That study talks mainly about China. The study notes that very high fluoride levels can cause neurotoxicity ("brain damage.") I can imagine that in China or other largely third world countries which may not closely regulate waste, etc., that you could get highly toxic doses.
That is not directly relevant to the discussion at hand- whether adding fluoride at very low levels to the water supply (versus in my example, giving fluoride drops, again at low levels) causes "brain damage" is not clearly shown. Dumping toxic doses into the water supply, as from run-off from chemical companies, etc. probably can cause problems.
