Abstract

Highlights

  • Electrochemical method development.
  • Fluoride levels in food.
  • Beverage analyses and risk assessment.
In this research paper, a potentiometric analytical method for the determination of Fluoride was developed and applied to analyse the most commonly consumed beverages. Considering all the beverages studied, the fluoride levels ranged from the detection limit (0.02 mg L-1) to 3.5 mg L-1, measured in tea samples obtained from an automatic dispenser. In conclusion, the investigated beverages do not pose a problem for humans if they are consumed in moderation. For coffees, barley-based drinks, infusions, chamomiles, herbal teas and teas, which are commonly prepared with tap or bottled water, the fluoride content of the water should also be added to the results obtained to assess the real contribution. The only drink potentially causing a risk, especially for children, could be tea prepared by infusing the leaves contained in paper filters because it contributes significantly to the daily dose of fluoride. This dose would increase if the fluoride contribution from water were taken into account.

Excerpts:

… Fluoride inhibits bacterial metabolism and forms fluorapatite resulting in increased structural stability. However, excessive intake, especially if prolonged over time, can show several negative effects. Fluoride accumulates in teeth and bones, especially during growth, causing a pathological condition known as fluorosis. Since the beneficial properties or adverse effects depend on the dose and time of exposure, it is important to identify and evaluate all potential sources of fluoride in order to maximize the anti-caries effect and minimize the fluorosis risk. The first reports of fluorosis date back to 1888 when a family from Durango (Mexico) was described as having black teeth, subsequently, in 1891, enamel erosion was described in residents of Naples (Fawell et al., 2006). In detail, during the early 1900s, it was observed that Italian immigrants from cities near Naples, developed brown spots on their teeth directly related to the fluoride content in drinking water. Subsequently, it was recognized that the intake of fluoride in optimal quantities provides protection against the development of dental caries without having any negative effect on the colour of the teeth. Considering what has been observed, since 1945 in the United States experiments of collective prophylaxis have begun through artificial fluoridation of drinking waters of some cities, in which NaF was added in quantities to have a protective effect against tooth decay, without being harmful to health. Most Western European countries did not follow the American example, while other countries discontinued this practice during the late twentieth century (Ozsvath, 2008). It has been estimated that children and some adults ingest between 0.016 to 0.15 mg of fluoride via the toothpaste for every cleaning procedure. Toothpaste, therefore, can account for up to 25% of the total fluoride dose for children aged between 2 and 6 years, depending on the amount of toothpaste ingested while cleaning teeth (Guth et al., 2020). Currently, drinking water is the main source of fluoride intake, therefore, the World Health Organization (WHO) has established that the concentration of this element, for it to play a fundamental role in the prevention and maintenance of tooth and bone health, must be in the range 0.5-1.5 mg L-1. It is estimated, however, that more than 200 million people, living in around 20 countries, consume drinking water with fluoride concentration higher than the levels established by the WHO. Although drinking water is the main source of F intake in humans, food and drink are also potential pathways exposure (Karami et al., 2019). Table 1, Table 2 show the concentrations of fluoride in several foods and drinks, respectively (Fawell et al., 2006, Cantoral et al., 2019).

Table 1. – Fluoride concentration (mg kg-1) in some foods.

Sample [F] Reference Sample [F] Reference
Vegetable and fruit 0.1-0.4 Fawell et al., 2006 Lemon 0.009 Cantoral et al., 2019
Barley, rice, potatoes 2.0 Fawell et al., 2006 Fast food 1.2 Cantoral et al., 2019
Meat e poultry 0.01-1.70 Fawell et al., 2006 Jelly 3.7 Cantoral et al., 2019
Fish 0.06-4.57 Fawell et al., 2006 Pre-cooked rice 4.3 Cantoral et al., 2019
Oil and fat 0.05-0.13 Fawell et al., 2006 Whole grain bread 5.9 Cantoral et al., 2019
Breast milk 0.005-0.010 Fawell et al., 2006 Seafood 1.9 Cantoral et al., 2019
Lard 0.003 Cantoral et al., 2019 Oysters 14.7 Cantoral et al., 2019
Papaya 0.007 Cantoral et al., 2019 Fried/oven pork rinds 14.7 Cantoral et al., 2019

Table 2. – Fluoride concentration (mg L-1) in some beverages.

Sample [F] Reference Sample [F] Reference
Coffee 1 0.10-0.58 Satou et al., 2021 Beer 1 0.05-0.10 Satou et al., 2021
Coffee 2 0.03-0.15 Satou et al., 2021 Beer 2 0.08-0.88 Jaudenes et al., 2018
Soluble coffee 0.15-0.56 Satou et al., 2021 Beer 3 0.06-0.66 Jaudenes et al., 2018
Alcohol 1 0.06-0.09 Satou et al., 2021 Beer 4 0.36-0.89 Jaudenes et al., 2018
Alcohol 2 0.01-2.15 Satou et al., 2021 Beer 5 0.07-0.80 Jaudenes et al., 2018
Infuses 0.07-0.17 Satou et al., 2021 Beer 6 0.28-1.66 Jaudenes et al., 2018
Beer 7 0.63-0.71 Jaudenes et al., 2018 Green tea 0.26-0.41 Liu et al., 2017
Beer 8 0.32-0.77 Jaudenes et al., 2018 Herbal teas 0.02-0.40 Liu et al., 2017
Tea 1.06-6.68 Satou et al., 2021 Fruit juice 0.02-0.04 Liu et al., 2017
Black tea 0.22-0.35 Liu et al., 2017 Carbonated drink 0.01-0.24 Liu et al., 2017
Differences in fluoride concentrations in beverages and foods, of different countries, can be attributed to proximity of the area from which the raw materials come from to a volcanic zone, the composition of the soil, the water used for irrigation or for food and drinks preparation (Cantoral et al., 2019).
***

Table 4. – Fluoride concentration (mg L-1) in some fruit juices and milks.

Sample [F] Sample [F]
1 Juice peach 1 0.196 ± 0.002 56 Juice 4 0.071 ± 0.002
2 Juice ace 3 0.205 ± 0.002 4 Milk 1 < 0.020
3 Juice ace 5 0.278 ± 0.003 60 Milk 2 < 0.020
19 Orange juice homemade < 0.034 61 Milk 3 < 0.020
35 Juice peach 2 0.052 ± 0.001 135 Milk 4 0.212 ± 0.002
In the carbonated soft drinks (Table 5), fluoride content is highly variable and ranges from the detection limit (0.020 mg L-1) to 0.47 mg L-1 (sample n°118). Probably, this depends on the fact that the aforementioned drinks are industrially prepared using different processes and raw materials and it is possible to hypothesize that the samples (n° 16, 53, 68, 121) having undetectable concentrations of fluoride (made by the same multinational industry) were prepared using demineralized water, while, the samples with measurable concentrations of fluoride were prepared with tap water. In particular, the drink called soda, generally, is produced by small local artisan companies and contains water, citric acid, sugar or sweeteners, flavourings and carbon dioxide. Since it does not contain phosphates, as in the case of cola, it can be produced with non-demineralised water.

Table 5. – Fluoride concentration (mg L-1) in carbonated drinks.

Sample [F] Sample [F]
14 Lemonade 1 0.078 ± 0.002 41 Chinotto 1 0.24 ± 0.002
33 Lemonade 2 0.36 ± 0.001 66 Chinotto 2 0.16 ± 0.002
16 Cola 1 < 0.020 42 Carbonated orange soda 1 0.29 ± 0.002
54 Cola 2 0.096 ± 0.001 95 Carbonated orange soda 2 0.038 ± 0.001
55 Cola 3 0.28 ± 0.001 132 Carbonated orange soda 3 < 0.020
68 Cola 4 < 0.020 53 Tonic water 1 < 0.020
40 Soda1 0.25 ± 0.002 10 Tonic water 2 0.089 ± 0.001
118 Soda 2 0.47 ± 0.002 121 Tonic water 3 < 0.020
80 Effervescent < 0.020
***

Table 8. Fluoride concentration (mg L-1) in some tea.

Sample [F] Sample [F]
20 Instant tea 1 0.26 ± 0.003 86 Tea bag 7 1.4 ± 0.002?
21 Instant tea 2 0.043 ± 0.002 87 Tea bag 8 1.8 ± 0.003?
112 Bottled tea 1 0.11 ± 0.002 88 Tea bag 9 1.9 ± 0.002?
129 Bottled tea 2 0.81 ± 0.001 91 Tea black oriental bag 10 3.2 ± 0.002?
130 Bottled tea 3 0.098 ± 0.002 92 Tea bag 11 0.84 ± 0.002?
127 Tea vending machine 3.5 ± 0.003 96 Tea bag 12 1.1 ± 0.002?
44 Tea bag 1 2.9 ± 0.003 97 Tea bag 13 2.6 ± 0.002?
47 Tea bag 2 2.2 ± 0.004 107 Tea bag 14 0.53 ± 0.002?
48 Tea bag 3 0.63 ± 0.001 108 Tea bag 15 1.6 ± 0.003?
49 Tea bag 4 2.8 ± 0.002 109 Tea bag 16 1.7 ± 0.002?
50 Tea bag 5 2.8 ± 0.003 129 Tea bag 17 1.6 ± 0.002?
51 Tea bag 6 2.7 ± 0,003
?
average concentrations at 5, 10 and 30 min of infusion.
Considering that the highest amount of fluoride is released from the tea bags during the infusion process, we evaluated a possible correlation between F concentration and infusion time (Table 9).

Table 9. – Fluoride concentration (mg L-1) in some tea at 5, 10 and 30 min.

Sample [F] 5 min. [F] 10 min. [F] 30 min. % Release 5 min % Release 10 min
86 Tea bag 7 1.2 ± 0.002 1.4 ± 0.002 1.7 ± 0.003 69 86
87 Tea green orange bag 8 1.8 ± 0.003 1.9 ± 0.001 1.9 ± 0.001 92 98
88 Tea breakfast bag 9 1.6 ± 0.002 1.9 ± 0.003 2.0 ± 0.003 80 92
91 Tea black oriental bag 10 3.2 ± 0.002 3.2 ± 0.002 3.3 ± 0.002 96 97
92 Tea bag 11 0.80 ± 0.002 0.87 ± 0.001 0.87 ± 0.001 91 99
96 Tea bag 12 0.90 ± 0.001 1.2 ± 0.002 1.2 ± 0.002 72 95
97 Tea bag 13 2.3 ± 0.001 2.6 ± 0.002 2.8 ± 0.002 80 93
107 Tea bag 14 0.46 ± 0.002 0.55 ± 0.003 0.57 ± 0.002 81 95
108 Tea bag 15 1.4 ± 0.003 1.6 ± 0.002 1.9 ± 0.002 74 85
109 Tea bag 16 1.6 ± 0.001 1.7 ± 0.002 2.0 ± 0.003 79 87
129 Tea bag 17 1.5 ± 0.002 1.5 ± 0.002 1.7 ± 0.003 89 92
Mean release 82 85
From the Table 9 and the Fig. 3 it is noted that most of fluoride (mean 82%) is released within the first 5 minutes of infusion, passing from 5 to 10 minutes, it increases to 0.1-0.2 mg L-1 (mean 85%) and at 30 minutes there is a further mean increase of 0.1 mg L-1.
***
Fluoride is present in all the analysed wines (Table 11), except for sample n°32. The predominant factors that determine its presence could be attributed both to the geographical origin, therefore to the soil on which the vines grow (Fabianowicz et al., 2019) and to the irrigation water. The concentration of fluoride in wine, however, can increase as result of accidental contamination and the use of fluorinated compounds as antiseptics and insecticides against parasites affecting the vineyards (Rodríguez Gómez et al., 2003). This source is responsible for increasing the concentration of fluoride in wine up to 3 mg L-1 (Paz et al., 2017). A high F concentration in wine was found in 1965 when Spanish alcoholics showed fluorosis which, due to its origin, was defined as vinic (Rodríguez Gómez et al., 2003). To prevent the toxic effects, the International Organization of Vine and Wine (OIV) has identified 1 mg L-1 as the maximum limit of fluoride in wine (Paz et al., 2017).

Table 11. – Fluoride concentration (mg L-1) in wine samples.

Sample [F] Sample [F]
5 Wine red 1 0.086 ± 0.001 32 Wine white 3 < 0.020
31 Wine red 2 0.18 ± 0.002 59 Wine white 4 0.062 ± 0.001
34 Wine red 3 0.13 ± 0.001 93 Wine white 5 0.070 ± 0.001
58 Wine red 4 0.12 ± 0.001 103 Wine white 6 0.094 ± 0.001
113 Wine red 5 0.082 ± 0.002 117 Wine white 7 0.200 ± 0.001
114 Wine red 6 0.047 ± 0.001 116 Wine Liqueurs 0.056 ± 0.003
115 Wine red 7 0.15 ± 0.002 101 Wine Moscato < 0.034
7 Wine white 1 0.15 ± 0.002 94 Wine Strawberry 0.073 ± 0.001
30 Wine white 2 0.16 ± 0.001
The wines analysed not exceed the limit identified by the Organizzazione Internazionale della Vigna e del Vino (OIV) and therefore all satisfy the quality criteria. The liquors and distillates, with few exceptions (sample n° 38 F = 0.11 mg L-1 and n° 120 F = 0.054 mg L-1), contain fluoride concentrations below the detection limit.
Fluoride concentrations from Teflon-coated tableware surfaces, measured on the water boiled in a small saucepan, were lower than detectable values. Ultimately, in our case, the Teflon coating does not release and does not contribute to the intake of fluori