Immobilization of As and Sb by combined applications Fe–Mn oxides with organic amendments and alleviation their uptake by Brassica campestris L

Abstract

Pot experiments were performed to investigate the efficiency of Fe–Mn oxides (FM) combined with two organic amendments, silkworm excrement organic amendment (FM-SE) and peat soil (FM-PS), in immobilizing antimony (Sb) and arsenic (As) in soils and thus reducing metalloids uptake by Brassica campestris L. The available As was significantly decreased by 87% and 70% and Sb was decreased by 51% and 29% in FM-SE and FM-PS amended soil, respectively. Sequential extraction analysis demonstrated that non-specifically and specifically sorbed Sb and As were transformed into well-crystallized hydrous oxides fraction, decreasing their mobility effectively, after addition of FM-SE and FM-PS. FTIR and XPS analysis showed that FM has surface hydroxyl groups (-OH) in large quantities, forming As/Sb–O complex by surface complexation to retain As and Sb. The amendments improved soil pH, nutrients and organic matter content, appreciably inhibited As and Sb uptake by Brassica campestris L. The content of As in leaves decreased from 0.61 mg/kg (control) to 0.07 mg/kg (FM-SE) and 0.09 mg/kg (FM-PS), lower than the Chinese National Food Safety Standard limit of 0.2 mg/kg (GB2762-2017). The bioavailability of As was found to be higher than Sb, which could be more easily transferred and accumulated by plants in exposed contaminated soil. The combined applications of SE and PS with FM shed light on simultaneously immobilizing As and Sb in soils and further inhibiting their uptake by plants.