For us non-scientists, a useful rule of thumb in inhalation toxicology is the finer the substance, the greater the possibility for adverse health effects — and vice versa. Preliminary studies indicate this may hold true for nanoparticles which have been shown to have fewer potential adverse health effects when they occur in cluster form (aggregates and/or agglomerates).  In the "good news" department, scientists studying aerosol dispersion of nanoparticles have found they tend to cling together when dispersed into the environment.  Curious scientists ask logical follow up questions:  What happens to these nanoclusters if they somehow make it into the lung? Do they react with the body and end up breaking back down into smaller (and theoretically more toxic) sizes?

A new study by four German researchers makes some in-roads on these questions. M. Maier, et al., “Does lung surfactant promote disaggregation of nanostructured titanium dioxide?,” Journal of Occupational and Environmental Medicine, Vol. 48, No. 12 (December 2006). 

Maier looked at the theoretical interaction between the primary substance found in lung wall lubricant/fluid — dipalmitoyl phosphatidylcholine (DPPC) — and titanium dioxide nanoclusters to determine whether DPPC facilitates their breakdown into smaller sizes. Apparently, it does not. The researchers conducted two tests to reach this conclusion.  The first used computer simulation to determine that the DCCP did not have enough energy to break the bonds between individual nanoparticles in the clusters.  In the second test, the researchers exposed titanium dioxide nanoclusters to a simulated biological lung fluid containing DPPC.  The test results showed no disaggregation in the clusters from exposure to increasing amounts of DPPC, nor did it show any time dependent disaggregation.

The authors “conclude that DPPC only covers [titanium dioxide] aggregates and agglomerates instead of splitting them, i.e., lung surfactant does not promote the disaggregation of [titanium dioxide] agglomerates and aggregates."