Scientists from Denmark
and Canada are worried by their new findings
showing that several bioaccumulative perfluoroalkyl
substances (PFASs) are crossing the blood
brain barrier of polar bears from Scoresby
Sound, East Greenland.
2013.07.23 | JENS CHRISTIAN
PEDERSEN
Polar bear. Photo: Rune Dietz, Aarhus University.
Scientists have been monitoring the polar
bear for contaminants in East Greenland
over the past 30 years. They are worried
by the findings of bioaccumulated perfluoroalkyl
substances (PFASs) in the brain. Photo:
Rune Dietz, Aarhus University.
PerFluoroAlkyl Substances
(PFASs) and precursor compounds have been
used in a wide variety of commercial and
industrial products over the past six decades.
Applications include water and oil repellent
coatings, e.g. for textiles, paper products,
carpets and food packaging, pharmaceuticals
and surfactants in cleaning products and
fire-fighting foams. PFASs are highly resistant
to chemical, thermal and biological degradation.
PFASs and their precursor
compounds have shown a dramatic increase
and dispersal around the world over the
past four decades. An increasing amount
of information is becoming available on
the toxicity of these compounds. Hence,
studies have documented the toxicity of
PFASs on wildlife and human health, including
carcinogenesis, genotoxicity and epigenetic
effects as well as reproductive and developmental
toxicities, neurotoxicity, effects on the
endocrine system and immunotoxicity.
Bioaccumulative PFASs
enter all parts of the brain
Despite the fact that the liver is considered
the major repository in the body for most
PFASs, some shorter chain compounds from
this grouping have previously been reported
in the brain of chicken embryos, suggesting
that they are able to cross the blood–brain
barrier.
Previous studies have
shown a dramatic biomagnification of several
PFASs, and particularly one known as perfluorooctane
sulfonate (PFOS) as well as several compounds
of the perfluorinated carboxylate (PFCAs)
grouping, in polar bears. PFOS have been
shown to be at concentrations in the liver
that are 100 fold higher than the ringed
seals on which they are predating. In a
new study Arctic researchers from Carleton
University in Canada and Aarhus University
in Denmark have used the polar bear as a
sentinel species for humans and other predators
in the top of the food chain. The researchers
demonstrated accumulation of PFOS and several
PFCAs in eight brain regions of polar bears
collected from Scoresby Sound, East Greenland.
Dr. Robert Letcher, Carleton University,
explains:
”We know that fat soluble
contaminants are able to cross the brain-blood
barrier, but is it quite worrying that the
PFOS and PFCAs, which are more associated
with proteins in the body, were present
in all the brain regions we analyzed.”
Professor Rune Dietz,
Aarhus University, is also worried about
the results:
“If PFOS and PFCAs can
cross the blood-brain barrier in polar bears,
it will also be the case in humans. The
brain is one of the most essential parts
of the body, where anthropogenic chemicals
can have a severe impact. However, we are
beginning to see the effect of the efforts
to minimize the dispersal of this group
of contaminants.”
Regions of polar bear
brain. Photo: Rune Dietz, Aarhus University
Different functional
parts of the Greenland polar bear brain
were investigated for transfer of contaminants
over the blood-brain barrier. The inner
regions of the brain closer to incoming
blood flow (pons/medulla, thalamus, and
hypothalamus) contained consistently higher
concentrations of perfluorooctane sulfonate
(PFOS) and several perfluorinated carboxylates
(PFCAs) compared to outer brain regions
(cerebellum, striatum, and frontal, occipital,
and temporal cortices). Photo: Rune Dietz,
Aarhus University.
Select environmentally labeled products
The eight carbon chain PFOS and perfluorooctane
carboxylate (PFOA) are PFASs have been phased
out and are no longer produced in the western
world. However, production in China, today
the only known production source of PFOS
and PFOA, has increased by roughly a factor
of 10, since it was phased out in the USA.
Unfortunately, no emission inventory is
so far available from this region. Furthermore,
replacements for PFOS and PFOA are now marketed
and produced in e.g. the U.S.A. and China,
which generally have perfluorinated carbon
chains that are shorter or branched.
Another recent study
from Aarhus University documents that PFOS
concentrations in Greenlandic polar bears
and ringed seals started to decline after
2006. Other wildlife populations closer
to the sources in Europe and North America
have shown a decline prior to the Greenlandic
animals. Rune Dietz comments:
”It is promising to
see that the PFAS are on the decline. This
development should be encouraged by the
authorities globally.
In the meantime my best
advice to the consumers is to go for environmentally
labeled products. But avoiding products
is difficult, because PFASs are so widespread
in many kind of products and they are rarely
declared.”
FACTS
With fluorine in the tail
Perfluoroalkyl substances (PFASs) constitute
a group of compounds where one end of the
molecule consists of a carbon chain in which
all the hydrogen atoms are replaced by fluorine
atoms. This so-called perfluoroalkyl ”tail”
can be short or long, but the strong C-F
bonds make the tail more or less impossible
to degrade, compared to the more well known
CFC-bonds. The best known PFAS is PFOS with
an eight-chained perfluoroalkyl tail.
