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Chromium and Chromium Compounds
Description: Chromium (C.A.S. 7440-47-3) is an odorless, hard, steel-gray, lustrous metal
available in crystals or powder. It has several different forms, the most common
of which are the metal, chromium (0); chromium (III) compounds; and chromium
(VI) compounds. Chromium (III) occurs naturally in the environment; types (0)
and (VI) are produced by industrial processes. Chromium is used as an alloying and plating element on metal and plastic substrates
for corrosion resistance in chromium-containing and stainless steels, and in
protective coatings for automotive and equipment accessories. It is also used
in nuclear and high temperature research. In 1987, consumption of chromium, ferro-alloys, metals, and other chromium-containing
materials by end use was: stainless and heat-resistant steel, 79%; full-alloy
steel, 8%; super-alloys, 3%; and other alloys, 10%. Trivalent chromium compounds (III) include chromic oxide (Cr2O3); chromium
acetate (Cr[CH3COO]3. H2O); chromium nitrate (Cr[NO3]3.9H2O); chromium chloride
(CrCl3); ferrochromite (FeCr2O4); chromium phosphate (CrPO4); chromium sulfate
(Cr2[SO4]3); and sodium chromite (NaCrO2). Hexavalent chromium compounds (VI)
include ammonium dichromate ([NH4]2Cr2O7); barium chromate (Ba.CrH2O4); calcium
chromate (CaCrO4); chromium trioxide (CrO3); lead chromate (PbCrO4); sodium
dichromate (Na2Cr2O7.2H2O); strontium chromate (SrCrO4); potassium chromate
(K2CrO4); potassium dichromate (K2Cr2O7); sodium chromate (Na2CrO4); and zinc
chromate (ZnCrO4). Other compounds include chromium carbonate (Ch2O3.xCr) and
lead chromate oxide (CrO4Pb.OPb). Chromium and its compounds are used in refractories, drilling muds, electroplating
cleaning agents in the metal finishing industry, mordants in the textile industry,
catalytic manufacture, fungicides and wood preservatives, and in the production
of chromic acid and specialty chemicals. They are also used as a constituent
of inorganic pigments, and as a sensitizer in the photographic industry. Chromium
compounds are used as dyes and pigments and in medicinal astringents and antiseptics.
Other uses for chromium and its compounds include organic chemical synthesis,
leather treatment, photomechanical processing, and industrial water treatment,
including treatment of cooling tower water. Chromium trioxide is used for metal plating and treatment, wood treatment and
preservative, and in the manufacture of chromated copper arsentate. Chromium
acetate, sodium chromate and potassium chromate are used in the tanning and
textile industries. Chemical properties: Chromium is insoluble in hot and cold water, nitric acid, and aqua regia, but
is soluble in dilute sulfuric acid and hydrochloric acid. Barium chromate is
insoluble in both cold and hot water but is soluble in mineral acid and acids.
Chromic oxides are soluble in cold water, but insoluble in alcohol; acrid smoke
and irritating fumes are emitted when it is heated to decomposition. Chromium
carbonate is soluble in water containing carbon dioxide, but insoluble in alcohol.
Chromium phosphate is slightly soluble in cold water, soluble in acids and alkalies,
and insoluble in acetic acid. Chromium trioxides are soluble in alcohol, ethanol, sulfuric acid, and nitric
acid; when heated to decomposition, chromium trioxides emit smoke and irritating
fumes. Lead chromate is insoluble in water, acetic acid, and ammonia, but is
soluble in acid and alkalies; when heated to decomposition, emits toxic fumes
of lead. Potassium chromate and potassium dichromate are soluble in cold and
hot water and insoluble in alcohol. Sodium chromed is soluble in cold water
and methanol, and only slightly soluble in alcohol. Sodium dichromate is soluble
in cold and hot water and insoluble in alcohol; toxic fumes of sodium monoxide
are emitted when this compound is heated to decomposition. Strontium chromate
is soluble in cold and hot water, hydrochloric acid, nitric acid, acetic acid,
and ammonium salts. Zinc chromate is insoluble in cold water and acetone, dissolves
in hot water, and is soluble in acid and liquid ammonia. Synonyms for chromium include alpaste RRA 030; alpaste RRA 050; chrome; chromium
element; and chromium fulleride (CRF20). Identification: Health effects: Chromium and certain chromium compounds are classified as substances known
to be carcinogenic, according to the National Toxicology Program's Fifth Annual
Report on Carcinogens. In the national Toxic Release Inventory, EPA classifies
chromium as a "de minimis" carcinogen, meaning that the minimum amount of the
chemical set by OSHA is considered to be carcinogenic. Chromium compounds vary greatly in their toxic and carcinogenic effects. Trivalent
chromium compounds are considerably less toxic than the hexavalent compounds
and are neither irritating nor corrosive. There is inadequate evidence for carcinogenicity
of chromium oxide, and chromium acetate. There is sufficient evidence for carcinogenicity
of barium chromate, calcium chromate, chromium trioxide, lead chromate, sodium
dichromate, and strontium chromate. These compounds have not been evaluated
for their carcinogenicity: chromium carbonate, chromium phosphate, cobalt chromium
alloy, lead chromate oxide, potassium chromate, potassium dichromate, sodium
chromate, and zinc chromate. The major acute effort from ingested chromium is acute renal tubular necrosis.
Exposure to chromium, particularly in the chrome production and chrome pigment
industries, is associated with cancer of the respiratory tract. Hexavalent chromium
compounds are corrosive and cause chronic ulceration and perforation of the
nasal septum. They also cause chronic ulceration of other skin surfaces. The
general populations can be exposed to chromium through the air, water, soils,
and food. Exposure Values: Economics: U.S. manufacturers of chromium are ALFA Products, Danvers, MA; Anderson Physics
Labs, Inc, Urbana, IL; Aran Isles Chemicals Inc, Rockport, MA; Atlantic Equip
Engineers Div of Micron Metals, Inc, Bergenfield, NJ; Atomergic Chemetals Corp,
Farmingdale NY; Belmont Metals Inc, Brooklyn, NY; Cerac, Inc, Milwaukee, WI;
Chemalloy Co, Inc, Bryn Mawr, PA; Elkem Metals Co, Pittsburgh, PA; GFS Chemicals
Inc, Columbus, OH; Metalsmart, Great Neck, NY; Noah Chemical Div, San Antonio,
TX; Reade Metals & Minerals Corp, Rumson, NJ; Sharpe Chemicals Co, Burbank,
CA; United Mineral & Chem Corp, New York NY; Var-Lac-Oid Chem Co, Inc, Bergenfield,
NJ; and Weinstein Chemicals Inc, Costa Mesa, CA. Regulations: EPA regulates chromium and its compounds under the Clean Water Act; Comprehensive
Environmental Response, Compensation, and Liability Act; Resource Conservation
and Recovery Act; Superfund Amendments and Reauthorization Act; and Toxic Substances
Control Act. The Food and Drug Administration regulates the use of chromium
as an indirect food additive, and the use of chromium oxide in drugs and cosmetics.
OSHA has established permissible exposure limits for chromium and chromium compounds. Under Section 313 of the Emergency Planning and Community Right to Know Act
of 1986, releases of more than one pound of chromium into the air, water, and
land must be reported annually and entered into the Toxic Release Inventory
(TRI). National Overview of 1998 Toxics Release Inventory See EPA's Toxic Release Inventory. Notations: The NIOSH recommended exposure limits (RELs) are time-weighted average
(TWA) concentrations for up to a 10-hour workday during a 40-hour workweek.
A short-term exposure limit (STEL) is designated by "ST" preceding
the value; unless noted otherwise, the STEL is a 15-minute TWA exposure that
should not be exceeded at any time during a workday. A ceiling REL is designated
by "C" preceding the value. Any substance that NIOSH considers to be
a potential occupational carcinogen is designated by the notation "Ca." The OSHA permissible exposure limits (PEL) are found in Tables Z-1,
Z-2, and Z-3 of the OSHA General Industry Air Contaminants Standard (29 CFR
1910.1000). Unless noted otherwise, PEL are TWA concentrations
that must not be exceeded during any 8-hour workshift of a 40-hour workweek.
A STEL is designated by "ST" preceding the value and is measured
over a 15-minute period unless noted otherwise. OSHA ceiling concentrations
(designated by "C" preceding the value) must not be exceeded during any
part of the workday; if instantaneous monitoring is not feasible, the ceiling
must be assessed as a 15-minute TWA exposure. In addition, there are a number
of substances from Table Z-2 (e.g., beryllium, ethylene dibromide, etc.) that
have PEL ceiling values that must not be exceeded except for specified excursions.
For example, a "5-minute maximum peak in any 2 hours" means that a 5-minute
exposure above the ceiling value, but never above the maximum peak, is allowed
in any 2 hours during an 8-hour workday. Information Sources:
Originally published in Environment Writer by the National Safety Council. Reprinted with permission. Environment Writer Metcalf Institute for Marine and Environmental Reporting University of Rhode Island Graduate School of Oceanography Office of Marine Programs Narragansett, RI 02882 Tel: 401-874-6211; Fax: 401-874-6485 Disclaimer * Copyright 2002-2006 * All rights reserved. * University of Rhode Island |