Chromium III or VI
Chromium is a naturally occurring element used in the production of metal alloys (with nickel, tungsten, cobalt and steel), ceramics, salts and pigments. Chromium is also used in leather tanning, as a catalyst for chemical synthesis reactions, and as a wood preservative (for example, chromated copper arsenate). Before 1961, chromium was mined in the U.S. as chromite ore, but it is now mostly imported into the U.S. from other nations, mainly South Africa (37 percent), Russia (18 percent) and Turkey (13 percent) (Hazardous Substances Data Bank (HSDB) 2002b).
Chromium 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 (metallic chromium), chromium III and chromium VI (also known as hexavalent chromium). Chromium VI is a highly toxic air and water contaminant that can damage the respiratory system and cause cancer. Ingesting high levels of chromium VI may result in anemia or damage to the stomach or intestines. Chromium III is an essential nutrient (Agency for Toxic Substances and Disease Registry (ATSDR) 2008b).
Chromium is released into the environment from the combustion of natural gas, oil and coal, and from its use in several industries including: industrial chemical production, steelworks, electrometallurgy and copper smelting. Chromium is also released into the environment from chromium-treated wood and chromium-containing paint pigments (U.S. Environmental Protection Agency (USEPA) 2002f).
In 2002, industrial facilities reported releasing 9,311,530 pounds of chromium into U.S. water, air, and land (USEPA 2009i). The reported releases of chromium underestimate the volume of chromium that was released into the environment, because the volume of chromium used as a wood preservative and as a paint additive is not included in these official estimates. Chromium has been found in at least 1,127 of the 1,669 National Priorities List sites, which are areas of known releases of hazardous substances, pollutants, or contaminants throughout the U.S. and its territories, also known as the Superfund sites (ATSDR 2008b; USEPA 2009c).
Hexavalent chromium is a known human carcinogen according to the National Toxicology Program, causing lung cancer in workers in the chromium industry (National Toxicology Program (NTP) 2002a). Oral exposure to hexavalent chromium has been associated with substantially elevated stomach cancer mortality in a study of residents in Chinese villages with hexavalent chromium-contaminated drinking water (Beaumont 2008). Ingestion of chromium VI in drinking water also produced sever gastrointestinal effects such as oral ulcers, diarrhea, abdominal pain, indigestion, vomiting and bloody diarrhea (ATSDR 2000a, 2008b).
According to the U.S. EPA, short-term exposure to chromium-contaminated drinking water can cause skin irritation and ulceration, and long-term exposure can cause damage to kidneys, the circulatory system, nervous system and skin (USEPA 2002f).
Hexavalent chromium exposure in workers has been linked to chromosome aberrations and damage to the pharynx, larynx, kidney, heart and liver (ATSDR 2000a, 2008b). Changes in white blood cell counts, decreased hemoglobin, increased bleeding times, stomach cramps, and stomach and intestinal ulcers have also been reported. Greater incidence of complications during pregnancy and childbirth has been reported in chromate-exposed Russian dichromate manufacturing factory workers. Higher incidences of diarrhea, constipation, headaches, tiredness, lightheadedness and eye irritation has been reported among residents living near a chromium-contaminated area of Tokyo, Japan compared to people living in an uncontaminated area.
Hexavalent chromium-contaminated drinking water from Pacific Gas and Electric (PG&E) was reported in Hinkley, California and formed the basis for the movie, "Erin Brockovich." The case against PG&E ultimately resulted in the largest legal settlement in U.S. history - $333 million.
In August 2009, the California Office of Environmental Health Hazard Assessment proposed a new public health goal for hexavalent chromium in drinking water that is hundreds of times lower than the amount contaminating some water supplies (California Environmental Protection Agency. 2009a; Environmental Working Group (EWG) 2009). The draft public health goal for hexavalent chromium is set at 0.06 parts per billion (ppb). A public health goal is the level of a chemical contaminant in drinking water that does not pose a significant health risk (California Environmental Protection Agency 2009b).
The recommendation culminates a decade of debate among scientists trying to decide what concentration is safe to drink (Cone 2009). The 0.06 ppb health guideline proposed by California state scientists, if adopted by regulators, would reduce the risk of cancer caused by chromium VI in drinking water to one in one million, the point at which the state of California considers the danger to public health to be minimal (EWG 2009).
Trivalent chromium compounds are considerably less toxic than hexavalent compounds. Chromium III is an essential nutrient in the diet of humans and animals in very small amounts. Other forms of chromium are not needed by living organisms and all forms of chromium can be toxic at high levels. People who are allergic to chromium may have asthma attacks after breathing high levels of chromium III in air. Repeated or prolonged skin contact may cause irritation, skin allergy, itching, redness and an eczema-like rash (Australian National Pollutant Inventory 2005).
Chromium III occurs as dissolved compound in natural waters as a result of weathering of minerals in rocks and soils. However, industrial emissions are a significant contributor to overall chromium pollution in drinking water, because manufacturing, disposal of products or chemicals containing chromium, and burning of fossil fuels are all processes that release chromium to the air, soil, and water. Research by scientists at the U.S. Environmental Protection Agency demonstrated that chromium III is converted into more toxic chromium VI when tap water is treated with chlorine, thus increasing overall risk to human health (Ulmer 1986).
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