The safety of low melting point bismuth/lead alloys: a review

Low melting temperature bismuth alloys that contain about 20% to 25% lead and 10% cadmium are widely used in radiotherapy to construct shielding blocks. Since 1980, five papers have addressed questions concerning potential metal toxicity, safe shop practices, measurement of airborne vapors and metal particulates, and the results of biological testing of personnel fabricating secondary field shaping blocks. In February, 1990, the Occupational Safety and Health Administration (OSHA), proposed new occupational air concentration safety standards for cadmium and cadmium compounds. This review presents the potential toxicity of the components metals in low melting temperature bismuth lead alloys, reviews the proposed OSHA air concentrations standards, and describes proper practices of shop safety required to minimize the hazards of these metals and other potentially hazardous materials used in the block fabrication process. The review reveals that if proper practices are followed, fabrication of those blocks, including those containing cadmium, should not produce a shop environment that would produce metal toxicity in employees, and radiotherapy mold room personnel are unlikely to generate air concentrations of cadmium that exceed new proposed standards.