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Arsenic exists in two distinct crystalline forms known as yellow arsenic and metallic arsenic. Yellow arsenic has a relatively low density (3.9 g/cc), is metastable, extremely volatile, and readily degrades to its metallic form. The low density implies an As4 structure that is similar to P4. The metallic form is a tin-white mineral that quickly tarnishes to dark gray. Metallic arsenic crystals have a density of 5.73 g/cc, are very brittle, and are good conductors of heat and poor conductors of electricity. Elemental arsenic is not common in nature.
Arsenic's principal ores are sulfides (As2S3, As4S4, and FeAsS), and arsenic sulfides are almost invariably found with other metal sulfides. The hydrogen form of arsenic is arsine, which is a poisonous gas. Arsenic also forms oxide compounds. Arsenic trioxide (As2O3) is a transparent crystal or white powder that is slightly soluble in water and has a specific gravity of 3.74. Arsenic pentoxide (As2O5) is a white amorphous solid that is very soluble in water, forming arsenic acid. It has a specific gravity of 4.32.
The most common forms of arsenic in groundwater are their oxy-anions, arsenite (As+3) and arsenate (As+5). Under moderately reducing conditions, arsenite is the predominant species. In oxygenated water, arsenate is the predominant species. Both anions are capable of adsorbing to various subsurface materials, such as ferric oxides and clay particles. Ferric oxides are particularly important to arsenate fate and transport as ferric oxides are abundant in the subsurface and arsenate strongly adsorbs to these surfaces in acidic to neutral waters. An increase in the pH to an alkaline condition will cause both arsenite and arsenate to desorb. Hence, they can be expected to be very mobile in an alkaline environment. The arsenic oxy-anions are also sensitive to redox conditions, and the speciation differential between them will change with changing redox (Henkel and Polette 1999).
Arsenic also forms organic compounds.
Arsenic in Ground Water of the Willamette Basin, Oregon
S. Henkel and D. Polette.
U.S. Geological Survey Water-Resources Investigations Report 98-4205, 1999
Arsenic Behavior under Sulfate-Reducing Conditions: Beware of the "Danger Zone"
Carol L. Stein, Gannett Fleming, Inc.
EPA Science Forum 2005: Collaborative Science for Environmental Solutions, May 16-18, 2005, Washington, DC.
Contact: Carol L. Stein, clsteinNH@adelphia.net
Arsenic in Groundwater: A Summary of Sources and the Biogeochemical and Hydrogeologic Factors Affecting Arsenic Occurrence and Mobility
Barringer , J.L. and P.A. Reilly.
Current Perspectives in Contaminant Hydrology and Water Resources Sustainability; P.M. Bradley (ed). InTech, Rijeka , Croatia . ISBN: 978-953-51-1046-0, Chapter 4: 83-116, 2013
ATSDR Toxicological Profile for Arsenic
Agency for Toxic Substances and Disease Registry, Aug 2007
Attenuation of Naturally Occurring Arsenic at Petroleum Impacted Sites
American Petroleum Institute, API Publication 4761, 90 pp, 2011
Naturally occurring arsenic can be mobilized into shallow groundwater by inputs of biodegradable organic carbon, including petroleum hydrocarbons. This manual identifies potential arsenic sources; explains the mobilization, transport, and attenuation mechanisms of naturally occurring arsenic in groundwater at petroleum-contaminated sites; and indicates tools for arsenic assessment and management. The report can be read on line. A summary paper is also available.
Behavior of Metals in Soils
McLean, J.E. and B.E. Bledsoe.
EPA 540-S-92-018, 25 pp, 1992
This paper covers the fundamental processes that control the mobility of metals (lead, chromium, arsenic, cadmium, nickel, zinc, copper, mercury, silver, and selenium) in soil and describes laboratory methods used to evaluate the behavior of metals in soil.
Environmental Chemistry of Arsenic
Frankenberger, W.T. (ed.)
Marcel Dekker, New York. ISBN: 0-8247-0676-5, 410 pp, 2002
Environmental Fate and Exposure Assessment for Arsenic in Groundwater
J.G. Hering, D. Burris, H.J. Reisinger, and P. O'Day.
SERDP, Project ER-1374, 27 pp, 2008
The fate and transport of arsenic were examined at Tyndall AFB, FL, where arsenic contamination has resulted from application of arsenical herbicides, and at Ft. Devens, MA, where naturally occurring arsenic has been mobilized by application of enhanced reductive dechlorination technology designed to remediate chlorinated solvent contamination. The comparison of to plume evolution, mechanism of arsenic mobilization in the source areas, and potential sequestration mechanisms at the two sites provides insight into the conditions under which MNA could be a feasible remedy for arsenic contamination.
Environmental Fate and Exposure Assessment for Arsenic in Groundwater: Final Report Addendum
O'Day, P. and V. Illera.
SERDP Project ER-1374, 38 pp, 2010
The results of this study indicate that sulfide phases can be a sink for As under sulfate-reduced conditions, particularly at low pH.
Field Study of the Fate of Arsenic, Lead,
and Zinc at the Ground-Water/
U.S. EPA, National Risk Management Research Laboratory, Ada, OK.
EPA 600-R-05-161, 91 pp, 2005
Final Report: Arsenic Fate, Transport and Stability Study, Groundwater, Surface Water, Soil and Sediment Investigation, Fort Devens Superfund Site Devens, Massachusetts
Ford, R., K.G. Scheckel, S. Acree, R. Ross, B. Lien, T. Luxton, and P. Clark
USEPA, Office of Research and Development, 193 pp, 2008
This document presents results from the Fiscal Years 2006-2007 field investigation at the Shepley's Hill Landfill Superfund site. The purpose of this study is to provide EPA Region 1 with a technical evaluation of the distribution and flux of arsenic in shallow groundwater adjacent to Red Cove and the fate, transport and stability of arsenic in sediments and surface water following groundwater discharge. Additional information: Ford et al. 2011. Delineating landfill leachate discharge to an arsenic contaminated waterway. Chemosphere 85(9):1525-1537 (Abstract).
Handbook of Elemental Speciation, II: Species in the Environment, Food, Medicine and Occupational Health
R. Cornelis, J. Caruso, H. Crews, and K. Heumann, eds.
John Wiley & Sons, New York. ISBN 0-470-85598-3, 768 pp, 2005.
Covers the speciation of elements from aluminum to zinc, including arsenic, chromium, and mercury.
The Impact of Ground-Water/Surface-Water Interactions on Contaminant Transport with Application to an Arsenic Contaminated Site
Robert Ford, U.S. EPA, National Risk Management Research Laboratory, Ada, OK.
EPA 600-S-05-002, 22 pp, 2005
This document provides a brief overview of the dynamics of chemical processes that govern contaminant transport and speciation during water exchange across the ground-water/surface-water transition zone and presents results from a field study examining the fate of arsenic during ground-water discharge into a shallow lake at a contaminated site.
Impacts of CCA-Treated Wood on Arsenic Concentrations in Soils and Plants
L. Ma, T. Chirenje, and J. Santos.
Florida Center for Solid and Hazardous Waste Management, Report 06-50892, 28 pp, 2006
The examination of soils and plants that have had 44 or more years of ground contact with chromated copper arsenate (CCA) provided a unique opportunity to study long-term migration of CCA constituents at several sites.
Natural Remediation of Arsenic Contaminated Ground Water Associated with Landfill Leachate
Kenneth G. Stollenwerk and John A. Colman.
U.S. Geological Survey Fact Sheet 2004-3057, 4 pp, 2004.
This fact sheet describes results of studies by the U.S. Geological Survey at the Saco Municipal Landfill, Saco, Maine. The source of arsenic in ground water and effects of landfill leachate on arsenic concentration in ground water are described.
Partition Coefficients for Metals in Surface Water, Soil, and Waste
Allison, Jerry D. (HydroGeoLogic, Inc., Herndon, VA); Terry L. Allison (Allison Geoscience Consultants, Inc., Flowery Branch, GA).
Report No: EPA 600-R-05-074, p , July 2005
This report presents metal partition coefficients for the surface water pathway and for the source model used in the multimedia, multi-pathway, multi-receptor exposure and risk assessment (3MRA) technology under development by U.S. EPA. Literature searches, statistical methods, geochemical speciation modeling, and expert judgment were used to provide reasonable estimates of partition coefficients for antimony, arsenic, barium, beryllium, cadmium, chromium, cobalt, copper, lead, molybdenum, mercury, methylated mercury, nickel, selenium, silver, thallium, tin, vanadium, and zinc.
Relation of Arsenic, Iron, and Manganese in Ground Water to Aquifer Type, Bedrock Lithogeochemistry, and Land Use in the New England Coastal Basins
J.D Ayotte, M.G. Nielsen, G.R. Robinson, Jr., and R.B. Moore.
U.S. Geological Survey Water Resources Investigations Report 99-4162, 70 pp, 1999
Contact: Joseph Ayotte, firstname.lastname@example.org
Rock-Bound Arsenic Influences Ground Water and Sediment Chemistry Throughout New England
G.R. Robinson Jr. and Joseph D. Ayotte. U.S. Geological Survey, Open-File Report 2007-1119, 18 pp, 2007
Both stream sediment chemistry and the solubility and mobility of arsenic in ground water in bedrock are influenced by host-rock arsenic concentrations. Stream sediment chemistry and the distribution of geologic units are useful parameters to predict the areas of greatest concern for elevated arsenic in ground water and to estimate the likely levels of human exposure to elevated arsenic in drinking water in New England; however, the extreme local variability of arsenic concentrations in ground water from these rock sources indicates that arsenic concentrations in ground water are affected by other factors in addition to arsenic concentrations in rock.