The Risk Assessment Information System

Toxicity Profiles

Formal Toxicity Summary for SULFATE

NOTE: Although the toxicity values presented in these toxicity profiles were correct at the time they were produced, these values are subject to change. Users should always refer to the Toxicity Value Database for the current toxicity values.

EXECUTIVE SUMMARY
1. INTRODUCTION
2. METABOLISM AND DISPOSITION
3. NONCARCINOGENIC HEALTH EFFECTS
3.1 ORAL EXPOSURES 3.2 INHALATION EXPOSURES 3.3 OTHER ROUTES OF EXPOSURE 3.4 TARGET ORGANS/CRITICAL EFFECTS
4. CARCINOGENICITY
5. REFERENCES

JUNE 1991

Prepared by: Cheryl Bast, Chemical Hazard Evaluation and Communication Group, Biomedical and Environmental Information Analysis Section, Health and Safety Research Division, Oak Ridge National Laboratory*, Oak Ridge, Tennessee.

Prepared for: Oak Ridge Reservation Environmental Restoration Program.

*Managed by Martin Marietta Energy Systems, Inc., for the U.S. Department of Energy under Contract No. DE-AC05-84OR21400.

EXECUTIVE SUMMARY

The sulfate ion, SO4, is one of the major anions occurring in natural waters (Daniels, 1988). The majority of sulfates are soluble in water with the exception of lead, barium, and strontium sulfates. Thus, dissolved sulfate is considered to be a permanent solute of water (WHO, 1984a).

The major health effect observed with sulfate ingestion is laxative action (Daniels, 1988; NAS, 1977), and the cation associated with the sulfate appears to have some effect on the salt's potency as a laxative (Daniels, 1988). Sulfate itself slowly penetrates mammalian cellular membranes and is rapidly eliminated through the kidneys (WHO, 1984a). Pursuant to the Safe Drinking Water Act, the U.S. EPA has proposed Maximum Contaminant Level Goals of either 400 or 500 mg/L to protect infants (based on Chien et. al., 1968; Peterson, 1951; and Moore, 1952), and has identified a LOAEL (Lowest-Observed-Adverse-Effect-Level) of 630 mg/L based on diarrhea in infants receiving formula made with high-sulfate water (U.S. EPA, 1990). The Drinking Water Standards of the U.S. Public Health Service recommend that sulfate in water should not exceed 250 mg/L, except when no more suitable supplies are or can be made available.

Sulfates can contribute to an undesirable taste in water. The taste threshold for the sulfate ion in water is 300-400 mg/L (NAS, 1977), and a guidance value of 400 mg/L based on aesthetic quality has been suggested (WHO, 1984b). The current U.S. EPA national Secondary Maximum Contaminant Level for sulfate, based on organoleptic effects, is 250 mg/L (U.S. EPA, 1990).

No inhalation, or developmental toxicity data were available, and no carcinogenicity data were located.

1. INTRODUCTION

The sulfate ion, SO4, is one of the major anions occurring in natural waters (Daniels, 1988). The majority of sulfates, with the exception of lead, barium, and strontium sulfates, are soluble in water (WHO, 1984a). Sulfate may be reduced to sulfide, volatilized to the air as H2S, precipitated

as an insoluble salt, or incorporated into living organisms (WHO, 1984a).

Sulfates are used for a variety of commercial purposes, including sulfuric acid for the steel and metal industries, as a reagent in manufacturing processes, and as products such as copper sulfate, which is used as a fungicide and algicide (U.S. EPA, 1990).

Sulfate occurs naturally in soils, sediments, and rocks (U.S. EPA., 1990). Sulfates are discharged into surface waters in the atmospheric fallout from coal-fired power plants, and from the metallurgical roasting process. Also, sulfur trioxide, produced by the photolytic or catalytic oxidation of sulfur dioxide, combines with water vapor to form sulfuric acid, which is precipitated as acid rain or snow (WHO, 1984a). Additionally, sulfate is emitted by diesel engines (Pierson and Brachaczek, 1983).

A 1969 community water study reported sulfate to be present in 645 of 658 groundwater supplies sampled at concentrations ranging from 1 to 480 mg/L (mean 43 of mg/L). Sulfate was present in all 106 surface water supplies sampled at concentrations ranging from 2 to 358 mg/L (mean 49 of mg/L). (U.S. EPA., 1990). A rural water survey, conducted in the late 1970s, reported that sulfate was present in 271 of 494 groundwater supplies with a range of 10 to 1000 mg/L (mean of 98 mg/L). In surface water, sulfate was detected in 101 of 154 samples, and ranged from 15 to 321 mg/L (mean of 53 mg/L) (U.S. EPA., 1990).

EPA reported ambient atmospheric sulfate levels to range from 0.2 to 199.4 ug/m3 (U.S. EPA., 1990). The measurements were taken from 1980 to 1986 in 54,000 samples from 381 sites. The range of mean ambient air levels from these sites was reported to be 1.4 to 20 ug/m3.

2. METABOLISM AND DISPOSITION

The sulfate ion is poorly absorbed from the human intestine (WHO, 1984a); however, some absorption of the component ions of sulfate salts does occur (Daniels, 1988). Sulfates have been shown to increase the absorption of fluoride from the rat intestinal tract. Sulfate is important in metabolism as a moiety that is conjugated to many metabolites or foreign substances, thereby increasing their water solubility and elimination (Daniels, 1988). Sulfate itself slowly penetrates mammalian cellular membranes and is rapidly eliminated through the kidneys (WHO, 1984a).

3. NONCARCINOGENIC HEALTH EFFECTS

3.1. ORAL EXPOSURES

3.1.1. Acute Toxicity

The major health effect observed following sulfate ingestion is laxative action (Daniels, 1988; NAS, 1977), and the cation associated with the sulfate anion appears to have some effect on the salt's potency as a laxative (Daniels, 1988). Calcium sulfate, for example, is much less potent than magnesium sulfate or sodium sulfate. This may be due to the laxative properties of the cations themselves or from differences in solubility products of the salts (Daniels, 1988).

The mechanism by which sulfate ions induce laxative effects is complex and poorly understood. However, retention of excess fluid in the intestinal lumen and increased motor activity in the intestinal tract appear to be involved. It may be that poorly absorbed, soluble ions exert an osmotic pressure that causes retention of fluid in the intestinal lumen, and this increase in bulk indirectly stimulates intestinal transit. In addition to osmotic effects, the sulfate ion may increase the fluid volume of the intestinal tract by decreasing water absorption in the small intestine and by stimulating increases in the secretion of pancreatic, gastric, and intestinal fluids. It is unknown if these effects are caused directly by the ion or by the ion-stimulated release of hormones such as cholecystokinin (Daniels, 1988).

Infants appear to be more sensitive to the laxative action of sulfate than adults. Infants, 5 to 12 months old, that were given formulas prepared with water containing 630 to 1150 mg sulfate/L developed diarrhea shortly after ingestion of the formula (Chien et. al., 1968). The effect was reversible after the use of high sulfate water was discontinued. Similar effects have been observed in adults; however, adults are able to acclimate to the high sulfate levels in a short period of time (U.S. EPA., 1990). Results of a questionnaire sent to North Dakota residents indicate that laxative effects increased at sulfate levels above 500 mg/L. At sulfate concentrations exceeding 1000 mg/L, the majority of respondents indicated a laxative effect (Peterson, 1951; Moore, 1952).

Pursuant to the Safe Drinking Water Act, the U.S. EPA has proposed Maximum Contaminant Level Goals of either 400 or 500 mg/L to protect infants (based on Chien et. al., 1968; Peterson, 1951; and Moore, 1952), and has identified a LOAEL (Lowest-Observed-Adverse-Effect-Level) of 630 mg/L based on diarrhea in infants receiving formula made with high-sulfate water (U.S. EPA, 1990). The Drinking Water Standards of the U.S. Public Health Service recommend that sulfate in water should not exceed 250 mg/L, except when no more suitable supplies are or can be made available. The World Health Organization, in the European Standards for Drinking Water, also set a sulfate limit of 250 mg/L (NAS, 1977). The Canadian guideline for the maximum acceptable concentration of sulfate in drinking water is 500 mg/L (U.S. EPA., 1990). The U.S. Army has set a standard of 100 mg sulfate/L for personnel in arid climates who consume up to 15 liters of water per day, and the Army standard for soldiers serving under less strenuous conditions, consuming 5 liters of water per day, is 100 mg/L (U.S. EPA., 1990).

Sulfates can contribute to an undesirable taste in water. The taste threshold for the sulfate ion in water is 300-400 mg/L (NAS, 1977), and a guidance value of 400 mg/L based on aesthetic quality has been suggested (WHO, 1984b). The current U.S. EPA Secondary Maximum Contaminant Level (SMCL) for sulfate, based on organoleptic effects, is 250 mg/L (U.S. EPA, 1990).

3.1.2. Subchronic Toxicity

Information on the oral, subchronic toxicity of sulfate in humans and animals is unavailable.

3.1.3. Chronic Toxicity

Information on the oral, chronic toxicity of sulfate in humans and animals is unavailable.

3.1.4. Developmental and Reproductive Toxicity

Information on the developmental and reproductive toxicity of sulfate in humans and animals is unavailable.

3.1.5. Reference Dose

No reference dose has been derived for sulfate; however, a LOAEL of 630 mg sulfate/L has been identified based on diarrhea in infants receiving formula made with high-sulfate water (U.S. EPA., 1990).

3.2. INHALATION EXPOSURES

3.2.1. Acute Toxicity

The sulfate ion is not a respiratory irritant; therefore, sulfate salts vary widely in irritant potency dependent on the conjugant (Amdur, 1986).

3.2.2. Subchronic Toxicity

Information on the inhalation, subchronic toxicity of sulfate in humans and animals is unavailable.

3.2.3. Chronic Toxicity

Information on the inhalation, chronic toxicity of sulfate in humans and animals is unavailable.

3.2.4. Developmental and Reproductive Toxicity

Information on the developmental and reproductive toxicity of sulfate in humans and animals is unavailable.

3.2.5. Reference Concentration

No reference concentration has been derived for sulfate.

3.3. OTHER ROUTES OF EXPOSURE

Information on other routes of exposure were unavailable.

3.4. TARGET ORGANS/CRITICAL EFFECTS

3.4.1. Oral Exposures

3.4.1.1. Primary Target: Gastrointestinal system.

The symptom is a laxative effect after ingestion of drinking water containing sulfates (Daniels, 1988; NAS, 1977; WHO, 1984), and children appear to be more sensitive than adults (U.S. EPA., 1990). Adults rapidly acclimate to the laxative effects of sulfates; however, it is unknown how rapidly this adaptation is acquired or lost (Daniels, 1988; U.S. EPA., 1990).

3.4.1.2. Other Target: Taste threshold.

Organoleptic taste thresholds are 200-500 mg/L for sodium sulfate, 250-900 mg/L for calcium sulfate, 400-600 mg/L for magnesium sulfate, and 300-400 mg/L for the sulfate ion in water (NAS, 1977; WHO, 1984).

4. CARCINOGENICITY

Data are presently unavailable to determine the carcinogenic potential of sulfate.

5. REFERENCES

Amdur, M.O. Air Pollutants. In: "Casarett and Doull's Toxicology: The Basic Science of Poisons." C.D. Klassen, M.O. Amdur, and J. Doull, Eds. Macmillan Publishing Company, New York. 1986. P. 810.

Chien, L., H. Robertson, and J.W. Gerrard. 1968. Infantile gastroenteritis due to water with high sulfate content. Can. Med. Assoc. J. 99:102-104. (Cited in: Federal Register. 1990. Vol. 55. No. 143. 30382-30383).

Daniels, J.I., Ed. 1988. Evaluation of Military Field-Water Quality. Volume 4. Health Criteria and Recommendations for Standards. Part 1. Chemicals and Properties of Military Concern Associated with Natural and Anthropogenic Sources. AD UCRL-21008 Vol. 4, Part 1.

Moore, E.W. 1952. Physiological Effects of the Consumption of Saline Drinking Water, in A Progress Report to the 16th Meeting of Subcommittee on Water Supply of the Committee on Sanitary Engineering and Environment. (National Academy of Sciences, Washington, DC). (Cited in: Federal Register. 1990. Vol. 55. No. 143. 30382-30383).

National Academy of Sciences (NAS). 1977. Drinking Water and Health. pp. 425-428.

Peterson, N.L. 1951. Sulfates in drinking water. Off. Bull. N.D. Water Sewage Works. 18 (10/11)11. (Cited in: Federal Register. 1990. Vol. 55. No. 143. 30382-30383).

Pierson, W.R. and W.W. Brachaczek. 1983. Particulate matter associated with vehicles on the road. II. Aerosol Sci. Technol. 2: 1-40.

U.S. EPA. 1990. National Primary and Secondary Drinking Water Regulations; Synthetic Organic Chemicals and Inorganic Chemicals. Federal Register. Vol. 55. No. 143. 30370.

World Health Organization (WHO). 1984a. Guidelines for Drinking Water Quality. Vol. 2. Health Criteria and Other Supporting Information.

World Health Organization (WHO). 1984b. Guidelines for Drinking Water Quality. Vol. 1. Recommendations.

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