fluoride concentrations of water sources in tibet

FLUORIDE CONCENTRATIONS OF WATER SOURCES IN TIBET
http://www.fluoride-journal.com/00-33-4/334-205.pdf

Jin Cao,a Yan Zhao, Jianwei Liu, Ruodan Xirao,b Sangbu Danzengb
Changsha and Tibet, China


SUMMARY: Fluoride concentrations of 60 samples randomly selected from surface and underground water sources in major population regions of northcentral, central, southern, and southern border regions of Tibet were determined with a fluoride-ion selective electrode. The concentrations ranged from 0.02 to 0.18 mg F/L with the highest levels in river and well waters. The results indicate that most drinking water sources in Tibet are low in fluoride and are therefore not responsible for the widespread occurrence of dental fluorosis that appears to be caused by early childhood intake of fluoride from highfluoride “brick tea”.

Keywords: Brick tea, Fluorosis from tea, Tibet water sources, Water fluoride.

INTRODUCTION

As a mountainous region with generally ample precipitation and runoff, Tibet has abundant supplies of surface waters. The plateau lake areas are among the highest and largest in the world, and there are plentiful water supplies in widely dispersed marshlands. Important sources of drinking water are from rivers, wells, and marshes. Because of the importance of water-borne fluoride effects in the human body, especially on the teeth and bones, and because of the widespread occurrence of dental fluorosis in Tibet without knowledge of F levels in the drinking water, we undertook a survey to determine the fluoride content of the principal domestic water sources.



MATERIALS AND METHODS

Areas included for study were randomly selected from six counties and two cities in northcentral, central, southern, and southern border regions of Tibet (see map).1 Fluoride determinations were made with a fluoride-ion selective electrode and potentiometer (ORION 868 type, USA).2 The calibration curve was plotted against standard NaF fluoride solutions containing 0.1, 0.5, 1.0, 5.0, and 10.0 mg F/L, and a total ionic strength adjustment buffer was used. The mV readings were linear against the logarithm of mg/L F concentration, E = 197.4 - 50.2 log F (mg/L), r = -0.9948. The 50 mL water samples were collected in September 1998 with water sample tubes (BOMEX, Beijing Glass Factory).



RESULTS

The location and description of the regions studied are presented in Table 1.

These regions typify the important economic and geographical features of Tibet.

Table 2 shows that the fluoride concentrations in the six water sources sampled
in Naqu County ranged from 0.03 to 0.18 mg/L. The mean value of the 18
samples was 0.09 mg/L.

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DISCUSSION

Dental fluorosis caused by fluoride in drinking water is a common sight in many parts of the world.3-5 In Tibet, however, water sources for domestic use come mainly from rivers, wells, and springs, which, in this study, were all found to have less than 0.2 mg F/L. Therefore, drinking water type dental fluorosis would not be expected from any of these waters. Although not often used as sources for drinking water, the 279 known hot springs in Tibet are reported to have 1.0 to 212 mg F/L, and the effects are readily seen. For example, in the village of Kacheng in Xietongmen County, where such water is used for drinking, the prevalence of dental fluorosis is 67.49%.6

Nevertheless, we found that dental fluorosis was fairly common in our study areas, even though the drinking water is quite low in fluoride. The explanation probably lies in the fact that people in Tibet, including young children, have a long-standing tradition of drinking high-fluoride brick tea made from old stems and leaves of tea bushes. A "brick tea" type fluorosis that results is prevalent among many minority populations in China, and it therefore probably accounts for most of the high prevalence of dental fluorosis we observed among children in our low-fluoride study areas.7-9




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