Improved geochemical baseline establishment based on diffuse sources contribution of potential toxic elements in agricultural alluvial soils

•Recent soils by land reclamation had a fingerprint of sediment in PTE distribution.•Intense and long-term diffuse sources elevated PTE level in old alluvial soils.•Agriculture-derived As and Cd led to bias in GBV calculated from the whole area.•GBV were established on subarea based on PTE source contribution.•Source-based GBV avoid underestimation of PTE contamination from diffuse sources.