Abstract

Radon and its progeny often exist in daily drinking water, and may pose a potential health threat to the public. In this study, the radon concentrations of 15 different brands of bottled drinking water and their radiological hazards were measured and evaluated. The results indicate that the concentration range of radon in water is 13.3 ± 4.7 to 300.0 ± 21.6 mBq/L, and is lower than the limit level (11.11 Bq/L). The results compared with radon concentrations from other countries or regions show that the radon concentrations in this study are almost within the range of those of all the others. The average annual effective dose for infants, children and adults in the three age-groups is 0.657, 0.535 and 0.665 μSv/y respectively, which is lower than the recommended level of 0.1 mSv/y. The results also show that the bottled water does not pose a major health hazard to the public. Moreover, combined with statistical analysis, it is concluded that the concentration of TDS and Ca2+ in bottled mineral water has a strong correlation with the radon concentration in the water.

HIGHLIGHTS

  • Radon and its progeny often exist in daily drinking water, and may pose a potential health threat to the public.

  • The radon concentrations of 15 different brands of bottled drinking water and their radiological hazards were measured and evaluated.

  • The results indicate that the concentrations of radon in drinking water are lower than the international recommended level.

  • The results show that the bottled water does not pose a major health hazard to the public.

  • Combined with statistical analysis, it is concluded that the concentration of TDS and Ca2+ in bottled mineral water has a strong correlation with the radon concentration in the water.

INTRODUCTION

Radon is a colorless and odorless natural radioactive inert gas, which is produced in three natural decay systems: uranium, thorium and actinium–uranium (Khattak et al. 2011). There are three natural radioactive isotopes of the element radon: 222Rn (T1/2 = 3.82d), 220Rn (T1/2 = 55.61 s) and 219Rn (T1/2 = 3.96 s). 222Rn and its daughters, such as 218Po, 214Pb, 214Bi and 214Po, are derived from the decay of uranium series radionuclides, 220Rn is derived from the decay of thorium series radionuclides, and 219Rn is derived from the decay of actinium–uranium series radionuclides. 222Rn has a long half-life and its parent 238U accounts for 99.3% of all uranium in the crust; it is a rich and dangerous radioactive isotope in the natural environment (Rangaswamy et al. 2015; Fakhri et al. 2016). Therefore, radon generally refers to 222Rn.

In nature, radon exists not only in air, soil and rock, but also in all water sources on the earth, including lakes, rivers, groundwater, springs and even rainfall (Khattak et al. 2011). The existence of radon promotes the exploration of mineral resources, the calibration of petroleum reserves, the prediction of seismic and volcanic activities, the location of geological fault zones and hydrological research and so on (Ajayi 2000; Ajayi & Kuforiji 2001; Karimdoust & Ardebili 2010; Ajiboye et al. 2018). However, the role of radon is dual, bringing benefits to human beings, but also posing a certain threat to human health and environmental safety (UNSCEAR 2000; Abuelhia 2018). The α-particles from radon and its progeny pose a radiation risk to human tissues and organs (Fakhri et al. 2016), and may damage DNA and cause cell concentration (Karimdoust & Ardebili 2010). Although the dose of radon-containing drinking water is less than that of direct inhalation, excessive radon intake due to drinking water can not only cause lung cancer, but can also increase the risk of gastric cancer and gastric cancer–colon cancer in some people (Kendall & Smith 2002; Bonotto 2004; WHO 2009a, 2009b; Anjos et al. 2010; ICRP 2010; Vogeltanz-Holm & Schwartz 2018). In the United States, radon is ranked as the second most common cancer factor after smoking, with 168 deaths a year from cancer caused by radon in drinking water (UNSCEAR 2000; Samet 2011).

Water is the source of life, and also the main factor of public health (WHO 2009a). With the rapid increase of global population, freshwater resources are becoming more and more valuable (Rodwan Jr 2012). In the past 30 years, the consumption of commercial bottled water has been increasing in developed and developing countries (Rožmarić et al. 2012; Fakhri et al. 2016). Commercial bottled water can be divided into drinking pure-water and drinking mineral-water according to the different mineral content in the water. Drinking pure-water mainly comes from surface water sources such as treated rivers and lakes, while drinking mineral-water generally comes from underground spring water. Different brands of mineral water have different sources and mineral content (Mehdizadeh et al. 2013). Radon from rock and soil is dissolved in water when it comes into contact with surface water or groundwater. Radon in groundwater is usually higher than that in surface water, which mainly comes from more minerals and compounds being dissolved (Tayyeb et al. 1998; Al Zabadi et al. 2012).

Many authorized agencies and researchers are anxious about the potential risk to health posed by dissolved radon in drinking water, and the content and measurement of radon concentration have attracted wide attention (WHO 2009a; Anjos et al. 2010; Alrefae 2012; Sola et al. 2013). Radium has the same chemical properties as calcium in the periodic table of elements, and Ca2+ is a common mineral ion in drinking mineral-water (Abo-Elmagd et al. 2006; Altıkulaç et al. 2015). It is of great significance to explore the statistical relationship between various ions in the brands of drinking mineral-water and radon concentration in drinking mineral-water to prevent the adverse consequences of the biological effects of radon (Abuelhia 2018). In this study, the radon concentrations of 15 different brands of commercial bottled drinking water produced in China were measured, and the impacts on human health from commercial bottled water were assessed. The relationship between different mineral content and radon concentration in drinking mineral-water was also explored.

MATERIALS AND METHODS

Sample collection

In this study, eight different brands of bottled drinking mineral-water and seven different brands of assembled drinking pure-water were purchased from local shops in Urumqi, China. Bottled water from different water sources was purchased according to the production address marked on the bottle body to ensure the difference of measurement values. The distribution of water sources is shown in Figure 1. Three samples for each brand were prepared, and the experimental samples were kept in a sealed state until use to reduce the errors caused by environmental factors.

Figure 1

The distribution of water sources of the 15 different brands of commercial bottled water.

Figure 1

The distribution of water sources of the 15 different brands of commercial bottled water.

Sample analysis

The radon concentrations of bottled water were measured by a portable environmental radon measuring instrument, model FD216. The scintillation flask method was used to measure radon concentration, the principle of which is as follows: the gas containing radon is sent into the scintillation chamber through the inflatable pump inside the instrument. The α-particles of 5.489 MeV and 6.002 MeV released from 222Rn and 218Po, respectively, can ionize and excite the ZnS (Ag) coating on the wall of the scintillation chamber, and then the scintillation is released by de-excitation. The light signals of these scintillating photons are converted into electric pulse signals through a photomultiplier tube. Through the control circuit and measurement circuit composed of a single-chip computer, the electric pulse output from the detector is shaped and counted regularly. The number of pulses per unit time is proportional to radon concentration, so the radon concentration in the gas filling the scintillation chamber can be determined. The measurement range of radon concentration in water is 0.003–100 Bq/L, and the diagram of the principle is shown in Figure 2. Constant velocity air was continuously brought into the sampling bottle through the inflatable pump, flowing through the water and extracting radon from the water continuously. The main connection accessories are shown in Figure 3: (A) sampling bottle; (B) desiccant tube installed on the outlet pipe of the sampling bottle, used for drying the air flowing out of the sampling bottle; (C) intake pipe of the sampling bottle, connected to the inflatable pump of the radon meter; (D) exhaust pipe of the sampling bottle; and (E) the host of measuring equipment.

Figure 2

The diagram of the principle of the measuring instrument for radon concentration in water, model FD216.

Figure 2

The diagram of the principle of the measuring instrument for radon concentration in water, model FD216.

Figure 3

The connection accessories diagram of the measuring instrument for radon concentration in water, model FD216.

Figure 3

The connection accessories diagram of the measuring instrument for radon concentration in water, model FD216.

The installation and measurement processes of the instrument accessories are based on the operating procedures given by the instrument manufacturers. Before the experiment, the sample bottle is cleaned with ultrapure water and dried in an oven, then the sample bottle is rinsed again with the water sample to be measured, and finally the water sample to be measured is poured into the 400 mL sample bottle quickly and sealed to avoid long-term exposure to the air, so as to reduce and ignore the interference of the environment in the measurement. The sampling bottle is connected to the radon measuring instrument, and the control panel chooses ‘radon in water’ and ‘large sample bottle (400 mL)’. The instrument will perform a background measurement of 600 seconds, then the inflatable pump starts with continuous operation of 300 seconds to make the radon in the water evenly distributed in the measurement system. After completion of closed-circuit operation, the radon concentration is measured in the scintillation chamber for 660 seconds. After the measurement, the instrument flushes the scintillation chamber by sucking the external air through the air inlet connected to the drying tube, and then connects the drying tube to the instrument to form a closed circuit. The gas in the scintillation chamber is continuously passed through the drying tube through the inflatable pump until the relative humidity in the scintillation chamber is lower than 10%. All measurement operations are automatically completed by the instrument. The instrument has been certified and calibrated by the National Institute of Metrology, China.

Assessment of effective dose

In the present work, the radiological hazard of annual effective dose was calculated by the following formulas (UNSCEAR 2000). 
formula
(1)
where is the annual effective dose of ingestion, in. is the radon concentration in water, in Bq/L. is the annual intake of drinking water, in L/y. The value for infants (1–2 years), children (7–12 years) and adults (more than 17 years) is 150 L/y, 350 L/y and 500 L/y respectively (UNSCEAR 2000). EDC is the ingested dose conversion factor; the value for infants, children and adults is 2.3 × 10−8 Sv/Bq, 5.9 × 10−9 Sv/Bq and 3.5 × 10−9 Sv/Bq, respectively (UNSCEAR 2000). 
formula
(2)
where is the annual effective dose of inhalation, in. is the transfer coefficient of radon from water to air, and the recommended value is 1 × 10−4 (UNSCEAR 1993). is the equilibrium factor between indoor radon and its progeny; the recommended value is 0.4 (UNSCEAR 2000; Anjos et al. 2010). is the average annual indoor occupancy factor (7,000 h/y). is the dose conversion factor for radon inhalation; the value is 13, 9 and 9 mSv/WLM for adult, infant and child, respectively (Tan et al. 2019).

The dose contribution of radon in drinking water to lung and stomach was obtained by multiplying the inhalation and ingestion dose by the tissue weighting factor (wT) of lung and stomach, respectively. The tissue weighting factors of lung and stomach are 0.12 and 0.12, respectively (UNSCEAR 2000).

RESULTS AND DISCUSSIONS

The radon concentrations in different brands of commercial bottled water are shown in Table 1. It is observed that the average radon concentration ranges from 13.34.7 to 300.0 21.6 mBq/L, with a mean for all samples of 90.1 mBq/L. The maximum, minimum and total average of radon concentration in the samples do not exceed the maximum contaminant level (MCL) of 11.11 Bq/L and the value of radon concentration in water for human consumption (4–40 Bq/L) (EPA 1999; UNSCEAR 2006). Meanwhile, the radon concentrations are also lower than the recommended safe limit of 100 Bq/L for drinking purposes (WHO 2011). The average radon concentration of the eight samples groups of mineral water (Pp1–Pp8) is 91.4 mBq/L, which is slightly higher than the average radon concentration of 90.1 mBq/L of the 15 sample groups and 85.0 mBq/L of the seven sample groups of pure water (Pp9–Pp15) in numerical value, but there is no significant difference in statistics.

Table 1

The radon concentrations (mBq/L) in commercial bottled water from different brands

Sample codeProduction batch dateRadon concentration (mBq/L)
Mineral water 
 Pp1 (3) May 29, 2019 133.3 ± 23.5 
 Pp2 (3) May 3, 2019 14.3 ± 4.1 
 Pp3 (3) April 29, 2019 13.3 ± 4.7 
 Pp4 (3) June 5, 2019 300.0 ± 21.6 
 Pp5 (3) June 1, 2019 60.0 ± 8.1 
 Pp6 (3) May 15, 2019 50.0 ± 8.2 
 Pp7 (3) May 22, 2019 73.3 ± 12.4 
 Pp8 (3) June 7, 2019 86.6 ± 4.7 
 average  91.4 
Pure water 
 Pp9 (3) June 22, 2019 66.6 ± 9.4 
 Pp10 (3) March 23, 2019 146.6 ± 12.4 
 Pp11 (3) May 26, 2019 113.3 ± 4.7 
 Pp12 (3) April 6, 2019 130.0 ± 16.3 
 Pp13 (3) May 13, 2019 36.6 ± 4.7 
 Pp14 (3) May 29, 2019 86.6 ± 16.9 
 Pp15 (3) May 28, 2019 15 ± 4.0 
 average  85.0 
Average of all samples  90.1 
Sample codeProduction batch dateRadon concentration (mBq/L)
Mineral water 
 Pp1 (3) May 29, 2019 133.3 ± 23.5 
 Pp2 (3) May 3, 2019 14.3 ± 4.1 
 Pp3 (3) April 29, 2019 13.3 ± 4.7 
 Pp4 (3) June 5, 2019 300.0 ± 21.6 
 Pp5 (3) June 1, 2019 60.0 ± 8.1 
 Pp6 (3) May 15, 2019 50.0 ± 8.2 
 Pp7 (3) May 22, 2019 73.3 ± 12.4 
 Pp8 (3) June 7, 2019 86.6 ± 4.7 
 average  91.4 
Pure water 
 Pp9 (3) June 22, 2019 66.6 ± 9.4 
 Pp10 (3) March 23, 2019 146.6 ± 12.4 
 Pp11 (3) May 26, 2019 113.3 ± 4.7 
 Pp12 (3) April 6, 2019 130.0 ± 16.3 
 Pp13 (3) May 13, 2019 36.6 ± 4.7 
 Pp14 (3) May 29, 2019 86.6 ± 16.9 
 Pp15 (3) May 28, 2019 15 ± 4.0 
 average  85.0 
Average of all samples  90.1 

The radiological hazard of annual effective dose from ingestion and inhalation and the total of the three different age-groups (infants, children, adults) is assessed in Table 2. As shown from Table 2, the annual effective ingestion dose of the three different age-groups was lower than that of inhalation, which was particularly obvious in the children group and the adults group. Although the annual ingestion of water for adults was higher than that for children and infants, the of the infants group are higher than those of the children and the adults group. In the three different age-groups, the of the infants, children and adults group varied from 0.046 to 1.035 μSv/y with a mean of 0.304 μSv/y, 0.027 to 0.619 μSv/y with a mean of 0.182 μSv/y and 0.023 to 0.525 μSv/y with a mean of 0.154 μSv/y, respectively. The of the infants, children and adults group ranged from 0.053 to 1.201 μSv/y with a mean of 0.353 μSv/y, 0.053 to 1.201 μSv/y with a mean of 0.353 μSv/y and 0.077 to 1.736 μSv/y with a mean of 0.510 μSv/y, respectively. The mean value of total annual effective dose in the adult groups was the largest, followed by the infants group and the children group. The mean value was 0.665, 0.657 and 0.535 μSv/y respectively. As shown from Figures 4 and 5, the maximum value of the total annual effective dose was 2.261 μSv/y in the Pp4 sample of the adults group, and the minimum value was 0.081 μSv/y in the Pp3 sample of the children group. All the values of the total annual effective dose, and are lower than the drinking water recommended limit level of 0.1 mSv/y (WHO 2009a), and are also lower than the recommended total annual effective dose of 1 mSv/y (UNSCEAR 2000). This indicates that long-term exposure to radon from commercial bottled drinking water does not pose a serious health risk to the public.

Table 2

The annual effective dose (μSv/y) of radon in commercial bottled water from different brands

Sample codeEing (μSv/y)
Einh (μSv/y)
Total annual effective dose (μSv/y)
infantschildrenadultsinfantschildrenadultsinfantschildrenadults
Pp1 0.460 0.275 0.233 0.534 0.534 0.771 0.994 0.810 1.005 
Pp2 0.049 0.029 0.025 0.057 0.057 0.082 0.107 0.087 0.108 
Pp3 0.046 0.027 0.023 0.053 0.053 0.077 0.099 0.081 0.100 
Pp4 1.035 0.619 0.525 1.201 1.201 1.736 2.237 1.821 2.261 
Pp5 0.207 0.123 0.105 0.240 0.240 0.347 0.447 0.364 0.452 
Pp6 0.172 0.103 0.087 0.200 0.200 0.289 0.373 0.304 0.377 
Pp7 0.253 0.151 0.128 0.293 0.293 0.424 0.547 0.445 0.553 
Pp8 0.299 0.178 0.151 0.347 0.347 0.501 0.646 0.526 0.653 
Pp9 0.230 0.137 0.116 0.267 0.267 0.385 0.497 0.405 0.502 
Pp10 0.506 0.302 0.256 0.587 0.587 0.848 1.094 0.890 1.105 
Pp11 0.391 0.234 0.198 0.454 0.454 0.655 0.845 0.688 0.854 
Pp12 0.448 0.268 0.227 0.520 0.520 0.752 0.969 0.789 0.980 
Pp13 0.126 0.075 0.064 0.146 0.146 0.212 0.273 0.223 0.276 
Pp14 0.299 0.178 0.151 0.347 0.347 0.501 0.646 0.526 0.653 
Pp15 0.051 0.030 0.026 0.060 0.060 0.086 0.112 0.091 0.113 
average 0.304 0.182 0.154 0.353 0.353 0.510 0.657 0.535 0.665 
Sample codeEing (μSv/y)
Einh (μSv/y)
Total annual effective dose (μSv/y)
infantschildrenadultsinfantschildrenadultsinfantschildrenadults
Pp1 0.460 0.275 0.233 0.534 0.534 0.771 0.994 0.810 1.005 
Pp2 0.049 0.029 0.025 0.057 0.057 0.082 0.107 0.087 0.108 
Pp3 0.046 0.027 0.023 0.053 0.053 0.077 0.099 0.081 0.100 
Pp4 1.035 0.619 0.525 1.201 1.201 1.736 2.237 1.821 2.261 
Pp5 0.207 0.123 0.105 0.240 0.240 0.347 0.447 0.364 0.452 
Pp6 0.172 0.103 0.087 0.200 0.200 0.289 0.373 0.304 0.377 
Pp7 0.253 0.151 0.128 0.293 0.293 0.424 0.547 0.445 0.553 
Pp8 0.299 0.178 0.151 0.347 0.347 0.501 0.646 0.526 0.653 
Pp9 0.230 0.137 0.116 0.267 0.267 0.385 0.497 0.405 0.502 
Pp10 0.506 0.302 0.256 0.587 0.587 0.848 1.094 0.890 1.105 
Pp11 0.391 0.234 0.198 0.454 0.454 0.655 0.845 0.688 0.854 
Pp12 0.448 0.268 0.227 0.520 0.520 0.752 0.969 0.789 0.980 
Pp13 0.126 0.075 0.064 0.146 0.146 0.212 0.273 0.223 0.276 
Pp14 0.299 0.178 0.151 0.347 0.347 0.501 0.646 0.526 0.653 
Pp15 0.051 0.030 0.026 0.060 0.060 0.086 0.112 0.091 0.113 
average 0.304 0.182 0.154 0.353 0.353 0.510 0.657 0.535 0.665 
Figure 4

The annual effective dose of ingestion and inhalation (μSv/y).

Figure 4

The annual effective dose of ingestion and inhalation (μSv/y).

Figure 5

Total annual effective dose (μSv/y) in the three different age-groups.

Figure 5

Total annual effective dose (μSv/y) in the three different age-groups.

The annual effective doses for internal organs are estimated as shown in Table 3. It can be seen that the mean annual effective dose for lung organs in the three age-groups is 0.037, 0.022 and 0.019 μSv/y, respectively. The mean annual effective dose for stomach organs is 0.042, 0.042 and 0.061 μSv/y, respectively. The annual effective doses for these internal organs are lower than the recommended limit for the public. The annual effective dose of 222Rn and its progeny for lung organs decreases gradually from the infants group to adults group, while the annual effective dose for stomach organs increases gradually. The lung organ effective dose caused by inhaled radon from water into air is lower than the stomach organ effective dose caused by directly ingested drinking water containing radon, so the main way of radon produced in drinking water to be a human health hazard is by direct ingestion.

Table 3

The annual effective (μSv/y) dose of the internal organs

Sample codeLunginh (μSv/y)
Stomaching (μSv/y)
infantschildrenadultsinfantschildrenadults
Pp1 0.055 0.033 0.028 0.064 0.064 0.093 
Pp2 0.006 0.004 0.003 0.007 0.007 0.010 
Pp3 0.006 0.003 0.003 0.006 0.006 0.009 
Pp4 0.124 0.074 0.063 0.144 0.144 0.208 
Pp5 0.025 0.015 0.013 0.029 0.029 0.042 
Pp6 0.021 0.012 0.011 0.024 0.024 0.035 
Pp7 0.030 0.018 0.015 0.035 0.035 0.051 
Pp8 0.036 0.021 0.018 0.042 0.042 0.060 
Pp9 0.028 0.017 0.014 0.032 0.032 0.046 
Pp10 0.061 0.036 0.031 0.071 0.071 0.102 
Pp11 0.047 0.028 0.024 0.054 0.054 0.079 
Pp12 0.054 0.032 0.027 0.062 0.062 0.090 
Pp13 0.015 0.009 0.008 0.018 0.018 0.025 
Pp14 0.036 0.021 0.018 0.042 0.042 0.060 
Pp15 0.006 0.004 0.003 0.007 0.007 0.010 
average 0.037 0.022 0.019 0.042 0.042 0.061 
Sample codeLunginh (μSv/y)
Stomaching (μSv/y)
infantschildrenadultsinfantschildrenadults
Pp1 0.055 0.033 0.028 0.064 0.064 0.093 
Pp2 0.006 0.004 0.003 0.007 0.007 0.010 
Pp3 0.006 0.003 0.003 0.006 0.006 0.009 
Pp4 0.124 0.074 0.063 0.144 0.144 0.208 
Pp5 0.025 0.015 0.013 0.029 0.029 0.042 
Pp6 0.021 0.012 0.011 0.024 0.024 0.035 
Pp7 0.030 0.018 0.015 0.035 0.035 0.051 
Pp8 0.036 0.021 0.018 0.042 0.042 0.060 
Pp9 0.028 0.017 0.014 0.032 0.032 0.046 
Pp10 0.061 0.036 0.031 0.071 0.071 0.102 
Pp11 0.047 0.028 0.024 0.054 0.054 0.079 
Pp12 0.054 0.032 0.027 0.062 0.062 0.090 
Pp13 0.015 0.009 0.008 0.018 0.018 0.025 
Pp14 0.036 0.021 0.018 0.042 0.042 0.060 
Pp15 0.006 0.004 0.003 0.007 0.007 0.010 
average 0.037 0.022 0.019 0.042 0.042 0.061 

As shown from Table 4, the radon concentrations in bottled water in some countries or regions vary in the range 0–22.8 Bq/L. When the radon concentrations of the aforementioned and measured 15 brand samples in this study are compared, it is seen that the radon concentration values in this study are almost within the range of those of all other countries or regions (Kralik et al. 2003; Desideri et al. 2007; Yakut et al. 2013; Bem et al. 2014; Fakhri et al. 2016; Abuelhia 2018).

Table 4

The radon concentration (Bq/L) of bottled water in different countries or regions

Countries/regionsRadon concentration (Bq/L)References
Dammam, Saudi Arabia 0.11–9.2 Abuelhia (2018)  
Poland 0.42–10.52 Bem et al. (2014)  
Austria 0.12–18 Kralik et al. (2003)  
Italy 0.69–20.3 Desideri et al. (2007)  
Turkey 0.74–22.8 Yakut et al. (2013)  
Hormozgan, Iran 0–0.901 Fakhri et al. (2016)  
China 0.01–0.33 Present study 
Countries/regionsRadon concentration (Bq/L)References
Dammam, Saudi Arabia 0.11–9.2 Abuelhia (2018)  
Poland 0.42–10.52 Bem et al. (2014)  
Austria 0.12–18 Kralik et al. (2003)  
Italy 0.69–20.3 Desideri et al. (2007)  
Turkey 0.74–22.8 Yakut et al. (2013)  
Hormozgan, Iran 0–0.901 Fakhri et al. (2016)  
China 0.01–0.33 Present study 
Table 5

Physical and chemical properties on the labels of the bottled mineral water

Sample codeMetasilicate (mg/L)TDS (mg/L)Mineral contents (mg/L)
Na+Ca2+Mg2+
Pp1 15.06 ± 0.07 156.42 ± 5.75 1.18 ± 0.03 5.65 ± 0.02 14.50 ± 0.14 
Pp2 46.22 ± 6.74 121.67 ± 19.87 11.52 ± 0.08 5.30 ± 0.07 8.1 ± 0.09 
Pp3 33.42 ± 0.73 63.46 ± 2.5 5.30 ± 0.07 6.07 ± 0.1 4.45 ± 0.12 
Pp4 28.25 ± 0.55 399.43 ± 18.94 31.18 ± 2.34 71.05 ± 4.15 7.69 ± 0.09 
Pp5 42.84 ± 1.88 68.05 ± 1.17 45.45 ± 0.12 59.70 ± 4.15 13.5 ± 0.14 
Pp6 50.82 ± 3.14 109.44 ± 0.84 7.01 ± 0.67 12.15 ± 0.06 3.98 ± 0.03 
Pp7 92.70 ± 4.15 116.23 ± 3.34 3.55 ± 0.15 33.35 ± 5.48 5.71 ± 0.05 
Pp8 108.05 ± 1.17 186.42 ± 5.75 43.16 ± 0.39 49.01 ± 0.22 22.46 ± 0.87 
Sample codeMetasilicate (mg/L)TDS (mg/L)Mineral contents (mg/L)
Na+Ca2+Mg2+
Pp1 15.06 ± 0.07 156.42 ± 5.75 1.18 ± 0.03 5.65 ± 0.02 14.50 ± 0.14 
Pp2 46.22 ± 6.74 121.67 ± 19.87 11.52 ± 0.08 5.30 ± 0.07 8.1 ± 0.09 
Pp3 33.42 ± 0.73 63.46 ± 2.5 5.30 ± 0.07 6.07 ± 0.1 4.45 ± 0.12 
Pp4 28.25 ± 0.55 399.43 ± 18.94 31.18 ± 2.34 71.05 ± 4.15 7.69 ± 0.09 
Pp5 42.84 ± 1.88 68.05 ± 1.17 45.45 ± 0.12 59.70 ± 4.15 13.5 ± 0.14 
Pp6 50.82 ± 3.14 109.44 ± 0.84 7.01 ± 0.67 12.15 ± 0.06 3.98 ± 0.03 
Pp7 92.70 ± 4.15 116.23 ± 3.34 3.55 ± 0.15 33.35 ± 5.48 5.71 ± 0.05 
Pp8 108.05 ± 1.17 186.42 ± 5.75 43.16 ± 0.39 49.01 ± 0.22 22.46 ± 0.87 

STATISTICAL ANALYSIS

Five physicochemical properties of bottled water from eight brands were measured by inductively coupled plasma–mass spectrometry (ICP-MS) to evaluate the correlation between radon concentration in the commercial bottled water and physicochemical properties of the bottled water, and the measurement results are shown in Table 5. In statistical analysis, the average of each group of measurements is used.

Multiple linear regression analysis

The method of multiple linear regression (MLR) is used to analyze the relationship between some physicochemical parameters and 222Rn in the bottled mineral water. The obtained multiple linear regression model is tested for a linear relationship, P = 0.02, R2 = 0.972, verifying the rationality of the regression model. The linear model of the concentration of 222Rn and some physical and chemical properties of bottle mineral water is as follows: 
formula
(3)

A significance test is carried out for each independent variable in the multiple linear regression model, and Sig. values are shown in Table 6. With a given significance level of α = 0.05, TDS and Ca2+ have a significant impact on the value of 222Rn, and their Sig. values are 0.023 and 0.044, respectively. However, Metasilicate, Na+ and Mg2+ do not have significant effects on the values of 222Rn. Among the two independent variables with significant effects, the t values of TDA and Ca2+ are both positive, which indicates that the values of TDS and Ca2+ have a significant positive effect on 222Rn. This indicates that the content of TDS and Ca2+ in bottled mineral water has a significant impact on the radon content of bottled water. The radon content increases with the increase of the concentration of TDS and Ca2+.

Table 6

Results of multiple linear regression analysis

ModelUnstandardized coefficients
Standardized coefficientstSig.
Bstandard error
constant −8.044 15.587 – −0.516 0.657 
Metasilicate −0.825 0.212 −0.285 −3.883 0.060 
TDS 0.526 0.080 0.611 6.545 0.023 
Na+ −3.232 0.847 −0.641 −3.816 0.062 
Ca2+ 2.703 0.587 0.780 4.601 0.044 
Mg2+ 4.000 1.411 0.273 2.836 0.150 
ModelUnstandardized coefficients
Standardized coefficientstSig.
Bstandard error
constant −8.044 15.587 – −0.516 0.657 
Metasilicate −0.825 0.212 −0.285 −3.883 0.060 
TDS 0.526 0.080 0.611 6.545 0.023 
Na+ −3.232 0.847 −0.641 −3.816 0.062 
Ca2+ 2.703 0.587 0.780 4.601 0.044 
Mg2+ 4.000 1.411 0.273 2.836 0.150 

Pearson correlation analysis

Pearson correlation is used to analyze the correlation between some physicochemical properties of 222Rn and mineral water; the correlation matrix is shown in Table 7, and the correlation heat map is shown in Figure 6. Obviously, TDS has a strong correlation with 222Rn (r = 0.941), Ca2+ has a correlation with 222Rn (r = 0.629), and Na+ has a correlation with Mg2+ (r = 0.628). 222Rn has a weak correlation with Metasilicate and Na+ and Mg2+.

Table 7

Pearson correlation matrix for 222Rn and physical and chemical properties of the bottled mineral water

222RnMetasilicateTDSNa+Ca2+Mg2+
222Rn      
Metasilicate −0.253     
TDS 0.941 −0.121    
Na+ 0.273 0.281 0.291   
Ca2+ 0.629 0.243 0.579 0.825  
Mg2+ 0.107 0.352 0.113 0.628 0.343 
222RnMetasilicateTDSNa+Ca2+Mg2+
222Rn      
Metasilicate −0.253     
TDS 0.941 −0.121    
Na+ 0.273 0.281 0.291   
Ca2+ 0.629 0.243 0.579 0.825  
Mg2+ 0.107 0.352 0.113 0.628 0.343 
Figure 6

Pearson correlation heat map and cluster analysis.

Figure 6

Pearson correlation heat map and cluster analysis.

Cluster analysis

Cluster analysis is a statistical method that divides the target objects into relatively homogeneous groups by finding their characteristics (Harikrishnan et al. 2018). Figure 6 shows the tree diagram obtained by system clustering analysis, and some relationships among the six variables can be found in the tree diagram. Six different variables are divided into two large groups, with Metasilicate and Mg2+as a group and the remaining four variables as a group, and then it is broken down, and the four variables are made up of 222Rn and TDS, Na+ and Ca2+.

CONCLUSION

In this study, the concentrations of 222Rn from 15 different brands of commercial bottled drinking water produced in China have been analyzed. The maximum radon concentration in bottled water is 300.021.6 mBq/L, the minimum is 13.34.7 mBq/L and the average is 90.1 mBq/L, and the values of all radon concentrations measured in this study are lower than the recommended maximum contaminant level of 11.11 Bq/L and the limit of radon concentration in domestic water (4–40 Bq/L). The radon concentration values in this study are almost within the range of those of all other countries or regions. , , the effective dose for some internal organs in the body and the total annual effective dose are calculated for three age-groups: infants, children and adults, which are lower than the annual effective dose limits of 0.1mSv/y. Though the different brands of commercial bottled water do not pose a threat to public health for long-term drinking, the public should be closely monitored for radon exposure to internal organs caused by drinking-water.

In addition, according to the data of some physical and chemical properties of bottled mineral water, the relationship between some physical and chemical properties and radon concentration were analyzed by using multiple linear regression, Pearson correlation analysis and cluster analysis. We find that TDS and Ca2+ in bottled water have a positive correlation with radon concentration, and the radon concentration in the bottled water can be roughly predicted based on the mineral content in the bottled water.

ACKNOWLEDGEMENTS

This work was supported by the National Natural Science Foundation of China (Project No. 11975177 and 11575149).

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Author notes

J. L. Yong and G. W. Feng are the first authors.