Some of you guys are mixing up ETHYLENE Glycol with PROPYLENE Glycol. Big difference.

Ethylene is the main ingredient in traditional "Green" antifreeze that is highly toxic to pets and people.
Propylene is a chemical used as an antifreeze, but it is generally non-toxic.

What the potato said.

We have several buildings on campus that have older 2-pipe heating and cooling--we have been converting over to Propylene in all the buildings. It makes any leaks in the future much simpler to clean up due to its non-toxicity.