Assessing contribution of bottled water in nutrient absorption using the bottled water nutritional quality index (BWNQI) in Iran

In this study, the contribution of bottled water in the absorption of nutritional minerals in Iran has been investigated. To calculate the nutritional quality index of bottled water (BWNQI) and evaluate the contribution of bottled water in nutrient absorption; the concentration of nutrient minerals, the standard level of these elements in bottled water, the recommended amount of nutrient mineral and the total consumption of drinking water in different age-sex groups were analyzed. The results showed that the average contribution of bottled water in absorbing the recommended amount of the nutrients of fluoride (F), magnesium (Mg), calcium (Ca), sodium (Na), copper (Cu), zinc (Zn) and manganese (Mn) was 12.16, 4.98, 4.85, 2.12, 0.49, 0.33 and 0.02%, respectively. According to the BWNQI index, the bottled water quality was as follows: 53.5% poor, 36.6% marginal, 7% fair, 2.81% good. Although most of the bottled water studied in this research were mineral water, a significant portion of them had poor nutritional quality, so the addition of minerals needed by the body through bottled water should be given more attention by the bottled water manufacturers and suppliers.

In addition to people's tastes, due to changing lifestyles and their tendency towards a healthy lifestyle and not only quenching their thirst, today different brands of bottled water are used around the world 12 . Demand for bottled water in North America has shown an annual growth rate of 25%. The annual bottled water consumption was reported 45 L/year per capita in 2003 in Europe 13 . Globally, the use of bottled water has obeyed a continuously increasing trend in recent 14 years. For example in Japan, the amount of water consumption was reported 31.7 L/year per capita in 2019 14 .
Global consumption of bottled water in 2013 was 70,371.6 million gallons which was 6.2% more than in 2008 11 . Iran is also facing a severe shortage of water due to dry and semi-arid climates in many provinces. The amount of renewable water in Iran is less than 2000 cubic meters per person per year, which according to the current population growth, is expected to reach less than 1000 cubic meters per year by 2025. Therefore, it is necessary to use alternative water resources to meet the country's water needs 15 .
Bottled water contains cations such as sodium (Na), calcium (Ca), magnesium (Mg), and potassium (K), and anions such as sulfate (SO 4 ), chloride (Cl -), and bicarbonate (HCO 3 ). They have good quality due to the special characteristics of the taste and content of various mineral compounds 16 . Generally, bottled water should have a high concentration of Ca and Mg and a low concentration of Na 17 . Some of the minerals in bottled water, including Ca, Cl -, Cu, F, I, Fe, Mg, Mn, P, K, Se, Na, Zn, etc., are among the nutrients necessary for the human body 18 . Elevated concentrations of these minerals can reduce the quality of bottled water and be harmful to human health. According to the standard of bottled drinking water in Iran, the maximum allowable amount of Ca, Mg, Na, Mn, Cu, Zn and F minerals is 40-80, 20-30, 200, 0.5, 1, 0.15 and 4 mg/L, respectively 3 . Some studies show that many of the minerals in bottled water can have negative effects on human health through toxic mechanisms 19 . For example, Cu at concentrations above 100 mg/L in the human body can lead to the destruction of the oxidative cell and eventually death 20 . Absorption of more than 1000 mg per day of Ca in the body can lead to kidney stones 21 . There are also concerns about high concentrations of F in bottled water [22][23][24] . High Na concentration raises blood pressure 25,26 . Mn and Zn minerals, which are in the heavy metals category, accumulate in high concentrations after entering the body in fat, muscle and bone, and generally cause neurological disorders, cancer and, in acute cases, death 27,28 . In addition to the harmful effects, some minerals have beneficial effects on human health. According to epidemiological studies, Mg can reduce sudden death and prevent Ca from osteoporosis 17,29 .
Studies have shown that proper nutrition is effective in absorbing essential minerals in the body, and drinking water has also an important role in the absorption of minerals 19,29,30 . Sajjala et al. studied several brands of bottled water in Oman in 2019. They found that the concentration of Ca in local brands was low compared to the imported brands and the contribution of this element for the recommended dietary allowances of Ca in adults was only 3% and the contribution of Na was also very low 29 . In another study in 2020, Cormick et al. reported that most of bottled water brands in Argentina had Ca levels below 50 mg/L. According to their study, the intake of 1 L of drinking water from Argentina could represent in averagely 1.2-8 percent of the Ca daily levels for an adult person 31 . Duka et al. in a study found that dietary reference intakes of Ca and Mg minerals from bottled water was averagely 8.29 and 4.27%, respectively in commercial bottled drinking water in Tirana, Albania During 2019 32 .
There are few studies in Iran regarding the contribution of bottled water in the intake of nutrients, therefore the study of nutritional quality of the bottled water in necessary. Herein, the aim of this study was to evaluate the contribution of bottled water in the absorption of Ca, Cu, F, Mg, Mn, Na, and Zn minerals in different age-sex groups and in the general population using bottled water quality food index (BWNQI).

Results and discussion
The concentration of mineral nutrients. The concentration of minerals in bottled water in 71 brands was shown in Table 1.
The maximum values of Ca, Cu, F, Mg, Mn, Na and Zn were 87837, 57.993, 1553, 19.326, 0.05, 161000 and 307 µg/L respectively. The results showed that the concentrations of all minerals in the study brands were within the maximum contaminant levels of the EPA standards 33 .
Determination of the contribution of bottled water in the absorption of the recommended amount of nutrients by the body in the entire population. The average contribution of bottled water in absorbing the recommended amount of nutritional minerals in 71 brands of bottled water in the entire population of Iran in different age-sex groups is shown in Table 2. Based on the results, the average contribution of 71 brands of bottled water in Ca absorption in the age-sex groups of infants aged 6-12 months, children aged 1-9 years, adult men and women were 5, 3.3, 4.84 and 4.17%. respectively. The average contribution of 71 brands of bottled water in Cu absorption in the sex-age groups of infants aged 6-12 months, children aged 1-9 years, male and female adults were 0.76, 0.36, 0.5 and 0.47%, respectively. For fluoride, this mean absorption in the age-sex groups of infants aged 6-12 months, children aged 1-9 years, adult males and females was 28.8, 15.93, 12.17 and 10.38%, respectively. Furthermore, The average contribution of bottled water in Mg absorption in the age-sex groups of infants in 6-12 months, children 1-9 years old, adult men and women was 9.75, 5.44, 4.58 and 4.95%, respectively.
Averagely, the contribution of bottled water in the absorption of Mn in the age-sex groups of infants aged 6-12 months, children aged 1-9 years, adult males and females was 0.029, 0.012, 0.02 and 0.024%, respectively.
Also, the average contribution of bottled water in the absorption of Na in the age-sex groups of infants aged 6-12 months, children aged 1-9 years, adult males and females was 5.93, 1.02, 2.37 and 2.21%, respectively.
The role of bottled water in the absorption of Zn in the age groups of infants aged 6-12 months, children aged 1-9 years, adult men and women was averagely 0. 22 37 .
In this study, the absorption of fluoride was higher than other nutrients. Viswanathan et al. in a study in 2010 found that daily more than 60 percent of all fluoride was absorbed through drinking water 38 . Adequate fluoride intake is effective in preventing tooth decay, but excessive and long-term use can cause fluorosis 1,39,40 . Rowell et al. in a study in Qatar found that bottled water provides 3, 5-6 and 4 percent of recommended amount of essential minerals including Ca, Mg and F in the adult body, respectively. In children, this amount was 2-3, 3-10 and 3-9%, respectively 41 . In this study, the percent of the recommended amount of essential minerals for Ca, Mg and F were higher than those reported in the Rowell's study.
Sodium deficiency is usually rare in different age groups, but there are more concerns about increasing sodium absorption 42,43 .
The nutrient minerals studied in this work have different biological functions as Ca strengthens bones, regulates muscle contraction, blood clots, etc. 44 , Cu controls the function of several enzymes in the blood and muscles of the body 45 , Mg is involved in bone formation, lipid metabolism and protein synthesis 46 ; Mn is responsible for www.nature.com/scientificreports/ the synthesis of several enzymes in protein and sugar metabolism and bone growth 47 . Like Mg, F is effective in bone growth and also plays an important role in protecting and preventing tooth decay; Na is a key regulator of cell permeability and body fluids 48 . Studies show that bottled waters in Europe have higher levels of minerals than in other countries. For example, about one liter of bottled water in Europe accounts for 20-58% of Ca absorption and 16-41% of Mg absorption and the highest contribution of Na absorption in adults. Bottled water in the United States generally has low mineral levels. Also, bottled water in the UAE has low mineral quality and has only a 3% contribution of Ca absorption 29,49 . In general, bottled water, which has a high mineral content, contributes 100% of the absorption of Ca, Mg and Na 34,35 . The average contribution of bottled water in absorbing the recommended amount of the nutrients of Ca, Cu, F, Mg, Mn, Na and Zn in the total population of Iran was 4.85, 0.49, 12.16, 4.98, 0.02, 2.12 and 0.33% (Fig. 1).
The mean SI scores of Ca and Mg in bottled water were 57.90 and 40.66, respectively. These results showed that Ca and Mg in bottled water did not exceed the maximum allowable amount. The mean SI score of F was 49.90 (Fig. 2).
The highest average SI score in bottled water was for Na ions, indicating that the concentration of this ion was lower than desired concentration. In general, the SI scores of Cu, Mn and Zn were much lower than other minerals.
Determination of the quality of bottled water using the quality index of bottled water. BWNQI in 71 brands of bottled water in Iran was 2.81, 7, 36.6, 53.5%, and classified as good, fair, marginal, poor quality, respectively. BWNQI index in Ardabil, Gilan, Qazvin, Karaj and Golestan provinces with score of 44.9 was in the poor range. BWNQI index in Chaharmahal and Bakhtiari and Kohkiluyeh and Boyer-Ahmad provinces with score range of 70.79-79 was in the good range (Fig. 3). More than half of bottled water in Iran have poor quality in terms of quality index. Also, BWNQI index only in two provinces in Iran was in good range.

Relationship between bottled water source and BWNQI index.
The sources of bottled water in this study were bottled natural mineral water and bottled drinking water. The results of this study showed that there was no significant relationship (P > 0.05) between bottled water sources and BWNQI index (Fig. 4).  Fig. 5. The effect of removal of the nutritional minerals on the average BWNAQI score was in the range of − 4.51 to 3.5. The highest positive and negative effects were related to Zn and Ca, respectively. The average BWNQI score represents the average SI score, so the removed nutritional minerals with negative effects including Ca, Na, F had an average SI higher than the average score of BWNQI and the removed nutritional minerals with positive effects such as Mg, Mn, Cu, Zn had lower mean SI score than the BWNQI mean score.
The lowest (R 2 > 0.8) and highest (R 2 > 0.9) correlation coefficient with the average BWNQI score was related to F and Na, respectively. The data showed that none of the input parameters had an effect on the BWNQI score, so this index can be a good indicator to show the contribution of bottled water in nutritional minerals absorption for human body.

Conclusions
Unfortunately, in some countries, especially in developing countries, there is no difference between drinking and bottled water. One of the reasons is that people are not aware of such waters. Due to the increasing number of such waters, people think that they receive large amounts of anions and cations. Therefore, knowing the contribution of bottled water can help the body absorb useful and essential minerals to check the percentage of essential minerals compared to their recommended amount and the role they play in people's health, as well as the nutritional quality of bottled waters are useful and effective. In this study, the contribution of bottled water consumed in Iran in the absorption of nutritious mineral elements such as calcium, fluoride, copper, manganese, zinc, magnesium and sodium was examined. According to the BWNQI index, the results of bottled water quality investigation was as follows: 53.5% poor, 36.6% marginal, 7% fair, 2.81% good. This study showed that the majority of bottled waters consumed in Iran are not good in quality and the nutrients should be added by the bottled www.nature.com/scientificreports/ water manufacturers based on the standards of bottled drinking water quality. Compared to nutrient minerals, fluoride absorbed more by drinking bottled water throughout Iran. Due to the increasing trend of bottled water consumption in recent years in Iran, the need for further study in the field of quality improvement and promotion of these waters and their contribution to the absorption of nutrients to the body is essential. In addition to public health issues, the nutritional value of such water should also be considered.

Materials and methods
Study area description. This study was conducted in Iran. Iran has an area of about 1,648,195 km 2 and a population of 85,539,819 people. The country has 32 provinces. It is located in Western Asia. About 99% of urban water supply is in the form of tap water. Given that most of the provinces are located in the dry places and the piped water tastes salty, therefore, more attention is paid toward bottled water. Study locations and sampling points are shown in Fig. 6. Quality assurance and quality control (QA/QC). Analytical techniques were confirmed based on quality assurance and quality control (QA/QC). The calibration range, the concentration range and the results of the accuracy QA/QC control are given in Table 3.

Checking the quality index of bottled water nutrients.
To determine the BWNQI index and evaluate the contribution of bottled water in the absorption of nutritional minerals 5 factors including: 1. the concen-  Table 4 shows the amount of bottled water consumption and recommended minerals required by the body in different age-sex groups. Also, the maximum desirable and weighted factor of nutritional mineral ions in bottled water according to the bottled water standard in Iran 55 is given in Table 5.
The following formulas were used to determine the BWNQI index 3 .   where Fij (%) is the contribution of bottled water in the absorption of nutrients in different age groups, Ci is nutrient concentration (mg/L), Vj is volume of bottled water consumption in different age groups (L) and Aij is the recommended amount of nutrients in different age groups (mg/d).
where, Fi (%) is the contribution of bottled water in nutrient absorption in the total population, Pj is population in different age groups, m is number of nutrient minerals and n is number of age-sex groups.
where Fi, u (%) is the maximum contribution optimal nutrient absorption of minerals in bottled water and BLi is the optimum nutrient concentration (mg/L). Since manganese, copper, and fluoride ions have adverse effects, the following SIi formula was used to calculate the absorption of these ions.

For Ci ≤ BLi
Where SIi is sub-index of nutritional minerals other than sodium element (unit less) and α is SIi constant and equal to 25.
where SVi is the optimum concentration of nutrient mineral at the standard level (mg/L), F`(%) is maximum optimal contribution of bottled water in the recommended adsorption of minerals based on the maximum desired element concentration.
For nutrient concentrations higher than BLi, the SIi 100 was considered. For concentrations higher than 2 times that of SVi, SIi 0 was considered.
For 200 mg/L < Na < 400 mg/L The above equation was used to calculate SINa at concentrations of 200-400 mg/L. For concentrations below 200 and above 400 mg/L, SINa was considered 100 and 0, respectively.
where Wi is nutritional weight factor, and β is BWNQI constant and equal to 0.9.

Sensitivity analysis.
In the sensitivity analysis, the effect of each input dietary element on the BWNQI score was considered. Each parameter was removed separately from BWNQI and then its effect on the original BWNQI score was measured. × 100