i live right next to a junior high school so i just throw them out the window when im done and they seem to dissapear fairly quick, just like they were never there.
j.k. you should just put the plastic top back on the needle so that nobody can be stabbed bye them and toss them in your trash on garbage day. last time i was at the local dumps i didnt see to many people playing in the piles of trash, just seagals and D8 cats.