Sequential Fractionation of Heavy Metals from Flooded and Non-Flooded Soils in Obunagha Community, Bayelsa State, Nigeria

Abstract

Soil samples from flooded and non-flooded areas of different farmlands in Obunagha community, Bayelsa State were collected for this study. The aim of the study was to investigate the chemical fractionation and bioavailability of Cr, Cd, Zn, Ni, & Fe in flooded and non-flooded farmlands. The soil samples were fractionated into six chemical fractions, each containing different heavy metal concentrations and analyzed using flame atomic absorption spectrophotometer. The highest average concentration for Cadmium (Cd) is 1.50g/kg, Zinc (Zn) is 7.53g/kg, Nickel (Ni) is 10.54g/kg, Iron (Fe) is 9.52g/kg, and Chromium (Cr) is 12.62g/kg all from the flooded areas of the farmlands. Sequential extraction showed heavy metals distributed throughout all extraction steps, with the water-soluble fraction prevailing, potentially increasing the mobility and bioavailability of these metals. The %bioavailability ranged from 37.98% – 90.00%.  The results indicated also that the average concentration of the metals in flood affected farmland were more than the non-flooded areas. The results indicated that floods affect farmland metal content by altering contaminant bioavailability, causing adverse environmental effects. Also, the results of the heavy metals analyses revealed that the levels of nickel, zinc, chromium, cadmium and iron in all the farmland soil samples are above the maximum allowable concentration for heavy metals in soil set by WHO Guidelines provided. Hence, the farmland soils are not safe for agricultural activities. We therefore, recommend regular monitoring of the soils to prevent excessive build-up of these toxic heavy metals.