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October 19, 2011
from
PreventDisease Website
Persistent organic compounds that are resistant to environmental
degradation will soon have very significant impacts on human health
with some scientists estimating that almost 50% of all babies
worldwide will have at least one birth defect.
A variety of long-banned and currently-released chemicals found in
pregnant women are associated with an increased risk of neural tube
defects in their babies.
The chemicals known as persistent organic
pollutants (POPs) include a variety of pesticides, industrial-use
chemicals and compounds released from the burning of fossil fuels
and other sources largely due to modern civilizations.
This study is the first to directly link placental levels of
multiple POPs to neural tube defects.
The results strongly suggest
that lingering environmental factors continue to damage fetal
development and health.
"This is a serious concern," said
Dr. Marvin Eastman from the Tobias environmental research centre
in New York City.
"According to our research, in less than two
decades the exponential rate of increase of POPs around the
world will soon prevent almost half of newborns worldwide from
developing normally and with at least one birth defect."
Many POPs are currently or were in the
past used as pesticides.
Others are used in industrial processes and
in the production of a range of goods such as solvents, polyvinyl
chloride, and pharmaceuticals. Most POPs are created by humans in
industrial processes, either intentionally or as byproducts.
POPs released to the environment have been shown to travel vast
distances from their original source. Due to their chemical
properties, many POPs are semi-volatile and insoluble. These
compounds are therefore unable to transport directly through the
environment. The indirect routes include attachment to particulate
matter, and through the food web. The chemicals' semi-volatility
allows them to travel long distances through the atmosphere before
being deposited.
Thus POPs can be found all over the world,
including in areas where they have never been used and remote
regions such as the middle of oceans and Antarctica.
The chemicals'
semi-volatility also means that they tend to volatilize in hot
regions and accumulate in cold regions, where they tend to condense
and stay. PCBs have been found in precipitation.
The ability of POPs to travel great distances is part of the
explanation for why countries that banned the use of specific POPs
are no longer experiencing a decline in their concentrations; the
wind may carry chemicals into the country from places that still use
them.
Researchers looked for an association between levels of POPs in the
placenta of Chinese women who had just given birth and neural tube
defects in their children.
Researchers examined 80 cases of fetuses or newborns with neural
tube defects and 50 healthy controls from rural counties in the
Shanxi Province in the People's Republic of China.
This province has
the highest
PAH emissions in the country. The pollutants in question
are produced mainly from mining and burning coal. The Shanxi
province also has the highest rates of neural tube defects in China
at 14 per every 1,000 births.
At birth, the scientists measured several types of POPs in placental
tissue, including 10 types of PAHs and multiple types of
organochloride pesticides:
They also measured
two types of the pesticide DDT and a number of DTT metabolites - the
common chemicals produced when the body breaks down DTT.
Measuring levels of chemicals in the placenta is commonly used to
approximate fetal exposure to chemicals.
Investigators reported that some POPs were associated with a higher
risk for carrying a baby with a defect. The strongest association
was found with PAHs, chemicals that were detected in 82 to 100
percent of mothers-to-be.
Researchers found that moms that carried a baby with a neural tube
defect were nearly five times as likely to have elevated levels of
up to 10 different PAHs in their placentas.
What's more, the higher
the level of placental
PAHs, the larger the risk.
Citizens and habitats in most developed nations are at risk from
POPs that have persisted in the environment from unintentionally
produced POPs that are released locally and elsewhere and then
transported by wind or water, for example, or from both. Although
most developed nations have taken strong action to control POPs, a
great number of developing nations have only fairly recently begun
to restrict their production, use, and release.
Although scientists have more to learn about POPs chemicals, decades
of scientific research have greatly increased our knowledge of POPs'
impacts on people and wildlife. For example, laboratory studies have
shown that low doses of certain POPs adversely affect some organ
systems and aspects of development.
Studies also have shown that
chronic exposure to low doses of certain POPs can result in
reproductive and immune system deficits.
Exposure to high levels of
certain POPs chemicals - higher than normally encountered by humans
and wildlife - can cause serious damage or death. Epidemiological
studies of exposed human populations and studies of wildlife might
provide more information on health impacts. However, because such
studies are less controlled than laboratory studies, other stresses
cannot be ruled out as the cause of adverse effects.
To address this global concern, the United States joined forces with
90 other countries and the European Community to sign a United
Nations treaty in Stockholm, Sweden, in May 2001. Under the treaty,
known as the Stockholm Convention, countries agreed to reduce or
eliminate the production, use, and/or release of 12 key POPs, and
specified under the Convention a scientific review process that has
led to the addition of other POPs chemicals of global concern.
Since
2001 POP proliferation has increased demonstrating the
ineffectiveness of the treaty and lack of initiative by
the United
Nations.
Of the original 12 POPs covered by the Stockholm Convention, six are
classified as carcinogens, according to the Eleventh Report on
Carcinogens, published by the National Toxicology Program:
-
DDT
-
hexachlorobenzene
-
mirex
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PCBs
-
TCDD dioxin
-
toxaphene
Lindane
is also classified as a carcinogen.
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