Poisoned waters, threatened lives

Non carcinogenic health effects of groundwater contamination are equally challenging as the carcinogenic risks. While groundwater is an important source for drinking water and irrigation in India, it is increasingly getting contaminated due to urbanisation,  industrialisation and poor farming practices leading to leaching of untreated sewage, industrial effluents, fertilisers and harmful chemicals into the groundwater . Over-exploitation of groundwater has also led to rock weathering, resulting in geogenic contamination.

What do studies on fluoride and nitrate contamination of groundwater reveal? What are the risks and who are vulnerable to the health effects of this contamination?

Nitrate in groundwater

The most common sources from which nitrate can contaminate groundwater include septic tanks, dairy lagoons, wastewater effluents percolation, and livestock waste as well as non-point sources such as fertilisers, pesticides, and manure and can enter the food chain via groundwater and surface water. Nitrates are also released into the groundwater by natural processes through rock-water interactions. In addition, nitrate contamination of groundwater can also occur during nitrogen fixation by legume plants and microbes. 

The Bureau of Indian Standards (BIS) recommends that the maximum permissible limit for nitrogen in drinking water should not be  more than 45 mg/L. High levels of nitrates in the water can lead to blue infant disorder (methemoglobinemia) in infants (under 6 months of age). In adults, it increases cancer risks like stomach tumours and colorectal cancer, Hodgkin's lymphoma as well as non cancer risks such as hypertension and thyroid dysfunction. Evidence shows that over 108.2 million people in India consume water with nitrate levels exceeding the permissible limit of 100 mg/L.

Fluoride in groundwater

Fluoride too can adversely affect human health and can occur naturally in granite terrain, get exposed in cases of over exploitation of groundwater, lead to mineral break down and release of fluoride, which can seep into the groundwater via soil moisture or rainfall infiltration.

Besides this anthropogenic sources including phosphate fertiliser plants, brick manufacturing, steel production, coal combustion, sewerage, are the major causes of high levels of fluoride in groundwater. Fluoride levels of 0.6 -1.5 mg/L in drinking water are considered safe by the World Health Organization (WHO) while fluorosis (dental and skeletal) can be caused by fluoride levels greater than 1.5 mg/L in drinking water. In addition, thyroid, arthritis, osteoporosis, infertility, and abortion have been linked to excessive fluoride intake.

Poisoned waters of the textile city

Coimbatore, often referred to as the textile city of South India, is experiencing a rapid deterioration in groundwater quality due to rapid urbanisation, industrialisation, intensive agricultural and mining activities and leaching of textile effluents and sewage. However, no studies exists on the non-carcinogenic hazards posed by nitrate and fluoride contamination on human health. This study aimed at assessing the spatial distributions of nitrate and fluoride, and evaluate the non-carcinogenic health risk for infants, children, and adults in Coimbatore.

The region is bisected by the Noyyal river, flowing east-west. It is one of the most important tributaries of the Cauvery River. The upper part of the river is used for drinking and agricultural purposes, but is polluted due to untreated direct discharge of municipal sewage and effluents from the industries and textile and leather tanning industries.

The study

Groundwater samples from different sites of the western Noyyal basin in Tamil Nadu were collected. The study found that:

• The nitrate range in the groundwater samples was between 0.12 and 5.21 (average 1.95) for infants, 0.07 and 3.22 (average 1.20) for children and 0.04 and 1.72 (average 0.64) for adults, while fluoride levels varied from 0.47 to 5.62 (average 2.82), 0.29 to 3.47 (average 1.74) and 0.15 to 1.85 (average 0.93) for infants, children and adults, respectively.
• The nitrate concentrations varied from 2 to 89 mg/L and 33.33 percent of the samples were found to be contaminated with nitrate concentrations above the permissible limit of 45 mg/L for drinking water. The fluoride concentration ranged from 0.2 to 2.4 mg/L, with 28.57 percent of the samples exceeding the safe value of 1.5 mg/L for drinking water.

• The overall non-carcinogenic health risk evaluation showed that 97.62 percent, 92.86 percent and 73.81 percent of the samples exceeded the recommended limits for infants, children, and adults, respectively.

• Infants and children were found to be more vulnerable to non carcinogenic health hazards than adults.

The study found that:

• Geogenic processes such as silicate, dolomite, halite and carbonate weathering along with calcite precipitation and ion exchange processes led to alteration of groundwater chemistry.
• High nitrate and fluoride concentrations were found in 54.8 percent and 18.5 percent of the samples.

• Risk assessment indices showed that the nitrate and fluoride toxicity via skin and intake through the mouth was 100 percent, 97.85 percent and 96.77 percent among children, female and male populations respectively.

• The hazard quotient through ingestion pathway was highest among children at 84.95 percent followed by women and men at 68.82 percent and 62.37 percent for nitrate respectively and 83.87 percent for children and 62.37 percent for women and 43.01 percent for men in the case of fluoride. 

• The risk assessment study highlighted very high toxicity and severe health impacts of ingestion of contaminated groundwater on public health and children were found to be more at risk as compared to women and men

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The studies recommend the need for:

• Proper management and treatment of water through reverse osmosis treatment and artificial recharge

• Adequate construction of landfills and septic tanks
• Avoiding excess use of fertilisers and pesticides
• Continuous monitoring and public awareness camps
• Use of techniques like surface water storage, check dams, recharge pits etc to minimise contamination and improve groundwater quality.

Both the papers are open access under the creative commons license (CC BY-NC-ND 4.0)