Contaminant Candidate
\ List Regulatory
Determination Support
Document for Sulfate
K.-r; Printed on Recycled Paper
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Contaminant Candidate List
Regulatory Determination Support Document
for Sulfate
U.S. Environmental Protection Agency
Office of Water (4607M)
Standards and Risk Management Division
Washington, DC 20460
http://www.epa.gov/SAFEWATER/ccl/cclregdetermine.html
EPA-815-R-03-16
July 2003
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Disclaimer
This document is designed to provide supporting information regarding the
regulatory determinations for sulfate as part of the Contaminant Candidate
List (CCL) evaluation process. This document is not a regulation, and it does
not substitute for the Safe Drinking Water Act (SDWA) or the Environmental
Protection Agency's (EPA's) regulations. Thus, it cannot impose legally-
binding requirements on EPA, States, or the regulated community, and may
not apply to a particular situation based upon the circumstances. Mention of
trade names or commercial products does not constitute endorsement or
recommendation for use.
K'.-T! Printed on Recycled Paper
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Regulatory Determination Support Document for Sulfate July 2003
ACKNOWLEDGMENTS
This document was prepared in support of the EPA Office of Ground Water and Drinking Water's
regulatory determination for sulfate as part of the Contaminant Candidate List (CCL) evaluation
process. Karen Wirth and Tom Carpenter served as EPA's Co-Team Leaders for the CCL regulatory
determination process, and Ephraim King as Standards and Risk Management Division Director.
Harriet Colbert served as Work Assignment Manager. The CCL Work Group provided technical
guidance throughout. In particular, Karen Wirth, Dan Olson, and Joyce Donohue provided scientific
and editorial guidance. External expert reviewers and many stakeholders provided valuable advice to
improve the CCL Program and this document. The Cadmus Group, Inc., served as the primary
contractor providing support for this work. The major contributions of Matt Collins, Emily Brott,
Ashton Koo, Richard Zeroka, and Brent Ranalli are gratefully acknowledged. George Hallberg served
as Cadmus' Project Manager.
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Regulatory Determination Support Document for Sulfate July 2003
USEPA, Office of Water Report: EPA 815-R-03-016, July 2003
CONTAMINANT CANDIDATE LIST
REGULATORY DETERMINATION SUPPORT DOCUMENT
FOR SULFATE
EXECUTIVE SUMMARY
Sulfate was a 1998 Contaminant Candidate List (CCL) regulatory determination priority
contaminant. Sulfate was one of the contaminants considered by the U.S. Environmental Protection
Agency (EPA) for a regulatory determination. The available data on occurrence, exposure, and other
risk considerations suggest that regulating sulfate may not present a meaningful opportunity to reduce
health risk. EPA presented preliminary CCL regulatory determinations and further analysis in the June
3, 2002 Federal Register (FR) Notice (USEPA 2002a; 67 FR 38222) and confirmed the final
regulatory determinations in a July 18, 2003 Federal Register Notice (USEPA 2003 a; 68 FR 42898).
To make the determination for sulfate, EPA used approaches guided by the National Drinking
Water Advisory Council's (NDWAC) Work group on CCL and Six-Year Review. The Safe Drinking
Water Act (SDWA) requirements for National Primary Drinking Water Regulation (NPDWR)
promulgation guided protocol development. The SDWA Section 1412(b)(l)(A) specifies that the
determination to regulate a contaminant must be based on a finding that each of the following criteria are
met: (i) "the contaminant may have adverse effects on the health of persons"; (ii) "the contaminant is
known to occur or there is substantial likelihood that the contaminant will occur in public water systems
with a frequency and at levels of public health concern"; and (iii) "in the sole judgement of the
Administrator, regulation of such contaminant presents a meaningful opportunity for health risk
reduction for persons served by public water systems." Available data were evaluated to address each
of the three statutory criteria.
Sulfate, a soluble, divalent anion (SO42"), is produced from the oxidation of elemental sulfur, sulfide
minerals, or organic sulfur. Sulfate is ubiquitous in the environment because of the abundance of sulfur
on earth. Anthropogenic sources of sulfate include the burning of sulfur-containing fossil fuels,
household wastes including detergents, and industrial effluents from tanneries, steel mills, sulfate-pulp
mills, and textile plants. Sulfate is also used in pickle liquor (sulfuric acid) for steel and metal industries,
as a feedstock or reagent in manufacturing processes, in some fertilizers, and exists as an end-product
in the form of copper sulfate in its use as a fungicide and algicide.
In 1979, EPA established a secondary maximum contaminant level (SMCL), a non-enforceable
guidance level for aesthetic quality, at 250 mg/L for sulfate in drinking water. In 1985, EPA proposed
a sulfate health advisory (HA) of 400 mg/L that was never finalized. The SDWA amendments of 1986
mandated an NPDWR for sulfate as well as the establishment of a maximum contaminant level goal
(MCLG). After a proposal of two alternative MCLGs of 400 and 500 mg/L in 1990, and a reproposal
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of a 500 mg/L MCLG and Maximum Contaminant Level (MCL) in 1994, a regulatory determination
had not been finalized when Congress amended the SDWA in 1996. Sulfate was monitored from 1993
to 1999 under the SDWA Unregulated Contaminant Monitoring (UCM) program.
The SDWA amendments of 1996 required EPA to finalize a sulfate regulatory determination by
August, 2001 and to complete a joint study with the Center for Disease Control and Prevention (CDC)
before NPDWR promulgation. The joint study was to determine a reliable dose-response relationship
for human health effects following exposure to sulfate in drinking water. EPA and CDC jointly
concluded it is unlikely that any adverse health effects will result from sulfate concentrations in drinking
water below 600 mg/L for adults. An expert panel of scientists convened in September, 1998, to
supplement the EPA/CDC study concluded there was insufficient scientific evidence regarding health
effects to justify a regulation, and suggested that a health advisory be issued in areas where sulfate
concentrations in drinking water exceed 500 mg/L.
Sulfate occurrence is ubiquitous in ambient waters monitored by the United States Geological
Survey's (USGS) National Water Quality Assessment (NAWQA) program. The NAWQA
monitoring results indicate nearly 100% of all surface and ground water sites have sample analytical
detections of sulfate. Although sulfate detection frequencies are high in surface and ground waters,
sulfate occurrence at levels of public health concern is low. Less than approximately 1.4% of all
surface water sites and about 1.8% of all ground water sites showed detections greater than a Health
Reference Level (HRL) of 500 mg/L, a preliminary health effect level used for this analysis. HRL
exceedances and 99th percentile concentrations are generally greatest in urban basins, while median
sulfate concentrations are similar for urban, mixed land use, and agricultural basins.
Sulfate has also been detected in public water systems (PWS) compliance monitoring samples
collected under SDWA. Occurrence estimates are very high by all measures. Approximately 87% of
all samples show detections, and the median and 99th percentile concentrations of all samples are 24
mg/L and 560 mg/L, respectively. Approximately 88% of systems, serving 95% of the national PWS
population (202 million people), report detections. An estimated 0.9% of PWSs, serving about 2
million people nationally, use water with sulfate levels above an HRL of 500 mg/L. Additional data,
including both ground water and surface water PWSs from select States, were examined through
independent analyses and also have shown substantial low-level sulfate occurrence.
The available lexicological data indicate that sulfate may cause adverse health effects in humans and
animals. Sulfate has a laxative effect in high doses, but adverse health effects are temporary and
recovery is rapid. Sub-populations sensitive to sulfate ingested through drinking water include formula-
fed infants, the elderly or invalids who use powdered nutritional supplements, and visitors who are not
acclimated to high sulfate concentrations in drinking water.
In summary, monitoring data indicate that sulfate is detected in the majority of drinking water
supplies, but is infrequently detected above the HRL of 500 mg/L. The risk of adverse health effects to
the general population is limited and acute (a short-duration laxative response), and such effects occur
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only at high drinking water concentrations (>500 mg/L, and in many cases >1,000 mg/L). People can
develop a tolerance for high concentrations of sulfate in drinking water. Also, because of the taste of
water high in sulfate (the taste threshold for sulfate is 250 mg/L), people tend to decrease the amount of
high-sulfate water they drink at one time, thus reducing the likelihood of acute exposure. For these
reasons, it is unlikely that regulation of sulfate would present a meaningful opportunity for health risk
reduction. EPA is, however, issuing an advisory to provide guidance to communities that may be
exposed to drinking water contaminated with high sulfate concentrations.
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Regulatory Determination Support Document for Sulfate July 2003
TABLE OF CONTENTS
ACKNOWLEDGMENTS i
EXECUTIVE SUMMARY iii
TABLE OF CONTENTS vii
LIST OF TABLES ix
LIST OF FIGURES xi
1.0 INTRODUCTION 1
1.1 Purpose and Scope 1
1.2 Statutory Framework/Background 1
1.3 Statutory History of Sulfate 2
1.4 Regulatory Determination Process 3
1.5 Determination Outcome 5
2.0 CONTAMINANT DEFINITION 5
2.1 Environmental Fate/Behavior 6
3.0 OCCURRENCE AND EXPOSURE 7
3.1 Use and Environmental Release 7
3.1.1 Production and Use 7
3.1.2 Environmental Release 8
3.2 Ambient Occurrence 11
3.2.1 Data Sources and Methods 12
3.2.2 Results 13
3.3 Drinking Water Occurrence 14
3.3.1 Data Sources, Data Quality, and Analytical Approach 15
3.3.1.1 UCM Rounds 1 and 2 16
3.3.1.2 Developing a Nationally Representative Perspective 16
3.3.1.2.1 Cross-Section Development 17
3.3.1.2.2 Cross-Section Evaluation 18
3.3.1.3 Data Management and Analysis 19
3.3.1.4 Occurrence Analysis 20
3.3.1.5 Supplemental CMR State Data 21
3.3.2 Results 22
3.3.2.1 Occurrence Estimates from SDWIS/FED Round 2 Data 22
3.3.2.2 Occurrence Estimates from the CMR State Data 22
3.3.2.3 Cross-Section Comparisons 23
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3.4 Conclusion 27
4.0 HEALTH EFFECTS 28
4.1 Hazard Characterization and Mode of Action Implications 28
4.2 Dose-Response Characterization and Implications in Risk Assessment 29
4.3 Relative Source Contribution 30
4.4 Sensitive Populations 31
4.5 Exposure and Risk Information 31
4.6 Conclusion 32
5.0 TECHNOLOGY ASSESSMENT 32
5.1 Analytical Methods 32
5.2 Treatment Technology 32
6.0 SUMMARY AND CONCLUSIONS - DETERMINATION OUTCOME 34
REFERENCES 36
APPENDIX A: Abbreviations and Acronyms 42
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LIST OF TABLES
Table 3-1: Abundance of sulfur in different environments 9
Table 3-2: Global production of sulfur dioxide (x 106 metric tons Sulfur per year) 11
Table 3-3: Sulfate detections and concentrations in streams and ground water 14
Table 3-4: Summary occurrence statistics for sulfate 24
Table 3-5: Occurrence summary by State for sulfate (CMR data) 26
Table 3-6: 20-State SDWIS/FED Round 2 cross-section compared to the 8-State CMR
cross-section for sulfate 27
Table 5-1: Analytical methods for sulfate 33
rx
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LIST OF FIGURES
Figure 2-1: The Sulfur Cycle 6
Figure 3-1: Annual weighted mean pH and sulfate concentration in precipitation in North America in
1985 10
Figure 3-2: Geographic distribution of cross-section States for Round 2 (SDWIS/FED) 19
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1.0 INTRODUCTION
1.1 Purpose and Scope
This document presents scientific data and summaries of technical information prepared for, and
used in, the Environmental Protection Agency's (EPA) regulatory determination for sulfate. Information
regarding sulfate's physical and chemical properties, environmental fate, occurrence and exposure, and
health effects is included. Analytical methods and treatment technologies are also discussed.
Furthermore, the regulatory determination process is described to provide the rationale for the decision.
1.2 Statutory Framework/Background
The Safe Drinking Water Act (SDWA), as amended in 1996, requires the EPA to publish a list of
contaminants (referred to as the Contaminant Candidate List, or CCL) to assist in priority-setting
efforts. The contaminants included on the CCL were not subject to any current or proposed National
Primary Drinking Water Regulations (NPDWR), were known or anticipated to occur in public water
systems, were known or suspected to adversely affect public health, and therefore may require
regulation under SDWA. The first Drinking Water CCL was published on March 2, 1998 (USEPA,
1998; 63 FR 10273), and a new CCL must be published every five years thereafter.
The 1998 CCL contains 60 contaminants, including 50 chemicals or chemical groups, and 10
microbiological contaminants or microbial groups. The SDWA also requires the Agency to select 5 or
more contaminants from the current CCL, and determine whether or not to regulate these contaminants
with an NPDWR. Regulatory determinations for at least 5 contaminants must be completed 3!/2 years
after each new CCL.
Language in SDWA Section 1412(b)(l)(A) specifies that the determination to regulate a
contaminant must be based on a finding that each of the following criteria are met:
Statutory Finding i: the contaminant may have adverse effects on the health of persons;
Statutory Finding ii: the contaminant is known to occur or there is substantial likelihood that the
contaminant will occur in public water systems with a frequency and at levels of public health
concern; and
Statutory Finding Hi: in the sole judgement of the Administrator, regulation of such
contaminant presents a meaningful opportunity for health risk reduction for persons served by
public water systems.
The geographic distribution of the contaminant is another factor evaluated to determine whether it
occurs at the national, regional, or local level. This consideration is important because the Agency is
charged with developing national regulations and it may not be appropriate to develop NPDWRs for
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regional or local contamination problems.
EPA must determine if regulating this CCL contaminant will present a meaningful opportunity to
reduce health risk based on contaminant occurrence, exposure, and other risk considerations. The
Office of Ground Water and Drinking Water (OGWDW) is charged with gathering and analyzing the
occurrence, exposure, and risk information necessary to support this regulatory decision. The
OGWDW must evaluate when and where this contaminant occurs, and what would be the exposure
and risk to public health. EPA must evaluate the impact of potential regulations as well as determine the
appropriate measure(s) for protecting public health.
For each of the regulatory determinations, EPA first publishes, in the Federal Register, the draft
determinations for public comment. EPA responds to the public comments received, and then finalizes
regulatory determinations. If the Agency finds that regulations are warranted, the regulations must then
be formally proposed within 24 months, and promulgated 18 months later. EPA has determined that
there is sufficient information to support a regulatory determination for sulfate.
1.3 Statutory History of Sulfate
Sulfate has been monitored under the SDWA Unregulated Contaminant Monitoring (UCM)
program since 1993 (USEPA, 1992a; 57 FR 31776). Monitoring ceased for small public water
systems (PWSs) under a direct final rule published January 8, 1999 (USEPA, 1999a; 64 FR 1494),
and ended for large PWSs with promulgation of the new Unregulated Contaminant Monitoring
Regulation (UCMR) issued September 17, 1999 (USEPA, 1999c; 64 FR 50556) and effective
January 1, 2001. At the time the UCMR lists were developed, the Agency concluded there were
adequate monitoring data for a regulatory determination. This obviated the need for continued
monitoring under the new UCMR list.
EPA established a secondary maximum contaminant level (SMCL) for sulfate in drinking water in
1979 (USEPA, 1979; 44 FR 42195). An SMCL is based on the negative aesthetic effects of a
contaminant in drinking water (i.e. taste, smell), and is not a federally enforceable standard. It is
estimated that humans detect sulfate in water starting at concentrations of between 250 and 350 mg/L.
For sulfate, the recommended SMCL is 250 mg/L (USEPA, 1979; 44 FR 42195). The World Health
Organization (WHO) advises that sulfate concentrations in drinking water not exceed 400 mg/L, based
on taste (USEPA, 1985; 50 FR 46936).
In 1985, EPA proposed a health advisory (HA) for sulfate of 400 mg/L. This advisory was
intended as an alternative to a federally enforceable maximum contaminant level (MCL), and was meant
to protect infants (USEPA, 1985; 50 FR 46936). The proposed HA was never finalized (USEPA,
1999b; 64 FR 7028). As a part of the CCL process, health effects data have been reviewed, and are
summarized in section 4.0 of this document.
The 1986 Safe Drinking Water Act mandated an NPDWR for sulfate, as well as the establishment
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of a maximum contaminant level goal (MCLG) (USEPA, 1999b; 64 FR 7028). In 1990, EPA
proposed two alternative MCLGs of 400 and 500 mg/L (USEPA, 1990; 55 FR 30370).
Promulgation of these standards was deferred, however, until EPA could identify proper
implementation techniques for target populations (USEPA, 1992a; 57 FR 31776). EPA reproposed
an MCLG and MCL for sulfate in drinking water of 500 mg/L in 1994, including in their proposal four
compliance options to facilitate implementation (USEPA, 1994; 59 FR 65578). A regulatory
determination had not been finalized when Congress amended the SDWA in 1996.
The SDWA amendments of 1996 contained specific regulatory authority for sulfate. The
amendments required that EPA finalize a regulatory determination by August, 2001. The amendments
also mandated the initiation and completion of a joint study by EPA and the Center for Disease Control
and Prevention (CDC) prior to promulgation of an NPDWR for sulfate. The joint study was to
determine a reliable dose-response relationship for human health effects in the general population
(including at-risk groups like transients and infants) following exposure to sulfate in drinking water
(SDWA, § 1412 (b) (12) (B)). Results from this study were published in January, 1999.
EPA and CDC were unable to complete the dose-response study for infants because of an
insufficient study population. EPA and CDC concluded that, for adults, it is unlikely that any adverse
health effects will result from sulfate concentrations in drinking water below 600 mg/L. There are no
significant dose-response associations between sulfate exposure and reports of diarrhea in adults (EPA
and CDC, 1999a). An expert panel of scientists was convened in a September, 1998, workshop to
supplement the EPA/CDC study. Participating scientists concluded that there was insufficient scientific
evidence regarding health effects to justify a regulation. The panel suggested that a HA be issued in
areas where sulfate concentrations in drinking water exceed 500 mg/L (EPA and CDC, 1999b).
1.4 Regulatory Determination Process
In developing a process for the regulatory determinations, EPA sought input from experts and
stakeholders. EPA asked the National Research Council (NRC) for assistance in developing a
scientifically sound approach for deciding whether or not to regulate contaminants on the current and
future CCLs. The NRC's Committee on Drinking Water Contaminants recommended that EPA: (1)
gather and analyze health effects, exposure, treatment, and analytical methods data for each
contaminant; (2) conduct a preliminary risk assessment for each contaminant based on the available
data; and (3) issue a decision document for each contaminant describing the outcome of the preliminary
risk assessment. The NRC noted that in using this decision framework, EPA should keep in mind the
importance of involving all interested parties.
One of the formal means by which EPA works with its stakeholders is through the National
Drinking Water Advisory Council (NDWAC). The NDWAC comprises members of the general
public, State and local agencies, and private groups concerned with safe drinking water, and advises
the EPA Administrator on key aspects of the Agency's drinking water program. The NDWAC
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provided specific recommendations to EPA on a protocol to assist the Agency in making regulatory
determinations for current and future CCL contaminants. Separate but similar protocols were
developed for chemical and microbial contaminants. These protocols are intended to provide a
consistent approach to evaluating contaminants for regulatory determination, and to be a tool that will
organize information in a manner that will communicate the rationale for each determination to
stakeholders. The possible outcomes of the regulatory determination process are: a decision to
regulate, a decision not to regulate, or a decision that some other action is needed (e.g., issuance of
guidance).
The NOW AC protocol uses the three statutory requirements of SDWA Section 1412(b)(l)(A)(i)-
(iii) (specified in section 1.2) as the foundation for guiding EPA in making regulatory determination
decisions. For each statutory requirement, evaluation criteria were developed and are summarized
below.
To address whether a contaminant may have adverse effects on the health of persons (statutory
requirement (i)), the NOW AC recommended that EPA characterize the health risk and estimate a
health reference level for evaluating the occurrence data for each contaminant.
Regarding whether a contaminant is known to occur, or whether there is substantial likelihood that
the contaminant will occur, in public water systems with a frequency, and at levels, of public health
concern (statutory requirement (ii)), the NOW AC recommended that EPA consider: (1) the actual and
estimated national percent of PWSs reporting detections above half the health reference level; (2) the
actual and estimated national percent of PWSs with detections above the health reference level; and (3)
the geographic distribution of the contaminant.
To address whether regulation of a contaminant presents a meaningful opportunity for health risk
reduction for persons served by public water systems (statutory requirement (iii)) the NOW AC
recommended that EPA consider estimating the national population exposed above half the health
reference level and the national population exposed above the health reference level.
The approach EPA used to make regulatory determinations followed the general format
recommended by the NRC and the NOW AC to satisfy the three SDWA requirements under section
1412(b)(l)(A)(i)-(iii). The process was independent of many of the more detailed and comprehensive
risk management factors that will influence the ultimate regulatory decision making process. Thus, a
decision to regulate is the beginning of the Agency regulatory development process, not the end.
Specifically, EPA characterized the human health effects that may result from exposure to a
contaminant found in drinking water. Based on this characterization, the Agency estimated a health
reference level (HRL) for each contaminant.
For each contaminant EPA estimated the number of PWSs with detections >/fflRL and >FIRL, the
population served at these benchmark values, and the geographic distribution, using a large number of
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occurrence data (approximately seven million analytical points) that broadly reflect national coverage.
Round 1 and Round 2 UCM data, evaluated for quality, completeness, bias, and representativeness,
were the primary data used to develop national occurrence estimates. Use and environmental release
information, additional drinking water data sets (e.g., State drinking water data sets, EPA National
Pesticide Survey, and Environmental Working Group data reviews), and ambient water quality data
(e.g., United States Geological Survey's (USGS) National Water Quality Assessment (NAWQA)
program, State and regional studies, and the EPA Pesticides in Ground Water Database (PGWD))
were also consulted.
The findings from these evaluations were used to determine if there was adequate information to
evaluate the three SDWA statutory requirements and to make a determination of whether to regulate a
contaminant.
1.5 Determination Outcome
After reviewing the best available public health and occurrence information, EPA has made a
determination not to regulate sulfate with an NPDWR. This decision is based on the weight of evidence
suggesting that regulating sulfate does not present a meaningful opportunity for health risk reduction for
persons served by public water systems. EPA is, however, issuing an advisory to provide guidance to
communities that may be exposed to drinking water contaminated with high sulfate concentrations. All
CCL regulatory determinations are formally presented in the Federal Register Notices (USEPA,
2002a; 67 FR 38222; and USEPA, 2003 a; 68 FR 42898). The following sections summarize the data
used by the Agency to reach this decision.
2.0 CONTAMINANT DEFINITION
Sulfate, a soluble, divalent anion (SO42") with molecular weight 96.06 g/mol, results from the
oxidation of either elemental sulfur, sulfide minerals, or organic sulfur (Alley, 1993; Field, 1972; Wetzel,
1983). The anion is often connected, through ionic bonds, to alkali, alkaline earth, or transition metals
(Field, 1972). Living organisms assimilate sulfate and reduce it to organic sulfur (R-SH, where R
denotes an alkyl group), an essential constituent of two amino acids (Madigan et al., 1997). Sulfate is
also incorporated into the structure of several polysaccharides, and is released to the environment
through degradation of fecal wastes and organic material. Terrestrial evaporite minerals and the ocean
are the largest reservoirs of planetary sulfate (Alley, 1993).
Anthropogenic sources of sulfate include the burning of sulfur-containing fossil fuels, household
wastes including detergents, and industrial effluents from tanneries, steel mills, sulfate-pulp mills, and
textile plants (USEPA, 1985; 50 FR 46936). Sulfate is also used in pickle liquor (sulfuric acid) for
steel and metal industries, as a feedstock or reagent in manufacturing processes, and as an end-product
such as copper sulfate, which is used as a fungicide and algicide (USEPA, 1990; 55 FR 30370).
Sulfate is constantly replenished by means of the sulfur cycle (explained below), and is ubiquitous in the
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environment because of the abundance of sulfur on earth.
2.1 Environmental Fate/Behavior
The environmental fate and transport of sulfate are inextricably linked to the physical and chemical
processes active in the earth's sulfur cycle (Figure 2-1). Sulfur reservoirs depicted in the upper portion
of Figure 2-1 are present in the oxidized sulfate form, whereas those portrayed in the lower part are
found as reduced sulfides.
Spray, etc.
Metamorphic
and Igneous
Rocks
7xl015
Sediments
Mainly Shales
2.7 X1015
Oxidized
Reduced
Metamorphism
Figure 2-1:
The Sulfur
Cycle
after Kaplan, 1972; masses in millions of metric tons
Sedimentary sulfur is present mostly in the form of evaporite sulfates, such as gypsum
(CaSO4»2H2O), anhydrite (CaSO4), magnesium sulfate, and sodium sulfate. Sulfate can be leached
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from these evaporites to fresh water (USEPA, 1985; 50 FR 46936; Kaplan, 1972). In general, sulfate
salts resulting from lower molecular weight alkali metals like sodium, potassium, and magnesium are
extremely soluble, while those salts of higher molecular weight metals like barium, iron, or lead have a
low solubility (USEPA, 1990; 55 FR 30370). Although adsorption has been documented in the field,
sulfate does not generally adsorb strongly to soils but instead is carried unchanged through soil by
percolating water (Drever, 1988). The weathering and oxidation of metallic sulfides, like pyrite (FeS2),
found in shales, limestone, and sandstone, are important sources for sulfate in fresh water (Kaplan,
1972).
Sulfur is oxidized to the sulfate anion in fresh water and is eventually transferred to the ocean by
streams or rain. The sulfate anion is very stable, and does not spontaneously reduce under normal
environmental conditions. However, the reduction of sulfate by sulfate-reducing bacteria (obligate
anaerobes) is extremely important to the sulfur cycle. Once in the ocean, the sulfate anion is either
reduced by bacteria and converted to pyrite at the mud-water interface, or is brought into the
atmosphere by sea spray. Oceanic sulfate can also be precipitated as gypsum (CaSO4»2H2O) in semi-
isolated basins in arid portions of the earth (at which point evaporation has increased sulfate levels to
four times the oceanic concentration). The approximate residence time for sulfate in the sea is 21 x 106
years (Kaplan, 1972). Sulfate is not expected to bioaccumulate in the aquatic food chain (Moore,
1991). The concentration of sulfate ions in rain can be highly variable depending on proximity to
industrial areas where sulfur-containing fuels are combusted and sulfur dioxide (SO2) is released
(Wehmiller, 1972). SO2 is converted to sulfate in the atmosphere by photooxidation and heterogenous
reactions, with the rate of conversion increasing in polluted areas that have high atmospheric
concentrations of oxidizing radicals (like HO, HO2, and CH3O2; Moore, 1991).
3.0 OCCURRENCE AND EXPOSURE
This section examines the occurrence of sulfate in drinking water. While no complete national
database exists of unregulated or regulated contaminants in drinking water from PWSs collected under
SDWA, this report aggregates and analyzes existing State data that have been screened for quality,
completeness, and representativeness. Populations served by PWSs exposed to sulfate are estimated,
and the occurrence data are examined for regional or other special trends. To augment the incomplete
national drinking water data and aid in the evaluation of occurrence, information on the use and
environmental release, as well as ambient occurrence of sulfate, is also reviewed.
3.1 Use and Environmental Release
3.1.1 Production and Use
Anthropogenic sources of sulfate include: the burning of sulfur-containing fossil fuels, household
wastes including detergents, and industrial effluents from tanneries, steel mills, sulfate-pulp mills, and
textile plants (USEPA, 1985; 50 FR 46936). Sulfate is also used in pickle liquor (sulfuric acid) for
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steel and metal industries, as a feedstock or reagent in manufacturing processes, and as an end-product
such as copper sulfate, which is used as a fungicide and algicide (USEPA, 1990; 55 FR 30370).
Ammonium sulfate is applied to the environment directly as a fertilizer. Sulfate is constantly replenished
by means of the sulfur cycle, and is ubiquitous in the environment because of the abundance of sulfur on
earth (See Figure 2-1).
Sulfur is the 14th most abundant element in the earth's crust, and the 8th or 9th most abundant in
sediments (Kaplan, 1972). See Table 3-1 for sulfur abundances in different environments.
Since the sulfate anion is naturally occurring and is readily generated by the oxidation of various sulfur
compounds, exact figures for its use and environmental release are unavailable. Production of sulfate
compounds is expected to be very high, however (in the thousands of tons per year), as the use of
sodium sulfate alone in 1987 was reported to be 792 tons (USEPA, 1990; 55 FR 30370).
3.1.2 Environmental Release
Sulfur dioxide (SO2) emissions have recently become a major concern for industrialized nations.
One of the most pressing of these concerns is related to the interaction of SO2 with atmospheric water
to produce sulfuric acid (H2SO4), causing acid rain (Moore, 1991; Wetzel, 1983). In addition, SO2
can be converted to sulfate in the atmosphere. Elevated SO4 concentrations in precipitation can lead to
the acidification of soil solutions and elevate sulfate concentrations in terrestrial waters (See Figure 3-1;
Drever, 1988). Note that in Figure 3-1, precipitation pH is lowest in regions where precipitation SO4
concentrations are highest.
Anthropogenic sulfur emissions have a significant impact on the sulfur cycle, with at least 80% of
global SO2 emissions and over 45% of riverborne sulfates traceable to man-made sources (Moore,
1991). Table 3-2 indicates that total global sulfur dioxide production continually increased from 1930-
1980 (the years when data were available).
In addition to acidification through precipitation, terrestrial waters are acidified through a process
called acid mine drainage. The process takes place in ground waters proximal to the mining and milling
of sulfur-bearing ores, where sulfur compounds, including sulfate, are important mineral components of
the hydrogeologic system. Acidified ground water produced through acid mine drainage can also affect
surface waters through ground water discharge (Moore, 1991).
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Table 3-1: Abundance of sulfur in different environments
Locale
Crustal Average
Ultramafic
Basalt
Granite
Shale
Sandstone
Carbonate
Deep-sea sediment
Soils
Terrestrial plants
Seawater
Freshwater
|ulfUrfppm3
260
300
250
270
2,400
240
1,200
1,300
850
500
885
5.5
after Field, 1972
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Figure 3-1: Annual weighted mean pH and sulfate concentration in precipitation in North
America in 1985
DJJ
after Drever, 1988
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Table 3-2: Global production of sulfur dioxide (x 106 metric tons Sulfur per year)
, Coojinent
Asia
Europe
North
America
Africa
South
America
Oceania
Total
19SG
5
21
22
0.5
0.4
0.4
49
194|)
9
25
17
0.7
0.5
0.5
53
/19$9
12
21
25
1
1
1
61
1960 . •
34
30
24
2
2
1
93
1970
,.4*'
43
30
34
3
3
1
114
. 1980
57
30
29
4
4
2
126
2000
30-90
12-30
25
6
6
2
81-159
after Dignon and Hameed, 1989; Hordijk, 1988;Molkr, 1984
The basic reaction taking place in acid mine drainage involves the bacterially-mediated conversion
of pyrite (FeS2) to ferric hydroxide in the presence of percolating ground water, releasing sulfate and
acid:
FeS2 + 3.5 O2 + H2O * Fe2+ + 2 SO42- + 2 H+
Fe2+ + 0.25 O2 +2.5 H2O * Fe(OH)3 + 2 FT
If more acid is produced than can be neutralized by the alkalinity of the surrounding aquifer, acid
water will result. The bacteria that catalyze the above reactions thrive under acidic conditions,
accelerating acidification once it has begun (Drever, 1988).
Sulfate concentrations from ~ 1,500 mg/L (coal mine in Pennsylvania) to 63,000 mg/L (zinc mine in
Idaho; Barton, 1978) have been detected in waste waters near mines. To put this in perspective, the
national secondary standard for sulfate is 250 mg/L.
Sulfate is almost always present in drinking water, and is often found in relatively high
concentrations. A 1985 survey by the American Water Works Association, conducted in 39 States
and 3 territories, detected sulfate concentrations above 250 mg/L in 1,466 cases (Moore, 1991).
3.2 Ambient Occurrence
To understand the presence of a chemical in the environment, an examination of ambient
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occurrence is useful. In a drinking water context, ambient water potentially (though not necessarily) is
source water existing in surface waters and aquifers before treatment. The most comprehensive and
nationally consistent data describing ambient water quality in the United States are being produced by
the USGS, particularly in their NAWQA program. (NAWQA, however, is a relatively young program
and complete national data are not yet available from their entire array of sites across the nation.)
3.2.1 Data Sources and Methods
The USGS instituted the NAWQA program in 1991 to examine water quality status and trends in
the United States. NAWQA is designed and implemented in such a manner as to allow consistency
and comparison between representative study basins located around the country, facilitating
interpretation of natural and anthropogenic factors affecting water quality (Leahy and Thompson,
1994).
The NAWQA program consists of 59 significant watersheds and aquifers referred to as "study
units." The study units represent approximately two thirds of the overall water usage in the United
States and a similar proportion of the population served by public water systems. Approximately one
half of the nation's land area is represented (Leahy and Thompson, 1994).
To facilitate management and make the program cost-effective, approximately one third of the
study units at a time engage in intensive assessment for a period of 3 to 5 years. This is followed by a
period of less intensive research and monitoring that lasts between 5 and 7 years. This way all 59 study
units rotate through intensive assessment over a ten-year period (Leahy and Thompson, 1994). The
first round of intensive monitoring (1991-96) targeted 20 study units, and the second round monitored
another 16 beginning in 1994.
Sulfate is an analyte for both surface and ground water NAWQA studies, with a Minimum
Reporting Level (MRL) of 0.1 mg/L.
Sulfate data from the first two rounds of intensive NAWQA monitoring have undergone USGS
quality assurance checks and are available to the public through their NAWQA Data Warehouse
(USGS, 2001). EPA has analyzed these data after further data quality review and occurrence results
are presented below. The descriptive statistics generated from the sulfate NAWQA data broadly
characterize the frequency of sulfate detections by sample and by site. Furthermore, detection
frequencies above a HRL of 500 mg/L are also presented for all samples, and by site. The HRL is a
preliminary health effect level used for this analysis (see section 3.3.1.4 for further discussion of the
HRL and its development). The median and 99th percentile concentrations are included as well, to
characterize the range of sulfate concentration values present in ambient waters sampled by the
NAWQA program.
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3.2.2 Results
Typical of many inorganic contaminants, sulfate occurrence in ambient surface and ground waters is
high (Table 3-3). This is not surprising, considering that the anion occurs naturally and is ubiquitous
because of the abundance of sulfur on earth. Anthropogenic sources are also numerous.
Surface and ground water detection frequencies are similar, between 89.9% and 100% across all
NAWQA sites, though ground water detections are somewhat lower (Table 3-3). Median sulfate
concentrations are also similar between surface and ground water, but HRL exceedances and 99th
percentile values are generally much greater in ground water. Locally high concentrations in ground
water, higher than most surface water concentrations, are not surprising given the possibility of long
contact times between ground water and rocks enriched in sulfide minerals or sulfates at a given
location (the natural oxidation of sulfides is an important source for sulfate in fresh water). Contact
times between surface waters and naturally occurring sulfides and sulfates are orders of magnitude
shorter, hence concentrations are lower. Furthermore, surface waters subject to large anthropogenic
inputs of sulfate are more easily diluted by waters integrated from other parts of the watershed where
sulfate concentrations may be lower.
Table 3-3 illustrates that low-level sulfate occurrence is ubiquitous. Surface water detection
frequencies are greater than 99% for all land use categories. However, detection frequencies greater
than the HRL are significantly lower. Forest/rangeland basins did not detect sulfate at levels greater
than the HRL, while urban, mixed, and agricultural basins show infrequent HRL exceedances (by site:
between 0.4%-3.6%). Median concentrations for sulfate in surface waters are similar for urban, mixed,
and agricultural basins, while forest/rangeland basins again show lower sulfate levels. Forest/rangeland
basins also have the lowest 99th percentile concentrations. The 99th percentile concentrations are
considerably higher for all other land use categories, with the highest concentrations found in urban
areas. These concentration percentiles are understandable because sulfate is used widely in both
industry and agriculture, is produced in the burning of fossil fuels, and can affect surface waters in urban
and agricultural basins. Sulfate occurrence in forest/rangeland basins is low by comparison, given
anthropogenic sources are few. Detections exceeding the MRL and HRL, by site, for all sites are
approximately 99.6% and 2.7%, respectively. These figures indicate that although sulfate is ubiquitous
in surface water, detections at levels of public health concern are low.
For ground water, detections frequencies for all samples, and by site, exceed 89% for all land use
categories. Urban and agricultural areas have the greatest median and 99th percentile concentrations,
and the highest frequency of HRL exceedances. Forest/rangeland basins report no detections greater
than the HRL, and have the lowest median and 99th percentile values. Detection frequencies above the
MRL and HRL, by site, for all sites are approximately 98.0% and 3.2%, respectively. Again, sulfate
detections at levels of public health concern are low relative to sulfate occurrence.
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Table 3-3: Sulfate detections and concentrations in streams and ground water
surface water
urban
mixed
agricultural
forest/rangeland
all sites
ground water
urban
mixed
agricultural
forest/rangeland
all sites
Detection frequency
>MRL*
% samples
100 %
99.9 %
99.8 %
99.9 %
99.8 %
91.1%
89.9 %
93.6 %
91.8%
91.6%
% sites
100 %
99.4 %
99.7 %
99.5 %
99.6 %
98.7 %
96.6 %
99.5 %
97.5 %
98.0 %
Detection
frequency
>HRL*
% samples
2.6 %
0.8 %
2.9 %
0.0 %
1.8%
5.3 %
2.1%
4.3 %
0.0 %
2.7 %
% sites
0.4 %
2.2 %
3.6 %
0.0 %
2.7 %
6.4 %
2.4 %
4.3 %
0.0 %
3.2 %
Concentrations
(all samples;
median
20
21
25
5
20
20
12
24
7
17
mg/L)
99th
perc entile
2000
440
670
160
680
2600
940
1200
71
1300
* The Minimum Reporting Level (MRL) for sulfate in water is 0.1 mg/L and the Health Reference Level (HRL) is 500 mg/L. The HRL
is a preliminary health effect level used for this investigation.
3.3 Drinking Water Occurrence
The Safe Drinking Water Act, as amended in 1986, required PWSs to monitor for specified
"unregulated" contaminants, on a five year cycle, and to report the monitoring results to the States.
Unregulated contaminants do not have an established or proposed NPDWR, but they are contaminants
that were formally listed and required for monitoring under federal regulations. The intent was to gather
scientific information on the occurrence of these contaminants in order to enable a decision as to
whether or not regulations were needed. All non-purchased community water systems (CWSs) and
non-purchased non-transient non-community water systems (NTNCWSs), with greater than 150
service connections, were required to conduct this unregulated contaminant monitoring. Smaller
systems were not required to conduct this monitoring under federal regulations, but were required to be
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available to monitor if the State decided such monitoring was necessary. Many States collected data
from smaller systems. Additional contaminants were added to the Unregulated Contaminant
Monitoring program in 1991 (USEPA, 1991; 56 FR 3526) for required monitoring that began in 1993
(USEPA, 1992a; 57 FR 31776).
Sulfate has been monitored under the SDWA UCM program since 1993 (USEPA, 1992a; 57 FR
31776). Monitoring ceased for small PWSs under a direct final rule published January 8, 1999
(USEPA, 1999a; 64 FR 1494), and ended for large PWSs with promulgation of the new Unregulated
Contaminant Monitoring Regulation issued September 17, 1999 (USEPA, 1999c; 64 FR 50556) and
effective January 1, 2001. At the time the UCMR lists were developed, the Agency concluded there
were adequate monitoring data for a regulatory determination for sulfate. This obviated the need for
continued monitoring under the new UCMR list.
EPA established a secondary maximum contaminant level for sulfate in drinking water in 1979
(USEPA, 1979; 44 FR 42195). An SMCL is based on the negative aesthetic effects of a contaminant
in drinking water (i.e. taste, smell), and is not a federally enforceable standard. It is estimated that
humans detect sulfate in water starting at concentrations of between 250 and 350 mg/L. For sulfate,
the recommended SMCL is 250 mg/L (USEPA, 1979; 44 FR 42195).
3.3.1 Data Sources, Data Quality, and Analytical Approach
Currently, there is no complete national record of unregulated or regulated contaminants in drinking
water from PWSs collected under SDWA. Many States have submitted unregulated contaminant
PWS monitoring data to EPA databases, but there are issues of data quality, completeness, and
representativeness. Nonetheless, a significant amount of State data are available for UCM
contaminants , and can provide estimates of national occurrence. The contaminant occurrence analyses
findings presented in this report are based on a national cross-section of aggregated State data (i.e., a
representative subset of available State data) derived from the Safe Drinking Water Information System
(Federal version; SDWIS/FED) database.
The National Contaminant Occurrence Database (NCOD) is an interface to the actual occurrence
data stored in the SDWIS/FED database and can be queried to provide a summary of the data in
SDWIS/FED for a particular contaminant. The drinking water occurrence data for sulfate presented
here were derived from monitoring data available in the SDWIS/FED database. Note, however, that
the SDWIS/FED data used in this report have undergone significant review, edit, and filtering to meet
various data quality objectives for the purposes of this analysis. Hence, not all data from a particular
source were used, only data meeting the quality objectives described below were included. The
sources of these data, their quality and national aggregation, and the analytical methods used to estimate
a given contaminant's national occurrence (from these data) are discussed in this section (for further
details see USEPA, 200la, 200Ib).
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3.3.1.1 UCM Rounds 1 and 2
The 1987 UCM contaminants included 34 volatile organic compounds (VOCs) (USEPA, 1987;
52 FR 25690). Sulfate, an inorganic compound (IOC), was not among these contaminants. The
UCM (1987) contaminants were first monitored coincident with the Phase I regulated contaminants,
during the 1988-1992 period. This period is often referred to as "Round 1" monitoring. The
monitoring data collected by the PWSs were reported to the States (as primacy agents), but there was
no protocol in place to report these data to EPA. These data from Round 1 were collected by EPA
from many States over time and put into a database called the Unregulated Contaminant Information
System (URCIS).
The 1993 UCM contaminants included 13 synthetic organic contaminants (SOCs) and sulfate, the
only IOC (USEPA, 1992a; 57 FR 31776). Monitoring for the UCM (1993) contaminants began
coincident with the Phase D/V regulated contaminants in 1993 through 1998. This is often referred to
as "Round 2" monitoring. The UCM (1987) contaminants were also included in the Round 2
monitoring. As with other monitoring data, PWSs reported these results to the States. EPA, during the
past several years, requested that the States submit these historic data to EPA and they are now stored
in the SDWIS/FED database.
Monitoring and data collection for sulfate, a UCM (1993) contaminant, began in Round 2.
Therefore, the following discussion regarding data quality screening, data management, and analytical
methods is restricted to SDWIS/FED. Discussion of the URCIS database is included where relevant,
but it is worth noting that the various quality screening, data management, and analytical processes were
nearly identical for the two databases. For further details on the two monitoring periods as well as the
databases, see USEPA (200la) and USEPA (200Ib).
3.3.1.2 Developing a Nationally Representative Perspective
The Round 2 data contain contaminant occurrence data from a total of 35 primacy entities
(including 34 States and data for some tribal systems). However, data from some States are
incomplete and biased. Furthermore, the national representativeness of the data is problematic because
the data were not collected in a systematic or random statistical framework. These State data could be
heavily skewed to low-occurrence or high-occurrence settings. Hence, the State data were evaluated
based on pollution-potential indicators and the spatial/hydrologic diversity of the nation. This evaluation
enabled the construction of a cross-section from the available State data sets that provides a reasonable
representation of national occurrence.
A national cross-section comprised of the Round 2 State contaminant occurrence databases was
established using the approach developed for the EPA report^ Review of Contaminant Occurrence
in Public Water Systems (USEPA, 1999d). This approach was developed to support occurrence
analyses for EPA's Chemical Monitoring Reform (CMR) evaluation, and was supported by peer
reviewers and stakeholders. The approach cannot provide a "statistically representative" sample
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because the original monitoring data were not collected or reported in an appropriate fashion.
However, the resultant "national cross-section" of States should provide a clear indication of the central
tendency of the national data. The remainder of this section provides a summary description of how the
national cross-section from the SDWIS/FED (Round 2) database was developed. The details of the
approach are presented in other documents (USEPA, 200la, 200Ib); readers are referred to these for
more specific information.
3.3.1.2.1 Cross-Section Development
As a first step in developing the cross-section, the State data contained in the SDWIS/FED
database (that contains the Round 2 monitoring results) were evaluated for completeness and quality.
Some State data in SDWIS/FED were unusable for a variety of reasons. Some States reported only
detections, or the data was recorded with incorrect units. Data sets only including detections are
obviously biased, over-representing high-occurrence settings. Other problems included substantially
incomplete data sets without all PWSs reporting (USEPA, 200la Sections n and HI).
The balance of the States remaining after the data quality screening were then examined to establish
a national cross-section. This step was based on evaluating the States' pollution potential and
geographic coverage in relation to all States. Pollution potential is considered to ensure a selection of
States that represent the range of likely contaminant occurrence and a balance with regard to likely high
and low occurrence. Geographic consideration is included so that the wide range of climatic and
hydrogeologic conditions across the United States are represented, again balancing the varied
conditions that affect transport and fate of contaminants, as well as conditions that affect naturally
occurring contaminants (USEPA, 2001b Sections ni.A. and IHB.).
The cross-section States were selected to represent a variety of pollution potential conditions. Two
primary pollution potential indicators were used. The first factor selected indicates pollution potential
from manufacturing/population density and serves as an indicator of the potential for VOC
contamination within a State. Agriculture was selected as the second pollution potential indicator
because the majority of SOCs of concern are pesticides (USEPA, 2001b Section in.A.). The 50
individual States were ranked from highest to lowest based on the pollution potential indicator data.
For example, the State with the highest ranking for pollution potential from manufacturing received a
ranking of 1 for this factor and the State with the lowest value was ranked as number 50. States were
ranked for their agricultural chemical use status in a similar fashion.
The States' pollution potential rankings for each factor were subdivided into four quartiles (from
highest to lowest pollution potential). The cross-section States were chosen equally from all quartiles
for both pollution potential factors to ensure representation, for example, from: States with high
agrochemical pollution potential rankings and high manufacturing pollution potential rankings; States
with high agrochemical pollution potential rankings and low manufacturing pollution potential rankings;
States with low agrochemical pollution potential rankings and high manufacturing pollution potential
rankings; and States with low agrochemical pollution potential rankings and low manufacturing pollution
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potential rankings (USEPA, 200Ib Section ni.B.). In addition, some secondary pollution potential
indicators were considered to further ensure that the cross-section States included the spectrum of
pollution potential conditions (high to low). At the same time, States within the specific quartiles were
considered collectively across all quartiles to attempt to provide a geographic coverage across all
regions of the United States.
The data quality screening, pollution potential rankings, and geographic coverage analysis
established a national cross-section of 20 Round 2 (SDWIS/FED) States. The 20 cross-section States
provide good representation of the nation's varied climatic and hydrogeologic regimes, and the breadth
of pollution potential for the contaminant groups (Figure 3-2).
3.3.1.2.2 Cross-Section Evaluation
To evaluate and validate the method for creating the national cross-sections, the method was used
to create smaller State subsets from the 24-State, Round 1 (URCIS) cross-section. Again, States
were chosen to achieve a balance from the quartiles describing pollution potential, and a balanced
geographic distribution, to incrementally build subset cross-sections of various sizes. For example, the
Round 1 cross-section was tested with subsets of 4, 8 (the first 4 State subset plus 4 more States), and
13 (8 State subset plus 5) States. Two additional cross-sections were included in the analysis for
comparison; a cross-section composed of 16 States with biased data sets eliminated from the 24 State
cross-section for data quality reasons, and a cross-section composed of all 40 Round 1 States
(USEPA, 2001b Section III.B.l).
These Round 1 "incremental cross-sections" were then used to evaluate occurrence for an array of
both high and low occurrence contaminants. The comparative results illustrate several points. The
results are quite stable and consistent for the 8-, 13- and 24- State cross-sections. They are much less
so for the 4-State, 16-State (biased), and 40-State (all Round 1 States) cross-sections. The 4-State
cross-section is apparently too small to provide balance both geographically and with pollution
potential, a finding that concurs with past work (USEPA, 1999d). The CMR analysis suggested that a
minimum of 6-7 States was needed to provide balance both geographically and with pollution potential,
and the CMR report used 8 States out of the available data for its nationally representative cross-
section (USEPA, 1999d). The 16- and 40-State cross-sections, both including biased States,
provided occurrence results that were unstable and inconsistent for a variety of reasons associated with
their data quality problems (USEPA, 2001b Section IHB.l).
The 8-, 13-, and 24-State cross-sections provide very comparable results, are consistent, and
are usable as national cross-sections to provide estimates of contaminant occurrence. Including greater
amounts of data from more States improves the national representation and the confidence in the
results, as long as the States are balanced related to pollution potential and spatial coverage. The 20-
State cross-section provides the best, nationally representative cross-section for the Round 2 data.
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Figure 3-2: Geographic distribution of cross-section States for Round 2 (SDWIS/FED)
Round 2 (SDWIS/FED) Cross Section
States
Alaska
Arkansas
Colorado
Kentucky
Maine
Maryland
Massachusetts
Michigan
Minnesota
Missouri
New Hampshire
New Mexico
North Carolina
North Dakota
Ohio
Oklahoma
Oregon
Rhode Island
Texas
Washington
3.3.1.3 Data Management and Analysis
The cross-section analyses focused on occurrence at the water system level; i.e., the summary data
presented discuss the percentage of public water systems with detections, not the percentage of
samples with detections. By normalizing the analytical data to the system level, skewness inherent in
the sample data is avoided. System level analysis was used since a PWS with a known contaminant
problem usually has to sample more frequently than a PWS that has never detected the contaminant.
Obviously, the results of a simple computation of the percentage of samples with detections (or other
statistics) can be skewed by the more frequent sampling results reported by the contaminated site. The
system level of analysis is conservative. For example, a system need only have a single sample with an
analytical result greater than the MRL, i.e., a detection, to be counted as a system with a result "greater
than the MRL."
Also, the data used in the analyses were limited to only those data with confirmed water source and
sampling type information. Only standard SDWA compliance samples were used; "special" samples,
or "investigation" samples (investigating a contaminant problem that would bias results), or samples of
unknown type were not used in the analyses. Various quality control and review checks were made of
the results, including follow-up questions to the States providing the data. Many of the most intractable
data quality problems encountered occurred with older data. These problematic data were, in some
cases, simply eliminated from the analysis. For example, when the number of problematic data were
insignificant relative to the total number of observations, those data were dropped from the analysis (for
further details see Cadmus, 2000).
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3.3.1.4 Occurrence Analysis
To evaluate national contaminant occurrence, a two-stage analytical approach has been developed.
The first stage of analysis provides a straightforward, conservative, non-parametric evaluation of
occurrence of the CCL regulatory determination priority contaminants as described above. These
Stage 1 descriptive statistics are summarized here. Based in part on the findings of the Stage 1
Analysis, EPA will determine whether more rigorous parametric statistical evaluations, the Stage 2
Analysis, may be warranted to generate national probability estimates of contaminant occurrence and
exposure for priority contaminants (for details on this two stage analytical approach see Cadmus, 2000,
2001).
The summary descriptive statistics presented in Table 3-4 for sulfate are a result of the Stage 1
analysis and include data from Round 2 (SDWIS/FED, 1993-1997) cross-section States. Included are
the total number of samples, the percent samples with detections, the 99th percentile concentration of all
samples, and the median concentration of all samples. The percentages of PWSs and population
served indicate the proportion of PWSs (or population served by PWSs) whose analytical results
include at least one detection of the contaminant (simple detection, > MRL) at any time during the
monitoring period; or a detection(s) greater than half the HRL; or a detection(s) greater than the HRL
(the HRL is a preliminary estimated health effect level used for this analysis).
The HRL used in evaluating the occurrence information for sulfate is 500 mg/L. This is the value
suggested by a panel of experts convened by EPA (USEPA, 1999e) as protective for sulfate-induced
diarrhea. The Agency adopted the HRL of 500 mg/L, based on the recommendations of the
CDC/EPA Panel (USEPA, 1999e), as a health-related benchmark for evaluating the occurrence data.
The 99th percentile concentration is used here as a summary statistic to indicate the upper bound of
occurrence values, because maximum values can be extreme values (outliers) that sometimes result
from sampling or reporting error.
As a simplifying assumption, a value of half the MRL is often used as an estimate of the
concentration of a contaminant in samples/systems whose results are less than the MRL. However, for
these occurrence data this is not straightforward. For Round 2, States have reported a wide range of
values for the MRLs. This is in part related to State data management differences as well as real
differences in analytical methods, laboratories, and other factors.
The situation can cause confusion when examining descriptive statistics for occurrence. For
example, most Round 2 States reported non-detections as zeros resulting in a modal MRL value of
zero. By definition the MRL cannot be zero. This is an artifact of State data management systems.
Because a simple meaningful summary statistic is not available to describe the various reported MRLs,
and to avoid confusion, MRLs are not reported in the summary table (Table 3-4).
In Table 3-4, national occurrence is estimated by extrapolating the summary statistics for the 20-
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State cross-section to national numbers for systems, and population served by systems, from the Water
Industry Baseline Handbook, Second Edition (USEPA, 2000). From the handbook, the total
national number of CWSs plus NTNCWSs is 65,030, and the total population served by CWSs plus
NTNCWSs is 213,008,182 persons (see Table 3-4). To generate the estimate of national occurrence
based on the cross-section occurrence findings, the national number of PWSs (or population served by
PWSs) is simply multiplied by the percentage value for the particular cross section occurrence statistic
(e.g. the national estimate for the total number of PWSs with detections (57,299) is the product of the
total national number of PWSs (65,030) and the percentage of PWSs with detections (88.1%)).
Because the State data used for the cross-section are not a strict statistical sample, national
extrapolations of these Stage 1 analytical results can be problematic. For this reason, the nationally
extrapolated estimates of occurrence based on Stage 1 results are not presented in the Federal Register
Notice. The presentation in the Federal Register Notice of only the actual results of the cross-section
analysis maintains a straight-forward presentation, and the integrity of the data, for stakeholder review.
The nationally extrapolated Stage 1 occurrence values are presented here, however, to provide
additional perspective. A more rigorous statistical modeling effort, the Stage 2 analysis, could be
conducted on the cross-section data (Cadmus, 2001). The Stage 2 results would be more statistically
robust and more suitable to national extrapolation. This approach would provide a probability estimate
and would also allow for better quantification of estimation error.
3.3.1.5 Supplemental CMR State Data
Occurrence data on sulfate submitted directly with other drinking water occurrence data by the
States of Alabama, California, Illinois, Montana, New Jersey, and Oregon, for the independent analysis
A Review of Contaminant Occurrence in Public Water Systems (USEPA, 1999d), was used to
augment the SDWIS/FED Round 2 occurrence analysis. These State supplemental CMR data provide
additional perspective on sulfate occurrence as five of the six States were not represented in the 20-
State cross-section. These CMR State data are also compared to the 20-State SDWIS/FED cross-
section. A Review of Contaminant Occurrence in Public Water Systems supported occurrence
analyses for EPA's CMR evaluation, and is therefore referred to in this document as the CMR report.
The occurrence data for sulfate used in the CMR analysis were submitted by States for an
independent review of the occurrence of regulated contaminants in PWSs at various times for different
programs (USEPA, 1999d). In the USEPA (1999d) review, occurrence data from a total of 14 States
were noted. However, because several States contained data that were incomplete or unusable for
various reasons, only 12 of the 14 States were used for a general overview analysis. From these 12
States, eight were selected for use in a national analysis because they provided the best data quality and
completeness, and a balanced national cross-section of occurrence data. These eight States were
Alabama, California, Illinois, Michigan, Montana, New Jersey, New Mexico, and Oregon. The CMR
8-State cross-section was developed in the same manner as, and was the model for, the 20-State
Round 2 cross-section (see sections 3.3.1.2, 3.3.1.3, and 3.3.1.4 for description).
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Only the Alabama, California, Illinois, Montana, New Jersey, and Oregon State data sets contained
occurrence data for sulfate. These results are presented in Table 3-5 and are described in section
3.3.2.2. The data represent more than 38,000 analytical results from about 5,800 PWSs mostly during
the period from 1993 to 1997, though some earlier data are also included. The number of sample
results and PWSs vary by State, however, with some States having considerably more data.
3.3.2 Results
3.3.2.1 Occurrence Estimates from SDWIS/FED Round 2 Data
The percentages of SDWIS/FED Round 2 PWSs with detections are high, as should be expected
for sulfate (Table 3-4). The cross-section findings indicate that 88% of PWSs (57,299 PWSs
nationally) experienced detections of sulfate above the MRL, affecting 95% of the population served
(about 202 million people nationally). Occurrence analyses are also provided relative to the Health
Reference Level of 500 mg/L; 1.8% of PWSs reported detections above the HRL. These statistics
indicate that nationally, about 1,163 PWSs would be affected by sulfate levels greater than the HRL of
500 mg/L (affecting approximately 2 million people).
Surface and ground water PWSs show similar detection frequencies for sulfate for all concentration
thresholds evaluated (> MRL, >!/2 HRL, and > HRL). The median concentration of all samples is 24
mg/L and the 99th percentile concentration of all samples is 560 mg/L.
The Round 2 national cross-section shows a proportionate balance in PWS source waters and
population served, compared to the national inventory. Nationally, 91% of PWSs use ground water
(and 9% surface waters); the Round 2 cross-section also shows 91% use ground water (and 9%
surface waters). The relative populations served are almost as comparable. Nationally, about 40% of
the population is served by PWSs using ground water (and 60% by surface water). For the Round 2
cross-section, 39% of the cross-section population is served by ground water PWSs (and 61% by
surface water). The resultant national extrapolation is affected by this slight disproportion, so that
adding the national extrapolation of an occurrence parameter for just ground water PWSs to the same
parameter for just surface water PWSs does not always produce the national extrapolation for all
PWSs.
3.3.2.2 Occurrence Estimates from the CMR State Data
Drinking water data for sulfate from the CMR States vary among States (Table 3-5). The number
of systems with sulfate data for Illinois is far less than the number of PWSs in the State. Hence, it is not
clear how representative these data are. Alabama, California, Montana, New Jersey, and Oregon have
substantial amounts of data and PWSs represented.
Sulfate detections by PWS range from about 83% in Oregon to 93% in California (Table 3-5).
Detection frequencies are relatively evenly distributed between surface water and ground water
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systems. These figures agree with simple sulfate detection frequencies from the SDWIS/FED Round 2
cross-section where an average of 88% of PWSs experienced detections greater than the MRL with
surface water and ground water detections were similar. The variability of SDWIS/FED Round 2
detections, with a range of 4.5% to 100% detections (Table 3-4), is greater than that for the CMR
data. However, comparisons made between data for simple detections need to be viewed with caution
because of differences in MRLs between the CMR State data sets and the SDWIS/FED Round 2 data
set, as well as differences in MRLs between the CMR States and the SDWIS/FED Round 2 States
themselves (see section 3.3.1.4).
Simple sulfate detection frequencies (i.e., >MRL)are significantly higher than detection frequencies
of levels greater than the HRL. At the HRL of 500 mg/L, data from the CMR States indicate PWS
exceedances from 0% to 6.32%. The SDWIS/FED Round 2 range of PWS detections greater than
the HRL of 500 mg/L is quite comparable (0%-5.24%), with an average of 1.79%
Population figures for the CMR States are incomplete, and are only reported for those systems in
the database that have reported their population data. For sulfate, approximately 85% of the PWSs
reporting occurrence data for these 6 States also reported population data.
3.3.2.3 Cross-Section Comparisons
An important comparison can be made between the two cross-sections analyzed in this report. The
20-State cross-section of SDWIS/FED Round 2 data was used in Table 3-4 to extrapolate national
estimates of sulfate occurrence. The cross-section States were chosen based on geographic coverage
and relative pollution potential distribution. The 8-State CMR cross-section of States were chosen in
the same manner (USEPA, 1999d). Significantly, of the 6 States that reported data for sulfate in the 8-
State CMR cross-section, only one (Oregon) was part of the 20-State SDWIS/FED cross-section.
Sulfate detection frequencies from these two cross-sections are very similar (Table 3-6). For
PWSs with simple detections (concentrations > MRL), the 20-State cross-section detection
frequencies are consistently about two percent less than the corresponding 8-State cross-section
detection frequencies, suggesting a possible variation in MRLs. For PWSs with detections greater than
the HRL of 500 mg/L, the 20-State cross-section and the 8-State cross-section differ by less than 1%
in all instances.
The proportion of ground water PWSs compared to surface water PWSs for the 20-State
SDWIS/FED and the 8-State CMR cross-sections are also almost identical; 91% ground water (9%
surface water) and 90% ground water (10% surface water), respectively.
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Table 3-4: Summary occurrence statistics for sulfate
Frequency Factors
Total Number of Samples
Percent of Samples with Detections
Health Reference Level
Minimum Reporting Level (MRL)
99"' Percentile Concentration of all Samples
Median Concentration of all Samples
Total Number of PWSs
Number of GW PWSs
Number of SWPWSs
Total Population
Population of GW PWSs
Population of SWPWSs
Occurrence by System
% PWSs with detections (> MRL)
Range of Cross-Section States
GW PWSs with detections
SW PWSs with detections
% PWSs > 1/2 Health Reference Level (HRL) (500 mg/L)
Range of Cross-Section States
GW PWSs > 1/2 HRL
SW PWSs > 1/2 HRL
% PWSs > HRL (500 mg/L)
Range of Cross-Section States
GW PWSs > HRL
SW PWSs > HRL
Occurrence by Population Served
% PWS Population Served with detections
Range of Cross-Section States
GW PWS Population with detections
SW PWS Population with detections
% PWS Population Served > 1/2 HRL (500 mg/L)
Range of Cross-Section States
GW PWS Population > 1/2 HRL
SW PWS Population > 1/2 HRL
% PWS Population Served > HRL (500 mg/L)
Range of Cross-Section States
GW PWS Population > HRL
SW PWS Population > HRL
20 State Cross-Section1
(Round 2)
40,484
87.0%
500 mg/L
Variable"1
560 mg/L
24 mg/L
16,495
15,009
1,486
50,370,291
19,649,749
30,720,542
88.1%
4.5-100%
87.8%
91.7%
4.97%
0-11.1%
4.61%
8.55%
1.79%
0-5.24%
1.83%
1.41%
95.1%
4.56 - 100%
94.0%
95.7%
10.2%
0-36.1%
5.29%
13.4%
0.89%
0-33.5%
1.61%
0.42%
National System &
Population Numbers2
-
-
-
—
-
-
65,030
59,440
5,590
213,008,182
85,681,696
127,326,486
National Extrapolation4
57,299
N/A
52,165
5,124
3,229
N/A
2,741
478
1,163
N/A
1,085
79
202,468,000
N/A
80,533,000
121,890,000
21,791,000
N/A
4,532,000
17,049,000
1,887,000
N/A
1,383,000
535,000
;. Summary Results based on data from 20-State Cross-Section, from SDWIS/FED, UCM (1993) Round 2.
2. Total PWS and population numbers are from EPA March 2000 Water Industry Baseline Handbook (USEPA, 2000).
3. See Section 3.3.1.4 for discussion.
4. National extrapolations are from the 20-State data using the Baseline Handbook system and population numbers.
- PWS = Public Water Systems; GW = Ground Water; SW = Surface Water; MRL = Minimum Reporting Level (for laboratory
analyses); HRL = Health Reference Level, an estimated health effect level used for preliminary assessment for this review; N/A = Not
Applicable
- Total Number of Samples = the total number of analytical records for sulfate
- 99th Percentile Concentration = the concentration value of the 99th percentile of all analytical results (in mg/L)
- Median Concentration of Detections = the median analytical value of all the analytical results (in mg/L)
- Total Number of PWSs = the total number of public water systems with records for sulfate
- Total Population Served = the total population served by public water systems with records for sulfate
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Table 3-5: Occurrence summary by State for sulfate (CMR data)
Frequency Factors
Total Number of Samples
Number of Ground Water Samples
Number of Surface Water Samples
Percent of Samples with Detections
Percent of Ground Water Samples with Detections
Percent of Surface Water Samples with Detections
99 Percentile Concentration (all samples)
Median Concentration (all samples)
Minimum Reporting Level (MRL)
Total Number of PWSs
Number of Ground Water PWSs
Number of Surface Water PWSs
Occurrence by System
% PWSs with detections (> MRL)
Ground Water PWSs with detections
Surface Water PWSs with detections
Health Reference Level (HRL) = 500 mg/L
% PWSs > 1/2 HRL
Ground Water PWSs > 1/2 HRL
Surface Water PWSs > 1/2 HRL
% PWSs > HRL
Ground Water PWSs > HRL
Surface Water PWSs > HRL
Occurrence by Population Served
% PWS Population Served with detections
Ground Water PWS Population with detections
Surface Water PWS Population with detections
Health Reference Level (HRL) = 500 mg/L
% PWS Population Served > 1/2 HRL
Ground Water PWS Population > 1/2 HRL
Surface Water PWS Population > 1/2 HRL
% PWS Population Served > HRL
Ground Water PWS Population > HRL
Surface Water PWS Population > HRL
Alabama
1,545
1,132
413
90.5%
87.8%
97.8%
72 mg/L
8.1 mg/L
\T ' Ul 1
Variable
547
478
69
90.9%
89.5%
100.0%
0.18%
0.00%
1.45%
0.00%
0.00%
0.00%
99.9%
97.2%
100.0%
0.23%
0.00%
0.13%
0.00%
0.00%
0.00%
California
29,050
26,682
2,368
95.7%
95.6%
96.2%
523 mg/L
33 mg/L
Variable
2,195
1,977
218
93.4%
93.4%
93.1%
10.4%
10.9%
5.96%
2.69%
2.98%
0.00%
99.9%
99.8%
99.9%
50.7%
43.9%
57.0%
22.6%
34.4%
0.00%
Illinois
280
210
70
86.4%
81.9%
100.0%
760 mg/L
60 mg/L
17 -II1
Variable
195
128
67
87.2%
80.5%
100.0%
7.18%
10.9%
0.00%
3.08%
4.69%
0.00%
95.8%
86.1%
100.0%
1.59%
5.19%
0.00%
0.67%
2.11%
0.00%
Montana
1,565
1,343
222
86.9%
86.8%
87.4%
1,200 mg/L
22 mg/L
Variable
775
722
53
88.4%
88.1%
92.5%
12.5%
12.5%
13.2%
6.32%
6.23%
7.55%
95.9%
93.8%
97.9%
10.2%
15.5%
5.34%
4.33%
5.41%
3.33%
New Jersey
5,055
4,446
609
86.9%
85.7%
96.1%
260 mg/L
15. 9 mg/L
Variable
1,443
1,410
33
88.6%
88.4%
97.0%
1.59%
1.42%
9.09%
0.69%
0.57%
6.06%
99.2%
98.0%
100.0%
12.0%
0.52%
19.4%
11.7%
0.11%
19.2%
Oregon
1,346
804
542
77.0%
79.1%
73.8%
79 mg/L
5.13 mg/L
,. ... i
Variable
656
507
149
82.9%
81.1%
89.3%
0.15%
0.20%
0.00%
0.00%
0.00%
0.00%
93.7%
85.2%
96.8%
0.00%
0.01%
0.00%
0.00%
0.00%
0.00%
'See section 3.3.1.4 for details
- PWS = Public Water Systems; GW = Ground Water; SW = Surface Water; MRL = Minimum Reporting Level (for laboratory
analyses); HRL = Health Reference Level, an estimated health effect level used for preliminary assessment for this review; N/A = Not
Applicable
- Total Number of Samples = the total number of analytical records for sulfate
- 99th Percentile Concentration = the concentration value of the 99th percentile of all analytical results (in mg/L)
- Median Concentration of Detections = the median analytical value of all the analytical results (in mg/L)
- Total Number of PWSs = the total number of public water systems with records for sulfate
- Total Population Served = the total population served by public water systems with records for sulfate
- % PWS with detections, % PWS > 'A Health Reference Level, % PWS > Health Reference Level = percent of the total number of
public water systems with at least one analytical result that exceeded the MRL, % Health Reference Level, Health Reference Level,
respectively
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Table 3-6: 20-State SDWIS/FED Round 2 cross-section compared to the 8-State CMR
cross-section for sulfate1
20-State Cross-Section2 8-State Cross-Section3
Total Number of PWSs
Number of GWPWSs
Number of SW PWSs
% PWSs with detections (> MRL)
GW PWSs with detections
SW PWSs with detections
% PWSs with detections > 500 mg/L
GW PWSs > 500 mg/L
SWPWSs > 500 mg/L
16,495
15,009
1,486
88.1%
87.8%
91.7%
1.8%
1.8%
1.4%
5,973
5,381
592
90.3%
89.9%
93.9%
2.1%
2.2%
1.0%
1 Only six States reported data for sulfate in the 8-State cross-section.
2 Summary Results based on data from 20-State Cross-Section, from SDWIS/FED, UCM (1993) Round 2; see Table 3-4 and Section
3.3.1.1.
2after USEPA, 1999d; see Table 3-5 and Section 3.3.1.5.
3.4 Conclusion
Low-level sulfate occurrence in ambient waters monitored by the USGS NAWQA program is
ubiquitous, with detections approaching 100% of all surface and ground water sites. The percent
samples with detections are similarly high for all surface and ground water sites. Forest/rangeland
basins show the lowest frequency of HRL exceedances, median concentrations, and 99th percentile
concentrations across all land use categories, for both surface and ground waters. HRL exceedances
and 99th percentile concentrations are generally greatest in urban basins, while median concentrations
are similar for urban, mixed, and agricultural basins. Although sulfate detection frequencies are high in
surface and ground waters, sulfate occurrence at levels of public health concern is low.
Sulfate has been detected in a high percentage of PWS samples collected under SDWA.
Occurrence estimates from SDWIS/FED Round 2 data are very high, with 87% of all samples showing
detections. The median concentration of all samples is 24 mg/L and the 99th percentile concentration of
all samples is 560 mg/L. Systems with detections constitute 88% of Round 2 cross-section systems.
National estimates for the population served by PWSs with detections are very high: about 202 million
people (95% of the national PWS population). At the HRL of 500 mg/L, approximately 2% of PWSs,
serving about 2 million people nationally, use water with sulfate levels above the HRL.
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Additional CMR data from the States of Alabama, California, Illinois, Montana, New Jersey, and
Oregon were examined through independent analyses and also show high levels of sulfate occurrence.
Systems with detections constitute between 83%-93% of systems from the six CMR States with sulfate
data. Approximately 0%-23% of the CMR populations are served by systems with sulfate detections
greater than the HRL of 500 mg/L. A comparison between the 20-State SDWIS/FED national cross-
section and the CMR 8-State national cross-section shows very similar results for sulfate detection
frequencies in public water systems.
4.0 HEALTH EFFECTS
A description of the health effects and the available dose-response information associated with
exposure to sulfate is summarized below. For more detailed information, please see Drinking Water
Advisory: Consumer Acceptability Advice and Health Effects Analysis on Sulfate (USEPA,
2003).
4.1 Hazard Characterization and Mode of Action Implications
Most data on human responses to sulfate are based on short-term exposure that are obtained from
controlled settings (i.e., studies and experimental trials). Reports on long-term exposure are based on
responses to questionnaires in North Dakota and South Dakota, States with high sulfate concentrations
in their drinking water supply. Data from animal studies on the reproductive, developmental, and
carcinogenic effects are available for both short-term and long-term exposures to sulfate.
The data from human studies demonstrate that sulfate induces a laxative effect following acute
exposures of concentrations greater than 500 mg/L (Anderson and Stothers, 1978; Fingl, 1980;
Schofield and Hsieh, 1983; Stephen et al., 1991; Cochetto and Levy, 1981; Gomez et al., 1995;
Heizer et al., 1997; USEPA, 1999f). However, the severity of the laxative effect that occurs from
acute sulfate exposures may be dependent on the sulfate salt, as well as how the dose is administered.
For instance, magnesium sulfate exerts a stronger laxative effect than sodium sulfate because magnesium
sulfate is absorbed less completely, and therefore has a more pronounced effect on the osmolality of the
intestinal contents (Morris and Levy, 1983b). Additionally, a single dose of sulfate that produces a
laxative effect does not have the same effect as when divided and administered in intervals (Cochetto
and Levy, 1981).
Since humans appear to develop a tolerance to drinking water with high sulfate concentrations,
chronic exposures do not appear to produce the same laxative effect as seen in acute exposures
(Schofield and Hsieh, 1983). While it is not known when this acclimation occurs in adults, researchers
believe that acclimation occurs within 7 to 10 days. In a 90-day study, rats who were administered
mineral waters containing up to 1,595 mg/L of sulfate showed no soft feces or diarrhea, indicating rapid
acclimation (Wurzner 1979). However, earlier reports have shown that chronic exposure to high
sulfate concentrations in drinking water does have laxative effects in humans (Peterson, 1951; Moore,
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1952; Cass, 1953). These reports are subject to response bias, however, since the data used was
based on questionnaires. For example, an inquiry on the questionnaire about the laxative effect (that
requested a YES or NO response) is subject to a respondent's interpretation of a laxative effect.
Furthermore, sulfate was probably not the only contaminant found in the drinking water.
High sulfate concentrations do not appear to exert adverse reproductive or developmental effects.
Following the ingestion of drinking water containing up to 5,000 mg/L of sulfates by mice and pigs, no
reproductive effects were observed (Andres and Cline, 1989). Furthermore, no adverse
developmental effects were observed following the administration of 2,800 mg/kg/day of sulfate to
pregnant mice (Seidenberg et al., 1986).
No tumor development was observed in a limited-duration study done on rats injected
intramuscularly with sodium every other day for 4 weeks (Kasprazak et al., 1980). Because of the
short-term experimental protocol and the injection route of exposure, it is impossible to draw
conclusions on the potential carcinogenicity of sulfate. Because of the limited data, EPA has classified
sulfate in Group D, or not classified as to human carcinogenicity (1993). This category is reserved for
contaminants with inadequate evidence to support a determination on carcinogenicity.
4.2 Dose-Response Characterization and Implications in Risk Assessment
Although several studies have been conducted on the long-term exposure of humans to sulfate in
drinking water, none of them can be used to derive a dose-response characterization (Peterson, 1951;
Moore, 1952; Cass, 1953). These studies utilized data collected from the North Dakota Department
of Health Survey, which was administered over a period of several years to determine the mineral
content of the drinking water and any correlated health effects (Moore, 1952). An increasing trend
was observed in the number of persons reporting laxative effects as sulfate concentrations increased
(i.e., 22, 24, 33 and 69 percent for sulfate concentrations 0-200, 200-500, 500-1,000 and >1,000
mg/L, respectively). However, the results of these studies cannot be used to derive a dose-response
characterization for the following reasons: (1) the results are based on recall with little scientific weight
(i.e., sulfate may have induced the laxative effects, but it cannot be proven), and (2) the water samples
had varying concentrations of magnesium and total dissolved solids in addition to sulfate. No laxative
effects were observed in rats or heifers following long-term exposure to sulfate in drinking water
(Wurzner, 1979; Digest and Weeth, 1976).
Because sulfate appears to exert its laxative effect with short-term as opposed to long-term
exposures, several short exposure studies were reviewed. Two short-term studies were identified that
evaluated the effect of various sulfate concentrations on bowel function in a controlled environment, one
in humans and one in animals. In the multiple dose study, sulfate concentrations of 0, 400, 600, 800,
1,000 and 1,200 mg/L were given to four subjects (2 men and 2 women) for six consecutive 2-day
periods (Heizer et al., 1997). A significant trend was only observed for a decreasing mouth-to-anus
appearance time for chemical markers with increasing sulfate concentration. For a single dose study by
the same researchers, 6 adults (3 men and 3 women) received drinking water with sulfate
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concentrations of 0 or 1,200 mg/L for two consecutive 6-day periods. A statistically significant
increase in mean stool mass per 6-day pool and in mean stool mass per hour were observed with the
higher dose. However, none of the subjects reported diarrhea.
In a study where neonatal piglets were exposed to various concentrations of sulfate to simulate the
effect of inorganic sulfate on the bowel function in infants, no diarrhea was observed in any of the piglets
at 0 and 1,200 mg/L concentrations (Gomez et al, 1995). However, concentrations greater than
1,200 mg/L resulted in an increased prevalence of diarrhea, while concentrations greater than 1,800
mg/L resulted in persistent, nonpathogenic diarrhea.
The studies discussed above suggest that there is a risk for a laxative-related response to sulfate in
drinking water at concentrations greater than 1,000 mg/L (USEPA, 1999f; Heizer et al., 1997; Moore,
1952). The observed effect is a response to changes in the net osmolality of the intestinal contents, and
thus is influenced not only by sulfate intake, but also by the presence of other osmotically active
materials in the drinking water or diet, and the temporal pattern of sulfate ingestion. The laxative effect
of sulfate can be manifest as an increase in stool mass, increased stool moisture, and decreased
intestinal transit time, and/or frank diarrhea. The tendency for a frank diarrhea! response increases with
increased osmolality of the intestinal contents, and therefore, with the amount of sulfate ingested.
At this time, it is not possible to characterize a dose-response relationship for laxative effects of
short-term or long-term exposure to sulfate based on the available data. A CDC panel favored a
Health Advisory for sulfate drinking water levels of 500 mg/L or greater (USEPA, 1999e). The
Advisory was designed to prevent osmotic diarrhea in infants. The panelists referred to the study by
Chien et al. (1968) which found that sulfate levels greater than 630 mg/L caused diarrhea in infants. It
should be noted that this effect was observed after the infants had ingested formula made with water
containing sulfate and other osmotically active agents: the total dissolved solid concentration of the
water used to prepare infant formulas was high, from 2,424 to 3,123 mg/L. The CDC further stated
that 500 mg/L seemed to be a safe sulfate level because 500 mg/L was shown to be safe in all reviewed
studies.
4.3 Relative Source Contribution
There is limited data on dietary exposure to inorganic sulfate. A study of per capita sulfate
exposure, from data on the use of sulfate additives by the food industry, estimates an average of 453
mg/day (FASEB, 1975). The median exposure to sulfates in drinking water is 48 mg/day for an adult
drinking 2 L of water per day. Abernathy (2000) estimates that sulfate exposure from ambient air
averages 0.4 mg/day given high end median air concentration. Under these conditions, food is the
major source of sulfate exposure, comprising 90% of the total. However, under conditions where the
water concentration is at the 99th percentile level of all samples, or 560 mg/L, and where the dietary
and inhalation exposures remain constant, drinking water is the major source of sulfate exposure,
contributing 70% of the total.
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Sulfate has little tendency to bioaccumulate through the food chain. Biologically, sulfate is
incorporated into complex carbohydrates by animal systems or reduced and used for the synthesis of
the sulfur-containing amino acids by microbial, plant and animal systems. Mammalian systems also
conjugate a number of xenobiotics with sulfate for excretion. Dissolved sulfate ion is removed by the
excretion in urine.
4.4 Sensitive Populations
Anecdotal data suggest that visitors to an area with high sulfate concentrations in the water may be
more sensitive than the local population. Acclimatization appears to occur approximately one week
after first water use. However, even permanent residents would experience an increase in their risk for
diarrhea if the water were used to prepare a beverage that contained additional osmotically active
materials. Thus, formula fed infants and invalids or elderly patients who use nutritional supplements
prepared with tap water could be more likely to experience laxative effects from the sulfate in the
drinking water than other individuals. In high sulfate areas, the use of bottled water for preparation of
formula or nutritional supplements could significantly reduce the risk of osmotic diarrhea.
4.5 Exposure and Risk Information
Estimates of the total exposed population, as well as the population exposed above the HRL
receive the highest consideration in determining whether a regulation would provide a meaningful
opportunity to reduce risk. The HRL for sulfate is 500 mg/L (see section 3.3.1.4). Estimates of the
populations exposed and the levels to which they are exposed are derived from the monitoring results,
presented in section 3.3.2, and are summarized below.
Approximately 95% of the population served by PWSs, about 202 million people nationally, are
exposed to sulfate concentrations above the minimum reporting level. However, only 1.8% of the
PWS-served population, about 2 million people nationally, are exposed to levels greater than 500
mg/L. The median concentration of all samples is 24 mg/L and the 99th percentile concentration of all
samples is 560 mg/L. One of the six States (Montana) that provided supplemental CMR data for the
independent analysis, A Review of Contaminant Occurrence in Public Water Systems., had a 99th
percentile level of 1,200 mg/L. However, Montana's median concentration was 22 mg/L, well below
the health and taste threshold.
The EPA is required to consider both the general public and sensitive populations, including the
fetus, infants, and children, in making its regulatory determination. Thus, identification and
characterization of sensitive populations are an important component of the regulatory determination.
Then, the EPA must carefully consider whether a national drinking water regulation can achieve any risk
reduction for such populations. There are some instances where the therapeutic course of treatment for
a genetic or physiological disorder renders the risk from exposure through drinking water
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Regulatory Determination Support Document for Sulfate July 2003
inconsequential. For example, in cases where individuals undergoing dialysis for renal disorders are
identified as a sensitive population, the risk would not be significantly reduced by regulation since the
primary control of risk would be by way of the dialysis process.
4.6 Conclusion
The estimated population exposed at concentrations of possible health concern is relatively small.
Furthermore, the critical health effect of sulfate, a laxative effect, is generally temporary and reversible.
Persons exposed repeatedly to water from affected systems seem to adjust to the sulfate in the drinking
water within a week or so of initial exposure. Effective, low-cost risk management options, such as use
of bottled water or minimization of the amount of water consumed at one time, is available for transient
visitors to an affected area. For these reasons, it is unlikely that the regulation of sulfate represents a
meaningful opportunity for health risk reduction for persons served by public water systems. All CCL
regulatory determinations and further analysis are formally presented in the Federal Register Notices
(USEPA, 2002a; 67 FR 38222; and USEPA, 2003a; 68 FR 42898).
5.0 TECHNOLOGY ASSESSMENT
If a determination has been made to regulate a contaminant, SDWA requires development of
proposed regulations within 2 years of making the decision. It is critical to have suitable monitoring
methods and treatment technologies to support regulation development according to the schedules
defined in the SDWA.
5.1 Analytical Methods
The availability of analytical methods does not influence EPA's determination of whether or not a
CCL contaminant should be regulated. However, before EPA actually regulates a contaminant and
establishes an MCL, there must be an analytical method suitable for routine monitoring. Therefore,
EPA needs to have approved methods available for any CCL regulatory determination contaminant
before it is regulated with an NPDWR. These methods must be suitable for compliance monitoring,
and should be cost effective, rapid, and easy to use.
Sulfate is an unregulated contaminant for which monitoring was required under the Unregulated
Contaminant Monitoring Program (USEPA, 1987; 52 FR 25690). Monitoring for sulfate was initiated
through rulemaking in 1992 (USEPA, 1992a; 57 FR 31776), and began in 1993. Sulfate has well-
documented analytical methods developed specifically for low-level drinking water analyses (see Table
5-1).
5.2 Treatment Technology
Treatment technologies also do not influence the determination decision. But before a contaminant
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July 2003
can be regulated with an NPDWR, treatment technologies must be readily available. Sulfate is one of
Table 5-1: Analytical methods for sulfate
Mefhod
/'
EPA 300.0
ASTM
D4327-91
SM4110B
EPA 375.2
SM
4500-SO42-
c
SM
4500-SO42-
c
SM
4500-SO42-
c
,^ype
Ion Chromatography
Ion Chromatography
Ion Chromatography
Automated Colorimetry
Automated
Methyllhymol Blue
Method
Gravimetric Method
with Ignition of Residue
Gravimetric Method
with Drying of Residue
5deth,ad Detection
Limit(j^L)
20
Test Range of method
2,850-95,000
Minimum detectable cone.
100
500
Cone, ranges from 10,000
to 30,000
Suitable for cone. > 10,000
Suitable for cone. > 10,000
three inorganic contaminants listed as Regulatory Determination Priorities on the CCL. The treatment
data for these inorganic compounds was obtained from technology and cost documents, Office for
Research and Development's (ORD) National Risk Management Research Laboratory (NRMRL)
Treatability Database, and published studies. The technologies reviewed include conventional
treatment, ion exchange, reverse osmosis, lime softening, and chemical precipitation.
Conventional treatment usually includes pre-treatment steps of chemical coagulation, rapid mixing,
and flocculation, followed by floe removal via sedimentation or flotation. After clarification, the water is
then filtered. Common filter media include sand, dual- and tri-media (e.g. silica sand, garnet sand, or
anthracitic coal).
Ion exchange involves the selective removal of charged inorganic species from water using an ion-
specific resin. The surface of the ion exchange resin contains charged functional groups that hold ionic
species by electrostatic attraction. As water containing contaminant ions passes through a column of
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resin beds, charged ions on the resin surface are exchanged for the contaminant species in the water.
Reverse osmosis (RO) is similar to other membrane processes, such as ultrafiltration and
nanofiltration, since water passes through a semi-permeable membrane. However, in the case of RO,
the principle involved is not filtration. Instead, it involves the use of applied hydraulic pressure to
oppose the osmotic pressure across a non-porous membrane, forcing the water from the concentrated
solution side to the dilute solution side. The water does not travel through pores, but rather dissolves
into the membrane, diffuses across, then dissolves out into the permeate. Most inorganic and many
organic contaminants are rejected by the membrane and will be retained in the concentrate.
In the lime-softening process, the pH of the water being treated is raised sufficiently to precipitate
calcium carbonate and, if necessary, magnesium hydroxide. Calcium and magnesium ions in water
cause hardness. After mixing, flocculation, sedimentation, and pH readjustment, the softened water is
filtered.
Results of a preliminary technology assessment and review indicate that ion exchange and reverse
osmosis are the most successful techniques for removing sulfate from water, though chemical
precipitation is also effective. No data are available for the efficacy of using conventional treatment or
lime softening to remove sulfate from water.
6.0 SUMMARY AND CONCLUSIONS - DETERMINATION OUTCOME
Three statutory criteria are used to guide the determination of whether regulation of a CCL
contaminant is warranted: 1) the contaminant may adversely affect the health of persons; 2) the
contaminant is known or is likely to occur in public water systems with a frequency, and at levels, of
public health concern; and 3) regulation of the contaminant presents a meaningful opportunity for health
risk reduction for persons served by public water systems. As required by SDWA, a decision to
regulate a contaminant commits the EPA to propose an MCLG and promulgate an NPDWR for the
contaminant. A decision not to regulate a contaminant is considered a final Agency action and is
subject to judicial review. The Agency can choose to publish a Health Advisory (a nonregulatory
action) or other guidance for any contaminant on the CCL that does not meet the criteria for regulation.
Sulfate in drinking water at concentrations greater than 500 mg/L appears to have a short-term
laxative effect. If other osmotically active materials are not present, the effect is usually not seen unless
sulfate concentration exceeds 1000 mg/L. The laxative effect can be manifested as an increase in stool
mass, increased stool moisture, decreased intestinal transit time, and/or frank diarrhea. Recovery from
laxative effects is rapid and complete, and acclimation to high levels of sulfates seems to occur within
one week. Available data do not indicate developmental or reproductive effects from long-term
exposure. Carcinogenicity of sulfate cannot be determined from available health effects data.
Available occurrence data show that sulfate is occasionally present in potable water supplies at
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concentrations that can produce a laxative effect. Nationwide, the 99th percentile concentration of
sulfate was 560 mg/L, greater than the HRL of 500 mg/L. Although such concentrations are not likely
to produce a laxative effect alone, they may be combined with other osmotically active materials such
as in infant formula preparation, creating a stronger laxative effect. Therefore, the contaminant is known
to occur in public water systems and at levels of public health concern. However, the population
exposed at concentrations of possible health concern is relatively small.
To make its regulatory evaluation, the EPA looks at total exposed population, as well as population
exposed to levels above the estimated HRL. To evaluate risk from exposure through drinking water,
the EPA compares net environmental exposure to drinking water exposure. EPA also considers
exposure to both the general public and sensitive populations, including fetuses, infants, and children.
Approximately 202,464,000 people are served by systems with detections greater than the minimum
reporting level, but only 1,887,000 are exposed to concentrations above the HRL, and 490,000 above
the concentrations that are most likely to have a laxative effect when other osmotically active materials
are not present (>1000 mg/L). At median water concentrations, food comprises 90% of sulfate
exposure, but at the 99th percentile level of 560 mg/L, water contributes 70% of total exposure.
Sensitive populations include visitors, formula-fed infants, and those who consume nutritional
supplement drinks from powdered preparations. In high sulfate areas, use of bottled water for sensitive
populations could significantly reduce the risk of laxative effects.
Available data indicate that regulation of sulfate would not present a meaningful opportunity for
health risk reduction. The population exposed at concentrations of possible health concern is relatively
small. The critical health effect is generally temporary and reversible. Those exposed chronically to
water high in sulfate tend to adjust within a week of initial exposure, or reduce their intake because of
taste in the water. To manage risk, sensitive populations can use bottled water during visits or to
prepare formula and supplement drinks. EPA is issuing an advisory to provide guidance to
communities that may be exposed to drinking water contaminated with high sulfate concentrations. All
CCL regulatory determinations and further analysis are presented in the Federal Register Notices
(USEPA, 2002a; 67 FR 38222; and USEPA, 2003a; 68 FR 42898).
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APPENDIX A: Abbreviations and Acronyms
CCL - Contaminant Candidate List
CDC - Center for Disease Control and Prevention
CMR - Chemical Monitoring Reform
CWS - Community Water System
EPA - Environmental Protection Agency
FR - Federal Register
g/mol - grams per mole
GW - ground water
HA - Health Advisory
HRL - Health Reference Level
IOC - inorganic compound
L - liters
mg - milligrams
MCL - Maximum Contaminant Level
MCLG - Maximum Contaminant Level Goal
MRL - Minimum Reporting Level
NAWQA - National Water Quality Assessment Program
NCOD - National Drinking Water Contaminant Occurrence Database
NOW AC - National Drinking Water Advisory Council
nm - nanometer
NPDWR - National Primary Drinking Water Regulation
NRMRL - National Risk Management Research Laboratory
NTNCWS - Non-Transient Non-Community Water System
OGWDW - Office of Ground Water and Drinking Water
ORD - Office of Research and Development
PGWD - Pesticides in Ground Water Database
pH - the negative log of the concentration of H+ ions
ppm - part per million
PWS - Public Water System
RO - reverse osmosis
SDWA - Safe Drinking Water Act
SDWIS/FED - the Federal Safe Drinking Water Information System
SMCL - Secondary Maximum Contaminant Level
SOC - synthetic organic compound
SW - surface water
UCM - Unregulated Contaminant Monitoring
UCMR - Unregulated Contaminant Monitoring Regulation/Rule
URCIS - Unregulated Contaminant Monitoring Information System
USEPA - United States Environmental Protection Agency
USGS - United States Geological Survey
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VOC - volatile organic compound
WHO - World Health Organization
pg - micrograms
>MCL - percentage of systems with exceedances
>MRL - percentage of systems with detections
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