Impact of a super typhoon on heavy metal distribution, migration, availability in agricultural soils

Heavy metal contamination in agricultural soils is a worldwide concerned environmental issue. However, a short-term extreme hydrodynamic event (e.g., a super typhoon) may significantly affect the distribution, migration, and availability of heavy metals in agriculture soils on a large scale. The limited understanding of such an impact prevents effective environment survey, risk assessment, and remediation strategy for heavy metal contaminated soils. Here, we show a massive migration of heavy metals during a super typhoon (Lekima) based on the field investigation, simulated experiments, and isotopic fingerprinting. The contaminations of heavy metals (Cd, Zn, Cu, Ni, Cr and As) of agricultural soils at 209 sampling sites over 3.59 × 10⁵ km², were significantly relieved by 10.3-42.0 % after the typhoon, because of the primary contribution of runoff erosion over interflow according to the simulated soil erosions. However, the available fractions (as % of the total amount of each metal) were metal-dependent, with Cd, Zn, Cu, and Ni increased (5.3-26.4 %), and Cr and As decreased (0.9-3.5 %). In contrary, the Pb contamination was slightly aggravated by 8.7 % after the typhoon, and the Pb isotopic signatures indicate its input and migration via wet precipitation and surface runoff. The soil properties (e.g., pH and organic matter) showed limited impact on the migration of heavy metals during this typhoon. These results suggest that a natural short-term extreme hydrodynamic event can drive the massive migration of heavy metals in agricultural soils and their trade-off with other environmental medias, providing valuable information for multi-medias environmental risk assessment and cooperative remediation that can be significantly disturbed by such an event.