Perchlorate is a chemical in rocket fuel that can leach into the ground and find its way into water supplies, but there is no evidence it is harmful to humans in small amounts. Indeed, the National Academy of Sciences released a report this week suggesting that 20 parts per billion perchlorate in drinking water is safe (and the Department of Defense makes a case for 200 parts per billion) -- but the anti-chemical activists at the Natural Resources Defense Council and Environmental Working Group want the permissible amount reduced to 1 part per billion or less, and the Environmental Protection Agency, which will ultimately determine the regulatory restrictions on perchlorate, is leaning toward adopting NRDC and EWG's recommendation.
As an ACSH report on perchlorate noted, the only documented negative effects on humans from perchlorate came from extremely high doses observed in the early days of its use, which now spans some fifty years. Nonetheless, as ACSH foresaw, activists have extrapolated from the high-dose effects to hypothetical neurological developmental effects on children (and they note the detection of perchlorate in the American Southwest, a region used for aerospace testing and construction). But perchlorate is not an "unknown" even by the usual paranoid standards of the anti-chemical activists. It has been studied extensively over decades. There is no reason to believe that a margin of safety tens or hundreds of times that suggested by science ought to be factored into perchlorate regulations -- especially not given the immense effect this whimsical safety margin will have on expensive clean-up efforts.
Nonetheless, activists including actor/director Rob Reiner have called for further investigation into the safety of the chemical. We'll stand by our take on the issue -- and with the National Academy of Sciences.