Chromium

Abstract

This chapter is intended to provide information on hexavalent chromium [Cr(VI)] human exposures and a weight of evidence analysis on the carcinogenicity of Cr(VI). The available scientific information demonstrates the importance of the chemistry of hexavalent chromium species in determining exposures, absorbed doses, and health risks via all routes of exposure. Cr(VI) is the second most stable oxidation state of chromium; however, it rarely occurs naturally. Most Cr(VI) compounds are manufactured as either products or produced as by‐products. General population exposures to Cr(VI) occur via inhalation of ambient air, ingestion of food and water, and nondietary ingestion of dust and dirt. Most human exposures to total Cr are from dietary intake of Cr(III) that is naturally present. Occupational exposures to Cr(VI) occur largely via inhalation and dermal contact and exceed general population exposures. The inhalation and oral toxicology of Cr(VI) have been evaluated by several agencies and groups. Most recently, the U.S. EPA released a draft risk assessment of Cr(VI) in October 2022 and stated that Cr(VI) is likely to be carcinogenic to the human GI tract. In this draft, the Agency derived an oral slope for Cr(VI), which was an update to the Agency's previous assessment, which contained only an inhalation slope factor. We present a summary of production and use, human exposures, chemistry, pharmacokinetics, oral and inhalation toxicology, mode of action research, and a comprehensive reference list. Chromium III [Cr(III)] was not discussed in detail in this chapter as it is essentially nontoxic and there are many review papers.