Risk assessment of uranium in drinking water in Hisar district of Haryana, India

Uranium is a naturally occurring radioactive element that is commonly present in groundwater. Studies show that the contribution of ingested uranium through food products accounts for 15%, whereas drinking water contributes to 85% of the ingested uranium. Hence, the health risk due to consumption of uranium-containing groundwater poses a greater risk compared to other causes (Cothern & Lappenbusch 1983; Rani et al. 2013; Adithya et al. 2019). Uranium concentration in groundwater depends on several factors, including lithological, geomorphologic and other geological conditions of the area. Uranium concentration can also result from human activities such as mining, combustion of coal and other fuels, the use of phosphate fertilizers, and nuclear power production (Kumar et al. 2016; Duggal et al. 2017).

Although uranium present in the environment, although it has no known positive metabolic functions and is regarded as a non-essential component, when accumulated in humans, it results in chemical and radioactive effects in the form of various health hazards (Sharma et al. 2019; Duggal et al. 2020). Most of the inhaled and ingested uranium is not absorbed and leaves the body in the feces. Absorbed uranium leaves the body in the urine. Some inhaled uranium can stay in the lungs for a long time. The uranium that is absorbed is deposited throughout the body; the highest levels are found in the bones, liver, and kidneys. Sixty-six percent of the uranium in the body is found in bones. It can remain in the bones for a long time; the half-life of uranium in bones is 70–200 days. Most of the uranium that is not in the bones leaves the body in 1–2 weeks (ATSDR 2013).

Physicochemical parameters (pH, total dissolved solids (TDS) and electrical conductivity (EC)) of groundwater are important in the sense that these parameters can provide important first hand in-situ information about the suitability of water for drinking purposes. TDS comprise inorganic salts (principally calcium, magnesium, sodium and potassium cations and carbonate, bicarbonate, chloride, sulphate and nitrate anions) and small amounts of organic matter that are dissolved in water. TDS in groundwater originate from natural sources, sewage, urban and agricultural run-off and industrial wastewater. pH is an another important monitoring parameter to assess the health of aquatic ecosystem, irrigation sources and discharges, livestock, drinking water sources, industrial discharges and intakes (Kumar et al. 2011; Bajwa et al. 2017).

There is a wide range of opinions on uranium standards, guidelines and health goals both nationally and internationally (Table 1). A review of the literature reveals that data on the concentration of uranium in groundwater is broadly available for many states of India, but no such study has been carried out earlier in the Hisar district of Haryana. This study aims to understand the uranium distribution in groundwater and compare the observed concentrations with drinking water quality guidelines/standards, to compute age-dependent annual effective doses (AEDs) and to determine radiological and chemical toxicity risks to humans due to ingestion of uranium in drinking water. The physicochemical parameters were also quantified to measure the groundwater quality and to find the correlation, if any, with the determined uranium concentrations.

Haryana State is situated in North India. Hisar is the west central most district of Haryana State with a total geographical area of 3,860 km² and lies between the north latitudes 28°56′00″ to 29°38′30″ and east longitudes 75°21′12″ to 76°18′12″. Figure 1 shows the geographic location of the Hisar district on the map of Haryana as well as the location of the sampling sites. The area forms a part of the Indo-Gangetic plain. The geological formations met within the district comprise unconsolidated alluvial deposits of quaternary age. The area falls in the Yamuna sub-basin of the Ganga Basin. The area is irrigated by shallow tube wells, the network of Bhakra canal systems and western Yamuna canal system. Groundwater occurs in the alluvium under a water table and is semi-confined to confined conditions. The district is divided into two geographic regions, that is, upload plain and sand dune clusters. The soils of the area are of three types: arid brown solonized, sierozem and desert soils. The study region is bounded by the Fatehabad district in the north, Hanumangarh district of Rajasthan in the west, Jind district in the east, and Bhiwani and Rohtak districts of Haryana in the south and southeast, respectively (CGWB Hisar 2017; Sharma et al. 2017).

A total of 68 water samples were collected from the Hisar district of Haryana (Figure 1). The sources of water comprise bore wells, electric motors, tube wells and hand pumps. Sampling sites were chosen where water is continuously used for human consumption as well as animals and in crop production. The sampling sites were also chosen in such a manner that the study area is uniformly represented. The position of each sampling site was determined by using portable global positioning system (GPS). The water freshness was maintained by pumping out enough water for about 10 min before sampling. Before collection, the water samples were filtered using 0.45 μm Whatman filter paper to remove suspended matter/sediments and then stored in pre-cleaned acid-washed polyethylene bottles until analysis. Physico-chemical parameters such as pH, TDS, and EC in groundwater samples were determined in situ using a portable microcontroller water analysis kit NPC 362D. The instrument was calibrated using standard solutions that bracketed the expected values.

The LED fluorimeter model LF-2a developed by Quantalase Enterprises Private Limited, Indore, India, was used for the analysis of uranium in drinking water. The instrument has lower and upper detection limits of 0.5 μg L⁻¹ and 1,000 μg L⁻¹, respectively, with an accuracy of ±10%. The instrument consists primarily of three components: light-emitting diodes (LEDs) as a source of excitation, a sample section, and a photomultiplier tube (PMT) as a detector (Figure S1 in the Supplementary Material). The LED source emits ultraviolet radiation with wavelength 400 nm carrying 20 μJ energy and pulse duration of 20 μs at a repetition rate of 1,000 pulses per second excites the uranyl ions present in the water sample placed in the sample section. On de-excitation, green fluorescence emitted by uranyl ions is measured by sensitive PMT.

The permissible limit for uranium in drinking water, as prescribed by various countries and environmental protection organizations, is very different. Therefore, it is better to compare the quality of groundwater on the basis of radiological and chemical toxicity caused by ingestion of uranium containing groundwater in the human body than to assess its suitability on the basis of its absolute concentration (Shin et al. 2016; Duggal et al. 2017; Sharma et al. 2019).

Table 2 presents the summary statistics of uranium concentrations (μg L⁻¹) in groundwater. The uranium concentrations varied from 1.2 to 274 μg L⁻¹ with a mean value of 32.5 μg L⁻¹ and a median of 16.5 μg L⁻¹, and approximately 30.9% of the samples exceeded the WHO (2011) provisional guideline level (PGV) of 30 μg L⁻¹ (Table S1 in the Supplementary Material). The standard deviation value is higher than the mean and median values, indicating that uranium concentrations are spread out over a wider range (Table 2). When comparing the mean and median values of uranium concentrations, it is observed that the data are not symmetrically distributed. It is a right-skewed distribution, as the mean value is approximately twice the median value. The kurtosis and skewness values are of a positive type. The data are highly skewed, which may be attributed to the variation in the geological formation of the study region. The measured uranium concentrations in groundwater follow a lognormal distribution. According to the literature survey, usually, the environmental samples and radioactive sampled data follow a lognormal distribution (Limpert et al. 2001).

The alluvium aquifers of the study region are composed of sand, clay and kankar and these aquifers are semi-confined, similar to the other alluvium aquifers in Northwest India, such as Punjab and Rajasthan (Bonsor et al. 2017). Many studies (Rani et al. 2013; Duggal et al. 2017; Mittal et al. 2017; Pant et al. 2017; Saini et al. 2018) have reported uranium concentrations above 30 μg L⁻¹ in the states of Punjab and Rajasthan, which are associated primarily with alluvial aquifers. The findings of these studies are consistent with our results, which find high uranium concentrations in groundwater from alluvial aquifers. Mann et al. (2018) reported high activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in soil samples collected from the Sirsa, Fatehabad, Hisar and Bhiwani districts of Haryana.

The observed concentrations were also compared with the worldwide literature (Table 3). The uranium concentrations in water samples from Canada, Sweden, Saudi Arabia and Northern Rajasthan; India are comparable with the present study. However, the uranium concentrations are higher in the drinking water of SW Punjab; India, NE Portugal and USA, whereas the uranium concentrations in Australia, Switzerland, Bangladesh, Mongolia, Korea, Kosovo, Jammu and Kashmir, Himachal Pradesh, Uttarakhand, Haryana, Uttar Pradesh, Bihar, Jharkhand, West Bengal, Chhattisgarh, Odisha, Maharashtra, Karnataka, Tamilnadu, and Kerala states of India are lower than the concentrations found in the present study.

The physicochemical parameters (pH, TDS and EC) of the groundwater samples are reported in Table 2 and Table S1. The groundwater of the study area is alkaline in nature. The acceptable limit for pH as prescribed by the Bureau of Indian Standards (BIS 2012) and WHO (2011) is 6.5–8.5. Only one water sample had a pH value above 8.5. The WHO (2011) has suggested that water pH has no direct impact on consumers. Activity increases the capacity of water to attack geological materials and leach toxic metals into the water, making it potentially harmful for human consumption. The TDS values in groundwater for whole of the studied area ranged from 181 to 13,150 mg L⁻¹ with an average value of 2,309 mg L⁻¹. Approximately 84% of the samples had TDS values above the acceptable limit of 500 mg L⁻¹ and 44% samples exceeded the permissible limit of 2,000 mg L⁻¹ recommended by BIS (2012). High concentration of TDS in the groundwater samples may be attributed to the dissolution or mineralization of organic and inorganic contents in aquifers. Residents of the study area are mostly illiterate farmers, who use this high TDS groundwater for irrigation and for domestic consumption without prior treatment. EC values varied from 359 to 26,200 μS cm⁻¹ with a mean value of 4,477 μS cm⁻¹. Approximately 84% of the samples had EC values above the maximum permissible limit of 1,000 μS cm⁻¹ recommended by the Water Act (1956).

In the present study, no correlation was observed between uranium and pH. A positive correlation was observed between uranium and TDS, indicating that the mobility of uranium in the groundwater was very much influenced and controlled by TDS (Figure 2). Due to high TDS in groundwater, solubility of uranium increases. All the groundwater samples followed the general rule; the higher the TDS (or EC), higher the radioactivity (Ortega et al. 1996; Singh et al. 2003; Kumar et al. 2011; Duggal et al. 2017).

Groundwater samples were collected from different depths ranging from 20 to 200 feet. No correlation was observed between uranium concentration and depth of the groundwater.

The estimated AED due to intake of uranium through drinking water for various age groups varied from 1.3 to 688 μSv y⁻¹, with an average value of 54 μSv y⁻¹ (Table 4). The large variations in the annual effective dose are due to the wide range of uranium concentrations in the investigated groundwater samples. The calculated annual effective dose values for different age groups follow a lognormal distribution. The WHO (2011) guidelines (fourth edition) and the European Union Council Directive (2013) prescribed the measurement of reference dose level (RDL) of the AED received from drinking water ingestion at 100 μSv y⁻¹. This RDL is ̃4.2% of the average AED of 2.4 mSv y⁻¹ from natural background radiation (UNSCEAR 2008; WHO 2011). Even though infants consume less water than other age groups, the AED is significantly higher in infants than in other age groups because of the differences in infants' metabolism and smaller organ weights, resulting in higher doses for many radionuclides (Duggal et al. 2017). The AED is slightly higher for the 7–12 months age group of infants as compared to 0–6 months due to higher annual water intake. Due to the lower water ingestion rate, all the age groups of females receive lower AEDs as compared to males. The higher AEDs during the lactation and pregnancy periods may be attributed to the need for more water in those periods.

The cancer mortality and morbidity risks as evaluated for the people who consume this water for drinking purposes is presented in Table 5. Mortality indicates the incidence of fatal cancers and morbidity indicates the incidence of total cancers (fatal and non-fatal). The cancer mortality and morbidity risks ranged from 0.18 × 10⁻⁵ to 40 × 10⁻⁵ and 0.27 × 10⁻⁵ to 61 × 10⁻⁵ with average values of 4.7 × 10⁻⁵ and 7.3 × 10⁻⁵, respectively. The estimated mean values of cancer mortality and morbidity risks were lower than the permissible limit of 1.67 × 10⁻⁴ as prescribed by AERB (2004). Some studies have reported 10⁻³ as the acceptable level for radiological risk (Tran et al. 2000; Kim et al. 2004). The cancer mortality risk from four locations (Dhani Raju H-6, Hansi H-17, Agroha H-53 and Balak H-67) exceeded the recommended permissible limit (Table S2 in the Supplementary Material). On the basis of maximum uranium concentrations, it can be concluded that due to continuous exposure to uranium through consumption of groundwater, there could be the occurrence of 40 cancer cases per one lakh of population. The values of cancer mortality risk are comparable to those reported in Northern Rajasthan, India (3.7 × 10⁻⁶ to 2.5 × 10⁻⁴) by Duggal et al. (2017), Uttarakhand State, India (5.04 × 10⁻⁸ to 1.79× 10⁻⁴) by Prasad et al. (2019), Punjab State, India (1.34 × 10⁻⁶ to 1.80 × 10⁻³) by Saini et al. (2016), Sonipat district, Haryana (2.60 × 10⁻⁵ to 4.39 × 10⁻⁴) and Panipat district, Haryana (4.2 × 10⁻⁵ to 3.49 × 10⁻⁴) by Daulta et al. (2018).

The lifetime average daily dose (LADD) of uranium due to ingestion of groundwater varied from 0.03 to 7.83 μg kg⁻¹ day⁻¹ and the HQ accordingly has the same numerical values because RfD is unity (WHO 2011) (Table 5). Approximately 23.5% of the samples showed a hazard quotient greater than unity (Table S2 in the Supplementary Material), indicating a significant risk due to the chemical toxicity of uranium. Therefore, periodic monitoring and management are needed for these areas. The LADD observed in the present study is comparable to those reported in Northern Rajasthan, India (0.07 to 4.89 μg kg⁻¹ day⁻¹) by Duggal et al. (2017), Uttarakhand State, India (0.001 to 3.69 μg kg⁻¹ day⁻¹) by Prasad et al. (2019), Jammu district, Jammu & Kashmir, India (0.01 to 1.52 μg kg⁻¹ day⁻¹) by Kumar et al. (2016), Sonipat district, Haryana (0.616 to 10.383 μg kg⁻¹ day⁻¹) and Panipat district, Haryana (0.998 to 8.259 μg kg⁻¹ day⁻¹) by Daulta et al. (2018).

• The results show that 30.9% of the samples exceeded the WHO PGV.

• Due to high TDS in groundwater of the study region, solubility of uranium increases.

• The mean AEDs for all age groups were well below the recommended RDL of 100 μSv y⁻¹. The infants have received relatively high mean AEDs compared to other age groups.

• The mean values of cancer mortality risk and cancer morbidity risk were well below the AERB's permissible limit.

• Approximately 23.5% of the samples showed HQ >1, indicating chemical toxicity due to the presence of uranium in groundwater, therefore, unsuitable for drinking.

• Remedial action is required at sampling sites with a high concentration of uranium.

The authors declare that they do not have any conflict of interest.

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

The authors are thankful to the residents of the study area for their cooperation during the field work and Department of Physics, Guru Nanak Dev University, Amritsar for providing state-of-the-art laboratory facilities.

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