Risk dynamic evolution index based on fraction transformation and its application to site risk assessment

Highlights: • A new index is hypothesized to assess site dynamic risk evolution. • The possibility factor indicated different properties of site dynamic risk evolution. • Toxic factor applied to soil was modified by a meta-analysis. • Dynamic risk evolution of specific element (e.g. Cd, Hg) should be particularly noticed. In this study, a potential ecological risk index for site dynamic risk evolution was proposed with the development trend of the Hakanson approach. The possibility factor $P_i$ was attached to the contamination factor $C_f^i$, representing the burst probability factor of dynamic risk arising from the transformation of metal(loid) fractions, ascertained by the delayed geochemical hazard (DGH) methodology. The toxic effects of different elements were explored through a meta-analysis. The effects of soil pH and soil organic matter on the mobile fraction of elements were examined, and the toxic factors (${\mathrm{Tr}}^i$) of six elements (arsenic, cadmium, chromium, copper, lead, and zinc) were modified for the site application. A total of 16 case studies representing four soil types (agricultural soil, industrial zone, mining area, and soil of river basin) were tested, and the results indicated that the proposed index could provide an early warning of site risk dynamics.