Toxicologists at Sweden's Karolinska Institute have determined that there is a high variation in cytotoxicity and DNA damage caused by carbon nanomaterials and metal oxide nanoparticles during in vitro tests (Chem. Res. Toxicol., DOI: 10.1021/tx800064j). As the manufacture and use of products containing nanomaterials ramps up—tires, sunscreen, inks, and electronics are just a few examples—concerns about occupational and consumer health and safety are growing. Yet for most products containing nanomaterials, toxicity data are not yet available. Lennart Möller and coworkers exposed human lung epithelial cells to carbon nanoparticles, multiwalled carbon nanotubes, and various metal oxide nanoparticles. They found that iron oxide nanoparticles caused little or no toxicity and DNA damage, whereas zinc oxide caused some cell toxicity and DNA damage, and titanium dioxide caused only DNA damage. The cells were most sensitive to multiwalled carbon nanotubes, which were the only materials that caused any DNA damage at the lowest dose tested. Copper oxide showed the most potent cytotoxicity and DNA damage and is the only material tested that the researchers say potentially poses a serious health risk.