Source apportionment, ecological and health risk assessment of potentially toxic elements in water, sediment and blackchin tilapia {Sarotherodon melanotheron (Rüppell 1852)} from Lagos and Ologe Lagoons, Lagos State, Nigeria

Background

Lagos and Ologe Lagoons are parts of the Lagos Lagoon Complex, which provide fish as an animal protein source to the locals. However, these fish species have a high propensity to accumulate pollutants including Potentially Toxic Elements (PTEs) from their environment. This potentially constitutes a health risk to fish consumers. Therefore, this study investigated concentrations of some PTEs (As, Cd, Cr, Cu, Fe, Pb, Ni, and Zn) in water, sediment, and fish (Sarotherodon melanotheron) from Lagos and Ologe Lagoons, the ecological and health risks associated with the consumption of the fish as well as the likely sources of the PTEs.

Methods

Water, sediment, and fish (S. melanotheron) samples were collected monthly for ten months (June 2022 - March 2023) from three sites: Badore and Baiyeku in Lagos Lagoon and Ologe Lagoon. The concentration of PTEs was determined in the environmental matrices {water, sediment, and three organs (gill, muscle, liver)}. The range of values for method detection limits (MDL), limits of detection (LOD), limits of quantitation (LOQ), and recovery rates were 0.01 – 0.025 mg kg⁻¹, 0.00002 – 0.002 mg L⁻¹, 0.0001 – 0.0067 mg L⁻¹ and 97.19±2.45 - 99.85±1.16% respectively. The ecological risk of PTE in water and sediment was assessed by various indices. Estimated dietary intake (EDI), health risk index (HRI), and target hazard quotient (THQ) were the human health risk assessment indices employed. The distribution and source of the PTEs were analyzed using the coefficient of variation, Pearson's correlation matrix, principal components analysis, and hierarchical cluster analysis.

Results

The water and sediment quality assessment indices indicated that the water and sediment from the lagoons had low contamination with respect to the eight PTEs studied. EDI values were generally less than 1 except for Fe and Zn. THQ for all PTEs in the three sampling stations and across the different population groups was less than 1 except for Fe. PCA revealed two major sources of PTE pollution which are natural and anthropogenic. As, Cd, Cr, Cu, and Pb were probably due to anthropogenic inputs like agricultural operations and industrial activities while Fe, Ni, and Zn may have occurred due to lithological sources like rock weathering and volcanic events.

Conclusion

Based on the result of the study, the waters from the lagoons are still suitable for agricultural usage. The sediments are also largely uncontaminated with respect to the eight PTEs studied. The EDI and THQ show that consumption of S. melanotheron from the sites may not constitute any significant health risk to humans and the sources of the PTEs are lithologic and anthropogenic.