Geochemical Partitioning of Metal Pollutants in Agricultural Soil as Index of Human Health Risk Assessment

Abstract

Bioavailability and toxicity of metals depend not only on their total concentrations but also on the form in which they exist. Therefore full understanding of the metals’ behavior and prediction of their potential risk in agricultural soil is possible only when all the geochemical forms in which they exist under different environmental conditions are identified. The aim of this study was to assess the geochemical partitioning of Cd and Pb in agricultural soil on the bank of Delimi River in Nigeria as an index of predicting their bioavailability to crop and potential toxicity to humans. The study area comprised of three farmlands irrigated with polluted water from River Delimi while the control area was a farmland irrigated with water from Lamingo Dam (a municipal water supply reservoir) all within Jos city. Total metals content in soil collected in the rhizosphere of Carrot and Cabbage were extracted using aqua-regia. A five-step sequential extraction procedure was used to determine the partitioning of the metals into different geochemical fractions of the soil. The metals extracted were determined using Atomic Absorption Spectrophotometer (AAS). The partitioning of both Pb and Cd into different geochemical fractions of soil showed that the samples collected on farmland at the study site were mostly partitioned to exchangeable and other non-residual fractions that can easily be released for uptake by crops. At the control site however the metals were mainly occluded to residual non-mobile fractions. It may be concluded that there is a higher risk of metal toxicity among people that consume crops cultivated on farmlands along Delimi River than those at Lamingo Dam.