Coupling of Biotic and Abiotic Arsenite Oxidation in SoilEPA Grant Number: FP917135
Title: Coupling of Biotic and Abiotic Arsenite Oxidation in Soil
Investigators: Jones, Laura Camille
Institution: University of Delaware
EPA Project Officer: Lee, Sonja
Project Period: August 31, 2010 through August 31, 2012
Project Amount: $74,000
RFA: STAR Graduate Fellowships (2010) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Fellowship - Ecosystem Services: Terrestrial Systems Soil and Plant Ecology
Arsenic (As) is a redox-active metalloid whose toxicity, bioavailability, and environmental mobility depend on oxidation state. This project investigates the kinetics and mechanisms of arsenic oxidation, which is a transformation to the less toxic and less mobile form of arsenic, by natural biotic and abiotic oxidants found in soils.
Millions of people are currently exposed to arsenic, a toxic metalloid, via contaminated food and drinking water. Complex chemical, bioloigical, and hydrological processes in soils mobilize arsenic from natural (i.e. rock) and anthropogenic (i.e. pesticide) sources to contaminate water. This study investigates coupled biological and abiotic pathways of a chemical reaction that transforms arsenic to a less mobile and less toxic form in soils. The results of this study will be used to understand how arsenic moves around in soils and for prediction and remediation of the worldwide human health hazards caused by arsenic.
Arsenite [As(III)], the more toxic and mobile form of inorganic As, can be oxidized to arsenate [As(V)] by both minerals and bacteria in soils. It has been noted in previous studies that, in isolation, manganese (Mn) oxide minerals can oxidize As(III) and sorb As(V). Numerous isolates of heterotrophic soil bacteria, including the bacteria used here (Alcaligenes faecalis and Pseudomonas fluorescens) have also been shown to oxidize As(III) in a detoxification mechanism. Despite having some experimental evidence for activity of these soil oxidants in isolation, not much is known about the coupling of biotic and abiotic oxidants in soils. This study investigates the rates and coupling of As(III) oxidation by model heterotrophic bacteria, A. faecalis and P. fluorescens, and a Mn oxide mineral, δ-MnO2 using batch experiments.
This project is expected to produce rate and kinetic information about As(III) oxidation in a model system with a mixture of mineral and microbial oxidants. Comparing the apparent kinetics of As(III) oxidation in mixed microbe-mineral batch experiments with isolated batch experiments, with the bacteria or the mineral alone, will give evidence for the mechanisms and reactivity of these pathways. In soils, minerals and microbes coexist and yet little is known about the rate and mechanisms surrounding this reaction in an experimental system with both types of oxidants. These results will contribute to understanding coupled microbe-mineral processes involved in the fate and transport of As.
Potential to Further Environmental/Human Health Protection:
Recent instances of human exposure to toxic levels of arsenic in drinking water have motivated investigation into the biogeochemical processes governing As mobility in soil. The rate information produced in this study can be used to model coupled biotic and abiotic arsenic redox processes and predict potential human health and environmental hazards posed by arsenic.