The chemical composition of coal, copper (7440508), and nickel (7440020) slags was studied. Proton induced X-ray emission and atomic absorption spectrophotometry were used to analyze the trace element contents of 12 coal slags, 3 copper slags from primary smelters, 2 copper slags from a secondary smelting operation, and 1 nickel slag. The slags contained varying amounts of suspect carcinogens, including beryllium (7440417), chromium (7440473), nickel (7440020), and arsenic (7440382). Concentrations of these elements generally were lowest in the coal slags and highest in slags from secondary copper smelters. Twelve coal slags contained 7 to 48 micrograms per gram (micrograms/g) of beryllium. Chromium was present in four coal slags, ranging in concentration from 110 to 200 micrograms/g. Ten coal slags contained nickel in concentration of 18 to 70 micrograms/g. Arsenic concentrations of 4 to 18 micrograms/g were present in five coal slags. Lead was present only in the coal slag with the highest arsenic content. Trace element concentrations in the primary copper slags varied according to the ore source. Secondary copper slags contained 125 to 180 micrograms/g beryllium, 2100 to 2400 micrograms/g chromium, 2200 to 2440 micrograms/g nickel, and 6600 to 8900 micrograms/g lead. The nickel slag contained 3700 micrograms/g chromium and 1400 micrograms/g nickel. The authors conclude that the coal and other mineral slags analyzed contain carcinogens or suspect carcinogens, as well as other toxic elements, and recommend further study to evaluate the health and safety aspects.