Dufour et al published a study in 2006 that is often cited by proponents of nanotechnology. In this study, the investigators applied ZnO to Chinese hamster ovarian cells under 3 conditions: in the dark, under simultaneous irradiation with UV light, or preirradiated with UV light, followed by treatment with ZnO in the dark. Interestingly, the nature, incidence, and severity of chromosome aberrations in preirradiated and simultaneously irradiated cells were nearly identical with regard to cytotoxicity. Given that Chinese hamster ovarian cells preirradiated in the absence of ZnO showed the same increase in the incidence and type of chromosomal aberrations as Chinese hamster ovarian cells receiving simultaneous ZnO treatment, the authors concluded that chromosome aberrations were a result of a UV mediated, enhanced susceptibility of the mammalian cells to ZnO. The authors thus concluded that ZnO is nonphotogenotoxic.