A better way to detect fluoride in water

Scientists have developed a portable and user-friendly device that can measure fluoride concentration accurately using only a few drops of water, and help address contamination in drinking water.

Adding fluoride to water has been common practice in a number of countries, including India, the US, Australia, Brazil, Malaysia and Vietnam, said researchers from the Ecole Polytechnique Federale de Lausanne (EPFL) in Switzerland.

In low concentrations - below 1.5 milligrammes per litre (mg/L) - fluoride can help prevent tooth decay and even strengthen bones, according to the study published in the Journal of the American Chemical Society.

However, going above that can have the opposite effect, causing serious dental and bone disease, especially in children and developing foetuses.

To keep things in check, the WHO has set 1.5 mg/L as the maximum limit for fluoride in drinking water.

“To determine whether drinking water is safe, we need to detect fluoride in water at the level of parts per million (ppm),” said Kyriakos Stylianou from EPFL. “Around 1-1.5 ppm is good for teeth, but in many countries the water sources have concentrations above 2 ppm, which can cause serious health issues.”

However, measuring fluoride at such low concentrations with sufficient accuracy is expensive and requires a well-equipped chemical lab.

Because of this, fluoride contamination in water affects a number of developing countries and even parts of developed countries.

Scientists have built a device that can accurately measure fluoride concentrations using only a few drops of water - even with low-level contamination - resulting in a simple change in colour brightness.

The device, named SION-105, is portable, considerably cheaper than current methods, and can be used onsite by virtually anyone.

The key to the device is the design of a novel material that the scientists synthesised. The material belongs to the family of “metal-organic frameworks” (MOFs), compounds made up of a metal ion - or a cluster of metal ions - connected to organic ligands, thus forming one-, two- or three-dimensional structures.

Because of their structural versatility, MOFs can be used in an ever-growing list of applications - separating petrochemicals, detoxing water and getting hydrogen or even gold out of it.

SION-105 is luminescent by default, but darkens when it encounters fluoride ions.

“Add a few droplets of water and by monitoring the colour change of the MOF one can say whether it is safe to drink the water or not,” said Mish Ebrahim, the first author of the research paper. “This can now be done onsite, without any chemical expertise.”

The researchers used the device to determine the fluoride content in different groundwater samples from Vietnam, the UAE and Saudi Arabia. The data corresponded very well when compared to measurements made using ion chromatography, a standard method for measuring fluoride concentration in water.

“This comparison showcases the performance and reliability of SION-105, which, coupled with the portability and ease-of-use of the device, make it a very user-friendly solution for water sampling in remote areas where frequent fluoride concentration monitoring is paramount,” said Stylianou.