A study used to determine "safe" levels of the rocket-fuel chemical perchlorate [3] in drinking water [4] is coming under increasing scrutiny. Perchlorate "can impair thyroid function and result in neurological impairment of fetuses and babies, metabolic disorders and other problems." The study - funded with $310,250 from perchlorate manufacturers and users Lockheed Martin [5], Kerr-McGee, Aerojet and Boeing, and submitted on behalf of the Perchlorate Study Group [6] - was used to support Defense Department [7] arguments for a 200 parts per billion limit. But independent analyses of the study's data by the Environmental Protection Agency [8] and health officials in California, Massachusetts, Connecticut and Maine suggest that perchlorate affects thyroid function at lower levels, especially in "fetuses, infants and people with impaired thyroids." The study, as originally published, did not disclose that three of seven people exposed to "safe" perchlorate levels for two weeks exhibited significant changes in thyroid function.