Posts Tagged ‘tooth decay’December 7, 2010
Fluoridation During Municipal Water Treatment
Municipal water treatment is very similar to a manufacturing process where the composition of the final product must meet certain specifications, many of these prescribed by regulation. There are several steps in the DMWW process: coagulation and sedimentation to remove dirt in the river water, hardness reduction, filtration, nitrate removal, disinfection, and fluoridation.
DMWW source water (Raccoon and Des Moines Rivers, and shallow groundwater under river influence) contains some fluoride, usually between 0.1 and 0.5 part per million (ppm). This is increased to about 1 ppm by addition of fluorosilicic acid. There are other ways to add fluoride, most notably with sodium fluoride. Fluorosilicic acid can be added in the liquid form, which is mechanically simpler than adding solid sodium fluoride. Fluorosilicic acid is the most economical vehicle for fluoride addition.
Fluorosilicic acid is a co-product formed during the production of fertilizer. Phosphate rock used to produce fertilizer contains significant amounts of fluoride. This is recovered as fluorosilicic acid and used in water treatment, brewing, and other applications. Like all chemicals used for municipal water treatment, fluorosilicic acid must meet stringent requirements for composition and impurities.
The addition of fluorosilicic acid to the water is monitored every minute of every day by DMWW staff, so that the proper amount of fluoride is always maintained in the drinking water delivered to your home.
How Fluoride Works
Archeologists know that tooth decay was rare in human beings until the Renaissance, when refined sugar became available to wealthy people. The problem became epidemic during the industrial revolution as sugar consumption increased among the entire population of industrialized societies. Queen Elizabeth I was known to have a fondness for sugar, and suffered greatly from tooth decay.
Until 1757, medical practitioners believed cavities were caused by worms. In 1556 Pope John XXI recommended inhalation of smoke from burning henbane seeds to kill the worms and assuage the pain. When dentistry became a recognized profession, researchers zeroed in on two potential causes for tooth decay: 1) bacteria, and 2) diet. It turns out both causes are correct.
The bacterium Streptococcus mutans colonizes tooth surfaces, forming plaque. They metabolize and ferment sugar, releasing acid in the process. The acid dissolves the mineral apatite which comprises tooth enamel, forming a cavity.
Fluoride forms a complex with the apatite mineral of the tooth enamel. The fluoro-apatite complex is much more acid-resistant than normal apatite, and forms a protective veneer on the teeth. Fluoro-apatite forms much more quickly than the body can naturally re-mineralize the teeth.
The original fluoride researchers felt the protective mechanism was entirely systemic (within the body). This has proved to be wrong. The primary protection mechanism is now known to be topical (on the surface of the tooth), but evidence for systemic protection continues to be revealed by research. An October 2010 article appearing in the American Journal of Public Health reports a strong relationship between fluoride levels in a resident’s county at the time of their birth, with tooth loss as an adult. It seems that fluoride exposure at birth affects tooth loss at age 40 and older, which is evidence for a systemic mechanism.
Fluoridation of municipal drinking water at safe levels (~1 part per million) provides dental protection through both topical and systemic mechanisms. This has helped reduce rates of tooth decay in the U.S. to the frequency archeologists observe in skeletons from 1000 years ago.
The history of fluoridated water is like many of the great scientific findings throughout the ages. It started with an observation.
Archeologists have long known that tooth decay is a modern problem that was rare until the Renaissance, when refined sugar became available to wealthy people. The problem reached epidemic proportions during the industrial revolution, when income levels grew to the point that sugar could be purchased by nearly everyone in an industrialized society.
During the 1870s, scientists and physicians began to notice that people living in some areas of the world seemed immune to tooth decay. Many of these same people also had brown-stained teeth. One of the first cities where this was observed was Naples, Italy. Medical examiners on Ellis Island also noticed many Italian immigrants with this same phenomenon. Similar observations were made in the American West, especially amongst miners in the gold fields of Colorado. It was eventually determined after many years of study that the water these people were drinking contained very high levels of naturally-occurring fluoride, which found its way into groundwater wells via the mineral deposits of the local area.
Researchers determined that these people were getting too much fluoride, and this caused the brown staining which is now known as dental fluorosis. The water they were drinking contained as much as 30 parts per million (ppm) of the element. Studies eventually determined that the optimum drinking water concentration which delivered protection from cavities but did not produce fluorosis was about 1 ppm.
Water intentionally fluoridated at the 1 ppm (parts per million) level was first produced in four cities in 1945: Grand Rapids, MI; Newburgh, NY; Evanston, IL; and Brantford, Ontario. These trials were overseen by an eminent scientist of time, H. Trendley Dean. The results were profound: a 40% reduction in cavities in four years, and up to 57% within 15 years.
It was near the end of this 15-year study, in 1959, that Des Moines Water Works (DMWW) began fluoridating water delivered to Des Moines and surrounding areas. Natural levels of fluoride are supplemented during treatment so that water leaves the treatment plants with the optimum level of 1 ppm.
This article is the first in a series of five articles addressing the subject of fluoride in City water. Please leave a comment, and come back to read the next articles in the series. Thanks for reading!