PeatBogs as Hotspots for Organoarsenical Formationand Persistence

Peatlands have received\nsignificant atmospheric inputs of As and\nS since the onset of the Industrial Revolution, but the effect of\nS deposition on the fate of As is largely unknown. It may encompass\nthe formation of As sulfides and organosulfur-bound As, or the indirect\nstimulation of As biotransformation processes, which are presently\nnot considered as important As immobilization pathways in wetlands.\nTo investigate the immobilization mechanisms of anthropogenically\nderived As in peatlands subjected to long-term atmospheric pollution,\nwe explored the solid-phase speciation of As, Fe, and S in English\npeat bogs by X-ray absorption spectroscopy. Additionally, we analyzed\nthe speciation of As in pore- and streamwaters. Linear combination\nfits of extended X-ray absorption fine structure (EXAFS) data imply\nthat 62–100% (average: 82%) of solid-phase As (A<i>s</i><sub>tot</sub>: 9–92 mg/kg) was present as organic As­(V) and\nAs­(III). In agreement with appreciable concentrations of organoarsenicals\nin surface waters (pH: 4.0–4.4, E<sub>h</sub>: 165–190\nmV, average A<i>s</i><sub>tot</sub>: 1.5–129 μg/L),\nour findings reveal extensive biotransformation of atmospheric As\nand the enrichment of organoarsenicals in the peat, suggesting that\nthe importance of organometal­(loid)­s in wetlands subjected to prolonged\nair pollution is higher than previously assumed.