Compounded chelating agent derived from fruit residue extracts effectively enhances Cd phytoextraction by Sedum alfredii

Abstract

Chelating agent is known as the enhancer for metal phytoextraction; however, there is still a lack of efficient and environmentally sustainable chelators. Here, lemon residue extraction (LRE), prepared from 11 kinds of fruit wastes, was combined with N, N-bis (carboxymethyl) glutamic acid (GLDA), and tea saponin (T.S.) for the compounded plant-derived chelator (CPC), and their influences on Cd phytoextraction by the hyperaccumulator Sedum alfredii was evaluated. Among these fruits, the lemon residue extracted the most significant amount of Cd from the soil. The most effective CPC was at the volume ratio of three agents being 15:4:1 (LRE:GLDA:T.S.). Compared with the deionized water, the solubility of three Cd minerals was increased by 85–256 times, and Cd speciation was substantially altered after CPC application. In the pot experiment, CPC addition caused evident increases in plant shoot biomass, Cd phytoextraction efficiency, and organic matter content compared with EDTA and nitrilotriacetic acid (NTA) application. CPC induced fewer changes in bacterial community composition compared with EDTA and had no pronounced influence on microbial biomass carbon and bacterial α-diversity, suggesting CPC had a subtle impact on the microbiological environments. Our study provides a theoretical base for the reutilization of fruit wastes and the development of environmental-friendly chelator that assists Cd phytoextraction.