How to wash dirty, pencil-lead-covered earbuds?

Hi, I left my iPod earbuds (come-in-the-box earbuds) in my backpack for a month and they got quite dirty and covered in pencil lead. I tried scrubbing the cord with a damp tissue, the tissue got some lead off but otherwise it looks really dirty still. Any suggestions on how to make my earbuds white again? Thanks.