Assessment of Fluoride Intake from Rice Consumption by Using Tap Water Containing Fluoride for Rice Soaking Water

The people in Thailand generally soak sticky rice in water for 12–24 h before steaming and rinse jasmine rice before cooking. This study aimed at estimating fluoride intake from rice by the measuring rice consumption and examining factors affecting fluoride adsorption on jasmine rice and sticky rice in Buak Khang Subdistict, Chiang Mai Province, Thailand. It was found that 65.7% of 35 households still use tap water containing fluoride at 5.94 ± 0.29 mg/L of fluoride for rice soaking and rinsing. The amount of jasmine rice and sticky rice consumption was 0.096 ± 0.05 kg/meal and 0.114 ± 0.06 kg/ meal, respectively. The fluoride taken up into rice exhibited a positive correlation with the initial fluoride in water, the duration and water volume for rice soaking. The fluoride intake from jasmine rice and sticky rice based on the field survey was 0.004 ± 0.007 mg/kg-bw/day and 0.025 ± 0.024 mg/ kg-bw/day, respectively. The results of this study indicated that eating rice can significantly contribute to the total amount of fluoride intake; thus, it is recommended to use fluoride-free water or reducing time duration for rice soaking in areas using fluoride-containing groundwaters.