Zinc is a dense, bluish-white, relatively soft metal used extensively in the galvanizing of iron and steel. Zinc oxide, the most valued of the variety of compounds formed by zinc is used principally in rubber products as an activator in the vulcanization process and in the treatment of burns, infections, and skin diseases. Zinc occurs naturally in the environment; however, zinc may also enter the environment as the result of mining and processing the production of zinc oxide and the manufacture and use of products containing zinc oxide, the combustion of coal and oil, the production of iron and steel, and the incineration of refuse. Humans are mainly exposed to zinc through the ingestion of food (between 8 and 18.6 mg/kg/day) and drink (averaging up to 10 mg/day). Based on annual average airborne zinc concentrations in areas throughout the United States without mines or smelters of generally < 1mg/cu. m., the contribution of zinc from inhaled air represents an insignificant amount of daily zinc exposure, averaging approximately 20 micrograms. The literature on the toxic effects of zinc is limited. The most widely known systemic effect resulting from acute inhalation of freshly formed zinc oxide fumes is a disease called 'metal fume fever'. Metal fume fever occurs in certain occupational settings and the exposure level at which the fever occurs is not known.