Media Centre World Health Organization/WHO
Fact sheet N°225
May 2010
Key Facts
- Dioxins are a group of chemically-related compounds that are persistent environmental pollutants.
- Dioxins
are found throughout the world in the environment and they accumulate
in the food chain, mainly in the fatty tissue of animals.
- More
than 90% of human exposure is through food, mainly meat and dairy
products, fish and shellfish. Many national authorities have programmes
in place to monitor the food supply.
- Dioxins
are highly toxic and can cause reproductive and developmental
problems, damage the immune system, interfere with hormones and also
cause cancer.
- Due to the omnipresence of dioxins,
all people have background exposure, which is not expected to affect
human health. However, due to the highly toxic potential of this class
of compounds, efforts need to be undertaken to reduce current
background exposure.
- Prevention or reduction of human exposure
is best done via source-directed measures, i.e. strict control of
industrial processes to reduce formation of dioxins as much as
possible.
Background
Dioxins
are environmental pollutants. They have the dubious distinction of
belonging to the “dirty dozen” - a group of dangerous chemicals known
as persistent organic pollutants. Dioxins are of concern because of
their highly toxic potential. Experiments have shown they affect a
number of organs and systems. Once dioxins have entered the body, they
endure a long time because of their chemical stability and their
ability to be absorbed by fat tissue, where they are then stored in the
body. Their half-life in the body is estimated to be seven to eleven
years. In the environment, dioxins tend to accumulate in the food
chain. The higher in the animal food chain one goes, the higher the
concentration of dioxins.
The chemical name for dioxin is:
2,3,7,8- tetrachlorodibenzo para dioxin (TCDD). The name "dioxins" is often used for the family of structurally and chemically related
polychlorinated dibenzo para dioxins (PCDDs) and
polychlorinated dibenzofurans (PCDFs).
Certain dioxin-like polychlorinated biphenyls (PCBs) with similar
toxic properties are also included under the term “dioxins”. Some 419
types of dioxin-related compounds have been identified but only about
30 of these are considered to have significant toxicity, with TCDD
being the most toxic.
Sources of dioxin contamination
Dioxins
are mainly by products of industrial processes but can also result
from natural processes, such as volcanic eruptions and forest fires.
Dioxins are unwanted by products of a wide range of manufacturing
processes including smelting, chlorine bleaching of paper pulp and the
manufacturing of some herbicides and pesticides. In terms of dioxin
release into the environment, uncontrolled waste incinerators (solid
waste and hospital waste) are often the worst culprits, due to
incomplete burning. Technology is available that allows for controlled
waste incineration with low emissions.
Although formation of
dioxins is local, environmental distribution is global. Dioxins are
found throughout the world in the environment. The highest levels of
these compounds are found in some soils, sediments and food, especially
dairy products, meat, fish and shellfish. Very low levels are found in
plants, water and air.
Extensive stores of PCB-based waste
industrial oils, many with high levels of PCDFs, exist throughout the
world. Long-term storage and improper disposal of this material may
result in dioxin release into the environment and the contamination of
human and animal food supplies. PCB-based waste is not easily disposed
of without contamination of the environment and human populations. Such
material needs to be treated as hazardous waste and is best destroyed
by high temperature incineration.
Dioxin contamination incidents
Many
countries monitor their food supply for dioxins. This has led to early
detection of contamination and has often prevented impact on a larger
scale. One example is the detection of increased dioxin levels in milk
in 2004 in the Netherlands, traced to a clay used in the production of
the animal feed. In another incident, elevated dioxin levels were
detected in animal feed in the Netherlands in 2006 and the source was
identified as contaminated fat used in the production of the feed.
Some dioxin contamination events have been more significant, with broader implications in many countries.
In
late 2008, Ireland recalled many tons of pork meat and pork products
when up to 200 times more dioxins than the safe limit were detected in
samples of pork. This finding led to one of the largest food recalls
related to a chemical contamination. Risk assessments performed by
Ireland indicated no public health concern. The contamination was
traced back to contaminated feed.
In July 2007, the European
Commission issued a health warning to its Member States after high
levels of dioxins were detected in a food additive - guar gum - used as
thickener in small quantities in meat, dairy, dessert or delicatessen
products. The source was traced to guar gum from India that was
contaminated with pentachlorophenol (PCP), a pesticide no longer in
use. PCP contains dioxins as contamination.
In 1999, high levels
of dioxins were found in poultry and eggs from Belgium. Subsequently,
dioxin-contaminated animal-based food (poultry, eggs, pork), were
detected in several other countries. The cause was traced to animal
feed contaminated with illegally disposed PCB-based waste industrial
oil.
In March 1998, high levels of dioxins in milk sold in Germany
were traced to citrus pulp pellets used as animal feed exported from
Brazil. The investigation resulted in a ban on all citrus pulp imports
to the EU from Brazil.
Another case of dioxin contamination of
food occurred in the United States of America in 1997. Chickens, eggs,
and catfish were contaminated with dioxins when a tainted ingredient
(bentonite clay, sometimes called “ball clay”) was used in the
manufacture of animal feed. The contaminated clay was traced to a
bentonite mine. As there was no evidence that hazardous waste was
buried at the mine, investigators speculate that the source of dioxins
may be natural, perhaps due to a prehistoric forest fire.
Large
amounts of dioxins were released in a serious accident at a chemical
factory in Seveso, Italy, in 1976. A cloud of toxic chemicals,
including 2,3,7,8-Tetrachlorodibenzo-p-dioxin, or TCDD, was released
into the air and eventually contaminated an area of 15 square
kilometres where 37 000 people lived. Extensive studies in the affected
population are continuing to determine the long-term human health
effects from this incident. These investigations, however, are hampered
by the lack of appropriate exposure assessments. A minor increase in
certain cancers and effects on reproduction have been detected and are
being further investigated. Possible effects on the children of exposed
people are currently being studied.
TCDD has also been
extensively studied for health effects linked to its presence as a
contaminant in some batches of the herbicide Agent Orange, which was
used as a defoliant during the Vietnam War. A link to certain types of
cancers and also to diabetes is still being investigated.
Earlier
incidents of food contamination have been reported in other parts of
the world. Although all countries can be affected, most contamination
cases have been reported in industrialized countries where adequate
food contamination monitoring, greater awareness of the hazard and
better regulatory controls are available for the detection of dioxin
problems.
A few cases of intentional human poisoning have also
been reported. The most notable incident is the 2004 case of Viktor
Yushchenko, President of the Ukraine, whose face was disfigured by
chloracne.
Effects of dioxins on human health
Short-term
exposure of humans to high levels of dioxins may result in skin
lesions, such as chloracne and patchy darkening of the skin, and
altered liver function. Long-term exposure is linked to impairment of
the immune system, the developing nervous system, the endocrine system
and reproductive functions. Chronic exposure of animals to dioxins has
resulted in several types of cancer. TCDD was evaluated by the WHO’s
International Agency for Research on Cancer (IARC) in 1997. Based on
animal data and on human epidemiology data, TCDD was classified by IARC
as a "known human carcinogen”. However, TCDD does not affect genetic
material and there is a level of exposure below which cancer risk would
be negligible.
Due to the omnipresence of dioxins, all people
have background exposure and a certain level of dioxins in the body,
leading to the so-called body burden. Current normal background
exposure is not expected to affect human health on average. However,
due to the high toxic potential of this class of compounds, efforts
need to be undertaken to reduce current background exposure.
Sensitive subgroups
The
developing fetus is most sensitive to dioxin exposure. The newborn,
with rapidly developing organ systems, may also be more vulnerable to
certain effects. Some individuals or groups of individuals may be
exposed to higher levels of dioxins because of their diets (e.g., high
consumers of fish in certain parts of the world) or their occupations
(e.g., workers in the pulp and paper industry, in incineration plants
and at hazardous waste sites, to name just a few).
Prevention and control of dioxin exposure
Proper
incineration of contaminated material is the best available method of
preventing and controlling exposure to dioxins. It can also destroy
PCB-based waste oils. The incineration process requires high
temperatures, over 850°C. For the destruction of large amounts of
contaminated material, even higher temperatures - 1000°C or more - are
required.
Prevention or reduction of human exposure is best done
via source-directed measures, i.e. strict control of industrial
processes to reduce formation of dioxins as much as possible. This is
the responsibility of national governments, but in recognition of the
importance of this approach, the Codex Alimentarius Commission adopted
in 2001 a Code of Practice for Source Directed Measures to Reduce
Contamination of Foods with Chemicals (CAC/RCP 49-2001), and in 2006 a
Code of Practice for the Prevention and Reduction of Dioxin and
Dioxin-like PCB Contamination in Food and Feeds (CAC/RCP 62-2006).
More
than 90% of human exposure to dioxins is through the food supply,
mainly meat and dairy products, fish and shellfish. Consequently,
protecting the food supply is critical. One approach includes, as
mentioned above, source-directed measures to reduce dioxin emissions.
Secondary contamination of the food supply needs to be avoided
throughout the food-chain. Good controls and practices during primary
production, processing, distribution and sale are all essential to the
production of safe food.
Food contamination monitoring systems
must be in place to ensure that tolerance levels are not exceeded. It
is the role of national governments to monitor the safety of food
supply and to take action to protect public health. When incidents of
contamination are suspected, countries should have contingency plans to
identify, detain and dispose of contaminated feed and food. The
exposed population should be examined in terms of exposure (e.g.
measuring the contaminants in blood or human milk) and effects (e.g.
clinical surveillance to detect signs of ill health).
What should consumers do to reduce their risk of exposure?
Trimming
fat from meat and consuming low fat dairy products may decrease the
exposure to dioxin compounds. Also, a balanced diet (including adequate
amounts of fruits, vegetables and cereals) will help to avoid
excessive exposure from a single source. This is a long-term strategy
to reduce body burdens and is probably most relevant for girls and
young women to reduce exposure of the developing fetus and when
breastfeeding infants later on in life. However, the possibility for
consumers to reduce their own exposure is somewhat limited.
What does it take to identify and measure dioxins in the environment and food?
The
quantitative chemical analysis of dioxins requires sophisticated
methods that are available only in a limited number of laboratories
around the world. These are mostly in industrialized countries. The
analysis costs are very high and vary according to the type of sample,
but range from over US$ 1700 for the analysis of a single biological
sample to several thousand US dollars for the comprehensive assessment
of release from a waste incinerator.
Increasingly, biological
(cell- or antibody) -based screening methods are being developed. The
use of such methods for food samples is not yet sufficiently validated.
Nevertheless, such screening methods will allow more analyses at lower
cost. In case of a positive screening test, confirmation of results
must be carried out via more complex chemical analysis.
WHO activities related to dioxins
Reducing
dioxin exposure is an important public health goal for disease
reduction, also with respect to sustainable development. In order to
give guidance on acceptable levels of exposure, WHO has held a series
of expert meetings to determine a tolerable intake of dioxins to which a
human can be exposed throughout life without harm.
In the
latest of such expert meetings held in 2001, the Joint FAO/WHO Expert
Committee on Food Additives (JECFA) performed an updated comprehensive
risk assessment of PCDDs, PCDFs, and “dioxin-like” PCBs. The experts
concluded that a tolerable intake could be established for dioxins on
the basis of the assumption that there is a threshold for all effects,
including cancer. The long half-lives of PCDDs, PCDFs and “dioxin-like”
PCBs mean that each daily ingestion has a small or even a negligible
effect on overall intake. In order to assess long- or short-term risks
to health due to these substances, total or average intake should be
assessed over months, and the tolerable intake should be assessed over a
period of at least one month. The experts established a provisional
tolerable monthly intake (PTMI) of 70 picogram/kg per month. This level
is the amount of dioxins that can be ingested over lifetime without
detectable health effects.
WHO, in collaboration with the Food and
Agriculture Organization (FAO), through the joint FAO/WHO Codex
Alimentarius Commission, has established a ‘Code of Practice for the
Prevention and Reduction of Dioxin and Dioxin-like PCB Contamination in
Foods and Feed’. This document gives guidance to national and regional
authorities on preventive measures. The establishment of Codex
guideline levels for dioxins in foods is under consideration.
Since
1976, WHO has been responsible for the Global Environment Monitoring
System’s Food Contamination Monitoring and Assessment Programme.
Commonly known as GEMS/Food, the programme provides information on
levels and trends of contaminants in food through its network of
participating laboratories in over 70 countries around the world.
Dioxins are included in this monitoring programme.
Since 1987, WHO
has conducted periodic studies on levels of dioxins in human milk,
mainly in European countries. These studies provide an assessment of
human exposure to dioxins from all sources. Recent exposure data
indicate that measures introduced to control dioxin release in a number
of countries have resulted in a substantial reduction in exposure to
these compounds over the past two decades.
WHO is now working with
the United Nations Environmental Programme (UNEP) on the
implementation of the ‘Stockholm Convention’, an international
agreement to reduce emissions of certain persistent organic pollutants
(POPs), including dioxins. A number of actions are being considered
internationally to reduce the production of dioxins during incineration
and manufacturing processes. In responding to the needs of the
Stockholm Convention on POPs, the WHO GEMS/Food has developed a new
protocol for a Global Survey of Human Milk for POPs in order to meet
the health, food safety and environmental objectives of WHO, UNEP and
their member countries. This protocol will assist national and regional
authorities to collect and analyse representative samples in order to
assess the current state of background exposure and in the future to
assess the effectiveness of measures taken to reduce exposure.
Dioxins
occur as a complex mixture in the environment and in food. In order to
assess the potential risk of the whole mixture, the concept of toxic
equivalence has been applied to this group of contaminants. TCDD, the
most toxic member of the family, is used as reference compound, and all
other dioxins are assigned a toxic potency relative to TCDD, based on
experimental studies. During the last 15 years, WHO, through the
International Programme on Chemical Safety (IPCS), has established and
regularly re-evaluated toxic equivalency factors (TEFs) for dioxins and
related compounds through expert consultations. WHO-TEF values have
been established which apply to humans, mammals, birds and fish. The
last such consultation was held in 2005 to update human and mammalian
TEFs. These international TEFs have been developed for application in
risk assessment and management, and have been adopted formally by a
number of countries and regional bodies, including Canada, Japan, the
United States and the European Union.
For more information contact:
WHO Media centre
Telephone: +41 22 791 2222
E-mail: mediainquiries@who.int
