What is hexavalent chromium?
Chromium is a naturally occurring metallic element that can be found in water and in soil or rocks. It is also present in the food we eat, either in the food itself or in residual soils that might remain on such items as produce. In addition, trace amounts of chromium exist in the environment as a result of industrial processes.
The most common forms of chromium are trivalent (chromium 3) and hexavalent (chromium 6); in its trivalent state, the chromium atom is missing three electrons, and in its hexavalent state, it is missing six electrons. In the environment, chromium usually exists in the trivalent form. It is possible for one form to change into the other when chemical conditions are right.
Chromium 3 is an essential nutrient and is necessary for the metabolism of sugars and for many enzyme reactions. The federal government recommends an adult daily intake of 50 to 200 micrograms (mg). Chromium is a common ingredient in many vitamin and mineral supplements.
Although the trivalent form of chromium shows very low toxicity, both the federal and California EPA have designated hexavalent chromium a carcinogen. Because of the carcinogenic properties of some chromium compounds, a risk-based drinking water standard of 50 micrograms per liter (mg/L) has been established for chromium. The federal EPA has proposed increasing the drinking water standard to 100 mg/L, but no action has been taken yet.
Potential health effects from chromium exposure are dependent on many factors. These include chemical form, the amount, the length of time the individual was exposed, and whether the chromium was ingested, inhaled, or absorbed through the skin. Reactions and their potential effects are highly dependent on such characteristic traits as age, sex, weight, and health of the individual. Chromium 6 is known to cause cancer in humans when inhaled. The hazards of airborne chromium 6 in the workplace environment have been extensively documented. A number of scientific studies have found elevated rates of lung cancer in workers with occupational exposure to chromium 6 by inhalation. A few studies of workers exposed to chromium 6 by inhalation have shown an increase in cancers of the gastrointestinal tract. There is substantial evidence from laboratory studies that chromium 6 can damage DNA and is a mutagen. There is limited evidence from a single laboratory study using mice that oral ingestion of high levels of chromium 6 may cause cancer in the gastrointestinal tract. There continues to be uncertainty in the scientific community whether or not chromium 6 can cause cancer when ingested at levels found in drinking water. Current scientific evidence indicates that chromium 6 is likely to be much more toxic when inhaled than when ingested. Although a drinking water standard has been established, long-term human health effects from consuming water containing more than 50 mg/L of hexavalent chromium have not been identified.
Hexavalent chromium in groundwater and surface water
Hexavalent chromium has been detected in groundwater under private property and elsewhere in the Davis area, as well as many other places. It appears to occur naturally in the soil in this region and is not considered a product of industrial contamination. These levels range from less than 1 mg/L to 180 mg/L.
The following treatment methods have been approved by the Environmental Protection Agency for removing chromium from water: Coagulation/Filtration, Ion Exchange, Reverse Osmosis, Lime Softening.
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