Description
Toner is a dense, powdery substance with carbon black as its main ingredient. According to the Environmental Protection Agency (EPA), toner can also contain cadmium, mercury and lead, considered hazardous substances by the EPA . The Food and Drug Administration (FDA) classifies carbon black toner as a Class-A carcinogen, meaning it has the potential to cause cancer; Health Canada also cites carbon black as a possible carcinogen.
Inhalation Danger
Because it is such a fine powdery dust, toner carcinogens are easily inhaled, causing respiratory distress and triggering asthma. Toner can also cause irritation, skin rash and eye problems if it comes in contact with skin and eyes, according to Symantec.
Allergic Reactions
In addition to contact with a potential carcinogen, toner can trigger allergic reactions in people who have sensitivities, according to Symantec. Reactions can be mild to severe.
Taking Precautions
When installing, removing or disposing of toner cartridges, or cleaning the insides of printers or copier machines, wear a dust mask and avoid contact with toner dust, according to Symantec. Try not to get dust residue on your hands or skin; wash all exposed skin surfaces after contact.
Please think twice before you DIY refill. Is the few $$ of savings worth it 
For people who want to read on the research findings
http://www.megafileupload.com/en/file/367106/Harmful-substances-in-toners-pdf.html
