In what may be the first large-scale study to use volunteers to test the effect of a water pollutant on humans, the aerospace behemoth Lockheed Martin is funding research in which 100 people are paid $1,000 each to take a pill containing the industrial chemical perchlorate every day for six months. The study, conducted by the Loma Linda University Medical Center in California, has its participants ingesting 3 milligrams a day of the chemical found in rocket fuel — 83 times more than the drinking-water limit set by California. At high doses, perchlorate can interfere with production of thyroid hormones; the scientists at the medical center are trying to determine whether lighter doses can also affect thyroid glands, which regulate the growth of young children and the metabolism of adults. The Environmental Working Group is opposing the tests on humans as unethical. No government agency regulates human experiments.