ABC Science Online is reporting that two new studies on the safety of zinc oxide nanoparticles will be presented at the International Conference on Nanoscience and Nanotechnology in Melbourne, Australia on February 25-29, 2008.

In the first in vivo study, researchers applied sunscreen containing nanoscale zinc oxide particles to human test subjects and then tested blood and urine samples for several following days. Evidently, the scientists found "very little" nanoscale zinc oxide in the subject blood and urine. We will definitely take a closer look at their study once it is formally released. Finding any nanoscale zinc oxide in blood and urine samples presumably indicates at least some dermal penetration is occurring.

In a second in vitro study, researchers found nanoscale zinc oxide particles are highly toxic to human immune cells. The nanoscale zinc oxide particles  were found to be more cytotoxic than silver, diesel exhaust, and silica dioxide nanoparticles — however, a very high dose was required to cause any cellular response.

Analyzing their possible combine implications, the researches theorize that any nanoscale zinc oxide possibly absorbed by the body in the first study will be cleared by the body before accumulating to toxic levels.