Application of DGT/DIFS and geochemical baseline to assess Cd release risk in reservoir riparian soils, China

Abstract As the sole drinking water source for Beijing City, Cd has been previously assessed as the major contaminant in Miyun Reservoir (MYR) riparian soils. However, the potential release risk of Cd in such soils, and the labile-Cd release–resupply process from the soil solid phase to solution after water impoundment remain poorly understood. We established a geochemical baseline concentration (GBC) of Cd in MYR riparian soils, combined with the diffusive gradient in thin films (DGT) technique and DGT-induced fluxes in soil (DIFS) model, to reveal a dynamic release–resupply process and influencing factors of labile Cd in riparian soils. The results showed that Cd GBC in riparian soils was 0.12 mg/kg, which was higher than the Cd background value (BV) for Beijing. Using Cd GBC as BV to assess the Cd contaminant level, the geo-accumulation index showed that Cd in riparian soils was at the uncontaminated level. In addition, Cd in the soils belonged to the non-residual fraction using the Community Bureau of Reference method. Cd mobility coefficients (F1/C Total -Cd) of soils at low elevation had relatively high values, implying that Cd may be released during the initial impoundment of the MYR. Moreover, correlation analysis was used to found the major influencing factors between DGT-labile Cd and several parameters. The results showed that the DGT-labile Cd was positively correlated to the reducible and oxidizable fraction, C DGT -Fe, and total organic carbon, illustrating that the release of Cd from soils was controlled by Fe oxides and organic matter. The resupply ability (R values) and DIFS model parameters revealed that Cd in MYR soils belonged to the partially sustained case, and the slow desorption rate suggested that the release risk of Cd was low in the MYR riparian soils.