Assessment of the distribution of potentially harmful trace elements in bedrocks and stream sediments of Okemesi-Ijero area, Southwestern, Nigeria

Abstract

Assessment and distribution of the concentration of potentially harmful trace elements (PHTEs) is important for environmental health management. The concentrations of thirteen PHTEs were determined in the stream sediments and rocks samples from the underlying bedrock with the use of inductively coupled plasma-mass spectrometry (ICP-MS). Multivariate statistics and principal component analyses were used to identify and characterize trace elemental associations in the system. Trace elements ranged from 0.01 mg/kg as found in Cd concentration to 1591.00 mg/kg as found in Mn. Trace element concentrations vary from one location to another. The geochemistry of the underlying rocks including granite, quartzite and banded gneiss were far lower in metal concentration compared to that of the stream sediments. The concentrations of U (0.40 – 14.40 mg/kg), Mn (51.00 -1591 mg/kg) and La (7.10 – 364.90 mg/kg) were of great concern to the ecosystem because of their relatively higher values in the stream sediments compared with the control, which is the average earth crust values. The results of enrichment factor and ecological risk index showed that Cu, Pb, As and Cd did not raise any eco-toxicological concern. From the results of the other elements analysed, there were considerable lower metal enrichment in terms of contamination status when compared with the background values. Metals such as Cr, Mn, Pb, Zn, Cu, Ni, V, As, Th, Cd, and La were positively correlated with each other (r = 0.51 -0.95), which indicated analogous sources of geochemical characteristics. However, from the result, it is seen that there is considerable input of the metal concentration in the stream sediments possibly from man induced activities of these PHTEs in the drainage system of the catchment areas.