Discovering the Nexus Between, and Quantifying the Rates of, the Physical and Biogeochemical Mechanisms Governing Arsenic Release From Soil and Sediment to Pore-Water Under Anaerobic ConditionsEPA Grant Number: FP917111
Title: Discovering the Nexus Between, and Quantifying the Rates of, the Physical and Biogeochemical Mechanisms Governing Arsenic Release From Soil and Sediment to Pore-Water Under Anaerobic Conditions
Investigators: Stuckey, Jason Wayne
Institution: Stanford University
EPA Project Officer: Jones, Brandon
Project Period: September 1, 2010 through August 31, 2013
Project Amount: $111,000
RFA: STAR Graduate Fellowships (2010) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Fellowship - Drinking Water
Millions of people around the world drink arsenic-contaminated groundwater. The protection of groundwater as a drinking water source requires that we develop the ability to identify areas of active arsenic release to pore-water, to identify areas without the capacity to release appreciable arsenic, and to predict how this spatial distribution will change temporally. This research project will quantify the biogeochemical and physical controls of arsenic transport rate in soils and sediments, supporting the accurate projection of site-specific groundwater arsenic concentrations in space and time.
Through a combination of field and laboratory techniques, this research seeks to quantify the factors controlling the release of arsenic from sediment to groundwater, namely the reactivity of organic carbon and iron oxides, as well as physical processes. The resulting parameterization will serve as the experimental basis for modeling dissolved arsenic concentrations in space and time, thereby informing drinking water well construction in areas of arsenic risk.
The three key aspects dictating microbial-driven release of arsenic from soil/sediment solids to pore-water under anaerobic conditions are the (i) reactivity and (ii) quantity of organic carbon and arsenic-bearing iron oxides, and (iii) the diffusion of arsenic and dissolved organic carbon between mobile and less mobile flow regimes. The first stage of research will be the development of batch assays for determining site-specific organic matter and arsenic reactivity representative of in situ conditions. Column studies using undisturbed sediment cores will discern whether physical (diffusion) or biogeochemical processes control arsenic transport. Quantifying the controls of arsenic transport rate will provide the necessary input parameters for modeling dissolved arsenic concentrations along a flow path.
This research will reveal what controls the rate of arsenic transport in soils and sediments. In a system with high water flow (both advection and diffusion) velocities, the availability of reactive catabolic substrate (either organic carbon or iron oxide) will govern the rate of arsenic release into advecting pore-water. Alternatively, a slow diffusion rate will limit the transfer of arsenic from micro-aggregates to pore-water, even in instances where microorganisms have plenty of reactive organic carbon and arsenic-bearing iron oxides at their disposal. The assays developed here to quantify the reactivity of arsenic and susceptibility of organic matter to oxidation coupled to arsenic(V)/iron(III) reduction will provide accurate parameters for identifying areas of active (and inactive) arsenic transfer from sediment to pore-water. Combined with hydraulic and physical transport data, the parameterization will form the experimental basis for a reactive transport modeling of arsenic in soils and sediments. Field calibration will facilitate transfer of this model parameterization method to aquifer systems worldwide.
Potential to Further Environmental/Human Health Protection:
Hundreds of millions of people rely on groundwater for drinking that is or has the potential to be contaminated with arsenic. The experimental approach developed here will allow scientists to accurately predict arsenic transport rates and residence times, and provide policy makers with an improved framework for making sound land and water management decisions, especially regarding drinking water well construction in rural areas.