Chromium (Hexavalent) Environmental Exposures
Chromium (Hexavalent) Environmental Exposures
Surface water is contaminated with chromium [VI] in many parts of Canada. Total chromium in Canadian drinking water is typically less than 5 µg/L.[1,2] Mean or median total chromium concentrations from rivers and streams in British Columbia, Alberta, Ontario, and Quebec were found to be between 4 – 7 µg/L, with 10 – 60% of the chromium as chromium [VI]. Total chromium levels in unpolluted surface water are typically below 1 µg/g. CAREX Canada’s estimates indicate that chromium [VI] levels in drinking water may result in an increased risk of cancer at a population level (moderate data quality).
Average levels of chromium [VI] in air near industrial areas may be 10 – 45 times higher than those in non-industrial areas. CAREX Canada estimates that exposures to chromium [VI] in outdoor air likely do not result in an increased risk of cancer (very low data quality). A data gap (moderate priority) was identified for chromium [IV] in indoor air.
Only monitoring data for total chromium concentration are available for soil. Total chromium levels in soil vary widely from 5 – 1,500 mg/kg, depending on the type of rock from which the soil formed and the presence of nearby industrial activities. Soil near wood preservation plants, which use hexavalent chromium, had 25 times more total chromium content than uncontaminated soil. Chromium [VI] may also leach into surrounding soil via treated wood structures such as building foundations, railroad ties, and decks.[2,3]
Searches of Environment Canada’s National Pollutant Release Inventory (NPRI) yielded the following results on current potential for exposure to hexavalent chromium in Canada:
NPRI Reported Releases
|Search Term:||‘Hexavalent chromium (and its compounds)’|
|Released into Environment||2.36 t||Power generation, pulp and paper,
metal plating, various manufacturing,
waste treatment (184 facilities)
|Disposed of||528 t|
|Sent to off-site recycling||97 t|
t = tonne
This map shows predicted levels of hexavalent chromium in outdoor air at residential locations by health region in Canada as of 2011. The average (median) concentration of hexavalent chromium within the health regions measured in outdoor air for 2011 was 0.00021 µg/m3, but concentrations of hexavalent chromium can be higher or lower than average in many locations. Concentrations should be compared to the applicable jurisdictional guidelines and standards for ambient air quality based on chronic, carcinogenic effects (or non-carcinogenic effects, if cancer is not the point of interest).
Predicted annual average hexavalent chromium concentrations in outdoor air at residential locations by health region, 2011
*Measured at the National Air Pollution Surveillance (NAPS) monitors in 2011
Cancer Risk Estimates
Potential lifetime excess cancer risk (LECR) is an indicator of Canadians’ exposure to known or suspected carcinogens in the environment. When potential LECR is more than 1 per million in a single pathway, a more detailed risk assessment may be useful for confirming the need to reduce individual exposure. If measured levels of hexavalent chromium in relevant exposure pathways (outdoor air, indoor air, indoor dust, drinking water, and food and beverages) decrease, the risk will also decrease.
Potential LECR is calculated by multiplying lifetime average daily intake (the amount inhaled or ingested) by a cancer potency factor or unit risk factor. More than one cancer potency factor may be available, because agencies interpret the underlying health studies differently, or use a more precautionary approach. Our results use cancer potency factors from Health Canada, the US Environmental Protection Agency (US EPA), and/or the California Office of Environmental Health Hazard Assessment (OEHHA).
The calculated lifetime daily intake and LECR results for hexavalent chromium are provided in the tables below. For more information on supporting data and sources, click on the Methods and Data tab below.
Calculated Lifetime Daily Intake
Lifetime Excess Cancer Risk (per million people)
*LECR based on average intake x cancer potency factor from each agency
Compare substances: Canadian Potential Lifetime Excess Cancer Risk, 2011
The data in this table are based on average intake and Health Canada’s cancer potency factor, assuming no change in measured levels. When Health Canada values are not available, United States Environmental Protection Agency values are used.
Click the second tab to view LECR data.
**Exposure not applicable: For indicated pathways, substance not present, not carcinogenic, or exposure is negligible
**Gap in data: No cancer potency factor or unit risk factor, or no data available
IARC Group 1 = Carcinogenic to humans, IARC Group 2A = Probably carcinogenic to humans, IARC Group 2B = Possibly carcinogenic to humans
NOTE: Chromium (hexavalent) estimates assume that 5% of total chromium measured in outdoor air is hexavalent and 8% total chromium measured in indoor dust is hexavalent.
Potential LECR assumes exposure occurs at the same level, 24 hours per day, for 70 years. This is rarely true for any single individual, but using a standard set of assumptions allows us to provide a relative ranking for known and suspected carcinogens across different exposure routes. While ongoing research continually provides new evidence about cancer potency and whether there is a safe threshold of exposure, our approach assumes there are no safe exposure levels.
Methods and Data
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