Processes Influencing the Mobility of Arsenic and Chromium in Reduced Soils and Sediments

EPA Grant Number: R825399
Title: Processes Influencing the Mobility of Arsenic and Chromium in Reduced Soils and Sediments
Investigators: Fendorf, Scott
Institution: Stanford University
EPA Project Officer: Hiscock, Michael
Project Period: January 28, 1997 through January 27, 2000
Project Amount: $293,573
RFA: Exploratory Research - Water Chemistry and Physics (1996) RFA Text |  Recipients Lists
Research Category: Water , Land and Waste Management , Engineering and Environmental Chemistry


Many studies have established that redox reactions profoundly affect the mobility, and thus risk, of both arsenic and chromium in the environment. More specifically, reactions changing Cr(VI) to Cr(III) can be expected to stabilize this element and decrease its mobility and toxicity. In contrast, reduction of As(V) to As(III) results in a more toxic product that is generally considered more mobile in the environment. Microbial activities may indirectly or directly affect these processes, but the reaction products will differ appreciably depending on the specific reduction mechanism. Aqueous Fe(II) and colloidal iron sulfides produced in reduced soils and sediments should be effective reductants of Cr(VI); aqueous and metal sulfides should be effective reductants of As(V). Depending on the environmental context, it is also possible that enzymatic reduction is the dominant mechanism by which As(V) or Cr(VI) is reduced. Detailed knowledge of both processes is necessary not only to properly assess the environmental risk of As or Cr, but also to help refine remediation/containment technologies. The specific questions we will address in this research are: (i) what are the contributions of abiotic versus biotic reduction of arsenate and chromate in soils and sediments, (ii) under what conditions does each mechanism dominate, and (iii) what are the resulting products and what are their mobilities? The objectives of this study too address these questions are also three-fold: (1) determine the extent and rate of Cr(VI) and As(V) reduction by FeS, (2) evaluate abiotic versus biotic reduction of As(V) and Cr(VI) in reduced soils, and (3) detail the solution and solid phase products. Two conditions for reduction in soils will be studied; one in which As or Cr is introduced to a reduced soil and a second where an aerated, As- or Cr-contaminated soils is subjected to flooding. X-ray absorption fine structure (XAFS) spectroscopy will be used to determine the chemical and structural state of As and Cr in the solid-phase; more conventional spectrophotometric methods will be used to speciate the solution phase products. The results of this study should help substantiate what processes control the fate of As or Cr in reduced environments, and it will substantiate the risk imposed by these reaction products. Such information is critical for risk assessment and for designing management or remediation strategies for As or Cr contaminated sites. Because As and Cr readily enter soils and waters from industrial and agricultural uses of these elements, and because they are hazardous to plants and animals, this study should be beneficial to agriculture, industry, and the public.

Publications and Presentations:

Publications have been submitted on this project: View all 15 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 5 journal articles for this project

Supplemental Keywords:

RFA, Scientific Discipline, Toxics, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, National Recommended Water Quality, Contaminated Sediments, Remediation, Environmental Chemistry, Ecosystem/Assessment/Indicators, Arsenic, Chemistry, Fate & Transport, fate, fate and transport, risk assessment, aquatic ecosystem, cellular redox status, colloidal particles, contaminant transport, human health effects, soil sediment, redox metabolism, arsenic transformation, agricultural watershed, Chromium, sediment transport, spectroscopic studies, contaminated sediment, adverse human health affects, chemical contaminants, kinetic studies, microbial pollution, processes influencing mobility, arsenic mobility, water quality, arsenic exposure, aquatic biota, exposure assessment

Progress and Final Reports:

  • 1997
  • 1998
  • Final Report