Heavy Metal Accumulation in Tubers Grown in a Lead-zinc Derelict Mine and their Significance to Health and Phytoremediation

Abstract

Four common tubers namely Colocosia and Xanthosama (Cocoa yam), Manihol eaculenhis (Cassava), Dioscoreu rolundata (White Yam) and Ipomoea batatas (Sweet potato) were grown within Enyigba lead-zinc derelict and samples of their leaves (aerial part) and roots (underground part) alongside the soil where they were grown were analyzed for heavy metal using Proton Induced X-ray Emission (PIXE) technique. The results revealed that heavy metals in soil (mean pH = 6.5±0.29) decreased in the order Pb > Zn > Cu > Mn > Cd > Ni > As > Cr. The mean concentration (mg/kg) of heavy metals in soil was found in the range of Pb (0.01-0.41); As (0.02-0.54): Cd (0.02-0.12); Cu (0.82-62.12); Cr (0.01-0.40); Zn (24.18-122.12); (Mn 18.46-624.26) and Ni (8.24-34.66). The results revealed that levels of Pb in white yam (0.41 mg/kg) and cassava (0.32 mg/kg); As in cassava (0.54 mg/kg), white yam (0.12 mg/kg) and sweet potato (0.14 mg/kg) and Cd in cocoyam (0.12 mg/kg) all exceeded the World health Organisation Maximum Limit (WHO ML) and thus they are unfit for human consumption. High value of bioaccumulation factor (BAF) observed for Mn in cassava (1.78) as well as high values of Translocation Factor (TF) observed in sweet potatoes for cadmium (2.0) and copper (1.47); in cocoyam for cadmium (1.2) and also in cassava for chromium (1.25) and zinc (1.13) suggest that the affected tubers were potential hyperaccumulators. The variation in the parameters determined were found to be statistically significant (p < 0.05) as determined by one way analysis of variance.