Plant Uptake and Ecotoxicity of Vanadium

This study examines the available literature on the role of soil chemistry for uptake and ecotoxicity of vanadium in terrestrial plants. Relatively few studies have been devoted to this topic, and most of these have related vanadium uptake/ecotoxicity to extractable vanadium fractions. Typically, vanadate uptake to roots is best correlated with easily extractable vanadium, suggesting that vanadium is mostly taken up from the soil solution. The effects of pH and o-phosphate have also been investigated in a few studies. A decreased pH appears to increase vanadate uptake as well as ecotoxicity, but the pH dependence is rather weak. Moreover, o-phosphate decreases vanadate uptake and ecotoxicity through competition for uptake, but recent studies on wheat root ecotoxicity suggest that this effect is small at concentrations below 100 µmol L⁻¹. These results were used to set up a BLM (biotic ligand model) for wheat, similar in design to models used for Ni²⁺ toxicity to fish. The suggested BLM fitted the wheat root data well. When combined with an earlier developed Freundlich model for vanadate adsorption to soil particles, the model predicted that when effect concentrations are defined on a dry soil basis, the effective concentrations are lowest (i.e., the toxic effects are largest) at high pH. This is a consequence of the much stronger vanadate sorption to iron and aluminum (hydr)ous oxides at low pH, which makes vanadium less available for uptake. However, for the vanadate-BLM (or any other model for vanadium ecotoxicity) to be used as a risk assessment tool, additional toxicity testing will need to be carried out, where interactions with H⁺, o-phosphate and other constituents such as Mg²⁺ are systematically studied for different plant species and/or assays.