During the 1950s and 1960s, the U.S. Army conducted atmospheric dispersion tests in many American cities using fluorescent particles of zinc cadmium sulfide (ZnCdS) to develop and verify meteorological models to estimate the dispersal of aerosols. Upon learning of the tests, many citizens and some public health officials in the affected cities raised concerns about the health consequences of the tests. This book assesses the public health effects of the Army’s tests, including the toxicity of ZnCdS, the toxicity of surrogate cadmium compounds, the environmental fate of ZnCdS, the extent of public exposures from the dispersion tests, and the risks of such exposures.