Acute Toxicity of Fire-Retardant and Foam-Suppressant Chemicals to Hyalella azteca (Saussure)
Results
Water quality
Throughout the tests, dissolved oxygen concentrations were maintained at or above 76.7% saturation. For tests conducted in soft water, the pH measured in pooled exposure water from the control treatments at 96 h ranged from 7.08 to 7.89 and in chemical treatments from 7.20 to 7.91. For hard water tests, the pH measured in pooled exposure water from the control treatments at 96 h ranged from 7.99 to 8.28 and in chemical treatments from 7.75 to 8.26.
Acute toxicity
Control mortality occurred in a few tests, but only tests with </=20% of the control mortality were accepted; this follows guidelines in ASTM [11]. Control mortality of 20% only occurred during the test with PC D75-F in soft water; three tests had 10% and one had 0% mortality. Control mortality of 10% occurred only once, during the hard water test with PC D75-F; all other tests had 0% mortality.
The 96-h LC50s for H. azteca tested in soft water with fire retardants ranged from 53 mg/L for PC D75-F to 127 mg/L for FT GTS-R and in hard water from 363 mg/L for FT GTS-R to 535 mg/L for FT LCG-R (Table 1). The foam suppressants yielded LC50s in soft water of 10 mg/L for PC WD-881 and 24 mg/L for Silv-Ex and in hard water, 22 mg/L for PC WD-881 and 27 mg/L for Silv-Ex.
The toxicity of four of the chemicals increased from the 24-h LC50 to the 96-h LC50 although not as substantially for Silv-Ex where the increase was less than two-fold for both hard and soft water. The PC D75-F tested in soft water produced the largest increase, eight-fold, from the 24-h LC50 to the 96-h LC50. Increases in toxicity between 24 and 96 h were less substantial in hard water than in soft water.
The toxicity of four of the chemicals to H. azteca was increased significantly in soft water. Only Silv-Ex was equally toxic in both water qualities.
The rank order of toxicity of the chemicals to H. azteca from most toxic to least toxic in soft water was: PC WD-881 > Silv-Ex > PC D75-F = FT LCG-R > FT GTS-R. In hard water the rank order from most toxic to least toxic was: PC WD-881 = Silv-Ex > FT GTS-R = PC D75-F = FT LCG-R.
Ammonia
Ammonia analysis indicated that the three fire retardants contained more total ammonia, as nitrogen and un-ionized ammonia, than did the fire-suppressant foams (Table 2). Because ammonia was analyzed only in control, and low, medium, and high concentrations and the pH of a solution at an LC50 would be difficult to predict, only a range of un-ionized ammonia concentrations bracketing the LC50s can be reported. Total ammonia, as nitrogen at test initiation, was estimated by regression analysis from the 96-h LC50 concentration in the fire-retardant tests. Total ammonia, as nitrogen, in soft water tests ranged from 7.44 mg/L in FT LCG-R to 24.63 mg/L in FT GTS-R and, in hard water tests, from 56.49 mg/L in FT LCG-R to 80.90 mg/L in PC D75-F Unionized ammonia is reported for the two concentrations bracketing the 96-h LC50 concentration. In soft water, the concentration of un-ionized ammonia ranged from 0.02 to 0.08 mg/L in FT LCG-R to 0.13 to 0.79 mg/L in FT GTS-R and, in hard water tests, from 0.24 to 1.09 mg/L in FT LCG-R to 0.53 to 2.40 mg/L in FT GTS-R. Total ammonia, as nitrogen, at the 96-h LC50 concentration in fire-suppressant foams in soft and hard water tests was 0.22 mg/L or less, and consequently, un-ionized ammonia was </= 0.02 mg/L.
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