Peat Bogs as Hotspots for Organoarsenical Formation and Persistence

Area of Science:

• Environmental Chemistry
• Geochemistry
• Biogeochemistry

Background:

• Peatlands receive atmospheric inputs of arsenic (As) and sulfur (S) since the Industrial Revolution.
• The impact of sulfur deposition on arsenic fate and immobilization in peatlands is poorly understood.
• Current knowledge does not consider biotransformation as a major arsenic immobilization pathway in wetlands.

Purpose of the Study:

• Investigate arsenic immobilization mechanisms in peatlands affected by long-term atmospheric pollution.
• Determine the role of sulfur deposition in the transformation and fate of atmospheric arsenic.
• Assess the significance of organoarsenicals in polluted wetland environments.

Main Methods:

• X-ray absorption spectroscopy (XAS) was used to analyze solid-phase speciation of As, Fe, and S in English peat bogs.
• Extended X-ray absorption fine structure (EXAFS) data were analyzed using linear combination fits.
• Speciation of As in pore water and stream water was also analyzed.

Main Results:

• Solid-phase arsenic predominantly existed as organic arsenic (As(V) and As(III)), averaging 82% (range 62-100%).
• Appreciable concentrations of organoarsenicals were found in surface waters.
• Extensive biotransformation of atmospheric arsenic and enrichment of organoarsenicals in peat were observed.

Conclusions:

• Atmospheric arsenic undergoes significant biotransformation in peatlands, forming organoarsenicals.
• Organoarsenicals are enriched in peat, indicating their importance in arsenic immobilization.
• The role of organometalloids in wetlands under prolonged air pollution is more significant than previously recognized.