Impact of organic matter on As sulfidation in wetlands: An in situ experiment.

Arsenic incorporation into newly formed As sulfides has recently been identified as an important As sequestration pathway in both laboratory experiments and natural As-wetlands. Here, we used an in situ experimental technique with double nylon experimental bags (10-μm mesh) to study the effect of low-cost organic materials (sawdust, wood cubes and hemp shives) on As sulfidation in three naturally As-enriched wetland soils under water-saturated (~1 m depth) and neutral pH conditions. After 15 months of in situ incubation, all of the organic materials and their corresponding inner bags were covered by yellow-black mineral accumulations, dominantly composed of crystalline AsS polymorphs (realgar and bonazziite) and reactive Fe(II) sulfides (probably mackinawite); while the major fraction of As (~80%) was sequestered as AsS minerals.

Arsenic fractionation and mobility in sulfidic wetland soils during experimental drying.

In this study, two Czech wetland soils enriched in authigenic sulfide minerals (especially realgar) were collected from the saturated zone (60-100 cm), flooded with local groundwater and allowed to dry for up to 98 days. The objective was to examine the mobility of As, Fe, S and trace metals using selective chemical extractions, S isotopes and X-ray diffraction through the drying process. During the initial stage of incubation (∼20 days), the re-flooding of the soils triggered a microbially-mediated SO reduction, which immobilized the Co, Cu and Ni.