FLUORIDATION

PURPOSE:
The addition of fluoride to water supplies is undertaken to reduce the number of dental caries (cavities) in the water consuming customers.

BACKGROUND:
A) This topic generates more heated discussion in both active support and direct opposition to, as fluoridation.
B) The use of chlorine, ozone, and other disinfectants does not produce nearly a fraction of the discussion that this topic creates!
C) The use of this chemical is largely dictated by political action.
D) As operators we implement the decision of whether to use it or not.
E) We will review the measures we use to fluoridate the water, as we must all know how to accomplish this task safely, and properly.

THE SCIENCE:
A) The fluoride ion, whether it occurs naturally or is injected into the water supply, is absorbed to some degree in the bone structure of the human body, which also includes the tooth enamel.
B) Incorporation of the fluoride into the tooth structure is most efficient while the teeth are in the development stage, although there is some absorption of fluoride into the tooth enamel at all ages.
C) The greatest benefit occurs when persons consume fluoridated water from infancy.
D) It has been clearly demonstrated that consumption of water containing one milligram per liter of fluoride ion results in protection of the tooth enamel from decay and does not discolor the enamel. It’s use has resulted in a 50- to 65-per cent reduction in dental caries in school children consuming the water from infancy.
E) Fluoride applied directly to tooth enamel does not provide the degree of treatment that occurs when fluoride is consumed, and the tooth enamel incorporates it into the enamel.

OBJECTIONS TO FLUORIDE USE:
The principle opposition to fluoridation has been based upon the principles that all supplied water should be free of "contaminates" or chemicals that affect ones consumption of it. Oppositions usually state also that "medications" (including fluorides) may not be given to him/her without their expressed consent.
Other objections to fluoridation include possible harmful effects. These objections have not withstood a detailed review by the scientific community.
This objection is the statement of possible discoloration (mottling) of the tooth enamel in a condition called "fluorosis". Fluorosis is the appearance of small opaque, white areas on the tooth enamel, which may start to occur when fluoride levels are twice the recommended levels.
An even greater amount of fluoride in the water may then cause an actual pitting of the tooth enamel, which can occur, if fluoride naturally occurs, or is over dosed at levels above 4 mg/L

FLUORIDE COMPOUNDS
The following fluoride compounds release fluoride ion (F-) when they are placed into the water supply:

a) ammonium silicofluoride ((NH4)2SiF6), also called ammonium fluosilicate
b) sodium silicofluoride (Na2SiF6), also called sodium fluosilicate
c) calcium fluoride (CaF2).
d) sodium fluoride (NaF), and
e) hydrofluosilicic acid (H2SiF6) also called Fluosilicic acid (the photo to the left is a bulk Fluosilicic acid tank).

All of these chemicals are normally supplied as a powder or in a crystalline form in bags or drums, except for hydrofluosilicic acid which is supplied in drums, or tanker trucks, as a liquid solution, usually in about a 25 to 30 per cent concentration.

As with the chemicals we discussed in coagulation, disinfection, etc., they all seem to have industrial grade qualities also. It is not unusual to have significant impurities in these industrial grades that make it unsuitable for use in water treatment. Therefore, purchase all chemicals using the American Water Works Association (AWWA) chemical standards to ensure that you do not create a "water quality" problem!

STORAGE
The liquid type chemicals are stored in appropriate tanks, or in the original shipping containers until use. It is always a better practice to keep them in a cool, out-of-the-sunlight place.
Fluoride chemicals supplied in the dry form are usually stored in their original containers until they are used also. At the time of usage, they are then transferred to the storage/feed containers at the feeders.

CHEMICAL FEED SYSTEMS
Calibrated, accurate equipment, which may be manually controlled under constant flow rate conditions has been used, especially in smaller facilities. If the flow rate is a variable one, then more elaborate instrumentation is required to control the feed equipment.

1. Dry form:
Sodium silicofluoride and sodium fluoride are usually applied in this manner. A dry feeder places the dry materials into a solution, which is then fed into the treatment stream. Sodium silicofluoride is the least expensive chemical to use. It is more difficult to make into a soluble form as the temperature decreases when compared to sodium fluoride.

2. Liquid form:
Hydrofluosilicic acid and sodium fluoride are usually applied in this manner, using metering pumps to feed the supplied liquid material directly into the treatment stream. Chemical feeding in this manner is usually much easier. More costly to transport, (due to the dilution water) may be the most expensive to purchase.

DOSAGE CONTROL
The dosage of fluoride and the other chemicals we feed into the water MUST be checked frequently. Key points to remember are:
a) After each dosage change we will check the fluoride ion concentration to insure that we have adjusted the dosage properly, and that our equipment is functioning properly at the new dosage level.
b) We will check the fluoride ion concentration daily to insure that we are feeding the chemical(s) at optimum dosages.

It is imperative that comprehensive training in the proper method(s) of determining the fluoride concentration is given to the operational and laboratory personnel.

SAFETY
There can not be enough written, nor stressed enough to convey the importance of safety concerning chemical usage!

Dry chemicals, use the following:
a) face masks to prevent dust inhalation
b) chemical-use goggles for eye protection
c) tight-fitting clothing to protect the body
d) rubber gloves

We always engineer in the protections whenever possible, first. We then use personal protective gear to enhance these measures, or mitigate that which can not be engineered and installed. In a case such as this, dust recovery and exhaust systems are mandatory, as the dusts when mixed with moisture or water vapors, can cause acid-type reactions.

Liquid chemicals are transferred either into storage facilities or are stored in their original containers until use. Usually, no precautions other than eye protection and long rubber gloves are required during the transfer of the chemicals. Large leaks or significant maintenance work may require an elevated level of protection:
Liquid solutions of fluoride may therefore require the use of the following:
a) chemical-use goggles for eye protection
b) acid resistant outer protective clothing and rubber boots to protect the body
c) rubber gloves
d) breathing protection in the form of respiratory masks with an appropriate cartridge to neutralize the acid fumes

Please note that the fluoride salts when placed into solution, and hydrofluorosilicic acid are very corrosive to metals. It has often been said in water plants that the first chemical to leak will be hydrofluorosilicic acid! Extra care must be taken during construction to reduce the potential for leaks in such systems. AWWA recommends plastic storage and feed containers, and PVC piping for all solutions.

Do not eat or drink around any chemical feed system, especially a crystalline dry feed system like for fluoride, as the chemical may be mistaken for slat or sugar!

OPERATIONAL AND MECHANICAL NOTES:
As stated during the previous discussions, most of the problems are associated with:

a) Proper calibration of the chemical feed equipment. This must be accomplished on a scheduled basis. Compare your "weighed dosage" values to your laboratory analysis values of the treated water.

b) Leaks in the piping always start out as a "weep", with an associated salt deposit…the proper repairs must be undertaken in a timely manner.

c) A buildup of insoluble deposits in the piping and/or fluoride feed equipment. Calcium fluoride deposits are formed when hard water is used to make up a concentrated fluoride solution to feed into the treatment stream. In such cases a water softener (an ion exchange type softener) to remove calcium and magnesium ions before adding the fluoride salts is a great improvement in this feed system Hydrofluorosilicic acid may be manufactured with an excess of silicic acid (SiO2) which causes a precipitate when the material is diluted with water. This problem may be reduced by metering the concentrated acid directly into the treatment stream without any dilution. Clean the diffusers at least four times each year of any precipitate buildup.

d) In smaller facilities, the use of water softeners, and such may still prove to be of little effect, and one basically has to perform predictive maintenance such as pump, pipe, feeder, etc cleaning in order to insure the proper feeding of the chemicals.
e) Insure that all manufacturer’s recommended preventative operational and mechanical maintenance items and their related schedules are followed.

OPTIMAL LEVELS OF FLUORIDE
The amount of fluoride that we require for optimal benefit is based upon a library of studies! We recognize as operators that the number of pounds per day to inject into the water is directly related to the quantity of water and the concentration of the dosage we require. The quantity of water that we each consume each day, is related to the ambient temperature that we are experiencing at the time. We know that people who are in a hot environment will drink more water than those in a freezing environment. State health departments therefore have worked out the optimal fluoride doses for use therefore, based on the ambient air temperature.

The United States Public Health Service recommends that where fluoridation is practiced, the average fluoride concentration shall be kept within the upper and lower control limits in the following table:

Annual average of maximum fluoride concentrations mg/L
Daily Air Temperatures* Lower Optimum Upper
50.0 - 53.7 0.9 1.2 1.7
53.8 - 58.3 0.8 1.1 1.5
58.4 - 63.8 0.8 1.0 1.3
63.9 - 70.6 0.7 0.9 1.2
70.7 - 79.2 0.7 0.8 1.0
79.3 - 90.5 0.6 0.7 0.8
· Based on temperature data for a minimum of five years.

A 60-65%. reduction in dental caries can be expected from fluoridation. However, the presence of fluoride in average concentrations greater than two times the optimum values in the table should constitute grounds for rejection of the supply.