Executive summary -- Introduction -- Perchlorate contamination plagues California's drinking water supplies -- The Colorado River -- Aquifers and wells -- Contamination in food -- Perchlorate threatens developing fetuses and infant children -- Perchlorate impairs the thyroid hormone system -- Impaired thyroid function leads to problems in brain development, learning, and behavior, Learning disabilities are a serious and growing problem in California -- Regulatory action: setting a cleanup standard that will protect children -- Recommendations of one part per billion -- California's publich health goal: six times weaker -- Policyt Recommendations -- Notes.