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Acute Toxicity of Fire-Control Chemicals, Nitrogenous Chemicals, and Surfactants to Rainbow Trout


Rainbow trout of the McConaughy strain were obtained as eyed eggs from Ennis National Fish Hatchery (Ennis, Montana). The fish were cultured in well water that was maintained at 12-13C, as described in Buhl and Hamilton (1998). The chemical characteristics of the culture water, which were monitored weekly according to standard procedures (APHA et al. 1989), were as follows: hardness 336-1,060 mg/L as CaCO3; alkalinity 204-289 mg/L as CaCO3; pH 7.4-7.8; and conductivity 903-1,890 S/cm at 25C. Dissolved oxygen concentrations were greater than or equal to 66% saturation, and un-ionized ammonia concentrations were less than or equal to 0.002 mg/L as nitrogen (N).

The fire-retardant formulations tested were Fire-Trol LCA-F, Fire-Trol LCM-R, and Phos-Chek 259F, and the foam concentrates tested were FireFoam 103B, FireFoam 104, Fire Quench, ForExpan S, and Pyrocap B-136. The chemicals were obtained from the USDA Forest Service, Intermountain Fire Sciences Laboratory (Missoula, Montana). The specific composition of these chemicals is proprietary, but it is reported by the manufacturer to the USDA Forest Service. The manufacturers and lot numbers of the formulations tested are given in the Appendix. Test solutions of the fire retardants and foam concentrates were prepared as described in Buhl and Hamilton (1998).

The reference chemicals tested were ammonium chloride (NH4Cl), sodium nitrate (NaNO3), sodium nitrite (NaNO2), and sodium dodecyl sulfate (SDS; CH3(CH2)11OSO3Na), obtained from J.T. Baker (Phillipsburg, New Jersey), and linear alkylbenzene sulfonate (LAS, 36.54% active ingredients) obtained from Condea Vista Company (Austin, Texas). The average alkyl chain length of LAS (as determined by the supplier) was 11.4 carbons (C11.4) with the following distribution of alkyl chain lengths: 14.8% C10, 38.9% C11, 38.7% C12, 6.3% C13, 1.3% C14; homologs with chain lengths < C10 and > C14 were not determined.

The acclimation and static test procedures used in this study closely followed those recommended by the American Society for Testing and Materials (ASTM 1989), and they are described in Buhl and Hamilton (1998). Two sets of tests were conducted because all of the chemicals could not be tested at the same time. In the first set of tests, the three fire retardants, NH4Cl, NaNO3, and NaNO2 were tested with 40-d-posthatch (dph) juveniles (mean SD weight, 251 63 mg; and mean SD total length, 33 3 mm). In the second set of tests, the five foam concentrates, LAS, and SDS were tested with 49-dph juveniles (weight, 403 89 mg; total length, 38 3 mm). Pyrocap B-136 was retested with 60-dph fish (weight, 604 84 mg; and total length, 44 2 mm) because of insufficient mortality in the first test.

Tests were conducted in standardized reconstituted soft water (ASTM 1989) maintained at 12 plus or minus 1°C with the following mean (range) characteristics (measured before use): hardness 41 (40-42) mg/L as CaCO3; alkalinity 31 (30-32) mg/L as CaCO3; pH 7.1 (7.0-7.2); and conductivity 159 (154-161) mhos/cm at 25C. Dissolved oxygen was measured in the control, low, medium, and high test concentrations with live fish at 0, 48, and 96 h of exposure, and pH and temperature were measured in all concentrations with live fish at 0 and 96 h of exposure using digital meters (Buhl and Hamilton 1998). Hardness and alkalinity were measured in the control, low, medium, and high test concentrations of each chemical at 24 h of exposure according to APHA et al. (1989). Reliable results for hardness could not be obtained for solutions of the three fire retardants because of matrix interferences with the colorimetric method used. Tests were conducted under ambient laboratory lighting.

Total ammonia-nitrogen (TA-N), nitrate-nitrogen (NO3-N), and nitrite-nitrogen (NO2-N) were measured in all test solutions of the three fire retardants and in reference nitrogenous chemicals with live fish at 0 and 96 h. Measurements were made using ion-selective electrodes (Orion Research 1990, 1991; ATI Orion 1994) connected to an Orion model 901 Ionalyzer (Orion Research, Boston, Massachusetts). Detection limits of the methods were 0.8 mg/L for TA-N, 0.1 mg/L for NO3-N, and 0.01 mg/L for NO2-N. Un-ionized ammonia-nitrogen (NH3-N) concentrations were calculated using the equations in Emerson et al. (1975) using measured TA-N, pH, and temperature values.

Concentrations of anionic surfactant were measured in all test solutions of the foam concentrates, LAS, and SDS at 0 h. Anionic surfactant concentrations were determined using the spectrophotometric method of Hach Company (1992), which was standardized with reference LAS (molecular weight 342) obtained from the U.S. Environmental Protection Agency Environmental Monitoring Systems Laboratory (Cincinnati, Ohio). This method measures alkyl benzene sulfonate and LAS (Hach Company 1992). Concentrations are expressed as milligrams of anionic surfactant per liter, calculated as LAS (molecular weight 342). Measurements of anionic surfactant concentrations at 96 h would not be informative, because the analytical method used cannot distinguish between the intact parent compound and the degradation intermediates. Consequently, aged solutions of the foams and two reference surfactants may have greatly reduced concentrations of the parent surfactant, but they do have similar measured anionic surfactant concentrations compared with fresh solutions, as was observed by Kimerle and Swisher (1977) for LAS measured as methylene blue active substances. Percent recoveries of anionic surfactant in solutions of LAS, Fire Quench, and Pyrocap B-136 spiked at 0 h with reference LAS were 87, 118, and 109%, respectively.

Median lethal concentrations (LC50s) and their 95% confidence intervals (CIs) were calculated by the moving-average angle method (Peltier and Weber 1985). The criterion of nonoverlapping 95% CI was used to determine significant differences (P = 0.05) between LC50 values (APHA et al. 1989). The LC50 values of the eight fire-control chemicals are based on nominal concentrations of the total formulation (because of their proprietary composition). The LC50 values of ammonia, nitrate, nitrite, LAS, and SDS are based on measured concentrations at 0 h, as recommended by ASTM (1989) for static tests. Concentrations of TA-N and NH3-N or anionic surfactant at the 96-h LC50s of the fire retardants or foams, respectively, were calculated by the moving-average angle method using measured concentrations at 0 h.

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