Will standard air filtration techniques work with nanoparticles?  This question has come up on several nanotechnology panels we have attended over the past 6 months.  Here is a short lay person’s analysis of the most helpful article I have found on the subject. — Kim S., et al., "Experimental study of nanoparticles penetration through commercial filter media." Journal of Nanoparticle Research (2007) 9:117-125.

This study measured silver nanoparticle (3nm – 20nm) penetration through several filter media.  The nine filter media selected for the tests fell into three categories: 4 were made of fiberglass, 4 were made of electret, and 1 was made of nanofiber. The four fiberglass media had effective pore diameters of 8.8nm, 13.4nm, 16.1nm, and 26.2nm.  Two of the four fiberglass media approached HEPA standards, while the other two were more in line with HVAC standards.  The three different face velocities used for the tests were: 5.3 cm/s (which is a standard face velocity for testing respirator filter media), 10 cm/s, and 15 cm/s.  Particle sampling times varied.

Results for all of the filter media were promising. The scientists found “. . . particle penetration decreases continuously down to 3nm as expected from the classical filtration theory, and there is no significant evidence of nanoparticle thermal rebound down to 3nm . . .”  Obviously, the study only looked at nanosilver particles, and then only looked at them down to 3nm.  What happens below that size-range still needs to be determined.  Additionally, will tests on nanomaterials other than pure silver (here 99.999% pure) produce similar results?  Or do different nanomaterials behave differently in filter media?  Is the shape of the nanoparticle relevant to the test; will nanofibers provide different results than nanospheres, etc.? 

This is a very helpful study for industrial hygienists and produces more questions in a very important area.