Identifying the potential of some heavy metals toxicity in urban and peri-urban cropping systems in Sierra Leone

Abstract

As an essential coping strategy for providing the vital augmentation of food stocks in urban centers, there has been a considerable expansion of urban and peri-urban agriculture in Sierra Leone since the end of the civil war in 2002. In many of these urban and peri-urban cropping sites, sources of water are usually polluted by urban wastes posing potential risk of heavy metal toxicity. This study was carried out to determine the risks associated with heavy metal contamination in urban and peri-urban cropping systems in Sierra Leone. Soil and plant samples were collected from 72 sites from the largest and second largest cities, Freetown and Bo. The samples were analyzed for Zn, Cu, Cr, Ni, Pb and Cd, and the results compared to established reference values. Heavy metals were detected across all sites, with highest concentrations found in Freetown. Values obtained were mostly below the reference values for both soil and plant samples. Some mild risk of toxicity by Cd was observed in densely populated areas of Freetown, but this was not reflected in the plant uptake of Cd. In general, the risk posed by heavy metals in the urban centers of Sierra Leone is minimal, but measures should be taken to prevent further increase in heavy metal concentration in urban cropping sites.