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Hexavalent chromium

Hexavalent chromium

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Hexavalent chromium (chromium VI) refers to chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

s that contain the element chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...

 in the +6 oxidation state
Oxidation state
In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...

. Virtually all chromium ore is processed via hexavalent chromium, specifically the salt sodium dichromate
Sodium dichromate
Sodium dichromate is the chemical compound with the formula Na2Cr2O7. Usually, however, the salt is handled as its dihydrate Na2Cr2O7·2H2O. Virtually all chromium ore is processed via conversion to sodium dichromate. In this way, many millions of kilograms of sodium dichromate are produced...

. Approximately 136000000 kilograms (299,828,676.6 lb) of hexavalent chromium were produced in 1985. Other hexavalent chromium compounds are chromium trioxide
Chromium trioxide
Chromium trioxide is the inorganic compound with the formula CrO3. It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name.This compound is a dark-red/orange brown solid, which dissolves in water concomitant with hydrolysis...

 and various salts of chromate and dichromate. Hexavalent chromium is used for the production of stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....

, textile dyes, wood preservation, leather tanning
Tanning is the making of leather from the skins of animals which does not easily decompose. Traditionally, tanning used tannin, an acidic chemical compound from which the tanning process draws its name . Coloring may occur during tanning...

, and as anti-corrosion and conversion coating
Conversion coating
Conversion coatings are coatings for metals where the part surface is converted into the coating with a chemical or electro-chemical process. Examples include chromate conversion coatings, phosphate conversion coatings, bluing, black oxide coatings on steel, and anodizing. They are used for...

s as well as a variety of niche uses. Chromium hexavalent (CrVI) compounds, often called hexavalent chromium, exist in several forms. Industrial uses of hexavalent chromium compounds include chromate pigments in dyes, paints, inks, and plastics; chromates added as anticorrosive agents to paints, primers, and other surface coatings; and chromic acid electroplated onto metal parts to provide a decorative or protective coating. Hexavalent chromium can also be formed when performing "hot work" such as welding on stainless steel or melting chromium metal. In these situations the chromium is not originally hexavalent, but the high temperatures involved in the process result in oxidation that converts the chromium to a hexavalent state.(29 CFR OSHA General Industry 1910)

Hexavalent chromium is recognized as a human carcinogen
A carcinogen is any substance, radionuclide, or radiation that is an agent directly involved in causing cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes...

 via inhalation. Workers in many different occupations are exposed to hexavalent chromium. Problematic exposure is known to occur among workers who handle chromate-containing products as well as those who perform welding, grinding, or brazing on stainless steel. Within the European Union
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...

, the use of hexavalent chromium in electronic equipment is largely prohibited by the Restriction of Hazardous Substances Directive
Restriction of Hazardous Substances Directive
The Directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment 2002/95/EC was adopted in February 2003 by the European Union. The RoHS directive took effect on 1 July 2006, and is required to be enforced and become law in each member state...



Hexavalent chromium compounds are genotoxic carcinogen
A carcinogen is any substance, radionuclide, or radiation that is an agent directly involved in causing cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes...

s. Chronic inhalation of hexavalent chromium compounds increases risk of lung cancer
Lung cancer
Lung cancer is a disease characterized by uncontrolled cell growth in tissues of the lung. If left untreated, this growth can spread beyond the lung in a process called metastasis into nearby tissue and, eventually, into other parts of the body. Most cancers that start in lung, known as primary...

The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...

s are especially vulnerable, followed by fine capillaries in kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...

s and intestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...

). Soluble compounds, like chromic acid
Chromic acid
The term chromic acid is usually used for a mixture made by adding concentrated sulfuric acid to a dichromate, which may contain a variety of compounds, including solid chromium trioxide. This kind of chromic acid may be used as a cleaning mixture for glass. Chromic acid may also refer to the...

, are much weaker carcinogens. Chromate-dyed textiles or chromate-tanned
Tanning is the making of leather from the skins of animals which does not easily decompose. Traditionally, tanning used tannin, an acidic chemical compound from which the tanning process draws its name . Coloring may occur during tanning...

Leather is a durable and flexible material created via the tanning of putrescible animal rawhide and skin, primarily cattlehide. It can be produced through different manufacturing processes, ranging from cottage industry to heavy industry.-Forms:...

 shoes can cause or exacerbate contact dermatitis
Contact dermatitis
Contact dermatitis is a term for a skin reaction resulting from exposure to allergens or irritants . Phototoxic dermatitis occurs when the allergen or irritant is activated by sunlight....

. Ingestion of chromium VI can also cause irritation or ulcers in the stomach and intestines.

Hexavalent chromium is transported into cells via the sulfate
In inorganic chemistry, a sulfate is a salt of sulfuric acid.-Chemical properties:...

 transport mechanisms, taking advantage of the similarity of sulfate and chromate with respect to their structure and charge. Trivalent chromium, which is the more common variety of chromium compounds, is not transported into cells. Inside the cell, Cr(VI) is reduced first to metastable pentavalent chromium (Cr(V)), then to trivalent chromium (Cr(III)). Vitamin C
Vitamin C
Vitamin C or L-ascorbic acid or L-ascorbate is an essential nutrient for humans and certain other animal species. In living organisms ascorbate acts as an antioxidant by protecting the body against oxidative stress...

 and other reducing agents combine with chromate to give Cr(III) products inside the cell. According to some researchers, the damage is caused by hydroxyl radical
Hydroxyl radical
The hydroxyl radical, •OH, is the neutral form of the hydroxide ion . Hydroxyl radicals are highly reactive and consequently short-lived; however, they form an important part of radical chemistry. Most notably hydroxyl radicals are produced from the decomposition of hydroperoxides or, in...

s, produced during reoxidation of pentavalent chromium by hydrogen peroxide
Hydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...

 molecules present in the cell.

In the U.S., the OSHA PEL for airborne exposures to hexavalent chromium is 5 µg/m3 (0.005 mg/m3).

For drinking water, no United States EPA Maximum Contaminant Level (MCL) exists. California has finalized a Public Health Goal of 0.02 parts per billion (ppb or micrograms per liter) and is now in the process of establishing an enforceable MCL.

Kooragang Island, New South Wales

Hexavalent Chromium was released from the Newcastle Orica
Orica is a multinational corporation that manufactures various chemical products. It is the largest supplier of mining explosives in the world. -History:...

 explosives plant on the 8th August 2011. Up to 20 workers at the plant were exposed and 70 nearby homes in Stockton
Stockton, New South Wales
Stockton is a suburb of Newcastle, New South Wales, Australia, located from Newcastle's central business district. It is the only suburb of Newcastle that lies north of the Hunter River.-Geography:...

. The town was not notified until 3 days after the release of the Hexavalant Chromium and a slight uproar of the townsfolk occurred.

Presence in major cities and pending regulation

In 2010, the Environmental Working Group
Environmental Working Group
The Environmental Working Group is an American environmental organization that specializes in research and advocacy in the areas of toxic chemicals, agricultural subsidies, public lands, and corporate accountability...

 studied the drinking water in 35 American cities. The study was the first nationwide analysis measuring the presence of the chemical in U.S. water systems. The study found measurable hexavalent chromium in the tap water of 31 of the cities sampled, with Norman, Oklahoma
Norman, Oklahoma
Norman is a city in Cleveland County, Oklahoma, United States, and is located south of downtown Oklahoma City. It is part of the Oklahoma City metropolitan area. As of the 2010 census, Norman was to have 110,925 full-time residents, making it the third-largest city in Oklahoma and the...

, at the top of list; 25 cities had levels that exceeded California's proposed limit.

The United States Environmental Protection Agency
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...

 set a standard of no more than 0.1 mg/L of total chromium in 1991. This includes both chromium VI and less toxic forms. There is currently no drinking water limit established by the EPA specifically for Chromium VI. The agency began a toxicology study in 2008, following a report by the National Toxicology Program
National Toxicology Program
The National Toxicology Program is an inter-agency program run by the United States Department of Health and Human Services to coordinate, evaluate, and report on toxicology within public agencies....

. EPA released a draft scientific assessment in September 2010 and expects to begin rulemaking in 2011 or 2012 based on the final assessment.

As of 2010, the California Environmental Protection Agency
California Environmental Protection Agency
The California Environmental Protection Agency is a state cabinet-level agency within the government of California. Cal/EPA is composed of six departments, boards and offices responsible for environmental research, regulating and administering the state's environmental protection programs, and...

 had proposed a goal of 0.2 parts per billion, despite a 2001 state law requiring a standard be set by 2005. A final Public Health Goal of 0.02 ppb was established in July 2011.

Hinkley, California

Hexavalent chromium was found in drinking water in the southern Californian town of Hinkley
Hinkley, California
Hinkley is an unincorporated community in the Mojave Desert in California, U.S., northwest of Barstow, east of Mojave, and north of Victorville. It sits just north of California State Highway 58....

 and was brought to popular attention by the involvement of Erin Brockovich
Erin Brockovich
Erin Brockovich-Ellis is an American legal clerk and environmental activist who, despite the lack of a formal law school education, or any legal education, was instrumental in constructing a case against the Pacific Gas and Electric Company of California in 1993...

. The 0.58 ppm Chromium VI in the groundwater in Hinkley exceeded the Maximum Contaminant Level (MCL) of 0.10 ppm for total Chromium currently set by the United States Environmental Protection Agency
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...

 (EPA). It also exceeded the California MCL of 0.05 ppm (as of November 2008). Note that since no MCL exists for Chromium VI the total Chromium standards apply.

A controversial study claimed that from 1996 to 2008, 196 cancers were identified among residents of the census tract that includes Hinkley — a slightly lower number than the 224 cancers that would have been expected given its demographic characteristics. 196 cases over 12 years for a population of 1915 equates to roughly 853 cases per 100k population per year. By comparison San Bernadino County averaged 359/100k/yr over the same period.

Average Cr(VI) levels in Hinkley were recorded as 1.19 ppb with a peak of 3.09 ppb. The PG&E Topock Compressor Station averaged 7.8ppb and peaked at 31.8ppb. Compare to the California proposed health goal of 0.06 ppb. The same day the study came out, the plume of contaminated water was reported to be spreading. Ongoing cleanup documentation is maintained at California EPA's page.

Midland, Texas

In June 2009, the ground water in Midland, Texas
Midland, Texas
Midland is a city in and the county seat of Midland County, Texas, United States, on the Southern Plains of the state's western area. A small portion of the city extends into Martin County. As of 2010, the population of Midland was 111,147. It is the principal city of the Midland, Texas...

 (U.S.), was found to be contaminated with chromium. The Midland groundwater reached higher levels of contamination than in Hinkley with 5250 ppb or 5.25 ppm.

Davenport, California

The Unified Air Pollution Control District reported high airborne levels of chromium(VI) at an elementary school and fire department in Davenport, California
Davenport, California
Davenport is a census-designated place in Santa Cruz County, California. Davenport sits at an elevation of . The 2010 United States census reported Davenport's population was 408.-Situation:...

. The substance apparently originated from a local Cemex
CEMEX is the world's largest building materials supplier and third largest cement producer. Founded in Mexico in 1906, the company is based in Monterrey, Mexico...

Portland cement
Portland cement is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout...

 plant. The levels of chromium(VI) were eight times the air district's acceptable level at Pacific Elementary School and ten times at the Davenport Fire Department. The levels detected did not exceed EPA limits. However, the air samples taken by the air district from June to August at the elementary school and fire department in Davenport registered measurements of hexavalent chromium that were up to ten times higher than allowed by Californian environmental standards. The case highlights the previously unrecognized possible release of chromium(VI) from cement-making.

Chicago, Illinois

In Chicago's first ever testing for the toxic metal contaminant, results show that the city's local drinking water contains levels of hexavalent chromium more than 11 times higher than the health standard set in California in July of 2011. The results of the test showed that the water which is sent to over 7 million residents had average levels of .23 parts per billion of the toxic metal. California's Office of Environmental Health Hazard Assessment designated the nation's new "public heath goal" limit as .02 parts per billion. Echoing their counterparts in other cities where the metal has been detected, Chicago officials stress that local tap water is safe and suggest that if a national limit is adopted, it likely would be less stringent than California's goal.

Milwaukee, Wisconsin

On January 7, 2011 it was announced that Milwaukee, Wisconsin had tested its water and hexavalent chromium was found to be present. Officials are saying it is in such small quantities that it is nothing to worry about, although this contaminant has been linked to cancer (In the draft human health assessment for chromium-6 that was released in September 2010 by EPA for independent expert peer review and public comment, EPA is proposing to classify hexavalent chromium (or chromium-6) as likely to cause cancer in humans when ingested over a lifetime. EPA will make a final determination by the end of 2011.). Further testing is being conducted and is expected to be completed by the end of the year.

Cameron, Missouri

In 2009, a lawsuit was filed against Prime Tanning Corporation of St. Joseph, Missouri, over alleged hexavalent chromium contamination in Cameron, Missouri
Cameron, Missouri
Cameron is a city in Clinton and DeKalb Counties in the U.S. state of Missouri. The population was 8,312 at the 2000 census.The Clinton County portion of Cameron is part of the Kansas City, MO–KS Metropolitan Statistical Area, while the DeKalb County portion is part of the St...

. A cluster of brain tumors had developed in the town that was above average for the population size of the town. The lawsuit alleges that the tumors were caused by waste hexavalent chromium that had been distributed to local farmers as free fertilizer. Legal proceedings are still ongoing


In 2008, defense contractor KBR was alleged to have exposed 16 members of the Indiana National Guard
Indiana National Guard
The Indiana National Guard is the armed force of the state of Indiana. It consists of the Indiana Army National Guard and the Indiana Air National Guard, and is part of the larger Army National Guard and the Air National Guard...

, as well as its own workers, to hexavalent chromium in Iraq
Iraq ; officially the Republic of Iraq is a country in Western Asia spanning most of the northwestern end of the Zagros mountain range, the eastern part of the Syrian Desert and the northern part of the Arabian Desert....

 in 2003. Later, 433 members of the Oregon National Guard
Oregon Military Department
The Oregon Military Department is an agency of the government of the U.S. state of Oregon, which oversees the armed forces of the state of Oregon...

's 162nd Infantry Battalion were informed of possible exposure to hexavalent chromium while escorting KBR contractors.
One of the National Guard soldiers, David Moore, died in February 2008. The cause was lung disease at age 42. His death was ruled service-related. His brother believes it was hexavalent chromium.

Eastern Central Greece

The chemistry of the groundwater in eastern Central Greece
Central Greece
Continental Greece or Central Greece , colloquially known as Roúmeli , is a geographical region of Greece. Its territory is divided into the administrative regions of Central Greece, Attica, and part of West Greece...

 (central Euboea
Euboea is the second largest Greek island in area and population, after Crete. The narrow Euripus Strait separates it from Boeotia in mainland Greece. In general outline it is a long and narrow, seahorse-shaped island; it is about long, and varies in breadth from to...

 and the Asopos
Asopos is a village and a former municipality in Laconia, Peloponnese, Greece. Since the 2011 local government reform it is part of the municipality Monemvasia, of which it is a municipal unit. Population 4,187 . The seat of the municipality was in Papadianika....

 valley) revealed high concentrations of hexavalent chromium in groundwater systems sometimes exceeding the Greek and the EU drinking water maximum acceptable level for total chromium. Hexavalent chromium pollution here is associated with industrial waste.

By using the GFAAS for total chromium, diphenylcarbazide-Cr(VI) complex colorimetric method for hexavalent chromium, and flame-AAS and ICP-MS for other toxic elements, their concentrations were investigated in several groundwater samples. The contamination of water by hexavalent chromium in central Euboea is mainly linked to natural processes, but there are anthropogenic cases.

Thiva – Tanagra – Malakasa (Asopos) Basin

In the Thiva
Thebes, Greece
Thebes is a city in Greece, situated to the north of the Cithaeron range, which divides Boeotia from Attica, and on the southern edge of the Boeotian plain. It played an important role in Greek myth, as the site of the stories of Cadmus, Oedipus, Dionysus and others...

 – Tanagra
Tanagra is a town and a municipality north of Athens in Boeotia, Greece. The seat of the municipality is the town Schimatari. It is not far from Thebes, and it was noted in antiquity for the figurines named after it...

 – Malakasa
Malakasa is a town and former community of Attica in Greece, it is also a suburb of Athens. Since the 2011 local government reform it is part of the municipality Oropos, of which it is a municipal unit....

 basin, Eastern Sterea Ellada, Greece
Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....

, which supports many industrial activities, concentrations of chromium (up to 80 μg/L Cr(VI)) and Inofyta (up to 53 μg/L Cr(VI) were found in the urban water supply of Oropos
Oropos is a small town and a municipality in East Attica, Greece.-Geography:It is situated on the southern Euboean Gulf, opposite Eretria. Oropos is located N of Avlona and Athens, E of Thebes and SE of Chalcis. Oropos is linked with the road linking Nea Palatia and Sikamino...

. Cr(VI) concentrations ranging from 5 to 33 μg/L Cr(VI) were found in groundwater that is used for Thiva's water supply. Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...

 concentrations up to 34 μg/L along with Cr(VI) levels up to 40 μg/L were detected in Schimatari
Schimatari is a town and a former municipality in Boeotia, Greece. Since the 2011 local government reform it is part of the municipality Tanagra, of which it is the seat and a municipal unit. Population 8,095 . The Asopus River is 3 to 4 km to the south. The Greek National Road 1 passes...

's water supply.
In the Asopos River
Asopus or Asôpos is the name of four different rivers in Greece and one in Turkey. In Greek mythology, it was the name of the gods of those rivers.-The rivers in Greece:...

, total chromium values were up to 13 μg/L, hexavalent chromium was less than 5 mg/L and other toxic elements were relatively low.

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