This is a composite generally made from different types of plastic.
Old toothbrushes should be placed in the general waste bin.
Eco-toothbrushes are becoming more popular and are now widely available. Eco varieties are generally made from bamboo or wood and can be composted at end of life. If you are interested in reducing the amount of plastic you generate consider swapping your plastic toothbrush to an eco one.
Old plastic toothbrushes can be used as cleaning tools for fiddly jobs.