Drinking Water Advisory: 

Consumer Acceptability Advice

and Health Effects Analysis

on Sulfate
 Printed on Recycled Paper

Drinking Water Advisory: Consumer Acceptability Advice and

 Health Effects Analysis on Sulfate

U.S. Environmental Protection Agency

Office of Water (4304T)

Health and Ecological Criteria Division

Washington, DC 20460

www.epa.gov/safewater/ccl/pdf/sulfate.pdf

EPA 822-R-03-007

February 2003
Sulfate — February 2003 iii

FOREWORD

The Drinking Water Advisory Program, sponsored by the Health and Ecological Criteria

Division of the Office of Science and Technology (OST), Office of Water (OW), provides

information on the health and organoleptic (taste, odor, etc.) effects of contaminants in drinking

water. The Drinking Water Advisory documents are a component of the OW Health Advisory

Program. Drinking Water Advisories differ from Health Advisories because of their focus on

aesthetic properties (e.g., taste, odor, color) of drinking water. A Drinking Water Advisory is

prepared when contaminants cause adverse taste and odor influences at concentrations lower

than those for adverse health effects.

A Drinking Water Advisory is not an enforceable standard for action. It describes nonregulatory

concentrations of the contaminant in water that are expected to be without adverse effects on

both health and aesthetics. Both Health Advisories and Drinking Water Advisories serve as

technical guidance to assist Federal, State, and local officials responsible for protecting public

health when emergency spills or contamination situations occur. They are not to be construed as

legally enforceable Federal standards. They are subject to change as new information becomes

available. This draft supersedes any previous draft advisories for this chemical.

The Advisory discusses the limitations of the current database for estimating a risk level for

sulfate in drinking water and characterizes the hazards associated with exposure. The Drinking

Water Health Advisory value was developed by a panel of experts through a workshop held on

September 28, 1998, and sponsored by the Centers for Disease Control (CDC) and the United

States Environmental Protection Agency (U.S. EPA). The experts who participated in the

workshop were:

Charles Abernathy, Ph.D. - U.S. EPA

David Cole, M.D., Ph.D. - University of Toronto

Marie Cassidy, Ph.D. - George Washington University

Marilyn Morris, Ph.D. - State University of New York: Buffalo

Guillermo Gomez, Ph.D. - North Carolina State University

Lorraine Backer, Ph.D. - National Center for Environmental Health at CDC

A workshop report was prepared that summarized the data considered at the workshop and its

findings. This report was published by EPA as Document Number 815-R-99-002 in January

1999 (EPA, 1999b). The workshop report was externally peer reviewed by the following

scientists (EPA, 1999c):

Laurence L. Brunton, Ph.D. - University of California San Diego

Paul E. Brubaker, Ph.D. - Brubaker Associates, New Jersey.

Michael L. Dourson, Ph.D. - Toxicology Excellence for Risk Assessment, Ohio
Sulfate — February 2003 iv

CONTENTS

FOREWORD ............................................................................................................................... iii

ABBREVIATIONS ........................................................................................................................ v

EXECUTIVE SUMMARY ............................................................................................................ 1

1.0 INTRODUCTION ................................................................................................................. 4

2.0 SULFATE IN THE ENVIRONMENT .................................................................................. 4

2.1 Water ............................................................................................................................. 4

2.2 Soil ................................................................................................................................ 6

2.3 Air ................................................................................................................................. 6

2.4 Food ............................................................................................................................... 7

2.5 Summary ....................................................................................................................... 7

3.0 CHEMICAL AND PHYSICAL PROPERTIES .................................................................... 7

4.0 TOXICOKINETICS .............................................................................................................. 9

4.1 Absorption ..................................................................................................................... 9

4.2 Distribution ................................................................................................................... 9

4.3 Metabolism .................................................................................................................. 11

4.4 Excretion ..................................................................................................................... 11

5.0 HEALTH EFFECTS DATA ................................................................................................ 12

5.1 Human ......................................................................................................................... 13

5.1.1 Short-Term Exposure Studies .............................................................................. 13

5.1.2 Long-Term Exposure Studies .............................................................................. 15

5.2 Animal ......................................................................................................................... 16

5.2.1 Short-Term Exposure Studies ................................................................................ 16

5.2.2 Long-Term Exposure Studies ................................................................................ 17

5.2.3 Reproductive and Developmental Studies ............................................................. 18

5.2.4 Cancer Studies ....................................................................................................... 18

6.0 ORGANOLEPTIC PROPERTIES ...................................................................................... 19

7.0 CHARACTERIZATION OF HAZARD AND DOSE-RESPONSE ................................... 20

7.1 Hazard Characterization .............................................................................................. 20

7.2 Characterization of Organoleptic Effects .................................................................... 21

7.3 Dose-Response Characterization ................................................................................ 21

8.0 REFERENCES .................................................................................................................... 24
Sulfate — February 2003 v

ABBREVIATIONS

CDC Centers for Disease Control and Prevention

CSF cerebrospinal fluid

g gram

kg kilogram

L liter

m3 cubic meters

mg milligram

min minute

mM millimolar

mmol millimole

NTP National Toxicology Program

OST Office of Science and Technology

OW Office of Water

PAPS 3N-phosphoadenosine-5N-phosphosulfate

ppm parts per million

PWS public water system

RfD Reference Dose

SDWA Safe Drinking Water Act

SDWIS/FED Safe Drinking Water Information System/Federal

SO4

2- sulfate

SMCL secondary maximum contaminant level

UCM unregulated contaminant monitoring

μg microgram

μmol micromole
Sulfate — February 2003 1

EXECUTIVE SUMMARY

The EPA Office of Water is issuing this advisory to provide guidance to communities that may

be exposed to drinking water contaminated with high sulfate concentrations. The advisory

provides an analysis of the current health hazard information and an evaluation of available data

on the organoleptic (i.e., taste and odor) problems associated with sulfate-contaminated water,

because organoleptic problems will affect consumer acceptance of water resources. This

advisory does not recommend a Reference Dose (RfD) because of limitations of available data

for assessing risks. However, the advisory does provide guidance on the concentrations above

which health and organoleptic problems would likely occur. This Drinking Water Advisory does

not mandate a standard for action; rather it provides practical guidelines for addressing sulfate

contamination problems and supersedes previous draft advisories for sulfate

Conclusion and Recommendation

In order to enhance consumer acceptance of water resources, this advisory recommends reducing

sulfate concentrations to or below 250 mg/L, the EPA=s Secondary Maximum Contaminant

Level (SMCL) for sulfate. The SMCL is based on taste considerations. It is not a federally

enforceable regulation, but is intended as a guideline for States. States may establish higher or

lower levels depending on the local conditions, such as unavailability of alternate source waters

or other compelling factors, provided that public health and welfare are not adversely affected.

A health-based advisory for acute effects (absence of laxative effects) of 500 mg of sulfate/L is

recommended. This value depends on the absence of other osmotically active materials in

drinking water, which could lower the sulfate level associated with a laxative effect. Where the

water contains high concentrations of total dissolved solids and/or other osmotically active ions,

laxative-like effects may occur if the water is mixed with concentrated infant formula or a

powdered nutritional supplement. In such situations, an alternate low-mineral-content water

source is advised. Infants are more susceptible than adults to diarrheal water loss because of 

differences in gastrointestinal structure and function.

The soft stool or diarrhea that results from sulfate is an osmotic diarrhea; that is, it happens when

the osmolality (number of dissolved particles) in the intestinal contents exceeds that of the body

fluids. When this occurs, water is drawn from the body fluids into the intestines, increasing the

moisture content and volume of the fecal matter. Whether or not diarrhea or soft stools occur

depends on the amount of sulfate and other osmotically active materials that are present in the

intestines; these materials include magnesium, sodium, and some sugars. An osmotic-induced

diarrhea ceases once the osmotically active gastrointestinal contents are excreted. In the case of

sulfate, adults appear to adapt within 1 or 2 weeks and are no longer affected by the sulfate in

their drinking water supply. Infants, however, may be more sensitive.

Sulfate in the Environment

Sulfates are naturally occurring substances that are found in minerals, soil, and rocks. They are

present in ambient air, groundwater, plants, and food. The principal commercial use of sulfate is

in the chemical industry. Sulfates are discharged into water in industrial wastes and through

atmospheric deposition. Sulfate concentration in seawater is about 2,700 milligrams per liter
Sulfate — February 2003 2

(mg/L). It ranges from 3 to 30 mg/L in most freshwater supplies, although much higher

concentrations ($ 1000 mg/L) are found in some geographic locations. In the United States, the

median concentration for a 20-State cross-section was 24 mg/L; the 99th percentile value was 560

mg/L. In general, food is the principal source of exposure. However, in areas with high sulfate

concentrations, exposure from water can exceed that from food. 

Studies of Sulfate Effects

Long-term and short-term exposure studies to determine a hazard assessment for sulfate are

currently available in humans and animals. The findings from cancer, noncancer, and taste and

odor studies are discussed below.

Cancer Studies. There has been no traditional NTP oral cancer bioassay for inorganic sulfate as

the ion of interest. In an 8-month preliminary study, no tumors were observed in Wistar rats

after intramuscular injection of 0.7 mg sodium sulfate every other day for 4 weeks. However, in

this study the sodium sulfate treatment was used as a control against which to evaluate the

effects of nickel sulfate and nickel hydroxide. Accordingly, the present database is of limited

value for evaluating the tumorigenicity of sulfate. After reviewing toxicity data on sulfates food

additives, the Select Committee of the Life Sciences Research Office concluded that there was

no evidence that sulfuric acid or ammonium, calcium, potassium, and sodium sulfates present a

hazard to the public health when they are used at levels that are current or that might reasonably

be expected in the future.

Noncancer Studies. The collective evaluation of the noncancer data in humans and animals

suggests that acute exposures to sulfate exert a laxative effect (loose stool) and sometimes

diarrhea (unusually frequent or unusually liquid bowel movements) following acute exposures to

high concentrations. However, these effects are not observed for longer term exposures. This

may be because of acclimation to sulfate over time. 

No adverse developmental effects were observed following the administration of 2,800

mg/kg/day of sulfate to pregnant ICR/SIM mice on gestation days 8 to 12. No reproductive

effects were observed following the ingestion of drinking water containing up to 5,000 mg/L of

sulfates by ICR/SIM mice and 3,298 mg/L of sulfates by Hampshire × Yorkshire × Duroc pigs . 

On the basis of these studies, sulfate does not appear to be a reproductive or a developmental

toxicant.

Studies on Taste and Odor. Few studies are available that report on the organoleptic properties

(i.e., taste and odor) of sulfate. None of the studies reported an odor threshold; therefore, all of

the reported values are based on taste thresholds. It is not possible to precisely identify a

specific taste threshold for sulfates in drinking water because the taste threshold concentration

varies among individuals. In addition, the associated cations, different water matrices, and

temperatures also influence taste. On the basis of the available data, no significant taste effects

have been found to occur at sulfate concentrations of about 200B300 mg/L.
Sulfate — February 2003 3

Characterization Summary

The data from short-term studies suggest that a mild laxative response can occur at sulfate

concentrations greater than 500 mg/L, especially if there are other osmotically active substances

present in the water. In the absence of other osmotically active materials, the laxative effects are

unlikely to be observed at concentrations up to about 1,000 mg/L sulfate. These effects are

exhibited as an increase in stool volume, moisture, and/or increased intestinal transit time rather

than frank diarrhea. 

Where drinking water contains high levels of sulfate or total dissolved solids, it should not be

used in the preparation of powdered infant formula or nutritional supplements. An alternate lowmineral water source should be used. Because laxative effects have not been observed with

long-term exposures to sulfate-containing water, the data suggest that acclimatization occurs as

exposures continue.

The available database does not permit EPA to construct a quantitative dose-response

assessment for the laxative effects of sulfate. The current SMCL of 250 mg/L should protect

almost all consumers from the esthetic effects of sulfate, and the health-based advisory value of

500 mg/L will protect against sulfate’s laxative effects in the absence of high concentrations of

other osmotically active chemicals in the water. 
Sulfate — February 2003 4

1.0 INTRODUCTION

This advisory provides information to Tribes, States, local drinking water facilities, and public

health personnel on the health and taste effects resulting from sulfate contamination of potable

water. There are limited scientific data on the health effects of sulfate, but adequate data are

available on the range of exposure concentrations that may pose a concern. 

2.0 SULFATE IN THE ENVIRONMENT

Sulfates occur naturally and are abundant in the environment, generally originating from mineral

deposits, soil, and rocks, or the combustion of sulfur-containing fuels. Sulfate, a soluble,

divalent anion (SO4

2-), results from the oxidation of elemental sulfur, sulfide minerals, or organic

sulfur (Alley 1993, Field 1972, Wetzel 1983). The anion is often associated with alkali, alkaline

earth, or transition metals through ionic bonds (Field 1972). 

Sulfates are used in mining, pulping, metal and plating industries, water and sewage treatment,

and leather processing, and in the manufacture of numerous chemicals, dyes, glass, paper, soaps,

textiles, fungicides, insecticides, astringents, and emetics (Greenwood et al. 1984). Various

sulfate salts are used in foods (FDA 1999), and ammonium sulfate is used in the fertilizer

industry. 

Sulfur is the 14th most abundant element in the earth's crust, and the 8th or 9th most abundant in

sediments (Kaplan 1972). It is constantly transferred among compartments by the sulfur cycle

and is ubiquitous in the environment. Anthropogenic sulfur emissions have a significant impact

on the sulfur cycle, with at least 80% of global sulfur dioxide (SO2) emissions and more than

45% of river-borne sulfates traceable to human activity (Moore 1991).

2.1 Water

Sulfate is found almost universally in natural waters at concentrations ranging from a few tenths

to several thousand milligrams/liter (mg/L). The highest concentrations are usually found in

groundwater and are considered to be a mixture of sulfates from atmospheric, geochemical, and

biological sources. Approximately 30% of sulfate in groundwater may be of atmospheric origin,

and the remainder from geologic and biological processes. Sulfates are discharged into surface

water through industrial wastes and atmospheric deposition of sulfur dioxide.

The sulfate concentration in seawater is about 2,700 mg/L (Hitchcock 1975) and ranges from 3

to 30 mg/L in freshwater lakes (Katz 1977). Sulfate content in drinking water ranges from 0 to

1,000 mg/L in the United States (Trembaczowski 1991). In a survey of rivers in western

Canada, sulfate concentrations ranged from 1 to 3,040 mg/L, with concentrations generally in

the range of 1 to 580 mg/L (Environment Canada 1984). 

Sulfate has been monitored under the Safe Drinking Water Act (SDWA) Unregulated

Contaminant Monitoring (UCM) program since 1993 (57 FR 31776). Monitoring ceased for

small public water systems (PWSs) under a direct final rule published January 8, 1999 (64 FR
Sulfate — February 2003 5

1494), and ended for large PWSs with promulgation of the new Unregulated Contaminant

Monitoring Regulation (UCMR) issued September 17, 1999 (64 FR 50556) and effective 

January 1, 2001. 

The Safe Drinking Water Information System (SDWIS/FED) is a database of analytical data on

the concentrations of contaminants in drinking water. Sulfate levels reported in the SDWIS/FED

database were analyzed from a 20-State cross-section (U.S. EPA 2001). The median

concentration of all PWS samples was 24 mg/L and the 99th percentile concentration of all PWS

samples was 560 mg/L. Minimum reporting levels varied from system to system and State to

State. The 99th percentile concentration is 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. 

Additional sulfate occurrence data submitted for EPA’s Chemical Monitoring Reform (CMR)

evaluation by the States of Alabama, California, Illinois, Montana, New Jersey, and Oregon

augment the SDWIS/FED 20-State cross-section analysis (U.S. EPA 2001). Five of these CMR

States are not represented in the cross-section. Data from the CMR States show that

concentrations are generally similar to those found in the 20-State cross-section (Table 1). Even

in states such as Montana, where the 99th percentile concentration is substantially greater than

that of the 20-State cross-section, the median concentration is still quite similar to the median of

the cross-section States (U.S. EPA 2001).

Table 1. Median and 99th percentile concentrations 

for sulfate in CMR States

State Median

concentration 

99th percentile

concentration

Alabama 8.1 mg/L 72 mg/L

California 33 mg/L 523 mg/L

Illinois 60 mg/L 760 mg/L

Montana 22 mg/L 1,200 mg/L

New Jersey 15.9 mg/L 260 mg/L

Oregon 5.1 mg/L 79 mg/L

Although 88% of the 16,495 systems included in the 20-State cross-section reported sulfate at

concentrations greater than the minimum reporting level, only about 5% exceeded the 250 mg/L

SMCL. Within the twenty individual States, the number of systems that exceeded the SMCL

ranged from 0 to approximately 11%. A greater percentage of surface water systems exceeded

the 250 mg/L threshold; however, groundwater systems do generally show the highest sulfate

concentrations (U.S. EPA 2001). 
Sulfate — February 2003 6

A survey of more than 900 community water supplies found that 25 (-3%) had sulfate

concentrations above 250 mg/L (McCabe et al. 1970). Another survey of approximately 650

rural water systems reported sulfate present in 271 of 495 groundwater supplies (55%), with a

mean sulfate concentration of 98 mg/L (a range of 10 to 1,000 mg/L). Sulfate was found in 101

of 154 surface water supplies at a mean concentration of 53 mg/L for those systems that detected

sulfate (a range of 15 to 321 mg/L) (U.S. EPA 1994).

Several surveys have been conducted in Canada on the occurrence of sulfates in drinking water. 

A study of 17 drinking water supplies in Ontario from 1985 through 1986 found mean sulfate

concentrations of 22.5 and 12.5 mg/L in treated and untreated water, respectively (Ontario

Ministry of the Environment 1987). A study of 78 municipal drinking water supplies in Nova

Scotia between 1987 and 1988 found mean sulfate concentrations of 14.2 mg/L in treated water

(Nova Scotia Department of Public Health 1988). Sulfate concentrations were significantly

higher in Saskatchewan, with median concentrations of 368 and 97 mg/L (range of 3 to 2,170

mg/L) reported for treated ground and surface waters, respectively (Saskatchewan Environment

and Public Safety 1989). Based on the mean sulfate concentration measured in Ontario (22.5

mg/L) and an average daily water consumption of 2 L per day for an adult, the average daily

intake from this source would be 45 mg. However, in areas with high sulfate levels in drinking

water, such as Saskatchewan, daily sulfate intake could be more than 4,000 mg (WHO 1996).

2.2 Soil

Sulfate can be formed from the oxidation of elemental sulfur, sulfide minerals, or organic sulfur

(Alley 1993, Field 1972, Wetzel 1983). It is one of the predominant anions in soil but is not

highly mobile. Sulfate anion is often associated through ionic bonds with alkali, alkaline earth,

or transition metals (Field 1972). Sulfur can be retained in soil through biochemical processes,

such as incorporation into the soil organic pool as sulfate esters of humic material or other

complex organic molecules. Sulfur can also be retained by adsorption onto soil particles, such as

hydrous iron and aluminum sesquioxides. The average sulfur (total) concentration in soils in the

United States is 1,600 parts per million (ppm or mg/kg; a range of <800 to 48,000 mg/kg)

(Shacklette and Boerngen 1984). The determinant in soil for the adsorption of sulfate is the

content of hydrous sesquioxides and organic matter. A strong correlation was found between pH

and the ability to remove sulfates from soil solutions; therefore, factors affecting soil acidity

would also affect sulfate retention (Patil et al. 1989).

2.3 Air

The main sources of atmospheric sulfate are sulfur oxides, which are primarily emitted to the

atmosphere from sulfur-containing fuel combustion. Total global sulfur dioxide production

continually increased from 1930 to 1980 (the years when data are available; Moore 1991). 

Global production of sulfur dioxide increased from 49 × 106

 metric tons per year to 126 × 106

metric tons per year between 1930 and 1980.

Sulfur dioxide (SO2) emissions have become a major concern for industrialized nations. Sulfur

dioxide interacts with atmospheric water and oxygen to produce sulfuric acid (H2SO4), causing

acid rain (Moore 1991, Wetzel 1983). In addition, SO2 is converted to sulfate in the atmosphere
Sulfate — February 2003 7

and deposited on soils. This can lead to the acidification of soil solutions and elevate sulfate

concentrations in terrestrial waters (Drever 1988).

Limited information is available on the concentration of sulfates in ambient air. In a study

consisting of 23,000 samples from 405 sites in 49 States, sulfate concentration was estimated to

range from 0.5 to 228.4 μg/m3. The median exposure concentrations (0.7 to 19.5 μg/m3) were

considered to be more representative of exposures than were the mean values. Using the upper

median exposure concentration (19.5 μg/m3) and assuming an inhalation rate of 20 m3/day for a

70-kg adult, the daily dose due to sulfate in ambient air would be 6 μg/kg/day (Abernathy et al.

2000).

2.4 Food

In foods, sulfate is present as the salts of sodium, calcium, iron, magnesium, manganese, zinc,

copper, ammonium, and potassium (FDA 1999). Sulfate salts are used in the food industry in a

wide variety of products, such as dietary supplements, breads, preserved fruits and vegetables,

gelatins, and puddings. The average daily intake of sulfate in food in the United States has been

estimated to be 453 mg, based on data on food consumption and the reported usage of sulfates as

additives (FASEB 1975). Many sulfate compounds in food are “Generally Regarded as Safe”

(GRAS) by the U.S. Food and Drug Administration (FDA 1999).

2.5 Summary

Average daily intake of sulfate from drinking water, air, and food is approximately 500 mg, with

food being the major source. However, in areas with high sulfate concentrations in the drinking

water supplies, drinking water may constitute the principal intake source (WHO 1996). 

3.0 CHEMICAL AND PHYSICAL PROPERTIES

Sulfate (SO4

2-) is a soluble, divalent anion; common salts include sodium, potassium,

magnesium, calcium, and barium sulfate. The majority of sulfate salts are soluble in water, the

exceptions being the sulfates of lead, barium, and strontium. The chemical and physical

properties for the common sulfate salts are detailed in Table 2 (NIOSH 1981, Budavari 1996,

Scofield and Hsieh 1983).
Sulfate — February 2003

8

Table 2. Chemical and physical properties of sulfates

Chemical Name Sulfuric acid Sodium sulfate Potassium sulfate Magnesium sulfate Calcium sulfate Barium sulfateChemical formula H2SO4 Na2SO4 K2SO4 MgSO4 CaSO4 BaSO4CAS No. 7664-93-9 7757-82-6 7778-80-5 7487-88-9 7778-18-9 7727-43-7Synonym Oil of vitriol; Hydrogen

sulfate

Thenardite(decahydrate isGlauber’s salt)

Tartarus vitriolatus;Arcanum duplicatum

Bitter salts;heptahydrate; epsomsalts

Anhydrite;Anhydrous gypsum;Anhydrous calciumsulfate

Barite; Blanc fixe;Raybar

Molecular weight 98.08 142.06 174.26 120.38 136.14 233.39Physical state Colorless to dark

brown, oily, odorlessliquid

White powder ororthorhombicbipyramidal crystals

Colorless or whiterhombic or hexagonalcrystals

Colorless rhombicbitter crystal

Orthorhomic crystalof variable color

Fine, heavy, odorlesspowder orpolymorphous crystals

Boiling point (oC) 315 - 338 NA 1,689 NA 1,193 1,149

Melting point (oC) 10.4 888 1,067 NA 1,450 1,580

Density (g/mL) 1.84 2.68 2.66 2.66 2.96 4.2 - 4.5Vapor pressure (mmHg) < 0.001 NA NA NA NA NASpecific gravity 1.84 2.68 2.66 1.67 2.96 4.2 - 4.5Water solubility(g/100 mL) Miscible 29l 12 

71 at 20°C and 

91 at 40°C

0.2 Practically insoluble, 

0.00025

Taste threshold in water(mg/L) NA 180 - 550 NA 400 - 600 250 - 900 NAOdor threshold (air)(mg/m3) >1 NA NA NA NA NA

NA - Not available.
Sulfate — February 2003 9

4.0 TOXICOKINETICS

4.1 Absorption

Estimates of sulfate absorption are derived indirectly from reported excretion data. Absorption

of sulfate from the intestine depends upon the amount of sulfate ingested. For example, Bauer

(1976) reported that when radiotracer doses of 60-80 μCi 35S-sodium sulfate were administered

orally to humans (eight adults), 80% or more of the radioactivity was recovered in the urine at 24

hours, suggesting that at least 80% of sulfate must have been absorbed. However, the high doses

of sulfate that induced catharsis exceeded intestinal absorption capacity, and thus were excreted

in the feces. 

The type of cation associated with sulfate may also influence absorption. Morris and Levy

(1983b) reported 30.2 ± 17.2% of the dose was excreted in 24-hour urine after oral

administration of magnesium sulfate (5.4 g sulfate) to seven healthy individuals, as compared to

43.5 ± 12.0% excreted after oral administration of sodium sulfate (5.4 g sulfate) in five healthy

men (Cocchetto and Levy 1981). This finding suggests that magnesium sulfate is absorbed to a

lesser extent than sodium sulfate. Morris and Levy (1983b) indicated that the comparison of

these two salts is limited in that data were obtained in separate experiments from a small number

of subjects rather than from parallel experiments with the same pool of subjects.

Florin et al. (1991) performed sulfate balance studies in normal subjects and subjects with

ileostomies (subjects with ileum removed surgically). The study authors wanted to determine

how much sulfate reached the colon and the extent to which diet and endogenous sources

contributed to colonic sulfate concentration. All subjects were fed diets containing between 1.6

and 16.6 mmol SO4/day (0.15-1.6 g/day). Sulfate was measured in the diet, urine, and feces to

determine sulfate balance (using anion exchange chromatography). There was a net absorption

of sulfate with a plateau at 0.48 g/day in the ileostomy patients. Sulfate absorption in normal

subjects did not plateau even at the highest dietary concentration examined. The dietary

contribution to the colonic sulfate pool was determined to be up to 0.86 g/day because linearity

was observed between diet and upper gastrointestinal loss for intakes greater than 0.67 g/day. 

The study authors concluded that diet and intestinal absorption were the principal factors

affecting the amount of sulfate reaching the colon. This study also suggests that the upper

digestive tract is primarily responsible for sulfate absorption. 

4.2 Distribution

Inorganic sulfate is freely distributed in blood and does not accumulate in tissues. Most sulfate

found in human tissues is biosynthetically incorporated into macromolecules and is organic. The

normal serum level of sulfate found in humans (0.3 mmol/L or 29 mg/L) is lower than that in

rodents (1 mmol/L or 96 mg/L) or in other animal species (Krijgsheld et al. 1980, Cole and

Scriver 1980).

A circadian variation of serum inorganic sulfate levels has been demonstrated in humans. 

Hoffman et al. (1990) fed seven male volunteers an identical diet, including fluids, a parameter

that is not typically included in dietary studies. Blood samples were collected in a total of 10

intervals over a 24-hour period. Average serum inorganic sulfate levels were lowest in the
Sulfate — February 2003 10

morning (302 μmol/L or 29 mg/L) and highest in the early evening (408 μmol/L or 39 mg/L). 

This difference is statistically significant (p < 0.005). The average 24-hour level was 360

μmol/L, or 35 mg/L. There was considerable variability among subjects. The authors speculated

that a portion of the variation in serum sulfate could be due to variation in the dietary sulfate

content.

It is reported that dietary protein could have major influence on the serum sulfate levels. For

example, Cole et al. (1991) studied 12 fasting subjects who were randomly fed an isocaloric

meal containing either high or low protein content and monitored their serum sulfate levels up to

3.5 hours after feeding. Serum sulfate levels increased from a baseline value of 276 to 314

μmol/L (27 to 30 mg/L) at 2.5 hours after the low-protein meal and returned to the baseline by

3.5 hours. Serum sulfate levels increased from baseline values of 253 to 382 μmol/L (24 to 37

mg/L) at 3 hours and remained significantly elevated at 3.5 hours after the high-protein meal. 

The increase in inorganic sulfate was attributed to the oxidation of sulfur containing amino acids. 

The reason for the differences in the time to reach peak sulfate levels between the low- and highprotein groups is not clear. The inorganic sulfate excreted in the urine was not measured in this

study. 

Ingesting drinking water containing high sulfate concentrations has only slight effects on serum

sulfate levels. Hindmarsh et al. (1991) compared serum levels of inorganic sulfate in 14 healthy

volunteers at 2 locations (Saskatoon: 8 men; Rosetown: 4 men and 2 women) using municipal

drinking water with varying sulfate concentrations. In Saskatoon the sulfate concentration was

77 ppm (mg/L) and in Rosetown the sulfate concentration was 1,157 ppm (mg/L). The cations

associated with the sulfate were not reported. Baseline serum levels of inorganic sulfate were

0.35 ± 0.06 mmol/L (34 mg/L) in the Saskatoon subjects and 0.50 ± 0.11 mmol/L (48 mg/L) in

the Rosetown subjects. These findings suggest that a 15-fold increase in sulfate concentration in

drinking water will result in only a 1.4-fold increase in serum sulfate. The reasons for observing

only a slight increase in serum sulfate in Rosetown subjects could be homoeostatic control

mechanisms and dietary differences.

Serum inorganic sulfate concentrations are reported to be higher in infants and young children

than in adults. For example, Cole and Scriver (1980) compared serum inorganic sulfate

concentrations in subjects under 3 years old (n = 46), children between 3 and 4 years old

(n = 27), adolescents in a hospitalized population (10 to 18 years old) (n = 12), and healthy

adults (n = 10). On the first day of life, mean sulfate concentrations were 0.47 mmol/L (45

mg/L) (95% confidence limits of 0.29 to 0.95 mmol/L), and by 3 years of age, concentrations

dropped to 0.33 mmol/L or 32 mg/L, (95% confidence limits of 0.22 to 0.67 mmol/L), which

was comparable to the adult levels 0.33 mmol/L or 32 mg/L (95% confidence limits of

0.22B0.43 mmol/L). The study authors state that the increased concentration in newborns might

be a result of lower glomerular filtration rates, increased resorption, and/or developmental needs.

Serum levels of inorganic sulfate were found to be increased in pregnant women in the third

trimester (0.434 ± 0.006 mmol/L [42 mg/L] compared to a nonpregnant control value of 0.328 ±

0.010 mmol/L [31 mg/L]) (Cole et al. 1985). It was suggested that the fetus may need to

concentrate inorganic sulfate to support its development. Similarly, Cole et al. (1992) reported

that inorganic sulfate levels in amniotic fluid were increased in the third trimester compared with

the second trimester. Levels in amniotic fluid were 0.317 ± 0.022 mmol/L (30 mg/L) in the
Sulfate — February 2003 11

second trimester, but were 0.693 ± 0.042 mmol/L (66 mg/L) in the third trimester. The sulfate

levels correlated with the creatinine and uric acid levels in the amniotic fluid, suggesting that

renal excretion by the fetus may be the major source of the inorganic sulfate in the amniotic fluid

in the late stages of gestation.

Levels of inorganic sulfate in the cerebrospinal fluid (CSF) were reportedly lower than those in

serum. Cole et al. (1982) measured inorganic sulfate in CSF from 25 infants and children. 

Mean CSF sulfate was 0.170 mmol/L (16.3 mg/L) in children less than 3 years of age and 0.095

mmol/L (9.1 mg/L; range 0.059 to 0.165 mmol/L) in children older than 3 years of age. Similar

to CSF concentrations, the serum sulfate concentration decreased from 0.5 mmol/L (48 mg/L) in

the newborn to 0.3 mmol/L (29 mg/L) in children older than 3 years of age. Because both CSF

and serum sulfate levels decrease in a similar fashion, the ratio of sulfate CSF/serum remains

constant at 0.33 in infants and children.

 

The levels of inorganic sulfate in human colostrum and milk were 0.066 ± 0.021 mmol/L (6.3

mg/L) and 0.029 ± 0.006 mmol/L (2.8 mg/L), respectively (McNally et al. 1991). The mean

sulfate level in the saliva in fasting adults (n = 17) was 0.072 ± 0.004 mmol/L, or 6.9 mg/L (Cole

and Landry 1985).

4.3 Metabolism

Inorganic sulfate is incorporated into several types of biomolecules, such as glycoproteins,

glycosaminoglycans, and glycolipids (Brown et al. 1965, Daughaday 1971, Morris and Sagawa

2000). Inorganic sulfate enters a metabolic pathway as an activated nucleotide intermediate, 3Nphosphoadenosine-5N-phosphosulfate (PAPS), which serves as a substrate for a number of

relatively specific sulfotransferases. Sulfotransferases are enzymes that catalyze the sulfation

process (or sulfamation in the case of aromatic amines). They are found in the intestinal

mucosa, liver, and kidney (Bostrom 1965, Mulder and Keulemans 1978) and in human platelets

(Rein et al. 1981). Sulfate plays an important role in the detoxification and catabolism of

various endogenous (catecholamines, steroids, bile acids) and exogenous (acetaminophen and

other drugs) compounds. Sulfate combines with several of these compounds to form soluble

sulfate esters (Mulder and Keulemans 1978, Weitering et al. 1979, Sipes and Gandolfi 1991).

Because inorganic sulfate is used in the metabolism of several compounds, sulfate levels could

be affected by the presence of drugs in the body. In humans, the effect of acetaminophen

administration on the serum sulfate pool has been studied (Morris and Levy 1983a). In eight

human volunteers orally administered 1.5 g of acetaminophen, the mean serum concentration of

inorganic sulfate was significantly (p < 0.001) reduced from 0.410 to 0.311 mmol/L (39 to 30

mg/L) within 2 hours. Similar findings were observed in other human studies (Hendrix-Treacy

et al. 1986), as well as in animals (Morris et al. 1984), after acetaminophen administration. 

4.4 Excretion

Sulfates are usually eliminated by renal excretion in free unbound form or as conjugates of

various chemicals. At high sulfate doses that exceed intestinal absorption, sulfate is excreted in

feces.
Sulfate — February 2003 12

Cocchetto and Levy (1981) conducted a study with five male volunteers who were orally

administered 18.1 g Na2SO4A10H2O (5.4 g sulfate) in 50 mL of water as a single bolus dose or as

four equally divided hourly doses. Urinary excretion of inorganic sulfate was measured at 24,

48, and 72 hours. Prior to dosing, the baseline excretion of inorganic sulfate (free form) was

measured several times for each individual. The normal baseline excretion of inorganic sulfate

ranged from 13 to 25 mmol/24 hours (1.3 to 2.4 g/24 hours). To calculate the amount of the

exogenous dose that was excreted, the individual baseline values were subtracted from the total

urinary inorganic sulfate. Over 72 hours, a mean of 53.4% of the single dose or 61.8% of the

divided dose was recovered in the urine. In general, at least two-thirds of the 72-hour sulfate

excreted appeared in the urine in 24 hours. The divided dose was fairly well tolerated, but the

single dose caused severe diarrhea. 

The excretion of inorganic sulfate in humans is dependent on the cation. Morris and Levy

(1983b) reported that orally administered magnesium sulfate in humans was absorbed less

completely and more variably than sodium sulfate. Seven male volunteers received 13.9 g of

MgSO4A7H2O (5.4 g sulfate) in four 1.4-g portions in 100 mL of water over a 4-hour period. 

Based on the concentration of free sulfate in 72-hour urine, at least 37% of the dose was

excreted. An average of 30.2% ± 17% of the sulfate was excreted in urine over 24 hours for

magnesium sulfate as compared with 43.5% ± 12% for sodium sulfate. There was high

intersubject variation. Compared to sodium sulfate administered in an identical fashion, the

magnesium salt was less bioavailable.

Bauer (1976) reported that when doses between 60 and 80 μCi 35S (as sodium sulfate) were

administered orally to eight humans, 80% was recovered in the urine at 24 hours. For

comparison, 86% of the same dose given intravenously was excreted in the urine in 24 hours.

The kidney regulates and maintains serum sulfate levels through a capacity-limited reabsorption

mechanism. In humans, the maximum rate of transport is 0.11 mM/min. If intestinal absorption

is slow or saturated, sulfates are eliminated in the feces. As a result, sulfates do not accumulate

in the body even after consumption of high levels (Morris and Levy 1983a, Cole and Scriver

1980).

5.0 HEALTH EFFECTS DATA

Data are available on the short- and long-term effects of sulfate in humans and animals. In

general, a laxative effect is the most common manifestation of exposure to high concentrations

of sulfate. The soft stool or diarrhea that results from sulfate is an osmotic diarrhea, i.e., one that

results when the osmolality of the intestinal contents exceeds that of the interstitial fluids. When

this occurs, water is drawn across the intestinal membrane into the lumen, increasing the

moisture content and volume of the fecal matter. This leads to an increased intestinal peristalsis

and evacuation of the intestinal contents. Poorly absorbed dissolved materials such as

magnesium sulfate, sorbitol, or lactulose are often associated with osmotic-induced diarrheas.

An osmotic-induced diarrhea ceases once the osmotically active gastrointestinal contents are

excreted (Stipanuk 2000). 

The osmotic diarrheal response to sulfate is influenced by the total temporal osmolyte load, as
Sulfate — February 2003 13

well as the sulfate concentration. For example, if water contains magnesium ion as well as

sulfate ion, the diarrheal response will be increased because both ions are osmotically active. 

This complicates interpretations of some of the ecological sulfate studies where data are reported

for sulfate concentrations but not for the presence of other drinking water constituents that may

be osmotically active. 

5.1 Human 

5.1.1 Short-Term Exposure Studies

Sulfate salts are known to have laxative properties in humans (Schofield and Hsieh 1983). A

dose of 15 g of magnesium or sodium sulfate will produce catharsis within 3 hours, but lower

doses can also produce this effect. For example, approximately 5 g of magnesium sulfate was

reported to cause significant laxative effects when administered in a dilute solution to a fasting

man (Fingl 1980). Cocchetto and Levy (1981) reported that a single dose of 8 g of anhydrous

sodium sulfate induced severe diarrhea lasting up to 24 hours in five human subjects. However,

the same amount of sodium sulfate taken at four equal hourly doses produced either no diarrhea

or mild diarrhea of short duration.

Humans appear to develop a tolerance to water containing high sulfate concentrations (Schofield

and Hsieh 1983). Although the rate at which acclimation occurs has not been determined, it is

generally considered to occur in adults within one to two weeks (U.S. EPA 1999b). No specific

data on the length of time necessary for humans to acclimatize to the cathartic effects of sulfates

were identified.

The sulfate salt is important in determining the extent and nature of any laxative effect. Morris

and Levy (1983b) reported that when humans were given the same millimolar dose of sulfate as

either magnesium or sodium sulfate, the magnesium sulfate induced more adverse effects,

ranging from upset stomach to diarrhea, than did sodium sulfate.

Chien et al. (1968) reported three cases of diarrhea in infants in Saskatchewan, Canada,

attributable to exposure to high sulfate concentrations in the water supply. In each case, local

well water with sulfate concentrations between 630 and 1,150 mg/L and a high total dissolved

solid concentration of 2,424 to 3,123 mg/L was used to prepare infant formulas. The total

dissolved solid concentrations reported in this study greatly exceeded the United States’

secondary standard for total dissolved solids of 500 mg/L.

When milk or water with low sulfate content, and presumably lower total dissolved solids,

replaced the local well water, recovery occurred (Chien et al. 1968). Diarrhea returned when the

original well water was re-introduced. The study authors concluded that waters with a sulfate

content higher than 400 mg/L were unsuitable for consumption by infants. Interpretation of this

study is limited by the number of the study subjects (n = 3) and by the lack of data on sulfate

concentration in and osmolarity of the infant formula.

In a case-control investigation to assess the association between infant diarrhea and ingestion of

water containing elevated sulfate levels, Esteban et al. (1997) reported that no significant

association existed between exposure to sulfate from tap water and subsequent diarrhea in
Sulfate — February 2003 14

infants. A total of 274 mothers of infants born in 19 South Dakota counties with high sulfate

concentrations in tap water were identified and interviewed using a telephone questionnaire

(n = 262) or in person (n = 12). The mothers were questioned on the frequency and consistency

of the infant=s bowel movements and on the amount of water that the infant drank in the previous

7 days. Diarrhea was defined as three or more loose stools in a 24-hour period. A sample of the

water used in the infant=s diet was also submitted by the mother and analyzed for sulfate. Two

hundred seventy-four infants were included in the study. Cases were defined as infants that

developed diarrhea (as identified by the mothers); controls were defined as infants that did not

develop diarrhea. 

The average sulfate concentration in drinking water for cases was 416 mg/L versus 353 mg/L for

controls. The corresponding median sulfate concentration for cases was 289 mg/L (range

0!1,271 mg/L); the median concentration for controls was 258 mg/L (range 0!2,787 mg/L). 

The median water intake for the controls was lower than for the cases (0.2 vs. 0.5 L/day). Mean

and median daily sulfate intake from water for all infants in the study was 29 and 17 mg/kg/day,

respectively. Mothers reported diarrhea in 19% of the infants living in households with sulfate

levels in tap water >500 mg/L and in 14% of infants living in households with sulfate levels

<500 mg/L. There was no significant correlation (OR = 1.4; 95% CI = 0.5!4.0) between the

incidence of diarrhea and the level of sulfate in water samples .

Heizer et al. (1997) examined bowel function in healthy adults following exposure to various

sodium sulfate concentrations in drinking water. In a single-dose study of six adults (three men

and three women), each subject received drinking water with sulfate concentrations of 0 or

1,200 mg/L for two consecutive 6-day periods. A fluid intake of 36 mL/kg/day was maintained

in these subjects. Stool mass, frequency, consistency, and mouth-to-anus appearance time for

colored markers were measured. When subjects received sulfate at 1,200 mg/L, mean stool mass

per 6-day pool period increased from 621 g to 922 g (p = 0.03). Mean stool mass per hour

increased from 4.8 g to 6.6 g (p = 0.03) with a change in sulfate concentration from 0 to 1,200

mg/L. However, stool frequency, consistency, and mouth-to-anus appearance time were not

significantly different for the high-sulfate water.

Heizer et al. (1997) also reported data from a multiple dose study in four subjects (two men and

two women). Each subject received drinking water with increasing sulfate concentrations of 0,

400, 600, 800, 1,000, and 1,200 mg/L over six consecutive 2-day periods. In this study, there

was a significant linear trend for decreasing mouth-to-anus marker appearance time with

increasing sulfate concentrations (p = 0.03). When the 10 subjects (4 subjects from the multipledose study and 6 subjects from the single-dose study reported above) were used to compare

effects of 0 mg/L and 1,200 mg/L sulfate, significant differences in stool consistency (p = 0.02)

and transit time (p = 0.03) were observed. However, none of the subjects reported diarrhea or

passed more than three stools per day. 

In order to determine the effects of high sulfate concentrations in transient populations (students,

visitors, hunters, etc.), the Centers for Disease Control (CDC), with funding from EPA (1999a),

conducted a study in adult human volunteers. The study was designed to determine if any

adverse effects would occur in persons suddenly changing drinking water sources from one with

little or no sulfate to one with high sulfate concentrations. A total of 105 participants were

randomly assigned to five sulfate-exposure groups and were exposed to sulfate in bottled water
Sulfate — February 2003 15

over a period of 6 days. The participants received water containing sulfate only for days 3

through 5 and were given sulfate-free bottled water for days 1, 2, and 6. Subjects were blinded

to the level of sulfate in the drinking water. The number of participants in each exposure

category varied: 0 mg/L (n = 24), 250 mg/L (n = 10), 500 mg/L (n = 10), 800 mg/L (n = 33), or

1,200 mg/L (n = 28). 

Several criteria were used to monitor whether the sulfate had a laxative effect. The subjects kept

track of the number of bowel movements they had on each day of the study. They were also

asked to rate the quality of their stools according to three definitions of diarrhea. Osmotic

diarrhea was defined as an increase in stool volume, diarrhea 1 was defined as paste-like or

liquid stools, and diarrhea 2 was defined as change in stool bulk and consistency. There were no

statistically significant differences in the mean number of bowel movements among the groups

on days 3, 4, 5, or 6; or in the mean number of bowel movements when days 3, 4, and 5 were

compared with days 1 and 2. There was also no apparent trend in the percentage of subjects that

reported diarrhea during the exposure period as opposed to the control period (days 1 and 2)

using any of the definitions of diarrhea.

The data were also evaluated using logistic regression analysis to determine the effects of sulfate

based on dose. The dose was calculated for each subject from the amount of water consumed, 

the amount of sulfate in drinking water, and the body weight of the participant. Using this

method, there were no statistically significant dose-response associations between sulfate dose

and reports of diarrhea (one-sided p = 0.099) using any of the three definitions. 

The authors also combined the incidence for diarrhea under any of the three definitions for the

lowest three dose groups (0, 250, and 500 mg/L) and compared it with the incidences of the 800

mg/L and 1,200 mg/L dose groups. There were no statistically significant differences between

groups for any of the three diarrhea categories. However, there was a dose-related trend for

increased stool volume (osmotic diarrhea) with increasing sulfate exposure when the three

groups were compared (9%, 15%, and 18%, respectively).

5.1.2 Long-Term Exposure Studies

Peterson (1951) analyzed the data from about 300 questionnaires that had been collected by the

North Dakota Department of Health as part of its routine monitoring of the mineral content of

groundwater supplies. The questionnaires had been distributed to private well owners along with

requests for samples of well water for analysis. The questionnaires solicited information on

odor, taste, effects on cooking, and laxative effects from the water. The questionnaires analyzed

by Peterson (1951) were a subset of about 2,500 submitted to the Department of Health. They

were selected because analytical data for the water were available and the questionnaire was

complete enough to be used for data analysis. Peterson (1951) plotted the concentration of

sodium sulfate and magnesium sulfate in the water against whether water use was associated

with a laxative effect. Both sodium and magnesium ions were present in most of the water

samples. He concluded that sulfate was likely to have a laxative effect when the concentrations

exceed 750 mg/L, but was unlikely to have such an effect at concentrations less than 600 mg/L. 

As the concentration of the magnesium in the water increased, the sulfate concentration that was

associated with a laxative response decreased.
Sulfate — February 2003 16

Moore (1952) analyzed data from 248 wells from the North Dakota Department of Health survey

(Peterson 1951 data). Questionnaires completed by the users of the wells provided a YES or NO

response for laxative effects for 176 of 248 wells. For 69 wells with positive responses for

laxative effects, the mean sulfate level was 1,250 mg/L and the median was 1,090 mg/L. For

107 wells with negative responses, the mean and median sulfate levels were 500 mg/L and 403

mg/L, respectively. When the data were separated into specific ranges, the percent of YES

responses for laxative effects was 22% (10/46) for wells with levels between 0 and 200 mg/L;

24% (9/37) for wells with levels between 200 and 500 mg/L; 33% (13/39) for wells with levels

between 500 and 1,000 mg/L; and 69% (37/54) for levels >1,000 mg/L. Moore (1952)

concluded that sulfate ion concentration is critical at 1,000 mg/L and at more than 2,000 mg/L is

almost certain to produce discernible physiological effects. For a combination of magnesium

and sulfate, effects are likely to occur when the total concentration exceeds 1,000 mg/L. Many

of the wells in this data set also contained high levels of total dissolved solids and magnesium. 

Similar results were obtained when Cass (1953) analyzed the data provided in the North Dakota

survey. 

5.2 Animal

5.2.1 Short-Term Exposure Studies

The oral LD50s of ammonium sulfate, sulfuric acid, and potassium sulfate in the rat are

3,000B4,000 mg/kg, 2,140 mg/kg (FASEB 1975), and 6,600 mg/kg (RTECS 2000), respectively. 

The oral LD50 of sodium sulfate in the mouse is 5,989 mg/kg (RTECS 2000).

Adams et al. (1975) supplied groups of three White Leghorn hens with drinking water containing

250 to 16,000 mg sulfate/L (as sodium or magnesium sulfate). At 16,000 mg/L, the hens

exhibited decreased body weight, decreased feed consumption, decreased egg production, and

increased water consumption. At this dose, mortality (100%) occurred by day 7 for hens

drinking water with magnesium sulfate, and by day 12 for hens drinking water with sodium

sulfate. Necropsy revealed focal necrosis of individual renal glomeruli, with uric acid

accumulation in both the kidney and gut. Similar, but less severe, histologic changes were seen

in hens receiving water at 4,000 mg/L for up to 3 weeks.

Paterson et al. (1979) administered drinking water containing 3,000 mg/L of added sulfate (as

either sodium sulfate or a 1:1 combination of both sodium and magnesium sulfate) for 28 days to

groups of 17 or 18 weanling pigs (7.7 to 8 kg). The control group (n = 16) received water

containing 320 mg/L sulfate. No significant changes (p > 0.05) in average daily weight gain or

feed/gain ratio were observed when the treated group was compared to controls. Fluid

consumption increased for both groups receiving the high concentration of sulfate in their water,

and stools were soft for these animals compared with controls.

Sulfate (sodium and magnesium sulfate in combination or independently) was administered to

young pigs at concentrations ranging from 600 to 1,800 mg/L in drinking water for 28 days.

Weight gain, feed consumption, water consumption, feed conversion, prevalence of diarrhea, and

evidence of common postweaning enteric pathogens were determined. Sulfate did not impair

performance or health of pigs. However, loose and watery stools appeared to be more prevalent

in the groups receiving 1,800 mg/L sulfate (both salts independently and in combination)
Sulfate — February 2003 17

compared to control, 600 mg/L, and 1,200 mg/L groups (Veenhuizen et al. 1992). Similar results

were observed in an earlier study by Anderson and Stothers (1978) in which groups of nine

young pigs given water containing 600 mg/L total solids as sodium sulfate displayed scouring

(soft stools), primarily during the first week of a 6-week experimental period.

Gomez et al. (1995) used neonatal piglets to study the effect of inorganic sulfate on bowel

function. Two experiments were conducted to evaluate the effect of high levels of inorganic

sulfate on the growth, feed intake, and feces consistency of piglets, and to determine the dose at

which at least 50% of piglets develop an osmotic diarrhea. In each experiment, 40 pigs with an

average age of 5 days were individually caged and reared with an automatic feeding device. 

Groups of 10 pigs were fed 1 of 4 liquid diets containing inorganic sulfate (anhydrous sodium

sulfate) at 0, 1,200, 1,600, or 2,000 mg/L (of diet) for an 18-day study, or 0, 1,800, 2,000, or

2,200 mg/L for a 16-day study. The levels of added sulfate did not affect (p > 0.05) the growth

of piglets or their feed intake. Whereas 1,200 mg sulfate/L had essentially no effect on feces

consistency, concentrations greater than 1,200 mg/L increased the prevalence of diarrhea. 

Concentrations greater than 1,800 mg/L resulted in a persistent diarrhea. The changes in feces

consistency suggest that the level of added dietary inorganic sulfate at which 50% of piglets

develop diarrhea is between 1,600 and 1,800 mg/L. Analysis of rectal swabs showed no

evidence of E. coli or rotavirus infection.

5.2.2 Long-Term Exposure Studies

In a 90-day subchronic study, Wurzner (1979) examined the effects of sulfate in drinking water

in Sprague-Dawley rats (25/sex/group). Treated animals received mineral waters containing low

(<10 mg/L), intermediate (280 mg/L), or high (1,595 mg/L) concentrations of sulfate. Control

animals were provided with tap water containing 9 to 10 mg/L sulfate. No information was

provided on the concentrations of minerals other than sulfate in the three different mineral

waters. No mortalities or effects on body weight, food consumption, food efficiency (a measure

of food intake versus body weight change), or water consumption were observed. No soft feces

or diarrhea were observed. No effects on hematology or serum chemistry (blood urea nitrogen,

glucose, triglycerides, cholesterol, total protein, and alkaline phosphatase activity) were

observed after 90 days. Organ weights were not affected, and no histologic changes were

observed at any tissue site. Five rats/sex/group continued treatment beyond the 90 days. Blood

urea nitrogen in the high-dose group tended to be decreased in both sexes, but this occurred only

after 6 months of treatment.

Digesti and Weeth (1976) supplied groups of four weanling Hereford-Angus heifers with

drinking water containing 110 to 2,500 mg/L sodium sulfate. After 90 days of dosing, no overt

toxicity was observed in any animals; feed consumption, water consumption, and growth were

not affected. Increased levels of methemoglobin and sulfhemoglobin were observed in the

animals consuming 1,250 and 2,500 mg/L sodium sulfate; this was attributed to the bacterial

reduction of sulfate to sulfide in the rumen. At 2,500 mg/L, renal filtration of sulfate was

increased by 37.7% and renal reabsorption was decreased by 23.7%.
Sulfate — February 2003 18

5.2.3 Reproductive and Developmental Studies

Three oral studies on reproductive and developmental effects were identified for sulfate. On the

basis of these studies, it appears that sulfate does not induce adverse reproductive or

developmental effects. 

Sodium sulfate was administered by gavage at a concentration of 2,800 mg/kg/day to pregnant

ICR/SIM mice on gestation days 8 to 12 (Seidenberg et al. 1986). There was no evidence of

maternal toxicity or increased resorption rate. Pup survival was 100%, and no adverse

developmental effects were observed. Neonatal birth weight was significantly increased in the

treated group compared with controls. 

Six groups of 10 female, randomly bred albino ICR mice were administered sodium sulfate in

drinking water at dose levels of 0 (distilled water control), 0 (sodium control), 625, 1,250, 2,500,

or 5,000 mg/L beginning 1 week prior to breeding (Andres and Cline 1989). The amount of

sodium in all groups, except the distilled water control, was kept constant by administering

sodium bicarbonate. Control mice, receiving only distilled water, consumed significantly less

(p < 0.05) than mice receiving sulfate treatments, and sodium-control mice drank significantly

more water (p < 0.05) than mice treated with sulfate. All mice were carried to term. No

differences were found in litter size, litter weaning weights, or gestational or lactational weight

gain of the dams among sulfate treatments. Histopathology evaluations were not performed. 

The authors concluded that water containing up to 5,000 mg/L sulfate is not toxic to the

gestating mouse.

Paterson et al. (1979) investigated the effects of water with a high sulfate content on swine and

their offspring. The pigs, 31 sows and 27 gilts of Hampshire × Yorkshire × Duroc breeding,

were randomly divided into three groups that received either tap water (320 mg sulfate/L) or

water with sodium sulfate added at 1,790 mg/L or 3,298 mg/L. The animals were given access

to these waters from prebreeding day 30 through lactation day 28. No significant differences in

gestation or lactation weight gain, number of pigs delivered, or average pig and litter birth

weights were reported. 

5.2.4 Cancer Studies 

In a study of the toxicity and carcinogenicity of nickel compounds (nickel hydroxide and nickel

sulfate) in Wistar rats, sodium sulfate (used as a control) did not appear to be tumorigenic

(Kasprazak et al. 1980). In this study, Wistar rats (100 males and 10 females) were injected

intramuscularly every other day for 4 weeks with 0.7 mg sodium sulfate/rat (approximately 2 mg

SO4

2-/kg in aqueous solution at pH 5.6). After 8 months, no tumors were observed in either the

sodium sulfate or nickel sulfate treated rats. However, the value of this study in assessing the

carcinogenic effects of sulfate ingestion is limited because of the route of exposure, the duration

of the study, and the nonstandard protocol.
Sulfate — February 2003 19

6.0 ORGANOLEPTIC PROPERTIES

Water contaminated with sulfates may have an unpleasant taste. Characteristics such as taste,

odor, and color, often referred to as organoleptic properties, are not used by EPA for developing

primary water standards. Organoleptic properties, however, can be used in the establishment of

secondary drinking water standards.

EPA established a secondary drinking water standard of 250 mg/L for sulfate in 1984 based on

taste properties (U.S. EPA 1984). This value was adopted from the Public Health Service

Drinking Water Standards (PHS 1962). Secondary standards are not enforceable by the Federal

Government; they are recommended to States as reasonable goals for contaminants, but there is

no obligation for the States to reach these goals. 

There is a paucity of actual experimental data available on the taste threshold for sulfate. Taste

threshold concentrations for several common sulfate salts have been reported. The taste

thresholds varied depending on the type of salt: 170-370 mg/L sulfate as sodium sulfate, 180-640

mg/L as calcium sulfate, and 320-480 mg/L as magnesium sulfate (Lockhart et al. 1955, as cited

in PHS 1962).

The detection of taste differs from the perception of a taste as unpleasant. Accordingly, the

results reported by Heizer et al. (1997) on the response of 10 subjects to sulfate in drinking water

are of interest. After completion of the exposure component of this study, 8 of the 10 subjects

rated the taste of 1,200 mg/L sulfate, as sodium sulfate, as neutral to slightly unpleasant. One

subject rated the water as moderately unpleasant and another as very unpleasant. This study

indicates there is variability in the response to the taste of sulfate, and the threshold for detecting

an unpleasant taste is apparently above the threshold of taste.

In the study of the laxative effects of sulfate that was conducted for EPA by CDC (U.S. EPA

1999a), the subjects were asked if the smell or taste of the water was different from that which

they usually consumed. All subjects received sulfate-free control water on days 1, 2, and 6 of

the study and either the sulfate-free water (controls) or a sulfate-containing water on days 3, 4,

and 5 of the study. There was a definite increase in the number of subjects who thought that the

water tasted differently on days 3, 4, and 5 for the 800 and 1,200 mg/L concentrations, with 79%

and 82% reporting a difference in taste, respectively. Average daily water consumption also

decreased in these same groups on days 3, 4, and 5 when compared with intakes on days 1, 2,

and 6. About half of the participants receiving the 250 and 500 mg/L concentrations reported a

difference in taste (57% and 50% respectively) on the days when they were exposed to sulfate. 

Water consumption showed a downward trend over this same period as well. Twenty-five

percent of the control group also reported that there was a difference in the taste of the water. 

For this group, there was no downward trend in water consumption across the 3-day exposure

period.

The ability to taste differs among individuals, as well as in the same individual at different times. 

Temperature and the presence of other dissolved solids in the water also influence taste. Given

the expected variability in taste, as well as the results in Heizer et al. (1997), the U.S. EPA

secondary maximum contaminant level (SCML) of 250 mg/L should be adequately protective

for adverse sulfate taste effects.
Sulfate — February 2003 20

7.0 CHARACTERIZATION OF HAZARD AND DOSE-RESPONSE

7.1 Hazard Characterization

Some data are available that report human responses to sulfate. Data include those from

controlled settings (i.e., studies and experimental trials) and uncontrolled settings (i.e., case

studies from areas with high sulfate concentrations in the drinking water). Most of the available

data are based on short-term exposure and were obtained from controlled studies. 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. In animals, data on

reproductive and developmental effects are available for short-term and long-term exposures to

sulfate. There are limited data on the potential carcinogenic effects of sulfate.

The available data demonstrate that sulfate induces a laxative effect following acute exposures to

relatively high concentrations (Anderson and Stothers 1978, Fingl 1980, Schofield and Hsieh

1983, Stephen et al. 1991, Cochetto and Levy 1981, U.S. EPA 1999a, Gomez et al. 1995, Heizer

et al. 1997). The concentrations of sulfate that induced these effects varied, but all occurred at

concentrations >500 mg/L. 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 example, magnesium sulfate exerts a stronger laxative effect than sodium sulfate. This

likely occurs because magnesium sulfate is absorbed less completely than sodium sulfate and has

a more pronounced effect on the osmolarity of the intestinal contents (Morris and Levy 1983b). 

Additionally, a single dose of sulfate that produces a laxative effect does not have the same

effect when divided and administered in intervals, i.e., a single dose produced severe diarrhea,

whereas divided doses produced only mild or no diarrhea (Cochetto and Levy 1981). 

Chronic and subchronic exposures to high concentrations of sulfate do not appear to produce the

same laxative effect as seen in acute exposures. In a 90-day study using Sprague-Dawley rats,

Wurzner (1979) did not observe soft feces or diarrhea in rats administered mineral waters

containing up to 1,595 mg/L of sulfate. However, earlier reports indicate that chronic exposure

to high sulfate concentrations in drinking water resulted in laxative effects in humans (Peterson

1951, Moore 1952, Cass 1953). These reports used data that were based on questionnaires,

which may be subject to bias. For example, the questionnaire included an inquiry about the

laxative effect that requested a YES or NO response. This type of question is subject to the

respondent=s interpretation of what constitutes a laxative effect. In addition, sulfate was

probably not the only contaminant found in the drinking water. Chronic exposure to sulfate may

not have the same laxative effect as an acute exposure because humans appear to develop a

tolerance to drinking water with high sulfate concentrations (Schofield and Hsieh 1983). It is

not really known when this acclimation occurs; however, in adults, acclimation is thought to

occur between one to two weeks (U.S. EPA 1999b).

No adverse developmental effects were observed following the administration of 2,800

mg/kg/day of sulfate to pregnant ICR/SIM mice on gestation days 8 to 12 (Seidenberg et al.

1986). No reproductive effects were observed following the ingestion of drinking water

containing up to 5,000 mg/L of sulfates by ICR/SIM mice (Andres and Cline 1989) or 3,298

mg/L of sulfates by Hampshire × Yorkshire × Duroc pigs (Paterson et al. 1979). Based on these

studies, sulfate does not appear to be a reproductive or a developmental toxicant.
Sulfate — February 2003 21

No tumors were observed after 8 months in a study using Wistar rats injected intramuscularly

with sodium sulfate every other day for 4 weeks (Kasprazak et al. 1980). Because of the shortterm observation period, the route of exposure, and the experimental protocol, it is not possible

to draw conclusions on the potential carcinogenicity of sulfate. Because of the limited data, U.S.

EPA/Office of Water (1993) has classified sulfate as Group D–not classified as to human

carcinogenicity. This category is reserved for contaminants with inadequate evidence to support

a determination on carcinogenicity.

7.2 Characterization of Organoleptic Effects

The ability to taste differs among individuals, as well as for the same individual at different

times. The temperature of the water, the companion ion, and the presence of other dissolved

solids impact the taste sensation. There is also a difference between the concentrations that

impart a taste to water and those that are classified as causing an unpleasant taste. Each of these

factors makes it difficult to define a taste threshold for sulfate. 

The experimental data on the organoleptic properties of sulfate in drinking water are limited. No

studies were identified that were conducted using standard taste-testing procedures. In the study

by Heizer et al. (1997), 8 of 10 subjects rated the taste of drinking water containing 1,200 mg/L

sulfate as neutral to only slightly unpleasant. Two subjects classified the taste as moderately to

extremely unpleasant. In the study conducted by CDC for EPA (1999a), about 50% of the

participants could not distinguish between the taste of sulfate-free water and water containing

either 250 mg/L sulfate or 500 mg/L sulfate. Even when the water contained 1,200 mg/L sulfate,

20% of the participants could not detect the taste. 

Given the variability in the ability of consumers to identify a taste in water that contains sulfate,

the present SMCL of 250 mg/L appears to be adequately protective of the aesthetic taste

properties of drinking water containing sulfate.

7.3 Dose-Response Characterization 

Although several studies (Peterson 1951, Moore 1952, Cass 1953) have examined the effects of

long-term exposure of humans to sulfate in drinking water, none of them can be used to derive a

dose-response characterization. These studies utilized data collected from the North Dakota

Department of Health Survey (Moore 1952). An increasing trend was observed in persons

reporting laxative effects as sulfate concentrations increased (i.e., 22%, 24%, 33%, and 69% for

sulfate concentrations of 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 (Wurzner 1979) or heifers (Digesti and Weeth 1976)

following long-term exposure to sulfate in drinking water. Consequently, these studies cannot

be used for a dose-response characterization. 
Sulfate — February 2003 22

Because sulfate appears to exert its laxative effect with short-term exposures rather than longterm exposures, several short-term exposure studies were reviewed. Three short-term studies

were identified that evaluated the effect of various sulfate concentrations on bowel function in a

controlled environment: two in humans and one in animals. In the multiple-dose study by

Heizer et al. (1997), sulfate concentrations of 0, 400, 600, 800, 1,000, or 1,200 mg/L were given

to four subjects (two men and two women) for six consecutive 2-day periods (2 days per

concentration). A significant trend was observed for a decreasing mouth-to-anus markerappearance time of chemical markers with increasing sulfate concentration. For a single-dose

study by the same researchers, six adults (three men and three women) received drinking water

with sulfate concentrations of 0 or 1,200-mg/L for two consecutive 6-day periods. Statistically

significant increases in mean stool mass per 6-day pool and in mean stool mass per hour were

observed in the 1,200-mg/L dose group. However, none of the subjects reported frank diarrhea.

CDC conducted a study for EPA (1999a) that examined the effect of sudden changes in sulfate

levels in drinking water in 105 subjects. The participants received water containing sulfate at 0,

250, 500, 800, or 1,200 mg/L from day 3 through day 5, and were given sulfate-free bottled

water for days 1, 2, and 6. There were no statistically significant differences in the mean number

of bowel movements in any group or a dose-response relationship between sulfate dose and

reports of diarrhea (one-sided p = 0.099). However, when the diarrhea incidence data for the

lowest three dose groups were compared to the incidence for the 800 mg/L and 1,200 mg/L dose

groups, there was a dose-related trend for increased stool volume (osmotic diarrhea) when the

three groups were compared (9%, 15%, and 18%). The dose-related trend, however, was not

statistically significant.

Neonatal piglets were exposed to various concentrations of sulfate to simulate the effect of

inorganic sulfate on the bowel function in infants (Gomez et al. 1995). No diarrhea was

observed in any of the piglets at 0 and 1,200 mg/L concentrations; however, concentrations

greater than 1,200 mg/L resulted in an increased prevalence of diarrhea, and concentrations

greater than 1,800 mg/L resulted in persistent, nonpathogenic diarrhea.

These studies as a group suggest that there is a risk for a laxative-type response to sulfate in

drinking water at concentrations greater than 1,000 mg/L (U.S. EPA 1999a, Heizer et al. 1997,

Moore 1952). The observed effect is a response to the net osmolarity 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 by the temporal pattern of sulfate ingestion. 

The laxative effect of sulfate can be manifest as an increase in stool mass, increased stool

volume, increased stool moisture, decreased intestinal transit time, and/or frank diarrhea. Frank

diarrhea did not occur in either of the controlled human studies of sulfate exposure (U.S. EPA

1999a, Heizer et al. 1997). There was merely a slight increase in stool mass or stool volume 

with sulfate concentrations of 800 to 1,200 mg/L.

At this time, it is not possible to characterize a dose-response relationship for laxative effects due

to short- or long-term exposure to sulfate. A Centers for Disease Control and Prevention (CDC)

panel favored a health advisory for situations where sulfate levels in drinking water are greater

than 500 mg/L (U.S. EPA 1999b). The most sensitive endpoint was considered by the panelists

to be osmotic diarrhea. The panelists concluded that the existing literature supports restricting

sulfate exposure, especially for infants, when the advisory value of 500 mg/L is exceeded. The
Sulfate — February 2003 23

panelists referred to the study by Chien et al. (1968), which found that sulfate levels $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. In

fact, the total dissolved solid concentration of the water used to prepare infant formulas was high

(2,424 to 3,123 mg/L) and in two cases contained substantial quantities of magnesium (124 and

130 mg/L). The CDC panel concluded that 500 mg/L seemed to be a safe level for sulfate

ingestion, as 500 mg/L was shown to be safe in all studies. For comparison, the osmolarity of

500 mg/L sulfate as sodium sulfate is 15.6 mOsmol/L whereas the osmolarity of the ions (Na,

K, Cl, and citrate) in Pedialyte, a preparation used to treat diarrhea and replenish electrolytes in

infants, is 110 mOsmol/L. When the dissolved sugars in Pedialyte are included the osmolarity 

increases to 250 mOsmol/L. 

The experimental data on the organoleptic properties of sulfate in drinking water are limited. In

a study by Heizer et al. (1997), 8 of 10 subjects rated the taste of drinking water containing 1,200

mg/L sulfate as neutral to slightly unpleasant. Only two classified the taste as moderately to

extremely unpleasant. In the study conducted by CDC for EPA (1999a), approximately 50% of

the participants stated that water containing 250 mg/L sulfate and 500 mg/L sulfate tasted

different from the sulfate-free control water.

Given the apparent variability in consumers’ ability to identify a taste in water that contains

sulfate, the present SMCL of 250 mg/L appears to be adequately protective of the esthetic taste

properties of drinking water containing sulfate. The health-based advisory value of 500 mg/L

will protect against sulfate’s laxative effects in the absence of high concentrations of other

osmotically active chemicals in the water. In situations where the water contains high

concentrations of total dissolved solids and/or other osmotically active ions, laxative-like effects

may occur if the water is mixed with concentrated infant formula or powdered nutritional

supplements. In such situations, an alternate low-mineral-content water source is advised. 

Infants are more susceptible to diarrheal water loss than adults because of differences in

gastrointestinal structure and function.
Sulfate — February 2003 24

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