Too much fluoride in India's groundwater

Many Indian lakes and rivers are polluted. Drinking from them makes you ill. This is why more and more people in India are pumping ever larger quantities of water from the depths - supposedly clean groundwater. But in many places, this water is also contaminated with fluoride. Too much fluoride is harmful to health and causes growth disorders, tooth damage and bone deformities in those affected. For the most part, fluoride enters the ground through natural weathering and accumulates in the groundwater. The World Health Organization (WHO) considers a concentration of 1.5 milligrams per liter or more to be a critical level. Now Eawag researchers led by geophysicist Joel Podgorski, in collaboration with experts from India, have shown that around 120 million people on the Asian subcontinent live in areas where the groundwater exceeds this limit. The study was published this week in the journal "Environmental Science and Technology". It was co-financed by the Swiss Agency for Development and Cooperation (SDC).

Over 13,000 fluoride measurement data as a starting point

In order to determine the extent of fluoride-contaminated groundwater resources in India, the researchers developed a computer model based on 13,000 existing fluoride measurement data. Employees of the Indian Central Ground Water Board collected this data throughout the country between 2013 and 2015. The model also included information on geology, topography, temperature and rainfall. This resulted in a geostatistical forecasting model that shows where on the Asian subcontinent there is a high risk of flooding. Limit value concentration of fluoride in groundwater is exceeded.

According to the study, there are many areas in the west and south of the country in particular that are suspected of producing fluoride-poisoned water. The researchers combined this result with current population figures and calculated that almost one in ten Indians could be affected by excessive fluoride concentrations. Geophysicist Podgorski emphasizes that the map cannot be used directly to determine safe and unsafe wells, as it does not have a high enough resolution for this. However, the hazard map allows local authorities to carry out targeted analyses in risk areas.

Not only fluoride, but also geologically enriched arsenic is a major problem in Indian groundwater. The researchers would therefore also like to draw up a hazard map for this substance. "Of course, a hazard map alone won't help anyone, but it will provide the authorities with an extremely important basis for targeted investigations and the development of future water strategies," says Podgorski.

Eawag: Water Research Institute of the ETH Domain