Age-dependent dose assessment of uranium intake from bottled water in Punjab state, India Free

The consumption of bottled water is increasing significantly worldwide, becoming an important factor in both economic and health issues. Bottled water is generally accepted as a safe source of water, which contains biological or chemical toxins at levels that are not critical to human health (WHO 2004). Uranium is a naturally occurring radioactive material that is present in our environment, including water, air, soil, and rocks. Natural uranium is composed of three long-lived isotopes: ²³⁸U, ²³⁵U, and ²³⁴U. The most common isotope is ²³⁸U, constituting over 99% of natural uranium (WHO 2011; ATSDR 2013). Uranium has two oxidation states with wide variation in their solubility. It occurs in both as tetravalent and hexavalent forms and only the latter form is soluble (Cothern & Lappenbusch 1983).

Uranium in the natural groundwater system depends on several factors such as lithology, geomorphology, and other geological attributes of the region. Furthermore, the spatial variation of uranium mainly depends on geochemical factors (rock-water interaction) and its residence time in groundwater (Bajwa et al. 2017; Duggal et al. 2017a). The contribution of uranium in drinking water and food to total ingested uranium is approximately 85 and 15%, respectively. Hence, the health risk due to consumption of uranium-containing groundwater poses a greater risk compared to other causes (Cothern & Lappenbusch 1983). Many studies have investigated uranium concentrations in bottled waters worldwide (Birke et al. 2010; Inam et al. 2010; Dinelli et al. 2012).

Several studies from Punjab State have reported higher concentrations of uranium in groundwater than the permissible limit prescribed by the WHO (2011); (Sharma & Singh 2016; Bajwa et al. 2017; Virk 2017; Saini et al. 2018; Kumar et al. 2019; Sharma et al. 2019; Pant et al. 2020). In the Malwa region of Punjab, the problem of uranium in groundwater has become very acute. Uranium in drinking water can be extremely dangerous because it becomes part of the entire ecological system of the Malwa region of Punjab (Mittal et al. 2014; Duggal et al. 2018). The Malwa region has been described as India's Cancer Capital. The cancer prevalence in the Malwa region is indicated to be 1,089/million/year, which is much higher than the national average cancer prevalence in India (800/million/year) (DHFW 2013). The Malwa region shows extensively higher concentrations of uranium in groundwater, which may be due to (a) the leaching of uranium from adjoining/basement granite rich rock formations (Bajwa et al. 2017); (b) runoff containing excessive fertilizers from agricultural fields (Saini et al. 2016); (c) leaching of uranium from industrial waste products by various industrial units including chemical factories, cement factories, National Fertilizers Limited (NFL), oil refinery and coal-fired power plant. Hence, the measurement of uranium concentration in bottled water from Punjab State assumes significance. The literature survey shows that no attempt has been made towards measuring uranium concentrations in bottled waters produced and consumed in India. The present work aims to determine the concentration of uranium in Indian bottled water and to compute age-dependent annual effective doses. Additionally, this paper aims to assess the compliance of Indian bottled water brands to several standards around the world, including the World Health Organization (WHO), United States Environmental Protection Agency (USEPA), European Commission, and Atomic Energy Regulatory Board (AERB), India.

Punjab state is located between 29°30′ and 32°32′ North latitudes and 73°55′ and 76°50′ East longitudes in North India. Figure 1 shows the geographic location of Punjab State on the map of India as well as the sampling districts on the map of Punjab. Hydrogeologically, the Punjab State can be divided into four units: (i) piedmont deposits occurring along a narrow belt along the Siwaliks, (ii) alluvial plains, (iii) aeolian deposits occurring in the SW part and (iv) intermontane valley at Anandpur Sahib of Ropar district. The vast Indo-Gangetic alluvial plain forms an excellent repository of groundwater resources. Groundwater in Punjab occurs under both confined and unconfined conditions (CGWB 2014).

In total, 27 different brands of commercially available bottled water were purchased from local stores and transported to the laboratory for analysis. The samples were taken from the districts of Punjab, where high concentrations of uranium were observed in groundwater. The bottled waters were given a code from BW1 to BW27 to keep the brand names anonymous. The samples were analyzed for uranium during May 2019. All bottled waters have a shelf life ranging from six months to one year. All bottled waters were in polyethylene terephthalate (PET) containers with plastic screw caps. The holding capacities of bottled water containers ranged from 1 to 2 L. Sampling of bottled water ‘from the shelf’ was preferred to achieve a realistic estimate of the ingestion dose for the consumer. Manufacturer labels on the bottled were used as a source of basic information on a particular water sample. Water samples were not filtered and acidified since we intended to collect and analyze them as ‘drunk’ by the consumer.

The methods that are commonly used for the determination of uranium in water are neutron activation analysis (NAA) (Zikovsky 2004), anodic stripping voltammetry (Satpati et al. 2010), pellet fluorimetry, fission track registration technique (Mehra et al. 2007), inductively coupled plasma mass spectrometry (ICPMS) (Rani et al. 2013a, 2013b; Duggal et al. 2018), laser fluorimeter (Duggal et al. 2017a) and LED fluorimeter (Duggal & Sharma 2017; Duggal et al. 2017b; Sharma et al. 2019). ICPMS is the most accurate, sensitive, and precise technique for uranium determination, but ICPMS is not used in most laboratories because of its high cost. The fission track registration technique involves irradiation with thermal neutrons in the reactor and manually tracks counting under an optical microscope. In the case of neutron activation analysis, a high level of chloride hinders uranium estimation in potable water. The pellet fluorimetric analysis is time-consuming. Laser fluorimetric analysis is a simple, reliable, sensitive, and rapid technique for uranium determination in water compared to other analytical techniques. Recently, the laser source has been replaced by a light-emitting diode (LED) in a fluorimeter system. In comparison to the laser source, the LED source is cost-effective, generates less heat, and has an extended lifetime.

The LED fluorimeter model LF-2a developed by Quantalase Enterprises Private Limited, Indore, India, was used for the analysis of uranium in bottled waters. This instrument works on the principle of measuring the fluorescence of uranium complexes in the aqueous sample. The optical assembly of the LED fluorimeter LF-2a is shown in Figure 2. The instrument mainly consists of three parts: light-emitting diodes (LEDs) as an excitation source, sample compartment, and photomultiplier tube (PMT) as a detector. The LED source emits ultraviolet radiation with a wavelength of 400 nm carrying an energy of 20 μJ and pulse duration of 20 μs at a repetition rate of 1,000 pulses per second excites the uranyl ions present in the aqueous sample placed in the sample compartment. On de-excitation, green fluorescence emitted by uranyl ion is measured by sensitive PMT.

Sodium pyrophosphate (Na₄P₂O₇.10H₂O) solution (Merck, Mumbai, India) (5%) was prepared in double-distilled water and its pH was adjusted to 7 by dropwise addition of orthophosphoric acid (Labo Chemie, Mumbai, India). This solution acts as a fluorescence-enhancing reagent. To give an estimate of the concentration of uranium in a given sample, the instrument takes an average of 1,280 pulses. After every five samples, blank measurements are repeated to arrest memory effects and contamination. All samples were analyzed in triplicate and the presented results are the mean of the three measurements.

• D = uranium effective dose per year for a specific age group (μSv y⁻¹);

• AC = activity concentration of uranium (Bq l⁻¹);

• DWI = daily water intake for the specific age group (l day⁻¹); and

• DCF = dose conversion factor for uranium for a specific age group (Sv Bq⁻¹).

The uranium activity concentration was calculated using a unit conversion factor of 1 μg l⁻¹ = 0.02528 Bq l⁻¹ (Sahoo et al. 2010; Duggal et al. 2017a). The ingestion dose conversion factors applied were from the International Atomic Energy Agency (IAEA 2011). According to the IAEA, the ingestion dose conversion factor is 3.4 × 10⁻⁷ Sv Bq⁻¹ for infants (≤1 y), 1.2 × 10⁻⁷ Sv Bq⁻¹ for children between 1 and 2 y of age, 8.0 × 10⁻⁸ Sv Bq⁻¹ between 3 and 7 y, 6.8 × 10⁻⁸ Sv Bq⁻¹ between 8 and 12 y, 6.7 × 10⁻⁸ Sv Bq⁻¹ between 13 and 17 y of age, and 4.5 × 10⁻⁸ Sv Bq⁻¹ for adults (≥18 y). The age-dependent water intake in litres per day was obtained by using daily water intake (DWI) recommended by the Water Institute (2003) and the average body-weight data from the Family Practice Notebook Website (Scoot 2003; Bronzovic & Marovic 2005; Porntepkasemsan & Srisuksawad 2008).

The data are scrutinized statistically to draw meaningful conclusions. Statistical analysis was performed using MS Excel.

The results of uranium concentration in bottled waters are presented in Table 1. Uranium concentration varied from 0.19 to 9.29 μg l⁻¹ with a mean value of 1.58 μg l⁻¹ and a standard deviation of 1.95 μg l⁻¹. By comparing the observed data with the permissible limits of 60 μg l⁻¹ (Atomic Energy Regulatory Board India 2004), 30 μg l⁻¹ (International Bottled Water Association 2003; US Food & Drug Administration 2003; United States Environmental Protection Agency 2011; World Health Organization 2011) and 20 μg l⁻¹ (Health Canada 1999), it can be seen that the values are far below the permissible limits for drinking water. However, the uranium concentrations in 26% of samples exceeded the acceptable limit of 1.9 μg l⁻¹ recommended by the International Commission on Radiological Protection (ICRP 1979). Table 1 shows that a large number of samples (52%) were found to be in the range of 0.0–1.0 μg l⁻¹. The present values of uranium concentration in bottled water are comparatively much lower than those reported in groundwater of Faridkot district (16–350 μg l⁻¹) by Pant et al. (2020), Sangrur district (2.47–119.95 μg l⁻¹) by Virk (2017), Amritsar district (0.6–65.3 μg l⁻¹) by Sharma et al. (2019), Jalandhar district (1.53–50.2 μg l⁻¹) by Kumar et al. (2019), Bathinda and Mansa districts of Punjab (0.13–676 μg l⁻¹) by Saini et al. (2018).

The summary statistics of uranium in bottled waters are presented in Table 2. It is not symmetrically distributed when comparing the mean and median values of uranium, as the mean value is around twice the median value. The arithmetic mean and median values were less than the standard deviation. Kurtosis and skewness values are of a positive type. The Kurtosis is more than 3, so the distribution is leptokurtic. The data are highly skewed with a skewness of 2.67, which may be attributed to the variation in the origin of bottled waters.

Table 3 shows that the concentration of uranium in bottled waters for Hellas (Demetriades 2010), Austria (Wallner & Jabbar 2010), Italy (Bagatti et al. 2003), Germany (Birke et al. 2010), and Argentina (Bombén et al. 1996) is in a close agreement with the present work. However, the uranium concentration is higher in the bottled waters of Italy (Dinelli et al. 2012) and Europe (Bertoldi et al. 2011), whereas in Poland (Astel et al. 2014), Nigeria (Inam et al. 2010), Japan (Maruyama et al. 2014), Slovenia (Kobal et al. 1979). In Poland (Kozlowska et al. 2007), Tunisia (Gharbi et al. 2010), and Egypt (Higgy 2000), the concentrations of uranium are lower than the values observed in the present study.

The results are summarized in Table 4. The prescribed limit of AED to humans from water consumption is 1 mSv y⁻¹ (ICRP 1990). Dependence on the age of the mean values of assessed uranium AEDs from the intake of bottled water is given in Figure 3. The large variation in the annual effective dose is due to the large range of uranium concentrations in the investigated bottled waters. Even though infants drink (365 l y⁻¹) less water than adults (730 l y⁻¹), the AEDs to infants are significantly higher than those to adults because of the differences in infants' metabolism and smaller organ weights, resulting in higher doses for many radionuclides. According to Figure 3, the measured mean AED reaches a peak in infants, being about 4 times higher than that in adults. This remarkably high value is followed by a dramatic fall in the second year of life and a very slow rise over the next few years. Values are again much lower for adults (≥18 y) due to the lower dose conversion factor for adults. The AEDs from the consumption of bottled water varied from 0.16 to 29.17 μSv y⁻¹ for different age groups. The mean AEDs in all age groups were found to be lower than the ICRP (1990) recommended level of 1 mSv y⁻¹. Hence, the results of this study indicate that bottled water is acceptable for all age groups.

All the most consumed brands of bottled water sold in Punjab, India, were analyzed to assess uranium content. In all brands of bottled water studied, the uranium concentrations were well below the permissible limits prescribed by the USEPA, WHO, and AERB (Indian standard) for drinking water. Hence, bottled water in the study region is quite safe for drinking purposes, as far as uranium toxicity is concerned. The AEDs of uranium for all age groups were found below the ICRP recommended limit. For infants, the highest doses were calculated, making them the most critical population group. The regular monitoring of uranium level in bottled waters should be performed by the public sector to prevent subjecting the population to unnecessary radiation exposure.

The authors are thankful to the residents of the study area for their cooperation during the fieldwork.

All relevant data are included in the paper or its Supplementary Information.