Transformation of exogenous hexavalent chromium in soil: Factors and modelling.

There is a great need, but not yet available, for quantitative transformation models and influencing factors of exogenous hexavalent chromium (Cr(VI)) in soil for environmental risk assessment and regulation. Therefore, the transformation processes of exogenous Cr(VI) in 13 soils across China were investigated. The changes in Cr forms in soils spiked with 100 mg kg of Cr(VI) over 90-120 days indicate that both the reduction and immobilization of Cr(VI) occurred with the decrease in availability of Cr(VI) and its reduced counterpart Cr(III).

Quantifying and normalizing the combined phytotoxicity of mixed-valence chromium in soil integrated by toxicity equivalence.

When Cr(VI) and Cr(III) coexist, the reasonable assessment of the combined toxicity of chromium in soil and its ecological risk is still not well resolved. In the present study, exogenous mixed concentration combinations were set up to determine the interaction and combined toxicity of Cr(VI) and Cr(III), which were quantified as measured total and resin extractable forms for dose-response experiments with barley root elongation. The concept of toxicity equivalence "α" (the ratio of toxicity intensity coefficient between Cr(VI) and Cr(III), which can be expressed as the relative toxic strength of Cr(VI) to Cr(III)) was proposed for the toxicity assessment of mixed-valence chromium in soil.