Application of Pollution Indices for the Assessment of Heavy Metal Pollution in Flood Impacted Soil

The flood in 2012, which was recorded as the most devastating in the past 40 years in Nigeria, that caused colossal loss in material wealth, could also be a source of heavy metal pollution, especially at the lower reaches of the flood where deposition of flood transported materials occurs. Heavy metals (Fe, Ni, Cd, Cr, Zn, Cu and Pb) concentrations were determined in soil samples from two locations, an area submerged by the flood water (flooded) and an area at a higher elevation than the flood water (unflooded), which served as the control. The soil pH, texture, Total Organic Carbon, and Cation Exchange Capacity were also determined. Standard laboratory methods were employed for all the analyses. The soil in this study was characterized as sandy/clay/loam soil following the particle size analysis, with an average pH of 4.6 in the flooded soils and 6.5 in the unflooded soils. Total Organic Carbon (TOC) ranged from (0.936-1.989)% in the flooded soil and (0.663-0.939)% in the unflooded soil. Cation Exchange Capacity (CEC) was higher in the flooded soil (1.936-3.234) meq/100 g, than in the unflooded soil (1.164-1.722) meq/100 g. The results of the heavy metals revealed that heavy metals concentrations where higher in the flooded soil samples compared to the unflooded soil samples. There was also evidence of leaching of heavy metals. Eight Pollution Indices for heavy metals were applied to the data which comprised of four single pollution indices (The Contamination Factor, Ecological Risk Factor, Enrichment Factor and Index of Geo-accumulation) and four integrated pollution indices (Average Pollution Index, Degree of Contamination, Ecological Risk Index and Nemerow Pollution Index) to evaluate the soil pollution status. Amongst the pollution indices, the Nemerow Pollution Index was the most stringent. It was recommended as the pollution index to be applied for safety considerations.