Evaluates the risks to human health and the environment posed by the mining, processing, and industrial use of barium. The opening sections review both natural and man-made sources of release into the environment, including nuclear fallout following the testing of weapons. A section on environmental behaviour notes the contribution of industrial emissions, especially from the combustion of coal and diesel oil, to the presence of barium in air. Particular concern centres on concentrations found in water, where barium may have a residence time of several hundred years. Water supplies and food are identified as the most important routes of exposure for the general population. Other sections review what is known about the kinetics and metabolism of barium, discuss its capacity to mimic the role of calcium in many physiological processes, and consider effects on organisms in the environment, including effects on the infectivity of several viruses.