Hexavalent chromium (chromium(VI), Cr(VI)) refers to chemical compounds that contain the element chromium in the +6 oxidation state. Virtually all chromium ore is processed via hexavalent chromium, specifically the salt sodium dichromate. Approximately 136,000 tonnes (300,000,000 lb) of hexavalent chromium were produced in 1985. Other hexavalent chromium compounds are chromium trioxide and various salts of chromate and dichromate. Hexavalent chromium is used in textile dyes, wood preservation, and as anti-corrosion and conversion coatings and a variety of niche uses. Chromium hexavalent compounds 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 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)
Inhaled hexavalent chromium is recognized as a human carcinogen. Workers in many occupations are exposed to hexavalent chromium. Problematic exposure is known to occur among workers who handle chromate-containing products and those who weld, grind, or braze stainless steel. Within the European Union, the use of hexavalent chromium in electronic equipment is largely prohibited by the Restriction of Hazardous Substances Directive.
- 1 Toxicity
- 2 Air and water pollution
- 2.1 Australia
- 2.2 United States
- 2.3 Iraq
- 2.4 Greece
- 2.5 Bangladesh
- 3 See also
- 4 References
- 5 External links
Hexavalent chromium compounds are genotoxic carcinogens. Chronic inhalation of hexavalent chromium compounds increases the risk of lung cancer. (The lungs are the most vulnerable, followed by the fine capillaries in kidneys and intestines). Soluble compounds, like chromic acid, are much weaker carcinogens. Chromate-dyed textiles or chromate-tanned leather shoes can cause or exacerbate contact dermatitis. Ingestion of chromium VI can also cause irritation or ulcers in the stomach and intestines.
Hexavalent chromium is transported into cells via the sulfate 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 and other reducing agents combine with chromate to give Cr(III) products inside the cell. According to Shi et al., the damage is caused by hydroxyl radicals, produced during reoxidation of pentavalent chromium by hydrogen peroxide 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). The National Institute for Occupational Safety and Health proposed a REL of 0.2 µg/m3 for airborne exposures to hexavalent chromium.
For drinking water, no United States EPA Maximum Contaminant Level (MCL) exists, though the current MCL for total chromium is based on the assumption that all of it is Cr(VI). California has finalized a Public Health Goal of 0.02 parts per billion (ppb or micrograms per liter) and established a MCL of 10 ppb.
Air and water pollution
Kooragang Island, New South Wales
The town was not notified until three days after the release of the hexavalent chromium and the accident sparked a major public controversy, with Orica criticised for playing down the extent and possible risks of the leak, and NSW state environment minister Robyn Parker and her department attacked for their slow response to the incident. In December 2011, the 8 August leak was the subject of a NSW parliament upper house inquiry, and the NSW Office of Environment and Heritage ordered Orica to undergo an environmental audit, due to be completed by May 2013.
Presence in major cities and pending regulation
In 2010, the Environmental Working Group 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, at the top of list; 25 cities had levels that exceeded California's proposed limit of VI and its 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. 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 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.
Hexavalent chromium was found in drinking water in the southern California town of Hinkley and was brought to popular attention by the involvement of Erin Brockovich. 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 (EPA). The source of contamination was from the evaporating ponds of a PG&E (Pacific Gas and Electric) power generating plant, which were used to dry the precipitate from the cleaning solution for the cooling stacks. 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 more recent study found 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. In June 2013 "Mother Jones" published an article regarding work by the Center for Public Integrity that was critical of the study, and some others by the same researcher.
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.
In June 2009, the groundwater in 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.
In 2007, ASTDR conducted a study of groundwater and soil pollution emanating from Cambridge Plating Company, Inc. in Belmont, Massachusetts (aka Pure Coat North, LLC) concluding that chromium was detected in 25 of the soil samples collected from property at Cambridge Plating Company, Inc., with total concentrations exceeding nine times the reference media evaluation guide (RMEG) value for childhood exposure to chromium VI (200 mg/kg) and three times exceeding the RMEG value for adult exposure to chromium VI(2,000 mg/kg). The incidence of leukemia among females was elevated in Belmont, MA during 1982–1999 (32 diagnoses observed vs. 23.2 expected). Elevations in females were due to four excess cases in each time period (11 diagnoses observed vs. 6.9 expected during 1988–1993; 13 diagnoses observed vs. 8.7 expected during 1994–1999) while elevations among males were based on one to three excess cases. Chromium soil contamination found on property at Cambridge Plating Company, Inc. is in close proximity to Belmont High School.
The Unified Air Pollution Control District reported high airborne levels of chromium(VI) at an elementary school and fire department in Davenport, California. The substance apparently originated from a local Cemex cement 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 California environmental standards. The case highlights the previously unrecognized possible release of chromium(VI) from cement-making.
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 2011. The results of the test showed that the water which is sent to over 7 million residents had average levels of 0.23 parts per billion of the toxic metal. California's Office of Environmental Health Hazard Assessment designated the nation's new "public health goal" limit as 0.02 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.
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 the EPA for independent expert peer review and public comment, the EPA is proposing to classify hexavalent chromium (or chromium-6) as likely to cause cancer in humans when ingested over a lifetime. The 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.
In 2009, a lawsuit was filed against Prime Tanning Corporation of St. Joseph, Missouri, over alleged hexavalent chromium contamination in Cameron, Missouri. 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, as well as its own workers, to hexavalent chromium at the Qarmat Ali water treatment facility in Iraq in 2003. Later, 433 members of the Oregon National Guard'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. On November 2, 2012, a Portand, Oregon jury found KBR negligent in knowingly exposing twelve National Guard soldiers to hexavalent chromium while working at the Qarmat Ali water treatment facility and awarded damages of $85 million to the plaintiffs.
Eastern Central Greece
The chemistry of the groundwater in eastern Central Greece (central Euboea and the Asopos 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.
Thebes – Tanagra – Malakasa (Asopos) Basin
In the Thebes – Tanagra – Malakasa basin, Eastern Central Greece, 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. 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 concentrations up to 34 μg/L along with Cr(VI) levels up to 40 μg/L were detected in Schimatari's water supply. In the Asopos River, total chromium values were up to 13 μg/L, hexavalent chromium was less than 5 μg/L and other toxic elements were relatively low.
Toxic poultry feed from quicker chromium-based leather tanning (as opposed to traditional slower vegetable tanning) is entering the food supply in Bangladesh, and chicken meat was the most common source of protein in the country. Tanneries in Hazaribagh, an industrial neighbourhood in Dhaka, emit around 21,600 cubic metres of toxic waste each day. The tanneries also generate as much as 100 tonnes per day of scraps - trimmed raw hide, flesh and fat - which are processed into feed by neighbourhood recycling plants and used in chicken and fish farms across the country. Chromium levels ranging from 350 to 4,520 micrograms (0.35 to 4.52 mg) per kilogram were found in different organs of chickens which had been fed the tannery-scraps feed for two months, according to Abul Hossain, a chemistry professor at the University of Dhaka. The study estimated up to 25% of the chickens in Bangladesh contained harmful levels of Cr (VI).
- Gerd Anger, Jost Halstenberg, Klaus Hochgeschwender, Christoph Scherhag, Ulrich Korallus, Herbert Knopf, Peter Schmidt, Manfred Ohlinger, "Chromium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005.doi:10.1002/14356007.a07_067
- IARC (1999-11-05) . Volume 49: Chromium, Nickel, and Welding (PDF). Lyon: International Agency for Research on Cancer. ISBN 92-832-1249-5. Retrieved 2006-07-16.
There is sufficient evidence in humans for the carcinogenicity of chromium[VI] compounds as encountered in the chromate production, chromate pigment production and chromium plating industries.
- Salnikow, K.; Zhitkovich, A. (2008). "Genetic and Epigenetic Mechanisms in Metal Carcinogenesis and Cocarcinogenesis: Nickel, Arsenic, and Chromium". Chem. Res. Toxicol 21 (1): 28–44. doi:10.1021/tx700198a. PMC 2602826. PMID 17970581.
- Shi, X.; Mao, Y.; Knapton, A.D. et al. (1994). "Reaction of Cr(VI) with ascorbate and hydrogen peroxide generates hydroxyl radicals and causes dnA damage: role of a Cr(IV)-mediated Fenton-like reaction". Carcinogenesis 15 (11): 2475–2478. doi:10.1093/carcin/15.11.2475. PMID 7955094.
- "OSHA: Small Entity Compliance Guide for the Hexavalent Chromium Standards" (PDF). Retrieved 2013-12-05.
- David Blowes (2002). "Tracking Hexavalent Cr in Groundwater". Science 295 (5562): 2024–25. doi:10.1126/science.1070031. PMID 11896259.
- "Criteria for a Recommended Standard: Occupational Exposure to Hexavalent Chromium" (PDF). Retrieved 2013-12-05.
- "Hexavalent Chromium PHG". Oehha.org. Retrieved 2013-12-05.
- "State Adoption of a Hexavalent Chromium MCL". California Department of Public Health. Retrieved 2014-10-08.
- Tovey, Joesphine (December 17, 2011). "Patches of carcinogen seen after Orica leak". The Sydney Morning Herald (Sydney Morning Herald). Retrieved 17 December 2011.
- Jones, Jackqui (11 August 2011). "Stockton residents fume over fallout from Orica". Newcastle Herald. Retrieved 12 August 2011.
- O'Brien & Aston, Natalie & Heath url=http://www.smh.com.au/environment/the-untold-story-of-oricas-chemical-leaks-20111112-1ncup.html (November 13, 2011). "The untold story of Orica's chemical leaks". Sydney Morning Herald.
- "US water has large amounts of likely carcinogen: study". Yahoo News. 2010-12-19. Retrieved 2010-12-19.
- "EPA’s recommendations for enhanced monitoring for Hexavalent Chromium (Chromium-6) in Drinking Water". Retrieved 2011-08-04.
- "IRIS Toxicological Review of Hexavalent Chromium". 2010-09-30. Retrieved 2011-08-04.
- "IRISTrack Detailed Report | IRIS | US EPA". Cfpub.epa.gov. 2006-06-28. Retrieved 2013-08-18.
- December 31, 2010 in Health and the Environment (2010-12-31). "California Finally Takes Leadership on Hexavalent Chromium in Drinking Water | Gina Solomon's Blog | Switchboard, from NRDC". Switchboard.nrdc.org. Retrieved 2013-08-18.
- U.S. Environmental Protection Agency, Consumer Factsheet on: Chromium.[dead link]
- "California Department of Public Health, Maximum Contaminant Levels and Regulatory Dates for Drinking Water." (PDF). Retrieved 2013-12-05.
- SCHWARTZ, NOAKI (December 13, 2010). "Survey shows unremarkable cancer rate in CA town". Associated Press. Retrieved December 2010.
- "California Cancer Registry". Cdph.ca.gov. 2013-02-05. Retrieved 2013-12-05.
- "PG&E Background Study" (PDF). Retrieved 2013-12-05.
- "OEHHA Water - Draft PHG for Hexavalent Chromium". Oehha.ca.gov. Retrieved 2014-01-06.
- Carrie Kahn (2010-12-13). "Erin Brockovich II? Activist Returns To Aid Town". NPR.
- "Lahontan Regional Water Quality Control Board". Swrcb.ca.gov. Retrieved 2014-01-06.
- "Environmental crusader Erin Brockovich is investigating contaminated well water in Midland, Texas". Therealnews.com. Retrieved 2013-12-05.
-  Evaluation of Environmental Concerns and Cancer Incidence in Belmont and Surrounding Communities, Middlesex County, Massachusetts 1982-2003
- Carcinogenic dust found in Davenport Santa Cruz Sentinel 4 Oct 2008
- Chromium 6 testing continues in Davenport, Cemex changes business practices Santa Cruz Sentinel 9 Oct 2008
- Cemex plant could have been unwittingly releasing chromium 6 MetroSantaCruz.com 15 October 2008
- Rodriguez, Robert (2011-08-06). "Toxic Metal Found in Chicago Drinking Water". NBC Chicago. Retrieved 2013-08-18.
- Hawthorne, Michael. "Toxic chromium found in Chicago drinking water". Chicago Tribune.[dead link]
- City defends water safety Milwaukee Wisconsin Journal Sentinel, January 7, 2011
- "Lawsuit Alleges Cameron Missouri Brain Tumors Linked to Fertilizer". AboutLawsuits.com. 2009-04-28. Retrieved 2013-08-18.
- Indiana Guardsmen Sue KBR Over Chemical from Democracy Now!, December 4, 2008
- Associated Press (February 12, 2009). "Oregon: Possible Chemical Exposure". New York Times. Retrieved on February 12, 2009.
- Associated Press (June 27, 2009). "Did toxic chemical in Iraq cause GIs' illnesses?". Associated Press. Retrieved on June 27, 2009.
- CNN (November 3, 2012). "Defense contractor ordered to pay millions to National Guard soldiers". CNN. Retrieved on November 3, 2012.
- [dead link]
- Dangers of Hexavalent Chromium, OSHA Standards, Engineering Controls
- Hexavalent Chromium, also known as Chromium 6 was a major carcinogenic in the Hinkley case, of which was the subject of the poignant movie, "Erin Brockovich."
- "I never thought I’d see another Hinkley, California, but I’m afraid I might be wrong." Hexavalent chromium was first discovered in April of 2009 at more than 50 times the acceptable federal levels in a water well near West County Road 112.
- ATSDR Case Studies in Environmental Medicine: Chromium Toxicity U.S. Department of Health and Human Services
- ATSDR Investigation of Chromium contamination of ground soil, Belmont, Massachusetts
- Hexavalent Chromium National Emphasis Program
- Factors controlling the heterogeneous distribution of Cr(VI) in soil, plants and groundwater: evidence from the Assopos basin, Greece by M. Economou-Eliopoulos, I. Megremi and Ch. Vasilatos. in the Chemie der Erde/Geochemistry, 71 (1), 39-52, 2011 Elsevier
- 3M US: OSHA Hexavalent Chromium Standard—An overview of the Chromium Six (CrVI) standard
- Environmental Health: "Selected science: an industry campaign to undermine an OSHA hexavalent chromium standard"
- Hexavalent chromium, a case study from defendingscience.org
- Australian National Pollutant Inventory Chromium VI fact sheet
- US OSHA Health and Safety Topics: Hexavalent Chromium"
- National Institute for Occupational Safety and Health - Hexavalent Chromium
- Evaluation of the CR(VI) and other toxic element contamination and their potential sources: The case of the Thiva basin (Greece)mby M. Economou-Eliopoulos, D. Antivachi, Ch. Vasilatos and Megremi, I., 2012. in Geoscience Frontiers, Elsevier