Richard writes: <<Some plants are known to aggregate selenium in toxic levels ("locoweed")>> I've never seen locoweed in the produce section of my natural food store. But, there is plenty of kale, with naturally occuring fluorine. <<Certainly there can be too many of a naturally occurring trace element in water that can be dangerous. Too much arsenic may be naturally occurring but toxic, for instance.>> But the question remains is fluorine dangerous? The answer is no, not in normal trace organic mineral amounts. Is fluoride dangerous? You bet. Siobhan