This study was conducted to determine the levels of uranium in groundwater and the radiological and chemical toxicity risks associated with its ingestion in Haryana, India. Uranium concentration was determined using LED fluorimeter. We find that uranium concentrations in 26 out of 105 (24.8%) samples tested in Bhiwani and 21 out of 68 (30.9%) samples tested in Hisar exceeded the WHO guideline level of 30 µg L-1. The high uranium concentration obtained in groundwater is due to local natural geology. The associated age-dependent annual effective dose is estimated by taking the prescribed water intake values of different age groups. The mean values of cancer mortality and morbidity risks are lower than a permissible limit recommended by the Atomic Energy Regulatory Board, India. About 21% and 23.5% of the samples from Bhiwani and Hisar, respectively showed hazard quotient higher than unity. The physico-chemical parameters have also been determined and correlated with uranium concentrations.
Keywords: Groundwater; Uranium; LED fluorimeter; Annual effective dose; Radiological risk; Chemical risk
Groundwater is an important water resource for drinking, industrial and agricultural uses in India. Intense abstraction has led to severe groundwater table declines in many parts of the country, especially in the Haryana, Rajasthan and Punjab states of India (Rodell et al., 2009). The Indian Central Groundwater Board reported that groundwater in most of the blocks (66?70%) in these three states was either critically exploited or overexploited (CGWB, 2013).
Uranium is a naturally occurring radioactive material that is present in our environment, including water, air, soil and rocks. The geochemical processes, geological setting and geographical location, influence the uranium concentration in the environment. Most of the uranium in water originates from uranium leached from rocks and soil (WHO 2011; ATSDR, 2013). Natural uranium is composed of three long-lived isotopes: 238U, 235U and 234U each with a different mass abundance and half-life: 238U (99.2745%, T1/2 = 4.47 ? 109 years), 235U (0.72%, T1/2 = 7.04 ? 108 years) and 234U (0.0055%, T1/2 = 2.44 ? 105 years) (UNSCEAR, 2008). Cothern and Lappenbusch (1983) have estimated that the food contributes about 15% of the ingested uranium, while drinking water contributes about 85% to the human population in the U.S.A.
Natural uranium induces chemical toxicity, especially nephrotoxicity, which is more harmful than radiotoxicity; whereas radium and radon are thought to induce solely radiotoxicity (ATSDR, 2013; Wrenn et al., 1985). Exposure to uranium has been linked with birth defects, certain types of genetic, developmental and metabolic damage and adverse effects on the kidneys, liver and neurologic, endocrine, immune, reproductive and cardiovascular systems (ATSDR, 2013; Weinhold, 2012).
There is a wide range of opinions on uranium standards, guidelines and health goals both internationally and nationally. The World Health Organization (WHO) in 2004 guidelines (third edition) cites a tolerable daily intake (TDI) of 0.6 µg kg-1 of body weight day-1 (based on animal studies by Gilman,1998 and Gilman et al., 1998), for a 60 kg adult consuming 2 litres of water per day and an 80% allocation of TDI to drinking water, giving a chemical provisional guideline value of 15 µg L-1, which was increased significantly from 2 µg L-1 in 1998 (second edition) (WHO, 2004; WHO, 1998). The WHO in 2011 guidelines (fourth edition) recommended a new provisional guideline value of 30 µg L-1 based on a TDI of 1.0 µg kg-1 of body weight day-1 (WHO, 2011). This higher guideline value is mainly sourced from recent human studies from Finland (Kurttio et al., 2002, 2005, 2006), Sweden (Seld?n et al., 2009) and the USA (Zamora et al., 2009). The United States Environmental Protection Agency publishes a maximum contaminant level (MCL) of 30 µg L-1 and states that their maximum contaminant level goal for uranium in drinking water is zero (USEPA, 2011).
Health Canada adopted a maximum acceptable concentration (MAC) of 20 µg L-1 based on nephrotoxicity (kidney effects in male rats). The guideline protects the health of Canadians, including the most vulnerable members of society, such as infants and children (Health Canada, 2019). There is currently no maximum level for uranium in drinking water in the European Union (European Union Council Directive, 2013). Some EU Member States and Third Countries have set maximum levels for uranium in drinking water. Germany has recently introduced a limit of 10 µg L-1 (Bundesministerium f?r Gesundheit, 2011).
The National Health and Medical Research Council, Australia determine a health based guideline value of 17 µg L-1 for uranium in drinking water using the TDI of 0.6 µg kg-1 of body weight day-1 (WHO, 2004), assuming the average weight of an adult 70 kg, drinking maximum 2 L of water per day and an 80% allocation of the TDI to drinking water (NHMRC, NRMMC 2011). The Atomic Energy Regulatory Board, India has set a radiological based limit for uranium in drinking water of 60 µg L-1 (AERB, 2004; Coyte et al., 2018). The Ministry of Health, New Zealand (2008) recommends a provisional maximum acceptable value for uranium in drinking water of 20 µg L-1.
The Russian Federation (2003) proposed the most acceptable concentration of 100 µg L-1 for uranium in drinking water. The Ministry of Health Malaysia (2004) recommended a maximum acceptable value of 2 µg L-1 for uranium. Japan sets the target value of 2 µg L-1 for uranium in drinking water (Japan Ministerial Ordinance Concerning Drinking-water Quality Standards, 2010). Japan placed the uranium in the category Complementary Items to Set Targets for Water Quality Management. The Uganda, South Africa, Singapore, Peru, Oman and Indonesia specified a standard of 15 µg L-1 for uranium in drinking water (Uganda Standard, 2008; South African National Standard, 2011; Environmental Public Health Regulations, Singapore, 2008; Ministerio de Salud, Lima-Per?, 2011; Omani Standard, 2012; Peraturan Menteri Kesehatan Republik Indonesia, 2010). Uranium is not specified in the list of maximum permissible values of metals in National Standards for Drinking Water Quality, Pakistan (NSDWQ-Pak, 2010). In the UK, there is no upper limit specified, neither for tap nor bottled water. Current advice from the Food Standards Agency is to avoid using natural mineral water to prepare infant food (COT, 2006).
The literature survey shows that no attempt has been made towards the measurement of uranium concentrations in groundwater of Bhiwani and Hisar districts, Haryana. The study area has attracted a lot of geological interest because of its lithography consists of various rock formations. The aims of the present work are to study: (a) the distribution of uranium in groundwater and compare the observed uranium concentrations with drinking water quality guidelines/standards; (b) correlation between uranium and physico-chemical parameters; (c) associated age-dependent annual effective dose; (d) radiological and chemical toxicity risks to humans due to ingestion of uranium in drinking water.
Geology of the study area
Haryana state is situated in the North India. Fig. 1 shows the geographic location of Bhiwani and Hisar districts on the map of Haryana. Bhiwani district (28?47?N and 76?8?E) is situated in the south western part of Haryana covering the geographical area of 5140 km2. The district consists of flat and level plain interrupted from place to place by clusters of sand dunes, isolated hillocks and rocky ridges. The geological formation met within the district is ferruginous chiastolite schist associated argillaceous rocks of Aravalli group, Alwar quartzite of Delhi system, Malani suite of volcanics of lower Vindhyan age, older alluvial deposits of quaternary age and aeolian sands of recent age. Older alluvium occurs extensively in the district consisting of interbedded, lenticular, interfingering deposits of gravel sand, silt, clay and kanker mixed in various proportions. The Tosham Igneous Complex in Bhiwani district is reported to be rich in acid volcanic and granite solids (Kochhar, 1983). The Tosham Igneous Complex has 3 main hills (Khanak, Tosham and Riwasa) and several other smaller rocky outcrops (Nigana, Dulehri, Dharan, Dadam and Kharkari Makhwan). These hills are mainly composed of granite porphyries. The granites and granite porphyries are high heat producing type (Kochhar, 1983). Its lithography structure has attracted researchers to this area. The groundwater occurs under water table conditions in-shallow aquifers zones whereas in the deeper zones, confined/semi-confined conditions exist, hard rocks comprised of Aravalli group of rocks, Malani suite of volcanics and Alwar quartzites of Delhi system are water bearing (CGWB Bhiwani, 2013; Kochhar, 1989, 2000).
Hisar district (29?9?N and 75?43?E) is situated in the west central most region of Haryana covering the geographical area of 3983 km2. The area forms a part of Indo-Gangetic plain. The geological formation met within the district comprise unconsolidated alluvial deposits of quaternary age. The area falls in Yamuna sub-basin of 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 water table and semi-confined to confined conditions. The district is divided into two geographic regions, i.e., upload plain and sand dune clusters. The soils of the area are of three types, i.e., arid brown solonized, sierozem and desert soils (CGWB Hisar, 2013; Sharma et al., 2017).
Materials and Methods
Sample collection and physico-chemical parameters
A total of 173 water samples were collected from Bhiwani (n=105) and Hisar (n=68) districts of Haryana (Fig. S1 in the Supplementary Data). The sources of water comprise hand pumps, tube wells, electric motors and bore wells. The sampling sites were chosen in such a manner that the whole geographical area get covered. We chose sampling sites whose waters are continuously used for human consumption as well as in animals and crop production. The freshness of water was ensured by pumping off a sufficient amount of water for about 10 minutes before sampling. Prior to 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 containers until analysis.
Physico-chemical parameters such as pH, total dissolved solids (TDS) and electrical conductivity (EC) in groundwater samples were measured in situ by using portable micro controller water analysis kit NPC 362D. The instrument was calibrated by using standard solutions that bracketed the expected values. The knowledge of physico-chemical parameters provides significant first hand in situ information about the suitability of water for drinking purpose.
LED fluorimeter model LF-2a (Quantalase Enterprises Pvt. Ltd., Indore, India) was used for the analysis of uranium in drinking water. This is one of the most efficient, sensitive and quick technique for uranium estimation in water samples with lower and upper detection limits of 0.5 and 1000 µg L-1, respectively, with an accuracy of ±10%. The instrument works on the principle of measurement of fluorescence of uranium complexes in the water sample. The instrument mainly consists of three parts: light emitting diodes (LEDs) as an excitation source, sample compartment and photomultiplier tube (PMT) as detector (Fig. S2 in the Supplementary Data). LED source emits ultraviolet radiation with wavelength 400 nm carrying energy of 20 µJ and pulse duration of 20 µs at a repetition rate of 1000 pulses per second excites the uranyl ion present in the water sample placed in the sample compartment. On de-excitation, green fluorescence emitted by uranyl ion is measured by sensitive PMT.
The groundwater sample also contains some other impurities. The organic matter present in the groundwater, when excited by UV light fluorescence in the blue green region. A long pass optical filter that allows the light only of wavelength above 475 nm is placed between LEDs and PMT to prevent the fluorescence from organic matter to fall on PMT. In addition, Pulsed excitation by proper time gating of PMT is carried out to block the fluorescence from organic matter having short lifetime of about 100 ns whereas fluorescence from uranyl ion is about 200 µs.
5% of sodium pyrophosphate was prepared in double distilled water and its pH was adjusted to 7 by drop-wise addition of orthophosphoric acid and then this solution was added to water sample in the ratio of 1:10 to convert all uranium species into single form that have fluorescence and also have property to enhance the fluorescence yield. The instrument was calibrated with known standards supplied by the Quantalase Enterprises Pvt. Ltd., Indore, India before uranium estimation in water samples. Details about the calculation of uranium concentration in water samples can be found in Sharma et al. (2019).
Age-dependent dose assessment
The annual effective dose due to the intake of uranium through drinking water for different age groups was determined using the International Atomic Energy Agency (IAEA, 2011) dose conversion factors and the water intake rates prescribed by the Institute of Medicine of the National Academies (2005). The uranium activity concentration was determined by using unit conversion factor 1µg L-1 = 0.02528 Bq L-1 (Sahoo et al., 2010; Rani et al., 2013).
The annual effective dose for different age groups from ingestion of uranium in water was determined as (Bronzovic and Marovic 2005):
Ingestion dose (Sv y-1) = Ua ? DWI ? DCF ? 365 (1)
where Ua = uranium activity concentration (Bq L-1), DWI = daily water intake for specific age group (L day-1) and DCF = dose conversion factor for specific age group (Sv Bq-1).
Radiological toxicity risk assessment
The radiological toxicity risk is expressed in the terms of excess cancer risk (ECR), which evaluated by multiplying the uranium activity concentration (Ua) (Bq L-1) and risk factor (RF) (L Bq-1) (USEPA, 2000).
ECR = Ua ? RF (2)
Risk factor (RF) was determined as follows:
RF (L Bq-1) = RC ? IRW ? ED (3)
where RC = uranium risk coefficient (Bq-1), IRW = water ingestion rate (2 L day-1) (WHO, 2011) and ED = exposure duration (70 years) i.e. 70 ? 365 = 25,550 days (WHO, 2011; Rani et al., 2013). We have evaluated the cancer mortality risk and morbidity risk by taking into consideration the cancer mortality risk coefficient as 1.13 ? 10-9 Bq-1 and cancer morbidity risk coefficient as 1.73 ? 10-9 Bq-1, respectively (USEPA, 1999).
Chemical toxicity risk assessment
The chemical toxicity risk from exposure to uranium is quantified in terms of lifetime average daily dose (LADD) and hazard quotient (HQ). LADD is defined as quantity of uranium ingested per kilogram of body weight per day and was evaluated by the following equation (USEPA, 2000; WHO, 2011; Shin et al., 2016; Duggal et al., 2017).
LADD (?g kg^(-1) day^(-1))=(U?IRW?EF?ED)/(AT?BW) (4)
where U = uranium concentration in water (µg L-1), IRW = water ingestion rate (2 L day-1) (WHO, 2011), EF = exposure frequency (365 days year-1) (Ali et al., 2019), ED = exposure duration (70 years) (Rani et al., 2013), AT = average time (25,550 days) and BW = body weight (70 kg for the Indian standard person) (USEPA, 2011; Duggal et al., 2017; Duggal and Rani, 2018).
The HQ was calculated by using the following equation:
where RfD = reference dose. Its value is 1.0 µg kg-1 day-1 (WHO, 2011). The RfD is an estimate of a daily ingestion of uranium for human populations that is likely to be without an appreciable risk of deleterious health effects during a lifetime. If HQ is found to be less than unity, then no adverse health effects are expected due to the exposure of uranium.