There are many diseases linked to the quality of the drinking water we consume, and nowadays, many people in the world suffer from various problems due to the difficult access to drinking water, especially those who must resort to groundwater extraction.
In many regions, access to quality drinking water is difficult. Source: pxhere.com.
That is why a group of scientists at the Tufts University School of Engineering has developed a new filtering method to remove fluoride ions from water using polymeric membranes. By using this filtering system, the researchers claim they can avoid water toxicity due to elevated fluoride levels.
We have all heard of some of the benefits of fluoride consumption, especially for tooth care, which is why it is incorporated in small amounts in dental hygiene products, but few of us are aware that there is a very narrow threshold between the beneficial effects of this element and the adverse effects on health. According to the WHO, the optimum concentration of fluoride in water should be below 1 mg/L, the limit value being 1.5 mg/L, since with prolonged exposure above this value there is a risk of developing a disease known as fluorosis, which affects dental health or bone tissue, with its effects on bones being the most relevant.
And although we have intentionally added fluoride in toothpaste and drinking water, in some parts of the world high concentrations of fluoride occur naturally in groundwater, causing serious fluorosis in the population that has this water as its only resource, according to some evidence from the WHO skeletal fluorosis is a disabling disease affecting thousands of people in Africa, India and China.
That is why the ability to reduce the high concentration of fluoride in water in an economical way could protect communities that can only access water through wells in the affected communities, and the use of membranes with high ionic selectivity could provide a sustainable technical solution to the shortage of this resource in these populations, without having to resort to water demineralization or systems that only remove solutes by size difference and not by charge.
And this team of researchers was inspired by biological membranes to create a synthetic membrane capable of differentiating between the ions present in water, just as cell membranes have a high selectivity to allow the passage of certain ions into a cell, even regulating the concentration of ions and molecules inside cells with great precision. In an article published in the journal Proceedings of the National Academy of Sciences, these researchers demonstrated that their membranes could separate fluoride ions among the various ions present in water.
Illustration of the membrane, nanochannels allow the passage of water and certain ions. Source: Image prepared in PowerPoint.
This group of researchers managed to develop a polymer with arrangements of positive and negative charges on a porous support, with which they created a membrane with very narrow channels, less than a nanometer in diameter, and due to the very small size of these pores, the ions present in the water are forced to interact with the molecular groups of the polymer, causing some of the ions to be repelled and others to pass much faster than others. In other words, the chemical composition of the polymer was made to orient the selectivity towards the fluoride ion, and by modifying the polymer composition the selectivity towards other ions could be changed.
Most current filtration systems separate molecules by preventing their size from passing through a given porous medium, i.e., they only limit their passage by the significant size difference, but are unable to retain single-atom ions because of their small size. In contrast, selective membranes such as this one would be able not only to filter large molecules but also to distinguish between ions due to their charge.
Hopefully, such membranes will be tested on a large scale to soon benefit regions whose only access to drinking water is through aquifers containing large amounts of fluoride, which has caused them serious health problems.
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