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Scientific Background and Terminology
Dioxins refer to a group of chemical compounds that share certain
chemical structures and biological characteristics. Sometimes the term
dioxin is used to specifically refer to 2,3,7,8-tetrachlorodibenzo-p-dioxin
(TCDD), which is the most studied and one of the most toxic of the
dioxins group of chemicals. The family of dioxin compounds includes
several hundred chemicals. These can be sub-divided into three closely
related sub-families: the chlorinated dibenzo-p-dioxins (CDDs,
also known collectively as dioxins), chlorinated dibenzofurans (CDFs,
also referred to furans) and some of the polychlorinated biphenyls (more
commonly known as PCBs).
The
term furan is often used to the describe dibenzofurans, but sometimes is
also used to describe a wider group of compounds and not all of
these have similar properties to the dioxin family of compounds.
Similarly, PCBs cover a wide range of compounds, some of which act in
similar way to the dioxin-like family grouping and some of which do
not.
This
short briefing is intended to provide information only on the compounds
that have biological properties which might impact on human health in
ways similar to the chlorinated dibenzo-p-dioxins family.
Dioxins, Furans, PCB’s and Human Health
These compounds are not new and have been present in the food chain for
many years. However, with the development of new detection and analysis
methods it is now possible to measure very low levels of these compounds
in a wide variety of foods, and for scientists to investigate their
impact on human health (if any) at very low levels.
Because these compounds exist throughout the environment, almost every
living creature, including humans, has been exposed to some degree to
them. The World Heath Organization (WHO) has advised that long-term
low-level exposure of humans to this group of compounds may lead to
impairment of the immune system, and impaired development of the nervous
system and the reproductive functions. Short-term high level exposure
may result in skin lesions and altered liver function.
The
International Agency for Research on Cancer (IARC) classifies dioxins as
a “known human carcinogen”. Furans are also considered as possibly
carcinogenic by the IARC, based on studies in laboratory animals exposed
to high levels of furans. However, most of the studies on toxicity of
dioxins and furans to humans are based on people who have been exposed
to high concentrations of dioxins either occupationally or through
industrial accidents, and currently there is insufficient evidence to
confirm or rule out the possibility that long-term low-level exposure to
dioxins and furans causes cancer in humans.
The
US Food and Drug Administration’s (US FDA) has stated that preliminary
estimate of consumer exposure is well below what might be expected to
cause harmful effects. The FDA is currently evaluating preliminary data
and additional studies will be conducted to better determine the
potential risk (if any) to human health. AFIC will continue to monitor
this and other related studies closely and provide updates as the
information becomes available.
Dietary sources of
dioxin, furans and PCBs
It
is estimated that over 95% of dioxins present in the environment have
originated from air pollution. Dioxins are then deposited in trace
amounts in soil, plant and water surfaces.
The
airborne particles that settle on fruits and vegetable as a result of
environmental exposure are removed by washing. Plants do not generally
absorb dioxins.
Dioxins most commonly enter the food chain as a result of animals
feeding and living in environments contaminated with trace amounts of
these compounds. For example, fish and other marine wildlife may
accumulate dioxins present in the water, and animals such as cattle,
pigs and goats may eat plants with dioxin particles on their surface.
Dioxins are fat soluble and accumulate in the fatty tissues of beef and
dairy cattle, poultry, pork or seafood. Levels of dioxins tend to
increase with age in these animals.
It
is believed that most (95%) of the dioxin detected in humans occurs as a
result of the consumption of animal fats.
As
in animals, dioxin is stored in human adipose tissue. As a result of
industry efforts to reduce dioxin pollution, levels in humans in those
countries who have monitored this issue over time, have declined
considerably in the last several decades. A study conducted by the US
Centers for Disease Control and Prevention showed that dioxin levels in
Americans declined from 189 parts per trillion (ppt) in 1976 to less
than 5 ppt in 1990. Some individuals or groups of individuals may be
exposed to higher levels of dioxins because of their diets (e.g. those
consuming large amounts of fish) or their occupations (e.g. workers in
incineration plants and at hazardous waste sites).
Furan is a liquid used in some chemical manufacturing industries, but
this is not thought to be the source of the low levels of furans found
in humans. Current knowledge suggests that furans are formed in the food
during traditional heat treatment techniques. The exact chemical process
resulting in the production of trace amounts of furan is not yet known
but early findings indicate that heating is probably an important, but
perhaps not the only contributing factor.
Established food processing and preservation techniques such as cooking,
jarring, and canning all require heating of foods. Moreover, heat
treatment processes, such as pasteurization and cooking are clearly
essential methods of safe food preparation and preservation. Further
research on the human health risk of furan in food is needed to
understand more fully if furan levels in food pose a health risk, and if
there are any measures that can be taken to minimize or reduce
quantities present. However, the information available currently does
not indicate this is an immediate health concern, or that any changes in
dietary habits should be recommended.
Dietary Recommendations to Consumers
Diet
and health experts including the U.S. Surgeon General, the Food &
Agriculture Organization and the World Health Organization of the United
Nations, continue to advise people to eat a balanced diet consistent
with national dietary guidelines. Elimination of any one food or food
group because of concerns about intake of dioxins, furans and PCBs is
not advised and could lead to serious dietary imbalance and health
problems.
However, those consumers who wish to take steps to limit the quantity of
dioxins, PCB’s and furans in the diet could take the following actions -
-
Limit visible
animal and fish fats in the diet by -
-
Selecting lean
cuts of beef, pork and poultry.
-
Trimming and
discarding fat from beef, poultry or seafood before eating,
including any skin.
-
Choosing low-fat
dairy products.
-
Eat moderate
portions of a wide variety of foods.
-
Washing vegetable
and plant material thoroughly before cooking.
-
Re-heating of
previously heat-treated foods such as jarred or canned food in open
pots, so that any furans present in the food may be vapourised from
the food.
Further information available at:
1)
Dioxins in Food: Questions and Answers (ANZFA)
http://www.foodstandards.gov.au/mediareleasespublications/factsheets/
factsheets2004/ dioxinsinfoodquestio2458.cfm
3)
Questions and Answers on the Occurrence of Furan in Food (FDA)
http://www.cfsan.fda.gov/~dms/furanqa.html
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