Distribution and ecological risks of toxic metals in the topsoils in the Kumasi metropolis, Ghana

Godfred Darko,David Dotse Wemegah,Marian Asantewah Nkansah,Matt Dodd,Lawrence Sheringham Borquaye,Eugene Ansah,Yaw Aduse-Poku,Peter Fantke

doi:10.1080/23311843.2017.1354965

Abstract

The distribution, and ecological risks due to toxic metals in topsoils of an urban commercial centre of Kumasi metropolis were determined. Concentrations of heavy metals in the samples were initially screened using field portable X-ray fluorescence spectrometer prior to confirmation on an inductively coupled plasma-mass spectrometer. The results from the two instruments correlated well with high linearity (R2 > 0.70). Concentrations of metals were in the order: Fe (45246.15 mg/kg) > Mn (347.86 mg/kg) > Zn (176.40 mg/kg) > V (173.10 mg/kg) > Cr (125.12 mg/kg) > Pb (53.47 mg/kg) > Ni (43.16 mg/kg) > Cu (39.85 mg/kg) > As (4.59 mg/kg) > Sn (3.69 mg/kg) > Cd (0.46 mg/kg) > Hg (0.28 mg/kg). Multivariate and geostatistical analyses exploring various hazard indices such as geo-accumulation, contamination, pollution load and ecological risks all suggest contamination of the topsoils with toxic metals and that the contamination due to Pb, Cu, Ni, Cr and Zn is mainly derived from anthropogenic origins whereas, As, Hg, Mn, V, Sn and Cd contaminations are attributable mainly to geological and atmospheric depositions. Contamination factor (CF) suggests that the topsoils were considerably contaminated (CF 3–6) with Zn, moderately contaminated (CF 1–3) with Ni, Hg, V, Sn and Cd and least contaminated (CF < 1) with As, Pb, Cu, Cr and Mn. In general, the soils were found to be moderately contaminated (average contamination factor (1 ≤ CF < 3) with toxic metals and may pose both human and ecological risks.

Highlights

IntroductionUsually present in varying concentrations in urban topsoils, may originate either from natural sources (through lithogenesis, pedogenesis) or from anthropogenic sources (including industrial activities) such as metal processing, combustion of fossil fuel, and mining (Luo, Yu, & Li, 2012; Rodríguez Martín, Arias, & Grau Corbí, 2006)
Metals, usually present in varying concentrations in urban topsoils, may originate either from natural sources or from anthropogenic sources such as metal processing, combustion of fossil fuel, and mining (Luo, Yu, & Li, 2012; Rodríguez Martín, Arias, & Grau Corbí, 2006)
Overall the data obtained in this study shows that the field portable X-ray fluorescence (FP-XRF) is a useful analytical instrument for screening a large number of samples of soil for most metals prior to the use of a more sensitive analytical instrument in the laboratory

Summary

Introduction

Usually present in varying concentrations in urban topsoils, may originate either from natural sources (through lithogenesis, pedogenesis) or from anthropogenic sources (including industrial activities) such as metal processing, combustion of fossil fuel, and mining (Luo, Yu, & Li, 2012; Rodríguez Martín, Arias, & Grau Corbí, 2006). Unmonitored industrial and human activities generally contribute significantly to the levels of metal contaminants in the top layers of the soil relative to contributions from natural sources. Toxic metals such as arsenic, cadmium, mercury and lead are mainly introduced into the topsoils of urban settings through human activities (Adelekan & Alawode, 2001; Bak, Jensen, Larsen, Pritzl, & Scott-Fordsmand, 1997) and could potentially pose a threat to the ecological environment as well as human health (Glennon, Harris, Ottesen, Scanlon, & O’Connor, 2014; Wong, Li, & Thornton, 2006). For micro-organisms, the toxic effects of the metals may occur at the surface of their external membranes.

Methods

Results

Conclusion