Occurrence, depth distribution and risk assessment of PAHs and PCBs in sediment cores of Lagos lagoon, Nigeria

Polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in sediment cores of the microtidal coastline of Lagos lagoon were investigated for the occurrence, sources and depositional contamination history. Sediment core samples were collected using the Wildco @ hand corer (50 cm) SS kit and extracted using a 40 mL mixture of hexane and acetone (1:1), and cleaned-up using 10 mm ID chromatographic column before the concentration of aliquots. In this investigation, 16 US EPA priority PAHs and PCB congeners were analysed in aliquots of sediment cores using Agilent 7820A gas chromatograph coupled to a 5975C inert mass spectrometer (with triple-axis detector) with an electron-impact source. PAHs and PCBs were detected at varying concentrations across the 50 cm depth of each sediment core. The total PAH concentrations ranged from 1.43–5.90 mg/kg, and were more widely distributed than the total PCBs. The total PCB concentrations ranged from BDL – 6.41 mg/kg. The PAH diagnostic ratios used identified the sources of the PAHs as pyrogenic rather than petrogenic. About 52% of the samples had concentrations above the ERM limit for total PCBs, suggesting that adverse effects on biota may occur in the long term. In general, the PAHs and PCBs concentrations detected in sediment cores of the Lagos lagoonal system may pose a considerable ecotoxicological risk to estuarine organisms