Use antifreeze that contains
propylene glycol rather than
ethylene glycol as it will eventually break down into water and carbon dioxide. However, both are very toxic

to pets and wildlife and the sweet taste of the antifreeze attracts animals to any spills. Large quantities of glycol can suffocate aquatic life and disrupt sewage treatment processes. Never pour used antifreeze down the drain or in the street. Both
ethylene glycol 
and
propylene glycol 
are toxic . Used antifreeze also picks up heavy metals like lead during use in the engine. These should not be released to the environment. Properly dispose of used antifreeze at an appropriate collection center. (Source: http://www.eetcorp.com/antifreeze/antifreeze-faq.htm)
Used antifreeze may be recycled offsite by an EPA-approved facility. If it is hazardous waste (because of its lead content), you must transport it by using a transporter with an EPA identification
number and prepare it for trans
port appropriately. Used antifreeze that is mixed with other fluids must be characterized to determine if it is hazardous waste, and disposed of accordingly. Nonhazardous used antifreeze also may be disposed at a landfill that is authorized to accept used antifreeze. Many landfills have a tank designated for used antifreeze disposal. Used antifreeze may not be dumped with regular trash, poured into the sewer, or poured onto the ground. Do's and Don'ts for Antifreeze Disposal
DO. . .Keep used antifreeze in a covered container and out of the way of animals, who are often attracted to its sweet flavor. Be sure your recycled antifreeze meets
manufacturers' warranties for the vehicle you are servicing. As described above, recycle antifreeze by purchasing or leasing onsite recycling equipment; or using an offsite recycling service. Handle filters and other recycling by-products as hazardous waste.
DO. . . Check your local state regulations and facilities for information on proper disposal. Search online for more information in your local area.
DO NOT. . . send antifreeze to the landfill by disposing of it in your garbage can.
DO NOT. . . pour antifreeze into sewers, on the ground, or into floor drains, or mix used antifreeze with any other waste. Keep it separate.
DO NOT. . . collect antifreeze in containers that have been used to hold other substances (e.g., gasoline) unless the containers have been thoroughly cleaned. Antifreeze can leach substances from the walls of a container.