Roundup, by itself, is not too awfully toxic, but as it is metabolized an organophosphorus is released, which is even less toxic than the mother chemical Roundup. Fluorine combines with phosphorus quite readily. Organophosphorous compounds are cumulative. This is so whether the chemical industry wants to admit it or not, the cumulative action of organophosphrous compounds is well established by the National Academy of Sciences. Therefore, a person's body begins to be hit by cumulative organophosphate action.
Organophosphates are also bio-cumulative.
That is to say, they cause damage in successive generations. Now, to understand the extreme, and the unobvious obvious, consequences of the dynamic described above. Fluoridated organophosphates are some of the most toxic substances known and can have a delayed effect. Sarin, the war gas in Desert Storm, is a fluoridated organophosphate. So are many of our pesticides used on crops.