United States
Environmental Protection
Agency
RESEARCH PROJECT
National Risk Management Research Laboratoi
Water Supply and Water Resources Division
Treatment Technology Evaluation Branch
DESORPTION OF ARSENIC FROM DRINKING WATER DISTRIBUTION SYSTEM SOLIDS
IMPACT STATEMENT
The U.S. Environmental Protection Agency (EPA) recently
revised the previous maximum contaminant level (MCL)
for arsenic in drinking water from 0.050 mg/L to 0.010
mg/L (Federal Register 2001) as a result of recent health
studies. The new arsenic standard for drinking water will
require thousands of drinking water systems to install
arsenic removal treatment processes or modify their
existing treatment to meet the new standard. Very few
documented studies exist that have measured elevated
arsenic levels in drinking water distribution systems
(DWDS). To the best of our knowledge, there is very little
information identifying the degree to which these
mechanisms of arsenic release take place. This
investigation adds to EPA's scientific knowledge
regarding soluble release of arsenic from DWDS solids, and enables EPA to continue to provide the best expertise and
guidance to drinking water utilities, engineers, the general public, and other stakeholders on issues of treatment and
compliance for arsenic under the new standard.
BACKGROUND:
The new arsenic standard for drinking water will require thousands of drinking water systems to install arsenic removal
treatment processes or modify their existing treatment to meet the new standard. Most of the current arsenic
treatment strategies are iron- and aluminum-based (e.g., coagulation, iron removal, adsorption media) due to the well
known adsorptive properties of iron and aluminum oxides' surfaces toward arsenic. Since drinking water distribution
systems (DWDS) contain many iron surfaces, such as corrosion by-products from corroding iron distribution pipes, it is
reasonable to assume that they could adsorb high concentrations of arsenic over time if arsenic is present in the
distribution system water. The concern would then be that these solids could release elevated concentrations of arsenic
back into the distributed water due to changes either in hydraulic (mechanical) or chemical processes. "Arsenic release"
could be particulate or soluble in nature. Particulate release refers to the disturbance and transport of arsenic-
containing particles in the water. Very few documented studies exist that have measured elevated arsenic levels in
drinking water distribution systems. To the best of our knowledge, there is no documented case study identifying the
degree to which these mechanisms of arsenic release take place.
DESCRIPTION:
Given the limited knowledge regarding the soluble release of arsenic from DWDS solids, the objectives of this research
were to: 1) investigate the effect of pH on the dissolution/desorption of arsenic from DWDS solids, and 2) examine the
effect of orthophosphate on the soluble release of arsenic from DWDS into the water at pH 7, 8 and 9.
Desorption experiments were conducted on distribution system solids collected from Midwest water utilities. The
utilities were selected because they had measurable levels of arsenic in their drinking water. The treatment processes
National Risk Management Research Laboratory
Water Supply and Water Resources Division
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for each utility played an important role in understanding scale formation and elemental composition. The study
investigated the mineralogy and elemental composition of the test solids; the effect of time and pH on arsenic release;
arsenic release in the presence of orthophosphate; and, additional element release.
EPA GOAL: Goal #2 - Clean & Safe Water; Objective 2.1.1- Water Safe to Drink
ORD MULTI YEAR PLAN: Drinking Water (DW), Long Term Goal - DW-2 Control, Manage, and Mitigate Health Risks
EXPECTED OUTCOMES AND IMPACTS:
The project will provide sound methods for improving and optimizing arsenic removal during iron removal to water
utilities, states, engineers, and consultants.
OUTPUTS:
Current outputs consist of several presentations and peer-reviewed journal articles.
JOURNAL ARTICLE: Copeland, R.C., Lytle, D.A., and D.D. Dionysiou. Desorption of Arsenic from Drinking Water Distribution
System Solids. Environ. Monit. Assess., 127:523-535 (2007) (On-line Issn. 0167-6369, Oct. 11, 2006).
RESOURCES:
EPA Arsenic Research: http://www.epa.Rov/nrmrl/wswrd/dw/arsenic/
NRMRL Drinking Water Research: http://www.epa.Rov/ORD/NRMRL/wswrd/dw/index.html
NRMRL Treatment Technology Evaluation Branch: http://www.epa.ROv/ORD/NRMRL/wswrd/tteb.htm
CONTACTS:
Darren Lytle, Principal Investigator - (513) 569-7432 or lytle.darren@epa.gov
Steven Doub, MediaRelations - (513) 569-7503 ordoub.steven@epa.gov
Michelle Latham, Communications - (513) 569-7601 orlatham.michelle@epa.gov
National Risk Management Research Laboratory
Water Supply and Water Resources Division
www.epa.gov/nrmrl EPA/600/F-10/002
February 2010
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