The claim that “fluoride is more toxic than lead and just slightly less toxic than arsenic” is frequently put forth by antifluoridationists as an argument against water fluoridation. This claim is based upon toxicity ratings of industrial commercial products, large quantities to which humans may be exposed at given times. In actuality, when one views such toxicity charts it can be seen that caffeine is also “more toxic than lead and slightly less than arsenic”, and that common table salt is equally as toxic as lead. Attempting to associate the minuscule amount of fluoride in optimally fluoridated water with the toxicity of arsenic and lead is entirely misleading, and yet one more example of the manner in which fluoridation opponents dishonestly utilize out-of-context and/or incomplete information to induce unwarranted fear about this public health initiative.
According to Gosselin, et al., both fluoride and caffeine have a toxicity rating of 4 (Very Toxic). Substances at this classification are toxic to humans at the level of 50-500mg/kg. As 1 kg = 2.2 pounds, a 200 pound individual would weigh 90.7 kg. Therefore, the range of toxicity for a substance at the industrial toxicity level of 4 would be 4,535 mg – 45,350 mg. One would have to ingest over 6,000 liters of optimally fluoridated water in a short period of time to even reach the threshold of toxicity of fluoride. As can plainly be seen, the level of daily fluoride intake is so minuscule that a comparison of such toxicity ratings is entirely irrelevant to optimally fluoridated water.
For this reason, the EPA sets maximum allowable levels of substances in drinking water based on the observed level at which adverse effects are known to occur, not on misleading industrial toxicity ratings.
—Gosselin, et al. (1984) Clinical Toxicology of Commercial Products