Researchers at North Carolina State in conjunction with the National Institute of Environmental Health Sciences have completed a study of the behavior of carbon nanotubes when inhaled by laboratory mice. Nanotubes are the basic molecular building blocks for nanotechnology, the construction and use of micro-sized devices to be used for medical purposes and in other applications.
Nanotechnology is still in its formative stages, but research in the field is moving rapidly. For some time there has been speculation on what these microscopic nanotubes might do if inhaled by humans. The research project was specifically focused on the speed with which these tubes might reach the pleural area, which is the outer lining of the lung. It is also the area in human lungs where asbestos fibers most commonly lodge when inhaled.
Eventually, asbestos fibers that lodge in human pleural tissue can cause pleural mesothelioma, the lethal and fast-moving cancer that has killed thousands of people who worked around asbestos products in the years when asbestos was found in over 3,000 products. It’s important at this point to note that mesothelioma cancer usually takes between twenty and forty years after the asbestos fibers are inhaled to develop as a disease. The inhaled fibers slowly work their way through the lungs into the protective outer layer, or pleura.
In the research project with carbon nanotubes and mice, the nanotubes passed through the lungs and into the pleura in one day, at which point clusters of immune cells began to cluster on the pleura. Within two weeks, fibrosis (scarring of the pleura) had occurred. These effects mimic the damage that asbestos fibers do in the human pleura. The earliest symptoms of asbestosis include fibrosis within the lung, caused by asbestos fibers that remain there. For many people with asbestos damage, benign pleural plaque develops from tissue accumulation (such as immune cells) that eventually calcifies.
The mice in the research study received exposure to the air contaminated with nanotubes for a single six hour period. Only those mice that received the highest doses showed damage in the pleura, which is consistent with the fact that lesser amounts of asbestos exposure are far less risky to humans than situations where the air is full of floating asbestos fibers.
Finally, the damage done to the mice by this single laboratory exposure was gone in three months. There has not yet been any research on what happens with repeated exposure to nanotubes in the air. Nevertheless, the similarity of inhaled nanotube behavior and inhaled asbestos fiber in the initial stages of exposure is startling.
