Contrary to popular belief, ink toner is not toxic. However the toner dust can irritate eyes and skin and definitely should not be inhaled! So before you throw it in the trash, seal the cartridge in a plastic bag or the replacement cartridge packaging.
If you are uncomfortable with handling these cartridges, consider using gloves and/or simple safety goggles. These may prevent the dusty printer toner from entering your airway or eyes. They are not necessary for safety but may make you feel more comfortable particularly if you are easily irritated by toner dust.