Polychlorinated dioxins and furans

Substance name	Polychlorinated dioxins and furans
CASR number	Not applicable
Molecular formula	Not applicable. This is a class of substances. The most toxic and widely studied is C12H4Cl4O2 2,3,7,8-tetrachlorodibenzodioxin (CAS 1746-01-6)
Synonyms	2,3,7,8-Tetrachlorodibenzodioxin; dioxin; TCDD; 2,3,7,8-tcdd; 2,3,7,8-T4CDD; 2,3,7,8-tetrachlorodibenzo[b,e][1,4]dioxin; TCDBD; dibenzo-dioxin, 2,3,7,8-tetrachlorinated; 2,3,7,8-tetrachlorodibenzo-1,4-dioxin; tetrachlorodibenzodioxin; tetradioxin; tetrachlorodibenzo-1,4-dioxin Polychlorinated dibenzo-p-dioxins (PCDDs) Polychlorinated dibenzofurans (PCDFs) Chlorinated dibenzo-p-dioxins (CDDs)

Physical and chemical properties

In the pure form, dioxins are crystals or colourless solids. They are generally present as mixtures containing a number of individual components. 2,3,7,8-TCDD is odourless; the odours of the other dioxins are not known. There are 75 compounds in the dioxin family and 135 compounds in the furan family. They have varying degrees of toxicity; the most toxic is 2,3,7,8-TCDD.

Melting point	305-306°C
Thermal decomposition	700°C

Other compounds in these families will have differing properties, depending on the number and position of chlorine atoms in the molecule.

Dioxins and furans are chemically classified as halogenated aromatic hydrocarbons. The most widely studied compound is 2,3,7,8-TCDD, which is often referred to simply as dioxin and is the reference for a number of compounds which are similar structurally and have dioxin-like toxicity. In general, the compounds have low water solubility and low vapour pressure; many are very stable and tend to bioaccumulate. There are also a number of dioxin-like PCBs, polybrominated biphenyls and mixed chlorinated and brominated congeners with dioxin-like properties.

Compounds in these families will have differing properties, depending on the number and position of chlorine atoms in the molecule.

Common uses Dioxins and furans are not manufactured intentionally other than for research. Their relevance to public and environmental health in Australia stems from their generation in small concentrations as byproducts of chemical manufacture and incomplete combustion.

Sources of emissions

Point sources The principal sources of dioxins are:

• combustion and incineration sources (emissions to air can result from the incineration of solid waste, sewage sludge and hospital wastes; high-temperature steel production, smelting operations and scrap metal recovery furnaces; and the burning of coal, wood petroleum products and used tires for energy generation);
• chemical manufacturing and processing (the manufacture of chlorine and chlorinated organic compounds may result in emissions to air or water); and
• industrial and municipal processes (including chlorinated bleaching processes used in pulp and paper production and in some cases municipal sewerage sludge) that may result in emissions to water (dioxins may also be formed in water during the chlorination of waste and drinking water treatment plants).

Diffuse sources, and point sources included in aggregated emissions data Dioxins and furans are ubiquitous and can be found in a wide range of environments and organisms, though normally in very small quantities. The persistent and hydrophobic nature of dioxins mean that they can accumulate in soils, sediments, organic matter and waste disposal sites. Disturbance of these sites (eg dredging) may re-release the dioxins.

Natural sources Dioxins may occur in natural fires.

Mobile sources Dioxins may be formed during the combustion of automotive fuel.

Consumer products that may contain polychlorinated dioxins and furans Dioxins may be present in products such as some pesticides where they are an inadvertent contaminant produced during the manufacturing process. They may be present in food substances due to contamination in the food chain.

Health effects

How might I be exposed to polychlorinated dioxins and furans? Eating food, primarily meat, dairy products, and fish, makes up more than 90% of the intake of dioxins for the general population. In addition, people may be exposed through breathing low levels in air or drinking low levels in water, or through skin contact with certain pesticides and herbicides. People may also be exposed by living near an uncontrolled hazardous waste site containing dioxins or incinerators releasing dioxins, or by working in industries involved in producing certain pesticides containing dioxins as impurities, working at paper and pulp mills, or operating incinerators.

By what pathways might polychlorinated dioxins and furans enter my body? Through breathing, ingestion or absorption through the skin.

Health guidelines There are no national guidelines.

What effect might polychlorinated dioxins and furans have on my health? The most noted health effect in people exposed to large amounts of 2,3,7,8-TCDD is chloracne, a severe skin disease with acne-like lesions that occur mainly on the face and upper body. Other skin effects noted in people exposed to high doses of 2,3,7,8-TCDD include skin rashes, discolouration, and excessive body hair. There may also be changes in blood and urine that may indicate liver damage. Exposure to high concentrations of dioxin may induce long-term alterations in glucose metabolism and subtle changes in hormonal levels. In some animal species, 2,3,7,8-TCDD is especially harmful and can cause death after a single exposure. Exposure to lower levels can cause a variety of effects in animals (eg weight loss, liver damage, and disruption of the endocrine system). In many species of animals, 2,3,7,8-TCDD weakens the immune system and causes a decrease in the system's ability to fight bacteria and viruses. In other animal studies, exposure to 2,3,7,8-TCDD has caused reproductive damage and birth defects. Some animal species exposed to dioxins during pregnancy had miscarriages, and the offspring of animals exposed to 2,3,7,8-TCDD during pregnancy often had severe birth defects, including skeletal deformities, kidney defects and weakened immune responses.

Several studies suggest that exposure to 2,3,7,8-TCDD increases the risk of several types of cancer in people. Animal studies have also shown an increased risk of cancer from exposure to 2,3,7,8-TCDD. The World Health Organization and the United States Department of Health and Human Services have determined that 2,3,7,8-TCDD is a human carcinogen.

Environmental effects

Environmental fate When released into the air, some dioxins may be transported long distances, even around the globe. When released in wastewater, some dioxins are broken down by sunlight and some evaporate to air, but most attach to soil and settle to the bottom sediment in water. CDD concentrations may build up in the food chain, resulting in measurable levels in animals.

Environmental transport Dioxins may be transported by air and water and in soils and sediments.

Environmental guidelines There are no national guidelines.

What effect might polychlorinated dioxins and furans have on the environment? Dioxins are very toxic to certain animals. Studies have shown dioxins to have a range of adverse effects on a wide number of animals. Dioxins are known to bioaccumulate and, therefore tend to be concentrated in the food chain.