The use of a colorimeter in analyzing the fluoride content of public well water.

Water samples from 110 public wells in Ohio were analyzed for fluoride content using both an ion-specific electrode and a coIorimeter. In addition to the fluoride testing, analyses were performed on selected known interfering substances in the water. Sixty per cent of the samples differed by > 0.1 ppm fluoride with a mean difference of+ O. 14 ppm. Prescriptions for dietary fluoride supplementation based on the colorimetric results would have been incorrect 44.6% of the time. Sulfate levels had a significant (P < 0.05) effect on the accuracy of the coIorimetric results. Without prior distiIlation, the colorimetric method is unsatisfactory for determining fluoride concentration of well water. Dental caries is the most prevalent chronic disease of childhood (Newbrun 1980; National Institutes of Health [NIH] 1981). Sixty-three per cent of the children between the ages of 5 and 17 years in the United States experience dental caries (NIH 1981). Fluorides are the most effective agents in the prevention of dental caries (Wei 1976; Ericsson 1978). Fluoridation of water supplies is the most efficient and costeffective method of supplying fluoride to communities (Backer Dirks et al. 1978; Driscoll 1985). Individuals who live in nonfluoridated communities and those using private wells with inadequate fluoride levels rely on appropriate use of dietary fluoride supplementation for protection against dental caries. When taken from infancy, systemic fluoride supplements approach water fluoridation in effectiveness in preventing dental caries (Aasenden and Peebles 1974). The Committee on Nutrition of the American Academy of Pediatrics (AAP) in 1986 made recommendations for the dietary supplementation of fluoride. This dosage schedule is nearly identical to the schedule recommended by the Committee on Dental Therapeutics of the ADA (1982) and the Committee on Nutrition of the AAP in 1979. This schedule resulted from several re-evaluations of previous fluoride supplementation schedules and included dietary and other sources of fluoride ingestion. These recommendations are based on the child’s age and the concentration of fluoride in his/her drinking water. Various methods of fluoride analysis of water samples have been used. The colorimetric and fluoride ion-specific electrode methods are currently the most common methods employed (American Public Health Assn. [APHA], American Water Works Assn. [AWWA], and Water Pollution Control Federation [WPCF] 1985). colorimetric method, the SPADNS {sodium 2-(parasulfophenylazo)-l,8-dihydroxy-3, 6-naphthalene disulfonate} method, is based on the reaction between fluoride and a dark red zirconium dye lake, forming a colorless complex anion (APHA, AWWA, WPCF 1985). This method results in a bleaching of the red color in an amount proportional to the fluoride concentration. As the amount of fluoride increases, the resulting color becomes lighter. Color then is determined photometrically using a filter photometer or spectrophotometer (Bellack 1972). Colorimetric methods are susceptible to interfering substances. High concentrations of alkalinity (CaCO3), aluminum (Al÷3), chloride (C1-), turbidity, color, (Fe÷3), hexamethaphosphate {(NaPO~)~}, phosphate ~), and sulfate (SOl 2) in the sample will result in error in the determination of fluoride content (Hach 1983; APHA, AWWA, WPCF 1985). The fluoride ion-specific electrode is designed to sense fluoride ions selectively. A standard reference electrode is attached to a pH meter which reads the potential established by the fluoride ions across a crystal between a standard solution and the sample solution (Bellack 1972). The fluoride ion-specific electrode method may be affected by the same substances to which the colorimetric methods are susceptible. With the exception of alkalinity, the concentrations of the interfering substances must be substantially higher to result in error in the electrode reading. Also, color and turbidity do not interfere with the results of the fluoride ion-specific electrode method (Bellack 1972; APHA, AWWA, WPCF 1985). This method also allows a wider range of fluoride concentrations (0.1-10.0 ppm) to be examined. The fluo204 CoeoRn~rmC FLUORIDE ANALYSIS: BROSSOK ET AL. ride ion-specific electrode has been found to be accurate to within 0.5% (Durst 1971). Appropriate fluoride supplementation requires accurate determination of the fluoride content of drinking water. Because of lower cost and convenience the colorimeter is being advocated for use by health professionals to perform this function (Love 1984; Crall 1985), although there is evidence that this method may not be accurate.’ The purpose of this study was to assess the degree of accuracy of the colorimetric method in determining fluoride concentrations of water samples for the purpose of prescribing fluoride supplementation. Methods and Materials Samples of drinking water obtained from public wells in Ohio were analyzed for fluoride content using a colorimeter and fluoride ion-specific electrode. A list of 182 new public wells with initial water analyses completed between January 1,1984, and November 30, 1985, was compiled from records at the Ohio Environmental Protection Agency, Division of Public Water Supply. The well site location, date of analysis, and test results of alkalinity, sulfate, chloride, fluoride, and iron levels were recorded for each well site included in the study. Of the original wells, samples were obtained from 110 sites. Most of the remainder were inactive (i.e., wells were closed off) by the initiation of this study. Collection of water samples was performed by dental hygienists employed by the Ohio Department of Health, Division of Dental Health. In addition to verbal instructions from the primary investigator, the hygienists were given specific written instructions for water sample collection. Two 120-ml, clear, flint glass bottles were used to collect water from each site. One sample from each well site was submitted to the Ohio Department of Health laboratory where analysis of fluoride content was performed on all samples by the same certified laboratory technician using a fluoride ion-specific electrode." The results from the ion-specific electrode served as the standard for fluoride content. The Ohio Department of Health laboratory consistently has had highly accurate fluoride determinations in the Centers for Disease Control proficiency testing. Prior to fluoride analysis, the second sample from each site was evaluated visually for sediment, turbidity, and color by two investigators (GEB, DJM). A trial examination of 10 samples was performed prior to examination of the entire group of samples to measure interexaminer reliability. Each sample was examined by both investigators independently and results were recorded. Total agreement was achieved in the trial examination. Initial interexaminer reliability for the entire group ~ Quentin 1967; Kondo 1969; Bellack 1972; APHA, AWWA, WPCF 1985. was very good (rho > 0.9). For the few samples where there was disagreement for a given property, the sample was re-examined by the investigators together until agreement was reached. Each of this second group of samples then was analyzed for fluoride using a colorimeter?The procedure described in the colorimeter manual was followed, except that there was no distillation of the samples performed. One reading was performed on each sample. Readings were recorded to 2 decimal places. The first decimal place was read directly from the meter scale on the colorimeter and the second decimal place was rounded to the nearest 0.05 mg/L. A logistic regression analysis was performed for each potential interfering factor (i.e., alkalinity, chloride, iron, sulfate, color, turbidity, sediment) to determine if the interference resulted in errors > 0.1 ppm. A linear regression analysis was performed for any interfering factors determined significant (P < 0.05) by logistic regression. The linear regression analysis was performed to quantify the influence of the individual interferences on the error of the colorimeter.