Most antifreeze contains ethylene glycol and nitrites, which are poisonous and flammable.
The sweet smell of antifreeze attracts pets, especially cats and dogs. If you drain your old antifreeze on the ground, cats and dogs may drink it and get sick or die. If you suspect this has happened, call your vet immediately. However, neither type of antifreeze is friendly to the environment. As antifreeze moves through your engine, it picks up heavy metals, which are toxic to fish and other wildlife in the water.