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Preliminary Regulatory Determination Support Document for Sulfate November, 2001
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Disclaimers
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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.
Dan Olson and Karen Wirth served as EPA's team leaders for the CCL regulatory determination process,
and James Taft as Standards and Risk Management Division Chief. Tara Cameron and Karen Wirth
served as Work Assignment Managers. 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, and Ashton Koo are gratefully
acknowledged. George Hallberg served as Cadmus'Project Manager.
ill
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Preliminary Regulatory Determination Support Document for Sulfate
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USEPA, Office of Water Report: EPA 815-R-01-015, November, 2001
CONTAMINANT CANDIDATE LIST
PRELIMINARY REGULATORY DETERMINATION SUPPORT
DOCUMENT FOR SULFATE
Executive Summary
Sulfate is a 1998 Contaminant Candidate List (CCL) regulatory determination priority contaminant.
Sulfate is 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 suifate inay not present a meaningful opportunity to reduce health risk. EPA
presents preliminary CCL regulatory determinations and further analysis in the Federal Register Notice.
To make the preliminary determination for suifate, EPA used approaches guided by me National
Drinking Water Advisory CounciTs (NDWAC) Workgroup 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 (SO,,2"), 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 suifate 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 suifate 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 suifate in drinking water. In 1985, EPA proposed a
suifate health advisory of 400 mg/L that was never finalized. The SDWA amendments of 1986 mandated
an NPDWR for suifate 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 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 hi 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 suifate 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 suifate in drinking water. EPA and CDC jointly concluded it
is unlikely that any adverse health effects will result from suifate concentrations in drinking water below
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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 L4% 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 human; 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
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.
VI
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Table of Contents
Disclaimers . ; i
Acknowledgments „ iii
Executive Summary v
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 4
2.0 CONTAMINANT DEFINITION .4
2.1 Environmental Fate/Behavior ... 5
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 11
3.2.2 Results 11
3.3 Drinking Water Occurrence ......;.... 13
3.3.1 Data Sources, Data Quality, and Analytical Approach 14
3.3.1.1 UCMRounds 1 and2 14
3.3.1.2 Developing a Nationally Representative Perspective 15
3.3.1.2.1 Cross-Section Development 15
3.3.1.2.2 Cross-Section Evaluation 17
3.3.1.3 Data Management and Analysis 18
3.3.1.4 Occurrence Analysis 18
3.3.1.5 Supplemental CMR State Data 19
3.3.2 Results 20
3.3.2.1 Occurrence Estimates from SDWIS/FED Round 2 Data 20
3.3:2.2 Occurrence Estimates from the CMR State Data . 20
3.3.2.3 Cross-Section Comparisons 21
3.4 Conclusion 24
4.0 HEALTH EFFECTS 25
4.1 Hazard Characterization and Mode of Action Implications 25
Vii
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4.2 Dose-Response Characterization and Implications in Risk Assessment 26
4.3 Relative Source Contribution 27
4.4 Sensitive Populations , 27
4.5 Exposure and Risk Information ; 27
4.6 Conclusion 28
5.0 TECHNOLOGY ASSESSMENT .. 1 28
5.1 Analytical Methods , 28
5.2 Treatment Technology , ,.. 29
6.0 SUMMARY AND CONCLUSIONS - DETERMINATION OUTCOME 30
References ,... 33
Appendix A: Abbreviations and Acronyms 37
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List of Tables
Table 3-1: Abundance of sulfur in different environments 8
Table 3-2: Global production of sulfur dioxide (x 106 metric tons Sulfur per year) 10
Table 3-3: Sulfate detections and concentrations in streams and ground water 13
Table 3-4: Summary occurrence statistics for sulfate 22
Table 3-5: Occurrence summary by State for sulfate (CMR data) . 23
Table 3-6: 20-State SDWIS/FED Round 2 cross-section compared to the 8-State CMR
cross-section for sulfate .. —..., 24
Table 5-1: Analytical methods for sulfate 29
IX
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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 9
Figure 3-2: Geographic distribution of cross-section States for Round 2 (SDWIS/FED) 17
XI
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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 FR10273),
and a new CCL must be published every five years thereafter.
The 1998 CCL contains 60 contaminants, including SO 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 3V2 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 me 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
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 Drinkmg Water (OGWDW) is charged wim garnering 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
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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 must first publish, in the Federal Register, the draft
determinations for public comment EPA will respond to the public comments received, and will then
finalize regulatory determinations. If the Agency finds that regulations are warranted, the regulations
must then be formally proposed within twenty-four months, and promulgated eighteen months later. EPA
has determined that mere is sufficient information to support a regulatory determination for sulfate.
13 Statutory History of Sulfate
Sulfate has been monitored under the SDWA Unregulated Contaminant Monitoring (UGM) 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 FR1494), 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 for sulfate of 400 mg/L. This advisory was intended as an
alternative to a federally enforceable mireimnm contaminant level (MCL), and was meant to protect
infants (USEPA, 1985; 50 FR 46936). The proposed health advisory was never finalized (USEPA,
1999b; 64 FR 7028). As apart 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 a National Primary Drinking Water Regulation for
sulfate, as well as the establishment 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 fouir
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 sulfete in drinking water (SDWA, § 1412 (b)
(12) (B)). Results from this study were published in January, 1999.
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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 hi 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 mere was insufficient scientific evidence regarding health
effects to justify a regulation. The panel suggested that a healm advisory be issued in areas where sulfate
concentrations in drinkingwaterexceed 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 mat 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 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 action1 is needed (e.g.; issuance of guidance).
The NDWAC protocol uses the three statutory requirements of SDWA Section 1412(b)(l)(A)(i)-Oii)
(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 NDWAC 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 NDWAC recommended that EPA consider: (1) the actual and
estimated national percent of public water systems (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.
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To address whether regulation of a contaminant presents a meaningful opportunity for health risk
reduction for persons served by public water systems (statutory requirement (Hi)) the NDWAC
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 preliminary regulatory determinations followed the general format
recommended by the NRC and the NDWAC 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 healtli
reference level (HRL) for each contaminant.
For each contaminant EPA estimated the number of PWSs with detections >3^HRL and >HRL, the
population served at these benchmark values, and the geographic distribution, using a large number of
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 date (e.g.,
NAWQA, State and regional studies, and the EPA Pesticides in Ground Water Database) 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 preliminary 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
preliminary determination not to regulate sulfate with an NPDWR. This preliminary 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 preliminary CCL regulatory determinations will be presented in the Federal
Register Notice. The following sections summarize the data used by the Agency to reach this preliminary
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
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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
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 hi 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.
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Figure 2-1: The Sulfur Cycle
Spray, etc.
1
Oxidized
Reduced
Metamorphism
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 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 me 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 (FeSj),
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). ;
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The concentration of sulfate ions in rain can be highly variable depending on proximity to industrial
areas where sultur-containing fuels are combusted and sulfur dioxide (SOj) is released (Wehrniller, 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 public water systems
(PWSs) collected under the Safe Drinking Water Act (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 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 8* or 9th most abundant in
sediments (Kaplan, 1972). See Table 3-1 for sulfur abundances in different environments:
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Table 3-1: Abundance of sulfur in different environments
Crustal Average
Ultramafic
Basalt
Granite
Shale
Sandstone
Carbonate
Deep-sea sediment
Soils
Terrestrial plants
Seawater
Freshwater
a/ia-FleU, 1972
260
300
250
270
2,400
240
1,200
1,300
850
500
885
5.5
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 i
Sulfur dioxide (SOj) 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 (BjSO^, 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
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Figure 3-1: Annual weighted mean pH and sulfate concentration in precipitation in North America
in 1985
so,
after Drever, 1988
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).
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Table 3-2: Global production of sulfur dioxide (xlO6 metric tons Sulfur per year)
pSiilSl
Asia
Europe
North
America
Africa
South
America
Oceania
Total
$930>i*4p
5
21
22
0.5
0.4
0.4
49
9
25
17
0.7
0.5
0.5
53
12
21
25
1
1
1
61
34
30
24
2
2
1
93
43
30
34
3
3
1
114
57
30
29
4
4
2
126
30-90
12-30.
25
6
6
2 .
81-159
eflerDlgnonandffameed, 1989; Hordljk, 1988; Matter, 1984
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).
The basic reaction taking place in acid mine drainage involves the bacterially-mediated conversion of
pyrite (FeSj) to ferric hydroxide in the presence of percolating ground water, releasing sulfate and acid:
Fe2* + 0.25 02 +2.5 H2O *> Fe(OH)3 + 2 IT
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).
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3.2 Ambient Occurrence
To understand the presence of a chemical in the environment, an examination of ambient 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 United
States Geological Survey (USGS), particularly in their National Water Quality Assessment (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 me 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 fpr 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 Health
Reference Level (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 99* percentile concentrations are included as well, to characterize
the range of sulfate concentration values present in ambient waters sampled by the NAWQA program.
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.
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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 freshwater). 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/rangelandbasins 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 hi surface waters are similar for urban, mixed, and
agricultural basins, while.fbrest/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
"Detection frequency "
>MRL*
surface water
urban
mixed
agricultural
forest/rangeland
all sites
ground water
urban
mixed
agricultural
forest/rangeland
all sites
% samples
100% i
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 % sites ,
2.6%
0.8%
2.9%
0.0%
1.8%
-
5.3 %
2.1%
-4.3 %
0.0%
2.7%
0.4%
2.2%
3.6 %
0.0%
2.7%
6.4%
2.4 %
4.3%
0.0 %
3.2%
Concentrations
(all samples; mg/L)
median
20
21
25
•• 5
20
20
12
24
7
17
22*
percentile
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 (URL) is 500 mg/L. TheHRL is a
preliminary health effect level used far 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 National Primary Drinking Water
Regulation, 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 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).
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Sulfate has been monitored under the SDWA Unregulated Contaminant Monitoring (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
ER 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 contorninant 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).
33.1 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 occlirrence 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, 2001 a
2001b).
*
v 33.1.1 UCM Rounds land 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 me Unregulated Contaminant Information System, or URCIS.
• The 1993 UCM contaminants included 13 synthetic organic contaminants (SOCs) and sulfate, the
only IOC (USEPA, 1992jj; 57 FR 31776). Monitoring for the UCM (1993) contaminants began
coincident with the Phase n/V regulated contaminants in 1993 through 1998. This is often referred to as
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"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 (2001s) and USEJPA (2001b).
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/hydrdlogic 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 .4 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 because the original
monitoring data were not collected or reported hi 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, 2001a, 2001b); readers are referred to these for more specific information.
.•«
33.1.2.1 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 hi 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, 2001a 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
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transport and fate of contaminants, as well as conditions that affect naturally occurring contaminants
(USEPA, 2001b Sections EI.A. and ffl.B.)-
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 ffl.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 SO. 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
bom 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 potential
rankings (USEPA, 2001b 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).
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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
33.1.2.2 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
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, I999d). 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 m.B.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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33.13 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 man 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) cam 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 Minimum Reporting Limit (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).
33.1.4 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 hi 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 detections) greater than half the Health Reference Level (HRL); or a detections) 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 apanel 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.
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The 99th percentile concentration is usedhere 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 Jbalfme MRL is often used as an estimate of the
concentration of a contaminant in samples/systems whose results are less than me 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 meaningfulsummary statistic is not available to describe the various reported MRLs; and to avoid
confusion, MRLs are not reported in me summary table (Table 3-4).
In Table 3-4, national occurrence is estimated by extrapolating the summary statistics for the 20-State
cross-section to national numbers for systems, and population served by systems, from th& Water Industry
Baseline Handbook, Second Edition (USEPA, 2000). From the handbook, the total national number of
community water systems (CWSs) phis non-transient, jion-community water systems (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 me
percentage of PWSs with'-aetections (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 me 20-State cross-
section. These CMR State data are also compared to the 20-State SDWIS/FED cross-section. AReview
of Contaminant Occurrence in Public Water Systems supported occurrence analyses for EPA's Chemical
Monitoring Reform (CMR) evaluation, and is therefore referred to in this document as the CMR report.
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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 froraa 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 mese 12 States, eight
were selected for use in a national analysis because they provided the best data quality and cornpletsness,
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).
ft ' - .... '•
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 dataare also included. The number of sample results and PWSs
vary by State, however, with some States having considerably more data.
33.2 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 nag/L; 1.8% df 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, >»/£ 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.
•! • i'
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 numtxar 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.
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Sulfete 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 systems.
These figures agree wim 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 man 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 me HRL. At me HRL of 500 mg/L, data from me 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 GMR States are incomplete, and are only reported for those systems in the
database that have reported their population data. For sulfate, approximately 85% of rne PWSs reporting
occurrence data for these 6 States also reported population data.
«*• , •
33.2.3 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 mat 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"* Perccntilc Concentration of all Samples
Median Concentration of all Samples
Total Number of PWSs
Number of GWPWSs
Number of SW PWSs
Total Population
Population of GWPWSs :
Population of SW PWSs
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
. GWPWSs>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%
500mg/L
Variable3
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
5390
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
1. Summary Results based on data front 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= GrotmdWater; 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 ofDetections = 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>% Health Reference Level, %PWS> Health Reference Level = percent of the total number of public water
systems vrith at least one analytical result that exceeded the MRL, '/> Health Reference Level, Health Reference Level respectively
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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) = 560 mg/L
% PWSs > 1/2 HRL
Ground Water PWSs > 1/2 HRL
Surfece 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
Variable1
547
478
69
90.9%
89.5%
100.0%
0.18%
0.00%
1.45%
0.00%
0.00%
0.00%
995%
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
Variable1
2,195
1,977
218
93.4%
93.4%
93.1%
10.4%
10.9%
5.96%
2.69%
2.98%
0.00%
995%
99.8%
99.9%
50.7%
435%
57.0%
22.6%
34.4%
0.00%
Illinois
280
210
70
86.4%
81.9%
100.0%
760 mg/L
60 mg/L
Variable1
195
128
67
87.2%
80.5%
100.0%
7.18%
105%
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
1465
1343
222
86.9%
86.8%
87.4%
1,200 mg/L
22 mg/L
Variable1
775
722
53
88.4%
88.1%
92.5%
12.5%
125%
13.2%
632%
6.23%
7.55%
95.9%
93.8%
97.9%
10.2%
15.5%
5.34%
433%
5.41%
3.33%
New Jersey
5,055
4,446
609
865%
85.7%
96.1%
260 mg/L
15.9 mg/L
Variable1
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
1346
804
542
77.0%
79.1%
73 JH
79mg/L
5.13 mg/L
Variable1
656
507
149
825%
81.1%
893%
0.15%
020%
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 estirnated health ejffect level used for preliminary assessment for this review; N/A - Not Applicable
- Total Number of Samples = the total number of analytical records for sulfate
-99thPercentileConcentration = theconcentrationvalueofthe99thpercentileofallana^icalresults(inmg/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'PopulationServed^thetotalpopulationservedbypublicwatersystemswithrecordsforsulfate
- % PWS with detections.'% PWS>'/i 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, Vi 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
Total Number of PWSs
Number of GWPWSs
Number of SW PWSs
% PWSs with detections (> MRL)
GW PWSs with detections
SW PWSs with detections
f;
% PWSs with detections > 500 mg/L
GW PWSs > 500 mg/L
SWPWSs > 500 mg/L
20-State Cross-Section2
16,495
15,009
1,486
88.1%
87.8%
91.7%
1.8%
1.8%
1.4%
8-State Cross-Section3
5,973
5,381
592
90.3%
89.9%
93.9%
2.1%
2.2%
1.0%
' Onfystx States reported data far sulfate in the 8-State cross-section.
' Summary Results based on data from 20-State Cross-Section, from SDW1S/FED, UCMQ993) Round 2; see Table 3-4 and Section 3.3.1.1.
'after 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 99* 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.
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-
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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, 2001c).
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 at, 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 LevVj 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).
Smce humans appear to develop a tolerance to drinking water with high siulfate concentrations,
chronic exposures do not appear to produce the same laxative effect as seen hi 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, 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 hi a limited-duration study done on rats injected intramuscularly
with sodium every other 8ay 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
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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 eit 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 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 sulfat&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 (0SEPA, 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 Centers for Disease Control and
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Prevention (CDC) panel favored a Health Advisory for sulfate drinking water levels of 500 mg/L or
greater (USEPA, 19996).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 mat 500 mg/L seemed to be a safe sulfate level because 500 mg/L was shown to be
safe in all reviewed sradies.
43 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. Abemathy (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.
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 1he 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 hi 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 Health
Reference Level (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 hi Section 3.3.2, and are summarized below.
Approximately 95% of the population served by public water systems (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
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of all samples is 560 mg/L. One of the six States (Montana) that provided supplemental (CMR) date for
the independent analysis, A Review of Contaminant Occurrence in Public Water Systems, had a 99*
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 tp 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 siuch
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 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 mat the regulation of sulfate represents a
meaningful opportunity for health risk reduction for persons served by public water systems. All
preliminary CCL regulatory determinations and further analysis will be presented in the Federal Register
Notice.
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
intheSDWA.
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 a Maximum Contaminant Level (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 rulemakmg 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-
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Preliminary Regulatory Determination Support Documentfor Sulfate
November, 2001
Table 5-1: Anal
Method
EPA 300.0
ASTM
D4327-91
SM4110B
EPA 375.2
SM
4500-SO/- C
SM
4500-SO/C
SM
4500-SO/-C
rtical methods for sulfate
Type
Ion Chromatography
Ion Chromatography
-J,
Ion Chromatography
Automated Colorimetry
Automated
Methylthymol Blue
Method
Gravimetric Method
with Ignition of Residue
Gravimetric Method
with Drying of Residue
Method Detection
Limit (ug/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
5.2 Treatment Technology
Treatment technologies also do not influence the determination decision. But before a contaminant
can be regulated with an IjfPDWR, treatment technologies must be readily available. Sulfate is one of
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 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 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
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Preliminary Regulatory Determination Support Document for Sulfate
November, 2001
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 me 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 preliminary 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 a Maximum Contaminant Level Goal (MCLG) and
promulgate a National Primary Drinking Water Regulation (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
concentrations that can produce a laxative effect Nationwide, the 99th percentile concentration of sulfate
was 560 mg/L, greater than the Health Reference level (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
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'Preliminary Regulatory Determination Stipport Document for Sulfate
November, 2001
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 preliminary CCL
regulatory determinations and further analysis are presented in the Federal Register Notice.
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Preliminary Regulatory Determination Support Document for Sulfate
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References
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Anderson, D.M. and S.C. Stothers. 1978. Effects of saline water high in sulfates, chlorides and nitrates
on the performance of young weanling pigs. J.Animal Sci. 47(4)900-907.
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Preliminary Regulatory Determination Support Document for Sulfate
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Preliminary Regulatory Determination Support Document for Sulfate
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Preliminary Regulatory Determination Support Document for Sulfate
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Preliminary Regulatory Determination Support Document for Sulfate
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CCL
CDC
CMR
CWS
EPA
FR
g/mol
GW
HA
HAL
HRL
IOC
L
mg
MCL
MCLG
MDL
MRL
NAWQA
NCOD
NDWAC
MRS
irm
NPDWR
NRMRL
NTNCWS
OGWDW
ORD
PGWD
pH
ppm
PWS
RO
SDWA
SDWIS/FED
SMCL
SOC
SW
SWP
UCM
UCMR
URCIS
USEPA
USGS
VOC
WHO
Appendix A: Abbreviations and Acronyms
- Contaminant Candidate List
- Center for Disease Control and Prevention
- Chemical Monitoring Reform
- Community Water System
- Environmental Protection Agency
- Federal Register
- grams per mole
-ground water
- Health Advisory
- Health Advisory Level
- Health Reference Level
- inorganic compound
-liters
-milligrams
- Maximum Contaminant Level
- Maximum Contaminant Level Goal
- Method Detection Limit
- Minimum Reporting Level
- National Water Quality Assessment Program
- National Drinking Water Contaminant Occurrence Database
- National Drinking Water Advisory Council
- National Inorganic and Radionuclide Survey
-nanometer
- National Primary Drinking Water Regulation
- National Risk Management Research Laboratory
- Non-Transient Non-Community Water System
- Office of Ground Water and Drinking Water
- Office of Research and Development
- Pesticides in Ground Water Database
- the negative log of the concentration of H* ions
-part per million
- Public Water System
- reverse osmosis
- Safe Drinking Water Act
- the Federal Safe Drinking Water Information System
- Secondary Maximum Contaminant Level
- synthetic organic compound
- surface water
- surface water - purchased
- Unregulated Contaminant Monitoring
- Unregulated Contaminant Monitoring Regulation/Rule
- Unregulated Contaminant Monitoring Information System
- United States Environmental Protection Agency
- United States Geological Survey
- volatile organic compound
- World Health Organization
- micrograms
37
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Preliminary Regulatory Determination Styport Document for Svlfate
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>MCL
>MRL
- percentage of systems with exceedances
- percentage of systems with detections
38
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