Transformation kinetics of exogenous lead in an acidic soil during anoxic-oxic alteration: Important roles of phosphorus and organic matter.

Lead (Pb) can enter soil environment during flooding events such as surface runoff and intensive rainfall. However, the key transformation processes of exogenous Pb during anoxic-oxic alteration remain poorly understood particularly how phosphorus and organic matter contribute to Pb immobilization/release. Here, a kinetic model was established to investigate the Pb transformation in an acidic soil with two levels of Pb contamination under alternating anoxic-oxic conditions, based on the results of seven-step sequential extraction, dissolved organic carbon, sulfate, iron, phosphorus, and surface sites.

Transformation kinetics of exogenous nickel in a paddy soil during anoxic-oxic alteration: Roles of organic matter and iron oxides.

Nickel is generally released from flooded soils; however, the key Ni transformation processes in soils that are freshly contaminated by Ni during anoxic-oxic alteration remain unclear. We developed a kinetic model to investigate the Ni transformation in paddy soils under anoxic and oxic conditions based on the results of the seven-step sequential extraction, determination of dissolved and soil organic matter, and surface site quantification, which provide the kinetic data of different Ni fractions, organic matter, and reactive sites for modeling. The dissolved, exchangeable, and specifically adsorbed Ni was gradually transferred to fulvic complex, humic complex, Fe-Mn oxide bound, and sulfide bound Ni after 40 d of anoxic incubation due to the increase in pH and soil surface sites, which were mainly induced by Fe(III) oxide reduction and soil organic matter release.