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

Abstract

24A field-trial with different application rates of converter lime (0.2, 0.7 and 1.0 kg m -2 ) was set up 25 in a pine forest stand in southern Sweden in 1984. The lime contained 14.6 g kg -1 vanadium. The aim 26 with this study was to evaluate the vanadium concentration and speciation in the soil 26 years after 27 application. Samples of the organic mor layer and the mineral soil were analysed separately. The 28 vanadium concentration decreased with soil depth, from 680 to 8 mg kg -1 soil. Analysis by vanadium 29 K-edge XANES spectroscopy showed that vanadium(IV) was the predominant species in the mor 30 layer. Further, iron and/or aluminium (hydr)oxides were important sorbents for vanadium(V) in the 31 mineral soil. The speciation of dissolved vanadium, as determined by HPLC-ICP-MS, was dominated 32 by vanadium(V), which is considered the most toxic vanadium species. However, the vanadium 33 sorption capacity of the soil was sufficient to reduce the total bioavailable vanadium below phytotoxic 34 levels. By combining two different vanadium speciation methods, this study was able to conclude that 35 vanadium speciation in soils is governed by soil properties such as pH. organic matter content and the 36 content of metal (hydr)oxides, but not by the vanadium species added to the soil. 37

Vanadium sorption by mineral soils: Development of a predictive model

“…if vanadate(V) is only slowly transformed to vanadyl(IV). However, in a previous paper we showed that the vanadium redox reactions are quick in soils (Larsson et al 2015b), and for this reason such slow transformations appear unlikely to be significant.…”

“…As discussed elsewhere (Larsson et al 2013;Larsson et al 2015b) the total V content of a soil is a poor predictor of V toxicity. Cappuyns and Slabbinck (2012) reviewed various risk-based norms for total V in soil in different European countries.…”

“…As an example, r 2 = 0.60 for the relationship between log (Fe ox +Al ox ) and log K dS after addition of 10 mg V kg -1 . However, differences in the content of primary mineral-bound V(IV), which contributes to total V but is essentially unreactive (Larsson et al 2015b), are probably also important for the K dS value. Red crosses represent samples with Fe ox +Al ox > 0.2 mol kg -1 , black circles are soils with Fe ox +Al ox ranging from 0.1 to 0.2 mol kg -1 , and green triangles are soils with Fe ox +Al ox < 0.1 mol kg -1 .…”

“…Vanadate(V) is considered the most toxic vanadium species (Martin and Kaplan, 1998;Larsson et al 2013). In three Swedish soils it was found that the soil appears to be dominated by vanadium(IV) bound in primary minerals (Larsson et al 2015a;Larsson et al 2015b); this V has probably a low bioavailability. However, when vanadium is added to soils (either as vanadium(IV) or vanadium(V) salts), it tends to accumulate as vanadate(V) sorbed to iron and aluminium hydrous oxides, except in acid organic soils, in which vanadyl(IV) complexed to organic matter will predominate (Larsson et al 2015a, Larsson et al 2015b).…”

“…Vanadium K-edge XANES data were collected at beamline 4-3 at the Stanford Synchrotron Radiation Lightsource (SSRL), Stanford, USA. The spectra for Pustnäs A and Säby A have been reported elsewhere(Larsson et al 2015b), but here we give further details on linear combination fitting results. Procedures for collecting spectra of standards (V oxides, vanadate(V) adsorbed to ferrihydrite, vanadyl(IV) complexed to organic matter, etc) are detailed inLarsson et al (2015a).…”