Concentrations and Distribution of Trace Metals in Water and Streambed Sediments of Orogodo River, Southern Nigeria

Abstract

The distribution of Cd, Pb, Ni, Cr, Cu, Mn, Fe, and Zn in sediment and surface water, and some physico-chemical characteristics of Orogodo river sediments, were evaluated. The sediment pH ranged from 5.1–7.3; conductivity values ranged from 34.5 to 389.0 μScm⁻¹. Total nitrogen values ranged from 0.06–0.10%, NH₃-N values ranged from 0.25–0.44 mgkg⁻¹, percent total organic carbon ranged from 0.21–1.68%, and total phosphorus values ranged from 0.004–0.02% for dry and wet seasons. The sand fraction consists of 87–95%, silt fractions ranged from 0–2%, and clay fraction between 4–13%. The mean concentrations of metals (dry weight basis) in the streambed sediments ranged from 1.92–17.37 mgkg⁻¹ for Cu, 0.98–4.78 mgkg⁻¹ for Ni, 0.01–32.98 mgkg⁻¹ for Mn, 353.22–2045.64 mgkg⁻¹ for Fe, 69.96–100.16 mgkg⁻¹ for Zn, 0.21–1.32 mgkg⁻¹ for Cr, and Cd was less than 0.001 mgkg⁻¹ for wet and dry seasons. The mean concentrations of metals in the surface water ranged between 0.01–0.05–0.05 mg/L for Cu, nd-0.11 mg/L for Ni, 0.001–0.31 mg/L for Pb, 0.001–1.82 mg/L Mn, 0.01–3.52 mg/L for Fe, 0.16–0.61 mg/L for Zn, nd-0.007 mg/L for Cr, and <0.001 mg/L for Cd. Based on principal component analysis, two main sources of metals in the Orogodo River can be identified: (i) Cr, Cu, Pb, and Fe are mainly derived from industrial sources; (ii) Mn, Zn, and Ni associated with traffic activities. No element examined had a contamination/pollution index value greater than unity (pollution ranges). This implies that the multiple pollution indices obtained from the analysis showed that Orogodo River sediments were not polluted with heavy metals.

Keywords:

• Metals
• contamination/pollution index
• sediment
• Orogodo River
• southern Nigeria

Acknowledgement

The authors are grateful to Dr. Kingsley Opuene of Nigeria Agip Oil Company, Nigeria, for his assistance in both the laboratory and statistical analysis.

Notes

*derived from global average (Alloway, 2005).