Discovery of uranium content in breastmilk and assessment of associated health risks for mothers and infants in Bihar, India

Abstract

In recent years, groundwater uranium [U²³⁸] poisoning has posed serious health hazards in the exposed population. In India, an estimated 151 districts and 18 states are reported with groundwater uranium contamination, and about 1.7% of groundwater sources are affected in the state of Bihar (India). The objective of the study is to evaluate the uranium contamination in the breastmilk of lactating mothers and their breastfed infants. To evaluate the uranium exposure in the infants exposed through their mother’s breastmilk, n = 40 lactating women were selected randomly from different districts of Bihar. After obtaining the written informed consent, their breast milk was collected and analysed for quantification of U²³⁸. The infants and their mother’s carcinogenic risk (CR) and hazard quotient (HQ) were also studied to know the potential health hazard effects of uranium. The uranium exposure to the infants through their mother’s breastmilk is at a hazardous level. All the analysed breastmilk samples had U²³⁸ contents, which could pose health impacts to infants. The infants are highly vulnerable to potential non-carcinogenic risk in comparison to their mothers due to the real-time uranium elimination from their bodies. The study reveals that the uranium content in the breast milk was significantly high. The 70% of the infant population had the potential to cause non-carcinogenic health effects. From the studied districts, Katihar breastmilk samples had the highest U²³⁸ content. The exposure of uranium to the infant’s body through breast milk is significantly high, which may impact their health. Furthermore, there is also a need for biomonitoring of U²³⁸ in these regions at a broader level.

Supplementary Information

The online version contains supplementary material available at 10.1038/s41598-025-25307-7.

Introduction

Uranium (U) is a naturally occurring radioactive element found widely in granite and other rocks. It can enter groundwater through natural processes, especially in oxygen-rich environments, and also due to human activities like mining, burning coal and fuel, emissions from the nuclear industry, and the use of phosphate fertilizers which contains uranium^1,2. The average concentration of uranium in the Earth’s crust is about 2.8 parts per million (ppm) to 4 ppm. Exposure to uranium can pose significant health risks, including kidney damage, bone damage, an increased risk of cancer, and also developmental issues^3–5. The World Health Organization (WHO) has set a provisional guideline limit of 30 µg/L in drinking water. Germany, for instance, has adopted a stricter limit of 10 µg/L in 2011⁶. Higher levels of uranium in groundwater have been also observed globally, including in North America -Canada⁷, United States^8,9, Europe - Finland⁵, Sweden¹⁰, Switzerland¹¹, United Kingdom¹², and in Asia, Bangladesh¹³, China^14,15, Korea¹⁶, Mongolia¹⁷, Pakistan¹⁸, and the lower Mekong delta¹⁹. Furthermore, several health studies have been also carried out in Finland. It was reported that the drilled wells for drinking water had uranium concentrations in the range of 5.6–3410 µg/L²⁰. However, no clear clinical symptoms have been observed among the exposed population.

In India, approximately 18 states and 151 districts are affected by uranium poisoning ²¹. There is prevalence of uranium concentration above the WHO permissible limit in some of the localized pockets of a few States/UTs in the country. The elevated groundwater uranium levels have been reported in numerous states of India such as Andhra Pradesh²², Bihar^23–25, Chhattisgarh²⁶, Haryana²⁷, Jammu & Kashmir²⁸, Jharkhand^29–31, Himachal Pradesh³², Karnataka³³, Kerala³⁴, Punjab³⁵, Rajasthan³⁶, Uttar Pradesh³⁷, and West Bengal³⁸. A report brought out by Duke University, USA in association with Central Ground Water Board (India) and State Ground Water departments reported that 151 districts in 18 states are partly affected by high (> 30 µg/L) concentration of uranium in ground water³⁹. The Indian Standard IS 10,500: 2012 for Drinking Water specification has specified the maximum acceptable limits for radioactive residues as alpha and beta emitters, values in excess of which render the water not suitable for drinking⁴⁰.

The state of Bihar is located in Eastern India. It is characterized by fertile land, dense population, and a complex interplay of environmental and socio-economic factors⁴¹. The extensive use of groundwater for drinking and irrigation has led to the contamination of the groundwater with various pollutants⁴². The discharge of untreated or inadequately treated industrial effluents into rivers and other water bodies contributes to the pollution of the aquatic ecosystem⁴³. This pollution can introduce heavy metals and other toxic substances into the food chain, ultimately affecting human health⁴⁴. The use of chemical fertilizers and pesticides in agriculture can lead to the contamination of soil and water resources with these harmful substances⁴⁵.

The implications of this contamination for human health, particularly for vulnerable populations like lactating mothers and infants, are a serious concern⁴⁶. Breast milk is the primary source of nutrition for infants, providing essential nutrients and antibodies that support their growth and development⁴⁷. However, if breast milk is contaminated with toxic substances like uranium, it can pose a significant threat to infant health⁴⁸. Infants are particularly vulnerable to the harmful effects of uranium exposure due to their organs and systems dysfunctioning, making them more susceptible to damage from toxic substances⁴⁹. They absorb certain substances, including heavy metals, more readily than adults. The concentration of toxic substances can be higher in infants due to their lower body weight⁵⁰. The presence of uranium in breast milk can have several potential consequences for infant health, including nephrotoxicity and exposure during infancy can lead to long-term kidney damage⁵¹. Its exposure may affect the neurological development of infants, potentially leading to cognitive and behavioural problems. It can also increase the risk of developing cancer later in life⁵². In recent studies on heavy metal contamination in Bihar has reported with arsenic, lead, and mercury poisoning in the biological samples of the exposed population^53–55. Various studies have reported the presence of uranium in groundwater in certain districts of Bihar. There are 11 districts reported with uranium poisoning in the state of Bihar such as Gopalganj, Saran, Siwan, East Champaran, Patna, Vaishali, Nawada, Nalanda, Supaul, Katihar, Bhagalpur⁵⁶. The potential contamination of breast milk with uranium in Bihar highlights the urgent need for further research and public health intervention. Hence, the present study aims to estimate the uranium exposure in the subjects inhabiting the Gangetic plains of Bihar (India) for the first time.

Materials and methods

Location of study

This study was conducted in selected districts of Bihar, India such as Bhojpur, Samastipur, Begusarai, Khagaria, Katihar and Nalanda. The study was carried out between October 2021 to July 2024 (Fig. 1).

Fig. 1.

Map showing the sampling districts and locations in Bihar, India, created using ArcGIS Desktop 10.3.1 (Esri, Redlands, CA, USA; https://www.esri.com). District boundary shapefiles were obtained from the Geological Survey of India GIS data sources.

Selection of study subjects

This study emphasizes on understanding uranium levels in the breast milk of lactating mothers and the potential exposure to their infants. Fourty mothers, aged between 17 and 35 years, took part in the research. Each participant gave written informed consent before providing their breastmilk sample for uranium analysis. To gain further insights, the mothers were also interviewed using a questionnaire that covered topics such as breastfeeding time period and moreover questions related to their child’s growth and development.

Sample collection

Each lactating mother who took part in the study voluntarily provided their 5 mL breast milk for the study. The samples were carefully collected in sterilized falcon tubes and kept at cool temperature between 2 °C and 6 °C, in a cool box. They were then safely transported to the Mahavir Cancer Sansthan & Research Centre (MCSRC) in Patna, Bihar, India for detailed uranium analysis.

Laboratory digestion process of breastmilk

To measure uranium (U²³⁸) levels, a volume of 0.5 mL breast milk samples were added in a 30 mL conical glass flask with 5 mL of nitric acid (HNO₃) and left for overnight reaction. The next day, the mixture was gently heated on a hotplate at temperatures between 90 °C and 120 °C until it reduced to about 3mL. At that point, a mixture of nitric acid and perchloric acid (HClO₄) in a 6:1 ratio was added, and heating was continued until the volume further reduced to 2mL. The resulting solution was then rinsed with 1% nitric acid, and the final volume was adjusted to 10 mL using distilled water. The solution was thereafter filtered using Whatman filter paper no. 41 and sample was stored in a 20 mL glass vial, ready for uranium content analysis using ICP-MS, as per the the ILO (1972) guidelines⁵⁸.

Quality control of the chemical analyses

Inductively Coupled Plasma–Mass Spectrometry (ICP-MS) was used to carry out the analysis in this study. To ensure reliable results and maintain safety throughout the process, careful quality control measures were followed. To avoid any risk of cross-contamination, all equipment used for preparing the samples were thoroughly cleaned. Glassware and plastic containers were soaked in a 6% nitric acid (HNO₃) solution for 24 h and then rinsed three times with high-pure deionized water (Millipore Milli-Q, 18.2 mΩcm). Teflon containers, used specifically for digesting the samples, were also cleaned by soaking in 2% HNO₃ for 24 h, followed by rinsing it with Milli-Q water and drying in a specially designed hot air oven.

Instrumentation and method conditions

The uranium (U²³⁸) content in the breast milk samples were measured using the Agilent 7850 LC-ICP-MS instrument from the USA. The uranium analysis was conducted at National Institute of Pharmaceutical Education and Research (NIPER)-Hajipur, Vaishali, Bihar, India. The samples were sprayed into the instrument as a fine mist through a peri-pump and an auto-sampler (SPS4). To ensure accurate uranium detection, the instrument settings were carefully adjusted and checked according to the standard operating procedures. An argon plasma was created, reaching an extremely high temperature of 10,000 K, powered by 1550 kW of radio-frequency energy. The flow of plasma gas and helium gas was maintained at 16.0 L/min and 4.3 mL/min, respectively. Inside the spray chamber, the argon plasma ionized and broke down the sample into atoms. To prevent any contamination from previous samples, the system was thoroughly cleaned by washing it repeatedly with a blank solution. The ions generated then passed through the instrument’s interface and entered the collision cell, where helium gas was added to remove any unwanted polyatomic interferences, ensuring a clean and precise measurement.

Calibration standards

To establish the calibration curve and determine detection limits (in parts per billion), a blank solution containing 2% nitric acid (HNO₃) was used. A calibration standard solution (IMS-102), containing 29 different analytes—including uranium (U-238), arsenic, selenium, aluminium, chromium, manganese, titanium, strontium, cobalt, rubidium, silver, iron, nickel, cesium, copper, zinc, cadmium, mercury, beryllium, and lead—was prepared from a 10ppm stock solution. The standards were made at various concentrations: 0.1, 0.2, 0.3, 0.5, 1, and 2 ppm. To ensure the method was accurate and reliable, several parameters were assessed, including the calibration curve’s r² value (which shows how well the data fit), the slope and intercept of the curve, and the background equivalent concentration (BEC). Breastmilk spike study was done for the calibration of the uranium (238) estimation by ICP-MS (Supplementary 1).

Spatial analysis

Arc-GIS software [version 10.3.1] was used to map with GPS coordinates overlaid on a shapefile to visually represent the study sites. In the background of this map, an earth imagery picture of Arc-GIS was used for a clear representation of the study sites. A different districts shape file of Bihar was used to represent the administrative boundary of the study area in the map. A total of 06 individual maps were prepared for 06 different sampling districts.

Human health risk assessment(Monte Carlo simulation by R studio software)

The health risk assessment was estimated with the uranium contaminated breastmilk fed by the infants. The health risk assessment is a way through which the potential adverse effects caused by any pollutant (Uranium) exposure is estimated. In the present study, Monte Carlo simulation technique in Oracle crystal ball software version 11.1.3 was used. This method involves random sampling from probability distributions assigned to key input parameters, such as contaminant concentration, ingestion rate, body weight, exposure duration, and frequency. By running 10,000 iterations, the simulation generates a range of possible outcomes for risk indicators like Average Daily Dose (ADD), Hazard Quotient (HQ), and Cancer Risk (CR). Unlike conventional deterministic methods, this probabilistic technique offers a more robust and realistic estimation of health risks, helping to identify vulnerable groups and guide evidence-based risk management decisions. The values used for this health risk estimation are given in Table 1. For the present study, USEPA^59,60 guidelines were used. Moreover, the human health risk assessment is also a technique through which the potential risk of carcinogenic as well as non-carcinogenic is evaluated. The health risk assessment has been calculated by using the formula given below.

1

Table 1.

References of the health risk assessment studies.

Parameters	Children	References
IR	0.741	USEPA, 200861 & USEPA, 201459
ED	0.25	Narsimha & Rajith, 201862 & USEPA, 200861
EF	182	USEPA, 201459
BW	7.4	USEPA, 200861 & ICMR, 200963
AT	45.5	USEPA, 200861 & USEPA, 201459
RfD	0.0002	ATSDR, 201364
CSF	6.4 × 10−11	USEPA, 199965
C(mg/L)		Present study

Where, C is the concentration of Uranium, IR is the ingestion rate, EF is the exposed frequency and ED is the exposed duration, BW is the body weight and AT is the average time (Eq. 1). The value of these variables is shown in Table 1.

2

Where, HQ = Hazard Quotient, ADD = Average Daily Dose, RfD = Oral Reference Dose.

The RfD is the reference dose which represents in mg/kg body weight/day; HQ is the hazard quotient which is determined by dividing the value of ADD with reference dose and the cancer risk (CR) was analysed by multiplying the value of ADD with Cancer Slope Factor (CSF) (Eq. 2). The value of all these parameters is given in Table 1. If the value of HQ is greater than 1 then it shows potential health risk for non-carcinogenic health effect. 1 × 10⁻⁴ to 1 × 10⁻⁶ is the threshold value for Carcinogenic Risk (CR). If CR value exceeds this threshold limit, then it may be the chance to develop cancer.

Statistical analysis

The statistical analysis was conducted using SPSS − 25.0 and Graph Pad Prism 8.0. For the present study, the concentrations of uranium in breastmilk were graphed. Data were analyzed to assess inter-district variations in uranium (U-238) concentrations in breast milk of lactating mothers from different regions of Bihar. Descriptive statistics were expressed as mean ± standard error of mean (SEM), while minimum and maximum concentrations were reported to indicate the distribution range. Prior to inferential testing, data normality and homogeneity of variance were evaluated using the Shapiro–Wilk and Levene’s tests, respectively. Since the data met the assumptions of normality, a one-way analysis of variance (ANOVA) was applied to compare the mean U-238 concentrations among districts. Tukey’s Honestly Significant Difference (HSD) post-hoc test was used to identify pairwise differences when significant overall effects were observed. Descriptive analysis was performed for uranium (U-238) concentration in breast milk and duration of inhabitation at the current residence among lactating mothers. The uranium concentration (U-238) ranged from X_min to X_max µg/L, with a mean ± standard deviation (SD) of ± SD µg/L and a median of X₅₀ µg/L, indicating moderate variability across samples. The duration of inhabitation ranged from Y_min to Y_max years, with a mean ± SD of ± SD years, suggesting a heterogeneous residential history among participants (Supplementary 2).

Results

Breastmilk uranium concentration

The results showed all n = 40 breastmilk samples had significant uranium concentrations between 0 and 6 µg/L. There is no permissible limit or benchmark specified for breast milk uranium concentration. The maximum uranium concentration observed in the breastmilk samples was 5.25 µg/L (Figure 2).

Fig. 2.

Showing the graph of breastmilk uranium [U²³⁸] concentration in the studied n = 40 samples of lactating mothers of Bihar.

District wise study

The following table gives information about the statistical analysis of the studied districts. The decreasing order of exposure to uranium [U²³⁸] contamination in the districts such as Katihar > Samastipur > Nalanda > Khagaria > Begusarai > Bhojpur. So, it can be concluded that the most uranium exposed district is Katihar with uranium concentration as 5.25 µg/L (Figure 3).

Fig. 3.

Showing the average Uranium²³⁸ concentration in the breastmilk samples of lactating mothers from studied districts of Bihar.

Spatial analysis

The mean uranium contamination in breastmilk samples in Samastipur district was 3.307 ± 0.3968 µg/L with highest contamination as 4.760 µg/L, in Begusarai district the mean uranium contamination was 3.180 ± 0.466 µg/L with highest contamination as 4.030 µg/L. In Bhojpur district the mean uranium contamination was 2.520 ± 0.5136 µg/L with highest contamination as 3.870 µg/L while in Katihar district the mean uranium contamination in breastmilk was 2.736 ± 0.4196 µg/L with highest contamination as 5.250 µg/L. Similarly, in Khagaria district, the mean uranium contamination was 4.035 ± 0.4450 µg/L with highest contamination as 4.480 µg/L while in Nalanda district the mean uranium contamination in breastmilk was 2.354 ± 0.2618 µg/L with highest contamination as 4.730 µg/L (Table 2; Fig. 4A–F).

Table 2.

Uranium contamination in breastmilk in lactating mothers from different districts of Bihar.

District	U238 Concentration (SEM) (µg/L)	Maximum U238 Concentration (µg/L)	Minimum U238 Concentration (µg/L)	p- Value	Groupa
Samastipur	3.307 ± 0.3968	4.760	2.240	0.0004	a
Begusarai	3.180 ± 0.4669	4.030	2.420	0.0209	a
Bhojpur	2.520 ± 0.5136	3.870	1.710	0.0162	ab
Katihar	2.736 ± 0.4196	5.250	0.9200	0.0002	b
Khagaria	4.035 ± 0.4450	4.480	3.590	0.0699	b
Nalanda	2.354 ± 0.2618	4.730	0.8500	< 0.0001	b

^aDistricts sharing the same letter are not significantly different (Tukey HSD, p < 0.05).

Fig. 4.

(A–F) Spatial maps of district-wise U-238 contamination in breast milk samples of lactating mothers, created using ArcGIS Desktop 10.3.1 (Esri, Redlands, CA, USA; https://www.esri.com) with Esri’s World Imagery basemap.

(Source: Esri, Maxar, Earthstar Geographics, and the GIS User Community).

Correlation analysis indicated a weak positive association between uranium concentration and both the age of mothers and duration of residence, suggesting that longer exposure may slightly contribute to elevated uranium levels in breast milk, though not at statistically significant levels.

Health risk assessment (Monte Carlo Simulation)

The health risk assessment of breast-feeding infants and their average daily dose of uranium consumption through breast milk was estimated and represented in the form of average daily dose (ADD), hazard quotient (HQ) and carcinogenic risk (CR) through this formula “C × IR × EF × ED/BW × AT” and “HQ = ADD/RfD”. The results reveals that 70% of studied infant population have the potential to cause non-carcinogenic health effects (Figure 5). The mean value of ADD was 0.00027491 mg/kg body weight/day and the Maximum value was 0.0005257 mg/kg body weight/day (Figure 6). For the hazard quotient study, the minimum value was 0.4242, the maximum value as 2.6287 and the mean value as 1.3745 (Figure 7). There was no carcinogenic risk observed in the exposed subjects (Figure 8).

Fig. 5.

Showing the box-plot of non-carcinogenic risk.

Fig. 6.

Showing the hazardous quotient graph of average daily dose.

Fig. 7.

Showing the graph of non-carcinogenic health effect.

Fig. 8.

Showing the graph of carcinogenic health effect.

Discussion

The present study reports 100% lactating mothers having their breastmilk highly contaminated with uranium. Presently, there is no specified permissible limit or benchmark for uranium concentration in breast milk. In the present study, the uranium contamination in the 70% of the infant population had the potential to cause non-carcinogenic health effects. The lowest mean value of U²³⁸ concentration in breastmilk was observed in Nalanda district as 2.35 µg/L, while highest mean value was observed in Khagaria district as 4.035 µg/L. However, the highest U²³⁸ concentration was observed in Katihar district as 5.25 µg/L. The study indicates that Katihar district samples had hazardous levels of U²³⁸ in the breastmilk samples. The source of U²³⁸ contamination in the studied districts could be drinking water sources or the food source cultivated in the same location. In a recent study carried out by our team on n = 273 groundwater samples, reported uranium contamination in Bihar⁵⁶. The study found uranium contamination in n = 20 water samples with levels > 30 µg/L, while n = 150 samples with uranium levels between 1 and 30 µg/L. The maximum uranium concentration was reported as 82 µg/L in Supaul district, followed by 77 µg/L in Nalanda district and 66 µg/L in Vaishali district of Bihar. This denotes that there is significant presence of uranium in groundwater samples of Bihar. Hence, water can be one of the significant sources for U²³⁸ contamination in the exposed population.

Similar findings were reported by Coyte et al.⁶⁶, with concerns related to groundwater overexploitation in India leading to depletion and raised concerns over water and food security. The study explored 16 states and 324 wells in Rajasthan and Gujarat (India) which revealed uranium levels exceeding the WHO permissible limit of 30 µg/L. High concentrations were linked to geogenic sources, such as uranium-rich rocks and favourable groundwater chemistry, as well as anthropogenic factors like water table decline and nitrate pollution. Similarly, Diwan et al.⁶⁷, assessed uranium levels and health impacts in groundwater from Rajnandgaon District, Chhattisgarh (India). Uranium concentrations exceeded the WHO/USEPA limit in two villages during summer and one in winter, and surpassed the AERB limit (60 µg/L) in one village during summer. Correlation analysis indicates that Ca²⁺ ions and total alkalinity significantly influence uranium mobilization, highlighting geochemical factors as key contributors to groundwater contamination in the region. Machiraju et al.⁶⁸, assessed uranium levels in 48 water samples from Narsipatnam, Visakhapatnam District, Andhra Pradesh (India), during pre- and post-monsoon seasons. Uranium concentrations ranged from < 0.2 to 25.4 ppb (mean 4.9 ppb) in pre-monsoon and < 0.2 to 19.4 ppb (mean 2.7 ppb) in post-monsoon was reported. All values were below AERB and WHO limits, indicating the water is safe for drinking and domestic use. Similarly, Sharma et al.⁶⁹, analyzed seasonal uranium variation and groundwater quality in Kapurthala, Jalandhar, and Hoshiarpur districts of Punjab (India). Uranium levels ranged from 5.6 to 18.8 µg/L, remaining below the WHO limit in over 90% of samples.

Sahoo et al.⁷⁰, investigated uranium (U) contamination in Punjab’s alluvial aquifers, revealing that shallow groundwater (< 60 m) in the Malwa region is more contaminated than deeper sources. Uranium mobility is linked to oxidizing, alkaline conditions (median pH 7.25–7.33), and high TDS, salinity, and ion concentrations (Na, Cl, HCO₃⁻, F⁻, NO₃⁻). Geogenic sources, irrigation, fertilizer use, and arid climate contribute to U enrichment. Sharma et al.⁷¹, conducted study in Punjab’s Amritsar, Gurdaspur, and Pathankot districts (India) assessed seasonal uranium variation in groundwater and related health risks. Average uranium levels ranged from 3.0 to 8.8 µg/L across seasons, remaining below the WHO limit. Physicochemical factors like TDS, EC, and bicarbonates showed positive correlation with uranium. Radiological and chemical risk assessments indicated values below WHO and AERB safety limits, suggesting no significant health threat from uranium exposure via drinking water in these regions. Yadav et al.⁷², also reported the co-occurrence of arsenic and uranium in groundwater of the Central Gangetic Plain, India, highlighting both natural and anthropogenic sources such as agriculture, mining, and industry. Spatial distribution and hydrogeochemical analysis revealed that silicate weathering controls uranium mobility, while arsenic is influenced by carbonate dissolution and ion exchange.

In the present study, the hazard quotient study correlated the health risk with the minimum value as 0.4242 and 1.3745 and the maximum value as 2.6287, which denotes non-carcinogenic risk. In a similar study, Deepika et al.⁷³, assessed uranium levels in groundwater near Manchanabele reservoir, southwest of Bengaluru (Karnataka, India) to evaluate radiological and chemical toxicity. Uranium concentrations ranged from 0.88 to 581.47 µg/L (GM: 20.82 ppb), with ~ 66% of samples within WHO’s safe limit. The lifetime cancer risk ranged from 0.0028 × 10⁻³ to 1.85 × 10⁻³ (GM: 0.066 × 10⁻³), while chemical toxicity risk ranged from 0.03 to 21.65 µg/kg/day (GM: 0.77 µg/kg/day), indicating potential health concerns in some areas. In another study carried out Thoothukudi district (Tamilnadu, India) assessed uranium contamination in drinking water in 286 samples. Uranium levels ranged up to 167 µg/L (pre-monsoon) and 190 µg/L (post-monsoon), with fertilizer use linked to elevated concentrations. Noncarcinogenic risk exceeded safe limits in 15–17% of samples, while cancer risks remained within permissible limits. Findings indicate that residents face greater chemical toxicity risks than carcinogenic effects from uranium exposure via drinking water⁷⁴. Singh et al.⁷⁵ assessed uranium contamination in Bastar district, Chhattisgarh (India), revealing concentrations from 0.50 to 26.4 µg/L in 70 groundwater samples, with 82% exceeding ICRP limits. Multivariate analysis identified geological patterns and four key factors influencing uranium levels. Chronic daily intake and hazard quotient values exceeded safe limits in over 34% of samples across all age groups. The findings highlight significant non-carcinogenic risk and indicate improved groundwater monitoring and management strategies.

The present study investigated uranium (U-238) concentrations in breast milk among lactating mothers residing in various districts of Bihar, with a particular focus on the relationship between uranium levels and the duration of inhabitation at their current residence. The findings revealed measurable but low uranium concentrations in breast milk across most samples, consistent with previous reports indicating limited uranium transfer through lactational pathways^64,76. Although the population under study inhabits regions with documented uranium presence in groundwater, the observed concentrations in breast milk remained within low microgram-per-liter levels. This supports earlier evidence that uranium exhibits a strong affinity for phosphate and carbonate groups, favoring deposition in bones and kidneys rather than in mammary tissue^77,78. The lack of a strong or statistically significant correlation between uranium concentration and duration of inhabitation further suggests that bioaccumulation of uranium in breast milk is minimal, and that exposure through lactation is largely dependent on environmental and dietary intake rather than the length of residence. The weak association between residence duration and uranium levels could be attributed to multiple factors, including variability in local groundwater uranium concentrations, differing water sources, and individual physiological characteristics affecting uranium metabolism and excretion. Moreover, uranium’s low solubility and poor translocation to milk components—lipids, proteins, and aqueous fractions—likely explain the limited concentration range observed⁷⁹. Comparative studies from uranium-exposed regions have reported higher uranium levels in human milk, especially where groundwater contamination exceeds safe limits (e.g., Iraq, Afghanistan, Punjab). However, the present data indicate that, despite environmental uranium presence, breast milk remains a relatively minor exposure pathway for infants. The primary route of uranium excretion remains urinary elimination, reflecting rapid renal clearance and low lactational transfer efficiency. Overall, these findings reinforce the concept that breast milk uranium concentration is a poor biomarker of chronic uranium exposure, as it reflects short-term equilibrium rather than cumulative body burden. Future studies with larger sample sizes, environmental uranium profiling (in water, soil, and diet), and isotope-specific measurements are warranted to better understand maternal–infant uranium kinetics in exposed populations.

Uranium enters the cellular environment through the clathrin-mediated endocytic pathway in CHO-K1 cells. Once inside, the acidic conditions of the endosome lead to the formation of uranyl ion precipitates, primarily composed of phosphates, potassium, and calcium, resulting in cytotoxic effects⁸⁰. Additionally, uranium has the ability to cross both the blood-brain barrier and the placental barrier, potentially impairing neurological function and foetal development⁷⁷. It causes serious health hazards to the infants to the vital parts of the body especially kidneys⁷⁸, neurodevelopment risks such as delayed cognitive development, impaired motor skills, reduced IQ levels⁸¹. Uranium also accumulates in bones and interferes with normal bone development and growth^5,82. Its toxicity may also increase the long-term cancer risks especially leukaemia and bone cancer depending on the dose duration⁸³. Moreover, it also disrupts the immune system development making infant more vulnerable to infections and autoimmune conditions^84,85. Moreover, uranium binds to plasma proteins and preferentially accumulates in bones and kidneys due to its affinity for phosphates and carbonate groups, rather than in breast milk. Its low affinity for milk components (lipids, proteins, and water), combined with the absence of specific transport mechanisms, results in low uranium concentrations in breast milk. The primary route of excretion is through urine which may lower the impact of uranium in the infant’s body^64,86–90. Hence, the study indicates that uranium toxicity has least impact on the exposed mother and their infants.

Conclusion

In the present study, breastmilk samples of 40 lactating mothers however had significant uranium [U²³⁸] contamination but had very least impact in the health of mother and infants. Moreover, 70% of the infants had potential to cause non-carcinogenic health effects. The mean U²³⁸ concentration in breastmilk as lowest was observed in Nalanda district, while highest mean was observed in Khagaria district. However, the highest U²³⁸ concentration was observed in Katihar district. The entire study indicates that U²³⁸ contamination in breastmilk could pose health concerns among the exposed infants and it can lead to low IQ, deteriorated neurological development and many mental health issues. Moreover, the evidence presented supports the statement that “all the samples had the uranium contents”; however, the reported concentrations are below the permissible limits hence, there could be least significant health threat from uranium exposure. It is also recommended to emphasize that breastfeeding is the optimal method for infant nutrition, and its discontinuation should only occur based on clinical indication.

Supplementary Information

Below is the link to the electronic supplementary material.

Author contributions

A.K, A.K.G, D.K, A.B, M.A., AB.S., T.P., A.S., Conceptualized the idea of the study, project administration, data curation, investigation, fund acquisition, manuscript writing and reviewing. field work study, manuscript writing- reviewing, visualization, investigation, data analysis, validation, funding acquisition, project administration. R.A., K.K., G.K., S.K., ME.S., R.K.: Field work, Data curation, methodology, validation, manuscript reviewing. R.L.G., S.D., K.M., N.P., R.P.: Data analysis, methodology, validation, manuscript reviewing. M.S., C.K., Project administration, fund acquisition, resource management, manuscript reviewing.

Funding

The fund for this research work was provided by the grant from Indian Council of Medical Research (ICMR F.No. 5/10/FR/79/2020-RBMCH, Dated. 09/08/2021), Government of India.

Data availability

The datasets evaluated in the present research are not publicly accessible owing to a lack of participant agreement to disclose data outside of the team of investigators, but they are available from the corresponding author upon reasonable request.

Declarations

Competing interests

The authors declare no competing interests.

Ethical approval

The study was conducted in line with the ethical principles outlined in the 2024 through “Declaration of Helsinki” by the World Medical Association⁵⁷, which guides medical research involving human participants. It was also approved by the Institutional Ethics Committee of the Rajendra Memorial Research Institute of Medical Sciences in Patna, Bihar, functioning under the Indian Council of Medical Research, Government of India. Ethical clearance for the study was granted through IEC Letter No. RMRI/EC/24/2020, dated 26th September 2020.

Informed consent

Written informed consent was obtained from all participants after they were informed about the study.