Assessing heavy metal contamination and ecological risk of urban topsoils in Tarkwa, Ghana.

This study aimed to assess the spatial distribution, contamination levels, pollution degree and ecological risks of eight heavy metals (Cd, Cr, Co, Cu, Mn, Ni, Pb and Zn) in topsoils of UMaT, Brahabobom, A'koon, Boboobo and Bogoso Junction (areas in Tarkwa, a mining town in Ghana). Eighty soil samples were collected, and metal concentrations were determined using atomic absorption spectroscopy (AAS). The results revealed that Cu, Ni, Pb and Zn concentrations exceeded the WHO/FAO (2001) standard in some areas. The geoaccumulation index (I) value of metals in soils under study revealed extreme contamination by Pb and Mn; however, Mn was in abundance due to the presence of Mn minerals in the study area. The study area was also moderately contaminated by Cd, Cu and Zn. Cd and Pb posed a considerable and very high potential ecological risk to the study area, respectively, especially at Bogoso Junction. The two metals were mainly from vehicular traffic and the activities of auto mechanics at Bogoso Junction. Nemerow's pollution index also revealed that about 20% of the study area was polluted, mainly from Cu and Pb concentrations.