While slurry mixes stifle forest fires, researchers have found in limited studies that the retardants and foams also have a dark side. The most commonly used mixtures can be toxic to fish, aquatic invertebrates, and algae, can harm rabbits, birds, and humans, and can reduce vegetative diversity and boost the growth of weeds. Slurries and foams are mostly water, but they also include ammonium fertilizer, detergent, and other ingredients. Current studies are showing that a corrosion inhibitor (sodium ferrocyanide) in some formulas becomes more toxic when exposed to sunlight. Very little study has been done on chronic effects. In the past five years, a total of 409,721 fires have burned 18,382,397 acres, and an average of more than 20 million gallons of retardant have been used each of the past 10 years. This year, more than 30 million gallons of retardant, plus an unknown quantity of foam, likely will be used.

• Susan Finger, [2] Environmental and Contaminants Research Center, 573-876-1850.
• Diane Larson, [3] U.S.G.S. Northern Prairie Wildlife Research Center, 612-625-9271.
• Cecilia Johnson, U.S. Forest Service, [4] 406-329-4819.
• Jeff Bass, National Interagency Fire Center, [5] 208-387-5459.
• "Ecological Effects of Fire Fighting Foams and Retardants," [6] Robyn Adams and Dianne Simmons.