a Soxhlet extraction with dichloromethane (DCM) and GC-MS was utilized to simultaneously determine the sixteen (16) US EPA listed priority PAHs. The total PAHs (∑16PAHs) concentrations was in 481.95–2,562.55 µg/Kg range with average 1,122.64±839.70 µg/Kg. The total PAHs range was below the 4,022 µg/Kg Effect Range Low (ERL) target value for sediment quality guidelines (SQG) indicating that biological health effects would rarely be observed. The dominant PAHs in the sediments were: Nap (13.26%), Flr (11.14%), DaA (11.14%), BaA (9.90%), Pyr (9.15%), and Acy (8.42%). However, the major contributors to sediments’ toxicities were: DaA (65.32%), BaP (23.55%), BaA (5.80%), BbF (2.27%), and IcP (1.36%). The order of toxicities of the locations based on normalized toxicity equivalence quotients (TEQs) were; LT-B > LT-E > LT-D > LT-A > LT-C.  Source diagnostic ratios of PAHs gave range of: ∑LMW/∑HMW (0.75–2.73), Ant/(Ant + Phe) (0.14–0.80), Flt/(Flt + Pyr) (0.10–0.77), BaA/ (BaA + Chr) (0.83–1.00), and IcP/ (IcP + BgP) (0.5); suggesting that the anthropogenic source of PAHs was of mixed origin–combustion (pyrogenic) and unburned petroleum. The result revealed the accumulation of PAHs in the sediments at elevated level, which need to be monitored regularly to avoid their negative impact on the living organisms.