Polychlorinated biphenyls (PCBs) in intertidal sediment and water from Lagos lagoon: Baseline report on occurrence, distribution and ecotoxicological risk assessment

To assess the occurrence and potential ecological risk associated with organic micropollutants in Lagos lagoon, 27 polychlorinated biphenyls (PCBs) were analysed in sediments and surface water. Sediment samples were obtained from 18 designated sites (SD1 - SD18) using a Van Veen grab sampler and extracted following standard procedures. Cleaned extracts were analysed using gas chromatography with electron capture detector (ECD). The concentration of EPCBs in sediment samples ranged between 6757.61 and 273.46 mu g/kg. The PCB homologues distribution patterns in sediments indicated that the low-chlorinated (Sigma di-PCB - Sigma penta-PCB) PCBs were more dominant with 61.1 % occurrence than the high-chlorinated ((Sigma hexa-PCB - Sigma nona-PCB) PCBs with 38.9 % relative abundance. The following is the decreasing order of the average homologue composition of PCBs in sediment samples: Sigma tetra-PCB (24.6%) > Sigma octa-PCB (21 %) > Sigma hexa-PCB (13.8 %) > Sigma penta-PCB (12.8) > Sigma tri-PCB (11.4 %) > Sigma hepta-PCB (7.8 %) > Sigma nona-PCB (4.9 %) > Sigma di-PCB (2.9 %). More so, the Sigma PCBs in surface water samples ranged from 69.28 to 440.90 ng/L, with the mean ranging between 7.21 and 16.33 ng/L. The class distribution of PCB homologue profiles in water samples indicated that highly-chlorinated (Sigma hexa-PCB to Sigma nona-PCB) PCBs were the dominant homologues, with 94.4 % occurrence, compared to the very low occurrence rate (5.6 %) of the low-chlorinated (Sigma di-PCB to Sigma penta-PCB) PCBs. Hexa-PCBs (PCB-138 and PCB153) were the dominant congeners in most water samples. The concentrations of Sigma PCBs in sediments and surface water were unprecedentedly high at almost all locations. The total toxicity equivalent concentrations (TTECs) of dioxin-like PCBs for the sediment samples ranged from 0.001 to 2.43 mu g/kg, with an average of 0.34 mu g/kg. These findings suggest that PCB congeners are pervasive from anthropogenic point sources of pollution. Intensive site-specific monitoring and remediation are recommended.