What are dioxins?
The dioxins are a ubiquitous group of environmental pollutants which have many undesirable health impacts, brought about by their long persistence in the body and in the environment. The main exposure is through food although exposure to airborne dioxins is also possible, particularly for those living near waste management facilities that are not well controlled or monitored.
The full name for the parent compound, dioxin itself, is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The term 'dioxins' refers to TCDD and a number of structurally and chemically related organic compounds. The polychlorinated biphenyls (PCBs) are often included under the dioxin umbrella because they have similar properties.
Why are airborne dioxins a concern?
Dioxins are long-lived. Their half life in the body is 7-11 years and, thus, there is no question of their being excreted rapidly like many other substances we inhale or ingest in everyday life. In the environment, dioxins tend to accumulate in the food chain. Experiments have shown that dioxins can affect many organs and systems and their long presence in the body means they have plenty of time to do so. There are actually around 420 different types of dioxin but only 30 are known to be toxic, with TCDD being the most toxic.
How are dioxins produced?
Dioxins enter the environment mainly through industrial processes, although some are produced naturally – by volcanic eruption and forest fires, for instance. Dioxins are emitted by the following industries:
- Paper and pulp (through chlorine bleaching)
- Herbicide and pesticide manufacture
- Smelting of metal ores
- Waste incineration
PCBs were once widely used as a coolant in the electricity supply industry and as a plasticiser in a number of applications. Their toxic effects have been known since the early 1970s and they are linked to cancer in humans. Therefore, a gradual ban on production and use was introduced in the years following and the problem now is where old supplies of PCBs are stored and persistent residues in the environment. Where these are not properly monitored or disposed of, there is a continuing risk of exposure to airborne dioxins.
Dioxins are globally distributed, even though they are produced locally. Highest levels are found in some soils, sediments and foods, especially dairy products, meat, fish and shellfish. Lower levels are found in plants, water and air.
What are the effects of dioxins on health?
Short-term exposure to high levels of airborne dioxins results in a disfiguring skin condition called chloracne and impaired liver function. Long-term exposure to airborne dioxins affects the immune system, the developing nervous system, the endocrine system and reproductive functioning. In animal experiments, dioxin exposure leads to several types of cancer.
The International Agency for Research on Cancer evaluated TCDD in 1997 and came to the conclusion that dioxins is a 'known human carcinogen'. However, it is thought that there is a lower limit below which health effects and cancer risk are likely negligible. Since dioxins are ubiquitous, we all have a certain level of this pollutant existing in our bodies. Normal background exposure is not likely to pose a particular hazard.
Some groups may be particularly sensitive to the health impact of dioxins, including:
- The developing foetus with its rapidly developing organ systems
- High consumers of fish in certain parts of the world
- Pulp and paper industry workers
- Incineration plant workers
- Hazardous waste site workers
Have there been serious incidents involving dioxins in the past?
In many countries, including the UK, food is routinely monitored for the presence of dioxins. This is useful as an early warning sign and may prevent wider and more serious exposure of the population. There have been a number of incidents:
- In 2008, Ireland recalled pork containing more than 200 times more dioxins than the safe limits (one of the largest food recalls involving chemical contamination).
- In 2007, the European Commission issued a warning about high levels of dioxins found in guar gum, a food additive. In this case, the produce had been imported from India and had been contaminated with the pesticide pentachlorophenol, which contains dioxins as a contaminant.
- In 1976, a large cloud of chemicals, including TCD, was released during a factory accident in Seveso, Italy. The population of 37,000 people who may have been affected is still being monitored and some minor increases in certain cancers have been noted, along with effects on reproduction.
What can people do to protect themselves from airborne dioxins exposure?
Strict control of industrial processes to reduce formation of dioxins is essential. Where waste incineration is involved, it is incomplete combustion that leads to dioxin formation – therefore technology which allows for complete combustion must be used. Such facilities need regular monitoring of airborne emissions. In the paper and pulp industry, replacing chlorine-based processes with oxygen bleaches reduces dioxin emissions. Appropriate filtration should be installed to secure the safety of employees and other people that might visit the facility.
Apart from those living near poorly controlled waste incineration facilities, and other industrial processes that may be emitting airborne dioxins who may be subject to exposures, for most people exposure is through food. A balanced diet, low in fat, is probably the best way of reducing dioxin exposure through this route. If you live near a waste incineration facilities, you should consider using appropriate gas and particulate filtration.