Water Fluoridation Additives

Introduction

The fact that fluoride occurring naturally in some drinking water supplies prevented tooth decay was discovered in the 1930s. After further years of study a safe optimal level of fluoride was determined and the first communities began to add fluoride to their drinking water for tooth decay prevention in 1945. Since that time, the effectiveness and safety of fluoridation have been analyzed by numerous studies and reviewed repeatedly by expert scientific groups over the past 60 years. Water fluoridation at optimal levels for oral health is safe, healthy, and effective in reducing tooth decay. The safety of water fluoridation at optimal levels (between 0.7 and 1.2 mg/L) has been documented extensively by scientific and public health organizations using thorough review of the scientific literature and expert panels (e.g., U.S. Public Health Service, National Research Council, World Health Organization, Institute of Medicine, and the University of York Center for Research Dissemination).

Community water systems in the United States use one of three additives for water fluoridation, based on cost of product, product-handling requirements, space availability, and equipment.

• Fluorosilicic acid: an aqueous solution used by most water fluoridation programs in the United States. Fluorosilicic acid is also referred to as hydrofluorosilicate, FSA, or HFS.
   
• Sodium fluorosilicate: a dry additive, dissolved into a solution before being added to water.
   
• Sodium fluoride: a dry additive, typically used in small water systems, dissolved into a solution before being added to water.

Sources of Fluoride Additives

FSA has been used for water fluoridation since the early 1950s, and has long been the predominant additive used for water fluoridation in the United States. Since the early 1980s, most fluoride additives used in the United States have been derived from the FSA produced as a co-product in the manufacture of phosphate fertilizer. This source is used because of the favorable cost and high purity of FSA.

The phosphate fertilizer manufacturing process begins with apatite rock, a limestone mineral with high phosphate and fluoride content, which is refluxed (heated) with sulfuric acid to produce a phosphoric acid-gypsum (calcium sulfate-CaSO4) slurry. Hydrogen fluoride (HF) gas, and silicon tetrafluoride (SiF4) are captured by vacuum evaporators and then condensed to FSA with a nominal solution concentration of 23%, with the remainder being water.

A minor source of FSA (approximately 5%) is produced by acidifying calcium fluoride (fluorite) with sulfuric acid to generate hydrogen fluoride, and then adding silicate (sand). Less than 1% of the FSA is derived from hydrogen fluoride etchings of silicon chips.

The dry additives sodium fluorosilicate and sodium fluoride are predominantly derived from FSA. FSA can be partially neutralized by either table salt (sodium chloride) or caustic soda to obtain sodium fluorosilicate. If sufficient caustic soda is added to completely neutralize the fluorosilicate, then the resulting product is sodium fluoride. A small percentage, less than 10% of the sodium fluoride used in the United States, is produced by mixing caustic soda with hydrogen fluoride.

Regulatory Purview on Additives

Almost all of the more than 40 water treatment additives that may be used at the water plant are toxic to humans in their concentrated form, e.g., chlorine gas used for disinfection. Questions sometimes arise regarding the toxicity, purity, and risk to humans from adding fluoride additives to drinking water. The U.S. Environmental Protection Agency (EPA) and the U.S. Food and Drug Administration (FDA) have a 1979 Memorandum of Agreement specifying that the EPA has purview over safe community drinking water in accordance with the Safe Drinking Water Act, and the FDA has purview over bottled water as a consumer beverage (Federal Register, Volume 44, No. 141, July 20, 1979). In addition, all additives used at a water treatment facility must meet strict quality standards. All of the additives used in drinking water treatment are subject to a system of standards, testing, and certificates by the American Water Works Association (AWWA) and the National Sanitation Foundation/American National Standards Institute (NSF/ANSI). Both of these entities are nonprofit, nongovernmental organizations.

AWWA and NSF International are standards used to manage the water quality delivered to consumers. The standards are consistent with practices by countries that have established ‘Guideline Values’ for substances that may enter the drinking water supply. A good reference on the practices by governmental authorities in various countries to provide quality assurance of drinking water treatment chemicals and the context to the AWWA and NSF International standards and practices is presented in an analysis by the Australian Drinking Water Treatment Chemical Working Party of the National Health and Medical Research Council at http://www.nhmrc.gov.au/publications/synopses/_files/watergde.pdf. (PDF–746KB)

EPA Regulatory Criteria for Fluoride Additives

The EPA sets standards for drinking water because its regulatory purview concerns the Maximum Contaminant Level (MCL) concentrations of various organisms or substances already in the source water or that are added to water during treatment, based on health effects resulting from drinking water consumption.

Because fluoride sometimes is naturally present in water at much higher levels than that added to community systems for the prevention of tooth decay (0.7 – 1.2mg/L), the EPA has conservatively established a Maximum Contaminant Level for fluoride of 4.0 mg/L ( parts per million), The EPA has not established an MCL for silicates, because there are no recognized health concerns, but NSF International Standard 60 has a Maximum Allowable Level of 16 mg/L (for sodium silicates as corrosion control agents), primarily for turbidity reasons. NSF International tests have shown the silicates from fluoride additives in the water samples to be well below these levels.

AWWA Standards

The AWWA sets the minimum requirements for a product’s design, installation, performance, and manufacturing.The AWWA standards for fluoride additives are ANSI/AWWA B-701-06 (sodium fluoride), ANSI/AWWA B702-07 (sodium fluorosilicate) and ANSI/AWWA B703-08 (FSA). AWWA’s standards are prepared by its Fluoride Standards Committee and are reviewed and updated at least every 5 years. AWWA standards stipulate product quality testing requirements and verification.

NSF International Standards

The NSF/ANSI standards 60 and 61 limit a chemical or product’s contribution of contaminants to drinking water applications. Standards 60 and 61 provide for product purity and safety assurance that aim to prevent adding harmful levels of contaminants from water treatment additives. Forty-six states have laws or regulations requiring product compliance with Standards 60 and 61. NSF/ANSI standards 60 and 61 were developed by a consortium of associations, including NSF International International, the AWWA, the ANSI, the Association of State Drinking Water Administrators, and the Conference of State Health and Environmental Managers. This consortium prepared Standards 60 and 61 in response to a competitive request for proposals by the EPA, which sought a basis to establish minimum requirements for controlling potential adverse effects from products added to water for its treatment. The standards replaced the former EPA Additives Advisory Program.

Compliance with the NSF/ANSI standards is provided by independent verification entities including NSF International International and Underwriters Laboratories. The independent certification entities must meet the criteria in the NSF/ANSI standard. Tests on the fluoride additives by the independent certification entities include the 11 regulated metal compounds that have an EPA MCL. For a product (e.g., FSA) to meet certification standards, regulated impurities at the tap (in the home) must not have a concentration that is more than 10% of the MCL.

Measured Levels of Impurities

As a requirement of NSF International 60, fluoride additives are analyzed for more than 13 impurities that have been identified as having the potential to occur including arsenic, lead, and radionuclides and verification on compliance with NSF International 60 must be certified. NSF International presents a detailed fact sheet on the documented quality of fluoride additives* (PDF–74KB) based on separate product samples analyzed in the 2000 to 2006 time period. Some consumers have raised questions concerning arsenic in drinking water. According to the NSF International quality testing, 57% of all samples did not have detectable levels of arsenic, and the average arsenic content that a consumer would experience at a maximum dosage of 1.2 mg/L of fluoride additive over a year would be 1.2% of the EPA allowable criteria for arsenic consumption in water of 10 parts per billion.

The typical U.S. consumer consumes less than the maximum dosage, and thus would be exposed to less than 1% of the EPA allowable criteria. This was also independently confirmed in Opflow and the AWWA Journal, both of which are published by the AWWA (October 2000, see references below). Other impurities in the NSF International-certified product were found to be even lower than the arsenic levels, with only 1%–3% of fluoride products containing detectable levels of metals, and the average exposure to a typical consumer would be less than 0.1% of the EPA allowable levels.

The claim is sometimes made that no health studies exist on the silicofluoride additives used in water fluoridation. Because of the equilibrium reached at the pH, temperature, and fluoride concentration used in water fluoridation, the silicofluorides achieve virtually complete dissolution and ionic disassociation when they are added to the drinking water. Consequently, the studies on health effects that used sodium fluoride in drinking water are applicable because the same dissociation results.

This finding was recently verified in a study on fluorosilicate ionic speciation, which reported that no intermediates or other products were observed at pH levels as low as 3.5. (Finney WF, Wilson E, Callender A, Morris MD, Beck LW. Reexamination of hexafluorosilicate hydrolysis by fluoride NMR and pH measurement. Environ Sci Technol 2006;40:8:2572).

FDA Regulatory Criteria for Fluoride

The FDA regulates fluoride in over-the-counter products, such as toothpaste and mouthwash, and in prescription items, such as fluoride supplements and professional-strength gels and foams, along with fluoride in bottled water that is marketed as a consumer beverage. In accordance with the 1979 EPA-FDA Memorandum of Agreement, the FDA does not regulate additives to community drinking water, because its regulatory purview concerns the safety and efficacy of food, drugs, or cosmetic-related products. The FDA does regulate the intentional addition of fluoride to bottled water and requires labeling identifying the additive used. In addition, in 2006, the FDA announced that bottled water with greater than 0.6 and up to 1.0 mg/L could be labeled with the statement “Drinking fluoridated water may reduce the risk of tooth decay.” A Fact Sheet on Questions About Bottled Water and Fluoride provides additional information on FDA requirements.

United States Pharmacopeia (USP) Grade Fluoride Products

Some people have incorrectly stated that “industrial-grade fluoride” is used at water facilities instead of pharmaceutical-grade products. All fluoride products used to adjust drinking water to the optimal fluoride levels are subject to AWWA and NSF/ANSI standards for drinking water additives. Pharmaceutical grading standards used in formulating prescription drugs are not appropriate for water fluoridation additives and if applied could actually increase the amount of impurities allowed in drinking water.

The United States Pharmacopeia-National Formulary (USP-NF) presents monographs on tests and acceptance criteria for substances and ingredients by manufacturers for pharmaceuticals. The USP 29 NF-24 monograph on sodium fluoride provides no independent monitoring or quality assurance testing, leaving the manufacturer with the responsibility of quality assurance and reporting. Some potential impurities have no restrictions by the USP including arsenic, some heavy metals regulated by U. S. Environmental Protection Agency, or radionuclides. The USP does not provide specific protection levels for individual contaminants, but tries to establish a relative maximum exposure level of a group of related contaminants. The USP does not include acceptance criteria for fluorosilicic acid or sodium fluorosilicate. The FDA does not have criteria on allowable impurities in sodium fluoride or fluorosilicates products.

NSF International requires independent testing for specific identified metals deemed to have a health effect in drinking water, while USP has a generalized test that is intended to represent the lead content, but also precipitates other contaminants. Therefore, given the volumes used in water fluoridation, a pharmaceutical grade of sodium fluoride for fluoridation could result in potentially higher exposure to the public of arsenic, radionuclides, and regulated heavy metals than could NSF International-certified product. FDA allows addition of fluoride additives to bottled water, but requires that the bottler list the additive that was used in the ingredients list. Bottlers typically use NSF International-certified product.

Fluoride Additives Are Not Different Than Natural Fluoride

Some consumers have questioned whether fluoride from natural groundwater sources, such as calcium fluoride, is better than fluorides added “artificially,” such as from the fluoride water treatment additives presently used. This allegation is not supported by scientific findings. The ionic speciation study mentioned previously (Finney et.al. 2006) also reported that water treatment additives dissociate to the same ions as present in groundwater .

• Frequently Asked Questions (FAQs)
   
• Temporary Shortages of Fluoridation Additives: FAQs
   
• American Water Works Association,* 6666 W. Quincy Ave., Denver, CO 80235–3098 for Fluoride Additives Standards B701–99, B702–99 and B703–00, and Manual of Practice No. 4, Water Fluoridation Principles and Practices, 2004.
   
• NSF International International,* 789 North Dixboro Road, Ann Arbor, MI, 48113–0140, for Drinking Water Treatment Chemicals Standards NSF/ANSI 60–2002 and NSF/ANSI 61–2002.
   
• Brown, Cornwell, MacPhee. Trace contaminants in water treatment chemicals: sources and fate. J Am Water Works Assoc 2004 Dec:111.

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Page last reviewed: August 13, 2008
Page last modified: August 13, 2008
Content source: Division of Oral Health, National Center for Chronic Disease Prevention and Health Promotion