Biogeochemical processes in heterogeneous soil-Solanum nigrum L. system control lead partitioning: Roles of strengite and oxalated zero-valent iron nanoparticle

Lead (Pb) can possess its solubility, bioavailability and toxicity modified with solid phase transformation, but the potential for such processes in heterogeneous soil-plant system remains unclear. Herein, we investigated the biogeochemical pathways controlling Pb partitioning mediated by strengite (Fe III PO 4 ) and oxalated zero-valent iron (Ox-nZVI). Batch tests verified that Fe III PO 4 and Ox-nZVI achieved the dissolution of stable P and Fe while fixing Pb. Pot experiments with Solanum nigrum L. further showed the simultaneous addition of Fe III PO 4 and Ox-nZVI to soil reduced porewater Pb and boosted the utilization efficiency of P and Fe as a result of favoring Pb retention in the soild phase as Pb 5 (PO 4 ) 3 OH and PbFe 12 O 19 . Characterization results revealed the liquid-solid transfer mass fluctuation depends on precipitation-dissolution and adsorption-desorption reactions of Pb-containing solids driven by Fe III PO 4 reductive dissolution and Ox-nZVI oxidative corrosion. Both Fe III PO 4 and Ox-nZVI promoted plant uptake of Pb in root cell wall as chloropyromorphite crystals but suppressed its upward translocation due to iron plaque barrier. Both Fe III PO 4 and Ox-nZVI recruited more Fe(II)-oxidizing genera and thus facilitated electron transfer processes in near-rhizosphere soil. These findings provide new insights into the role of Fe III PO 4 and Ox-nZVI in microscale Pb stabilization coupled with Fe and P cycling for contaminated media.