Stimulation of oxalate root exudate in arsenic speciation and fluctuation with phosphate and iron in anoxic mangrove sediment. (April 2023) - Mei, Kang
Abstract: Mutual transformations of rhizospheric arsenic (As) in pollution-prone mangrove sediments affected by root exudate oxalate were simulated. This study focuses on the effect of oxalate on As release, mobilization, and phase speciation associated with P and Fe was examined under anoxic conditions in time-dependent changes. Results showed that oxalate addition significantly facilitated As–Fe–P release from As-contaminated mangrove sediments. Sediment As formed the adsorptive and the carbonate-binding fractionations, facilitating the re-adsorption processes. Solution As and As 5+ correlated with NaOH–P positively but with NaHCO3 –P and HCl–P negatively. Dominant Fe 3+ (>84 %) from the amorphous Fe regulated suspension changes and then time-dependent co-precipitation with As and P. Sediment P formed strong complexes with Fe oxides and could be substituted for As via STEM analysis. Oxalate ligand exchange, competitive adsorption of oxalate, and Fe-reduced dissolution are confirmed to involve, allowing for an insight As/P/Fe mobilization and fate in mangrove wetland. Graphical abstract: Unlabelled Image Highlights: The effect of common root exudate oxalate on As release, mobilization and phase fractionation was explored. The mechanisms involved in the oxalate-enhanced release of As were dominated by Fe oxide/hydroxide co-precipitation. The dynamics of rhizospheric interfaces were oxalate ligand exchange, competitive adsorption and P/Fe-reduced dissolution. The P formed strong complexes with Fe oxides and could be substituted for As via STEM analysis. Results outlined concerns on the potential risk of mobilization of arsenic in the mangrove rhizospheric sediments.