Assessment of bioavailability and mobility of major and trace elements in agricultural soils collected in Port St Johns, Eastern Cape, South Africa using single extraction procedures and pseudo-total digestion

Purpose: The aim of this study was to evaluate the applicability of ultrasound assisted single extraction and pseudo-total digestion procedures to investigate the bioavailability and mobility of major and trace elements collected from agricultural soil collected in Mzimvubu farmstead area located in Port St Johns, Eastern Cape Province (South Africa). Materials and methods: The potential metal availability was assessed using complexing agent (ethylenediaminetetraacetic acid (EDTA)), mild (cacium chloride (CaCl₂) and ammonium nitrate (NH₄NO₃)), deionized water and acidic (CH₃COOH) extractants with the assistance of ultrasound to evaluate mobility and bioavailability of metals. The ultrasound radiation was used to assist the single extraction of major and trace metals from agricultural soils as well shortening the extraction time. The pseudo-total metal content in agricultural soils was obtained using pseudo-total digestion employing aqua-regia. Results and discussion: The results obtained using different solvents for single extraction procedures, revealed that higher extraction of Al (256–681 mg kg⁻¹), Fe (172–430 mg kg⁻¹) and Mn (35–136 mg kg⁻¹), was observed compared to other metals. Among the investigated solvents, deionized water, acetic acid and EDTA proved to be the most aggressive extractants. The geo-accumulation index (2–6) and contamination factor (3–6) demonstrated that Fe, Cr, Mn, Co, Cu, Ni, and Zn could pose significant environmental contamination risk. Conclusions: Based on the results obtained, it can be concluded that the high levels of some studied metals was due to anthropogenic activities.