Effects of brewing conditions on infusible fluoride levels in tea and herbal products and probabilistic health risk assessment

Excessive ingestion of fluorides might adversely affect the health of humans. Hence, this study aimed to investigate the concentrations of infusible fluoride in five different types of tea and herbal products; additionally, the probabilistic health risks associated with the ingestion of fluoride in drinking tea and herbal products were estimated. The highest and lowest concentrations of infusible fluoride were detected in black and white tea, respectively. On average, the highest amount of infusible fluoride was extracted following a short brewing time of 5 min in the case of black tea (2.54 mg/L), herbal tea (0.40 mg/L), and white tea (0.21 mg/L). The level of infusible fluoride during brewing was inversely associated with the leaf size of the tea and herbal products. Furthermore, the type of water used influenced the release of infusible fluoride; purified water yielded lower amounts of infused fluoride. The findings of the probabilistic health risk assessment indicated that the consumption of black tea can increase the fluoride intake leading to chronic exposure. Thus, the health risk posed by fluoride intake from drinking tea needs to be evaluated in more details in the future. Appropriate measures for health risk mitigation need to be implemented to minimize the total body burden of fluorides in humans.


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Fluorine is the 13th most abundant element in the Earth's crust (0.054% by weight) and is 59 mostly present in the form of fluoride in various minerals. Fluoride is an essential micronutrient, 60 and an appropriate amount of intake of this mineral, daily, can prevent the development of dental 74 Tea (Camellia sinensis) is one of the most popular nonalcoholic beverages extensively 75 consumed by health-conscious people in many societies 11,12 . The numerous types of teas 76 available in the market could be broadly categorized into four types depending on the number of 77 oxidation steps required during processing: black tea (fully oxidized), green tea (nonoxidized), 78 oolong tea (semioxidized), and white tea (lightly oxidized) [13][14][15] . Herbal tea products, in which 79 some contain the leaves of Camellia sinensis 11 , are also widely popular among consumers in Thailand and across the world 16 . The consumption of tea daily is increasing, and large amounts 81 are consumed by adults (nearly 1 L per person per day on average) in oriental countries 11 . The 82 positive health benefits of tea include the presence of nutrients and minerals, antioxidant activity, 83 favorable taste, aroma, and anticancer properties [17][18][19] . 84 Tea contains a greater amount of fluoride than other plants, predominantly because it is 85 an efficient fluoride accumulator 20 . Most of the fluoride in tea (nearly 98%) is accumulated in the 86 leaves, particularly the mature leaves 21 , and can be easily released during tea infusion 22,23 .

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Hence, the ingestion of fluoride from tea can lead to potential detrimental health effects.

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According to previous studies 13, 22 -C is the fluoride concentration in tea infusion (mg/L).
-DI is the average daily intake rate of tea (L/day).
-EF is the exposure frequency (day(s)/year).
-ED is the exposure duration (year).
-AT is the averaging time (days).
-CDI is the chronic daily intake (mg/kg/day).
-RfD is the reference dose (mg/kg/day).   Tea is generally infused for a few minutes using hot water 11 . Therefore, a brewing time of    reported that a change in the size of the tea particle affected the rate of infusion of fluoride; tea 245 14 products with large particle size could have a slower rate of infusion because of the lower surface 246 area when compared with those with small particle size.

Note:
The concentration of fluoride in distilled water, ultrapure water, and RO water was lower than the detection limit (DL) of 0.02 301 mg/L. ND, not detected.      variance ranging from −0.5% to −12.5%.

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Fluoride concentration had the highest influence on the risk estimation with a 374 contribution to variance ranging from 53% to 92% in teens and 48% to 95% in adults.

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Furthermore, the contribution to variance for exposure frequency and DI respectively ranged 376 3%-37% and 5%-31% in teens and 3%-30% and 1%-21% in adults. Hence, based on these 377 results, the concentration of fluoride in tea could be the most important variable in estimating the 378 health risk among the age groups evaluated in this study because of its high sensitivity 379 (approximately >50%).