The retardant it's dropping consists of ammonium sulfate or ammonium polyphosphate with attapulgite clay thickener or diammonium phosphate with a guar gum derivative thickener, colored with ferric oxide to mark where it's been dispersed. Not only is it non-toxic, but after the fire is out it'll act as a fertilizer to promote new growth. Be thankful one doesn't have to buzz by your house, and be sure to visit The Big Picture for a lot more incredible photos from the recent CA wildfires. [The Big Picture; Wikipedia]