Assessment of Uranium concentration in groundwater and its 1 human health impact in a part of Northern Tamil Nadu , India 2

Ground water is the major source of drinking water in India. Over exploitation of this water resource 13 has exacerbated the situation of providing good quality water, due to the presence of major ions, minor ions, 14 trace elements and radioactive elements. A study has carried out in Vellore, a city in the Northern part of the 15 Tamilnadu, to understand the levels of Uranium concentrations and other geochemical parameters in drinking 16 water. Samples were collected and the analysed for various water quality parameters in the laboratory and as 17 well as insitu. Uranium concentration was estimated using the Quantalase Laser Fluorimeter and nearly 10 % of 18 the samples show that the concentration of Uranium is exceeding the permissible limit .The low observed 19 adverse effect level and No observed adverse effect level values were also assessed for to understand the risk 20 due to the presence of the uranium in drinking water and it was observed that there is a slight risk on the public 21 health due to the consumption of ground water in this region. 22 23


Introduction
Uranium (U) occurs on earth by natural means.Minute quantities of uranium can be found in humans, animals, plants, soil, water and rocks.Even though it is radioactive, it exhibits weak radioactivity and adds to the low levels of radiation occurring naturally in the environment.Since U is present mostly everywhere in earth, it is also present in significant quantities in water, especially in drinking water.Due to natural erosion and weathering process, uranium mobilized from the rocks to groundwater and surface water.Some of the methods by which U can get into drinking water are human activities and geogenic sources such as mining and dissolution of U containing minerals in groundwater respectively (Bruce et al., 2014).Mainly U is present in groundwater rather than surface water, so there is a need to assess the amount of U present in groundwater.Alagarsamy Rahul 1 , arahul.2016@vitstudent.ac.inDrink.Water Eng.Sci.Discuss., https://doi.org/10.5194/dwes-2019-3 Manuscript under review for journal Drink.Water Eng.Sci. Discussion started: 13 March 2019 c Author(s) 2019.CC BY 4.0 License.

Sampling and analysis
Study area was divided into 2 km by 2 km grid in order to ensure the uniform distribution of sample locations and later, the coordinates of the centre of each grid were identified with the help of satellite images.The groundwater samples were collected from hand pumps and bore wells at these locations within a radius of 5 km during the month of September 2017 (Fig. 1).The parameters such as Electrical conductivity, pH, and Dissolved oxygen were analysed in situ using YSI digital multi-parameter instrument kit whereas the Alkalinity and Hardness were measured by the titration method in the laboratory.
The concentration of U in the groundwater samples was estimated using Quantalase LF2a Laser Fluorimeter.
The instrument was calibrated in the range of 1 to 100 ppb using a standard stock solution and the Phosphoric acid in ultra-pure water was used as fluorescence reagent in the analysis.To obtain blank counting, a blank sample with same amount of fluorescing reagent was measured for U concentration.

Results and Discussion
The concentration of uranium and other physiochemical parameters at different locations in the study area are tabulated in the Table 1.Weathering and dissolution of rocks and soils constitute TDS naturally into groundwater.In the present study the minimum and maximum values of TDS varied from 328 μgl -1 to 4671 μgl - 1. TDS of groundwater in this study area is very high when compared with standards such as WHO and SEPA.
Similar to TDS, the values for the EC ranging from 489 μScm -1 to 6971 μScm -1 .As this area is mostly covered by hard rocks, the samples results show the high TDS and EC values.84 % of groundwater samples are exceeding the limit i.e. 500 mgl -1 .The pH values are lies between 6.1 and 7.85.Whereas the minimum and maximum ranges of DO vary from and 3.8 mgl -1 to 7.3 mgl -1 respectively.The mean, maximum and minimum values of this data are given in the Table 2.
Figure 2 shows the relationship between percentage U and its concentration.It is observed that maximum of 62.26 % of samples in the study area has U concentration of 0-10 ppb while 16.98 %, 7.55 %, 13.2 % of samples are in the range of 11-20, 21-30, >30 ppb respectively.
The minimum U concentration value observed was 0.3 ppb and the maximum value observed was 69.5 ppb with an average value of 12.94 ppb.The permissible limits of the uranium concentration in the drinking water across the different bodies of the world are given in the Table 3.As per the AERB the guideline limit is 60 ppb, in this study at only one location it has crossed this prescribed limit.As per, WHO and USEPA the permissible limit of U concentration in drinking water is 30 ppb and it is been observed that out of the 53 ground water samples, in 7 samples the concentration of Uranium is exceeding this prescribed limit (i.e.>30ppb).Spatial distribution of U in the study area is shown in Fig. 3.The high concentration of U in Northern side is may be due to leaching of charnokite, gneiss and granite present in that region.The correlation between U and other parameters are shown in Fig. 4. It is observed that there is no strong correlation of U with pH, Dissolved Oxygen and alkalinity but a slight positive correlation is observed between the U and TDS.Coefficient of correlation of the Uranium concentration with the various parameters in drinking water is given in Table 4.This implies that 'U' may be present in water due to the increased presence of dissolved solids.Since there is no strong correlation with these parameters it implies that the presence natural uranium in this area might be due to geological formations and other factors.

Human health impact of Uranium
Uranium is a radionuclide that emits primarily alpha particles and is associated with many health risks.Uranium is a health hazard only if it is taken in to the body as it is an alpha emitter.The Uranium contaminated water does not cause any radiological effects although chemically it can affect the human body.Kidneys are the primary targets of U contamination.A higher Uranium trace causes the failure of the functioning of the kidneys.
Oesophagus and stomach cancers are also an effect of continuous consumption of U contaminated water.

NOAEL/LOAEL
Various researches have been carried out in order to understand the toxicological effect of U in drinking water.
No observed adverse effect level (NOAEL) is the highest toxic point at which there is no adverse effect to any human due to the toxicity, whereas, low observed adverse effect level (LOAEL) is the lowest toxic point at which there is adverse effect occurs due to the toxicity.LOAEL is slightly higher than NOAEL in one dosage.The NOAEL and LOAEL for natural U are estimated as 0.2 mg -1 kg -1 day -1 (Public Health Goals 1997) and 0.06 mg -1 kg -1 day -1 (Gilman 1998) respectively.In the present study LOAEL of 0.06 mg -1 kg -1 day -1 is considered for comparison of U in groundwater.LOAEL varied from 0 mg -1 kg -1 day -1 to 0.05 mg -1 kg -1 day -1 which is lower than 0.06 mg -1 kg -1 day -1 in all sampling locations.The LOAEL for uncertainty factor of 100 varied from 0 mg -1 kg -1 day -1 to 0.5 mg -1 kg -1 day -1 .The spatial distribution of this LOAEL values less than and greater than 0.06 mg -1 kg -1 day -1 is shown in Fig. 5. Hence, 40% samples are considered to be under stress with an UF of 100, there is considerable amount of threat due to consumption of groundwater in this study area with respect LOAEL values.

Conclusion
A study was conducted to understand the levels of concentrations of U and other drinking water parameters in the Vellore and Katpadi regions.It was observed that few samples are above the prescribed limit of uranium (30 ppb) while most of the samples fall within the range (mean = 13 ppb).Though the presence of higher uranium concentration is not fully understood through this study but the positive correlation between U and TDS indicated that natural U may be present due to the dissolution of these ions from rocks and the higher depth of the wells is also a possible factor for the high presence of the Uranium.Further these results are used to derive the LOAEL and NOEL values to assess the risk due to the presence of the uranium in drinking water in the Vellore region, for which a value of 0.06 mg kg -1 day -1 was considered for the comparison of U in groundwater.
The LOAEL for uncertainty factor of 100 varied from 0 mg kg -1 day -1 to 0.5 mg kg -1 day -1 , for which 40 % of the samples found greater than 0.06 mg kg -1 day -1 in, which signifies that there is a slight risk on the public health due to the consumption of ground water in this region.
In the current study the correlation of Uranium Concentration is restricted only with few quality parameters, hence, by considering other physiochemical parameters and factors in further studies, the concluding confirmation can be drawn for the proper remedial measures which may be adopted to reduce the Uranium content in those locations in Vellore region.Table 1: Geochemistry and U concentrations of groundwater samples
According to Public Health Goal (PHG 2001) NOAEL or LOAEL is given as following Equation health-protective concentration for U in drinking water (mgl -1 ) NOAEL/LOAEL = No observed adverse effect level / low observed adverse effect level RSC = Relative source contribution (40 %) BW = Body weight of an adult human (70 kg) W = Daily water consumption for an adult (2 lpd) UF = Uncertainty factor 10 for extrapolation from 91 day study to life time exposure Uncertainty factor 100 which includes 10 for extrapolation from 91 day study to life time exposure and a factor of 10 for inter individual differences in sensitivity to U toxicity Drink.Water Eng.Sci.Discuss., https://doi.org/10.5194/dwes-2019forjournal Drink.Water Eng.Sci. Discussion started: 13 March 2019 c Author(s) 2019.CC BY 4.0 License.

Figure 1 :Figure 2 :Figure 3 :Figure 4 :Figure 5 :
Figure 1: Location map of the study area Figure 2: Relationship between percentage of Uranium and its concentrations Figure 3: Spatial distribution of Uranium concentration in the study area Figure 4: The correlation of the Uranium concentration with the various parameters in drinking water Figure 5: The spatial distribution of the LOAEL Drink.Water Eng.Sci.Discuss., https://doi.org/10.5194/dwes-2019forjournal Drink.Water Eng.Sci. Discussion started: 13 March 2019 c Author(s) 2019.CC BY 4.0 License.

Figure 1 :
Figure 1: Location map of the study area

Figure 2 :
Figure 2: Relationship between percentage of Uranium and its concentrations

Figure 3 :Figure 4 :
Figure 3: Spatial distribution of Uranium concentration in the study area

Figure 5 :
Figure 5: The spatial distribution of the LOAEL

Table 4 : Co efficient of correlation of the Uranium concentration with the various parameters in drinking water
Drink.Water Eng.Sci.Discuss., https://doi.org/10.5194/dwes-2019-3Manuscript under review for journal Drink.Water Eng.Sci. Discussion started: 13 March 2019 c Author(s) 2019.CC BY 4.0 License.