Ageing of vanadium in soils and consequences for bioavailability

Abstract

Total vanadium (V) concentrations in soils commonly range from 20 to 120 mg kg−1. Vanadium added directly to soils is more soluble than geogenic V and can be phytotoxic at doses within this range of background concentrations. However, it is unknown how slow sorption reactions change the fate and effect of added V in soils. This study addresses the changes in V solubility, toxicity and bioavailability in soils over time. Four soils were amended with pentavalent V in the form of a soluble vanadate salt, and extractable V concentrations were monitored over 100 days. The toxicity to barley and tomato plants was evaluated in freshly spiked soils and in the corresponding aged soils that were equilibrated for up to 330 days after spiking. The V concentrations in 0.01 m CaCl2 soil extracts decreased approximately two‐fold between 14 and 100 days after soil spiking, and the reaction kinetics were similar for all soils. The phytotoxicity of added V decreased on average two‐fold between freshly spiked and aged soils. The reduced toxicity was associated with a corresponding decrease in V concentrations in the isolated soil solutions and in the shoots. The V speciation in the soil solution of the aged soils was dominated by V(V); less than 8% was present as V(IV). Oxalate extractions suggest that the V(V) added to soils is predominantly sorbed onto poorly crystalline oxyhydroxides. It is concluded that the toxicity of V measured in freshly spiked soils may not be representative of soils subject to a long‐term V contamination in the field.

Vanadium bioavailability in soils amended with blast furnace slag

“…Further, pot experiments testing phytotoxicity by adding V 2 O 5 to an artificial soil at different nutrient levels had similar ranges of EC50 values (21-180 mg V kg -1 ) in a selection of five different plant species [24]. The wide range of threshold values becomes smaller if expressed as vanadium concentrations in soil solution [15,25].…”

“…The threshold values increased to >180 and 530 mg V kg -1 after 10 months of ageing [25]. In comparison, the BF slag-amended soils reached a maximum soil vanadium concentration of 150 mg V kg -1 soil.…”

“…Another set of the same soils, referred to as "aged" soils, was spiked with the above vanadate(V) concentrations and kept outside for 10 months, in the same manner as described above for the slag amended soils, before conducting the assay. A detailed description of the freshly spiked and aged soils is found in Larsson et al [15] and Baken et al [25], respectively.…”

“…The suspensions were equilibrated in an end-over end shaker for 24 hours and the supernatant was subsequently isolated by centrifugation (3000 g for 15 min) and membrane filtration (0.45 µm). For the freshly spiked and aged soils, the dissolved vanadium concentrations were determined by extraction of the pore water by centrifuging the soils at 3000 g [25]. All solutions were analyzed for major elements and vanadium (ICP-OES, Perkin Elmer Optima 3300DV, vanadium measured at 290.880 nm), dissolved organic carbon (non-purgeable organic carbon, Analytik Jena Multi N/C 2100) and pH.…”

Vanadium: Global (bio)geochemistry

“…In general, most V in soils appears to have low mobility except under strongly acidic conditions (Cappuyns and Swennen, 2014). The mobile V in soils occurs mainly as V(V) and only minor amounts are present as V(IV) (Baken et al, 2012;Burke et al, 2012). Vanadate is also the most available form for plants (Tian et al, 2015).…”