nose, usually the first line of defense against inhaled
airborne particles that could damage the lungs, may
itself be susceptible to the dangers of extremely
small particles, called nanoparticles, which are
less than 100 nanometers in size. One nanometer is
one-billionth of a meter.
According to research presented by Michigan State
University researchers at seminar at the annual American
Association for the Advancement of Science conference
titled "Nanotechnology 2006: Toxicology of Nanoparticles," combustion-derived
nanoparticles, or CDNPs, have the ability to collect
in the nasal airways, potentially causing a number
of ailments, including rhinitis, inflammation of
the mucous membranes.
CDNPs are byproducts of coal-fired power plants,
waste incinerators and diesel-powered vehicles. They
are also found in the production of carbon black,
an elemental carbon that is widely used in rubber
tires, gaskets, and in pigments for paints, plastics
"This is concerning because carbon black can be
found practically anywhere," said Jack Harkema, a
University Distinguished Professor of pathobiology
and diagnostic investigation at MSU, who conducted
the research with colleagues from the University
of Rochester. "It's found in ink jet printers, car
tires, pretty much anything that is black. However,
our primary concern is the potential adverse health
effects to people who manufacture large amounts of
these CDNPs and are daily exposed to these nanoparticles."
Most of the toxicology studies of inhaled nanoparticles
have focused on its harmful effects on the lung.
However, nasal toxicity of nanoparticles has not
been previously examined.
"This study was the first to show that inhaled nanoparticless
of any sort can cause nasal pathology such as rhinitis,
epithelial cell injury, and remodeling of the nasal
mucous membranes that may compromise its function
for smell and for defending the lung from harmful
airborne agents," Harkema said.
In the laboratory, carbon black NPs are often used
as surrogates for other CDNPs, like those found in
diesel exhaust, to identify which physical or chemical
features of extremely small particles are most responsible
for their toxic effects to cells and tissues in the
nose and lungs. This knowledge is important for setting
occupational and environmental exposure limits to
maintain air quality and protect human health.
The fact that the nasal passages could be susceptible
to the dangers of such nanoparticles is alarming
because the nose, in addition to its smelling duties,
serves to not only humidify and warm inhaled air,
but also filter it.
"It basically acts as a scrubbing tower, removing
inhaled gases, vapors and small airborne particles – including
nanoparticles – that may be harmful to the lung," he
said. "It turns out, nasal airways may also be targets
of toxicity caused by inhaled nanoparticles."
To look into the potential toxicity of these carbon
black nanoparticles, Harkema and colleagues exposed
laboratory rodents to high levels of the material.
They found that rats developed a number of lesions
on the surface epithelium, or the lining, of the
nasal airways, as well as rhinitis, an inflammation
of the mucous membranes of the nasal airways. They
also found that the smaller the size of the NPs the
more severe the toxic injury to the noses of these
Mice had similar but less severe rhinitis and epithelial
lesions, while hamsters did not develop rhinitis
at all and only minimal alterations to the nasal
epithelium. Why one rodent species is more susceptible
to nasal injury than another is not yet known.
Although the effects of inhaled nanoparticles on
humans have yet to be determined, "these initial
findings in laboratory rodents suggest that our nose,
like our lungs, is a potential target organ for toxicity
of inhaled NPs," Harkema said.
This work was supported by grant from the International
Carbon Black Association and by a National Institute
of Environmental Health Sciences Environmental Health
Sciences Center grant.