I put a request at the city to provide a toxicology test for HSFA. They forwarded the request to the health unit. This is what I got back. Plain bullshit. We have received a request from Mr. N. Benkovich, Manager of Water and WasteWater Services of the City of Greater Sudbury, to reply to your request for information on studies that demonstrate that HFSA does not cause harm when ingested. It is important to note that hydrofluorosilicic acid is not ingested in its pure form. In the concentrated form, as it would be in manufacture and use before dilution, this acid deserves care and respect to ensure safe handling. However, when dissolved at very low concentrations in pH-regulated water we are no longer dealing with the concentrated original substance. Haneke and Carson (2001)write: “In water, fluorosilicic acid readily hydrolyzes to hydrofluoric acid and various forms of amorphous and hydrated silica. At the concentration usually used for water fluoridation, 99% hydrolysis occurs and the pH drops to 4.2. As pH increases, hydrolysis increases. At the pH of drinking water, the degree of hydrolysis is ‘essentially 100%’ (Crosby, 1969; Urbansky and Schock, 2000)”, meaning that essentially none of the original compound remains. Put another way, if one were to analyse the water for hydrofluorosilicic acid, it would be below the detection limit, only its ionic constituents would be detectable. It must be emphasized that a fluoride ion is identical to every other fluoride ion, regardless of its source, so its source is not relevant with respect to its toxicological study. Toxicology is used in the regulatory process in the context of a risk assessment framework that typically has four components: 1. hazard identification (qualitatively, can a chemical cause an adverse health effect in humans?), 2. dose-response evaluation (quantitatively, what is the relationship between the dose and the incidence or severity of adverse health effects in the exposed population?), 3. exposure assessment (what is the amount of chemical to which humans are exposed?), and 4. risk characterization (predicting the frequency and severity of effects in the exposed population). Mathematically, risk is a function of the magnitude of a hazard and the probability of its occurrence. Put another way, risk is a function of hazard times exposure. Therefore, given the complete hydrolysis of hydrofluorosilicic acid in pH controlled drinking water, the equation, risk = hazard x exposure, is essentially zero times zero. One has to ask a different question, and that is what is the risk of fluoride ions at the concentration of 0.7 ppm? This question has been answered, allowing us to state that for drinking water fluoridation at 0.7 ppm safety (and effectiveness) has been sufficiently demonstrated, the Health Canada guidelines being one of many high-level reviews of evidence for this conclusion. Sincerely, Manager, Dental Health Program Clinical and Family Services Division
Posted on: Sat, 08 Mar 2014 04:31:14 +0000
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