Complex sentence: Peer-reviewed studies show that mountaintop mining has serious environmental impacts, including loss of biodiversity, that mitigation practices cannot successfully address, as well as human health impacts from contact with affected streams or exposure to airborne toxins and dust.
Split into simpler sentences: Peer-reviewed studies show that mountaintop mining has serious environmental impacts, including loss of biodiversity, that mitigation practices cannot successfully address. There are also adverse human health impacts which result from contact with affected streams or exposure to airborne toxins and dust.