AQ Monitoring Results:
Crockett: Hexavalent Chromium at John Swett
This page last reviewed September 27, 2010
Chromium is an odorless, steel-gray, hard metal that is lustrous and takes a high polish, which is often seen as bright metallic coating on plastic or metal products such as shower heads or car bumpers. Hexavalent chromium can get into the air as mist if it is in sprayed liquids, dust if solid material containing this chemical is dumped, scooped, or ground, and as fumes during welding or melting of metals containing hexavalent chromium. California has determined under Proposition 65 and Assembly Bill 1807 that hexavalent chromium is a cancer-causing compound. Hexavalent chromium is one type of chromium compounds (with a 6+ oxidation state chromium). The ARB has taken regulatory action to reduce hexavalent chromium emissions.
Exposure to inhaled chromium may result in lung cancer. Non-cancer effects of human exposure to hexavalent chromium by ingestion and inhalation include renal toxicity, gastrointestinal hemorrhage, intravascular hemolysis, contact dermatitis, and skin ulcers. Hexavalent chromium concentrations are usually highest near the sources of emissions. As a result, local exhaust ventilation systems are considered a good way to reduce exposure to people working near emission sources.
Chrome plating, welding, spray painting, leather tanning, and ship/boat building are examples of activities resulting in hexavalent chromium emissions. Chromium is extremely resistant to corrosive agents and is therefore used for surface coating to protect steel or other products. In California, stationary sources contribute 51% emissions, while other mobile sources such as jet aircraft and ships contribute 38%. There is no significant indoor source of hexavalent chromium, and there is no identified natural source of hexavalent chromium.
The ARB adopted an airborne toxic control measure in 1988 to reduce emissions of hexavalent chromium from chrome plating and chromic acid anodizing operations and to prohibit the use of hexavalent chromium in the circulating water of a cooling tower. Based on available data, the 2000 statewide-average ambient hexavalent chromium concentration was approximately 60% lower than that in 1990.
Ambient Monitoring Results
Ambient levels of hexavalent chromium are routinely monitored at approximately twenty sites in the California air toxics monitoring network. The statewide average concentration of hexavalent chromium during 1998-2000 was 0.12 ng/m3 (nanograms per cubic meter), with values ranging from 0.1 ng/m3 to 1.2 ng/m3. The current routine monitor
closest to Crockett is in Fremont. Relative to the statewide average, the Fremont region was 17% lower, with an average concentration of 0.10 ng/m3 for the same time period. In the monitoring done at John Swett through May 2003, most of the values measured for hexavalent chromium were below the limit of detection.
The ambient monitoring results at John Swett are provided here:
- A graph comparing the monthly summaries of hexavalent chromium at the community with historical statewide and regional levels
- A table of summary statistics
- Raw data in Excel format
Cancer risk is the number of excess cancer cases among a million people if the people are exposed to levels of a toxic air pollutant over 70 years. Hexavalent chromium represents approximately 14% of the potential cancer risk of the nine measured compounds, excluding diesel particulate matter. Hexavalent chromium represents approximately 3% of the potential cancer risk of the nine measured compounds and the estimated diesel particulate matter.