Assessment of sepiolite for immobilization of cadmium-contaminated soils

The current study investigated the remediation effects of sepiolite on soils artificially polluted with cadmium (Cd) using a set of variables (soil pH, available Cd content, plant Cd concentration, soil enzyme activities, and microorganisms). Results showed that increasing pH after the application of sepiolite favored the stabilization of Cd as well as displayed a significant negative correlation between soil pH and extractable Cd concentration (P < 0.05). Sepiolite addition (0.5%–5%) significantly inhibited Cd absorption in spinach shoots, resulting in from 28.0% to 63.7%, from 29.4% to 67.8%, and from 17.2% to 72.1% reductions, respectively, when compared with unamended soil. At 1.25 mg kg− 1 Cd contamination, the concentrations of Cd in the edible portions of spinach at 1% sepiolite amendment were lower than 0.2 mg kg− 1 fresh weight, the maximum permissible concentration (MPC) for Cd in vegetables. MPC was met at higher concentrations of Cd (2.5 and 5 mg kg− 1) when the treatment of sepiolite was up to 5%. The changes in soil enzymatic activities and microbial numbers proved that certain metabolic recovery occurred after the application of sepiolite. Sepiolite-assisted remediation was shown to reduce successfully, on a field scale, Cd entry into the food chain.