Acute Toxicity of Fire Control Chemicals to Daphnia magna (Straus) and Selenastrum capricornutum (Printz)
Results
Water Quality
Daphnia magna. Throughout the daphnid tests dissolved oxygen concentrations were maintained at or above 72.5% saturation. For tests conducted in soft water, pH measured in test vessels in the control treatments ranged from 7.84 to 7.97 and in the chemical treatments from 6.91 to 7.97. For hard water tests, pH measured in the control treatments ranged from 8.22 to 8.40 and in the chemical treatments from 6.78 to 8.37.
Selenastrum capricornutum. Algal assay medium was adjusted to a pH of 7.5 ± 0.1 one day prior to testing. When tests were initiated, pH of the solution in the test vessels ranged from 6.55 to 7.13 in the control treatments and 6.24 to 6.62 in the chemical treatments. When the tests were terminated after 96 hr, pH ranged from 8.00 to 8.41 in the control treatments and from 4.32 to 8.48 in the chemical treatments.
Cell growth in test concentrations with pH below 6.0 for two chemicals was not substantially inhibited when compared to cell growth in other test concentrations and the control. A decrease in pH was observed in algal tests with Fire-Trol GTS-R (pH 5.77) and Phos-Chek D75-F (pH 4.32) at 96 hours. Both test chemicals contain ammonium sulfate and the decrease in pH may be in response to the formation of acids such as sulfuric acid.
Acute Toxicity
Daphnia magna. The three non-foam retardants (Fire-Trol GTS-R, Fire-Trol LCG-R, and Phos-Chek D75-F) were less toxic to the daphnids than the foam suppressants (Phos-Chek WD-881 and Silv-Ex) (Table 2). The 48-hr EC50s of the non-foam retardants for D. magna in soft water ranged from 140 mg/liter for Phos-Chek D75-F to 848 mg/liter for Fire-Trol LCG-R, and in hard water from 280 mg/liter for Phos-Chek D75-F to 813 mg/liter for Fire-Trol LCG-R. The foam suppressants had 48-hr EC50s in soft water of 7 mg/liter for Silv-Ex and 11 mg/liter for Phos-Chek WD-881, and in hard water of 4 mg/liter for Phos-Chek WD-881 and 7 mg/liter for Silv-Ex. Toxic effects were not substantially different between the 24-hr and 48-hr EC50s for the foam suppressants or Phos-Chek D75-F; however, toxicity of the two Fire-Trol compounds nearly doubled.
Water quality did not affect the toxicity of the chemicals to daphnids in a consistent manner (Table 2). The toxicity of Phos-Chek D75-F, the most toxic non-foam retardant in both water qualities, was significantly increased twofold in soft water compared to hard water. In contrast, the toxicity of Phos-Chek WD-881 was significantly decreased threefold in soft water compared to hard water. The remaining three chemicals had similar toxicities in both water qualities.
Selenastrum capricornutum. The IC50 values for S. capricornutum in static 96-hr acute toxicity tests were not different between foam and non-foam chemicals (Table 3). The 96-hr IC50s for non-foam retardants ranged from 10 mg/liter for Fire-Trol LCG-R to 48 mg/liter for Phos-Chek D75-F, whereas foam suppressant 96-hr IC50s were 15 mg/liter for Silv-Ex and 24 mg/liter for Phos-Chek WD-881.
Chemical concentrations of four of the five chemicals produced stimulatory growth effects in lower treatments as compared to the control treatments. Fire-Trol GTS-R treatments produced 12-16% more biomass than the control treatment when test chemical concentrations ranged from 3.6 to 6 mg/liter. Fire-Trol LCG-R produced 6% more biomass when test chemical concentrations ranged from 3.6 to 6 mg/liter; half as much as Fire-Trol GTS-R. Phos-Chek D75-F produced the greatest stimulation; at 10 mg/L there was a 43% increase in biomass. Phos-Chek WD-881 increased biomass when test chemical concentration ranged from 2.16 mg/liter to 10 mg/liter. Increases ranged from 3 to 16% with greater increases in the lowest treatment and smaller increases in the highest treatment exhibiting stimulation. Silv-Ex did not stimulate growth in any test concentration. Fire-Trol LCG-R was the least toxic to daphnids, but the most toxic to algae.
Ammonia
Ammonia analysis indicated that the three non-foam retardants contained more total ammonia as nitrogen and un-ionized ammonia than the foam suppressants (Table 4). Initial total ammonia as nitrogen was estimated by regression analysis at the EC50 values of non-foam retardants conducted with daphnids. In soft water tests, estimated total ammonia concentrations ranged from 24 mg/liter in Phos-Chek D75-F to 91 mg/liter in Fire-Trol LCG-R, and in hard water tests from 52 mg/liter in Phos-Chek D75-F to 95 mg/liter in Fire-Trol LCG-R. Un-ionized ammonia is reported for the two concentrations bracketing EC50 values of these tests. In soft water the concentration of un-ionized ammonia present ranged from 0.15-0.32 mg/liter in Phos-Chek D75-F to 0.73-2.7 mg/liter in Fire Trol GTS-R, and in hard water from 0.48-0.89 mg/liter in Phos-Chek D75-F to 2.0-4.9 mg/liter in Fire-Trol GTS-R.
Total ammonia as nitrogen concentrations at the EC50 value for daphnids exposed to foam suppressants in soft water was 0.08 mg/liter in Phos-Chek WD-881 and 0.12 mg/liter in Silv-Ex, and in hard water, 0.05 mg/liter in Phos-Chek WD-881 and 0.11 mg/liter in Silv-Ex. Un-ionized ammonia concentrations for both foam suppressants was 0 mg/liter in Phos-Chek WD-881 and 0-0.02 mg/liter in Silv-Ex in either water quality.
In algae tests, total ammonia as nitrogen in the test concentrations decreased between 0 and 96 hr (Table 5), apparently because algae used the nitrogen as a nutrient. The decrease was substantial for the non-foam retardants at lower test chemical concentrations, but not at higher test chemical concentrations. The ammonia concentration of the foam suppressants, which were composed primarily of surfactant compounds, were low. There was little or no un-ionized ammonia present in all concentrations of both foam and non-foam chemicals.
Nitrate and Nitrite
Nitrate and nitrite analysis indicated that the three non-foam fire retardants contained more nitrite-nitrogen (NO2--N) than nitrate-nitrogen (NO3--N) (Table 6). Nitrate-nitrogen concentrations in soft water tests ranged from 0.08 mg/liter in Fire-Trol GTS-R to 3.79mg/liter in Fire-Trol LCG-R, and in hard water tests ranged from 0.15 mg/liter in Fire-Trol GTS-R to 3.93 mg/liter in Fire-Trol LCG-R. Nitrite-nitrogen concentrations in soft water tests ranged from 0.20 mg/liter in Phos-Chek D75-F to 33.2 mg/liter in Fire-Trol LCG-R, and in hard water tests ranged from 0.22 mg/liter in Phos-Chek D75-F to 31.2 mg/liter in Fire-Trol LCG-R.
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