Water Fluoridation Additives

On this page:

• Types of Fluoride Additives

• Sources of Fluoride Additives

• Regulatory Scope on Additives

• EPA Regulatory Criteria for Fluoride Additives

• AWWA Standards

• NSF International Standards

• Measured Levels of Impurities

• FDA Regulatory Criteria for Fluoride

• United States Phamacopeia (USP) Grade Fluoride Products

• Fluoride Additives Are Not Different From Natural Fluoride

Types of Fluoride Additives

Community water systems in the United States use one of three additives for water fluoridation. Decisions on which additive to use are 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.

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Sources of Fluoride Additives

Most fluoride additives used in the United States are produced as a co-product in the manufacture of phosphate fertilizer. The phosphate fertilizer manufacturing process begins with phosphorite rock. This is a calcium phosphate mixed with limestone (calcium carbonates) minerals and apatite, a mineral with high phosphate and fluoride content. It is refluxed (heated) with sulfuric acid to produce a phosphoric acid-gypsum (calcium sulfate-CaSO4) slurry. Hydrogen fluoride (HF) and silicon tetrafluoride (SiF4) gases are captured by vacuum evaporators. These gases are then condensed to FSA with a solution concentration of approximately 23%. The remainder is water.

The process of acidifying calcium fluoride (fluorite) with sulfuric acid to generate hydrogen fluoride produces a minor source of FSA. That amount is less than 5%. Less than 1% of the FSA comes from hydrogen fluoride etchings in the manufacturing process of silicon chips used in computers and electronics.

Since the early 1950s, FSA has been the chief additive used for water fluoridation in the United States. The favorable cost and high purity of FSA make it a popular source. Sodium fluorosilicate and sodium fluoride are dry additives that come largely from FSA. FSA can be partially neutralized by either table salt (sodium chloride) or caustic soda to get sodium fluorosilicate. If enough caustic soda is added to neutralize the fluorosilicate completely, it results in sodium fluoride. Less than 10% of the sodium fluoride used in the United States is produced by mixing caustic soda with hydrogen fluoride.

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Regulatory Scope on Additives

All additives used at water treatment plants must meet strict quality standards that assure the public’s safety. Nevertheless, the addition of fluoride additives to drinking water sometimes raises questions about the toxicity, purity, and risk to humans. The U.S. Environmental Protection Agency (EPA) has authority over safe community drinking water, as specified in the Safe Drinking Water Act. 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.

The Australian Drinking Water Treatment Chemical Working Party of the National Health and Medical Research Council presents a good reference on the practices by governmental authorities in various countries to provide quality assurance of drinking water treatment chemicals. It also gives context to the United States AWWA and NSF/ANSI standards and practices. http://www.nhmrc.gov.au/publications/synopses/_files/watergde.pdf* (PDF–746KB)

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EPA Regulatory Criteria for Fluoride Additives

The EPA sets standards for drinking water in accordance with the Safe Drinking Water Act. It sets the Maximum Contaminant Level (MCL) concentrations of various organisms or substances already in the source water or that are added to water during treatment. This is based on health effects resulting from drinking water consumption.

The EPA has established a Maximum Contaminant Level for fluoride of 4.0 mg/L (parts per million). It did so because fluoride is sometimes naturally present in water at much higher levels than that added to community water systems (0.7 – 1.2mg/L). The EPA has not established an MCL for silicates, because there are no recognized health concerns. NSF/ANSI Standard 60, however, has a Maximum Allowable Level of 16 mg/L (for sodium silicates as corrosion control agents. This is mainly for turbidity (a measure of water clarity or how much the material suspended in water decreases the passage of light through the water) reasons. NSF tests show the silicates from fluoride additives in the water samples to be well below these levels.

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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 B701-06 (sodium fluoride), ANSI/AWWA B702-07 (sodium fluorosilicate) and ANSI/AWWA B703-08 (FSA). AWWA’s standards are prepared by its Fluoride Standards Committee, with oversight by the Standards Council, concurrence by the AWWA Board of Directors, and concurrence by ANSI. AWWA standards are reviewed and updated at least every 5 years. AWWA standards stipulate product quality testing requirements and verification.

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NSF International Standards

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

Independent verification entities, including NSF International and Underwriters Laboratories, verify compliance with the NSF/ANSI standards. 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 metal compounds at the tap (in the home) must not have a concentration that is more than 10% of the MCL.

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Measured Levels of Impurities

Fluoride additives are analyzed for more than 13 impurities that have been identified as having the potential to occur. Those impurities include arsenic, lead, and radionuclides. Verification on compliance with NSF/ANS standard 60 must also be certified. NSF presents a detailed fact sheet on the documented quality of fluoride additives* (PDF–74KB) The fact sheet is based on separate product samples analyzed from 2000 to 2006. Some consumers have raised questions concerning arsenic in drinking water. According to the NSF quality testing, 57% of all fluoride additive samples did not have detectable levels of arsenic. For those samples that did test positive for arsenic the arsenic content that an average 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 (10 parts per billion) for arsenic consumption in water. 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. 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. Not true. Studies find that silicofluorides achieve virtually complete dissolution and ionic disassociation at the concentrations they are added to the drinking water. The equilibrium reached at the pH, temperature, and fluoride concentration used in water fluoridation account for this. The same studies on health effects that used sodium fluoride in drinking water apply here, because the same disassociation results.

A study on fluorosilicate ionic speciation verifies this finding, which reports 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).

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FDA Regulatory Criteria for Fluoride

The U.S. Food and Drug Administration (FDA) does not regulate additives to community drinking water, because its regulatory reach concerns the safety and efficacy of food, drugs, or cosmetic-related products. Because the FDA has authority over bottled water as a consumer beverage (Federal Register, Volume 44, No. 141, July 20, 1979), they do regulate the intentional addition of fluoride to bottled water and requires labeling identifying the additive used. Bottlers typically use NSF/ANSI Standard 60-certified fluoride product. 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.”  Questions About Bottled Water and Fluoride provides additional information on FDA requirements. Fluoride in bottled water that is marketed as a consumer beverage is also included. The FDA also regulates fluoride in over-the-counter drug products, such as toothpaste and mouthwash, and in prescription items, such as fluoride supplements and professional-strength gels and foams.

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United States Pharmacopeia (USP) Grade Fluoride Products

Reports that suggest “industrial grade fluoride” is used at water facilities instead of pharmaceutical grade products are false. Pharmaceutical grading standards used in formulating prescription drugs are not appropriate for water fluoridation additives. If applied, those standards could actually increase the amount of impurities as allowed by AWWA and NSF/ANSI 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. That leaves 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 the U.S. EPA, and 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.

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/ANSI Standard 60-certified product.

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Fluoride Additives Are Not Different From 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.

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• 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: October 8, 2008
Page last modified: October 8, 2008
Content source: Division of Oral Health, National Center for Chronic Disease Prevention and Health Promotion