title: Fluoride: A naturally-occurring health hazard in drinking-water resources of Northern Thailand.
abstract: In Northern Thailand, incidences of fluorosis resulting from the consumption of high-fluoride drinking-water have been documented. In this study, we mapped the high-fluoride endemic areas and described the relevant transport processes of fluoride in enriched waters in the provinces of Chiang Mai and Lamphun. Over one thousand surface and sub-surface water samples including a total of 995 collected from shallow (depth: ≤ 30 m) and deep (> 30 m) wells were analysed from two unconnected high-fluoride endemic areas. At the Chiang Mai site, 31% of the shallow wells contained hazardous levels (≥ 1.5 mg/L) of fluoride, compared with the 18% observed in the deep wells. However, at the Lamphun site, more deep wells (35%) contained water with at least 1.5mg/L fluoride compared with the shallow wells (7%). At the Chiang Mai site, the high-fluoride waters originate from a nearby geothermal field. Fluoride-rich geothermal waters are distributed across the area following natural hydrological pathways of surface and sub-surface water flow. At the Lamphun site, a well-defined, curvilinear high-fluoride anomalous zone, resembling that of the nearby conspicuous Mae Tha Fault, was identified. This similarity provides evidence of the existence of an unmapped, blind fault as well as its likely association to a geogenic source (biotite-granite) of fluoride related to the faulted zone. Excessive abstraction of ground water resources may also have affected the distribution and concentration of fluoride at both sites. The distribution of these high-fluoride waters is influenced by a myriad of complex natural and anthropogenic processes which thus created a challenge for the management of water resources for safe consumption in affected areas. The notion of clean and safe drinking water can be found in deeper aquifers is not necessarily true. Groundwater at any depth should always be tested before the construction of wells.
authors.affiliation: Department of Geography, National University of Singapore, Singapore. Electronic address: joon.chuah@u.nus.edu.
authors.forename: C Joon
authors.initials: CJ
authors.lastname: Chuah
authors.affiliation: Department of Geography, National University of Singapore, Singapore.
authors.forename: Han Rui
authors.initials: HR
authors.lastname: Lye
authors.affiliation: Department of Geography, National University of Singapore, Singapore.
authors.forename: Alan D
authors.initials: AD
authors.lastname: Ziegler
authors.affiliation: Department of Geosciences, Boise State University, Boise, ID, USA.
authors.forename: Spencer H
authors.initials: SH
authors.lastname: Wood
authors.affiliation: Inter-Country Centre for Oral Health, Chiang Mai, Thailand.
authors.forename: Chatpat
authors.initials: C
authors.lastname: Kongpun
authors.affiliation: Inter-Country Centre for Oral Health, Chiang Mai, Thailand.
authors.forename: Sunsanee
authors.initials: S
authors.lastname: Rajchagool
mesh_terms: D060766:Drinking Water / Q000737:chemistry*; D004781:Environmental Exposure / Q000706:statistics & numerical data*; D005459:Fluorides / Q000032:analysis*; D009050:Fluorosis, Dental / Q000453:epidemiology*; D060587:Groundwater / Q000737:chemistry; D013785:Thailand; D014874:Water Pollutants, Chemical / Q000032:analysis*; D062066:Water Resources; D060986:Water Wells
chemical_list: D060766:Drinking Water; D014874:Water Pollutants, Chemical; D005459:Fluorides
keywords: Drinking-water; Fluorosis; Geothermal water; Groundwater