Effects of household water filters on fluoride concentrations

2004 Fiscal Year Final Research Report Summary

• Project/Area Number: 15592218
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Social dentistry
• Research Institution: Nippon Dental University
• Principal Investigator: SATO Tsutomu Nippon Dental University, School of Dentistry at Tokyo, Associate Professor, 歯学部, 助教授 (60130671)
• Co-Investigator(Kenkyū-buntansha): TANAKA Tomoko Nippon Dental University, School of Dentistry at Tokyo, Assistant Professor, 歯学部, 講師 (70307958)
• Project Period (FY): 2003 – 2004
• Keywords: Fluoride / fluoridation / Water filters / Prevention of dental caries

Research Abstract

The fluoridation of tap water is an excellent method from a public hygiene point of view for preventing dental caries. Fluoridation is now possible in Japan as well (Ministry of Health, Labour, and Welfare, 2000), provided the citizens in the area are in agreement. Interest in the supply of safe drinking water among Japanese citizens has increased, and as a result, there has been an increase in the number of households installing water filters on their taps. Therefore, when fluoridation is carried out, there is a need to study the concentrations of fluoride (F) after the water passes through the filter. In the present study, we have produced a water filter using 2 types of filter materials that are commonly used in household water filters and examined the effects of the filter materials on F concentrations.
A simple water filtration device was constructed using activated charcoal filters and hollow fiber filters, both of which are widely employed as filters in household water filtration systems. NaF was added to purified water or tap water to prepare a variety of test solutions with F concentrations ranging from 0.1 to 10mg/mL. Each test solution was passed through the filtration system at a pressure normally used and then the F concentration after filtration was determined with an F ion electrode (direct reading method). The F concentration in the filter after filtration was measured using a flow-injection apparatus.
The F concentration after filtration through the activated charcoal filter was approximately 1/10 that of before filtration for all test solutions up to a filter volume of 10L. Subsequent to this, the F concentration increased as the volume filtered increased. No change in the F concentration before and after filtration was observed for the hollow fiber filter. The activated charcoal filters contained high concentrations of F after completion of the experiments.
The results clearly indicate that the F concentration in tap water after fluoridation is affected by household water filters that use activated charcoal filters. Therefore, the type of water filter used must be taken into consideration in order to ensure the anti-dental caries effect of water fluoridation. Negative and positive ions other than F (Cl, Mg, and Ca) were adsorbed to the activated charcoal and hollow fiber filters. Definitive results were not obtained for any other ions.