Fluorine and chlorine, the two elements at the top of Group 17, are both important for keeping us healthy. The elements themselves are highly reactive toxic gases and if inhaled cause severe lung damage. Several chemists were injured, some fatally, in attempts to isolate elemental fluorine, and chlorine gas was put to devastating use in the trenches of World War I. But in their ionic form or added to water, fluorine and chlorine have huge health benefits.
Most toothpastes contain fluoride ions, F– (formed when an atom of fluorine gains one electron), and by brushing the fluoride-containing paste round our teeth we introduce the ions into any small cavities or soft areas that might be forming. The fluoride ions combine with calcium and phosphate ions from our saliva to form hard crystals of fluoroapatite that repair and protect our teeth.
Fluoride is also present in the water we drink and ingesting it in this way also helps keep our teeth healthy. Most water sources naturally contain small amounts of fluoride ions leached from rocks and soil and since the 1960s (before it was added to toothpaste in the 1970s) fluoride has been added to the water supply in some areas of the UK, including the West Midlands and parts of East Anglia.
The water that comes out of our taps is safe to drink because it is treated with chlorine or chlorine-containing compounds, killing bacteria (including those that cause cholera, typhoid and dysentery) and inactivating viruses. Experiments on the chlorination of water for public health began in the late 19th century, with the first permanent chlorination of the water supply in the UK being in Lincoln in 1905 to combat a typhoid outbreak. By the end of the 1900s, Life magazine declared chlorination of the water supply to be “probably the most significant public health advance of the millennium.”
If you are interested in how much fluoride or chlorine there is in your water, and whether it is fluoridated, you should be able to find out from your water board’s website. For instance Anglian Water customers can enter their postcode to find out the specifics.