Normal automotive antifreeze uses ethylene glycol to lower the freezing temperature of the coolant. This substance is very toxic to animals and fish and in general is bad news for the environment.
Sierra and some other engine antifreeze / coolants use propylene glycol as to lower the point that the coolant freezes. Propylene glycol is safe enough to be used in foods such as ice cream although I donít suggest drinking your engine coolant.
The pink RV antifreeze is used in r/v pluming and boat ballast tanks to keep the water systems from freezing during the winter. It can even be used to treat potable water systems.