TOXICOLOGICAL PROFILE FOR CHROMIUM - Davidborowski.com

CHROMIUM 2112. HEALTH EFFECTSor environmental exposures experienced by humans, they have been useful in identifying the carcinogenicpotential of specific compounds. No significant alterations in the number of malignant tumor-bearing ratsor in the incidence of lung tumors were observed in rats administered soil suspensions containing calciumchromate(VI) via intratracheal instillation (Snyder et al. 1997).NTP (1998) lists certain chromium compounds as substances that are known to be human carcinogens.This classification is based on sufficient evidence for a number of chromium(VI) compounds (calciumchromate, chromium trioxide, lead chromate, strontium chromate, and zinc chromate). IARC (1990)classifies chromium(VI) in Group 1, carcinogenic to humans, based on sufficient evidence in humans forthe carcinogenicity of chromium(VI) compounds as encountered in the chromate production, chromatepigment production, and chromium plating industries; sufficient evidence in experimental animals for thecarcinogenicity of calcium chromate, zinc chromates, strontium chromate, and lead chromates; limitedevidence in experimental animals for the carcinogenicity of chromium trioxide and sodium dichromate;and data that support the concept that chromium(VI) ions generated at critical sites in the target cells areresponsible for the carcinogenic action observed. EPA has classified chromium(VI) as Group A, a knownhuman carcinogen by the inhalation route of exposure. For the oral route, chromium(VI) is classified asGroup D, not classified as to human carcinogenicity (IRIS 2000b).There is inadequate evidence for the carcinogenicity of elemental chromium and trivalent chromiumcompounds in experimental animals (IARC 1990; NTP 1998). IARC (1990) classifies chromium(0) andchromium(III) in Group C, that is, not classifiable as to carcinogenic potential. EPA has classifiedchromium(III) in Group D, not classifiable as to its human carcinogenicity (IRIS 2000a).The genotoxic action of chromium(VI) compounds in cells depends on the reduction of chromium(VI)compounds inside the cell to generate a highly reactive chromium species as well as the formation ofhighly reactive free radical species that forms complexes with DNA. The highly reactive intermediatemay be chromium(V) (Norseth 1986). It is possible that all chromium(VI) compounds have carcinogenicpotential depending upon their bioavailability. However, there are some forms of chromium(III) that areessential nutrients. There are also mechanisms that limit the bioavailability and attenuate the potentialeffects of chromium(VI) compounds in vivo; hence, it may not be practical to consider all chromiumcompounds equally carcinogenic (Petrilli and De Flora 1987).