§ Mr. David Mitchellasked the Secretary of State for the Environment what is the chemical formula of the substance put into the water supply in order to bring about fluoridation of drinking water; and what is the chemical formula of the form of fluoride found naturally in ground water in those parts of the United Kingdom where the level of fluoride is such that his Department does not consider it necessary to recommend the addition of fluoride to drinking water.
§ Mr. Denis HowellTo bring the fluoride concentration in water up to the level of 1 part per million—as recommended by my right hon. Friend the Sec-170W retary of State for Social Services—either sodium silicofluoride (Na2SiF6) or fluorosilicic acid (H2SiF6) is usually added as a source of fluoride ions. Naturally occurring fluoride in groundwater and surface water is an equilibrium mixture of fluoride ions—usually associated with sodium ions (NaF) or with calcium ions (CaF2)—and sodium or calcium aluminofluorides (Na3A1F6, Ca3 (A1F6)2) and sodium or calcium ferrofluorides (Na3FeF6, Ca3(FeF6)2).