Contamination levels of potentially toxic elements within the Ogun River estuary sediments, southwest Nigeria: Ecological and human health risk assessments

Background

The Ogun River estuary is located at the northwestern corner of the Lagos Lagoon in southwest Nigeria. Metal smelting, petroleum products transport, sewage disposal and chemical production are activities within this region, which could lead to the release of potentially toxic elements (PTEs) into the immediate environment. This study investigates the contamination levels of PTEs in the Ogun River estuary sediments, with emphasis on ecological and human health risks.

Methods

Fourteen sediment samples were collected from the estuary through the Ogun River and Majidun environments. These samples were analyzed for PTEs including Cd, Co, Cu, Fe, Mn, Ni, Pb and Zn using Inductively Coupled Plasma-Mass Spectrometer (ICP-MS). The contamination levels of sedimented PTEs from selected sample sites in the estuary were documented for ecological and health risk assessments.

Results

The analysis revealed bulk concentrations of PTEs across the sampling stations. The contamination factor (CF) showed high contamination levels for Cd and Zn at sample sites 2, 14 and 16; while the other metals revealed moderate pollution indices across all the sites. The risk factor (Er) values of Cd at stations 2, 15 and 16 showed potential contamination. The canonical correspondence analysis (CCA) signified that the distribution of the PTEs is independent of the environmental factors, exposing significant anthropogenic input. Evaluations of the sediment quality revealed that PTEs such as Cd, Cu, Ni, Pb, and Zn, whose concentrations are above their TECs and ERLs, have little to no detrimental effects on sediment living organisms. The health risk assessment has shown that HI values for the elements fall within the non-carcinogenic risk range. The effects of the mean concentrations of these metals on the non-carcinogenic risk (HQ) for adults and children in decreasing order of impact are Co > Pb > Mn > Ni > Cd > Cu > Zn > Fe for both ingestion and dermal pathways. The human health risk index varies from low cancer risk in adult (LCR = 4.4 × 10⁻⁵) to moderate cancer risk in children (LCR = 4.1 × 10⁻⁴).

Conclusion

This study has revealed the significance of anthropogenic input of PTEs into the environment. The sedimented PTEs are within permissible range, but monitoring and assessment activities should be focused on the Majidun axis since most metals show high concentration in this region.