Coal combustion releases a number of trace metals to air, cement manufacture also. Table 15.9 lists the trace metals and their sources - generally, the trace metals listed are toxics. From the table, it is noted that metals manufacture is the major source of As, Cd, Cr, Cu, Ni, and Pb. Lead is also significantly contributed by metals extraction and cement manufacture, and has the highest emission amount of the trace metals. These are amines, sulfides, mercaptans, and organics such as aldehydes.
Major sources are food processing, tanneries, composting, and pulp and paper mills.