What type of substance is it?
Dioxin are a family of complex chemicals containing chlorine, known as polychlorinated-p-dioxins (PCDDs) and the related furans (PCDFs). There are several hundred dioxin substances. Some dioxin-type compounds are toxic at very low levels. The most toxic is 2,3,7,8-tetrachloro-dibenzo-p-dioxin, which is often referred to 2,3,7,8-TCDD, or just TCDD.
How is it released?
PCDDs and PCDFs have never been intentionally manufactured on an industrial scale but are formed inadvertently by a number of human activities. They are also formed by several natural processes. Man-made sources of PCDDs and PCDFs include burning of fuels and wastes, metallurgical processing and pulp and paper processing. Dioxins have also been recorded as trace contaminants of certain chlorine containing chemicals. Traces are also found in cigarette smoke. Natural sources include forest fires and volcanoes.
Detailed information
Scientific name:
Polychlorinated dibenzo-p-dioxins (PCDDs - 75 compounds), polychlorinated dibenzofurans (PCDFs - 135 compounds).
Other names:
'Dioxin' is the generic term for two groups of closely related substances : the polychlorinated -p - dioxins (PCDDs) and the polychlorinated dibenzofurans (PCDFs).
CAS Number:
Not available - applies only to single substance
Because dioxins are formed in many types of uncontrolled combustion processes, there have been emissions to the environment throughout geological time, although natural sources such as forest fires and volcanoes are thought to contribute relatively little to present day background levels. Exposure levels have declined considerably in the UK since the 1970s when dioxins were first recognised as highly toxic chemicals and actions to reduce pollution were introduced. In the UK, exposure fell by 71% between 1982 and 1992, largely due to the reduction in emissions from waste incinerators. Dioxins are highly persistent trace chemicals found in soils, sediment in freshwater and the sea, plants and animals - including humans. They belong to the family of chemicals known as 'Persistent Organic Pollutants' (POPs), which are subject to international treaty agreements to reduce exposure. POPs are characterised by their resistance to decomposition (persistence), their ability to concentrate through the food chain (bioaccumulation) and toxicity.
PCDD/Fs have never been intentionally manufactured, other than for research and analytical purposes. They therefore have no other uses.
PCDD/Fs are crystalline solids, virtually insoluble in water, but readily soluble in organic solvents, fats and oils.
Where is it released?
The most significant sources of release to the air include accidental fires and open burning of agricultural wastes, iron and steel works, power stations and vehicles. Incineration of waste used to be the biggest single source of emissions into the atmosphere in the UK but has declined as older incinerators have been closed. Modern incinerators are equipped with flue-gas cleaning technology required to achieve an emission limit of 0.1 nanogram I-TEQ (i.e. one thousand millionth of a gram) of dioxin per cubic meter of stack gas.
Local environmental effects
Once released into the atmosphere, dioxins exist both in the gas phase and bound to tiny particles. They eventually deposit onto soil and vegetation. Being highly insoluble in water, dioxins bound to soils or sediments and are resistant to leaching out, and degrade very slowly, so persisting for many years. Dioxins deposited onto grass (and to a lesser extent, soil) may be taken up by livestock and enter the human food chain in milk and meat. Dioxins in aquatic sediments can also enter the human food chain via fish. A wide range of toxicological effects have been observed in wildlife experimentally exposed to dioxins. They range from chronic to acute effects and include reduction in reproductive success, growth defects, suppression of the immune system and development of cancer.
Global environmental effects
Dioxins may be transported for many thousands of kilometres from their original site of release by the processes of evaporation / re-suspension and re-deposition from the atmosphere, leading to a net transfer from warm parts of the world to the cold polar regions. Dioxins bound onto soil particles can be transported large distances in rivers to deposit in freshwater and marine sediments.
Possible health concerns
Excessive exposure to dioxins may affect the heart, immune system, liver, skin, thyroid gland and the unborn child, and may cause cancer. The Environment Agency aims to ensure that environmental exposures are too low to harm human health.
Legislation
Why was this substance selected for the Pollution Inventory?
Included in : European Pollutant Emission Register (EPER) reporting requirements; United Nations Economic Commission for Europe (UNECE) Convention on Long-Range Transboundary (LRTAP) reporting requirements; Environment Agency categorisation as a hazardous Volatile Organic Compound (VOC).
Standard risk phrases for the pure substance
The standard risk phrases provided here are generally those used by suppliers of chemicals to describe substances - for example on packaging materials. The most important source of these phrases are the CHIP Regulations - Chemicals (Hazard Information and Packaging for Supply) - provided by the Health and Safety Executive. Some substances do not have CHIP risk phrases and in these circumstances we have used other risk phrases, the sources of which are indicated.
Because this is a large family of chemicals rather than a single substance, it is not possible to provide risk phrases, which are generally provided for a single substance whose properties can be precisely determined.
Controlling legislation and international agreements
In the UK dioxin releases are controlled under the Pollution Prevention and Control Regulations. The proposed new European incineration directive (COM(1999) 330 final) will replace three existing directives on the incineration of municipal and hazardous waste, amongst other things, setting a maximum emission limit of 0.1 nanograms I-TEQ of dioxins per normal cubic metre of stack gas. Releases of dioxins above a certain threshold are subject to recording in the European Pollution Emission Register (EPER) under the IPCC Directive (96/61/EC. Control of dioxin releases is subject to international treaty as a protocol under the UNECE Convention on Long-range Transboundary Air Pollutants (LRTAP), to which the UK is a signatory. Dioxins will also be controlled by international treaty under the UNEP POPs Convention, which will eventually be implemented as a legally-binding global agreement to reduce risks to human health and the environment from POPs (Persistent Organic Pollutants). Dioxin is listed as a substance for priority action on its control under the OSPAR and Helsinki Conventions.
These factsheets have been compiled to provide users with information on the Pollution Inventory substances and represent our best efforts to summarise a large number of disparate and sometimes conflicting data sources. We emphasise that this information describes potential hazards rather than actual effects and that the Environment Agency seeks to regulate releases to minimise emissions and hence any risk of detrimental effects occurring.
