I recently did some research about chemicals emitted by printers.  Basically, what I found is: Laser copy machines are worse than ink jets or all-in-one's.  Anything with toner is going to be worse.  They are all worse when working than when in standby. 
Here are a couple of sites for further info:
 
http://www.osti.gov/energycitations/servlets/purl/924853-0FJ4YK/924853.PDF - A scientific study, see page 27 for a breakdown of chemicals found from copiers, ink jets, and all-in-one's. 
 
http://www.aerias.org/DesktopModules/ArticleDetail.aspx?articleId=87#printer-pollutants - a simple primer
"Operating equipment such as computers, laser printers, and photocopiers has been associated with building-related symptoms and health effects due to the release of chemical gases and particles. These emissions can result from the inks and toners, papers, carbonless paper, coatings on transparencies, glue on adhesive labels, the mechanical print process, plastic construction materials, circuit boards, and residual cleaning chemicals. Many of these chemicals will decrease with usage of the product such as computers. Others are the result of the mechanical operation and will always be there when the machine is operating."