In Fighting Wildfires, Concerns About Chemicals The red clouds of fire retardant dropped onto the flames near Santa Barbara, Calif., on Friday were a welcome sight for owners of the hillside homes there. “Critical,” Bill Payne, deputy chief of aviation for the California Department of Forestry and Fire Protection, said of the retardant’s role in helping to steer the fire away from populated areas, including the exclusive enclave of Montecito. Retardant, whether released by small planes that sweep low through smoky canyons or by DC-10s in 12,000-gallon bursts, has become an increasingly common tool for fighting wildfires. Yet while many residents praise — and even demand — the use of retardant to protect their homes and neighborhoods, the potent mix of chemicals in the most common type can leave scars of its own, hurting watersheds and the fish and other animals that live in them. The use of the most common type of retardant, a fertilizer-like, phosphate-based compound, can vary by state or by who oversees the land where a fire is spreading. Among federal agencies, the Park Service is relatively cautious with retardant because part of its mission is to protect natural and cultural resources for public use. The State of California, however, has the largest aviation fire operation of any state and uses retardant aggressively not only to contain fires — retardant’s intended purpose — but also to try to extinguish them before they reach populated areas. The Forest Service, which oversees the largest share of the nation’s wildfire-fighting operations, has a laboratory devoted to testing retardant produced by private companies. In a sign of how contentious the issue has become, the agency is being sued in federal court in Montana by a group that says retardant threatens endangered species, including salmon, a claim the agency rejects....