sodium fluoride – noun a colorless, crystalline, water-soluble, poisonous solid, NaF, used chiefly in the fluoridation of water, as an insecticide, and as a rodenticide. Fluorine compounds, or fluorides, are listed by the US Agency for Toxic Substances and Disease Registry (ATSDR) as being in the top 20 of 275 toxic substances which pose the most significant threat to human health.  Here are two good sources: https://articles.mercola.com/sites/articles/archive/2014/07/01/water-supply-fluoridation.aspx http://poisonpaste.com/fluoride-history.php