Cd isotope fractionation during simulated and natural weathering

In practice, stable Cd isotope ratios are being applied to trace pollution sources in the natural environment. However, Cd isotope fractionation during weathering processes is not yet fully understood. We investigated Cd isotope fractionation of Pb−Zn ore in leaching experiments and in the environment under natural weathering processes. Our leaching experiments demonstrated that the leachate was enriched with heavy Cd isotopes, relative to initial and residual samples (Δ^114/110Cd_{leachate − initial state} = 0.40–0.50‰, Δ^114/110Cd_{leachate −residual state} = 0.36–0.53‰). For natural samples, δ^114/110Cd values of stream sediments were higher than those of the corresponding soil samples collected from the riverbank, Δ^114/110Cd_{stream sediment −soil} can be up to 0.50‰. This observation is consistent with our leaching experiments, which indicate significant Cd isotope fractionation during natural weathering processes. Therefore, natural contributions should be considered when using Cd isotopes to trace anthropogenic pollution in water and sediment systems. - Highlights: • Cd isotope fractionation was investigated during simulated and natural weathering. • Supergene weathering can result in significant Cd isotopic fractionation. • Natural contributions should be considered when using Cd isotope ratios to trace anthropogenic pollution. - The supergene weathering and leaching can result in significant Cd isotopic fractionation under natural and experimental conditions.