India, the world’s largest user of groundwater, consumes 87 per cent of it for irrigation and 11 per cent for domestic use.
However, this vital resource is increasingly polluted, driven by complex interactions between natural processes and human activities, highlights the Annual Ground Water Quality Report released by the Central Ground Water Board (CGWB) on December 31.
According to the report, nearly a fifth of the samples collected exceeded permissible limits for pollutants such as nitrates, with significant quantities of radioactive uranium also present.
“With increasing population pressures, industrial activities, and agricultural practices, maintaining and improving groundwater quality has become more challenging,” the report says. It cites urbanisation and climate change as additional contributing factors.
The report is prepared based on 15,259 groundwater samples collected in May 2023 for a comprehensive groundwater quality assessment.
Among the samples, 19.8 per cent exceeded the permissible limit for nitrate, 9.04 per cent for fluoride and 3.55 per cent for arsenic. A significant portion of the sample was found to exceed the permissible limits for iron (13.20 per cent), chloride (3.07 per cent), electrical conductivity (EC) (7.25 per cent), and uranium (6.60 per cent).
“Arsenic, fluoride, uranium, nitrate pose serious health risks, either through direct toxicity or long-term exposure,” the report says.
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With the increasing extraction of water over time, the water levels continue to drop, exposing us to some of the channels high in uranium concentration.
Alok Srivastava, professor, Panjab University
Nitrate, a major groundwater pollutant
The report identifies nitrate pollution as the “most significant concern”. About 56 per cent of India’s districts have been found to have nitrates beyond the safe limit of 45 mg/L in their groundwater.
This contamination is particularly severe in states like Rajasthan, Karnataka and Tamil Nadu, with more than 40 per cent of water samples exceeding the nitrate permissible limit.
States like Maharashtra, Telangana, Andhra Pradesh, and Madhya Pradesh have also shown notable levels of nitrate contamination, pointing towards a growing concern, the report says. Of the 15 most severely affected districts, nearly half belong to Maharashtra, i.e., seven districts. Telangana, which stands second, has three nitrate-affected districts.
The nitrate contamination is primarily caused by agricultural runoff and overuse of nitrogen-based fertilisers. It also emerged in pre- and post-monsoon analysis of 4,982 groundwater samples that CGWB had done to assess the impact of seasonal recharge on groundwater quality.
The study reveals a slight increase in nitrate contamination levels beyond the permissible limit after the monsoon recharge, i.e., from 30.77 per cent of samples pre-monsoon to 32.66 per cent post-monsoon.
The report highlights the dual effect of rainfall, which dilutes nitrates in some areas but leads to a higher leaching of contaminants from the surface to the groundwater in states with intensive, synthetic fertiliser-dependent agricultural activities.
The report also highlights livestock farming and improper management of animal waste that can contribute to nitrate pollution. The report underlines the risk of high nitrate levels in drinking water, which can cause a potentially fatal condition in infants known as methemoglobinemia, commonly called “blue baby syndrome.”
Uranium contamination, a notable concern
The report terms elevated levels of uranium in several regions as a notable concern. As per the report, 6.60 per cent of the samples have levels of the radioactive element uranium that exceed the safe limit of 30 ppb (parts per billion). Around 42 per cent and 30 per cent of these uranium-contaminated samples are from Rajasthan and Punjab, respectively, where levels exceed even 100 ppb, says the report.
The CGWB report identifies excessive fertiliser use as a potential cause of uranium contamination in Punjab’s groundwater, while it attributes contamination in Tamil Nadu, Karnataka, and Chhattisgarh to geogenic factors.
There are differing views on the issue of uranium contamination. Alok Srivastava, a former chemistry professor at Panjab University, says, “Our study on uranium toxicity in Punjab, particularly in the Malwa region, suggests that this issue could have a geogenic origin. This is based on our findings of uranium-rich fossils and paleosols found in the geochannels of lower Himalayan Shiwalik regions. These fossils and paleosols were likely exposed to the ancient uranium-enriched geogenic channels before being uplifted by tectonic activity, which may still be feeding the current groundwater channels in Malwa.”
Water samples from states such as Haryana, Karnataka, Uttar Pradesh, Madhya Pradesh, Tamil Nadu, Chhattisgarh, Maharashtra, and Bihar were also found to have uranium concentration above the permissible limit in some localised pockets.
While Madhya Pradesh and Karnataka saw a decrease, Uttar Pradesh showed a significant increase in the number of districts with uranium-contaminated groundwater with levels exceeding 30 ppb in 2023 compared to 2019. However, this increase in observations in 2023 is because of more water samples were collected and tested in 2023 (by approximately 700 samples), which likely led to the identification of more contaminated areas, the report clarifies.
Another study mentioned in the CGWB report found a strong correlation between uranium concentration in drinking water and uranium in human bones, suggesting that bones are good indicators of uranium exposure via ingestion of drinking water. Uranium enters human tissues mainly through drinking water, food, air and other occupational and accidental exposures and can lead to cancer and kidney damage.
Fluoride contamination and elevated arsenic levels
The report says that 9.04 per cent of samples had fluoride levels above the limit, while 3.55 per cent had arsenic contamination. This is particularly worrying because long-term exposure to both contaminants can have severe health consequences, including fluorosis (for fluoride) and cancer or skin lesions (for arsenic), the report says.
Arsenic concentration has been reported in West Bengal, Jharkhand, Bihar, Uttar Pradesh, Assam and Manipur, Chandigarh, Punjab and Chhattisgarh.
Adding to the concern is fluoride contamination found in 263 districts in the country. Fluoride contamination refers to a situation when levels exceed the permissible limit of 1.5 mg/L. This fluoride contamination is severely prevalent in several districts of states like Rajasthan (31 mg/L), Haryana (17), Karnataka (19), Telangana (28), Gujarat (25), Punjab (17) and Andhra Pradesh (17).
“The fluoride contamination in India occurs in pockets, particularly in confined aquifers of Rajasthan and in select villages of Uttar Pradesh’s Central Ganga Alluvial region, like Fatehpur, where high levels of fluoride have been detected,” says Venkatesh Dutta, a professor at School of Earth & Environmental Sciences (SEES), Babasaheb Bhimrao Ambedkar University, Lucknow.
Although the monsoon season led to some improvement in fluoride levels in states like Rajasthan, Haryana, Karnataka, Andhra Pradesh and Telangana, the overall contamination levels remain alarmingly high, the report states.
Overexploitation fuels contamination
The CGWB report reveals a correlation between areas with high uranium concentrations in groundwater and regions facing significant groundwater stress.
“This overlap points to the exacerbating effect of overexploitation and deepening water levels on uranium contamination in these regions,” the report says. This implies groundwater is being overexploited beyond what rainfall or other irrigation sources can replenish.
“With the increasing extraction of water over time, the water levels continue to drop, exposing us to some of the channels high in uranium concentration,” says Srivastava.
In an accompanying report, Dynamic Ground Water Resource of India 2024, the CGWB estimates groundwater extraction at 60.4 per cent in 2024, which hasn’t changed much since 2009, when measurements began biennially (and annually since 2022).
“This is hard to believe, with rising population, agricultural intensity, and urban settlements heavily relying on groundwater instead of surface water. There is a rise in construction on recharge areas and encroachment on floodplains. As a result, we are losing the net total recharge areas. It is concerning that paved areas are expanding at the cost of unpaved lands that are crucial for groundwater recharge,” says Dutta.
This story was published with permission from Mongabay.com.