Chromium (from the Greek word for color, chroma) is a naturally occurring element that may be found in oxidation states of –2 to +6 but primarily exists in the trivalent (Cr3+) and hexavalent (Cr6+) forms. It was first discovered in 1797 in the form of Siberian red lead (crocoite: PbCrO4), and it occurs only in combination with other elements, primarily as halides, oxides, or sulfides (Table 93–1).
TABLE 93–1.Common Forms of Chromium |Favorite Table|Download (.pdf) TABLE 93–1. Common Forms of Chromium
|Name ||Chemical Formula ||Oxidation State ||Uses |
|Barium chromate ||BaCrH2O4 ||6+ ||Safety matches, anticorrosive, paint pigment |
|Calcium chromate ||CaCrO4 ||6+ ||Batteries, metallurgy |
|Chromic acid ||H2CrO4 ||6+ ||Electroplating, oxidizer |
|Chromic chloride ||CrCl3 ||3+ ||Supplement in total parenteral nutrition |
|Chromic fluoride ||CrF3 ||3+ ||Mordant in dye industry, moth- proofing agent for wool |
|Chromic oxide ||Cr2O3 ||3+ ||Metal plating, wood treatment |
|Chromite ore ||FeCr2O4 ||3+ ||Water tower treatment |
|Chromium picolinate ||C18H12CrN3O6 ||3+ ||Nutritional |
|Lead chromate ||PbCrO4 ||6+ ||Yellow pigment for paints and dyes |
|Potassium dichromate ||K2Cr2O7 ||6+ ||Oxidizer of organic compounds, leather tanning, porcelain painting |
Elemental chromium (Cr0) does not occur naturally but is extracted commercially from ore. Chromium is found most abundantly in chromite ore (FeCr2O4).9 Elemental chromium is a blue-white metal that is hard and brittle. It can be polished to a fine, shiny surface, affords significant protection against corrosion, and can be added to steel in order to form stainless steel (an alloy of chromium, nickel, and iron). One of the most important uses of chrome plating is to apply a hard, smooth surface to machine parts such as crankshafts, printing rollers, ball bearings, and cutting tools. This is known as “hard” chrome plating. Elemental chromium is also used in armor plating, safes, and is used in forming brick molds due to its high melting point and limited thermal expansion.
The carcinogenic potential of hexavalent chromium was first recognized as a cause of nasal tumors in Scottish chrome pigment workers in the late 1800s. In the 1930s, the pulmonary carcinogenicity of hexavalent chromium was first described in German chromate workers.13 Chromium toxicity may result from occupational exposure, environmental exposure, or a combination of both routes. Like many metals, the clinical manifestations of chromium toxicity depend upon whether the exposure is acute or chronic and on the chemical form of chromium.
Chromium is an essential element involved in glucose metabolism. This may be through facilitation of insulin binding to insulin receptors or by amplification of the effects ...