Uranium and fluoride enriched saline groundwater around Punjab

Scarcity of fresh surface water increases dependency on groundwater for agriculture and domestic consumption which itself is unsafe in many instances by excess salinity, fertilizer inputs and heavy metals. The present study examined groundwater geochemistry up to 460 ft depth around a semi-arid region of Punjab, India where fluorosis, cancer and poor crop yield are serious concerns. Groundwater from bore wells and tube wells demonstrate neutral to slight alkaline (pH 7.1–8.4) Na–HCO₃ and Na–Cl water types with excess salinity (up to 9500 mg L⁻¹). Sodium and HCO₃⁻constitute the predominant ions in the order Na⁺>Mg²⁺≈Ca²⁺>K⁺>Si⁴⁺>Fe(T)>Al³⁺ and HCO₃⁻ > Cl⁻ > SO₄²⁻ > NO₃⁻ ≈ CO₃²⁻ > PO₄³⁻ > F⁻, whereas trace metal contents are insignificant except U that contaminates >83% groundwater (up to 283 μg L⁻¹). Both dental and skeletal fluorosis is common in the region. Groundwater up to 250 ft depth contains relatively greater cations, anions, salinity, and trace metals, in general, implying both geogenic and anthropogenic contributions. The southern part of the district is severely contaminated, especially with U (up to ∼283 μg L⁻¹) and salinity (up to 9500 mg L⁻¹) witnessing surface salt deposits widely. The sodium absorption ratio (0.4–36.7), residual sodium carbonate (-49-97) and %Na (17–94) data represents most of the shallow and intermediate depth groundwater is unsafe for irrigation purposes with an evaporite and silicate weathering dominance control where cation exchange process predominates over reverse ion exchange at all depths. Poor productivity, excess salinity, agricultural inputs of NO₃⁻, PO₄³⁻, F⁻ and U along alluvial plane groundwater of dry arid climatic terrains is a global implication from this research.

 

Contaminated groundwater is becoming an emerging threat globally for drinking and irrigation use because of its chronic effect on public health, crop growth and productivity, soil fertility and ultimately the global economy. Inadequate fresh surface water availability increases societal dependency on groundwater exponentially overseas. Because ∼80% of the diseases and deaths in the developing countries are related to water contamination (UNESCO, 2007) caused by climate change, rapid urbanization and industrialization, intensive irrigation, overexploitation, aquifer material and groundwater interactions, inputs from surface contamination etc. (Senthilkumar and Elango, 2013; Shrestha et al., 2016; Lapworth et al., 2017; Malki et al., 2017), knowledge on groundwater geochemistry is rapidly being prioritized.

Punjab is known as the agricultural hub of India and agricultural role model of the country with extensive cultivation practices for rice, wheat, sugarcane, sarson, maize etc. where >80% population are dependent on agricultural occupation and >73% of the total cultivated land is irrigated by groundwater resources (Chopra and Krishan, 2014a). About 40–50% decline of annual rainfall in Punjab during last few decades (PHRED, 2014) caused sharp increase in dependency on groundwater resources that consequently lowered the regional water table. On the other hand, waterlogging and salinity is also a matter of concern around SW Punjab because of poor drainage patterns, flat topography, and minimal groundwater use due to canal irrigation systems (Karma and Keledhonker, 2007; Singh, 2013; Chopra and Krishan, 2014b). This is further amplified by general SW groundwater flow direction in Punjab with hydraulic gradient of 0.32 m km⁻¹ and hydraulic conductivity 5–12 m day⁻¹ (Singh et al., 2018). Increase of water table up to 0.7 m in Fazilka and Muktsar district between 2000 and 2019 has been reported by Prasad et al. (2019) with a normal rise of 0.5–1.0 m y⁻¹ for last several years along SW Punjab (Joshi and Tyagi, 1991). About 6.3 lakh hectares out of 17.2 lakh hectares has a rising waterlogging issue of which Fazilka district is the most affected (Pandey, 2014; CGWB, 2017) and this ultimately caused change in cropping pattern from cotton/bajra/maize-wheat/gram rotation to paddy-wheat crop rotation and abandonment of cotton farms (Singh, 2013). Extreme shallow water table (e.g., ∼2 m bgl) is reported from Muktsar (Singh et al., 2018), Mansa and Bathinda (Sharma et al., 2017a) district and are unfit for irrigation in most part of SW Punjab due to high salinity caused by greater evaporation and poor precipitation as typical of semi-arid climatic terrains (Pandey, 2014; Sharma et al., 2017b).

Threats of alarming NO₃, F, U, Se, As and salinity is widely documented since last few years from SW Punjab (Singh et al., 1995; Singh, 2014; Saini and Bajwa, 2016; Sharma et al., 2017a, 2017b). Around the alluvial plain of Sutlej River sub-basin, elevated groundwater U up to 645, 324, and 376 μg L⁻¹ from neighboring Mansa, Bathinda and Faridkot district, respectively (Saini and Bajwa, 2016) with frequent incidences of nephrotoxicity, genotoxicity and cancer in SW Punjab is documented (Singh et al., 2013; Singh, 2014). Similar alluvial plain F⁻ enrichments are globally reported in recent studies (Anshumali, 2015; Sharma et al., 2016; Haji et al., 2018; Aravinthasamy et al., 2020; Gao et al., 2020). Although fine grained aquifer soils often host high U (e.g., Ulrich et al., 2019), elevated U contents have been found from plutonic bedrocks worldwide (Reimann et al., 2005; Babu et al., 2008; Shin et al., 2016; Navarro et al., 2016; Post et al., 2017). Besides geogenic origin, U containing phosphate fertilizers have been recognized as a major contributor of groundwater U along alluvial deposits where alkaline conditions with high HCO₃⁻ content promote its release (Wu et al., 2010; Nolan and Weber, 2015). Considering intensive agriculture in this district, fertilizer seems to play an important role on U behavior across the investigated depths. Favorable mobilization under oxic alkaline conditions and binding of reduced form of U to organic matter in anaerobic environment usually controls U mobilization around alluvial plains (Wu et al., 2014; Seder-Colomina et al., 2018).

Although endemic fluorosis is a long standing issue in Punjab (Jolly et al., 1969), frequent incidences of dental and skeletal fluorosis from SW Punjab has been documented in recent studies even up to 11.3 mg L⁻¹ F⁻ from Sangrur district (Krishan et al., 2014, 2015; Sharma et al., 2016). Sharma et al. (2017b) observed that ∼72% groundwater of neighboring Bathinda district is fluoride contaminated and the intermediate aquifers (60–150 ft) is more contaminated compared to shallow and deep aquifers (Krishan et al., 2014, 2015, 2017). Fluorite and fluorapatite in alluvial soils are believed to be major sources of F⁻ to groundwater from other parts of India in addition to fertilizers input (e.g., Rao et al., 2017; Raj and Shaji, 2017). Long residence time of groundwater in continuous interaction with alluvial soils under alkaline pH conditions with high Na⁺ and HCO₃⁻ was proposed to trigger F⁻ mobilization from aquifers (Xiao et al., 2015; Rao et al., 2017; Li et al., 2020). Ion exchange process between Na⁺ and Ca²⁺ around saline aquifer systems initiates dissolution of CaF₂ ultimately adding F⁻ to groundwater with parallel precipitation of CaCO₃ (Rao et al., 2017; Li et al., 2020). Semi-arid climate with high evaporation and poor precipitation along agricultural dominant terrains, exactly the present study region, are more favorable for F⁻ releases (e.g., Machender et al., 2014) that warrant to be examined.

A detailed geochemical study in respect of groundwater quality at different depths, pollutant behaviour and processes governing their mobilization and spatial variability are yet to be understood from Fazilka district. Because of SW flow direction (Sharma et al., 2017b), Fazilka district is most prone to all pollutant richness as found for F⁻ in Kolar Region, Karnataka (Babu et al., 2008) compared to other parts of Punjab which demands an intensive investigation. Although radioactive elemental concentrations in surface and groundwater resources are normally low to be a threat to public health, recent reports of high U from alluvial plains is an alarming concern overseas, particularly along Malwa region of SW Punjab that witness many deaths in last three decades due to incidences of cancer. The only research work so far in Fazilka district suggests that most of the groundwater have dissolved solids >1000 mg L⁻¹ and the water table has risen ∼70 cm in year 2019 (Prasad et al., 2019), but lacks knowledge on contaminant behaviour and groundwater quality. Hence, this study was aimed to examine the geochemistry of groundwater at all depths in use to understand the origin and possible mechanisms governing poor groundwater quality as often reported.

Study area geology and hydrology

This extreme SW district of Punjab, India was part of Firozpur district before July 2011. The Fazilka district shares political boundary with Ferozpur, Faridkot and Muktsar district, Punjab along north and east side, Rajasthan along south and Pakistan along west. The SW Punjab experiences a semi-arid climatic condition with average annual temperature of 24.6 °C. With the extreme temperature variations annually, the district suffers from low rainfall of ∼200–400 mm y-¹ mainly during SW monsoon

Field parameters

Maximum depth groundwater sample obtained was 460 ft below ground level (bgl) and minimum was 22 ft. No deeper tube wells beyond 120 ft were found south of Fazilka city (sample no. 23–36, Table 1) where water logging is a serious concern during monsoon season because of overall SW hydraulic gradient of the state (Joshi and Tyagi, 1991). With a general flat topography of the district, sampled tube well/hand pump depths did not show significant correlations with the respective elevations

Conclusions

The present research findings provide knowledge on geochemical variations of groundwater across different depths and in spatial scale of a poorly explored semi-arid terrain of SW Punjab, India. Overall Na–HCO₃ and Na–Cl water type of moderately hard to very hard nature with exceptionally high salinity, conductivity, and dissolved solids characterize the groundwater. The extent of such concerns worsens southward of the district where surface salt deposits resulting no cultivation are common. The

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

The authors acknowledge CSIR, India and UGC, India for financial support. Ms. Navjot Kaur, Mr. Tanuj Mahajan and Mr. Kuldip helped for field work and sample analysis. Authors are thankful to Department of Geology, Panjab University for providing infrastructural support and Department of Earth Sciences, IIT Kanpur, India for trace metal analysis. Valuable feedbacks of reviewers and editor are greatly acknowledged.

 

Courtesy: https://www.sciencedirect.com/science/article/abs/pii/S0883292721002985

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