adults in Mexico City have a somewhat
worse sense of smell than those living in
cleaner cities. Roberto Lucchini of the
University of Brescia in Italy reported
much the same for adolescents living in
communities around now-closed iron-alloy manufacturing plants. Both groups’
data also turned up signs the youngsters
have been experiencing at least subtle
nerve damage.
The findings, the researchers say, are
especially worrisome since a number of
studies have shown that a sense of scents
wanes in people developing Alzheimer’s
and Parkinson’s.
Though metal pollution hasn’t been
confirmed as a cause of these diseases,
Lucchini was able to link pollution in
Brescia to reduced smelling abilities and
to motor impairments.
Until 2001, alloy plants in northern
areas of the province spewed a number of metals into the air. Manganese
remains a substantial pollutant in the
air, soil and house dust in this part of
Italy. Work by Lucchini’s team uncovered unusually high rates of symptoms
including tremors, slowed movement
and rigidity among adults living near
the now-defunct plants. The local prevalence of these and other Parkinson’s-like symptoms is about 400 per 100,000
Traces of nanoparticles a growing
body of research is documenting the type and
amount of nanoparticles that can end up in
a rodent brain. The images at right show that
manganese particles can travel into a rat’s
olfactory bulb and olfactory tract by four days
after inhalation. The chart below reveals that
inhaled iridium particles can motor to the
liver and the brain, where the particles remain
detectable even after a few months.
0.01
Inhaled particles retained in rat organs
Retained fraction of iridium
0.001
0.0001
0.00001
0
Liver
Brain
Days
cribriform plate
olfactory
bulb
nasal
cavity
nasal
cavity
nasal
cavity
Human
inhabitants. That’s two and a half times
the usual rate in Italy.
Lucchini’s team, which had already
planned to examine 300 middle schoolers for neural effects of local pollution,
included a smell assay in the tests. To
measure exposures, the researchers
collected blood and urine from the 11-
to 13-year-olds. A third of the kids also
carried a backpack fitted with an air-sampling device and a GPS to pair up
readings and precise locations. Some
children lived near the former alloy
plants, others at Garda Lake, a relatively
clean comparison region in the province.
Day 0
Day 1
Day 4 olfactory
bulb
olfactory
tract
olfactory
bulb
SouRce: d. doRman e T al./journal of toxicology and
environmental health 2002
From nostril to brain
Radioactively tagged nanoparticles have been
shown in rodents to make their way through
the nasal cavity, across the cribriform plate
and into the olfactory bulb—part of the brain.
But scientists are not sure how these findings
translate to people. Humans rely on smell
much less than rats and mice, and thus have
less efficient nose-to-brain connections.
cribriform
plate
olfactory
bulb
Rat
At the toxicology meeting, Lucchini
reported that among kids living near
the alloy plants, “Odor identification was
clearly impaired compared to children
living in the [Garda Lake] region.” The
smell-threshold reduction was “
preclinical,” he explains, meaning the children
wouldn’t notice the change but it could
be picked up with testing.
His team also linked exposures to
manganese-rich dust particles with
motor impairments — such as a reduction in the speed at which children could
clench their hands or sequentially touch
the fingers of each hand to the thumb.
Though it’s too early to speculate about
whether the symptoms will evolve into
something resembling Parkinson’s disease, Lucchini says, these are the first
data to link such motor impairments to
inhaled manganese.
Nosing out the problem
While these data are just coming in, a
growing body of evidence suggests that
nerves in the nose can provide a highway
along which some inflammatory pollutants, such as metals, motor directly from
the outside world to the brain.
How efficient the conduit is varies
by pollutant particle, according to new
experiments by Wolfgang Kreyling of
the Helmholtz Center and the German
Research Center for Environmental
Health in Munich. In rats, 20-nano-
meter–diameter agglomerations of at
least 100 radioactively labeled iridium
Top: Human: BSIp/pHo To ReSeaRcHeRS, Inc.; Roden T: T. duBÉ
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