Fluoride in Drinking Water: Friend and Foe

Image credit: Lauren Borja, BSR Design Team.

Americans really care about our teeth—that’s why our water utilities add small concentrations of fluoride to our water to prevent tooth decay.

Fluoride, as may be familiar to you, is often an ingredient in mouthwashes that dentists give you after a teeth cleaning or toothpastes you can buy at the store. Fluoride is part of a salt that forms when the element fluorine combines with minerals in the ground and, in small doses dissolved in water, it strengthens the enamel on our teeth.

But fluoride use isn’t without risk. A serious negative health effect called skeletal fluorosis can result from consuming too much fluoride, and this possibility is causing some confusion and controversy about when it is appropriate to add fluoride to water.

A simple Google search reveals a variety of strong opinions on water fluoridation—some assure us of fluoride’s safety in small doses, while others argue that the risk of illness isn’t worth fluoridating drinking water. It’s up to us to educate ourselves on when and how fluoride will affect our bodies in varying doses, and to understand that fluoridation is safe in low concentrations.

Most know that bones and teeth are primarily made out of calcium; for this reason, we are told to drink lots of milk growing up. The specific calcium compound is called hydroxyapatite (HA) and is composed of calcium, phosphate, and hydroxide ions (OH). HA makes up between 60 and 70% of our bone mass.

Fluoride is similar to OH in that they both have a charge of negative one. As a result, when HA is in the presence of fluoride, the fluoride can actually replace the OH, creating a slightly different version of HA. Instead of the formula Ca5(PO4)3OH, the HA is transformed to Ca5(PO4)3F, called FHA.

FHA is harder and tougher, which is why, in small doses, it can strengthen bones and teeth. However, when there is a lot of fluoride present, converting more of the HA into FHA, the bones get harder, gain more mass and, consequently, become more brittle. As concentrations increase, symptoms can include pain in bones in joints, calcification of spinal ligaments, paralysis, and deformation of the spine and joints. These symptoms characterize the condition known as skeletal fluorosis.

Since fluoride is naturally occurring in the earth, it is found in groundwater around the world. Unfortunately, many places naturally have fluoride concentrations greater than 1.5 mg/L, causing fluorosis after prolonged and repeated exposure. These areas include parts of Asia, North and eastern Africa, the western United States, and southern South America. The negative health effects are exacerbated in regions where a hot or humid climate encourages people to drink lots of water (Africa) or when heavy tea drinking is a cultural norm (Asia).

In the United States, the Environmental Protection Agency (EPA) does not require fluoridation of drinking water. The Center for Disease Control and Prevention (CDC) has given a recommended fluoride concentration of 0.7-1.2 mg/L for the prevention of tooth decay. In order to prevent fluoride concentrations getting too high, the EPA has set an enforceable maximum limit of 4.0 mg/L of fluoride in drinking water. The EPA’s secondary fluoride standard, which is not enforceable but recommended, is 2.0 mg/L of fluoride.

Image credit: Lauren Borja, BSR Design Team. Information from <a href="http://www.sciencedirect.com/science/article/pii/S0301479709002928">Mohapatra <i>et al</i>.</a>

Image credit: Lauren Borja, BSR Design Team. Information from Mohapatra et al.

Fluoridation of drinking water has been studied for approximately 70 years and many water services in America choose to follow the CDC’s recommendation of adding fluoride to prevent tooth decay. In areas where concentrations are naturally too high, there are treatment technologies able to physically remove the fluoride.

Technologies able to remove fluoride have been studied for a few decades. Mostly, the technologies use membrane techniques (using a membrane with small enough pores to remove the larger fluoride particles) or adsorption techniques (inducing adhesion between the fluoride and some sort of surface).

However, not all countries have the water treatment infrastructure that the United States has, making the implementation of membrane techniques such as reverse osmosis or nanofiltration challenging. For this reason, there are research efforts underway to removal fluoride in developing countries using adsorption, which is simple and inexpensive.

Adsorption involves adding an element such as iron oxide, alumina, or silica to induce an adherence of fluoride onto these particles. Some studies have even tested adsorption of fluoride to bone char or ground up cattle bones. The same process that turns our bones brittle (the HA turning into FHA) induces the removal of the fluoride in the water. None of these fluoride removal methods are perfect—adsorption techniques often do not achieve a fluoride concentration less than or equal to 1.5 mg/L.

Fluorosis is a heavily studied problem, being a hot-topic in both drinking water treatment and in human health research. So, hopefully, a more perfect fluoride removal technique will be soon found and implemented in the developing regions of the world that need it most.

In the meantime, however, we must understand that the simple presence of fluoride in our drinking water will not cause skeletal fluorosis. Repeated exposure to high concentrations over long periods of time will lead to severe negative health effects, and that necessitates fluoride removal in some parts of the world. However, in the rest of the world, where fluoride levels are within safe limits, fluorosis is not a risk. Where fluoride levels are naturally low, adding a little extra isn’t dangerous—and our smiles will thank us for it.

Featured image credit: Lauren Borja, BSR Design Team.

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  1. Anonymous

    Nice graphics!

  2. Anonymous

    There is a close connection between the interests of the author and the subject of this article. Emily Cook is “studying the biological and chemical transformation of the groundwater contaminants sourced from fire-fighting foams.” These fire-fighting foams have perfluorinated compounds, which means they contain the element fluorine. 2 fluorine atoms combined together create fluoride ions.

    Like the perfluorinated contaminants Emily is studying, fluoride is a water contaminant. It has a “maximum contaminant level” set by the EPA. Water fluoridation is essentially adding a contaminant for a perceived benefit. And you probably don’t want to know too much about the source of the fluoride added to your drinking water.

    In February I attended a symposium on flame retardants and fluorinated compounds at UC Berkeley. I hope Emily also attended that conference. An EPA scientist, in response to my question, told us that the fluorinated compounds he studies would essentially be nothing more than harmless fatty acids if you take out the fluorine atoms.
    What is happening to ground water due to the chemicals like those Emily is studying is disturbing to many environmentalists. Here’s an article about these chemicals called “Poisoning the Well.” https://theintercept.com/2015/12/16/toxic-firefighting-foam-has-contaminated-u-s-drinking-water-with-pfcs/

    This is why there is so much controversy over water fluoridation. It’s due to the toxic nature of fluorine and fluoride and what science and experience has shown us about the harmful effects on plants, animals, and humans.

    This article got a few things wrong, which I quote below.

    “Small amounts of fluoride strengthens teeth and bone.” So does that mean people with low fluoride intake have weaker teeth, which are more likely to chip or crack? No authority says that. Are people with low fluoride intake going to have more bone fractures? Nobody says that either. So while small amounts may create hardness it does not necessarily mean “strength.” A National Research Council committee of experts was tasked with advising the EPA on the maximum contaminant goal of 4ppm for fluoride in drinking water. Their 2006 report recommended that the EPA reduce that level due to increased bone fracture risk from the high levels many American ingest in their water. The EPA has ignored that advice.

    “For this reason, there are research efforts underway to removal fluoride in developing countries using absorption, which is simple and inexpensive.” And “Some studies have even tested absorption of fluoride to bone char or ground up cattle bones.” It’s way beyond just “research efforts” and “studies.” Bone char to remove fluoride from ground water has been used for many decades in developing countries and was used years ago in the United States to remove fluoride from water. Activated alumina has also been used for decades for the same reason. There is a new method being developed using crushed Bauxite, which is cheaper than activated alumina.

    “In the meantime, however, we must understand that the simple presence of fluoride in our drinking water will not cause skeletal fluorosis.” People in parts of the U.S. with high fluoride levels in their tap water could get crippling skeletal fluorosis according to what the EPA says. It only takes 10 milligrams a day for a period of 10 years according to the EPA. Nobody knows how much skeletal fluorosis exists in the U.S. because it is not a reportable disease and few doctors even know what it is or how to detect it. While the U.S. may not have many cases of stage 3 crippling skeletal fluorosis, there could be many people with less severe stage 1 or 2 skeletal fluorosis as well as non-skeletal fluorosis that also affects the body.

    The graphics in this article are well done. One thing to point out is that ingested fluoride also increases fluoride in the dentin of the tooth and can make changes there. On the lower graphic it shows .5 to 1.5mg/L as the ideal concentration for health teeth. But there also is dental fluorosis at this concentration as well as the higher levels. That’s why the national recommendation was lowered to .7ppm two years ago. Government experts were seeing too much dental fluorosis in children.

    It is true that the EPA does not mandate water fluoridation. Congress prohibited a national mandatory fluoridation law decades ago. But some states like California do have mandatory laws to force fluoridation on unwilling communities. These mandatory state laws are the primary reason fluoridation has increased in recent years. They take away local democracy and referendums.

    Like the author, I also like pecan pie a great deal. And not all bacteria is bad.

    • Emily Cook

      Hello, and thank you so much for taking the time to read my article and comment about it! I’m so glad you are interested in the topic.

      I did in fact attend the symposium called Flame Retardant Dilemma and Beyond. It was an excellent event and I got a lot out of it! To be clear, I am studying how to clean groundwater that has been contaminated with per and polyfluorinated compounds, which are called perfluorinated alkyl substances (PFASs). My bio says I’m studying the transformation of contaminants sourced from fire-fighting foams, which means I am attempting to break these compounds down until they are simple hydrocarbons which do not harm human health. I will make that more clear in my bio.

      PFASs are not the source of fluoride in groundwater or drinking water; they are an entirely different water contaminant. They are long carbon chains (anywhere between 4 and 15 carbons) with fluorine atoms attached to most (or all) of the carbon atoms. The carbon chain often has a carboxyl group or a sulfonate group at the end. PFASs are known to cause certain types of cancer, endrocrine disruption, and birth defects. Any concentration of PFASs for any length of time (but especially longer exposure) can harm human health.

      Fluoride, on the other hand, only harms human health at higher doses for long periods of time.

      I am not as familiar with the doctor’s perspective skeletal fluorosis, but I am under the impression that it is a condition that can be tested for in a hospital. Doctors can test for fluoride concentrations in the patient’s urine and they can look for the hardening of bone (increase in bone density) using a radiograph. In addition, severe skeletal fluorosis is something that you can see very easily; people’s bones are bent or bowed. Finally, dental fluorosis is also something that you can visually identify, as it causes a discoloration in your teeth.

      I apologize if any of my wording was off or incorrect, especially regarding the strength versus hardness argument. This is one reason why fluoridating water is so controversial. There is the belief that increasing hardness increases strength to an extent, after which point the increase in hardness causes brittleness. This brittleness is what causes problems.

      Please let me know if you would like me to comment on anything else! I appreciate your time!