Ecological Risk Assessment of Heavy Metals in Soil of an Open Dump along Old Ikare Road Owo, Ondo State, Nigeria

Abstract

Aims: To investigate the heavy metal concentrations in soil samples collected from an open dumpsite in a rural community (Aba Idi-Mangoro) in Owo, Ondo State and to compare the observed values with the regulatory limits. This study also aimed to determine the pollution levels using tools like contamination factor, pollution load index and geoaccumulation index. Study Design: Field study design was use in this study. Place and Duration of Study: Soil samples were collected from Aba Idi-Mangoro in Owo, Ondo State, Nigeria between July 2015 and February 2016 to represent the wet and dry seasons. Methodology: A total of 96 soil samples were collected (6 samples on each visit and the site was visited twice a month). The samples were taken to the Prof. Julius Okojie Central Research Laboratory at the Federal University of Technology, Akure, Ondo State, Nigeria. In the laboratory, samples were air dried to remove the moisture. 2 g of the sampes were digested into HNO3, HCl, HF and HClO4, and AA Spectrophotometer was used to analyse the concentrations of the heavy metals. Results: Out of the 8 heavy metals assessed, 6 were above the regulatory limits. The order of heavy metal concentrations for the wet season is: Fe>Mn>Zn>Cu>Pb>Ni>Cr>Co>Cd and the dry season is as follows: Fe>Zn>Mn>Pb>Cu>Ni>Co>Cr>Cd. When the mean concentrations of the samples for the wet season were compared to the dry season, Mn (0.009), Cd (0.035), Cr (0.044) and Co (0.014) differ significantly (p<0.05). No significant difference was found in Fe, Co, Ni and Zn. It was observed from the overall results that the concentrations of heavy metals were higher during the dry season than in the wet season. The contamination factor (CF), pollution load index and geo-accumulation index values of Fe was extremely high in the two seasons while it varies at different collection times for the other metals. Conclusion: Due to the high presence of some of the heavy metals found in the soil, the study suggests that water and sediment samples from nearby river(s) within the community should also be examined.