TOXICOLOGICAL PROFILE FOR CHROMIUM - Davidborowski.com

CHROMIUM 2815. POTENTIAL FOR HUMAN EXPOSURE5.1 OVERVIEWTotal chromium has been identified in at least 1,036 and chromium(VI) has been identified in at least120 of the 1,591 hazardous waste sites that have been proposed for inclusion on the EPA NationalPriorities List (NPL) (HazDat 2000). However, the number of sites evaluated for chromium is notknown. The frequency of all these sites can be seen in Figures 5-1 (total chromium) and 5-2(chromium(VI)). Of the total chromium NPL sites, 1,028 are located within the United States, 7 arelocated in the Commonwealth of Puerto Rico, and 1 is located in Guam (not shown). Of thechromium(VI) sites, 120 are located within the United States and none are located in the Commonwealthof Puerto Rico or Guam.Chromium occurs naturally in the Earth's crust. Continental dust is the main source of exposure to naturalchromium present in the environment (Fishbein 1981). As a result of human activities, however,chromium is released into the environment in larger amounts. This is indicated by the value of theenrichment factor (ratio of concentration of the element in air to the aluminum concentration in air overthe ratio of concentration of the element in the Earth's crust to the aluminum concentration in the Earth'scrust) of 3.5–8.1 (Dasch and Wolff 1989; Milford and Davidson 1985). Elements with enrichment factors>1.0 are assumed to have originated from anthropogenic sources (Schroeder et al. 1987). Of theestimated 2,700–2,900 tons of chromium emitted to the atmosphere annually from anthropogenic sourcesin the United States, .35% is in the hexavalent form (EPA 1990b). Electroplating, leather tanning, andtextile industries release large amounts of chromium to surface waters (Fishbein 1981). Disposal ofchromium-containing commercial products and coal ash from electric utilities and other industries are themajor sources of chromium release into the soil (Nriagu and Pacyna 1988). Solid waste and slagproduced during the roasting and leaching processes of chromate manufacturing when disposed ofimproperly in landfill or when used as fill can be potential sources of chromium exposure.Chromium released into the environment from combustion processes and ore processing industries ispresent mainly as chromium(III) oxide (Cr 2 O 3 ). However, chromium(VI) has been detected in fly ashfrom coal-fired power plants (Stern et al. 1984) and from chromate manufacturing and user sites.Chromium is primarily removed from the atmosphere by fallout and precipitation. By analogy withcopper, the residence time of chromium in the atmosphere is expected to be