As merlin said, it's easy enough to dispose of safely. Remove the bullet, pour out the powder, and set off the primer with a hammer. The powder can easily be disposed of with a match and a piece of paper. Alternatively, just take it to the police station. They won't get p***y about a single .22LR round, they turn up all over the place. I've found them under floorboards and stuck in the corners of cupboards a few times.