Is it forbidden to personally benefit from or sell items that the company considers environmentally harmful and discards for disposal, given that they are under my responsibility?

If the owner of items does not permit their taking, and one is entrusted with them, then the employee is not allowed to take them without permission. This is because he is entrusted with what is under his hand, and he is not allowed to dispose of anything except what he has been explicitly or customarily permitted to do. Otherwise, it is a betrayal of trust, for Allah says: "O you who have believed, do not betray Allah and the Messenger or betray your trusts while you know."