Reaction and Transport of Arsenic in Soils: Equilibrium and Kinetic Modeling

Arsenic contamination of the soil and groundwater poses great risk to human and animal health. There is a growing public interest in developing risk assessment framework, environment regulations, and remedial strategies for protecting ecosystems and human from arsenic poisoning. Although extensive research efforts have been made over the past four decades, the prediction of the fate and transport of arsenic in soils are often inaccurate due to the complex biogeochemical reactions of various arsenic species in soil and water environments. In-depth knowledge of factors that influence the behavior of arsenic in aqueous and solid phases are critical in making accurate determinations of the mobility, bioavailability, and toxicity of arsenic in the soil root zone. In this contribution, we present a review of the state of knowledge on reactions and transport of arsenic in soils with emphasis on modeling of the physical, chemical, and biological interactions of arsenic in soil environment. Specifically, we present an overview of (i) biogeochemical mechanisms of arsenic adsorption desorption, oxidation reduction, and precipitation dissolution; (ii) reactive transport mechanisms of arsenic in the natural environment as affected by factors including arsenic species, redox potential, solution chemistry, flow regime, and colloid-facilitated transport; and (iii) equilibrium and kinetic modeling approaches to simulating the geochemical reactions and transport mechanisms of arsenic in porous media. A range of remedial technologies have been reviewed and their effectiveness and feasibility in the removal or in situ stabilization of arsenic in contaminated soils are discussed. Future research needs are also outlined.