>Guo and her colleagues placed rat models into the same chamber as a typical laser printer. The models stayed in the chamber for five hours a day, for 21 days,

>Guo and her colleagues placed rat models into the same chamber as a typical laser printer. The models stayed in the chamber for five hours a day, for 21 days, as the printer ran nonstop. How do they know it was toner instead of, for example, ozone?