Just because you can find two parts per quadrillion of dimethyl chickenwire in something doesn't make it mean anything.
This is a hilarious kick in the pants for Boxer! :-)
Around here the perchlorate is found in water samples from wells adjacent to a onetime munitions manufacturer.
Halifax Explosives and later, Bermite Powder, both manufactured munitions, dynamite, and just about everything else that goes flash and bang. In those days residue was just dumped in a hole out yonder and all that stuff has just percolated through the soil until it reached the water table.
There are other areas however, where perchlorate contamination is widespread and unattributed to any particular source.
We do know that perchlorate turns up in breast milk and we know that it can cause irreversible problems. What we don't know is how much will it take to cause those problems in the unborn babies that the lovely young ladies in the neighborhood are carrying.
I suppose it's kind of like the problem of arsenic contamination in wells. I may decide it's not worth the hassle to deal with the arsenic in my well but I should at least have the knowledge of it's presence in my area and if I sell, the prospective buyer should know.