ELEVEN YEARS OF MONITORING FLUORIDE CONTENT IN PUBLIC WATER SUPPLIES : METHODS , PRODUCTS , AND IMPORTANCE TO PUBLIC HEALTH

This study aimed to assay the development process and the characteristics of a program in uninterrupted activity for over 11 years, which monitors fluoride content in public water supplies, emphasizing the methodology used in the research, the services provided to cities and specificities of water distribution networks, the products derived from project implementation, the main results obtained in its course, and its importance in favor of public health. Monitoring is necessary to reach the maximum benefit in the prevention of tooth decay and minimum risk in fluorosis development. To develop the study, documents and reports of the project’s database and the results of water samples were analyzed. A survey of the intellectual productions generated by the project was performed, maps of water distribution networks of 40 cities in the northwest region of São Paulo state included in the project were analyzed, and the research methodology was presented. The activities carried out in the project have been described with details regarding the main methodological aspects, such as the form of establishment of sample collection points, the laboratory methodology used for the analysis of water samples, the extension experience the project offers to all parties involved, the results of 11 years of sample analyses, the benefits generated to health managers and those responsible for water treatment, among other considerations on the cities. The methodology adopted by the project allows identifying areas where the population may be exposed to higher fluoride concentrations. From November 2004 to December 2015, 50.98% of water samples from all cities were within the optimal parameters.


INTRODUCTION
Public water fluoridation is one of the main and most important public health strategies, and it may be regarded as the most effective measure for controlling tooth decay, considering its wide scope (RAMIRES; BUZALAF, 2007).The method was so effective that the United States Center for Disease Control and Prevention (CDCP) considered it one of the top ten public health achievements of the twentieth century (CENTERS FOR DISEASE CONTROL AND PREVENTION, 2000).
The preventive effects of fluoride were discovered as a result of investigations on its toxic effect on dental enamel development, resulting from intake (PRADO et al., 2014).In 1942, a directly proportional correlation between the prevalence of dental fluorosis and fluoride ion concentration in drinking water was observed.On the other hand, a significant inversely proportional correlation was verified between the presence of fluoride ion and the prevalence of tooth decay.After determining these relations, new studies were designed to establish the best fluoride concentration in the water to generate the maximum benefit for preventing tooth decay and the lowest risk for developing dental fluorosis in the populations exposed (EIDELWEIN, 2010).Adding fluoride in public water supplies, as a public health measure to prevent tooth decay, began in 1945 with three pilot studies in cities of the United States (Grand Rapids, Michigan, and Newburgh, in the state of New York) and Canada (Brantford, Ontario).Control-cities were set for each of the aforementioned cities to compare the results, as follows: Muskegon and Kingston (United States), and Sarnia (Canada).These pioneering studies were seeking evidence that fluoridation might be a safe and feasible strategy to prevent tooth decay.It was concluded that the fluoride present in drinking water in a concentration of about 1 milligram per liter (mg/L) would promote the maximum reduction in the DMFT index, but values above 1.5 mg/L would not significantly improve the index and would increase the risk of developing dental fluorosis (NARVAI, 2000;KOZLOWSKI;PEREIRA, 2003).
The water intake by the population may vary depending on the temperature of each location, because consumption tends to be higher in places with elevated temperatures.Thus, it was established that for each region the ideal levels of fluoride in drinking water should be recommended considering this variable (GALAGAN; VERMILLION, 1957).
In Brazil, the first city to adopt fluoridation in their water supply was Baixo Guandu, Espírito Santo, in 1953, and the Special Services Foundation in Public Health of the Ministry of Health was the public agency responsible for its operation (MOIMAZ;SANTOS, 2015).A study performed in this location proved that in the age group of 12 years, the DMFT index is 82% lower than before fluoridation (SALIBA et al., 2007).However, only in the 1970s the method became more effective through the approval of Federal Law n. 6050 of 1974, which stated the mandatory fluoridation in public water supply systems in locations with treatment plants (BRASIL, 1974).Ordinance n. 2,914 of 2011 issued by the Ministry of Health establishes the parameters considered acceptable for the potability of public water supplies for human consumption (BRASIL, 2011).According to this ordinance, the maximum fluoride content allowed is 1.5 milligrams per liter of water (mgF/L).
When the preventive properties of fluoride were discovered, it was believed that the beneficial effects occurred through the ion ability to form fluorapatite instead of hydroxyapatite in the stage of dental enamel production, allowing teeth to become more resistant to the acid surroundings caused by bacterial metabolism and their substrates (CHAVES, 1977).This current view considered that, once exposed to fluoride in the development stages of teeth, its preventive properties would be permanent for the individual (VIEGAS, 1989).However, it was proved that such a mechanism does not occur.Fluoride will provide higher teeth resistance through the enamel surface by periodic processes of surface demineralization and remineralization caused by the pH drop from the production of acids from dietary carbohydrates.The fluoride-containing tooth surface has lower solubility in acid surroundings compared to the original enamel surface (FEATHERSTONE, 1999).It is known that the beneficial effects attributed by fluoride are due to their continued presence in small amounts throughout the life of individuals (CURY, 1992).
Several researches indicate the need for monitoring fluoride content in the water to obtain the recommended standards (MAIA et al., 2003) (MOIMAZ;SANTOS, 2015).Therefore, external control, which is the control and periodic analysis of water fluoridation conducted by an institution apart from the one responsible for water treatment and supply, becomes an important strategy for the method to achieve its maximum benefit in preventing tooth decay and minimizing risks in the development of dental fluorosis.
Universities, due to their potential research implementation, their infrastructure, and for having professionals who do not only act in their own academic field but also benefit the population through research and extension projects, may play an important role for the community.Since 1991, the School of Dentistry of Araçatuba (FOA -Unesp) conducts a project that renders services to several cities in the northwest region of São Paulo state (Brazil), through the external control of fluoride in their public water supplies.
This study aimed to assay the development process and the characteristics of a program in uninterrupted activity for over 11 years, which monitors fluoride content in public water supplies, emphasizing the methodology used in the research, the services provided to cities and specificities of water distribution networks, the products derived from project implementation, the main results obtained in its course, and its importance in favor of public health.

MATERIAL AND METHODS
Descriptive study that verified activities performed, results, and products created from a research and extension project promoting the external control of fluoride.The study period covers the years between 1991 and 2015.
The fluoride ion-monitoring project developed by the School of Dentistry of Araçatuba (FOA -Unesp) began in 1991 through an agreement between the university and the APCD (Paulista Association of Dental Surgeons); at that time, the analyses were conducted discontinuously.In its early years, the project aimed to comply with the request of the APCD to measure whether the water supply of some cities in the region of Araçatuba (São Paulo, Brasil) were presenting clinical conditions of dental fluorosis among their population.
To develop the study, documents and reports of the project's database and the results of water samples were analyzed.A survey of the intellectual productions generated by the project was performed, maps of water distribution networks of 40 cities in the northwest region of São Paulo state included in the project were analyzed, and the research methodology was presented.
The activities carried out in the project have been described with details regarding the main methodological aspects, such as the form of establishment of sample collection points, the laboratory methodology used for the analysis of water samples, the extension experience the project offers to all parties involved, the results of 11 years of sample analyses, the benefits generated to health managers and those responsible for water treatment, among other considerations on the cities.
The sample collection points were determined according to the amount and location of each water supply source.For each source, three collection points were chosen in the region supplied by it.The addresses of each point were selected, most of them in public places (schools, health centers, squares, among others), due to the easy access to collect water.Some studies determined the amount of collection points by population size; also some external control studies found in the literature showed specific results because their analyses were based on cross-sectional studies.The methodology adopted by the project of the FOA (Unesp) allows identifying areas where the population is most likely exposed to dental fluorosis, in addition to performing monthly and systematic monitoring of fluoride content, which is essential to obtain the maximum benefit and minimum risk of the method.Thus, considering the events showing results of inadequate fluoride content in samples, if the location has more than one source of water catchment, it is possible to know the specific areas where the population is prone to higher risks, assisting monitoring and water treatment services to identify and solve potential problems.
The project activities are implemented as follows: in the NEPESCO (Research Center in Public Health) laboratory, 40-ml polyethylene airtight bottles are properly cleaned and decontaminated with deionized water, receiving an identification tag with data relating to collection site, day, month, time, and name of the responsible person; these bottles are sent to the cities.After the water is collected, the samples are sent back to the FOA (Unesp) where the analyses are carried out within 150 days.
The method used to analyze fluoride content is based on that described by Maia et al. (2003) with an ORION EA 940 potentiometer coupled to a combined electrode (Orion 9609BN) designed for reading the fluoride ion.
The equipment is calibrated in triplicate by constructing a calibration curve in order to reduce the margin of error, taking into account the expected values for the samples with standards ranging from 0.1 to 2.0 mgF/L.Thus, dilutions from a standard 100 mg/L fluoride solution (Orion 940907) were used.From each one of the five standards, a volume of 1 ml was collected, which was later added by 1 ml of Total Ionic Strength Adjuster Buffer (TISAB II), a pH, ionic strength adjusting buffer commonly used in fluoride analyses.The values obtained in the readings of the duplicate samples, also added by TISAB II (1:1), were transferred to a Microsoft Excel spreadsheet and converted from millivolts (mV) to milligrams of fluoride per liter (mgF/L), and analyzed using descriptive statistics.
Those responsible for water treatment -Secretary of Health and municipal Oral Health Coordinator, are informed monthly about the results of sample analyses, becoming aware of the situation of their cities concerning fluoride content.
For the analysis of results on fluoride content, the project uses the classification prepared by the Collaborating Center of the Ministry of Health in Oral Health Surveillance (CECOL) of the Public Health School of the University of São Paulo, which is based on the principle of higher benefit for preventing caries and lower risk of developing dental fluorosis, also considering the average maximum temperature of each location (Chart 1) (UNIVERSIDADE DE SÃO PAULO, 2011).
Chart 1. Fluoride concentrations and the benefit and risk levels of locations whose average maximum temperatures are between 32.5°C and 26.3ºC, according to the CECOL.

Total 29398 100
In Table 1, comparing the means of the first year of implementation of monthly analyses of the project (2005) to the year 2015 showed that some cities have adapted the fluoride content in their drinking water to the recommended values, as follows: Auriflama, Braúna, Buritama, Clementina, Glicério, Guaraçaí, Itapura, and Santo Antônio do Aracanguá.Not every city, however, has adopted the method.It is also observed that most of the cities, in 2015, presents optimal amounts of fluoride.In Table 2, the percentage distribution of water sample results of all cities, from November 2004 to December 2015, by monthly analyses, clearly shows that half of them are within the range that provides the greatest benefit and minimal risk.
Some cities, such as Birigui, show a complex distribution network with several water catchment sources composing its supply system, including deep wells.The deep wells are namely Aqua Pérola and Matéria, both from the Guarani aquifer.Studies conducted in the cities show that the fluoride content of these wells are above the recommended values, with approximately 51% of their samples with values above 0.84 milligrams of fluoride per liter (mgF/L) (MOIMAZ; SANTOS, 2015).An epidemiological study conducted in the city of Birigui also found high presence of fluorosis in 12 year-old children enrolled in public educational institutions, showing a significant association between the presence of the disease and the areas with excess fluoride in the water supply (MARQUES, 2008); hence the importance of establishing collection points according to the supply sources.In 2011, an agreement between the city of Birigui and the School of Dentistry of Araçatuba (FOA process-1457/2010, additive-term 01) was signed, so to officially continue the project activities.
Studies aiming to investigate the prevalence of dental fluorosis in Brazil have begun in 1970 with a survey conducted in the city of Pereira Barreto (one of the cities included in the project of external control), where fluoride concentration in the water was 20 mgF/L, an extremely high value.From 442 children examined, only 21% were fluorosis-free (SALIBA; UCHÔA, 1970).During the year of 2015, with monthly collections of water, the mean fluoride concentration of this city was 0.75 mgF/L and standard deviation was 0.14.The source of water supply for this location is a deep well.
Chart 2. Papers published in scientific journals by the project, since 1991.
Reduction in the prevalence of dental caries after ten years of public water supply fluoridation in the city of Birigui, SP, Brazil.
locations, especially those where fluoride in drinking water was assumed to cause risks to the population.The contributions that these studies provide are not restricted to the scientific community.The findings and conclusions of each of them contribute to the maximum understanding of the characteristics, qualities, and potential limitations of the method, so that new knowledge is disseminated nationally and internationally, expanding the technical and scientific knowledge on the subject for researchers, teachers, and professionals responsible for water treatment.
In 2011, Ordinance n. 518/2004 was revoked, and therefore, Ordinance n. 2914 has become the current regulation for the potability of water intended for human consumption.The review of Ordinance MS n. 518/2004 considered advances in technical and scientific knowledge, international experiences, and the recommendations of the 4th Edition of the Guidelines for Drinking-Water Quality from the World Health Organization, adapted to the Brazilian reality (BRASIL, 2012).According to the ordinance, the maximum fluoride ion allowed is 1.5 mgF/L.Ordinance n. 635/GM/MS of 01/30/1976, which approves norms and standards on water fluoridation of public water supply systems for human consumption, sets recommended limits to fluoride concentration based on the maximum daily average temperatures.Thus, states may create laws by setting minimum and maximum amounts of fluoride contained in their municipal water supplies according to the average maximum temperature of each location, however, not exceeding the maximum allowed of 1.5 mgF/L.For the state of São Paulo, for example, the SS Resolution -250/95 sets an optimal concentration of fluoride in water intended for human consumption in the range of 0.6 to 0.8 mgF/L (SÃO PAULO, 1995).
The project contributes to the professional qualification of undergraduate students, postgraduate students, teachers, and technicians, training them for research and field activities, generating benefits for all parties involved -the cities, the university, and the community.The cities are benefited with information about the fluoride content present in their drinking water provided monthly to health coordinators, oral health secretaries, and technicians responsible for water treatment.One of the challenges of the water fluoridation method is that external control is difficult in small-and medium-sized cities, due to the lack of laboratory infrastructure and technical expertise to carry out periodic analyses (SALIBA et al., 2009).The university is favored by the research conducted, thus spreading their work to the academic world, helping to improve the method with new findings, reducing risks, and maximizing benefits.The university also provides the involved students with the experience of participating in a project that works directly in association with the Regional Board of Health and the cities, providing the most extensive operational knowledge on guidelines and public health service, technical standards, reports, and federal laws that govern and regulate fluoridation, and on the operation of water distribution networks.Hence, the community eventually becomes the main beneficiary of the project activities, with access to water within the ideal standards of fluoride content.
Over the years of the project, several meetings were held with the heads of each city to update the information on their respective water supply systems.In these meetings, the main difficulties in obtaining control of the optimal fluoride content are checked, analyzed, and discussed with the municipal authorities, besides promoting discussions about the importance of external control in public water supplies to prevent tooth decay and to the risks of dental fluorosis development.In cities with greater variability of results, meetings were carried out "in situ" with the technicians responsible for water treatment, aiming to identify and try to solve the difficulties detected regarding the settlement of adequate fluoride content in water.This service provides managers and health professionals with conditions to plan their actions in public health and ensure that the entire population may receive quality water.
The integration of universities with health and surveillance services and other social institutions is important and should be encouraged, because they generate benefits to all involved.Fluoridation of public water supplies is an already established method and several studies prove its benefits.However, monitoring is necessary so that contents are within the ideal parameters.Clinical cases of dental fluorosis, although rare today, may occur in certain locations.In order to study and reverse this phenomenon, it is important to have information regarding the mapping of distribution networks in each city, as well as constantly monitoring its waters.Locations with no fluoridated water supplies should be encouraged to adopt the method, so it continues providing benefits for tooth decay prevention.

CONCLUSION
For over 11 years, the project of external control of fluoride, carried out by the School of Dentistry of Araçatuba monthly analyzes water samples from 40 cities in northwestern São Paulo (Brazil).The methodology adopted by the project allows identifying areas where the population may be exposed to higher concentrations of fluoride.From November 2004 to December 2015, 50.98% of water samples from all cities were within the optimal parameters.Monitoring is necessary to reach the maximum benefit in the prevention of tooth decay and minimum risk in fluorosis development.

Figure 1 .
Figure 1.Map of the State of São Paulo with the region from the DRS-II circled in red, showing the area with the cities included in the project of fluoride external control.

Table 1 .
Cities, amount of water collection points, origin of fluoride in water, means and standard deviations for the years 2005 and 2015.

Table 2 .
Percentage distribution of water samples according to the fluoride content of the 40 cities included in the project of external control, with data from November 2004 to December 2015.