2023-02-03

Chromium is a chemical element with the symbol Cr and atomic number 24. It is a steely-grey, lustrous, hard and brittle metal, which takes a high polish, resists tarnishing, and has a high melting point. [1] Chromium is a naturally occurring element found in rocks, animals, plants, and soil. It can exist in several different forms. Depending on the form it takes, it can be a liquid, solid, or gas. The most common forms are chromium(0), chromium(III), and chromium(VI). No taste or odour is associated with chromium compounds. [2]

Uses [2,3]

The metal chromium, which is the chromium(0) form, is used for making steel. Chromium(VI) and chromium(III) are used for chrome plating, dyes and pigments, leather tanning, wood preserving and water treatment.

In the Environment [4]

Chromium is released into the atmosphere via industrial, commercial, and residential fuel combustion of natural gas, oil, and coal and from emissions from metal industries such as chrome plating and steel production.

Approximately 1/3 of atmospheric releases are believed to be in the form of chromium(VI).

Electroplating, leather tanning, and textile industries release large amounts of chromium to surface water.

Chromium is primarily removed from the atmosphere by fallout and precipitation, the residence time is expected to be <10 days.

Most of the chromium released in water will be deposited in the sediments.

Chromium is not believed to biomagnify in the food chain.

Sources & Routes of Exposure

Sources of Emission [3]

Industry sources: Emissions to air and water from chemical manufacturing industry e.g. dyes for paints, rubber and plastic products, metal finishing industry e.g. chrome plating, manufacturers of pharmaceuticals, wood, stone, clay and glass products, electrical and aircraft manufacturers, steam and air conditioning supply services, cement producing plants as cement contains chromium, incineration of council refuse and sewage sludge and combustion of oil and coal.
Diffuse sources: Facilities below the reporting threshold.
Natural sources: Chromium (VI) compounds are not found in nature. Chromium is usually found as the Cr(III) form, as the mineral Chromite and in many soils.
Transport sources: Emission to air from the wearing down of brake linings containing chromium. Motor vehicle exhaust (crude oil contains traces of chromium (III) compounds, these may oxidise to the chromium (VI) state during fuel combustion in vehicle engines).
Consumer products: Some inks, paints and paper. Some rubber and composite floor coverings. Some treated (preserved) timber products. Some toner powders used in copying machines.

Routes of Exposure [2,4]

Exposure to chromium may occur by eating food containing chromium(III).
Breathing contaminated workplace air or skin contact during use in the workplace.
Drinking contaminated well water.
Living near uncontrolled hazardous waste sites containing chromium or industries that use chromium.

The major routes of exposure are as follows:

Inhalation – Predominant route of exposure for occupational populations.
Oral – Predominant route of exposure for the general population.
Dermal – Minor route of exposure for the general population.

Health Effects [5]

Acute Effects

Chromium VI

Chromium (VI) is much more toxic than chromium (III), for both acute and chronic exposures. The respiratory tract is the major target organ for chromium (VI) following inhalation exposure in humans. Shortness of breath, coughing, and wheezing were reported in cases where an individual inhaled very high concentrations of chromium trioxide.

Other effects noted from acute inhalation exposure to very high concentrations of chromium (VI) include gastrointestinal and neurological effects, while dermal exposure causes skin burns in humans.

Ingestion of high amounts of chromium (VI) causes gastrointestinal effects in humans and animals, including abdominal pain, vomiting, and haemorrhage.

Acute animal tests have shown chromium (VI) to have extreme toxicity from inhalation and oral exposure.

Chromium III

Chromium (III) is an essential element in humans, with a daily intake of 50 to 200 µg/d recommended for adults.

Acute animal tests have shown chromium (III) to have moderate toxicity from oral exposure.

Chronic Effects

Chromium VI

Chronic inhalation exposure to chromium (VI) in humans results in effects on the respiratory tract, with perforations and ulcerations of the septum, bronchitis, decreased pulmonary function, pneumonia, asthma, and nasal itching and soreness reported.

Chronic human exposure to high levels of chromium (VI) by inhalation or oral exposure may produce effects on the liver, kidney, gastrointestinal and immune systems, and possibly the blood.

Rat studies have shown that, following inhalation exposure, the lung and kidney have the highest tissue levels of chromium.

Dermal exposure to chromium (VI) may cause contact dermatitis, sensitivity, and ulceration of the skin.

The Reference Concentration (RfC) for chromium (VI) (particulates) is 0.0001 mg/m3 based on respiratory effects in rats.

The Reference Concentration (RfC) for chromium (VI) (chromic acid mists and dissolved Cr (VI) aerosols) is 0.000008 mg/m3 based on respiratory effects in humans.

The Reference Dose (RfD) for chromium (VI) is 0.003 mg/kg/d based on the exposure at which no effects were noted in rats exposed to chromium in the drinking water.

Chromium III

Although data from animal studies have identified the respiratory tract as the major target organ for chronic chromium exposure, these data do not demonstrate that the effects observed following inhalation of chromium (VI) particulates are relevant to inhalation of chromium (III).

EPA has not established an RfC for chromium (III).

The RfD for chromium (III) is 1.5 mg/kg/d based on the exposure level at which no effects were observed in rats exposed to chromium (III) in the diet.

Reproductive/Developmental Effects

Chromium VI

Limited information on the reproductive effects of chromium (VI) in humans exposed by inhalation suggest that exposure to chromium (VI) may result in complications during pregnancy and childbirth.

Animal studies have not reported reproductive or developmental effects from inhalation exposure to chromium (VI).

Oral studies have reported severe developmental effects in mice such as gross abnormalities and reproductive effects including decreased litter size, reduced sperm count, and degeneration of the outer cellular layer of the seminiferous tubules.

Chromium III

No information is available on the reproductive or developmental effects of chromium (III) in humans.

A study of mice fed high levels of chromium (III) in their drinking water has suggested a potential for reproductive effects, although various study characteristics preclude a definitive finding.

No developmental effects were reported in the offspring of rats fed chromium (III) during their developmental period.

Cancer Risk

Chromium VI

Epidemiological studies of workers have clearly established that inhaled chromium is a human carcinogen, resulting in an increased risk of lung cancer. Although chromium-exposed workers were exposed to both chromium (III) and chromium (VI) compounds, only chromium (VI) has been found to be carcinogenic in animal studies, so EPA has concluded that only chromium (VI) should be classified as a human carcinogen.

Animal studies have shown chromium (VI) to cause lung tumours via inhalation exposure.

EPA has classified chromium (VI) as a Group A, known human carcinogen by the inhalation route of exposure.

EPA used a mathematical model, based on data from an occupational study of chromate production workers, to estimate the probability of a person developing cancer from continuously breathing air containing a specified concentration of chromium. EPA calculated an inhalation unit risk estimate of 1.2 × 10-2 (µg/m3)-1.

Chromium III

No data are available on the carcinogenic potential of chromium (III) compounds alone.

EPA has classified chromium (III) as a Group D, not classifiable as to carcinogenicity in humans.

EPA has stated that “the classification of chromium (VI) as a known human carcinogen raises a concern for the carcinogenic potential of chromium (III)”.

Safety [6]

First Aid Measures

Eye Contact: Check for and remove any contact lenses. In case of contact, immediately flush eyes with plenty of water for at least 15 minutes. Get medical attention.
Skin Contact: In case of contact, immediately flush skin with plenty of water. Cover the irritated skin with an emollient. Remove contaminated clothing and shoes. Wash clothing before reuse. Thoroughly clean shoes before reuse. Get medical attention.
Serious Skin Contact: Wash with a disinfectant soap and cover the contaminated skin with an anti-bacterial cream. Seek medical attention.
Inhalation: If inhaled, remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. Get medical attention.
Ingestion: Do NOT induce vomiting unless directed to do so by medical personnel. Never give anything by mouth to an unconscious person. Loosen tight clothing such as a collar, tie, belt or waistband. Get medical attention if symptoms appear.

Fire & Explosion Information

Chromium is a moderate fire hazard when it is in the form of a dust (powder) and burns rapidly when heated in flame. Chromium is attacked vigorously by fused potassium chlorate producing vivid incandescence. Pyrophoric chromium unites with nitric oxide with incandescence. Incandescent reactions occur with nitrogen oxide or sulfur dioxide.

Powdered Chromium metal +fused ammonium nitrate may react violently or explosively. Powdered Chromium will explode spontaneously in air.

Exposure Controls & Personal Protection

Engineering Controls

Use process enclosures, local exhaust ventilation, or other engineering controls to keep airborne levels below recommended exposure limits.
If user operations generate dust, fume or mist, use ventilation to keep exposure to airborne contaminants below the exposure limit.

Personal Protective Equipment

The following personal protective equipment is recommended when handling chromium:

Splash goggles;
Lab coat;
Dust respirator (be sure to use an approved/certified respirator or equivalent);
Gloves.

Personal protective equipment in case of a large spill:

Splash goggles;
Full suit;
Dust respirator;
Boots;
Gloves;
A self contained breathing apparatus should be used to avoid inhalation of the product.
Suggested protective clothing might not be sufficient; consult a specialist BEFORE handling this product.

Regulations [3,7,8]

United States

<b> Regulations and Guidelines for Chromium</b>
<b>Agency</b>	<b>Focus</b>	<b>Level</b>	<b>Comments</b>
American Conference of Governmental Industrial Hygienists	Air: workplace	10 ug/m3 as Cr	Advisory; TWA* to avoid carcinogenic risk from insoluble Cr(VI) compounds
		50 ug/m3 as Cr	TWA for water-soluble Cr(VI) compounds
		500 ug/m3 as Cr	TWA for chromium metal and Cr(III) compounds
National Institute for Occupational Safety and Health	Air: workplace	1 ug/m3 as Cr	Advisory; TWA (10-hour) for chromic acid and all Cr(VI)compounds
National Institute for Occupational Safety and Health	Air: workplace	500 ug/m3 as Cr	Advisory; TWA (10-hour) for chromium metal and Cr(II) and Cr(III) compounds
Occupational Safety and Health Administration	Air: workplace	5 ug/m3 as CrO₃/m3	Regulation; PEL** for chromic acid and chromates, (8-hour TWA)
		500 ug/m3 as Cr	PEL for Cr(II) and Cr(III) compounds (8-hour TWA)
		1,000 ug/m3 as Cr	PEL for chromium metal and insoluble compounds (8-hour TWA)
Environmental Protection Agency	Air: environment	Not available	Chromium is listed as a hazardous pollutant
Environmental Protection Agency	Drinking water	100 ug/L	Regulation; current MCL^ for total chromium
TWA (time-weighted average): TWA concentration for a normalworkday and a 40-hour workweek to which nearly all workers may be repeatedlyexposed. *PEL (permissible exposure limit): highest level of chromiumin air, to which a worker may be exposed, averaged over an 8-hour workday. ^MCL (maximum contaminant level) enforceable level fordrinking water.

Australia

Safe Work Australia has established the following exposure limits for Chromium:

<b>Chemical Name</b>	<b>CAS No.</b>	<b>TWA (ppm)</b>	<b>TWA (mg/m³)</b>	<b>Advisory Carcinogen Category</b>	<b>Other Advisory Information</b>
Chromium (II) Compounds (as Cr^–)			0.5
Chromium (III) Compounds (as Cr)			0.5
Chromium (metal)	7440-47-3		0.5
Chromium (VI) Compounds (as Cr), certain water insoluble			0.05	Carc. 1A	Sens
Chromium (VI) Compounds (as Cr), certain water soluble			0.05		Sens

Australian Drinking Water Quality Guidelines (NHMRC and ARMCANZ, 1996) specify a limit of 0.05 mg/L (i.e. 0.00005 g/L).

References

http://en.wikipedia.org/wiki/Chromium

http://www.atsdr.cdc.gov/toxfaqs/tf.asp?id=61&tid=17

http://www.npi.gov.au/resource/chromium-vi-compounds

http://www.atsdr.cdc.gov/toxguides/toxguide-7.pdf

http://www.epa.gov/ttn/atw/hlthef/chromium.html

http://www.sciencelab.com/msds.php?msdsId=9927136

http://www.atsdr.cdc.gov/csem/csem.asp?csem=10&po=8

http://www.safeworkaustralia.gov.au/sites/SWA/about/Publications/Documents/772/Workplace-exposure-standards-airborne-contaminants.pdf