Aircraft battling fires raging through the Los Angeles area are dropping more than water: Hundreds of thousands of gallons of hot-pink fire suppressant have been dumped ahead of the flames in a desperate effort to stop them before they destroy more neighborhoods. Fire agencies say the suppressants — most often used to fight forest fires — are an invaluable tool. But what should we know about them? One expert said they’re generally a mixture of water, ammonium phosphate — essentially fertilizer — and iron oxide, which is added to make the retardant visible. They’re seen as safe for humans but some worry about their effects on wildlife or the environment. Still, they’re seen as essential to stopping fires that can be even greater threats.