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Ecological Effects of Fire Retardant
Chemicals and Fire Suppressant Foams

Details of the Research


Research Objectives

Terrestrial Vegetation. Our goal was to determine the effect of Silv-Ex and Phos Chek G75-F, alone and in combination with fire, on growth and community characteristics of terrestrial vegetation. We applied the chemicals to vegetation in plots to assess growth and community responses and to individual sagebrush plants to determine the effects on reproductive characteristics. Finally, we examined the effects the chemicals had on insects that rely on vegetation as a food source by looking at the incidence of galling insects on new growth and by counting the number of chewed leaves after treatment.

Fish, Aquatic Invertebrates, and Algae -- Laboratory. Our goal was to determine the toxicity of Fire-Trol GTS- R, Fire-Trol LCG-R, Phos-Chek D75-F, Phos-Chek WD- 881, and Silv-Ex on one to four life stages of three fish (rainbow trout [eyed egg, sac-fry, 60 day old fry, 90-day old fry], fathead minnow [eyed egg, fry, 30-day old fry, 60-day old fry], and chinook salmon [30-day old fry]), two invertebrates (an amphipod Hyalella azteca, and a cladoceran Daphnia magna [<24-hour old]}, and a green algae (Selenastrum capricorntum [cells in log-growth phase]). To determine the effects of water quality on the toxicity of these five chemicals to fish and aquatic invertebrates, tests were conducted in two standard water qualities (soft water had hardness 42 mg/liter as CaCO3, alkalinity 32-33 mg/liter as CaCO3, and pH 7.5- 7.6; hard water had hardness 162-163 mg/liter as CaCO3, alkalinity 112 mg/liter as CaCO3, and pH 8.2). Standard acute toxicity tests were conducted. A 96-hour LC50 (lethal concentration to 50% of the test animals) value was calculated for each life stage of fish and for the amphipod tests and 48-hour EC50 (effect [immobilization] concentration to 50% of the test animals) value was calculated for cladoceran tests.

Tests with algae were conducted in standard ASTM algal assay medium and a 96-hour IC50 (inhibition [inhibition of cell reproduction as indicated by chlorophyll a production] concentration to 50% of the cells present) value was calculated.

Terrestrial Vegetation Study Locations

North Dakota Mixed-Grass Prairie. The mixed-grass prairie vegetation study was conducted at the Woodworth Station (T142 N R66W), a research facility of the Northern Prairie Science Center, Jamestown, N.D.

jpg -- Aerial Photo of Study Site
Aerial view of mixed-grass prairie study site in North Dakota.

The 65-ha field containing the study site has never been plowed. Biologists burned the field in 1969, 1970, 1971, 1972, 1976, 1979, 1981, and 1990; it has not been grazed since 1974. Currently, vegetation in the study area is dominated by Poa pratensis, an invasive cool-season grass. Other grass species found during previous studies include Stipa viridula, S. comata, Agropyron repens, Muhlenbergia cuspidata, and Bromus inermis. Rosa arkansana, Elaeagnus commutata, and Symphoricarpos occidentalis are common woody plants.

Nevada Shrubsteppe. The shrubsteppe vegetation study was conducted on the North Fork of the Humboldt River (T45N R41E, Sec. 19) and Cabin Creek (T44N R40E, Sec. 5) drainages, in the Santa Rosa Mountains of northern Nevada at an elevation of approximately 1800 m. The study sites are grazed by cattle on a rotational system. Woody vegetation is predominantly sagebrush (Artemesia spp.) and rabbitbrush (Chrysothamnus spp.) in the uplands, and mainly willows (Salix spp.) near the rivers. Reeds (Juncus spp.), sedges (Carex spp.), and bluegrass (Poa pratensis) are most common in the riparian zones; predominant upland species include Poa secunda and Agropyron trachycaulum (Table 1). Soils are loamy, with gravel inclusions on stream terraces. Average annual precipitation is 30.8 cm (12 in.); the frost-free season averages 80 days.

JPG -- NV Fire Retardant Treatments
Applying chemical to study plot in shrub steppe study site.

Detailed Results

Mixed-Grass Prairie Vegetation

Great Basin Shrub Steppe Vegetation. NB: The results of this study are under review at a journal. The major points are summarized below. When the article has been published, it will be made available on this web site.

The majority of vegetative characteristics we measured in our Great Basin study sites showed no response to chemical application over the course of the growing season in which the chemicals were applied (Table 2). We detected no treatment effect on species diversity or evenness, or on any characteristic of the two woody plants we examined. Flowering progressed normally in Artemesia. Chemicals did not disrupt the well-known post-fire sprouting of Chrysothamnus. Activity of galling insects was not influenced by either chemical.

In most respects, the effects of Phos-Chek G75-F, 0.5% or 1.0% Silv-Ex on vegetation in our Great Basin study sites did not vary substantially from each other or from the control. A canonical variate analysis illustrates this point: burning produced a greater change in the plant community than did any chemical application, and by the end of the study, chemically-treated plots were generally similar to control plots.

With few exceptions, effects we observed did not persist to the end of this one-year study. Effects that did persist were related to lower stem density on Silv-Ex plots. We observed a dramatic, but transient, decline in species richness after Phos-Chek application, but by the end of the study no effects were evident. As in the work in North Dakota mixed-grass prairie described above, this change in species richness may reflect the addition of nitrogen to the soils, which is known to reduce species richness.

Riparian habitat was marginally more sensitive to chemical treatments than upland habitats. Of the 10 vegetative characteristics we measured, only species richness showed a significant treatment effect in upland habitat, and this effect was a subtle change in trend between burned and unburned treatments. Change in stems/m2 and change in species richness both showed significant treatment effects in riparian habitat. The reason for greater response on riparian plots may be related to moisture availability. Because moisture is limiting in this shrub steppe study site, the capacity for response is greater in the more mesic (i.e., riparian) compared to the more xeric (i.e., upland) sites.

In general, chemical effects that appeared after June applications also appeared after July applications in riparian habitat, although statistical significance tended to be greater in June applications. The only effects that persisted at the end of the study were related to June applications.

Unlike the North Dakota study, in which P. pratensis increased its growth dramatically in response to fertilization by nitrogen in Phos-Chek, no single species (including P. pratensis, which was common in riparian plots; Table 1) seemed to respond out of proportion to any other in this study. We suspect this difference was related to lack of precipitation at the Nevada study sites. Precipitation was less than half the 30-year mean near our study sites in 1994 (2.03 cm for June - September 1994 compared with a yearly average of 4.90 cm for 1966-1995; NOAA National Climatic Data Center, U.S. Surface Data for Paradise Valley, NV; http://www.ncdc.noaa.gov/ol/climate/climatedata.html). The lack of precipitation likely limited late season growth of most species, independent of nitrogen availability.

The lack of significant differences among most chemical treatments applied after burning may reflect the short duration of the study rather than an actual lack of effect. Responses to burning in the sagebrush steppe are more appropriately measured over the course of several years, or even decades. Many upland species, after early-spring growth that largely occurred before roads were passable to the study site, were dormant through most of the study. It should be kept in mind, however, that most natural fires also will occur during this dormant season. If chemicals do not persist in the soils until the next growing season, there may, in fact, be little long-term effect of their use. This is an area that still requires research.

Algae and Aquatic Invertebrates. Acute toxicity tests were conducted exposing Daphnia magna Straus (daphnid) in soft and hard reconstituted waters (hardness 42 mg/liter and 162 mg/liter as CaCO3, respectively), and Selenastrum capricornutum Printz (algae) in ASTM algal assay medium (hardness 15 mg/liter as CaCO3) to fire retardants Fire-Trol GTS-R, Fire-Trol LCG-R, and Phos-Chek D75-F, and foam suppressants Phos-Chek WD-881 and Silv-Ex. The chemicals ranked from slightly toxic to practically harmless to daphnids and moderately toxic to algae. Water quality did not consistently alter the toxicity of the test chemicals to daphnids. The most toxic chemical to daphnids was Silv-Ex (48-hour EC50 7 mg/liter in soft and hard waters), whereas the least toxic chemical to daphnids was Fire-Trol LCG-R (48-hour EC50 848 mg/liter in soft water, 813 mg/liter in hard water). The most toxic chemical to algae was Fire-Trol LCG-R (96-hour IC50 10 mg/liter), and the least toxic chemical was Phos-Chek D75-F (96-hour IC50 79 mg/liter). Un-ionized ammonia concentrations near the EC50 or IC50 value were frequently less than reported LC50 un-ionized ammonia concentrations. Other toxic components present in the compounds probably contributed to their toxicity. When compared to the daphnids tested in ASTM soft water, the Fire-Trol compounds were most toxic to algae, Phos-Chek D75-F and the foam suppressants were most toxic to daphnids. The results of these tests are comparable to those obtained from research conducted in other laboratories with the same species and similar chemicals. Accidental entry of fire fighting chemicals into aquatic environments could adversely affect algae and aquatic invertebrates, thus disrupting ecosystem function.

Acute toxicity tests were conducted exposing Hyalella azteca Saussure (amphipod) in soft and hard reconstituted waters to Fire-Trol GTS-R, Fire-Trol LCG-R, and Phos-Chek D-75-F, fire retardants, and Phos-Chek WD-881 and Silv-Ex, foam suppressants. The chemicals were slightly to moderately toxic to amphipods. Soft water increased the toxicity of the chemicals to amphipods. The most toxic chemical to amphipods in soft and hard water was Phos-Chek WD-881 (96-hour LC50 10 mg/liter, and 22 mg/liter, respectively), and the least toxic chemical to amphipods in soft water was Fire-Trol GTS-R (96-hour LC50 127 mg/liter) and in hard water Fire-Trol LCG-R (96-hour LC50 535 mg/liter). Un-ionized ammonia concentrations near the LC50 value were frequently less than reported LC50 ammonia concentrations for amphipods. Other toxins present in the compounds contributed to their toxicity. The results of these tests were not comparable to previous testing exposing amphipods to a Fire-Trol and a Phos-Chek compound. The difference in results may be attributed to differing species and chemicals.

Fish. Laboratory studies were conducted with four early life stages of fathead minnow, Pimephales promelas, to determine the acute toxicity of five fire-fighting chemical formulations in standardized soft and hard water. Egg, fry, 30-day post-hatch, and 60-day post-hatch life stages were tested with three fire retardants (Fire-Trol GTS-R, Fire-Trol LCG-R, and Phos-Chek D75-F) and two fire-suppressant foams (Phos-Chek WD-881 and Ansul Silv-Ex). Fry were generally the most sensitive life stage tested, whereas the eggs were the least sensitive life stage. Formulation toxicity was greater in hard water than in soft water for all life stages tested. Fire-suppressant foams were more toxic than the fire retardants. The 96-hour LC50s derived for fathead minnows were rank ordered from the most toxic to the least toxic formulation as follows: Phos-Chek WD-881 (13 - 32 mg/liter) > Silv-Ex (19 - 32 mg/liter) > Fire-Trol GTS-R (135 - 787 mg/liter) > Phos-Chek D75-F (168 - 2250 mg/liter) > Fire-Trol LCG-R (519 - 6705 mg/liter) (ranges are the lowest and highest 96-hr LC50 for each formulation).

Laboratory studies were conducted with five early life stages of rainbow trout, Oncorhynchus mykiss, to determine the acute toxicities of five fire-fighting chemical formulations in standardized soft and hard water. Eyed egg, embryo-larvae, swim-up fry, 60- and 90-day post-hatch juveniles were exposed to three fire retardants (Fire-Trol LCG-R, Fire-Trol GTS-R, and Phos-Chek D75-F), and two fire-suppressant foams (Phos-Chek WD-881 and Silv-Ex). Swim-up fry of rainbow trout were generally the most sensitive life stage, whereas the eyed-egg life stage was the least sensitive. Toxicity of fire-fighting formulations was greater in hard water than soft water for all life stages tested with Fire-Trol GTS-R and Silv-Ex, and 90-day old juveniles tested with Fire-Trol LCG-R. Fire-suppressant foams were more toxic than the fire retardants. The 96-hour LC50s were rank ordered from the most toxic to the least toxic formulation as follows: Phos-Chek WD-881 (11 - 44 mg/liter) > Silv-Ex (11 - 78 mg/liter) > Phos-Chek D75-F (218 - >3,600 mg/liter) > Fire-Trol GTS-R (207 - >6,000 mg/liter) > Fire-Trol LCG-R (872 - >10,000 mg/liter); (ranges are the lowest and highest 96-hour LC50 calculated for each formulation). Toxicity values suggest that accidental entry of fire-fighting chemicals into aquatic environments could adversely affect fish populations.

Laboratory studies were conducted to determine the acute toxicity of three fire retardants (Fire-Trol LCG-R, Fire-Trol GTS-R, and Phos-Chek D75-F), and two fire-suppressant foams (Phos-Chek WD-881 and Ansul Silv-Ex) to early life stages of chinook salmon, Oncorhynchus tshawytscha, in hard and soft water. Regardless of water type, swim-up fry and juveniles (60- and 90-day posthatch) exhibited similar sensitivities to each chemical and these life stages were more sensitive than eyed eggs. Foam suppressants were more toxic to each life stage than the fire retardants in both water types. The descending rank order of toxicity for these chemicals tested with swim-up fry and juveniles (range of 96-hour LC50s) was: Phos-Chek WD-881 (7-13 mg/liter) > Silv-Ex (11-22 mg/liter) > Phos-Chek D75-F (218-305 mg/liter) > Fire-Trol GTS-R (218-412 mg/liter) > Fire-Trol LCG-R (685-1,141 mg/liter). Water type had a minor effect on the toxicity of these chemicals. Comparison of acute toxicity values with recommended application concentrations indicates that accidental inputs of these chemicals into stream environments would require substantial dilution to reach concentrations equivalent to their 96-hour LC50s.

Laboratory studies were conducted to determine the acute toxicity of three ammonia-based fire retardants (Fire-Trol LCA-F, Fire-Trol LCM-R, and Phos-Chek 259F), five surfactant-based fire-suppressant foams (Fire-Trol FireFoam 103B, Fire-Trol FireFoam 104, Fire Quench, ForExpan S, and Pyrocap B-136), three nitrogenous chemicals (ammonia, nitrate, and nitrite) and two anionic surfactants (linear alkylbenzene sulfonate [LAS] and sodium dodecyl sulfate [SDS]) to juvenile rainbow trout, Oncorhynchus mykiss, in soft water. The descending rank order of toxicity (96-hour LC50) for the fire retardants was: Phos-Chek 259F (168 mg/liter) > Fire-Trol LCA-F (942 mg/liter) = Fire-Trol LCM-R (1,141 mg/liter). The descending rank order of toxicity for the foam suppressants was: Fire-Trol FireFoam 103B (12.2 mg/liter) = Fire-Trol FireFoam 104 (13.0 mg/liter) > ForExpan S (21.8 mg/liter) > Fire Quench (39.0 mg/liter) > Pyrocap B-136 (156 mg/liter). Except for Pyrocap B-136, the foam suppressants were more toxic than the fire retardants. Un-ionized ammonia (NH3; 0.125 mg/liter as N) was about 900 times more toxic than total ammonia (112 mg/liter as N) at pH 6.7-6.8. Nitrite (0.79 mg/liter NO2-N) was about 2,100 times more toxic than nitrate (1,658 mg/liter NO3-N). LAS (5.0 mg/liter) was about five times more toxic than SDS (24.9 mg/liter). Measured total ammonia and NH3 concentrations at the 96-hour LC50s of the fire retardants indicated that ammonia was the primary toxic component in these formulations. Except for Pyrocap B-136, anionic surfactant concentrations at the 96-hour LC50 of the foams were within a factor of 2 of the 96-hour LC50 of LAS. Based on recommended application concentrations, accidental inputs of these chemicals into streams would require substantial dilution to reach concentrations equivalent to their 96-hour LC50s.


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