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| ORIGINAL ARTICLE |
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| Year : 2018 | Volume
: 16
| Issue : 2 | Page : 165-168 |
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Effect of different reverse osmosis water filters on fluoride content of drinking water
Mahesh Ravindra Khairnar1, Vardhaman Mulchand Jain2, Umesh Wadgave1, Rohit Ishwar Dhole3, Sandeep J Patil4, Swapnil Ramchandra Chopade3
1 Department of Public Health Dentistry, Bharati Vidyapeeth Deemed University Dental College and Hospital, Sangli, Maharashtra, India
2 Department of Public Health Dentistry, A.C.P.M. Dental College and Hospital, Dhule, Maharashtra, India
3 Department of Prosthodontics, Bharati Vidyapeeth Deemed University Dental College and Hospital, Sangli, Maharashtra, India
4 Department of Periodontology, Bharati Vidyapeeth Deemed University Dental College and Hospital, Sangli, Maharashtra, India
| Date of Submission | 05-Jan-2018 |
| Date of Acceptance | 13-Apr-2018 |
| Date of Web Publication | 24-May-2018 |
Correspondence Address:
Dr. Mahesh Ravindra Khairnar
Department of Public Health Dentistry, Bharati Vidyapeeth Deemed University Dental College and Hospital, Sangli, Maharashtra
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/jiaphd.jiaphd_8_18
Background: Reverse osmosis (RO) technology is an efficient method of reducing organic and inorganic contaminants of drinking water. It regulates the fluoride concentration in drinking water which influences the burden of dental caries and dental fluorosis in the general population. This study was designed with an aim to assess the effect of different RO water filters on fluoride content of drinking water. Materials and Methods: Ten different RO water filters available in the local market of Dhule city, Maharashtra, India, were tested in this study. Samples of filtered and nonfiltered tap water were collected from these RO filters installed in ten different households in the same area in Dhule city on three successive days, and fluoride analysis was done using fluoride ion selective electrode. Results: The amount of fluoride removed by different RO purification systems varied from 0.270 to 0.457 ppm (50.37%–84.62%). RO filters with total dissolved solid (TDS) controller showed more fluoride removal capacity (mean, 0.41 ppm) as compared to filters without TDS controller (mean, 0.36 ppm) (P > 0.05). Conclusion: RO is an effective defluoridation method. However, considering the beneficial effect of fluorides in reducing dental caries, when drinking water is subjected to water purification systems that reduce fluoride significantly below the optimal level, fluoride supplementation may be necessary. Keywords: Defluoridation, dental caries, drinking water, purification
How to cite this article:
Khairnar MR, Jain VM, Wadgave U, Dhole RI, Patil SJ, Chopade SR. Effect of different reverse osmosis water filters on fluoride content of drinking water. J Indian Assoc Public Health Dent 2018;16:165-8 |
| Introduction | |  |
Dental caries and dental fluorosis are significant public health problems in India.[1] Over the last few decades, India has witnessed an increasing trend in the prevalence of dental caries.[2] Around 40%–45% of the population in India suffer from dental caries and the number continues to rise day by day, whereas 230 districts of 19 states in India are endemic for dental and skeletal fluorosis.[3] Both the diseases are multifactorial; however, fluoride consumption is one crucial factor which can influence both the diseases. The major source of fluoride to the body is through drinking water.[4] Fluoride concentration in water is directly proportional to dental fluorosis and inversely related to dental caries. It has been proven through extensive research that optimum concentration of fluoride is required in drinking water to maintain the integrity of oral tissues.[5]
Use of home water purifiers has been on the rise in the past few years because of excessive contamination of drinking water. Among various water purifiers, reverse osmosis (RO) water purifier segment has the maximum share (39%) in the home water purifier industry.[6] RO process is efficient in terms of filtering out contaminants such as fluoride, especially in areas where water is heavily contaminated.[7],[8],[9] Indian commercial markets are equipped with a variety of RO filters which differ in the type of membrane used (cellulose based or thin film composite membrane) and stages of filtration (5 stages/6 stages/7 stages). These variations in RO filters may influence the filtrate quality. However, data regarding the effect of different types of RO filters on fluoride level in drinking water for the Indian scenario are lacking. Furthermore, Dhule city has suboptimal fluoride level in drinking water,[10] and subjecting the drinking water to further RO filtration may reduce the fluoride to an unacceptable level. Hence, the present study was designed with an aim to determine the extent to which domestic RO water filters remove fluoride from drinking water.
| Materials and Methods | | |
The present study was carried out after obtaining approval from the institutional review board (Ref No. 2798/ACPMMC/Dhule).
Collection, storage, and transportation of water samples
The study was conducted on water samples obtained from ten different households from one region with ten different RO systems [Table 1], which were supplied by a common municipal water unit. To standardize the filtration capacity of all filters, only those RO filters which were serviced in the last 3 months were selected. Three water samples before RO filtration and three water samples after RO filtration were collected for 3 consecutive days from all the ten households. The samples were collected in plastic bottles (polyethylene) that had been previously rinsed twice with deionized water to remove any fluoride residue. All the collected water samples were transported immediately to the laboratory where they were subjected to fluoride estimation analysis on the same day. All the samples were precoded from 1 to 20 and not disclosed to the technician so as to eliminate any potential bias. | Table 1: Concentration of fluoride in drinking water before and after filtration
Click here to view |
Analysis of fluoride content
All the samples were analyzed at the Maharashtra Public Health Engineering Department, District Laboratory, Dhule. Fluoride concentrations in all the samples were analyzed using a standard method given by the American Public Health Association using fluoride ion selective electrode.[11] It was standardized using fluoride solutions of 0.1–10 ppm. For fluoride analysis, equal amounts (20 ml) of each water sample and total ionic strength adjustment buffer solution were combined in a plastic beaker and agitated to remove air bubbles. For each sample, before taking readings, the electrode was rinsed, blot dried, and then placed into the test solution. The solution was stirred thoroughly with the electrode, and the steady readings on the meter were noted. The instrument was calibrated every half an hour.
Statistical analysis
The obtained values were subjected to statistical analysis using the Statistical Package for the Social Sciences (SPSS, IBM Corporation, Armonk, NY, USA) version 16 software. Mean fluoride concentration before and after filtration and mean difference in fluoride concentration were reported using descriptive statistics. Mean difference in the fluoride removal capacity of filters with and without total dissolved solid (TDS) controller was compared using Mann–Whitney U-test. P < 0.05 was considered statistically significant.
| Results | | |
The mean fluoride concentration before and after RO filtration, mean difference in fluoride concentration, and percentage reduction were determined for each of the test groups. The baseline (before RO filtration) water fluoride concentration was in the range of 0.53–0.54 ppm. In the present study, all the water samples showed a reduction in fluoride content in the range of 0.270–0.457 ppm after passing through various RO filters [Table 1]. Furthermore, mean difference in the fluoride removal was compared for RO filters with and without TDS controller [Table 2]. Mean difference in fluoride removal was found to be 0.41 and 0.36 ppm for RO filters with TDS controller and without TDS controller, respectively, in which the difference was not statistically significant (P = 0.286). | Table 2: Mean fluoride concentration in the filtrate of reverse osmosis systems with and without total dissolved solid controller
Click here to view |
| Discussion | | |
RO filters are mainly used to modify or remove the impurities from water. The hydraulic pressure exerted on one side of the semipermeable membrane in RO filters forces the water across the membrane, leaving the salts behind.[12] RO purification system was selected for the present study owing to its increased popularity in India and certain advantages over other methods of water purifications such as TDS controller, constant water quality assurance, long life of membranes, and less or no interference by other ions.[13]
In the present study, fluoride concentration in the public drinking water supply was found to be in the range of 0.53–0.54 ppm, which is far below the recommended levels of the Bureau of Indian Standard IS 10500:2012 (1–1.5 ppm). Upstream policy actions are required to regulate fluoride concentration in drinking water, as the fluoride supply to body through water plays a pivotal role in controlling dental caries and bone ossification to all the populations.
This is the first attempt to evaluate the extent to which various commercial RO filters with and without TDS controller available in Indian markets can remove fluoride in drinking water. Fluoride concentration in drinking water substantially reduced (range, 50.37%–84.62%) after filtration in all the filters. The study findings are in accordance with the previous studies.[7],[8],[9],[14] Previous researchers have reported the reduction of fluoride in the range of 22%–100%. The differences in the fluoride reduction capacity of RO systems in various researches can be explained by differences in the type of membranes used, water pressure, pH and temperature of the water, baseline fluoride concentration, and techniques of fluoride estimation employed. The rise in temperature leads to dissolution of the solvents which can easily pass through the RO membrane; while at the acidic pH, the hydrogen ions bind with the fluoride, thereby decreasing the filtering capacity of RO membrane.[15] In addition, feed water pressure is directly proportional to the filtration capacity of RO membrane.[15]
Few of the RO water purifiers are equipped with TDS controller. The role of TDS controller is to maintain essential minerals in drinking water. Totally four out of the ten RO filters selected for the study had TDS control feature. However, no substantial difference was found in fluoride removal capacity of the RO filters with and without TDS controller.
Drinking water is the most important source of fluoride for the human beings, and knowledge of the fluoride content of drinking water is essential for the public as well as health professionals to know, especially dentists. Available literature shows that consumption of nonfluoridated community and bottled water may put children at the risk of developing dental caries.[16] Hence, it is necessary to consume fluoride in required optimum amount for better oral health. Therefore, estimation of concentration of fluoride ion in drinking water becomes necessary in low- and high-fluoridated areas from a health perspective.
This fluoride reduction quality of RO systems proves to be beneficial in fluorosis-affected regions. However, RO system will worsen the existing condition in areas where water fluoride concentration is suboptimal or low and intake of fluoride from other sources is insufficient. According to the American Academy of Pediatric Dentistry, children consuming fluoridated water at <0.6 ppm should receive fluoride supplements.[17]
Implications
The results of the present study showed variation in fluoride removal of different RO filters. RO filters with multiple stages (RO + ultraviolet + ultrafiltration + TDS controller) removed more amount of fluoride as compared to RO filters with single-stage filtration system. Hence, people should be wise enough while selecting RO filters. Filtration capacity as discussed earlier is influenced by various factors. Hence, this provides a choice for RO filter manufacturers as well as people residing in different areas with different levels of fluoride in drinking water. RO filter manufacturers can alter their technology for controlling the levels of essential elements in water according to the need of the specific area and manufacture the filters accordingly. Furthermore, consumers have the choice of selecting RO filters based on the need of fluoride and other essential elements in the area they reside, cost-effectiveness of the filters, etc.
Limitations
Only surface water supplies were included and bore well water and open well water supplies were not included. In addition, pH and temperature of the water samples were not recorded.
| Conclusion | | |
The present study showed low levels of fluoride in drinking water and further reduction in this element after purification by RO filters. RO water filters are effective in reducing fluoride levels in drinking water, indicating their potential in fluoride-endemic areas. However, considering the beneficial effect of fluorides in reducing dental caries, when drinking water is subjected to water purification systems that reduce fluoride significantly below the optimal level, fluoride supplementation may be necessary for prevention of dental caries.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2]
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