BIOCHEMICALLY IMPORTANT MINERAL ELEMENTS 



193 



Fluorine. Fluorine has not been proved to be an essential element for 

 either plant or animal life, although it is normally present in many living 

 tissues. The element tends to be accumulated in the bones and teeth of 

 animals in the form of the mineral, fluoroapatite, [Ca3(P04)2]3 * CaF2. 

 Normal bones of animals and human beings contain about 0.02-0.1 per 

 cent of fluorine, but much higher percentages (up to 1 per cent or over) 

 have been found in cases of excessive fluorine intake. Much interest has 

 been aroused in fluorine because of its effect on the skeleton of animals 

 and man and because of its ability to reduce human caries (tooth decay). 



Fluorine is unevenly distributed in the soils of various parts of the 

 world, being found particularly in phosphate rock and in cryolite (a 

 sodium aluminum fluoride). The amount in drinking water is likewise 

 variable, ranging from none to 15 parts per million (ppm.), or more. 

 In those areas where the water supply contains 1 to 2 ppm., or over, many 

 people are afflicted with "mottled" teeth, a condition characterized by 

 soft, chalky areas in the tooth enamel which gradually become discolored 

 and pitted. The threshold level for mottling appears to be near 1 ppm., 

 since this amount of fluorine in the water supply produces mild mottling 

 in about 10 per cent of the growing children. The first teeth are not 

 affected in this condition, but the damage is done to the permanent teeth 

 before eruption. 



Larger fluorine intakes, corresponding to about 5 ppm. or more in the 

 water, lead to thickening and other malformation of the bones — both in 

 animals and in human beings. Severe malformation of the spine has been 

 reported among people living in certain areas in India, where about 5 ppm. 

 of fluorine is naturally present in the water, and has been attributed to 

 abnormally liigh fluorine intake. 



It has been well established that increasing amounts of fluorine (or 

 more exactly, soluble fluorides) in drinking water up to about 2 ppm. 

 result in decreased tooth decay in children, provided they have received 

 such water since infancy. In order to avoid, insofar as possible, any 

 danger of mottling, the amount of fluorine added to the water supplies 

 of communities experimenting with this method of controlling tooth decay 

 is ordinarily such as to raise the level to 1 ppm., but no higher. It is 

 probable that fluorine acts to reduce caries by inhibition of bacterial 

 enzymes, possibly by combining with and rendering unavailable such 

 metals as zinc, cobalt, manganese, copper, calcium, and others, which 

 activate various enzymes. The fact that fluoroapatite is considerably 

 harder than normal calcium phosphate may also be a factor in the reduc- 

 tion of tooth decay by fluorine. 



Boron, Molybdenum, and Silicon. The essential nature of boron for 

 plant growth was discovered in rather recent times. It was first shown to 

 be needed by corn in 1915, broad beans in 1923, tomatoes and potatoes 



