Contaminant Candidate
^ List Regulatory
Determination Support
Document for Sodium
K.-r; Printed on Recycled Paper
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Contaminant Candidate List
Regulatory Determination Support Document
for Sodium
U.S. Environmental Protection Agency
Office of Water (4607M)
Standards and Risk Management Division
Washington, DC 20460
http://www.epa.gov/SAFEWATER/ccl/cclregdetermine.html
EPA-815-R-03-15
July 2003
f\ Printed on Recycled Paper
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Disclaimer
This document is designed to provide supporting information regarding the
regulatory determinations for sodium as part of the Contaminant Candidate
List (CCL) evaluation process. This document is not a regulation, and it does
not substitute for the Safe Drinking Water Act (SDWA) or the Environmental
Protection Agency's (EPA's) regulations. Thus, it cannot impose legally-
binding requirements on EPA, States, or the regulated community, and may
not apply to a particular situation based upon the circumstances. Mention of
trade names or commercial products does not constitute endorsement or
recommendation for use.
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Regulatory Determination Support Document for Sodium July 2003
ACKNOWLEDGMENTS
This document was prepared in support of the EPA's Office of Ground Water and Drinking Water
regulatory determination for sodium as part of the Contaminant Candidate List (CCL) evaluation
process. Karen Wirth and Tom Carpenter served as EPA's Co-Team Leaders for the CCL regulatory
determination process and Ephraim King as Standards and Risk Management Division Director.
Harriet Colbert served as Work Assignment Manager. The CCL Work Group provided technical
guidance throughout. In particular, Karen Wirth, Dan Olson, and Joyce Donohue provided scientific
and editorial guidance. External expert reviewers and many stakeholders provided valuable advice to
improve the CCL Program and this document. The Cadmus Group, Inc., served as the primary
contractor providing support for this work. The major contributions of Matt Collins, Emily Brott,
Ashton Koo, Richard Zeroka, and Brent Ranalli are gratefully acknowledged. George Hallberg served
as Cadmus' Project Manager.
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Regulatory Determination Support Document for Sodium July 2003
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Regulatory Determination Support Document for Sodium July 2003
USEPA, Office of Water Report: EPA 815-R-03-015, July 2003
CONTAMINANT CANDIDATE LIST
REGULATORY DETERMINATION SUPPORT DOCUMENT
FOR SODIUM
EXECUTIVE SUMMARY
Sodium was a 1998 Contaminant Candidate List (CCL) regulatory determination priority
contaminant. Sodium was one of the contaminants considered by the U.S. Environmental Protection
Agency (EPA) for a regulatory determination. The available data on occurrence, exposure, and other
risk considerations suggest that regulating sodium may not present a meaningful opportunity to reduce
health risk. EPA presented preliminary CCL regulatory determinations and further analysis in the June
3, 2002 Federal Register Notice (USEPA, 2002a; 67 FR 38222), and confirmed the final CCL
regulatory determinations in the July 18, 2003 Federal Register Notice (USEPA, 2003 a; 68 FR
42898).
To make this regulatory determination for sodium, EPA used approaches guided by the National
Drinking Water Advisory Council's (NDWAC) Work Group on CCL and Six-Year Review. The
Safe Drinking Water Act (SDWA) requirements for National Primary Drinking Water Regulation
(NPDWR) promulgation guided protocol development. The SDWA Section 1412(b)(l)(A) specifies
that the determination to regulate a contaminant must be based on a finding that each of the following
criteria are met: (i) "the contaminant may have adverse effects on the health of persons"; (ii) "the
contaminant is known to occur or there is substantial likelihood that the contaminant will occur in public
water systems with a frequency and at levels of public health concern"; and (iii) "in the sole judgement
of the Administrator, regulation of such contaminant presents a meaningful opportunity for health risk
reduction for persons served by public water systems." Available data were evaluated to address each
of the three statutory criteria.
Sodium (Na) is a naturally occurring element ubiquitous in the environment. It is the sixth most
abundant element in the Earth's crust and the most abundant anion in the hydrosphere. Sodium in the
ocean is associated with chlorine in the form of sea salt. In the lithosphere, most sodium minerals exist
as soluble salts found primarily in evaporite deposits and silicate minerals, and more rarely as halides or
aluminohalides. The sodium cation (Na+) is necessary for a number of biochemical processes in many
living organisms.
Sodium chloride (NaCl) is the most economically and industrially important form of sodium with
thousands of uses. Among other things, salt is used as a flavor enhancer or food preservative, as a road
deicer, in water softening treatment, in powdered soaps and detergents, as the electrolyte in saline
solutions, in rubber manufacture, and as a pesticide. Sodium chloride is also used in oil and gas
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Regulatory Determination Support Document for Sodium July 2003
exploration, textile and dyeing industries, metal processing, pulp and paper production, tanning and
leather treatment, and in the chemical industry to manufacture other chemicals. Widespread
environmental releases of five other sodium compounds reported through the Toxic Release Inventory
(TRI) underscore the heavy use and release of sodium in the environment.
A Health Advisory (HA) has until now never been issued for sodium, though a Drinking Water
Equivalent Level (DWEL) is available. The DWEL of 20 mg/L is a non-enforceable guidance level
considered protective against non-carcinogenic adverse health effects and is based on an American
Heart Association recommendation issued in 1965. Also, EPA has issued a non-enforceable guidance
of 250 mg/L for salinity and dissolved solids in ambient waters (USEPA, 1997; 62 FR 52194).
The sale, use, and distribution of pesticide products containing sodium chloride and sodium bromide
are controlled under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). The
Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA, or
"Superfund") also includes sodium and many of its compounds on its list of hazardous substances. A
number of sodium compounds are also listed as hazardous constituents under the Resource
Conservation and Recovery Act (RCRA).
Sodium occurrence in ambient waters and stream bed sediments monitored by the United States
Geological Survey's (USGS) National Water Quality Assessment (NAWQA) program is ubiquitous,
approaching 100% of water and sediment sampling sites for all land use categories. Although sodium
detection frequencies are high, sodium occurrence at levels of public health concern is low. Less than
6% of all surface water sites and less than 8% of all ground water sites report detections greater than
120 mg/L, a benchmark concentration level used for this analysis.
Sodium has been detected in ground water PWS samples collected through the National Inorganic
and Radionuclide Survey (MRS) study. Occurrence estimates are high with 100% of samples showing
detections, affecting 100% of the national population served. The 99th percentile concentration of all
samples is 517 mg/L. About 13.2% of the MRS systems exceeded the 120 mg/L benchmark level,
affecting approximately 7.1 million people nationally. Additional data, including both ground water and
surface water PWSs from select States, were examined through independent analyses and also show
substantial sodium occurrence.
The weight of evidence favors the conclusion that high sodium intakes can have an adverse effect
on blood pressure, especially for sodium-hypertensives. Hypertension affects almost 50 million people
in the United States, and along with factors such as body weight, alcohol intake, and cholesterol, is a
risk factor for heart disease. However, hyptertension is influenced more by lifestyle, behavior, and
other nutrient intake than by sodium intake.
IV
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Regulatory Determination Support Document for Sodium July 2003
Sodium is known to occur in public water systems and in a few cases at levels of public health
concern, particularly for salt-sensitive hypertensives. However, at these same concentrations, taste is
generally affected and would likely lead consumers to decrease consumption. In addition, when
compared with other intake routes, sodium from drinking water has a minor impact. For these reasons,
regulation of sodium is unlikely to present a meaningful opportunity for health risk reduction for persons
served by public water systems. However, EPA may choose to issue a non-enforceable Drinking
Water Advisory, based on current health effects, taste effects, and occurrence data, to provide
guidance to communities that may be exposed to elevated concentrations of sodium chloride or other
sodium salts in their drinking water. In addition, under EPA-required sodium monitoring, test results
must be reported to State and local public health authorities, who may advise sensitive populations of
any risk they may face.
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Regulatory Determination Support Document for Sodium July 2003
TABLE OF CONTENTS
ACKNOWLEDGMENTS i
EXECUTIVE SUMMARY iii
TABLE OF CONTENTS vii
LIST OF TABLES ix
LIST OF FIGURES xi
1.0 INTRODUCTION 1
1.1 Purpose and Scope 1
1.2 Statutory Framework/Background 1
1.3 Statutory History of Sodium 2
1.4 Regulatory Determination Process 3
1.5 Determination Outcome 5
2.0. CONTAMINANT DEFINITION 5
2.1 Physical and Chemical Properties 6
2.2 Environmental Fate and Transport 6
3.0 OCCURRENCE AND EXPOSURE 7
3.1 Use and Environmental Release 7
3.1.1 Production and Use 7
3.1.2 Environmental Release 11
3.2 Ambient Occurrence 13
3.2.1 Data Sources and Methods 13
3.2.2 Results 14
3.3 Drinking Water Occurrence 16
3.3.1 Analytical Approach 16
3.3.1.1 National Inorganic and Radionuclide Survey (MRS) 16
3.3.1.2 Supplemental IOC Data 17
3.3.1.3 Data Management and Analysis 18
3.3.1.4 Occurrence Analysis 18
3.3.2 Results 19
3.4 Conclusion 24
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Regulatory Determination Support Document for Sodium July 2003
4.0 HEALTH EFFECTS 24
4.1 Hazard Characterization and Mode of Action Implications 24
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 28
4.6 Conclusion 29
5.0 TECHNOLOGY ASSESSMENT 29
5.1 Analytical Methods 29
5.2 Treatment Technology 30
6.0 SUMMARY AND CONCLUSIONS - DETERMINATION OUTCOME 30
REFERENCES 33
Appendix A: Abbreviations and Acronyms 41
vui
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Regulatory Determination Support Document for Sodium July 2003
LIST OF TABLES
Table 3-1: End uses of sodium chloride in 1990 (in thousands of short tons) 9
Table 3-2: U.S. sodium chloride statistics, 1990-1998 (in thousands of metric tons) 10
Table 3-3: Environmental fate of post-consumer sodium chloride, 1990 (in millions of short tons) ..11
Table 3-4: Sodium detections and concentrations in streams and ground water 16
Table 3-5: Sodium occurrence in ground water systems (MRS survey) 22
Table 3-6: Occurrence summary of ground and surface water systems by State for sodium 23
Table 5-1: Analytical methods for sodium 30
rx
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LIST OF FIGURES
Figure 3-1: Abundance of sodium chloride (salt) in the ocean 8
Figure 3-2: Average sodium concentrations in precipitation over the United States 8
XI
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Regulatory Determination Support Document for Sodium July 2003
1.0 INTRODUCTION
1.1 Purpose and Scope
This document presents scientific data and summaries of technical information prepared for, and
used in, the U.S. Environmental Protection Agency's (EPA) regulatory determination for sodium.
Information regarding sodium'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, and were known or suspected to adversely affect public health. These contaminants therefore
may require regulation under SDWA. The first Drinking Water CCL was published on March 2, 1998
(USEPA, 1998c; 63 FR 10273), and a new CCL must be published every five years thereafter.
The 1998 CCL contains 60 contaminants, including 50 chemicals or chemical groups, and 10
microbiological contaminants or microbial groups. The SDWA also requires the Agency to select 5 or
more contaminants from the current CCL and determine whether or not to regulate these contaminants
with an NPDWR. Regulatory determinations for at least 5 contaminants must be completed 3l/2 years
after each new CCL.
Language in SDWA Section 1412(b)(l)(A) specifies that the determination to regulate a
contaminant must be based on a finding that each of the following criteria are met:
Statutory Finding i: the contaminant may have adverse effects on the health of persons;
Statutory Finding ii: the contaminant is known to occur or there is substantial likelihood that the
contaminant will occur in public water systems with a frequency and at levels of public health
concern; and
Statutory Finding Hi: in the sole judgement of the Administrator, regulation of such
contaminant presents a meaningful opportunity for health risk reduction for persons served by
public water systems.
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Regulatory Determination Support Document for Sodium July 2003
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 Drinking Water (OGWDW) is charged with gathering and analyzing the
occurrence, exposure, and risk information necessary to support this regulatory decision. The
OGWDW must evaluate when and where this contaminant occurs, and what would be the exposure
and risk to public health. EPA must evaluate the impact of potential regulations as well as determine the
appropriate measure(s) for protecting public health.
For each of the regulatory determinations, EPA first publishes in the Federal Register the draft
determinations for public comment. EPA responds to the public comments received, and then finalizes
regulatory determinations. If the Agency finds that regulations are warranted, the regulations must then
be formally proposed within 24 months, and promulgated 18 months later. EPA has determined that
there is sufficient information to support a regulatory determination for sodium.
1.3 Statutory History of Sodium
Sodium chloride (NaCl), otherwise known as halite, salt, sea salt, or table salt, is the most
economically and industrially important form of sodium, with an estimated 14,000 direct and indirect
uses. Among other things, salt is used as a flavor enhancer or preservative in food, as a road deicer, in
water softening treatment, in powdered soaps and detergents, as the electrolyte in saline solutions, in
rubber manufacturing, and as a pesticide. Sodium chloride is also used in oil and gas exploration, textile
and dyeing industries, metal processing, pulp and paper production, tanning and leather treatment, and
in the chemical industry (Kostick, 1993; Gornitz, 1972). Because salt has so many human end uses
and is abundant in the ocean, sodium is ubiquitous in the environment.
A Health Advisory (HA) for sodium has never been issued, though a Drinking Water Equivalent
Level (DWEL) is available. The DWEL of 20 mg/L is a non-enforceable guidance level considered
protective against non-carcinogenic adverse health effects and is based on an American Heart
Association recommendation issued in 1965. Also, EPA has issued a non-enforceable guidance of 250
mg/L for salinity and dissolved solids in ambient waters (USEPA, 1997; 62 FR 52194).
The sale, use, and distribution of pesticides, including those containing sodium, is controlled under
the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). FIFRA was most recently amended
in 1996 under the Food Quality Protection Act (FQPA). FIFRA requires registration of all pesticides
with EPA, as well as certain labeling, application, and use restrictions. Moreover, pesticide
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Regulatory Determination Support Document for Sodium July 2003
manufacturing plants must be registered, and the manufacturer must provide EPA with scientific data
regarding the product's efficacy and demonstrating that it does not pose an unreasonable risk to people
or the environment (USEPA, 1998a).
Pesticide products containing sodium chloride and sodium bromide have been registered under
FIFRA since 1954 and 1975, respectively. Currently, thirty-two sodium bromide pesticide products
and two pesticide products containing sodium chloride are registered in the United States (USEPA,
1993).
The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA, or
"Superfund") includes sodium and many of its compounds on its list of hazardous substances.
CERCLA's listing requires reporting of releases over a certain "reportable quantity" which, for
elemental sodium, is ten pounds (USEPA, 1998b). A number of sodium compounds are also listed as
hazardous constituents under the Resource Conservation and Recovery Act (RCRA) (USEPA,
1998b). Furthermore, data are available for five sodium compounds through the Toxic Release
Inventory (TRI). The TRI was established by the Emergency Planning and Community Right-to-Know
Act (EPCRA). EPCRA requires certain industrial sectors to publically report the environmental release
or transfer of chemicals included in this inventory (USEPA, 2000a).
1.4 Regulatory Determination Process
In developing a process for the regulatory determinations, EPA sought input from experts and
stakeholders. EPA asked the National Research Council (NRC) for assistance in developing a
scientifically sound approach for deciding whether or not to regulate contaminants on the current and
future CCLs. The NRC's Committee on Drinking Water Contaminants recommended that EPA: (1)
gather and analyze health effects, exposure, treatment, and analytical methods data for each
contaminant; (2) conduct a preliminary risk assessment for each contaminant based on the available
data; and (3) issue a decision document for each contaminant describing the outcome of the preliminary
risk assessment. The NRC noted that in using this decision framework, EPA should keep in mind the
importance of involving all interested parties.
One of the formal means by which EPA works with its stakeholders is through the National
Drinking Water Advisory Council (NDWAC). The NDWAC comprises members of the general
public, State and local agencies, and private groups concerned with safe drinking water, and advises
the EPA Administrator on key aspects of the Agency's drinking water program. The NDWAC
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
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Regulatory Determination Support Document for Sodium July 2003
stakeholders. The possible outcomes of the regulatory determination process are: a decision to
regulate, a decision not to regulate, or a decision that some other action is needed (e.g., issuance of
guidance).
The NOW AC protocol uses the three statutory requirements of SDWA Section 1412(b)(l)(A)(i>
(iii) (specified in section 1.2) as the foundation for guiding EPA in making regulatory determination
decisions. For each statutory requirement, evaluation criteria were developed and are summarized
below.
To address whether a contaminant may have adverse effects on the health of persons (statutory
requirement (i)), the NOW AC recommended that EPA characterize the health risk and estimate a
health reference level (or, in the case of sodium, a benchmark) for evaluating the occurrence data for
each contaminant.
Regarding whether a contaminant is known to occur, or whether there is substantial likelihood that
the contaminant will occur, in public water systems with a frequency, and at levels, of public health
concern (statutory requirement (ii)), the NOW AC recommended that EPA consider: (1) the actual and
estimated national percent of public water systems (PWSs) reporting detections above half the health
reference level (or benchmark); (2) the actual and estimated national percent of PWSs with detections
above the health reference level (or benchmark); and (3) the geographic distribution of the contaminant.
To address whether regulation of a contaminant presents a meaningful opportunity for health risk
reduction for persons served by public water systems (statutory requirement (iii)) the NOW AC
recommended that EPA consider estimating the national population exposed above half the health
reference level (or benchmark) and the national population exposed above the health reference level (or
benchmark).
The approach EPA used to make regulatory determinations followed the general format
recommended by the NRC and the NOW AC to satisfy the three SDWA requirements under section
1412(b)(l)(A)(i)-(iii). The process was independent of many of the more detailed and comprehensive
risk management factors that will influence the ultimate regulatory decision making process. Thus, a
decision to regulate is the beginning of the Agency regulatory development process, not the end.
Specifically, EPA characterized the human health effects that may result from exposure to a
contaminant found in drinking water. Based on this characterization, the Agency estimated a health
reference level (HRL) for each contaminant. In the case of sodium, a benchmark was chosen based on
taste effects, which occur at lower concentrations than health effects.
For each contaminant EPA estimated the number of PWSs with detections >/£HRL (or
benchmark) and >HRL (or benchmark), the population served at these values, and the geographic
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Regulatory Determination Support Document for Sodium July 2003
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 data (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 determination of whether to regulate a
contaminant.
1.5 Determination Outcome
After reviewing the best available public health and occurrence information, EPA has made a
determination not to regulate sodium with an NPDWR. This determination is based on the finding that
regulation of sodium may not present a meaningful opportunity for health risk reduction for persons
served by public water systems. However, EPA may issue an advisory to provide guidance to
communities that may be exposed to drinking water contaminated with sodium chloride or other sodium
salts. All CCL regulatory determinations and further analysis are formally presented in the Federal
Register Notices (USEPA, 2002a; 67 FR 38222; and USEPA, 2003a; 68 FR 42898). The following
sections summarize the data used to reach this decision.
2.0. CONTAMINANT DEFINITION
Sodium (Na) is a naturally occurring element ubiquitous in the environment. It is the sixth most
abundant element in the Earth's crust and the most abundant anion in the hydrosphere (the hydrosphere
is all water, including atmospheric and oceanic water, on earth; Gornitz, 1972). The sodium cation
(Na+) is necessary for biochemical processes like sodium pumps and concentration gradients in many
living organisms (Madigan et al, 1997). The earth's oceans contain roughly 18.4 quadrillion short tons
(1 short ton = 2000 Ibs) of sodium associated with chlorine in the form of sea salt (Kostick, 1993). In
the lithosphere, most sodium minerals exist as soluble salts found primarily in evaporite deposits, as
intricate rock-forming silicates, or as rare halides or aluminohalides (Gornitz, 1972).
Sodium chloride (NaCl), otherwise known as halite, salt, sea salt, or table salt, is the most
economically and industrially important form of sodium, with an estimated 14,000 direct and indirect
uses. Among other things, salt is used as a flavor enhancer or preservative in food, as a road deicer, in
water softening treatment, in powdered soaps and detergents, as the electrolyte in saline solutions, in
rubber manufacturing, and as a pesticide. Sodium chloride is also used in oil and gas exploration, textile
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Regulatory Determination Support Document for Sodium July 2003
and dyeing industries, metal processing, pulp and paper production, tanning and leather treatment, and
in the chemical industry to manufacture such chemicals as chlorine, sodium metal, sodium hydroxide,
sodium carbonate, and sodium sulfate (Kostick, 1993; Gornitz, 1972).
2.1 Physical and Chemical Properties
Sodium is an alkali metal located in group 1A of the periodic table, and has an atomic weight of
22.99 g/mol, melting point of 97.82 °C, and boiling point of 892 °C. Sodium metal is a soft solid with a
shiny metallic luster and is an excellent conductor of electricity. Sodium does not occur in nature in its
pure form because the metal readily gives up its single valence electron, making it highly reactive
(Brown et al., 1994). Elemental sodium reacts violently with water to form sodium hydroxide and
hydrogen gas, and oxidizes in the presence of oxygen to sodium monoxide. Sodium commonly occurs
as sodium halides (NaCl, NaBr), sodium carbonates (Na2CO3, NaHCO3), sodium sulfates (Na2SO4,
NaHSO4), sodium hydride (NaH), or sodium nitrate (NaNO3) (Gornitz, 1972).
2.2 Environmental Fate and Transport
A sodium salt is formed when the sodium cation replaces some or all of the hydrogen cations in an
acid. Sodium salts that occur in seawater can be classified as "cyclic" salts because they traverse
different atmospheric, terrestrial, and aquatic environments before returning to the ocean. More
specifically, cyclic salts are conveyed from the ocean into the atmosphere by spray and then
transported inland dissolved in suspended water droplets. The salts are transferred to the soil through
precipitation or dry deposition and eventually leach to freshwater streams and ground water. From
these freshwater reservoirs, the salts return to the ocean, thus completing the cycle (Fairbridge, 1972).
Sodium chloride that has been used in industry and released into the environment either directly or by
means of landfills is also expected to cycle back to the ocean (Kostick, 1993).
Sodium salts can occur on earth as evaporite deposits, formed when the rate of evaporation
exceeds the rate of precipitation plus runoff. Ancient deposits were formed chiefly by the evaporation
of retreating seas (Kostick, 1993; Feldman and Cruft, 1972). Recent evaporite deposits are
predominantly non-marine in origin and occur in hot, arid climates or in windy, restricted basins
(Feldman and Cruft, 1972). Evaporite deposits of halite (NaCl) can become deformed under
increasing temperatures and pressures, disrupting surrounding sediment layers and forming salt domes.
Salt domes can extend vertically downward more than 20,000 feet and are common in the Gulf Coast
region of the United States (Gornitz, 1972; Kostick, 1993).
Sodium salts are water soluble and can leach to freshwater (Fairbridge, 1972). Sodium does not
adsorb strongly to clay, and therefore can be leached from clay sedimentary rock (Creasey, 1972).
Sodium salts are natural constituents of ground water because of the abundance of evaporite minerals in
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the earth's crust. Ground water sodium levels may be increased in areas where salt is used to deice
highways (Hackett, 1972).
3.0 OCCURRENCE AND EXPOSURE
This section examines the occurrence of sodium in drinking water. While no complete national
database exists of unregulated or regulated contaminants in drinking water from public water systems
(PWSs) collected under SDWA, this report aggregates and analyzes existing federal and State data
that have been screened for quality, completeness, and representativeness. Populations served by
PWSs exposed to sodium 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 sodium,
is also reviewed.
3.1 Use and Environmental Release
3.1.1 Production and Use
The earth's oceans contain approximately 46 quadrillion short tons (1 short ton = 2,000 Ibs) of
sodium chloride, or 18.4 quadrillion short tons of sodium (sodium chloride is 40% sodium by weight)
(Figure 3-1). Sodium chloride is also known as salt, sea salt, halite, or table salt.
Sodium is transported from the ocean to the atmosphere by spray and is suspended in water
droplets until it is either precipitated or introduced to the soil by dry deposition (Fairbridge, 1972).
Sodium levels in precipitation are higher near coastal areas and decrease further inland (Figure 3-2).
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Regulatory Determination Support Document for Sodium
July 2003
Figure 3-1: Abundance of sodium chloride (salt) in the ocean
World «oesn voLum?
;rf « HI ion cubic m lies Has
4i Quadrillion ttart tone- of sail
o Weighs 4.7 billion short
o voiyrne 1,1 triifon
Q eontaina 18S million
tons of
of which 139 million eJiort
l» ssli
after Kostick, 1993
Figure 3-2: Average sodium concentrations in precipitation over the United States
after Drever,
1997
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Regulatory Determination Support Document for Sodium
July 2003
Table 3-1: End uses of sodium chloride in 1990 (in
Sectors and subsectors
Chemicals:
Chlorine and sodium hydroxide manufacture
Manufacture of other chemicals, like sodium carbonate and sodium
Ice control/stabilization:
Commercial
Food processing
Meat packers
Dairy
Canning
Baking
Grain mill processing
Grocery wholesale
Total food processing
General Industrial
Textiles and dyeing
Metal processing
Rubber
Oil
Tanning and leather
Agricultural
Feed retailers and/or dealers-mixers
Feed manufacturers
Distributors
Institutional wholesalers and end users
U.S. Government resale
Water treatment
Government
Commercial
Distributors
Total water treatment
Other
Grand total
thousands of short tons)
NaCl consumed
19 182
2,046
21228
10757
545
11302
598
140
318
171
97
298
671
2,293
227
346
45
793
283
109
288
2091
1,101
546
55
619
2321
223
96
9
1 851
2030
297
198
1,123
1,618
2,030
Percent of Total
47
25
5
5
5
5
4
4
100
after Kostick, 1993
Sodium chloride is the most economically and industrially important form of sodium, with an
estimated 14,000 direct and indirect uses (Kostick, 1993). As depicted in Table 3-1, sodium chloride
use can be broken down into eight major categories: chemical (47%), ice control (25%), food
processing (5%), general industrial (5%), agricultural (5%), distributors (5%), water treatment (4%),
and miscellaneous (4%).
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Regulatory Determination Support Document for Sodium July 2003
Two sodium end uses with the most probable immediate effect on drinking water quality are water
treatment and road deicing. In water treatment, sodium is used as a softener by substituting the sodium
cation, Na+, for calcium (Ca2+) and magnesium (Mg2+), both of which make water "hard." Water is
considered "hard" when calcium and magnesium ions occur in high concentrations and leave caked
mineral deposits in household and commercial equipment. Various softening processes exchange
sodium cations for calcium and magnesium cations and release sodium directly into the drinking water
supply (Kostick, 1993). Many sodium salts are used for water treatment, for example sodium chloride,
sodium hydroxide, sodium bicarbonate, and sodium carbonate.
Sodium chloride that has been used to deice roads can also be a problem for drinking water
systems. The salt and ice mixture creates a brine with a lower freezing point than water, effectively
melting ice (Kostick, 1993). Sodium chloride is a cheap and effective solution to frozen roads, but can
become an environmental concern when run-off affects local vegetation and soil quality, as well as
ground water and surface water supplies. In one study, sodium levels eight times the norm were
detected forty-five feet from the highway in areas where deicing salt had been used for 18 years
(USEPA, 1990). A different study, undertaken by the Federal Government and University
researchers, found that highway deicing with sodium chloride made a significant impact on the salinity of
the nation's streams between the years 1974-1981. Data for the investigation came from the National
Water Quality Surveillance System and from United States Geological Survey (USGS) National
Stream Quality Accounting Network sampling stations (Smith et al., 1987).
The United States produces more sodium chloride than any other country in the world, with other
major producers including Russia, England, Germany, Canada, and France (Gornitz, 1972; Kostick,
1993). From 1990 to 1998, United States NaCl consumption was between three to ten million metric
tons greater than its production (1 metric ton = 2,205 Ibs), with imports three to thirteen times higher
than exports (Table 3-2).
Although these figures suggest that the U.S. relies on foreign sources to meet consumption needs,
most imports were supplied by foreign subsidiaries of major U.S. sodium chloride producers (Kostick,
1998). For the years 1994-1998, United States salt statistics analyzed by State indicate that Louisiana
sold, or used, the most sodium (35%), followed by Texas (23%), New York (11%), Kansas (7%),
and Utah (4%) (Kostick, 1994; Kostick 1995; Kostick, 1996; Kostick, 1997; Kostick, 1998).
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Table 3-2: U.S. sodium chloride statistics, 1990-1998 (in thousands of metric tons)
Tfear
1998
1997
1996
1995
1994
1993
1992
1991
1990
Production
41,200
41,400
42,200
42,100
40,100
39,200
36,000
36,300
36,800
Export^
731
748
869
670
742
688
992
1,780
2,270
Imports
,-•'
8,770
9,160
10,600
7,090
9,630
5,870
5,390
6,190
5,970
. Confurjiptieo,
reporJ64*
44,200
49,500
52,800
46,500
47,200
44,400
39,700
40,600
no data
after Kostick, 1994 and Kostick, 1998
^Reported consumption is sales or use as reported by the salt companies including their imports and exports.
3.1.2 Environmental Release
Beyond raw production and use data, the disposal and release of sodium products to the
environment is of special concern to drinking water systems. The end use of some sodium products
involves direct environmental application, as with pesticides like sodium chloride or sodium bromide
(USEPA, 1993). Other sodium products are dispersed post-consumption to the environment or are
disposed of in landfills. Table 3-3 outlines the environmental fate of products from general sodium
chloride use categories.
Dispersive losses of sodium chloride are those released to the environment directly after
consumption. Examples include salt in run-off following highway deicing, effluents in industrial sewage,
or salt released into the drinking water supply following water softening treatment. Sodium chloride can
also be dispersed to the environment through use in dry cleaning compounds, perfume, gasoline
additives, pharmaceuticals, and cosmetics. Products disposed of in landfills include those products
brought to municipal sanitary landfills or toxic/hazardous landfills (Kostick, 1993).
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Table 3-3: Environmental fate of post-consumer sodium chloride, 1990 (in millions of short
tons)
Dispersive Losses
Chemicals-as waste effluent, sewage
Food-through excretion, assimilation
Industrial-as waste effluent, sewage
Agriculture-through excretion,
assimilation
Water treatment-through sewage
Deicing-runoff
Other
Total
12.5
2.1
1.7
2.3
1.6
11.3
3.2
34.7
Disposed to Landfill and Incineration
Chemicals-plastics, glass, paper
Food-discarded waste food
Industrial-rubber, textiles
Agricultural
Water treatment
Deicing
Other
Total
8.7
0.2
0.4
0
0
0
1.0
10.3
after Kostick, 1993
The environmental release of some potentially toxic sodium compounds, including sodium azide,
sodium dicamba, sodium dimethyldithiocarbamate, sodium hydroxide, and sodium nitrite, is regulated
by the TRI (USEPA, 2000b). The Toxic Release Inventory of hazardous chemicals was established by
the Emergency Planning and Community Right-to-Know Act (EPCRA) in 1986. EPCRA is also
sometimes known as SARA Title m. EPCRA mandates that larger facilities publicly report when TRI
chemicals are released into the environment. This public reporting is required for facilities with more
than 10 full-time employees that annually manufacture or produce more than 25,000 pounds, or use
more than 10,000 pounds, of a TRI chemical (USEPA, 1996; USEPA, 2000a).
Facilities are required to report the pounds per year of TRI chemicals released into the environment
both on- and off-site. Forty-two States reported releases of sodium azide, sodium dicamba, sodium
dimethyldithiocarbamate, or sodium nitrite (1995-1998). Only AK, HI, ID, MT, NV, NM, ND, and
VT reported no releases of any of these compounds. In 1988, all fifty States, Puerto Rico, the Virgin
Islands, and American Samoa reported releases of sodium hydroxide (USEPA, 2000c). Sodium
hydroxide, also known as caustic soda or lye, is used in such industries as pulp and paper, organic and
inorganic chemical production, petroleum, soaps and detergents, water treatment, and textiles (Kostick,
1993). The compound is important because of its myriad of uses and its toxicity. In 1988, the TRI
reported on- and off-site releases of sodium hydroxide totaling approximately 108 million pounds. The
on-site quantity is subdivided into air emissions, surface water discharges, underground injections, and
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Regulatory Determination Support Document for Sodium July 2003
releases to land. Approximately thirteen million pounds of sodium hydroxide, or roughly 20% of total
on-site releases, were discharged directly to surface water in 1988. The chemical was taken off of the
TRI list in 1989 (USEPA, 2000c).
In conclusion, because sodium has so many human end uses and is abundant in the ocean, sodium
is ubiquitous in the environment. Two sodium uses of particular significance to drinking water supplies
are salt for highway deicing and salt for water softening treatment. Sodium chloride is the most
economically and industrially important form of sodium, with an estimated 14,000 direct and indirect
uses. The United States is the largest sodium chloride producing country in the world, with production
quantities averaging 40 million metric tons from 1990-1998.
The disposal and release of sodium products to the environment is of great concern to drinking
water supplies. Approximately 34.7 million short tons of sodium chloride were dispersed to the
environment post-consumption in 1990, while roughly 10.3 million short tons were disposed of in
landfills. The Toxic Release Inventory has reported releases of toxic sodium compounds like sodium
azide, sodium dicamba, sodium dimethyldithiocarbamate, or sodium nitrite in 42 States. Sodium
hydroxide, though listed as a TRI chemical only for reporting year 1988, had documented releases in all
50 States as well as Puerto Rico, the Virgin Islands, and American Samoa.
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 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 through USGS's 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 the United
States and a similar proportion of the total population served by public water systems. Approximately
one half of the nation's land area is represented (Leahy and Thompson, 1994).
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To facilitate management and make the program cost-effective, approximately one third of the
study units at a time are engaged 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. In 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.
Sodium is an analyte for both surface and ground water NAWQA studies, with a Minimum
Reporting Level (MRL) of 0.2 mg/L. Sodium occurrence in bed sediments is also assessed (MRL =
0.005%).
Sodium 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). Occurrence results are presented below. The descriptive statistics generated from the
sodium NAWQA data broadly characterize the frequency of sodium detections by sample and by site.
Furthermore, detection frequencies above a benchmark level of 120 mg/L are also presented for all
samples, and by site (see Section 3.3.1.4 for further discussion of this benchmark level and its
development). The median and 99th percentile concentrations are included as well to characterize the
spread of sodium concentration values in ambient waters sampled by the NAWQA program.
3.2.2 Results
Typical of many inorganic contaminants, sodium occurrence in ambient surface and ground waters
is high (Table 3-4). This is not surprising, considering that sodium is the sixth most abundant element in
the Earth's crust, the most abundant anion in the hydrosphere, and is used in many products. Surface
and ground water detection frequencies are similar, between 90% and 100% in all cases, though
ground water detections are somewhat lower. Median sodium concentrations and benchmark
exceedances are also similar between surface and ground water, but ground water benchmark
exceedances are generally higher than surface water exceedances, while median concentrations are
lower for ground water. The 99th percentile concentrations are variable but are generally higher for
ground water.
Table 3-4 illustrates that low-level sodium occurrence is ubiquitous. Surface water detection
frequencies are 100% for all land use categories. Detection frequencies > 120 mg/L (by site) are
similar for urban, mixed, and agricultural areas, while forest/rangeland areas show extremely low
frequencies of benchmark exceedances. These results are understandable because forest/rangeland
basins are not as affected by anthropogenic inputs of sodium (like agrochemical applications) as other
land use categories.
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Regulatory Determination Support Document for Sodium July 2003
Median concentrations for sodium in surface waters range from 4.7 mg/L in forest/rangeland areas
to 21.9 mg/L in urban areas. The median level in urban basins is substantially higher than in other land
use categories and may reflect the effects of road salt applications, more prevalent in areas with greater
population densities. The 99th percentile concentrations are similar for all land use categories except for
forest/rangeland areas, with a lower 99th percentile concentration. Simple detections and detections
exceeding the benchmark by site, for all sites, are approximately 100% and 5.5%, respectively. These
figures indicate that although sodium is ubiquitous in surface water, detection frequencies at levels
exceeding the benchmark concentration level are relatively low.
For ground water, detections approach 100% of sites for all land use categories. Urban areas
show the greatest median concentration and frequency of benchmark exceedances. Forest/rangeland
areas show no detections greater than the benchmark, and exhibit the lowest median and 99th percentile
values. These results suggest that urban and agricultural releases of sodium can leach to ground water,
as forest/rangeland areas have such consistently low detection values. Detection frequencies above the
MRL and the benchmark level for all sites are approximately 99.9% of sites and 7.5% of sites,
respectively. Again, sodium detection frequencies in ground water at levels exceeding the benchmark
concentration level are low compared to sodium occurrence.
Similar to surface and ground water, 100% of bed sediment sampling sites showed detections in all
land use categories. Sodium concentrations in bed sediments are measured by the percent of sodium
by weight in the sediment sample analyzed. The median concentrations range from 0.4%
(forest/rangeland basins) to 0.8% (urban basins) and the 99th percentile concentrations range from
1.8% (forest/rangeland and agricultural) to 2.0% (urban). Again, similar to surface and ground waters,
urban basins and forest/rangeland basins occupy the extremes of the concentration percentile spectrum.
However, bed sediment concentration percentiles are generally comparable across land use types. The
occurrence of sodium in stream sediments is pertinent to drinking water concerns because some
desorption of the compound from sediments into water will occur through equilibrium reactions,
although at very low rates.
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Table 3-4: Sodium detections and concentrations in streams and ground water
Detection frequency
>MRL*
Detection frequency
>120mg/L**
Concentration
(all samples; mg/L)
surface water
urban
mixed
agricultural
forest/rangeland
all sites
ground water
urban
mixed
agricultural
forest/rangeland
all sites
% samples
100 %
100 %
100 %
100 %
100 %
90.7 %
93.1 %
93.1 %
94.9 %
93.0 %
% sites
100 %
100 %
100 %
100 %
100 %
99.7 %
100.0 %
99.9 %
100.0 %
99.9 %
% samples % sites median
4.4% 6.2% 21.9
2.9 % 6.6 % 12.2
4.6% 6.0% 11.0
0.1% 0.5% 4.7
3.6% 5.5% 11.0
9.3% 11.0% 13.2
6.4 % 6.8 % 9.7
6.4% 6.8% 8.1
0.0 % 0.0 % 2.9
6.6 % 7.5 % 8.8
99th
perc entile
310
270
330
97
298
410
502
788
33
480
! The Minimum Reporting Level (MRL) for sodium in water is 0.2 mg/L.
'* See Section 3.3.1.4 for a discussion of this benchmark level used to evaluate the occurrence data for sodium.
3.3 Drinking Water Occurrence
3.3.1 Analytical Approach
3.3.1.1 National Inorganic and Radionuclide Survey (NTRS)
In the mid-1980s, EPA designed and conducted the National Inorganic and Radionuclide Survey
(MRS) to collect national occurrence data on a select set of radionuclides and inorganic chemicals
being considered for National Primary Drinking Water Regulations. The MRS database includes 36
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Regulatory Determination Support Document for Sodium July 2003
inorganic compounds (lOCs) (including 10 regulated lOCs), 2 regulated radionuclides, and 4
unregulated radionuclides. Sodium was one of the 36 lOCs monitored.
The MRS provides contaminant occurrence data from 989 community PWSs served by ground
water. The MRS does not include surface water systems. The selection of this group of PWSs was
designed so that the contaminant occurrence results are statistically representative of national
occurrence. Most of the MRS data are from smaller systems (based on population served by the
PWS) and each of these statistically randomly selected PWSs was sampled a single time between 1984
and 1986.
The MRS data were collected from PWSs in 49 States. Data were not available for the State of
Hawaii. In addition to being statistically representative of national occurrence, MRS data are designed
to be divisible into strata based on system size (population served by the PWS). Uniform detection
limits were employed, thus avoiding computational (statistical) problems that sometimes result from
multiple laboratory analytical detection limits. Therefore, the MRS data can be used directly for
national contaminant occurrence analyses with very few, if any, data quality, completeness, or
representativeness issues.
3.3.1.2 Supplemental IOC Data
One limitation of the MRS study is a lack of occurrence data for surface water systems. To
provide perspective on the occurrence of sodium in surface water PWSs relative to ground water
PWSs, SDWA compliance monitoring data that were available to EPA were reviewed from States
with occurrence data for both ground and surface water.
The State ground water and surface water PWS occurrence data for sodium used in this analysis
were submitted by States for an independent review of the occurrence of regulated contaminants in
PWSs at various times for different programs (USEPA, 1999). In the USEPA (1999) review,
occurrence data from a total of 14 States were noted. However, because several States contained
data that were incomplete or unusable for various reasons, only 12 of the 14 States were used for a
general overview analysis. From these 12 States, 8 were selected for use in a national analysis because
they provided the best data quality and completeness and a balanced national cross-section of
occurrence data. These eight were Alabama, California, Illinois, Michigan, Montana, New Jersey,
New Mexico, and Oregon.
Only the Alabama, California, Illinois, New Jersey, and Oregon State data sets contained
occurrence data for sodium. The data represent approximately 36,000 analytical results from more
than 5,500 PWSs mostly during the period from!993 to 1997, though some earlier data are also
included. The number of sample results and PWSs vary by State.
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3.3.1.3 Data Management and Analysis
The data used in the State analyses were limited to only those data with confirmed water source
and sampling type information. Only standard SDWA compliance samples were used; "special"
samples, "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 that provided 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 they were dropped from
the analysis (for further details see USEPA, 1999).
3.3.1.4 Occurrence Analysis
The summary descriptive statistics presented in Table 3-5 for sodium are derived from analysis of
the MRS data. Included are the total number of samples, 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 and PWS population served whose analytical results showed a
detection(s) of the contaminant (simple detection, > MRL) at any time during the monitoring period; or
a detection(s) greater than half the benchmark level; or a detection(s) greater than the benchmark level.
The benchmark level used to evaluate the occurrence information for sodium is 120 mg/L, which
was derived from the National Research Council's dietary guideline (NRC, 1989a) for adults of 2.4
g/day for sodium from sodium chloride (table salt). The Drinking Water Equivalent concentration is 1.2
g/L given a drinking water intake of 2 L/day. A Relative Source Contribution (RSC) of 10% was
applied, giving rise to the benchmark of 120 mg/L ([2400mg/2L]* 0.10).
In Table 3-5, national occurrence is estimated by extrapolating the summary statistics for sodium to
national numbers for systems, and population served by systems, from the Water Industry Baseline
Handbook, Second Edition (USEPA, 2000d). From the handbook, the total number of ground water
community water systems (CWSs) plus ground water non-transient, non-community water systems
(NTNCWSs) is 59,440, and the total population served by ground water CWSs plus ground water
NTNCWSs is approximately 85.6 million persons (see Table 3-5). To arrive at the national
occurrence estimates, the national estimate for ground water PWSs (or population served by ground
water PWSs) is simply multiplied by the percentage for the given summary statistic (e.g., the national
estimate for the total number of ground water PWSs with detections (i.e., > MRL; 59,440) is the
product of the percentage of ground water PWSs with detections (100%) and the national estimate for
the total number of ground water PWSs (59,440)).
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The nationally extrapolated occurrence estimates for sodium are not presented in the Federal
Register Notice. While the MRS data were collected in a statistically appropriate fashion suitable for
extrapolation, the data available for many CCL regulatory determination priority contaminants were not
a strict statistical sample. National extrapolations of these data can be problematic. Also, the MRS
data only represent ground water PWSs. Thus, national extrapolations from MRS data do not
represent national occurrence for all PWSs. Therefore, to maintain consistency across all CCL
regulatory determination priority contaminants, a straight-forward presentation, and data integrity, only
the actual occurrence results for all CCL regulatory determination priorities are presented in the
Federal Register Notice for stakeholder review. The nationally extrapolated occurrence values for
sodium are presented here, however, to provide additional perspective.
In Table 3-6, occurrence data on sodium directly submitted by the States of Alabama, California,
Illinois, New Jersey, and Oregon for^4 Review of Contaminant Occurrence in Public Water
Systems (USEPA, 1999) were used to augment the MRS study which lacked surface water data.
Included in the table are the same summary statistics as Table 3-5, with additional information
describing the relative distribution of sodium occurrence between ground water and surface water
PWSs in the 5 States.
The State data analysis was focused on occurrence at the system level because a PWS with a
known contaminant problem usually has to sample more frequently than a PWS that has never detected
the contaminant. The results of a simple computation of the percentage of samples with detections (or
other statistics) can be skewed by the more frequent sampling results reported by the contaminated site.
The system level of analysis is conservative. For example, a system need only have a single sample
with an analytical result greater than the MRL, i.e., a detection, to be counted as a system with a result
"greater than the MRL."
When computing basic occurrence statistics, such as the number, or percent, of samples, or
systems, with detections of a given contaminant, the value (or concentration) of the MRL can have
important consequences. For example, the lower the reporting limit, the greater the number of
detections (Ryker and Williamson, 1999). As a simplifying assumption, a value of half the MRL is often
used as an estimate of the concentration of a contaminant in samples/systems whose results are less
than the MRL. However, for these occurrence data this is not straightforward. 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. Because a
simple meaningful summary statistic is not available to describe the various reported MRLs, and to
avoid confusion, MRLs are not reported in the summary table (Table 3-6).
3.3.2 Results
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The MRS data in Table 3-5 show that approximately 100% of ground water PWSs (this
extrapolates to all 59,440 systems nationally) had detections of sodium, affecting about 100% of the
ground water PWS population served (approximately 85.6 million people nationally). Approximately
23% of the MRS PWSs had detections greater than Y2 the benchmark level of 120 mg/L (about
13,500 ground water PWSs nationally), affecting approximately 18.5% of the population served
(estimated at 15.9 million people nationally). The percentage of MRS PWSs with detections greater
than the benchmark level of 120 mg/L was approximately 13% (about 8,000 ground water PWSs
nationally), affecting 8.3% of the population served (estimated at approximately 7.1 million people
nationally)
Drinking water data for sodium from the supplemental individual States vary among States (Table
3-6). Sodium monitoring has not been required under SDWA, though these States had obviously
conducted some monitoring. Alabama, California, New Jersey, and Oregon have substantial amounts
of data and PWSs represented. However, the number of systems with sodium data for Illinois is far
less than the number of PWSs in this State. Hence, it is not clear how representative these data are.
Because the MRS data only represent sodium occurrence in ground water PWSs, the supplemental
State data sets provide some perspective on surface water PWS occurrence.
For simple detections, the supplemental State data show a range from 99.3% to 100% of ground
water PWSs (Table 3-6). These figures are comparable to the MRS ground water PWS results:
100% greater than the MRL (Table 3-5). The supplemental State data show 100% simple detections
for surface water PWSs. Comparisons made between data for simple detections need to be viewed
with caution because of differences in MRLs between the State data sets and the MRS study, and
among the States themselves (see Section 3.3.1.4), though these numbers for sodium are very
comparable. For further perspective, the median concentration of all samples for the MRS data (16.4
mg/L) is bracketed by the range of median concentrations from the States' data (5.26 mg/L to 31
mg/L).
The supplemental State data sets indicate that ground water PWS detections greater than the
benchmark level of 120 mg/L are between 3% and 15% (Table 3-6). The MRS national average is
within this range at 13.2% of PWS greater than the benchmark level of 120 mg/L (Table 3-5). As
might be expected, surface water PWSs showed slightly fewer exceedances of the benchmark level
than ground water PWSs, ranging from 0% - 3%.
Reviewing sodium occurrence by PWS population served shows that from 0.5% - 50% of the
States' ground water PWS populations were served by systems with detections greater than the
benchmark level of 120 mg/L (Table 3-6). However, the figure of 50% is the maximum among the
supplementary States. Three of the 5 States show ground water PWS populations receiving more than
120 mg/L at percentages lower than that for MRS, which is 8.3%. Populations served by surface
water PWSs with detections greater than 120 mg/L ranged from 0% - 1.4% among the five
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supplemental States. Population figures for the supplemental States are incomplete and are only
reported for those systems in the database that have reported their population data. For sodium,
approximately 82% of the PWSs reporting occurrence data for these 5 States also reported population
data.
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Table 3-5: Sodium occurrence in ground water systems (NIRS survey)
Freauencv Factors
Total Number of Samples/Systems
99* Percentile Concentration (all samples)
Median Concentration (all samples)
Minimum Reporting Level (MRL)
Total Population
Orrnrrpnrp hv Samnlps/Svstpm
% Ground Water PWSs with detections (> MRL)
Range of Cross- Section States
% Ground Water PWSs > 60 mg/L (1/2 benchmark level)
Range of Cross- Section States
% Ground Water PWSs > 120 mg/L (benchmark level)
Ranee of Cross- Section States
Orrnrrpnrp hv Pnniilatinn SprvpH
% Ground Water PWS Population Served with detections
Range of Cross- Section States
% Ground Water PWS Population Served > 60 mg/L
Range of Cross- Section States
% Ground Water PWS Population Served > 120 mg/L
Ranee of Cross- Section States
Benchmark Level
= 120 mg/L
989
517ms/L
16.4 mg/L
0.91ma/L2
1 48? 133
100%
100%
22.6%
0 - 100%
13.2%
0 - 73 7%
100%
100%
18.5%
0 - 100%
8.3%
0 - 89 5%
National System &
Population Numbers
59,440
-
-
-
85,681,696
National Extrapolation
59,440
N/A
13,463
N/A
7,873
N/A
85,682,000
N/A
15,859,000
N/A
7,147,000
N/A
1 Total PWS and population numbers are from EPA 's March 2000 Water Industry Baseline Handbook.
2 Because all data reported for sodium were detections, the minimum value is presented here instead of the MRL for sodium.
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Table 3-6: Occurrence summary of ground and surface water systems by State for sodium
Freniiencv 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 fall samples")
Median Concentration (all samples)
Minimum Reporting Level (MRL)
Total Number of PWSs
Number of Ground Water PWSs
Number of Surface Water PWSs
Total Population Served
Ground Water PWS Population Served
Surface Water PWS Population Served
Occurrence hv Svstem
% PWSs with detections (> MRL)
Ground Water PWSs with detections
Surface Water PWSs with detections
Renrhmnrk 1 .e.vc.1 = 1 20 mff/T ,
% PWSs > 1/2 Benchmark Level
Ground Water PWSs > 1/2 Benchmark Level
Surface Water PWSs > 1/2 Benchmark Level
% PWSs > Benchmark Level
Ground Water PWSs > Benchmark Level
Surface Water PWSs > Benchmark Level
Occurrence hv Population Served
% PWS Population Served with detections
Ground Water PWS Population with detections
Surface Water PWS Population with detections
Benchmark Level = 120me/L
% PWS Population Served > 1/2 Benchmark Level
Ground Water PWS Population > 1/2 Benchmark
Surface Water PWS Population > 1/2 Benchmark
% PWS Population Served > Benchmark Level
Ground Water PWS Population > Benchmark Level
Surface Water PWS Population > Benchmark Level
Alabama
1,327
917
410
99.3%
99.0%
99.8%
260 ma/L
5.26mg/L
Variable1
435
366
69
3,662,222
1,820,214
1,837,743
100%
100%
100%
22.3%
26.2%
1.5%
9.7%
11.5%
0.0%
100%
100%
100%
17.5%
33.2%
0.0%
5.0%
8.1%
00%
California
27,494
25,111
2,383
99.5%
99.6%
99.5%
209 ma/L
31mg/L
Variable1
2,433
2,214
219
45,375,106
27,791,117
30,740,138
99.8%
99.8%
100%
29.4%
30.5%
18.3%
11.4%
12.2%
2.7%
100%
100%
100%
76.5%
69.4%
77.2%
33.3%
49.4%
1 4%
Illinois
383
313
70
100%
100%
100%
370 ma/L
25 mg/L
Variable1
227
160
67
1,995,394
724,635
1,270,179
100%
100%
100%
19.4%
26.3%
3.0%
10.6%
15.0%
0.0%
100%
100%
100%
11.2%
30.2%
0.3%
8.7%
24.0%
00%
New .Tersev
4,417
3,941
476
99.0%
99.1%
98.1%
150 ma/L
14 mg/L
Variable1
1,444
1,411
33
6,350,025
2,478,067
3,871,958
99.4%
99.4%
100%
11.0%
11.0%
12.1%
3.6%
3.6%
3.0%
100.0%
99.9%
100%
13.7%
21.2%
8.9%
1.8%
4.3%
0 2%
Oregon
2,319
1,506
813
98.8%
98.8%
100%
166 ma/L
9.78 mg/L
Variable1
1,032
863
169
2,101,401
1,261,661
1,497,224
99.4%
99.3%
100%
10.5%
11.7%
4.1%
2.8%
3.1%
1.2%
100.0%
99.9%
100%
3.5%
4.6%
1.1%
0.4%
0.5%
0 1%
1 See Section 3.3.1.4 for details
23
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Regulatory Determination Support Document for Sodium July 2003
3.4 Conclusion
The Toxic Release Inventory has reported releases of toxic sodium compounds like sodium azide,
sodium dicamba, sodium dimethyldithiocarbamate, or sodium nitrite in 42 States. Sodium hydroxide,
though only listed as a TRI chemical for reporting year 1988, had documented releases in all 50 States
as well as Puerto Rico, the Virgin Islands, and American Samoa.
Low-level sodium occurrence in ambient waters and stream bed sediments monitored by the
USGS NAWQA program is ubiquitous, approaching 100% of water and sediment sampling sites for all
land use categories. Forest/rangeland basins show the lowest frequency of benchmark level
exceedances, median concentrations, and 99th percentile concentrations across all land use categories
for ambient waters and bed sediments. Benchmark level exceedances, median, and 99th percentile
concentrations are generally similar for all other land use categories, although urban and agricultural
basins sometimes exhibit higher levels. Although sodium detection frequencies are high in ambient
waters and stream bed sediments, sodium occurrence at levels of public health concern is low.
Sodium has been detected in ground water PWS samples collected through the MRS study.
Occurrence estimates are high with 100% of samples showing detections affecting 100% of the national
population served. The 99th percentile concentration of all samples is 517 mg/L. At the benchmark
level of 120 mg/L, 13.2% of the MRS systems showed exceedances, affecting approximately 7.1
million people nationally.
Additional SDWA data from the States of Alabama, California, Illinois, New Jersey, and Oregon,
including both ground water and surface water PWSs, were examined through independent analyses
and also show substantial levels of sodium occurrence. These data provide perspective on the MRS
estimates that only include data for ground water systems. The supplemental State data show that all
five States reported almost 100% detections in both ground water and surface water systems. At
detections above the benchmark level of 120 mg/L, surface water PWS detection frequencies are
generally lower than those for ground water. If national data for surface water systems were available,
the occurrence and exposure estimates would be substantially greater than from MRS alone.
4.0 HEALTH EFFECTS
A full description of the health effects associated with exposure to sodium are presented in
Drinking Water Advisory: Consumer Acceptability Advice and Health Effects Analysis on
Sodium (USEPA, 2003). A summary of the pertinent findings are presented below.
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Regulatory Determination Support Document for Sodium July 2003
4.1 Hazard Characterization and Mode of Action Implications
Sodium is physiologically necessary for maintaining normal body fluid volume, blood pressure, and
cell function. The major source of sodium generally comes from the intake of food, with only a small
contribution from drinking water. Normal sodium level in the blood is about 154 mEq/L.
According to the National Research Council, the estimated minimum daily requirements for sodium
are 120-225 mg for infants (0 months-1 year), 300-400 mg for children (2-9 years), and 500 mg for
individuals 10 years and older (NRC, 1989a). Sodium requirements increase during pregnancy and
lactation. The American Heart Association and the National Institutes of Health recommend that
healthy adults restrict their sodium intake to no more than 2,400 mg/day in order to lower the risk of
hypertension (AHA, 2000; NIH, 1993). Typically, the average sodium intake ranges from 3,500 to
4,500 mg/day (Karanja et al., 1999).
About 3% of the U.S. population is on sodium restricted diets. In general, sodium exposure is
limited to levels of 250, 500, 1,000 or 2,000 mg/day in these diets. A no-added-salt diet restricts only
foods that are high in sodium. However, these so called no-added-salt diets still average about 4,000
mg of sodium per day, indicating the abundance of sodium in the food supply (Cataldo and Whitney,
1986). Individuals on sodium restricted diets may need to consider the level of sodium in drinking
water supply when planning their diet (Cataldo and Whitney, 1986).
Experimental studies performed on rats and human adults suggest a positive correlation between
excessive sodium intake and hypertension (NAS, 1977; WHO, 1979; NIH, 1993). One study, based
upon 10,079 subjects in 32 countries, reports an increase in systolic pressure of 2.2 mm Hg for every
2,300 mg increase in sodium intake (ICRG, 1988; Elliot et al., 1989). Extreme hypertension is
associated with coronary artery disease and stroke (Stamler, 1991). In addition, high sodium intake
may result in increased heart muscle thickness in response to increased blood pressure (Schmieder et
al., 1988).
Despite consistent reports on adults, blood pressure and sodium intake reports on children are
inconsistent. While some studies associate an increase in blood pressure with a high sodium diet
(Calabrese and Tuthill, 1977, 1981; Tuthill and Calabrese, 1979), other studies fail to find a correlation
(Pomrehn et al., 1983; Faust, 1982; Armstrong et al., 1982; Tuthill et al., 1980).
Earlier clinical trial studies have indicated that lower sodium intake does not yield convincing
evidence for risk reduction of cardiovascular disease in populations with normal blood pressures
(Muntzel andDrueke, 1992; Salt Institute, 2000; NIH, 1993; Callaway, 1994; Kotchen and
McCarron, 1998; McCarron, 1998). However, results of the recent Dietary Approaches to Stop
Hypertension (DASH) trials at Brigham and Women's Hospital suggest that restricted dietary intake of
sodium is, in fact, beneficial for many people with hypertension (Harsha et al., 1999; Sacks et al.,
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Regulatory Determination Support Document for Sodium July 2003
2001). In addition to sodium restriction, lifestyle and dietary changes such as weight reduction,
exercise, stress reduction, and adequate dietary potassium, calcium, and magnesium are effective non-
medicinal treatments against hypertension. Limiting cholesterol, dietary fat, and alcohol intake is also
recommended (Whitney et al., 1987).
While sodium salts are generally not considered acutely toxic to humans, acute effects and death
have been reported in cases of very high sodium intake (RTECS, 2000; WHO, 1979). The effects of
high sodium levels from ingestion appear to be more severe for infants than adults because infant
kidneys are not yet able to process the sodium (Sax, 1975).
Data on the reproductive toxicity of sodium are sparse. In a study done on rats, excessive sodium
chloride (1,570 mg sodium/kg body weight) caused fetal and maternal toxic effects. Maternal toxicity
effects included decreased pregnancy rates and decreased body weight gain, while fetotoxic effects
included high mortality rate (Karr-Dullien and Bloomquist, 1979). Developmental effects were
observed only in a strain of rat pups bred to be hypertensive that were fed high sodium diets for up to 4
months after birth. No developmental effects in rat strains with normal blood pressure were noted in
this study.
Although sodium is not considered carcinogenic, it may influence genotoxic events, thus increasing
the likelihood of tumor development. High oral doses of sodium chloride in the presence of
carcinogens may cause damage to the gastrointestinal tract and lead to an increase in DNA synthesis
and cell regeneration. Gastric tumors could, therefore, be a potential adverse health effect (Tatematsu
et al, 1975; NRC, 1989b; Takahashi et al, 1983).
4.2 Dose-Response Characterization and Implications in Risk Assessment
Although numerous human studies have examined sodium intake and blood pressure effects, they
cannot serve to characterize dose-response relationships. First, the results are inconsistent; second, the
sodium intake measurements are indirect (as determined by the amount of sodium excreted in the
urine); and third, the results are influenced by other factors such as nutrients in the diet, lifestyle, and
behavioral patterns rather than sodium itself (Muntzel and Drueke, 1992; Salt Institute, 2000; NIH,
1993; Callaway, 1994; Kotchen and McCarron, 1998; McCarron, 1998).
Dose-response data are controversial. As noted above, the American Heart Association
recommends that healthy adults restrict their sodium intake to 2,400 mg/day (2000). In the DASH
study, sodium sensitive individuals who reduced their sodium intake by 2,300 mg/day from average
levels of 3,50054,500 mg/day lowered their systolic blood pressure by 3.7 mm Hg (compared to 1 mm
Hg in normal individuals). Furthermore, hypertensive individuals that increase dietary calcium,
potassium, magnesium, and fiber (by following the high fruit and vegetable DASH diet), but do not
change sodium levels, achieve similar reductions in systolic pressure (Harsha et al, 1999). A
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Regulatory Determination Support Document for Sodium July 2003
combination of the DASH diet with sodium restriction yields additional reductions in blood pressure
among hypertensive and normotensive subjects (Sacks et al., 2001). Thus, dose-response effects are
difficult to characterize because they are population and lifestyle dependent.
4.3 Relative Source Contribution
Food is the principle source of exposure to sodium. Of the total amount of sodium present in food,
only a relatively low amount (10%) is naturally occurring (Sanchez-Castillo et al., 1987a,b). The
majority of dietary sodium comes from sodium chloride that is added during food processing and
preparation. Sanchez-Castillo et al. estimate that 15% of dietary sodium comes from salt added during
cooking and at the table, whereas 75% is from salt added during food processing and manufacture
(1987a,b). The first National Health and Nutrition Examination Survey reported that approximately
32% of the sodium chloride consumed comes from baked goods and cereals, 21% from meats, and
14% from dairy products (Abraham and Carroll, 1981). Using data from a two-year dietary survey,
Subar et al. found that 23.4% of the dietary salt intake comes from table salt and processed foods such
as cold cuts and other processed meats, condiments, and snack foods (i.e. chips, popcorn; 1998).
Yeast breads provide 10.9% of the sodium, cheese, 5.6%, and ham, 4.1%. Together, these foods
contribute 44.1% of total sodium intake.
Reported dietary intakes of sodium from various studies range from 1,800 mg/day to 5,000
mg/day, depending on the methods of assessment used (Abraham and Carroll, 1981; Dahl, 1960;
Pennington et al.; 1984, Karanja et al., 1999; Kurtzweil, 1995). The amount of discretionary sodium
intake is highly variable and can be quite large. The Food and Drug Administration found that most
American adults tend to eat between 4,000 and 6,000 mg of sodium/day, while individuals on a
sodium-restricted diet usually ingest less than 1,000 to 3,000 mg/day (Kurtzweil, 1995). In the
assessment of pretreatment diets for the participants in the DASH trials, sodium levels range from about
3,500 to 4,500 mg/day (Karanja et al., 1999).
If the relative source is calculated from the median value for sodium in drinking water (16 mg/L)
using 4,000 mg sodium/day as a baseline for dietary sodium and 2 L/day as a water intake, drinking
water contributes only 0.8% of the total dietary sodium. If the relative source is calculated from the
99th percentile value (about 500 mg/L), drinking water contributes 25% of the daily sodium. If the 2.4
g/day recommended intake is used as a baseline, systems at the median concentration contribute 1.3%
of the recommended intake, but systems at the 99th percentile contribute 41.6% of the total. Habitual
intake of 2 L of water per day at this concentration is not advisable. However, the palatability of the
water could be adversely affected by high sodium concentration, which would likely diminish total water
intake and lead to corrective measures.
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Regulatory Determination Support Document for Sodium July 2003
4.4 Sensitive Populations
Populations expected to have an increased sensitivity to sodium include infants/children, individuals
with hypertension, the elderly (blood pressure increases with age), African Americans (the incidence of
hypertension is disproportionally high among African Americans) and individuals with renal diseases.
Several studies indicate that younger children are more sensitive to high sodium levels than are
adults (Elton et al. 1963; Gauthier, 1969; DeGenaro and Nyhan, 1971). This heightened sensitivity is
associated with the immature kidney's decreased ability to control sodium levels. On a mg sodium per
kg body weight basis, however, the sodium requirement for infants and children is greater than for
adults (NRC, 1989a).
The elderly are also more sensitive to high sodium exposure because they have a higher incidence
of cardiovascular disease (including hypertension) than younger subjects (Sowers and Lester, 2000).
In addition, since the elderly tend to have a higher taste threshold for salt, they may also have a higher
dietary salt intake (Hyde and Feller, 1981; Stevens, 1996). African-Americans, in particular, are more
susceptible to sodium-induced adverse health effects because of high incidence of hypertension
(Sullivan, 1991; Svetkey et al., 1996).
Individuals with decreased renal function comprise another group that is sensitive to high sodium
intake. One study demonstrates that 4,600 mg/day of sodium chloride significantly elevates systolic
blood pressure in patients with chronic renal failure (Muntzel and Drueke, 1992). In addition, Muntzel
and Drueke postulated that abnormal kidney function is a factor in salt retention by salt-sensitive
individuals. Sodium retention has also been reported in rats given high doses of sodium chloride,
following partial nephrectomy (Muntzel and Drueke, 1992). Dietary sodium restrictions are
recommended for individuals with acute or chronic renal problems and for those with nephrotic
syndrome (Whitney, et al. 1987). Renal problems are associated with about 10% of the population
with hypertension (Whitney, et al. 1987).
Among the sodium-sensitive population, dietary restrictions alone are insufficient for preventing
adverse heath effects that result from high sodium levels. Programs for hypertensives include weight
reduction, exercise, stress reduction, and adequate dietary potassium, calcium, and magnesium, in
addition to sodium restriction. As mentioned earlier, limiting cholesterol, dietary fat, and alcohol intake
is also recommended. At blood pressures over 95/160 mm Hg (diastolic/systolic), diet and behavior
modification are often combined with pharmaceutical measures.
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Regulatory Determination Support Document for Sodium July 2003
4.5 Exposure and Risk Information
While nearly the entire public water system population is exposed to sodium through their drinking
water, only about 7 million, or 8%, are exposed to water at concentrations above the 120 mg/L
benchmark, a level that comprises about 10% of the dietary guideline for sodium. The dietary guideline
level, however, is habitually exceeded by most of the U.S. population by 1,100 to 2,100 mg/day
(Abraham and Carroll, 1981; Dahl, 1960; Pennington et al., 1984; Karanja et al., 1999; Kurtzweil,
1995).
4.6 Conclusion
Despite the evidence that sodium may have adverse health effects in humans by contributing to
hypertension, data from studies indicate that the most effective hypertension reduction programs do not
involve supplementation or restriction of a single element. Instead, a well balanced, nutritionally sound
diet combined with other behavioral changes such as exercise and stress reduction are the most
effective measures. In addition, since sodium levels in drinking water are usually low, water from public
water systems is unlikely to significantly contribute to adverse health effects. For these reasons,
regulation may not present a meaningful opportunity for health risk reduction for persons served by
public drinking water systems. However, the EPA may issue a Drinking Water Advisory to provide
guidance to communities that may be exposed to drinking water contaminated with sodium chloride or
other sodium salts. All CCL regulatory determinations and further analysis are formally presented in the
Federal Register Notices (USEPA, 2002a; 67 FR 38222; and USEPA, 2003a; 68 FR 42898).
5.0 TECHNOLOGY ASSESSMENT
If a determination has been made to regulate a contaminant, SDWA requires development of
proposed regulations within 2 years of making the decision. It is critical to have suitable monitoring
methods and treatment technologies to support regulation development according to the schedules
defined in the SDWA.
5.1 Analytical Methods
The availability of analytical methods does not influence EPA's determination of whether or not a
CCL contaminant should be regulated. However, before EPA actually regulates a contaminant and
establishes 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. Sodium can be measured
by well-documented analytical methods (see Table 5-1).
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Regulatory Determination Support Document for Sodium
July 2003
Table 5-1: Analytical methods for sodium
Method
EPA 200.7
SM3111 B
Type
>•••** /
Inductively Coupled
Plasma Optical Emission
Spectroscopy
(ICP)/Atomic Emission
Spectrometry
Atomic Absorption (AA),
Direct Aspiration
MetlMfd Detection
Linuyjigffij)
30
IDL2
Optimum
concentration range
30-1000
5.2 Treatment Technology
Because sodium is being dealt with through guidance, treatment technologies have not been
reviewed.
6.0 SUMMARY AND CONCLUSIONS - DETERMINATION OUTCOME
Three statutory criteria are used to guide the determination of whether regulation of a CCL
contaminant is warranted: 1) the contaminant may adversely affect the health of persons; 2) the
contaminant is known or is likely to occur in public water systems with a frequency, and at levels, of
public health concern; and 3) regulation of the contaminant presents a meaningful opportunity for health
risk reduction for persons served by public water systems. As required by SDWA, a decision to
regulate a contaminant commits the EPA to propose a Maximum Contaminant Level Goal (MCLG)
and promulgate a National Primary Drinking Water Regulation 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.
The weight of evidence favors the conclusion that sodium concentrations greater than 120 mg/L can
have an effect on blood pressure, especially for sodium-hypertensives. Hypertension affects almost 50
million people in the United States. Control of body weight, adequate intake of nutrients such as
30
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Regulatory Determination Support Document for Sodium July 2003
potassium, calcium and magnesium, sodium restriction, exercise, and stress all influence blood pressure.
In addition to hypertension, cholesterol, dietary fat and alcohol intake are risk factors for cardiovascular
problems.
Sodium is known to occur in nearly all public water systems and, in a few cases, at levels of public
health concern for salt-sensitive hypertensives (greater than 120 mg/L). However, these concentrations
exceed the taste threshold of 30 mg/L and affected consumers would likely reduce their intake and
implement corrective measures.
Based on available monitoring data, 7.1 million people are exposed to sodium at levels above the
benchmark level of 120 mg/L, a concentration that would provide about 10% of the dietary guideline
for sodium. The majority of sodium intake is from salt added to food during processing or preparation.
An estimate of daily sodium intake in American diets, and median sodium concentrations in water, show
that water contributes only 0.8% of the total dietary sodium. Sensitive populations include the elderly,
because blood pressure increases and taste sensitivity to salt decreases with age, infants and children,
and African Americans. Sodium may have a stronger effect on hypertensive individuals with renal
disease. Those with normal blood pressure may be influenced by sodium to a lesser extent. Blood
pressure is influenced more by nutrients in the diet, lifestyle, and behavioral patterns rather than by
sodium intake.
In conclusion, sodium generally occurs at low levels in drinking water, and when it occurs at high
levels the taste may be expected to cause people to reduce their consumption. In addition, drinking
water is only a minor source of dietary sodium compared with food, and sodium is only one factor
among many that contributes to hypertension and heart disease. Therefore, regulation of sodium in
drinking water is unlikely to represent a meaningful opportunity for health risk reduction. The most
effective means to protect the health of PWS users is to identify groups who are more sensitive than the
general population, and provide dietary guidance through the public health community. The EPA may
issue an advisory to provide guidance to communities that may be exposed to elevated concentrations
of sodium chloride or other sodium salts in their drinking water. The advisory would provide
appropriate cautions for individuals on low-sodium or sodium-restricted diets. In addition, EPA
presently requires periodic monitoring of sodium at the entry point to the distribution system. This
requirement provides the public health community with information on sodium levels in drinking water to
be used in counseling patients and is the most direct route for gaining the attention of the affected
population. All CCL regulatory determinations are formally presented in the Federal Register Notices
(USEPA, 2002a; 67 FR 38222; and USEPA, 2003a; 68 FR 42898).
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Regulatory Determination Support Document for Sodium July 2003
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Regulatory Determination Support Document for Sodium July 2003
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Appendix A: Abbreviations and Acronyms
AA - atomic absorption
CAS - Chemical Abstract Service
CCL - Contaminant Candidate List
CDC - Center for Disease Control and Prevention
CERCLA - Comprehensive Environmental Response, Compensation & Liability Act
CWS - community water system
DWEL - drinking water equivalent level
EPA - Environmental Protection Agency
EPCRA - Emergency Planning and Community Right-to-Know Act
FIFRA - Federal Insecticide, Fungicide, and Rodenticide Act
FQPA - Food Quality Protection Act
FR - Federal Register
g/mol - grams per mole
GW - ground water
HA - Health Advisory
HAL - Health Advisory level
HRL - Health Reference Level
TCP - inductively coupled plasma
ICRG - Intersalt Cooperative Research Group
DDL - instrument detection level
IOC - inorganic compound
MCL - maximum contaminant level
MCLG - maximum contaminant level goal
mEq/L - milliequivalent per liter
mg - milligram
mg/kg-day - milligram per kilogram per day
mm Hg - millimeter mercury
MRL - minimum reporting level
Na - sodium
NaCl - sodium chloride (salt)
NAS - National Academy of the Sciences
NAWQA - National Water Quality Assessment Program
NDWAC - National Drinking Water Advisory Council
NIH - National Institutes for Health
MRS - National Inorganic and Radionuclide Survey
nm - nanometer
NPDWR - National Primary Drinking Water Regulation
NRC - National Research Council
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NTNCWS - non-transient non-community water system
OGWDW - Office of Ground Water and Drinking Water
PGWD - Pesticides in Ground Water Database
pH - the negative log of the concentration of H+ ions
ppm - part per million
PWS - public water system
RCRA - Resource Conservation and Recovery Act
RTECS - Registry of Toxic Effects of Chemical Substances
SARA - Superfund Amendments and Reauthorization Act
SDWA - Safe Drinking Water Act
SDWIS/FED - Federal Safe Drinking Water Information System
SOC - synthetic organic compound
SW - surface water
TRI - Toxic Release Inventory
UCM - Unregulated Contaminant Monitoring
UCMR - Unregulated Contaminant Monitoring Regulation/Rule
USEPA - United States Environmental Protection Agency
USGS - United States Geological Survey
VOC - volatile organic compound
pg - micrograms
>MCL - percentage of systems with exceedances
>MRL - percentage of systems with detections
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