Keywords
Uranium, heavy metals, hydrogeology, aquifer contamination
This article is included in the Public Health and Environmental Health collection.
Chintamani village, Chikkaballapura district, Karnataka, India was found to possess high aquifer uranium concentrations. Geologically, Chintamani village is located on bedrock that is rich in elements like potassium (K) that naturally contain high levels of radioactive elements, such as uranium and thorium, due to the presence of alkali-feldspar granites and gneisses. Aquifer depletion has caused the concentration of these elements in groundwater to increase over time, posing a potential health hazard to the residents of Chintamani village.
Here, we report the sampling of groundwater from 12 borewells located in Chintamani village in between the period of August 2024 to December 2024. We observed groundwater uranium concentrations of 0.018 ppm to 8.64 ppm. Data for borewell depth, the quantity of total dissolved solids (TDS), and the elemental composition of TDS is also reported. We observed a statistically significant spatial distribution of uranium concentrations in Chintamani village. Borewells possessing the highest observed concentrations of uranium were clustered towards the northwestern region of the village.
This dataset is expected to serve as a resource for guiding potential remediation efforts in these locations.
Uranium, heavy metals, hydrogeology, aquifer contamination
This version addresses comments made by Reviewer 2 and Reviewer 3.
Reviewer 2 requested a spatial map of uranium concentrations. This has been done and presented in Figure 1B. We used local kernel density estimate (KDE) smoothing to predict area-wide uranium concentrations.
We have also discussed the implications of our findings and the need for further work in order to address the environmental and public health effect of groundwater uranium concentrations.
As per the request of Reviewer 3, we have included a rationale for including elemental analysis in our study. We have also briefly discussed the correlation between uranium and nitrogen concentrations. We found no correlation between these variables, indicating that nitrate fertilizers may not play a role in mobilizing uranium from bedrock in this location.
See the authors' detailed response to the review by Daniel O. Omokpariola
See the authors' detailed response to the review by Wasiu Mathew Owonikoko
Uranium in groundwater primarily originates from natural geological sources, particularly from uranium-rich bedrock. Uranium may occur at high concentrations in intrusive igneous rocks, including two-mica granite, calc-alkaline granites, and alkalic plutonic rocks at concentrations of 3–300 ppm.1 The crystal structures of igneous minerals like biotite, muscovite, K/Na-feldspar, and quartz may incorporate uranium in the percent range.2,3 Uranium is also found in sedimentary rocks such as shales (2-4 ppm), bauxite (11.4 ppm) and lignite (<50-80 ppm).1
Deep, water-stressed aquifers are frequently in contact with uranium-rich bedrock, enabling uranium to leach out into the surrounding groundwater. While this is a geogenic process, human activities can further exacerbate uranium contamination in groundwater. The use of nitrate-based fertilizers enhances the mobility of uranium by making it more soluble in water.4 Additionally, over-extraction of groundwater lowers the water table, requiring deeper borewells to be drilled into uranium-rich bedrock. Diverse regions across the world experiencing water stress also display higher groundwater uranium content. Uranium concentrations in San Joaquin Valley, California, were observed to exceed federal and state drinking water standards of ≤30 ppb.5 Groundwater in the Datong Basin, China, displayed uranium concentrations of <0.02–288 ppb, with a mean of 24 ppb.6 Likewise, high groundwater uranium concentrations have been reported in southern Finland, Germany, Portugal,7 Japan, Mongolia, Uzbekistan and, India.8
Uranium adversely affects crops grown on soil irrigated with contaminated groundwater. Uranium’s phytotoxic effects include inhibition of photosynthesis, inhibition of plant growth, protein and lipid membrane oxidation, overproduction of reactive oxygen species, and DNA breakage.9 Uranium primarily accumulates in root systems, with negligible amounts found in aerial parts of plants10 and is therefore a greater concern for root and tuber crops.
Dermal exposure results in minimal toxicity, particularly if Uranium is in an insoluble form.11 Uranium in groundwater is typically present as sparingly soluble uranyl carbonate complexes,12 minimizing the risk of absorption through the dermal route. Insteal, oral consumption of uranium through drinking untreated uranium-contaminated groundwater is of more concern. Although uranium is weakly radioactive, its primary health risk stems from its chemical toxicity rather than its radioactivity. Chronic exposure to uranium-contaminated water is associated with nephrotoxicity,13,14 with adverse renal effects reported in both laboratory animals and humans.15 Uranium excretion in urine is correlated with phosphate and calcium excretion.15 Other adverse effects include inhibition of bone function and development,16 reproductive and developmental toxicity.17
In this data note, we report data obtained from five randomly selected borewells in Chintamani village, Chikkaballapura District, Karnataka, India. Subsequently, seven additional borewells were selected in the vicinity of the borewell exhibiting the highest uranium concentration among the initial five. The site selection was based on accessibility and its proximity to our university. We report the uranyl concentrations (ICP-MS), and TDS elemental compositions (SEM-EDS) of groundwater obtained from all the wells sampled. A previous survey conducted by R. Srinivasan et al. fluorimetrically measured concentrations of groundwater uranium from 73 borewells spread across 13 districts of Eastern Karnataka,18 reporting high uranium concentrations of >1 ppm in Chitradurga, Tumkur, Kolar, and Chikkaballapura districts of southeastern Karnataka. The bedrock in these districts is composed primarily of Neoarchean granites, gneisses, and migmatites.18 The borewells we sampled displayed uranium concentrations ranging from 0.018 ppm to 8.64 ppm, confirming the concentration ranges reported in the previous survey. Furthermore, most wells sampled possessed groundwater uranium concentrations exceeding the permissible limits established by WHO (30 ppb) and AERB (60 ppb) supported by ICP-MS data.19 We have mapped the spatial distribution of groundwater within Chintamani village. We observed a significantly higher concentration of uranium was observed in borewells clustered at the northeastern region of Chintamani village, meriting further investigation of the village’s local geological features.
Groundwater samples from Chintamani village were collected using the purge and sample method. Each borewell was pumped for five minutes to remove stagnant water from the well casing and tubing. After purging, a 2 L water sample was collected in a clean polypropylene bottle. Table 1 lists the latitude, longitude, and date of collection for every sample.
Concentrations ≥ 0.03 ppm are underlined. Concentrations ≥ 0.06 ppm are in bold.
For every borewell sample, 1 L of water was dried in a hot-air oven at 80°C in a clean Borosil ® borosilicate 1L glass beaker until only the salt residue remained. This residue was weighed using a Shimadzu AXT224R precision balance (least count = 0.1 mg) and subjected to SEM-EDS in order to determine its elemental composition.
ICP-MS experiments to quantify uranium concentration in the parts per million (ppm) range was performed by Eurofins Scientific India using a PerkinElmer ® 350X instrument. A 20-40 mL sample from each borewell was submitted. The sample was acidified with nitric acid to adjust the pH to ≤2. The instrument was set to detect elemental uranium concentrations. Raw data were interpreted using the Syngistix™ software (version 4.0, PerkinElmer®). Raw data may also be interpreted using openMS. ICP-MS reports for each sample can be found in Supplementary Dataset S1.20
An FEI (Field Electron and Ion Company) Quanta 200 scanning electron microscope at Icon Labs Pvt. Ltd., Mumbai was used to perform SEM-EDS experiments. Samples were observed under a low vacuum mode at 20 kV, and with a chamber pressure of 65 Pascal. SEM-EDS has a least count of 0.1% (by weight) and cannot detect elements below this concentration. SEM-EDS spectra and reports quantifying the elemental composition of each sample can be found in Supplementary Dataset S2.21
All statistical analyses were performed using the R programming language (version 4.4.2). The Leaflet package22 was used to generate a physical map of Chintamani village ( Figure 1). The Welch 2-sample T-test (one-tailed) was used to determine whether there existed a statistically significant difference between uranyl concentrations in different spatial locations in Chintamani village ( Figure 1). This was performed using the function t.test. Pearson’s correlation coefficient and the statistical significance (p-value) between uranyl concentrations and the other variables discussed was calculated using the function cor.test ( Tables 1, 2).
Groundwater from 12 borewells in Chintamani village, Chikkaballapura District, Karnataka, India were sampled from August 2024 to December 2024. Initially, we collected groundwater samples from borewells 1-5 that were evenly distributed around the geographical area of Chintamani village. Groundwater from borewell 1 displayed the highest uranium concentration from this cohort (0.771 ppm U), leading us to sample groundwater from more borewells around borewell 1 in the northwestern region of Chintamani village. We found a statistically significant difference (p = 0.048, Welch 2-sample T-test, one-tailed) between the uranium concentration of groundwater in the northwestern region (NW, borewells 1, 6-12) compared to groundwater in the rest of Chintamani village (borewells 2-5).
Table 1 depicts uranium concentrations quantified using ICP-MS from these 12 groundwater samples. Uranium concentrations ranged from 0.018 ppm (Borewell 2) to 8.64 ppm (Borewell 8). There exists a weak correlation (r = 0.49, Pearson’s coefficient) between uranium concentration and well depth. However, the correlation is not statistically significant (p = 0.14). ICP-MS reports quantifying uranium content for each sample can be found in Supplementary Dataset S1.20
Table 2 represents the elemental composition of the total dissolved solids (TDS) obtained after drying groundwater samples collected from Chintamani village. For each borewell water sample, we calculated correlation coefficients between the absolute and relative elemental compositions of each element and the uranium concentration. This was done in order to determine if uranium concentrations are correlated with those of other elements, suggesting co-occurrence or common geochemical behavior. The elemental composition of dried TDS was determined using SEM-EDS. Elemental composition is expressed in absolute terms (mg of element per liter of groundwater, mg/L) and in relative terms (% composition compared to all other elements present in dried TDS). Pearson’s correlation coefficients are provided for both expressions of elemental composition by comparing the values for every element with the corresponding uranium concentration (in ppm) (refer Table 1). It was observed that the % composition of K (r = 0.49, p = 0.1) and Mg (r = 0.45, p = 0.14) were weakly correlated with uranium concentration, although these correlations were not statistically significant. No significant correlation was observed between nitrogen and uranium concentrations, in either absolute (r = –0.10, p = 0.75) or relative (r = 0.06, p = 0.85) terms. This suggests that nitrate fertilizers are unlikely to play a role in mobilizing uranium from bedrock in Chintamani village. SEM-EDS spectra and reports quantifying the elemental composition of each sample can be found in Supplementary Dataset S2.21
We have presented a dataset containing uranyl concentrations from groundwater obtained from 12 borewells across Chintamani village, Chikkaballapura district, Karnataka, India. Uranyl concentrations ranged from 0.018 ppm (borewell 2) to 8.64 ppm (borewell 8). According to World Health Organization (WHO),9 and Atomic Energy Regulatory board (AERB) recommendations, the uranium concentration in drinking water should remain ≤30 ppb (0.03 ppm) and ≤60 ppb (0.06 ppm) respectively to minimize health risks. 10 out of the 12 borewells sampled possessed uranium concentrations >0.03 ppm, and 9 wells possessed uranium concentrations >0.06 ppm, indicating cause for concern. Uranium concentrations >0.03 ppm were observed both in the northwest region (borewells 1, 6-12) as well as outside (borewells 4, 5), indicating a wide distribution across the water table of Chintamani village. Borewell 8 possessed 8.64 ppm uranium, a concentration 288× greater than the WHO recommended maximum.
Nephrotoxicity,10,11 bone function impairments,16 developmental and reproductive toxicity17 are known adverse health effects associated with chronic uranium exposure. It is therefore worth studying the prevalence of such health effects in the residents of Chintamani village.
R Srinivasan et al.18 previously conducted a survey on the groundwater uranium concentrations of villages in eastern Karnataka. Their study was broader in scope and sampled 73 villages. As a consequence, the samples collected per village were low. R Srinivasan et al. reported uranium concentrations of 5267 ± 6 ug/g and 5913 ± 6 uranium from 2 borewells sampled in Chintamani village. Here, we show a far greater variation in uranium concentrations, ranging from 0.018 ppm to 8.64 ppm (mean = 1.39 ±2.55 ppm), from the 12 borewells we sampled in Chintamani village. We have measured groundwater uranium concentrations using ICP-MS, which helps confirm previous fluorimetric measurements.18 Our study provides greater insights into groundwater uranium concentrations in Chintamani village, but is nevertheless limited by our larger but still modest sample size (n=12) and lack of temporal data.
We have provided two datasets: ICP-MS data for groundwater uranium concentration (Dataset S119), and SEM-EDS data for the elemental compositions of TDS obtained from these groundwater samples (Dataset S220). These datasets, along with our kernel density estimate of groundwater uranium distributions (Figure 1B), could potentially be used as resources for guiding remediation efforts by displaying borewells and areas possessing the highest uranium concentrations. Further work, such as direct health or exposure assessments, is required to determine the environmental and public health effect of groundwater uranium in Chintamani village and its surroundings.
Authors Sadashiva Rampur, Mahesh Kumar V.K., and Pavan R. Pelli surveyed and collected water samples from Chintamani village. Authors Senjuti Sarkar, Samayeta Pramanik, Upama Majumdar, Shravanthi S., and Bhavana Meenakshi T. processed groundwater samples to quantify TDS content, and processed samples for SEM-EDS and ICP-MS experiments. Authors Srinidhi G. Santhanakrishnan and Rushi Pendem analyzed and interpreted all data. Authors Senjuti Sarkar, Tanushree Ghosh, and Deepesh Nagarajan conceived the project and designed all experiments. All authors took part in drafting the manuscript and provided final approval before submission.
Data are available under the terms of the Creative Commons Attribution 4.0 International license (CC-BY 4.0). All raw data have been made publicly available for use by the research community.
Repository name: Dataset S1: ICP-MS data for groundwater uranium concentration in ppm. https://doi.org/10.6084/m9.figshare.28491125.v1.20
The project contains the following underlying data:
• dataset-s1.pdf ICP-MS reports (generated by Eurofins India, Bangalore) for the uranium concentrations of groundwater samples from borewells 1-12 (reported in ppm). Water samples were collected from Chintamani village, Chikkaballapura district, Karnataka, India, during the period of August 2024 to December 2024.
Repository name: Dataset S2: SEM-EDS spectra of groundwater TDS, https://doi.org/10.6084/m9.figshare.28491146.v1.21
The project contains the following underlying data:
• dataset-s2.pdf SEM-EDS spectra and reports (generated by Icon Labs Pvt. Ltd., Mumbai) for the elemental composition of total dissolved solids (TDS) obtained after drying groundwater samples from borewells 1-12. Water samples were collected from Chintamani village, Chikkaballapura district, Karnataka, India, during the period of August 2024 to December 2024.
The authors extend their thanks to Mr. Kiran Rambhau Bhotkar (Assistant Manager - Application Support, SEM-EDS) and Mrs. Sunita Samgir (Senior Executive - Application Support, SEM-EDS) from Icon Labs Pvt. Ltd., Mumbai, for their excellent work as our scanning electron microscopy technicians.
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Competing Interests: No competing interests were disclosed.
Reviewer Expertise: Development of environmentally sustainable technologies for heavy metal ion remediation in ground water
Is the rationale for creating the dataset(s) clearly described?
Partly
Are the protocols appropriate and is the work technically sound?
Partly
Are sufficient details of methods and materials provided to allow replication by others?
Partly
Are the datasets clearly presented in a useable and accessible format?
Partly
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: Development of environmentally sustainable technologies for heavy metal ion remediation in ground water
Is the rationale for creating the dataset(s) clearly described?
Yes
Are the protocols appropriate and is the work technically sound?
Yes
Are sufficient details of methods and materials provided to allow replication by others?
Partly
Are the datasets clearly presented in a useable and accessible format?
Yes
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: Environmental Chemistry and Toxicology; Remote Sensing; Atmospheric and Water chemistry; Risk assessment and Project Management
Is the rationale for creating the dataset(s) clearly described?
Yes
Are the protocols appropriate and is the work technically sound?
Yes
Are sufficient details of methods and materials provided to allow replication by others?
Partly
Are the datasets clearly presented in a useable and accessible format?
Yes
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: Environmental Physiology and Toxicology
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