Environmental tobacco smoke is just as damaging to DNA as mainstream smoke.

This study demonstrates the ability of tar isolated from environmental tobacco smoke (ETS) to nick DNA in mammalian cells. Solutions of ETS tar behave similarly to aqueous solutions of cigarette tar from mainstream smoke. Both solutions contain the tar semiquinone radical, and this radical associates with the DNA in viable rat alveolar macrophages. Solutions of tar from ETS cause single-strand DNA breaks in rat thymocytes in proportion to the amount of tar present, until a plateau is reached. ETS tar solutions, like mainstream tar solutions, produce hydrogen peroxide. Hydrogen peroxide appears to be an essential component of the mechanism by which both ETS tar and mainstream tar cause DNA damage in rat thymocytes, as catalase substantially protects against DNA damage. Glutathione also protects against DNA nicking by both ETS and mainstream tar solutions by scavenging radicals and/or oxidants. The chelator diethylenetriamine pentaacetic acid also provides partial (40%) protection. The studies demonstrate that the water-soluble components of ETS tar can enter cells, associate with, and then nick DNA.