TCDD Environmental Exposures
2,3,7,8-Tetrachlorodibenzo-para-dioxin Environmental Exposures
The primary source of 2,3,7,8-Tetrachlorodibenzo-para-dioxin (TCDD) exposure for the general population is by ingesting contaminated foods. CDDs are highly persistent in the environment and accumulate in the food chain, with meat, fish, and dairy products having the highest levels. A secondary source of TCDD exposure may include contaminated drinking water or beverages. However, this is a data gap since no recent data or studies were identified.
Other minor pathways of exposure include inhalation from municipal, medical, and industrial waste incinerators or other combustion processes. The most significant sources of environmental contamination are municipal incinerators, the production and use of pentachlorophenol as a wood preservative, and use of chlorine for bleaching in pulp and paper mills. Other sources include emissions from iron and steel production, various types of fuel burning (including wood, diesel and heating oil), backyard burning of household waste, electric power generation, and tobacco smoke.[2,3] Release data from the National Pollutant Release Inventory (NPRI) for 2014 is summarized in the table below. Natural sources of TCDD release include forest fires and volcanoes.
CAREX Canada’s environmental estimates indicate that TCDD levels in outdoor air do not result in higher risks of cancer (low data quality). It should be noted that no exposure data was available on TCDD concentrations in indoor air.
Searches of environmental and consumer product databases yielded the following results on current potential for exposure to TCDD in Canada:
|Substance name: ‘dioxins and furans – total’|
|Released into Environment||12.33 g TEQ||Pulp and paper mills,|
electric power generation, transmission and distribution,
waste treatment and disposal,
iron and steel mills (243 facilities)
|Disposed of||216.4 g TEQ|
|Sent to off-site recycling||10.98 g TEQ|
g TEQ = grams toxic equivalent
No household products are listed for TCDD in the US Household Products Database.
This map shows predicted levels of TCDD in outdoor air at residential locations by health region in Canada as of 2011. The average (median) concentration of TCDD within the health regions measured in outdoor air for 2011 was 0.00083µg/m3, but concentrations of TCDD 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 TCDD 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 TCDD 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 TCDD 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
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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