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The concentrations of 28 polychlorinated biphenyls (PCBs) were determined in soils collected at three depths from thirteen different sites along the floodplain of the lower reaches of the River Niger (LRRN) in Nigeria. The aim of the study was to provide data on the levels of contamination, sources of the contaminants, and risks to the ecosystem and humans. Soil samples were Soxhlet extracted with a solvent mixture of dichloromethane (DCM)/n-hexane and cleaned up on a column packed with Florisil and silica gel. The PCBs in the samples were quantified by gas chromatography-mass spectrometry. The Ʃ28 PCB concentrations in the floodplain soils varied between not detected (nd) and 11,151 ng g−1 for different sampling sites and depths. The PCB concentrations and homologue distribution patterns in soil profiles of the floodplain of the LRRN showed remarkable differences with respect to sites and depths. The results obtained were used to evaluate the ecological and human health risks, which indicated that there is a potential risk to organisms and humans from exposure to PCBs in these soil profiles. The source evaluation as determined by principal component analysis suggested that PCBs in these soil profiles came from burnt circuit boards, cable wires, use of paints, discharges from transformers, long-range migration, and deposition. [ABSTRACT FROM AUTHOR]

The concentrations of the 16 US EPA polycyclic aromatic hydrocarbons (PAHs) were determined in the floodplain soils of the lower parts of the River Niger, Nigeria in 2013 and 2014 after recent flood waters had receded completely into the river channels. The aim of the research was to provide data on the spatiotemporal changes in the contamination levels, compositional patterns, sources and human health risks linked with exposure to PAHs in these soils through non-dietary ingestion, inhalation and dermal contact pathways. The PAHs in the soil samples were extracted by ultrasonication with hexane/dichloromethane, followed by clean-up on a silica gel/alumina column, and gas chromatography-mass spectrometry was used for their separation, detection and quantification. The concentrations of the 16 PAHs varied from 812 to 10,700 µg kg−1 in 2013 after an extreme flooding event, and from 12.2 to 2630 µg kg−1 in 2014 after a natural flooding event. The benzo[a]pyrene (BaP) potency factors and incremental life cancer risks (ILCR) were used to evaluate the risks of human exposure to PAHs in these soils. The average total ILCR values obtained for 2014 (a year after the extreme flooding) indicated that there was a probability of 443 children and 308 adults in a population of one million equally exposed individuals at risk of developing cancer or cancer-related illnesses in their lifetime as opposed to 6450 children and 4480 adults in 2013 immediately after the extreme flooding event. This study has shown that flooding events can cause significant variations in pollutant concentrations of floodplain soils that markedly alter human health risks. [ABSTRACT FROM AUTHOR]