Seasonal congener survey for polychlorinated biphenyls in sediments of south-western rivers, Nigeria: Occurrence, sources, and ecotoxicological risks

Abstract

In this work, sediment samples from major rivers within southwestern Nigeria were collected to study the seasonal distribution, transport, and ecological risk assessment of polychlorinated biphenyls (PCB) using gas chromatography coupled with an electron capture detector (GC–ECD). The ΣPCB concentrations ranged from 9.86–77.56 μg/kg and 11.88–80.76 μg/kg in dry and wet seasons respectively. The most predominant PCBs congener in all the sediments was 2,2’,4,5,5’-PeCB(#101) with mean concentrations of 4.35 ± 2.96 and 6.10±3.38μg/kg across all locations in dry and wet seasons respectively. Relevant guidelines including sediments quality guidelines (SQGs) mean effect range-median quotient (m-ERM-Q), and toxic equivalent factor (TEF) were used for risk assessment and to evaluate the ecological risks of PCBs across the rivers. The toxic equivalent quantity (TEQ) ranged from 0.044–0.807 μg-TEQ/kg and 0.055–0.825 μg-TEQ/kg for the dry and wet seasons respectively. The non-ortho PCBs congeners constituted ≥ 99.8% of the ∑TEQ values. The seven indicators PBCs for evaluating non-dioxin-like PCBs ranged from 3.70–32.69 μg/kg across the seasons and accounted for 33.4%, 39.8%, 36.8%, 37.9%, 41.4%, and 40.4% of the ∑PCBs at Asejire, Odo Ona, Ogbese, Ogun, Ikorodu rivers and Third Mainland Bridge Ocean respectively. In two out of six rivers, the ∑PCBs exceeded the Canadian SQG threshold effect level of 21.5 and 34.1μg/kg for fresh and marine sediments respectively. The results of the study call for a concerted effort toward holistic monitoring of PCB residues in rivers in Nigeria to ensure ecological integrity and the protection of human health.