Monday, September 21, 2009

Team Gamma Project 1: Chromium VI

Introduction & General Information about Chromium VI (CrVI)

Chromium is a naturally occurring element, a transition metal, found as a silvery, steely-gray metallic solid in its pure form. Chromium can be found in 6 different oxidation states; however the most common of these are trivalent chromium, Cr(III) and hexavalent, Cr(VI) due to the instability of the other forms. Due to their stability, trivalent and hexavalent chromium are important forms of chromium compounds.

Chromium VI, also known as hexavalent chromium, exists in many different compounds such as sodium dichromate and chromic acid, for example. It is very prevalent in industrial processes where chromium is converted to chromium VI oxidation state. It very rarely found naturally in the environment. One reason that Chromium (VI) is hazardous to the soil environment is that it is mobile, meaning that it can spread to ground water and the subsurface. Another reason Chromium +6 is hazardous to the environment is that it can be absorbed by other compounds to keep the Chromium + 6 oxidation state. These two characteristics of chromium + 6 result in exposure of Chromium +6 to general population through ingestion of drinking water and food.

Chromium VI is the predominant form of Cr found in fire-impacted soil and ash samples. Soils and Ashes from residential areas have higher Cr(VI) than wild land area. Alkaline pH resulting from contact of ash with water and water-based fluids may have a stabilizing effect on Cr(VI). Chromium deposits are mined from the earth in the form of chromite (FeCr2O4). In industrial processes, trivalent chromium compounds are formed by dissolving chromium in hydrochloric or sulfuric acid, while hexavalent chromium is often formed by smelting chromite ore in the presence of calcium or sodium carbonate.

The existence of one of the two predominant species of Cr in the environment is heavily dependent on two important factors; the environmental pH and the oxidative potential of the same environment. Oxidation states exist as a result of the likeliness of that particular state to either gain or lose electrons. In chemistry, this likeliness is described by the reduction potential (Eº) of two oxidation states. If Eº is positive relative to a new species, it will have a tendency to gain electrons; this scenario means that Cr3+ will be “reduced” to Cr2+. Conversely, if Eº is negative relative to a new species, it will have a tendency to lose electrons; this scenario means that Cr5+ will be “oxidized” to Cr6+.

The pH, or acidity, of the environment will help determine the prevailing chromium compound found in the area. However, it is not enough to know the pH and the reduction potential, the existence of other chemical agents has a large influence as well. These are complex associations but it important to note that Cr(VI) in natural waters is readily reduced to Cr(III) over time. There is a potential human health impact from high pH and for exposure to Cr(VI)-containing ash and soils by first-responders and clean-up crews. Air monitoring data during fire clean-up/recovery operations would be useful to assess potential exposure to Cr(VI) per OSHA PEL.

Toxic Effects of Chromium:

Chromium VI (Cr VI) is considered the most hazardous form of Chromium, unlike the Cr III is not needed by the body for normal functioning. The reason that Chromium +6 is so toxic is that it can be absorbed by cells. Chromium (0) and Chromium +3 are not absorbed by cells and therefore not as toxic. After Chromium +6 enters cells it is reduced to Chromium +3 where it damages cells or DNA and result in cancer. Exposure may be through inhalation, absorption and to a lesser degree ingestion. Cr VI has been shown to penetrate cell walls through the process of facilitated diffusion, this can result in it being spread rapidly to the bloodstream.

The organs affected by Cr VI vary with the means of exposure. For inhalation exposure the lungs are primarily affected. Acute exposures to Cr VI may result in shortness of breath, coughing and wheezing. Other symptoms of acute exposure via inhalation include gastrointestinal and neurological effects. Acute exposure to skin may result in dermatitis and burns. Acute exposure via ingestion may result in abdominal pain, vomiting, and hemorrhaging.

The organs affected by acute exposure are also affected by chronic exposure, the difference being largely the severity of the symptoms. Inhalation of Cr VI on a chronic basis may affect the liver, kidney, gastrointestinal and immune systems, and possibly the blood. Symptoms may include perforations and ulcerations of the septum, bronchitis, decreased pulmonary function, pneumonia and asthma. The EPA has classified Cr VI and a known human carcinogen via the inhalation route, this is based on the strong link between long term exposure and an elevated risk of lung cancer.

Ingestion exposure of Cr VI has also been shown to have serious affects in the reproductive/developmental areas. In mice it has been shown to cause gross abnormalities and reproductive effects including decreased litter size and reduced sperm count.

Chromium VI In The Workplace: Exposure Limits, PPE, First Aid, and Spill Cleanup:

Chromium VI is and extreme poison, oxidizer, and corrosive. It is non-combustible but acts as and accelerant for other combustible materials. It will react with combustible, organic, or other readily oxidizable materials such as paper, wood, sulfur, aluminum, and plastics. It is also corrosive to metals. The IDLH limit for Chromic Acid and other Chromates is 15 mg/m3. Per OSHA, the Permissible Exposure Limit (PEL) is based on a Time Weighted Average (TWA) of .005 mg/m3. The ceiling limit is .1 mg/m3. The NIOSH REL is .001 mg/m3.

Occupational exposures to Cr(VI) occur during the production of stainless steel, chromate chemicals, and chromate pigments. Cr(VI) exposures also occur during other work activities such as stainless steel welding, thermal cutting, chrome plating.

When working with Chromic Acid, skin and eye contact should be prevented. Proper PPE includes impervious protective clothing, including boots, gloves, lab coat, apron or coveralls, as appropriate, to prevent skin contact. To prevent eye contact, the PPE includes chemical safety goggles and/or full-face shield where dusting or splashing of solutions is possible. An eye wash fountain and quick-drench facilities in work area should be maintained. A system of local and/or general exhaust is recommended to keep employee exposures below the Airborne Exposure Limits. Local exhaust ventilation is generally preferred because it can control the emissions of the contaminant at its source, preventing dispersion of it into the general work area.

When dealing with an exposure, the following first aid measures should be taken. In case of inhalation, move the victim to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. Get medical attention immediately. In case of ingestion, do not induce vomiting. Give large quantities of water. Never give anything by mouth to an unconscious person. Get medical attention immediately. In case of skin contact, immediately flush skin with plenty of water for at least 15 minutes while removing contaminated clothing and shoes. Get medical attention immediately. In case of eye contact, immediately flush eyes with plenty of water for at least 15 minutes, lifting lower and upper eyelids occasionally. Get medical attention immediately.

In case of an accidental spill or release in the workplace, the following measures should be taken. Isolate the spill in all direxction for at least 50 meters for liquids and at least 25 literes for solids. Ventilate the area of the leak or spill. When evacuating, stay upwind and out of low areas.

In case of a fire, use water, however, the decomposing material will form a hot viscous foam and caution should be exercised against the possibility of a steam explosion. Chromium is not combustible, but it is a strong oxidizer and its heat of reaction with reducing agents or combustibles may cause ignition. It will ignite on contact with acetic acid and alcohol and it releases oxygen upon decomposition, increasing the fire hazard. Contact with oxidizable substances may cause extremely violent combustion. Containers may explode when involved in a fire. Full protective clothing and NIOSH-approved self-contained breathing apparatus with full facepiece operated in the pressure demand or other positive pressure mode should be worn.

Contamination Site: Clarks Summit, PA

A former chrome plating shop for locomotives is located in Clarks Summit, Pennsylvania. The shop first went into operation in 1956 and is owned by Precision National Plating Services. According to site description listed on epa.gov the site began contaminating the groundwater in the 1970’s. The EPA performed an expanded site investigation when it was informed of a chromic acid spill at the site. Groundwater testing was performed and hexavalent chromium water was detected in the groundwater, a nearby stream, and lake. It was also detected in nearby water wells used by local residents. Precision National Plating voluntarily removed 5,300 cubic yards of contaminated soil and stored it off-site. A seep collection system was installed to collect groundwater that was seeping onto the ground surface. Precision plating also paid for the installation of municipal water to connect to the homes that had contaminated drinking wells. The site is continually monitored through water sampling of the wells. The investigation determined that there was not a significant risk to human health.

Contamination Site: San Fernando Valley, CA

One incident of chromium VI contamination is in San Fernando Valley located in Southern California. The discharge of chromium waste by several industrial plants into the area’s waterways was first reported in 1941 to the Bureau of Water Works and Supply. It was not until 1989 that testing by the Environmental Protection Agency revealed chromium contamination in the San Fernando Valley. After the contamination was discovered monitoring of chromium levels and investigation into possible sources began. Source investigations have lead to multiple contamination sites in which cleanup efforts have been taking place. These efforts include treating water, removing chemicals and drums, dismantling buildings, and excavating, removing, and replacing soil.

Contamination Site: Cameron, MO

Cameron, Missouri is a suspected chromium VI contamination area which stretches over four counties. It has been alleged there are statistically significant number of brain tumor cases within the Cameron area. The Missouri Department of Health and Senior Services are conducting a cancer inquiry to determine if this is true. Two local tanneries are accused of discarding toxic chromium waste, which was used to remove hair from hides in the tanning process, by giving it to farms as fertilizer. The Missouri Department of Natural Resources, the Missouri Department of Health and Senior Services, and the Environmental Protection Agency are working together to test the area for contamination and determine if the allegations of improper hazardous waste disposal hold true. A law firm with Erin Brockovich and a team of environmental scientists has also begun investigating the cluster of brain tumors and are conducting their own environmental testing. It is undetermined at this time if chromium VI contamination is the cause of the usual number of tumors in the Cameron area but this suspicion is being deeply investigated.

Contamination Site: Midland, TX

The hexavalent chromium contamination at West County Road 112 in Midland, Texas, is an example of the initial phases of evaluation and remediation for this compound. The Texas Commission on Environmental Quality (TCEQ) was called by a resident in March 20009 to assess a drinking water complaint, and through sampling discovered that the water contained 5250 parts per billion (ppb) hexavalent chromium, well over the Environmental Protection Agency (EPA) standard of 100 ppb.

Initial actions by TCEQ included notification of the EPA and joint determination of a strategy for evaluation and treatment of the contamination, as well as notification of the local residents. A system of 150 sampling wells has been drilled around the contaminated area for the purposes of determining the overall extent of the contamination (figure 1), and anion-exchange water filtration systems (figure 2) have been installed at homes where the levels of hexavalent chromium higher than the standard have been detected. Regular town meetings have been held to distribute information about current project activities and to ensure that the residents are up to date with current developments on the evaluation and remediation of the site.

TCEQ is continuing to monitor the movement of the contaminant plume through the Trinity Aquifer, and the site is being screened by the EPA under the Superfund Site Assessment Program. Most recently, 400 access agreements were distributed to local property owners to allow further sampling of wells in the area as TCEQ continues to determine the full extent of the contamination, and a meeting is scheduled for September 24th between residents and TCEQ and County staff to answer any questions about the current approach for this site. The source of the contamination has not yet been determined.

References:


http://www.chemguide.co.uk/inorganic/transition/chromium.html

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

http://pubs.usgs.gov/of/2008/1345/pdf/OF08-1345_508.pdf

http://www.lhsfna.org/index.cfm?objectID=B7EA97FF-D56F-E6FA-960D8827D1588555

http://www.cdc.gov/niosh/topics/hexchrom/

http://www.jtbaker.com/msds/

http://www.phmsa.dot.gov/

http://www.webelements.com/

U.S. Environmental Protection Agency(September, 2002) Precision National Plating Services. Retrieved September 19, 2009.

http://www.epa.gov/reg3hscd/npl/PAD053676631.htm

U.S. Environmental Protection Agency(September, 2002) Precision National Fact Sheet. Retrieved September 19, 2009.

http://www.epa.gov/reg3hwmd/super/sites/PAD053676631/fs/1999-09.pdf

Kracov, G. (2001, June). Chromium 6: How the State Legislation Ought to Respond. Metro Investment Report. Retrieved September 16, 2009, from http://gideonlaw.net/news/0601metro.pdf

United States Environmental Protection Agency. (2008, December 16). Addressing Chromium Contamination in the San Fernando Valley. Retrieved September 16, 2009, from http://www.epa.gov/region09/superfund/chromium/index.html

United States Environmental Protection Agency. (2008, March 10). Response to Chromium Contamination. Retrieved September 16, 2009, from http://yosemite.epa.gov/r9/sfund/r9sfdocw.nsf/91f8ceee903fc0f088256f0000092934/f7880395be7082af88257007005e93fc/$FILE/EPA%20Response%20to%20Cr%20Contamination%20-%20SFV%20CrWorkshop%2020080310.pdf

Missouri Department of Natural Resources. (2008,June). Hazardous Waste Management Commission Report. Retrieved September 16, 2009, from http://www.dnr.mo.gov/env/hwp/commission/docs/hwmc-qt-rpt-2008-2nd.pdf

Lang, A. & Kates, K. (2009, April). A Search for Life-saving Answers in Cameron, MO. University News. Retrieved September 15, 2009, from http://media.www.unews.com/media/storage/paper274/news/2009/04/27/News/A.Search.For.LifeSaving.Answers.In.Cameron.Mo-3728033.shtml

Testing to Continue on Farm Field. (2009, August 10). My Cameron News. Retrieved September 15, 2009, from http://www.citizen-observer.com/articles/2009/08/19/news/doc4a80520e00695599425187.txt

Kotaś, J., Stasicka Z. (2000). "Chromium occurrence in the environment and methods of its speciation". Environmental Pollution 107 (3): 263–283.

Texas Commission on Environmental Quality Site Remediation – Cr112 (September 16, 2009). Retrieved September 20th, 2009 from http://www.tceq.state.tx.us/remediation/sites/cr112.html

Midland residents play waiting game as state continues identifying contamination plume (August 25, 2009). My San Antonio News. Retrieved September 20th, 2009 from http://www.mysanantonio.com/news/environment/Midland_residents_play_waiting_game_as_state_continues_identifying_contamination_plume.html

Case Studies in Environmental Medicine (CSEM): Chromium Toxicity: What Are the Physiologic Effects of Chromium Exposure? (Online). Available at http://www.atsdr.cdc.gov/csem/chromium/cr_physiologic-effects.html [2009,September 15]

Pichtel, John. (2007).Fundamentals of Site Remediation. Government Institutes, Lanham

Environmental Protection Agency. (2004, October 4). Federal Register Environmental Documents. Retrieved September 16, 2009, from Occupational Exposure to Hexavalent Chromium : http://www.epa.gov/EPA-IMPACT/2004/October/Day-04/i21488.htm

Environmental Protection Agency. (2000, Januaury). Chromium Compounds. Retrieved September 16, 2009, from Air Toxics Web Site: http://www.epa.gov/ttnatw01/hlthef/chromium.html

No comments:

Post a Comment