Toner

Toner is a powder commonly used in photocopiers and Laser printers to draw images and text onto paper. The early forms of toner were just carbon powder. Modern toners mix carbon with a thermoplastic and other materials.
In early machines, the user had to pour the toner into a reservoir on the machine itself. Current machines feed from a sealed cartridge which is normally a proprietary design. Although manufacturers try to make the process complicated, empty cartridges are sometimes refilled by third-party vendors.
Toner particles are melted by the heat of the fuser, and bind to the paper.
Health Risks.
Since toner is a fine dust, it can remain in the air for a long time, and is considered to have health effects similar to inert dust.
It can be very painful to people with respiratory conditions such as asthma or bronchitis.
Impact on the environment.
Many companies selling laser printers will also provide a way to return empty toner cartridges. These are commonly re-used, with new toner. Today, many toners have chips which tell the printer how much toner is left. These chips also need to be re-programmed, when the toner is re-filled.