Long-term fate and transformations of vanadium in a pine forest soil with added converter lime

Abstract

A field-trial with different application rates of converter lime (0.2, 0.7 and 1.0kgm−2) was set up in a pine forest stand in southern Sweden in 1984. The lime contained 14.6gkg−1 vanadium. The aim with this study was to evaluate the vanadium concentration and speciation in the soil 26years after application. Samples of the organic mor layer and the mineral soil were analyzed separately. The vanadium concentration decreased with soil depth, from 680 to 8mgkg−1 soil. Analysis by vanadium K-edge XANES spectroscopy showed that vanadium(IV) was the predominant species in the mor layer. Further, iron and/or aluminum (hydr)oxides were important sorbents for vanadium(V) in the mineral soil. The speciation of dissolved vanadium, as determined by HPLC-ICP-MS, was dominated by vanadium(V), which is considered the most toxic vanadium species. However, the vanadium sorption capacity of the soil was sufficient to reduce the total bioavailable vanadium below phytotoxic levels. By combining two different vanadium speciation methods, this study was able to conclude that vanadium speciation in soils is governed by soil properties such as pH, organic matter content and the content of metal (hydr)oxides, but not by the vanadium species added to the soil.