A family of industrial chemicals turning up in public water supplies around the country is even more toxic than previously thought, threatening human health at concentrations seven to 10 times lower than once realized, according to a government report released Wednesday. The chemicals are called perfluoroalkyl and polyfluoroalkyl. They were used in such goods as fire-suppressing foam, nonstick pans, fast-food wrappers, and stain-resistant fabric and carpet, but are no longer used in U.S. manufacturing. Water sampling has found contamination in water around military bases, factories and other sites.