Vanadium in thirteen different soil profiles originating from Germany and Egypt: Geochemical fractionation and potential mobilization

Abstract

Knowledge about geochemical fractions of vanadium (V) in different soils is required to understand its potential mobilization which we assessed in thirteen soil profiles originating from Germany and Egypt using the sequential extraction technique of the Commission of the European Communities Bureau of Reference (BCR). The concentrations of total, AB-DTPA-extractable, and the geochemical fractions [acid soluble (F1), reducible (F2), oxidisable (F3), and residual (F4) fraction] of V in the soils were determined. The total V concentrations ranged from 20.7 to 133.1 mg kg−1 and correlated positively with clay content and the total concentrations of iron (Fet), aluminum (Alt), and manganese (Mnt). The total V was stronger affected by free Fe and Mn oxides (Fed and Mnd) in the Egyptian soils than in the German soils. The residual fraction of V was dominant in the soils followed by the reducible and the oxidisable fraction and showed a similar behavior to total V. The reducible V was higher in the Egyptian soils than in the German soils and was positively correlated with Fet, Alt, Mnt, Fed, and Mnd. The impact of Fet, Alt, and Mnt on the reducible V was stronger in the Egyptian soils than in the German soils, while the impact of Fed and Mnd on the reducible V was stronger in the German soils than Egyptian soils. The oxidisable V was affected by soil organic matter and total sulphur (St) in the German soils and by carbonates and St in the Egyptian soils. The acid soluble fraction of V was lower than the detection limits in all soils. The AB-DTPA-extractable V concentrations (potential available V) ranged between 0.04 and 4.04 mg kg−1. The potential mobile fraction (PMF = ∑F1−F3) accounted 4.4–64.7% of the total V. The alkaline soils showed the highest potential mobility and availability of V compared to the acidic soils, and thus the AB-DTPA-extractable V correlated positively with soil pH as well as clay content, cation exchange capacity, and Fet. The reducible fraction contributed stronger to the potential mobility and availability of V than the oxidisable fraction. The canonical discrimination analysis explained 64% of the variability of the geochemical behavior of the different soil groups and showed that the different groups of soils could differentiate from each other. The German soil groups (Eutric Fluvisols, Calcic Luvisols, Tidalic Fluvisol and Haplic Gleysol (Marsh soils)), showed a different geochemical behavior; while the Egyptian Eutric Fluvisols and Sodic Fluvisols were relatively similar in their geochemical behavior and the Haplic Calcisols was relatively close to them. Our results demonstrate that the potential mobilization of V was high in the soils (except for Luvisols) - especially under alkaline conditions-which indicate a release of this toxic metal from the soils to soil solution. This release may cause potential environmental risks such as the transfer of V into the groundwater, the vegetation and food chain. Future studies should elucidate the temporal kinetics of V and the determining factors under different flooding conditions and remediation approaches are necessary to ameliorate V-contaminated soils.