Requesting Vulcanel´s opinion

on the statement in an email below that states that "theres a big difference between fluorine and fluoride". Would the naturally occuring fluorine present in water coming from a so called "gallery" on a volcanic island, be toxic for human consumption? We´re talking about levels around 4 ppm. that I´ve seen on an analysis of the water. Also what exactly is ppm - parts per ???m
Very grateful for a reply! THANKS. Tweet