Contamination Levels and Sources of Heavy Metals and a Metalloid in Surface Soils in the Kumasi Metropolis, Ghana
Background. Environmental contamination with heavy metals and metalloids due to
industrial, smelting and mining activities have become common in large and growing cities.
Kumasi is one of the most industrialized cities in Ghana and experiences metal pollution
due to recent and past activities. Although metals are naturally abundant in the area, their
accumulation in soils could potentially lead to adverse effects on local ecosystems.
Objectives. The aims of this study were to determine the distribution, enrichment, geoaccumulation
and sources of metals in Kumasi soils and to estimate the contamination factor
(CF) and pollution load index (PLI) of these metals in soils.
Methods. Concentrations of eight heavy metals and a metalloid were determined in 112 soil
samples randomly collected from 31 sampling sites in the area. In addition, 5 soil samples
were collected from a pristine site (Kwame Nkrumah University of Science and Technology
Botanical Gardens) for data comparison, to determine the local background values for metal
concentrations and to evaluate the extent of metal pollution in the study area.
Results. Heavy metals such as zinc (Zn), lead (Pb), cadmium (Cd) and chromium (Cr) were
enriched in 65, 32, 58 and 93% of the sampling sites, respectively, and geo-accumulation
indexes for Cr, Zn, Cd, mercury (Hg) and Pb showed moderate to extreme contamination
in 100, 97, 77, 65 and 45% of the sampling sites, respectively. Principal component and
cluster analyses revealed that industrial activities including mining were the major sources of
metals in Kumasi soils with high metal input in the community of Suame. Distribution maps
revealed hotspots of Cd, nickel (Ni), arsenic (As), cobalt (Co), copper (Cu) and Pb in Suame.
The highest CFs for Cu, Cd, Ni, As, Co and Pb highlighted anthropogenic inputs in Suame,
while Hg was highest in Mbrom, Zn in Suntreso, and Cr in Aboabo.
Conclusions. The PLI of metals revealed Suame as the most polluted study site, while
Anomangye and Bomso were the least polluted.
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