Effects of water and organic manure coupling on the immobilization of cadmium by sepiolite

Abstract

Natural sepiolite (SP) has proven effective on the in-situ immobilization remediation of Cd-contaminated soils. But the practical remediation effect may largely influenced by water management and the application of organic manure. The effects of chicken manure (CM) on SP-amended soils were investigated under normal and saturated water conditions using a pot experiment with Brassica campestris L. Cd-contaminated paddy soils were amended with CM, SP, and CM + SP with no amendment as control. The amount of sepiolite was 0.5% (w/w, the same below) either in SP or CM + SP amended soils, while the amount of CM was 0.5, 1.0, and 2.0% in CM and CM + SP-amended soils. The plant metal contents, fresh weight, and soluble sugar content of plant edible parts were measured on harvest. Soil Cd was extracted by diethylenetriaminepentaacetic acid (DTPA) and HCl to estimate the mobility of heavy metal. Soil pH and dissolved organic matter (DOM) of rhizosphere soil were determined. The electronegative charges of soils were also measured using the zeta potential. The application of CM and increasing soil moisture on SP-amended soil increased plant growth to a greater extent than the application of SP alone. The application of CM along with the increase of soil moisture decreased Cd uptake and translocation in plants grown on SP-amended soil compared to the application of SP alone. Cd content of edible plant parts reached a minimum of 0.24 mg kg−1 with the application of 2.0% CM on SP-amended soils under water-saturated conditions, which was approximately 50% lower than the Cd concentration found when applying SP alone. The results of this study suggest that the application of sepiolite on Cd contaminated soil can effectively reduce Cd uptake by B. campestris L., and the addition of CM combined with effective water management also appears to further reduce Cd absorption and accumulation.