Polychlorinated biphenyls (PCBs) in rivers of Southwestern Nigeria: sources, seasonal distribution, and assessment of human health risks.
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This study investigated the pollution of polychlorinated diphenyl (PCB) in six major rivers in Southwest Nigeria. Twenty-five PCB compounds were determined using high-resolution gas chromatography coupled with an electron capture detector (GC-ECD). Total PCB (∑PCBs) concentrations varied from 21.92 to 186.17 ng/L during the dry season and 35.22 to 262.32 ng/L during the wet season. Mean concentrations of coplanar PCBs were between 12.84 and 97.41 ng/L across all locations and seasons. Low halogenated PCBs are dominant, accounting for 61.2 % of the total, and show a consistent distribution of homologs. A 3-dimensional principal component analysis (PCA) indicated that most PCBs in the rivers come from similar sources. The ∑PCB concentrations exceeded the USEPA standard of 14 ng/L, posing risks to aquatic life and human health and necessitating further investigation. The Toxic Equivalent Concentration (TEQ) ranged from 0.165 to 1.826, with PCB 126 as the main driver with the highest toxic potency. The estimated hazard index (HI) values for ingestion were between 9.97 × 10-5 and 1.50 × 10-2 for both children and adults, while dermal exposure values ranged from 9.17 × 10-6 to 6.74 × 10-4. However, cancer risk (CR) from water consumption was significant (>10-6) for both age groups, and CR from dermal exposure was substantial (10-6 < CR < 10-4) only for adults. The TEQ, HI, and CR levels indicate that PCB contamination in Nigerian rivers poses significant health risks.