Context - Dioxins are mainly released by human activities such as incineration and fuel
combustion. Some dioxins and some "dioxin-like" PCBs are known to be harmful.
In 2008, the facts presented here are still considered a valid reference. Since 1998, there have
been no big changes in our scientific understanding of dioxins - other than to
strengthen the conclusions that dioxins are bad actors. General dioxin levels have since
continued to drop both in the environment and in people.
1. What are dioxins?
"Dioxins" refers to a group of
chlorinated organic chemicals with
similar chemical structures. Some have harmful properties, depending on
the number and position of chlorine
atoms in their chemical structure. One of the most harmful dioxins is
known as TCDD. Some
PCBs, which have similar
properties, are considered
Unlike PCBs which were used in
several industrial applications,
dioxins have no uses. They are
formed unintentionally and predominantly released as byproducts of human
activities such as incineration and fuel combustion. They are also
formed in minor quantities by natural processes such as forest fires and
Dioxins travel through the air and
deposit on water or land. In water, dioxins initially bind to small
particles or plankton. On land, dioxins deposit on plants or bind to the
soil, most often without contaminating
accumulate dioxins in fat through
their food; concentrations increase
at each step in the food chain.
2. How are humans exposed to dioxins?
Over 90% of the human intake of
dioxins is through food, mainly
from animal origin. The
is ten to hundred times higher for breast fed babies than for adults
with respect to their body weight. In most industrialized countries, dioxin
exposure has been reduced by almost
50% compared to the early 90's.
Local populations have been accidentally
exposed to high
dioxin levels, e.g. in
Seveso (Italy) after an explosion
at a chemical factory, or in Japan and Taiwan with people eating
rice oil accidentally contaminated
with PCBs and
dioxins. In the past, some workers
have also been highly exposed to dioxins in waste incineration or
Dioxins are slowly bio-transformed
in the body and are not easily eliminated. They tend to
accumulate in fat and in the liver.
By interacting with a
cellular receptor, dioxins can
trigger biological effects such as hormonal disturbances and alterations
in cell functions. The mechanism of
dioxin toxicity is similar in man
and other vertebrates.
3. What are the effects of dioxins in laboratory animals?
dioxins may cause
non-cancer effects to animals,
affecting development, reproduction, the immune system and the uterus.
Human background exposures in
industrialized countries have sometimes reached levels at which these
effects were seen in animals.
In laboratory testing, TCDD and
some other types of dioxins
increase the number of cancers in
several animal species, in both sexes. They do not initiate cancers but
promote the growth of existing precancerous
4. What are the effects of dioxins on human health?
For workers accidentally exposed to
the highest doses of
dioxins, studies estimate that the
risk of cancer increases by about
40%. However, the average exposure of
the general population is much lower.
Some delay in nervous system development as well as changes of
behavior were seen in children of mothers who had been highly
PCBs. In some cases these effects
occurred even at current
background levels. The effects were
likely due to exposure through the
placenta rather than through breast milk. However, at least in one case
high levels of PCBs and dioxins in breast milk were shown to affect
Other non-cancer effects observed
on adults accidentally exposed to
high levels of toxic
dioxins include: diabetes, liver
and heart diseases, skin problems (e.g.
conjunctivitis, fatigue, malaise
and slowed nervous reactions.
6. Evaluation and conclusions
Dioxin levels in food,
environmental samples and breast
milk have decreased over the 1990s. In most industrialized countries,
daily dioxin intake
is currently in the order of 1 to 3
pg I-TEQ/kg body weight per day.
At very high dioxin
risk for all
cancers combined appears to
increase. Non-cancer effects
include cardiovascular diseases,
diabetes and changes in blood composition. Infants of accidentally
highly exposed mothers showed severe
A Tolerable Daily Intake
(TDI) of 1 to 4
pg I-TEQ per kg body weight per day
has been established for dioxins by
the World Health Organization
The upper limit of 4 is provisional: the ultimate goal is to reduce
levels below 1
pg I-TEQ per kg body weight per day.
This value was derived from the lowest
doses causing adverse effects in
experimental animals, divided by a safety factor of 10. This Tolerable
Daily Intake (TDI) should be seen as an average over a life-time,
implying that this value may be exceeded occasionally for short periods
without expected health consequences.
Although breast-fed infants are more
dioxins, under normal conditions
the many beneficial effects of human milk generally outweigh the
Dioxin levels in human milk have
been reduced since the early 90's.
Note from the editor: In 2008, these conclusions are still considered valid.
Since 1998, there have been no big changes in our scientific understanding of
dioxins - other than to strengthen the conclusions that dioxins are bad actors.
General dioxin levels have since continued to drop both in the environment and in people.