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Northern Prairie Wildlife Research Center

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Ecological Effects of Fire Retardant
Chemicals and Fire Suppressant Foams

Manager's Summary

Terrestrial vegetation effects of Phos Chek G75F. The primary effect of applying this fire retardant chemical to terrestrial vegetation was comparable to the light application of a nitrogen fertilizer. Species richness declined in both shrub steppe and mixed-grass prairie ecosystems. We do not know how persistent this effect will be. If conditions are sufficiently moist, biomass production will likely increase during the growing season when the chemical is applied, but the effect will not persist. Under dry conditions, no effect on biomass production is likely. Weedy species that can exploit the additional nitrogen are likely to gain an advantage over more desirable native plants, especially under moist conditions.

Terrestrial vegetation effects of Silv-Ex. Application of this Class A foam resulted in a decrease in species richness in prairie vegetation, but not in shrub steppe vegetation. We found fewer live stems on plots treated with Silv-Ex in June, and this effect was still present at the end of the growing season on both burned and unburned plots. Overall, burning produced a far greater change in plant communities in shrub steppe habitat than did any chemical treatment we applied.

Laboratory studies with algae, aquatic invertebrates, and fish. Short-term toxicity tests showed that both fire-retardant and foam-suppressant chemicals were very toxic to aquatic organisms including algae, aquatic invertebrates, and fish. Foam-suppressant are more toxic than fire-retardant chemicals. The primary toxicant in fire-retardants is the ammonia component, whereas the nitrite and nitrate components do not seems to contribute much to the toxicity of the formulations. In foam suppressants the primary toxicant is the surfactant component. The most sensitive life-stage for fish is the swim-up stage.

Accidental spills of fire-fighting chemicals in streams could cause substantial fish kills depending on the stream size and flow rate. For example, the retardant Fire-Trol GTS-R is prepared for field use by mixing 1.66 pounds per gallon of water to produce 1.1 gallons of slurry, which is equivalent to 198,930 mg/liter. Comparing the concentration of FT GTS-R field mixture to the acute toxicity values for the most sensitive life stage for rainbow trout gives a ratio of 853 in soft water and 1474 in hard water. Applying a safety factor of 100 to this ratio suggests a dilution of 85, 300 in soft water and 147,400 in hard water is needed to lower the chemical concentration in a receiving water to limit adverse effects, i.e., fish kill, in a stream. For rainbow trout, other dilution factors would be 52,100 for Fire-Trol LCG-R, 85,600 for Phos-Chek D75-F, 71,400 for Phos-Chek WD-881, and 50,000 for Silv-ex. Fire-fighting chemicals are very toxic in aquatic environments and fire control managers need to consider protection of aquatic resources, especially if endangered species are present.

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