Found this so far...

Perchlorates block thyroid function and are known to cause thyroid cancer, birth defects and more. The U.S. National Academy of Sciences (NAS) 2005 report summary stated that they are at least ten times more toxic than their Dept. of Defense said was safe. Actual data shows that they are 100 times more toxic. As with so much else, we do not know how synergistic they are with ionizing radiation and fluorides. There has been a sharp increase in thyroid cancers in young people in New Jersey, California, Florida and other states. Perchlorates turned up in organic salad greens grown with Colorado River irrigation water and in dairy samples and breast milk. The NAS report recommends no more than .0007 mg per kilogram of body weight.

from
http://www.iicph.org/docs/water-reg-20060830.htm