2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a colourless to white crystalline solid. It belongs to the chlorinated dibenzo-p-dioxins (CDDs) group, which is a group of hydrocarbons that are similar in structure and occur as contaminants in chemical production, or as by-products of industrial emissions and combustion.[2,3] TCDD, a persistent environmental chemical, is considered to be one of the most toxic compounds in the group.[3,4] TCDD may also be referred to as 2,3,7,8-TCDD, TCDBD, dioxin, or tetradioxin.[2,4] There are numerous other synonyms and product names; see the Hazardous Substances Data Bank (HSDB) for more information.
TCDD is classified by the International Agency for Research on Cancer (IARC) as Group 1, carcinogenic to humans. Epidemiological studies in humans found increased risk for overall cancer, lung cancer, and non-Hodgkin lymphoma. Studies in experimental animals showed that TCDD causes tumours at various tissue sites in multiple species.
Other health effects following exposure to TCDD include chloracne (characterized by acne-like lesions on the face and upper body), liver damage, developmental effects, and function impairment in the immune, endocrine and reproductive systems.[3,6]
No occupational exposure limits for TCDD were found in Canada or the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV). TCDD is listed as a designated substance in Nunavut and Saskatchewan.
Canadian Environmental Guidelines
Ontario Ambient Air Quality Criteria
MAC = maximum allowable concentration
TEF = WHO Toxic Equivalency Factor
*Standard is specific for total trihalomethanes. Sum of the concentrations of bromodichloromethane (BDCM), dibromochloromethane (DBCM), bromoform (tribromomethane), and chloroform (trichloromethane) must not exceed the standard specified
TCDD was not included in other Canadian government environmental guidelines reviewed.[9-13,15]
Schedule 1, paragraph (a) (c)
National Classification System for Contaminated Sites
Rank: "High hazard"
* CEPA = Canadian Environmental Protection Act. Designation is for polychlorinated dibenzodioxins and polychlorinated dibenzofurans, which includes TCDD. Dioxins and furans have also been classified as Track 1 substances under CEPA, which means they are targeted for virtual elimination. Industries participating in the reduction strategy include the forest products industry, incineration, steel manufacturing, and wood preservation sectors.
TCDD was not included in other Canadian government chemical listings reviewed.[19-21]
TCDD is used for research purposes, but has no other commercial applications.[2,4] TCDD and/or other CDDs also occur as contaminants or by-products in chemical production (such as for chlorophenoxy herbicides), chlorine bleaching at pulp and paper mills, PCB-filled electrical transformer fires, and pentachlorophenol production for wood preservation.[2-4]
Canadian Production and Trade
No quantitative information on Canadian commercial production and trade was found for TCDD in Camford Information Services profiles or the TradeMap database.[22,23]
Inhalation and dermal contact are the most important routes of occupational exposure.
Main industries where CDDs may be present include waste incineration, fire-fighting, chemical research, paper bleaching, production and use of chlorinated compounds, and chlorophenoxy herbicide production, use, and disposal. Occupationally exposed individuals show higher blood levels of CDDs compared to the general public.
CAREX Canada has not prioritized TCDD for exposure estimate development. This is because the likelihood of exposure in Canadian workers is very low.
The primary source of 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.[6,17] 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.
For more information, see the CAREX Canada environmental exposure estimates for TCDD. 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)
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.
Our team has performed a detailed scan of exposure control resources and assembled a compilation of key publications and resources. These are organized by type of exposure (environmental or occupational) and by specificity (general or carcinogen-specific). Please visit our Exposures Reduction Resources page to view.
We also recommend exploring the Prevention Policies Directory, a freely-accessible online tool offering information on policies related to cancer and chronic disease prevention. Providing summaries of the policies and direct access to the policy documents, the Directory allows users to search by carcinogen, risk factor, jurisdiction, geographical location, and document type. Click here to learn more about policies specific to TCDD in the Directory. For questions about this resource, please contact a member of the Prevention Team at the Canadian Partnership Against Cancer, at firstname.lastname@example.org.