There are a lot of factors that actually determine just how 'environmentally friendly' bamboo is. There are some manufacturers that are not using proper methods to ensure that they are not harming the environment during cultivation and production. For example, in some areas, they are clearing forests to create what is called a 'monoculture' in which bamboo is the the only type of plant being grown. They are also using chemical fertilizers or weeders. Some manufacturers are using formaldehyde in their products as well.
That should answer your question, but please let me know if you need any other info.