The Earth Report   ed. E Goldsmith, N Hildyard.  London: 
Mitchell Beazley 1988  p. 149

Fluoridation    Technique of adding fluorides to public water 
supplies, with the intention of reducing tooth decay.
	Fluoridation transformed a liability of the aluminium 
industry (bulk sodium fluoride) into a commercial product.  Some 
fluoridation is done with fluosilicic acid, a waste from manufacture 
of superphosphate fertiliser.
	Tooth decay turns out to have declined by about two-thirds 
since the 1950s in the wealthy countries that gather dental 
statistics.  This welcome trend is not understood; possible causes 
may include improved diet and brushing, widespread antibiotics 
secreted in saliva, and, recently, fluoride in toothpaste, a 
concentrated direct application that may well be effective.  But 
thorough surveys have corrected the earlier claim that natural 
fluoride in water is correlated with relative freedom from tooth 
decay.  Trials claimed to demonstrate benefit from fluoridation have 
been severely criticized for lack of controls, and other major 
defects.
	In some still-controversial studies, fluoridation has, on the 
other hand, been rather closely correlated with cancer.  Various 
other types of harm have been suspected; the one established beyond 
dispute is dental fluorosis  -  bilaterally symmetrical diffuse white 
mottling of the teeth, a form of damage commonly observed among 
children drinking water fluoridated to 1 ppm.  The margin, if any, is 
uncomfortably slim between 1 ppm and levels known to cause serious 
damage to bones (skeletal fluorosis).  In addition, there is the 
possibility of adverse synergistic reactions between the fluoride 
added to water and the thousands of other chemicals to which modern 
industrial systems expose us.

	[as the original author I've taken the opportunity to correct 
a few editing errors  -  RM]