Toxic chlorine pollutants were found at unsafe levels in 40 percent of D.C. tap water samples tested this spring during the water utility’s annual chlorine surge, according to a national environmental group’s report to be released today.

The nonprofit Environmental Working Group conducted tests at 18 sites — including private homes, an elementary school, the U.S. Capitol and the Environmental Protection Agency — to measure the levels of chlorine toxins that could cause cancer, reproductive problems and developmental delays in children. In 90 percent of the samples, the tests found another class of chlorine toxin at levels that some epidemiological studies have associated with low birth weight and serious birth defects. […]