Fact sheet: Dioxins and Furans

From: Public Services and Procurement Canada

Discover a list of a contaminant's important chemical properties, how it will react in the environment, main sources of contamination related, and a brief overview of health and safety issues.

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General information

CAS number

1746-01-6 (2,3,7,8-TCDD)
51207-31-9 (2,3,7,8-TCDF)
Not applicable – Family of 210 compounds

Molecular formula

C12H4Cl4O2 (2,3,7,8-TCDD)
C12H4Cl4O (2,3,7,8-TCDF)
Not applicable – Family of 210 compounds

Formula weight

322 g/mol (2,3,7,8-TCDD)
306 g/mol (2,3,7,8-TCDF)
Not applicable – Family of 210 compounds

Family

Chlorinated Organic Compounds

Chemical structure of polychorinated dibenzo-p-dioxins (PCDDs) – 2,3,7,8-TCDD example

Chemical structure of polychlorinated dibenzofurans (PCDFs) – 2,3,7,8-TCDF example

Source : Washington State Department of Ecology, 2016.

Description of the image The image presents 4 graphic representations of chemical structures. The top-left ont is a polychorinated dibenzo-p-dioxins (PCDD). The top-right is an example of 2,3,7,8-TCDD. The bottom-left image is the chemical structure of polychlorinated dibenzofurans (PCDFs) and the bottom-right is for 2,3,7,8-TCDF.

Polychlorodibenzo-p-dioxins (PCDD) and polychlorodibenzo-furanes (PCDF) commonly named dioxins and furans form two distinct families of chlorinated planar tricyclic aromatic hydrocarbons with similar chemical structures and similar physicochemical properties (75 congeners for the PCDD and 135 for the PCDF).

Properties (at room temperature where applicable)

Few investigations have been conducted to determine the physical and chemical properties of the whole PCDD/F family. The different congeners physicochemical properties vary according to their chlorination degree. Nevertheless, 2,3,7,8-TCDD and 2,3,7,8-TCDF physicochemical properties are widely documented.

Compound properties list
ParameterValueComment
Melting/boiling point305-306 °C (2,3,7,8-TCDD)
227-228 °C (2,3,7,8-TCDF)		Solid phase
Relative density1,8 g/cm3 (2,3,7,8-TCDD)Sinks in the water
Vapour pressure1,50 x 10-9 mm Hg (2,3,7,8-TCDD)Low volatility compounds, decreases with rising chlorination degree
Vapour density
Solubility in water1,93 x 10-5 mg/L (2,3,7,8- TCDD),
4,19 x 10-5 mg/L (2,3,7,8- TCDF)
0,135 x 10-5 mg/L (1,2,3,4,6,7,8-HpCDF)		Very low solubility in water, decreasing solubility with rising chlorination degree
Henry's law constant3,29 x 10-5 atm·m3/mol (2,3,7,8-TCDD)
1,65 x 10-5 atm·m3/mol (2,3,7,8-TCDF)		Low volatility compounds when dissolved
log Koc (Depending on soil or sediment characteristics)6,8 (2,3,7,8-TCDD)
6,53 (2,3,7,8-TCDF) 		Increase with a rising number of chlorinated substituents

In the environment, PCDD and PCDF are generally found as a combination of congeners. As these substances do not have the same toxicity, Toxicity Equivalency Factors (TEF) were developed to standardize their toxicity to a toxicologically equivalent amount of 2,3,7,8-TCDD, the most toxic congener. Toxic equivalents of 2,3,7,8-TCDD are usually expressed as TEQ (Toxic Equivalent). The TEQ is calculated with the summation of the product of a given congener and its TEF. The World Health Organization (WHO) developed the TEF for PCDDs and PCDFs as shown below.

Toxicity Equivalency Factors (TEF) for PCDD/F

Compounds TEF (WHO)
Humans/Mammals Fish Birds
Chlorinated Dibenzo-p-dioxins
  • 2,3,7,8-TCDD
  • 1,2,3,7,8-PeCDD
  • 1,2,3,4,7,8-HxCDD
  • 1,2,3,6,7,8-HxCDD
  • 1,2,3,7,8,9-HxCDD
  • 1,2,3,4,6,7,8-HpCDD
  • OCDD
  • 1,0
  • 1,0
  • 0,1
  • 0,1
  • 0,1
  • 0,01
  • 0,001
  • 1,0
  • 1,0
  • 0,5
  • 0,01
  • 0,01
  • 0,001
  • <0,0001
  • 1,0
  • 1,0
  • 0,05
  • 0,01
  • 0,1
  • <0,001
  • 0,0001
Chlorinated Dibenzofurans
  • 2,3,7,8-TCDF
  • 1,2,3,7,8-PeCDF
  • 2,3,4,7,8-PeCDF
  • 1,2,3,4,7,8-HxCDF
  • 1,2,3,6,7,8-HxCDF
  • 1,2,3,7,8,9-HxCDF
  • 2,3,4,6,7,8-HxCDF
  • 1,2,3,4,6,7,8-HpCDF
  • 1,2,3,4,7,8,9-HpCDF
  • OCDF
  • 0,1
  • 0,05
  • 0,5
  • 0,1
  • 0,1
  • 0,1
  • 0,1
  • 0,01
  • 0,01
  • 0,0001
    0,05
  • 0,05
  • 0,5
  • 0,1
  • 0,1
  • 0,1
  • 0,1
  • 0,01
  • 0,01
  • <0,0001
  • 1,0
  • 0,1
  • 1,0
  • 0,1
  • 0,1
  • 0,1
  • 0,1
  • 0,01
  • 0,01
  • 0,0001

Environmental behaviour

In the atmosphere, PCDD/F are generally adsorbed on particles and can be carried over great distances. These compounds can be degraded in the atmosphere through photodegradation and wet or dry depositing (precipitation, deposit, etc.). Although these compounds may undergo photochemical degradation or biodegradation, they are generally very stable and hardly degrade. These substances are mostly adsorbed to soil and sediment due to their hydrophobic nature. In surface water, these compounds are usually sorbed to particles or sediments. PCDD/F finally end in lipid-rich tissues of aquatic organisms. These substances tend to bioaccumulate which leads to detectable levels in animals.

Health and safety

In addition to being bioacumulate and persistent in the environment, PCDD/F are very toxic. Humans are mainly exposed through contaminated food ingestion. This contamination is the result of the accumulation of these substances throughout the food chain and lipid-rich food such as dairy, eggs, meat, and fish. This exposure pathway would represent 90% of the daily exposure to dioxins and furans.

In addition to food ingestion, three PCDD/F exposure sources are possible: dermal contact with certain pesticides and herbicides; contaminated water ingestion; and inhalation. Workers from the pesticide industries, pulp and paper mills and incineration plants may also be exposed to PCDD.

Health effects associated with human exposure to PCDD/F include skin disorders, hepatic disorders or impairment of the immune system, the endocrine system and reproductive functions. Human exposure to dioxins would also have effects on the developing nervous system. The effects associated with these substances depend on many factors including the way a person is exposed, how much and the frequency of exposure.

Principal resources

Even if dioxins and furans may be the result of natural causes such as wildfires and volcanic eruptions, these chemical substances are mainly manmade. They are usually produced unintentionally as by-products of several industrial processes. These processes are, but not limited to:

  • Chemical substance production (for example, chlorophenols or hexachlorobenzene);
  • Herbicides or pesticides production;
  • Pulp chlorine bleaching;
  • Production of dyes and pigments;
  • Waste incineration (municipal, biomedical, sewage sludges);
  • Biomasse combustion (domestic fires);
  • Some metallurgical processes (steel and iron production);
  • Fuel, diesel, farming fuels, burning of heating oil.

Dioxins and furans are exclusively synthesized at a small scale for toxicological investigation purpose. Municipal and medical waste incineration constitute their main emission source in Canada.

A few studies mention the presence of ambient concentration of PCDD/F in the environment not attributable to point sources or anthropogenic contamination. In Canadian soils, the average ambient concentration for PCDD/F is estimated to be 4 nanograms as TEQ per kilogram of soil (ng TEQ kg-1).

References

Agency for Toxic Substances and Disease Registry (ATSDR), 1998. Toxicological Profile for Chlorinated Dibenzo-p-dioxins (CDDs). Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service. 678 pages. (PDF, 10.92 MB)

Agency for Toxic Substances and Disease Registry (ATSDR). 1994. Toxicological Profile for chlorodibenzofurans. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service. 226 pages. (PDF, 3.76 MB)

Canadian Council or Ministers of the Environment. 2002. Canadian Soil Quality Guidelines for the Protection of Environmental and Human Health – Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) dans Canadian Environmental Quality Guidelines, 1999, Winnipeg, Canadian Council or Ministers of the Environment.

Government of Canada, 1990. Canadian Environmental Protection Act. Priority Substances List Assessment Report no. 1. Polychlorinated Dibenzodioxins and Polychlorinated Dibenzofurans. Ottawa; Government of Canada. 64 pages.

United Nations. Dioxin and Furan Inventories. National and Regional Emissions of PCDD/PCDF [Online]. Switzerland: United Nations Environment Programme (UNEP) / Chemicals ; May 1999, 114 pages. (PDF, 538 KB)

Health Canada, 2001. Dioxins and furans [Online]. Ottawa: Health Canada’s Management of Toxic Substances Division, Government of Canada; 2001 (updated on September 2005). 3 pages. (PDF, 60 KB)

Sofian Kanan, Fatin Samara, Dioxins and furans: A review from chemical and environmental perspectives, Trends in Environmental Analytical Chemistry, Volume 17, 2018, pages 1-13.

Ravichandran Rathna, Sunita Varjani, Ekambaram Nakkeeran, Recent developments and prospects of dioxins and furans remediation, Journal of Environmental Management, Volume 223, 2018, pages 797-806.

Washington State Department of Ecology, 2016. Dioxins, furans, and Dioxin-Like PCB Congeners: Ecological Risk Calculation Methodology for Upland Soil: Implementation Memorandum No. 13. Publication No. 16-09-044 (July 2016). (PDF, 569 KB)

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