Migration and transformation characteristics and potential risk assessment of heavy metals under different rainfall conditions in contaminated soil

Abstract

Contaminated mining soils cause heavy metal environmental pollution such as the soil, river, groundwater and plants under rainfall conditions. In this work, the copper, zinc, lead and chromium leaching characteristics, leaching efficiency, fractions variation, binding intensity, mobility and potential environmental risks were investigated under different rainfall conditions. Results demonstrated that Zn obtained a high leaching concentration under the 19.6, 13.1 and 6.5 mL.min ⁻¹ , which concentrations were 180.3, 154.7 and 123.5 μg.L ⁻¹ , respectively. On the surface soil particles, Cu, Zn, Pb and Cr migrated into the water with the rainwater runoff, indicating a sustainable increase with rainfall intensity raising and obtained a high solubility and mobility, promoting heavy metals to migrate via the soil surface rainwater runoff. Exchangeable and reducible fractions of Pb and Cr have decreased and transformed into the metal ions, which migrated into the outflow, whereas the oxidizable and residual fractions have increased under the rainfall conditions. Cu and Pb obtained more stable fractions, such as the oxidizable and residual fractions. Cu, Zn, Pb and Cr I _R values were affected by their concentration and fractions under the rainfall conditions. Heavy metal mobility order was Zn > Pb > Cr > Cu, with M _F values of 4.34%, 3.52%, 2.67% and 2.45%, respectively. These results can provide significant support for the mining soils of efficient remediation methods to promote the mines' ecological environmental improvement.