In more than 60 years if study, no research has shown perchlorate causes adverse health effects. Theorectically, a sequence of three events would be required for perchlorate to have a potential adverse effect on health, each requiring higher doses.
First, perchlorate exposure must be high enough to prevent the thyroid from getting its usual amount of iodide. This may begin to happen at around 245 ppb of perchlorate in drinking water. Second, exposure must be high enough to overwhelm the body’s normal adaptive process, thereby lowering the amount of thyroid hormones in the body (scientific research indicates this does not occur at levels below 14,000 ppb). Third, exposre must be sustained long enough to reduce thyroid hormone levels for a long period of time. An adverse health effect would require daily consumption of more than 14,000 ppb in drinking water. To put this in perspective, more than 98% of perchlorate detections in U.S. water systems are below 10 ppb1– that’s 24 times lower than the recognized no effect level.
To put this all in perspective, at 10 ppb, a human would have to drink almost 740 gallons of water a day before a health risk could be possible.
1U.S. EPA unregulated contaminant monitring rule testing, 2001 (UCMR 1)