Chromium toxicity results 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. Acute toxicity is more likely to involve multiple-organ failure, whereas chronic exposure is more likely to lead to cancer.
Chromium (from the Greek word for color, chroma) is a naturally occurring element that is found in oxidation states of –2 to +6, but it 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 occurs only in combination with other elements, primarily as halides, oxides, or sulfides (Table 90–1). Elemental chromium (Cr0) does not occur naturally but is extracted commercially from ore. Chromium is found most abundantly in chromite ore (FeCr2O4).7
TABLE 90–1Common Forms of Chromium ||Download (.pdf) TABLE 90–1 Common Forms of Chromium
|Name ||Chemical Formula ||Oxidation State ||Uses |
|Barium chromate ||BaCrO4 ||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, mothproofing for wool |
|Chromic oxide ||Cr2O3 ||3+ ||Metal plating, wood treatment |
|Chromite ore ||FeCr2O4 ||3+ ||Water tower treatment |
|Chromium picolinate ||C18H12CrN3O6 ||3+ ||Nutritional supplement |
|Lead chromate ||PbCrO4 ||6+ ||Yellow pigment for paints and dye |
|Potassium dichromate ||K2Cr2O7 ||6+ ||Oxidizer of organic compounds, leather tanning, porcelain painting |
Elemental chromium is a blue-white metal that is hard and brittle. It is typically polished to a fine, shiny surface, affords significant protection against corrosion, and added to steel 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 because of its high melting point and moderate 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.10
Chromium is an essential element involved in ...