Complex sentence: Formerly distribution transformers for indoor use would be filled with a polychlorinated biphenyl (PCB) liquid; because these liquids persist in the environment and have adverse effects on animals, they have been banned.
Split into simpler sentences: Formerly distribution transformers for indoor use would be filled with a polychlorinated biphenyl (PCB) liquid. Because these liquids persist in the environment and have adverse effects on animals, they have been banned.