Uranium travels nerves from nose to brain.
Jul 31, 2009
Tournier, BB, S Frelon, E Tourlonias, L Agez, O Delissen, I Dublineau, F Paquet,
and F Petitot. 2009. Role of the olfactory receptor neurons in the direct
transport of inhaled uranium to the rat brain.
Toxicology Letters doi:10.1016/j.toxlet.2009.05.022.
Paul Eubig, DVM
Radioactive uranium that is inhaled by soldiers on the battlefield and by
workers in factories may bypass the brain's protective barrier by following
nerves from the nose directly to the brain.
Nerves can act as a unique conduit, carrying inhaled uranium from the nose
directly to the brain, finds a study with rats. Once in the brain, the uranium
may affect task and decision-related types of thinking.
This study provides yet another example of how some substances can use the
olfactory system – bypassing the brain's protective blood barrier – to go
directly to the brain.
Titanium nanoparticles and the metals manganese, nickel, and thallium
have been shown to reach the brian using the same route.
Military personnel and people who work in uranium processing plants are exposed
to the weak radioactive element via wounds or by breathing. Exposure may affect
brain function; cognitive skills are lowered in soldiers who carry uranium-laced
Uranium has various industrial and military uses. A form of uranium called
depleted uranium is very dense and is used in armor-piercing ammunition and
military vehicle armor.
Battlefield exposure can occur through wounds – such as with some US military
personnel who were injured during the Gulf War. These exposures can be higher
than with civilians who work with the element. A study of Gulf War veterans who
have uranium shrapnel in their bodies showed that they perform more poorly on
general brain cognitive tests of performance efficiency and accuracy.
Uranium can also be inhaled. Soldiers in vehicles hit by uranium rounds and
workers in uranium-processing facilities can breathe it in.
The researchers – taking advantage of the fact that uranium can exist in
different forms, or isotopes – used rats to compare how the element travels
through the body if it is inhaled or injected into the blood. The animals
breathed in one isotope at levels similar to those encountered on a battlefield
where depleted uranium weapons are used. They were also injected with a
different isotope. Researchers compared the levels of the two isotopes in
different regions of the brain.
The inhaled isotope accumulated at 2 to 3 times higher levels than the injected
isotope in the olfactory (smell) paths from the nose to the brain and in the
frontal cortex and hypothalamus of the brain. This is concerning because the
front part of the brain controls executive function, which is the broad ability
to gather information, make decisions and initiate action.
The scientists then chemically damaged the olfactory nerves in the nose. The
rats with the damaged nerves had three times less uranium in the olfactory
system than the rats with intact olfactory nerves.
These finding suggests that inhaled uranium can travel directly from the nose
along the olfactory nerves to the front of the brain. The olfactory pathway,
then, plays an important role in inhaled uranium reaching the brain.
It is not known from this study if soldiers and civilian workers that breathe
uranium could be at an even higher risk for cognitive effects or if inhaled
uranium may affect brain function in similar ways as when it is carried through
the blood. It is also unclear if these findings would hold true for the human
brain since the rat brain is much more developed for smelling than the human
Assessing these possible risks and determining if people's relatively
underdeveloped sense of smell could protect the brain would require further
studies of people exposed to uranium through inhalation.