Contaminations evaluation and ecological risk assessment of selected potentially harmful elements in dusts, sediments and soils of Akure, Nigeria

Abstract

Indiscriminate discharge of waste and high traffic density as well as incessant flooding are major challenges that characterised Akure metropolis. Potentially harmful elements such as Pb, Cd, Ni, Zn are toxins that after exposure may pose a potential lifetime health risk especially to children. This study investigated and traced the contamination levels and the ecological risk of some Potentially-Harmful-Elements (PHEs) (Cu, Zn, Cd, Pb and Ni) in soils, drainage sediments and dusts of the city of Akure, southwestern Nigeria. Composite samples consisting of 40-soils, 30-stream-sediments, 20-road-dust samples and ten representative rock samples were collected for the study. The samples were air dried, pulverized, sieved and digested using aqua regia while the elemental compositions were determined using the ICP-MS. The level of contamination and the ecological risk assessment were determined by comparing with statutory guidelines and calculation of contamination indices, and ecological risk factors. The results (mg/kg) showed that Zn ranged from 13.50 to 384.60; Cu, 3.77 to 99.43; Pb, 13.60 to 69.10; Ni, 2.40 to 27.60 and Cd, 0.02 to 0.31 in sediments. For the soils, Zn ranged from 25.00 to 552.00; Cu, 10.00 to 71.00; Pb, 12.00 to 158.00; Ni, 5.00 to 32.00 and Cd, 0.50 to 1.50 while in dusts, Zn ranged from 118.00 to 876.00; Cu, 35.00 to 148.00; Pb, 52.00 to 487.00; Ni, 9.00 to 23.00; and Cd, 0.50 to 1.40. The concentrations of the analysed PHEs were observed to be elevated in samples from city center characterized by high population and traffic density. The soils, sediments and dusts of Akure metropolis were found to have been moderately contaminated with Cu, Pb, and Zn. The ecological-risk-indices of the three media showed that Ni and Zn were of low to considerable risk, while Cu, Pb and Cd were low to very high risk. The potential ecological risk factor in sediments, soils and dusts was of low to considerable risk, low to high risk and considerable risk to high risk, respectively. The status of the quality of the environmental media requires urgent remediation attention in order to ensure clean and sustainable environment for the city dwellers.