Assessment of Potential Ecological Risk of Heavy Metals in Soils from Waste Dumpsites in Military Formations in Makurdi, Nigeria

Abstract

Chemical fractionation of toxic metals (As, Cd and Zn) along the soil profile at waste dumpsites in military formations for dry and wet seasons using Tessier’s sequential extraction procedure was determined using AAS techniques. The order of yield across the fractions was mainly: exchangeable (F 1 ) < carbonate-bound (F 2 ) < Fe/Mn oxide-bound (F 3 ) < organic matter-bound (F 4 ) < residual (F 5 ). Statistical analysis (p < 0.05) indicated that there was no significant variation between the values of results obtained from dumpsites A and B of each sampling station. However, the variation between the dumpsites and control was significant (p > 0.05) in most stations. The pollution index was assessed using the degree of contamination (C d ), the modified degree of contamination (mC d ), potential ecological risk and mobility factor. The C d indicated that NFB top soil was considerably contaminated (16.3) while the soils (20 - 40 and 40 - 80 cm) recorded moderate (13.6) and low (5.60) contaminations respectively. Top soil of NSM was moderately contaminated while the contamination status of NPS, NFB and SFB waste dump soils across the depths was “low”. The mC d index for NFB dump soil was “moderate” (2.33) and subsoils (20 - 40 and 40 - 80 cm) were “low” (1.94) and “Nil to very low” (0.800) respectively. The mC d for the other three dumpsites was “Nil to very low” except the top soil of NSM which was “low”. The order of the toxic metals mobility in the studied soils using the Mobility factor (M f ) for dry and wet seasons was Cd > As > Zn and Zn > Cd > As respectively.