Silly question, but you can get a second life out of your toothbrush after its done cleaning your teeth. I store any I have to replace in an old jam jar under the sink - so that when I need one for a particularly fiddly job (my fingers are not as dexterous as they were as a result of the arthritis) and I find them really useful for applying leverage and pressure on a particularly fiddly items to clean.
I recycle mine for use in cleaning nooks and crannies and places where I cannot get my fingers in like cleaning in the groove around the base of taps; and cleaning grouting and the seal around the bath. I also use them for removing any debris on the fridge and cooker seals. I also use them for getting into delicate pieces of jewellery. I use the brushes both dry and wet. Sometimes I dip the brush in dry salt and then use lemon juice as it helps eradicate lime scale from dripping taps. So next time you have to replace the toothbrush recyle it don't bung it