This report describes soil ecotoxicity assays conducted as a part of the environmental risk assessment of vanadium. Vanadium toxicity to plants (barley and tomato) and to soil dwelling micro-organisms was evaluated, and multiple endpoints were used. Phytotoxicity was evaluated using a root elongation assay (ISO 11269-1) and a plant growth assay (ISO 11269-2). Microbial toxicity was evaluated using a nitrification assay (ISO 14238) and a respiration assay (OECD 217). The toxicant used was sodium metavanadate (NaVO3). The tests were conducted in five different European soils with varying properties (pH 5.2—7.8; total V 15—58 mg V/kg). In addition, the effect of ageing after spiking was evaluated in three soils; i.e. the respective toxicity of freshly spiked and aged soils was compared (1 week vs. 6—12 months-old V additions).
Phytotoxicity thresholds, expressed as V added to the soil, varied widely for the different soils and depending on the endpoint differed by a factor ranging from 10—19 for the different soils tested. Tomato growth was the most sensitive phytotoxic endpoint considered. Phytotoxicity was observed at EC10 (concentrations at which the response variable is reduced by 10%) of 10 mg added V/kg dry soil. Differing V concentrations in soil solution explained differences observed in V phytotoxicity reasonably well. Thus, phytotoxicity thresholds, expressed as dissolved V in soil solutions differed by a factor ranging from 2.6—5.8. Phytotoxic thresholds in long-term contaminated soils were, on average, twofold higher than those in corresponding freshly spiked soils. Furthermore, V concentrations in soil solutions of long-term contaminated soils were approximately twofold lower than those in corresponding freshly spiked soils. This suggests that, over a period of 6—12 months, V phytotoxicity is approximately reduced twofold due to immobilization of V during ageing.
Microbial toxicity thresholds differed by a factor ranging from 30 to 440 depending on the respective endpoint, when expressed as V added to the soil. Toxicity results of the respiration assay were variable, i.e., toxic thresholds have wide statistical confidence intervals. Ageing did not consistently decrease V toxicity in all soils, contrary to the phytotoxicity tests. The V concentration in soil solution does not explain the observed differences in V toxicity to micro-organisms in different soils. The reason for this discrepancy between phytotoxicity and microbial toxicity is not clear. However, different microbial communities in varying soils may respond differently to soil ageing treatments, which may partly explain the lack of coherence with soil chemical data.
Soil solution analysis indicates a higher solubility of the added vanadate than the vanadium due to geogenic background in soils. An added risk approach seems therefore most appropriate and is a pragmatic choice since toxicity thresholds when expressed as added V overlap with observed background concentrations of V range in soils.
Report for compliance with European legislative (REACH)