Fluoride: All about it
I’m posting this from the Water Quality Association’s website as a reminder of what fluoride is and is not. This week we had a lady call in and tell us that her friend, the chemical engineer had insisted that the only way to reduce fluoride in drinking water was through reverse osmosis. Not so. We use AA Media very successfully in our alkaStream water filter.
I chose the very conservative US EPA as source.
What it is:
Fluoride compounds are salts that form when fluorine combines with water and minerals in soil or rocks.
Fluoride is added to public drinking water supplies at about 1 milligram per liter (mg/L) for the purpose of reducing tooth decay. The Centers for Disease Control and Prevention (CDC) now recommends 0.7 mg/L.
Fluoridation of municipal water is achieved by injecting or feeding a solution of hydrofluosilicic acid, sodium silicofluoride or sodium fluoride into the treated water stream.
Fluorine is not found in nature due to its high reactivity. It is an irritating and toxic halogen gas that is one of the most powerful oxidizing agents known. It therefore occurs naturally only in the reduced (fluoride, Fl-) form in combination with other minerals.
Some fluoride compounds, such as sodium fluoride and fluorosilicates, dissolve easily into groundwater as it moves through gaps and pore spaces between rocks.
Most water supplies contain some naturally occurring fluoride.
Fluoride releases occur from aluminum plants which utilize hydrofluoric acid (HF) in the refining process.
Children under nine years of age exposed to levels of fluoride greater than about 2 mg/L may develop a condition known as mottling or discoloration of the permanent teeth. In certain cases the teeth become chalky white in appearance. Mild fluorosis is barely noticeable.
The MCL for fluoride is 4 mg/L to protect against skeletal fluorosis, which is a serious bone disorder characterized by extreme density, hardness and abnormal fragility of the bones.
Fluoride has been used in treatment of osteoporosis.
Some small water systems with naturally occurring fluoride must treat their water supply to remove the excess fluoride to comply with the Safe Drinking Water Act limits. However, the cost is substantial and alternatives are employed where possible.
The maximum contaminant level goal (MCLG) established by the federal government for fluoride in drinking water is 4.0 mg/L.
The U.S. Environmental Protection Agency (EPA) has also set a secondary maximum contaminant level (SMCL) limit of 2.0 mg/L for aesthetic dental fluorosis.
Activated alumina is probably the most common fluoride removal technology used in municipal systems. Activated alumina requires a two-step, caustic (NaOH) regeneration followed by acid (H2SO4) neutralization regeneration process. Iron modified alumina, and iron oxides and hydroxides are very effective.
Other effective fluoride removal technologies include: Reverse osmosis, electrodialysis, deionization and distillation.
Sources: U.S. Environmental Protection Agency (EPA), Water Quality Association (WQA).