Abstract
Trace metal pollution is a global problem and therefore, analysis of metals in environmental matrices has drawn a worldwide attention due to the health risk they pose to humans and the environment as a whole. Due to anthropogenic activities such as use agrochemicals, mining and industrialization among others, have elevated the concentration of these metals within the environmental matrices. Therefore, it is imperative to obtain information about level of concentration of these metals in agricultural soils, water and vegetables as well as their speciation in order to determine their potential toxicity. Therefore, the objectives of this study was to determine the concentration of major and trace metals in agricultural soils, river water (used as irrigation water source) and vegetables (spinach), collected from Port St. Johns agricultural area (Eastern Cape, South Africa). The concentration of As, Cr, Co, Cd, Cu, Fe, Mn, Ni, Pb, Tl, and Zn, among others, in the samples was achieved using inductively coupled plasma optical emission spectrometry (ICP-OES). The pseudo-total digestion, single extraction and modified BCR sequential extraction procedures were used to solubilize the metals from the agricultural soil samples. The validation of these procedures was performed by analysing certified reference materials such as CRM005 (trace metal sewage sludge), BCR 483 (extractable trace elements in sewage amended soil) and BCR 701 (extractable fractions) and the percentage recoveries ranged from 95-107%. The above mentioned objectives were carried out into three different parts.
Firstly, the bioavailability and mobility of major and trace metals present in agricultural soil was assessed using BCR single extraction technique. To achieve this, five different extractants (that is, EDTA, CaCl2, acetic acid, de-ionized water and NH4NO3) that represented different rhizosphere conditions ranging from complexing, mild to acidic conditions were evaluated. The results obtained revealed that EDTA, acetic acid and deionized water were able to extract the most metals (Al, As, Cd, Co, Cr, Cu, Fe, Mo, Mn, Ni, Pb, Sb, Tl, Ti, V and Zn) with highest concentrations compared to other extracting solvents. Various environmental risk assessment indices such as contamination factor, Igeo and pollution load index, among others, were used to evaluate the bioavailability and potential contamination posed by these metals. All results obtained from the indices revealed the presence of metals within the soil samples as result of contamination and these metals maybe bioavailable for plant uptake...
M.Sc. (Applied Chemistry)