Scientists at the Queensland University of Technology in Australia found that the office laser printer can be hazardous to your health:
An investigation of a range of printer models showed that almost a third emit potentially dangerous levels of toner into the air. [...]
Conducted in an open-plan office, the test revealed that particle levels increased five-fold during working hours, a rise blamed on printer use.
The problem was worse when new cartridges were used and when graphics and images required higher quantities of toner.
Link - via Wicked Boring
Among the machines that had no emissions were eight HP LaserJet 4050 series printers and four Ricoh Aficio models.
High emitters included the HP LaserJet 1320 and 4250, which, when printing, increased the particle number in the air more than tenfold.
The study did not consider variables such as printer age or cartridge type, leading to variations even among printers of the same model. The scientists noted that they found one HP LaserJet 5 to be a high emitter, while another was a non-emitter.