UN level

“A democratic and equitable international order requires, inter alia, the realisation of the right of every person and all peoples to a healthy environment.”

United Nations Human Rights Commission; in Resolution 2005/57

As you will be able to research under "For lawyers to use", there have been many UN documents specifically mentioning a healthy environment to be a human right. But nothing "officially" and binding.

The time has come for The Right to (a clean and healthy) Environment to be codified as a binding right under an International Convention. Either through an additional protocol to one of the existing Conventions or in a specific - separate - one.