Iron nanoparticles can be toxic to human lung cells.

Aug 12, 2009

 Keenan, CR, R Goth-Goldstein, D Lucas and DL Sedlak. 2009. Oxidative stress induced by zero-valent iron nanoparticles and Fe(II) in human bronchial epithelial cells. Environmental Science and Technology doi:10.1021/es9006383.

Iron nanoparticles that are poised for use in large-scale pollution remediation can rapidly react with oxygen and cause lung cells to die.

The number of oxygen molecules associated with iron nanoparticles is an important factor in its toxicity to cells, finds a study published in the journal Environmental Science and Technology. Iron-based nanoparticles without attached oxygen molecules can react quickly when exposed to oxygen to form other reactive varieties that can damage lung cells.

It is important to understand which types of nanoparticles may be most harmful to cells. Of most concern are the health and safety of the workers who could be highly exposed when they make the materials.

Nanoparticles are very small materials usually made from carbon or metals. They are increasingly used in far-ranging applications such as consumer products, medical therapies and industrial processes. Because of their small sizes, nanoparticles react differently with their surroundings than the bulk materials they are made from.

One type – called zero-valent iron nanoparticles (nZVI) – has great potential for remediating pollutants such as chlorinated organic solvents, pesticides and metals found in contaminated groundwater. nZVI is already commercially available, and its use could introduce large amounts of the nanoparticles into the environment.

However, the same qualities that make these particles potentially useful in environmental clean-up – namely their high reactivity – also make them potentially harmful to living things. Some of the reactions can release free radicals that can damage cell DNA in a process broadly called oxidative stress. Prior studies have found that particulates can cause toxicity to lung cells via oxidative processes.

To test how the nZVI nanoparticles might affect human lung cells if they were inhaled, researchers exposed lung cells to different levels of the nZVI nanoparticles and of another more volatile form called ferrous oxide (Fe(II)). They then compared the effects.

Both types damaged the lung cells in a similar fashion. After an hour, about three-quarters of the cells were still alive for both nZVI and Fe(II) at the lowest dose tested. Only about one-quarter survived at the higher dose tested. nZVI allowed to sit and oxidize (react with oxygen) for four hours before testing did not cause similar cell damage.

This suggests that as the nZVI nanoparticles contact oxygen, their form rapidly changes and releases oxygen radicals that can damage lung cells. The results support prior studies that have found the nanoparticles first convert into the highly reactive Fe(II) and then into the more stable ferric iron. It is the further reaction of Fe(II) with oxygen that leads to the oxidative stress that damages the cells.

The authors conclude that the oxidation state of the iron in nanoparticles is an important factor in its toxicity.