Ecological Risk Assessment of Trace Metal Pollution in an Urban Agricultural Area of Yaoundé (Cameroon)

The presence of trace metals in urban agriculture is considered as a major factor for ecological risk. The aim of this research was to determine the concentrations of metals in market garden soils in the city of Yaoundé, Cameroon, in order to assess the degree of soil pollution and evaluate potential ecological risks. Forty-five composite soil samples were taken from three market garden sites in Yaoundé. Trace metals (Cd, Cr, Cu, Mn, Ni, Pb, and Zn) were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). The geochemical background threshold values for trace metal contents were determined and the multi-element indices of pollution and ecological risk were calculated. The results showed that concentrations of selected metals in soil varied considerably from one element to another ranging from very high to low levels: Mn > Cu > Zn > Cr > Pb > Ni > Cd. The median valuesof Cd, Cr, Cu, Mn, and Zn were below the geochemical background threshold values. For the Ni and Pb metals, the median values were higher than those of the geochemical background threshold values. The Nemerow Pollution Index (NPI) indicated that 60% of the samples had a significantly high level of pollution. However, the Potential Ecological Risk Index (PERI) indicated that only 16% showed a very strong ecological risk. This study can be used as a baseline to develop future long-term risk assessment strategies on the potential of metal migration in agricultural soils.