Bamboo toothbrushes are indeed 100% biodegradable, but not all bamboo toothbrushes are.
First of all, the handle of bamboo toothbrush is made of bamboo, then the handle is definitely naturally degradable. But the bristles of many bamboo toothbrushes are not biodegradable, such as the Nylon 6 bristles. To be biodegradable, you need to use the Nylon – 1010 bristles, which are made from castor oil extract.