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The two fire suppressant foams, Phos-Chek WD-881 and Silv-Ex, were more toxic than the fire retardants tested (Table 3). Both had LC50 values that were at least 10 times lower than the LC50 for the next two most toxic formulations, PC D75-F and FT GTS-R, and approx. 67 times lower than the LC50 for FT LCG-R. For all life stages, the rank order of the fire chemicals tested for both soft and hard water tests, based on the Friedman test, from most toxic to least toxic was PC WD-881, Silv-Ex, PC D75-F, FT GTS-R, and FT LCG-R (all were significantly different; p = 0.05).

Both fire-suppressant foams had very similar 96-h LC50s, ranging from 10 to 44 mg/L for PC WD-881 and 11 to >78 mg/L for Silv-Ex (Table 3). Phos-Chek D75-F and FT GTS-R had similar ranges, 218 mg/L to >3,600 mg/L for PC D75-F and 207 mg/L to >6,000 mg/L for FT GTS-R (Table 3). Phos-Chek D75-F and FT GTS-R were 19 to 77 times less toxic than PC WD-881 and Silv-Ex. Fire-Trol LCG-R was the least toxic formulation tested, with 96-h LC50s ranging from 872 to >10,000 mg/L (Table 3).

ASTM = American Society for Testing and Materials.
^bAsterisks denote a significant difference (p≤0.05) in toxicity of test formulations between soft and hard water. Common uppercase letters denote no significant difference (p≤0.05) among life stages within a test formulation and water quality. dph = Days posthatch.
^cNo partial kills; 95% confidence interval: lower limit = highest test concentration with 0% mortality, upper limit = lowest test concentration with 100% mortality.
^dLC50 calculated using binomial test.
^eTest were started with true sac-fry.
^fLC50 calculated by binomial test; less than 70% mortality in highest test concentration.

Life stage and water type

Life stage and water type played important roles in determining the relative sensitivity of rainbow trout to the five formulations. For all test chemicals, the rank order of the life stages tested, based on the Friedman test, from most sensitive to least sensitive was as follows:

(common underline, not significantly different; p ≥ 0.05). Most mortality occurred within the initial 24 h of exposure for most life stages. The embryo-larvae life stage was an exception in that LC50 values decreased at hatching, suggesting that the larval stage was more sensitive than the egg stage. Based on the 96-h LC50s, eyed eggs were between 1.3 and 25.6 times less sensitive to toxicants than other life stages. 96-h LC50s for swim-up fry were 2 to 30 times less than the 96-h LC50s of eyed eggs. The eyed-egg stage, regardless of water type, was the least sensitive life stage, with the highest 96-h LC50 values (Table 3).

The 96-h LC50 determined for swim-up fry (910 mg/L) tested with FT LCG-R in soft water was not significantly less than that for the 60-dph juveniles (1,080 mg/L) but was significantly lower than the values determined for the other life stages tested. In hard water tests with FT LCG-R, swim-up fry had a 96-h LC50 (872 mg/L) that was not significantly less than the 96-h LC50 determined for 90-dph fish (1,006 mg/L). Swim-up fry and 90-dph juveniles were significantly more sensitive than the other life stages tested with FT LCG-R in hard water.

Soft and hard water results for FT GTS-R were similar because for both water qualities, the swim-up fry and the 60- and 90-dph juveniles were not significantly different in their sensitivity but were significantly more sensitive than the embryo-larvae (Table 3). The latter was significantly more sensitive than the eyed-eggs.

The embryo-larvae, swim-up fry, and 60- and 90-dph life stages tested with PC D75-F in soft water were not significantly different from each other, but all were significantly more sensitive than the eyed egg life stage (Table 3). This pattern was the same in tests with hard water and PC D75-F.

Embryo larvae, swim-up fry, and 60-dph juveniles tested with PC WD-881 were significantly more sensitive than 90-dph juveniles tested in soft water. The eyed-egg life stage tested with PC WD-881 in soft water was significantly less sensitive than all other life stages tested. No significant differences existed between the embryo-larvae, swim-up fry, and 60- and 90-dph juvenile life stages tested in hard water (Table 3).

Embryo-larvae tested with Silv-Ex in soft water were not significantly more sensitive than the swim-up fry life stage but were significantly more sensitive than the other life stages tested. The 96-h LC50s determined for the swim-up fry and 60- and 90-dph juveniles were not significantly different. The eyed-egg life stage tested in soft water was significantly less sensitive than all other life stages. Tests conducted with Silv-Ex in hard water resulted in no significant differences between the 96-h LC50s for embryo-larvae, swim-up fry, or 60- and 90-dph juvenile stages. Rainbow trout eyed eggs tested with Silv-Ex in hard water were significantly more resilient than the other life stages.

Water type affected the toxicity of three fire-control chemicals. The formulations FT GTS-R and Silv-Ex were generally more toxic in hard water than in soft water (Table 3). Swim-up fry and 60- and 90-dph juveniles were significantly more sensitive to FT GTS-R in hard water than in soft water (Table 3). For tests conducted with Silv-Ex, the eyed egg was the only life stage not significantly more sensitive when tested in hard water as compared to soft water , probably because insufficient mortality at the high concentration occurred and precluded determination of a 96-h LC50. Water quality did not influence toxicity in tests with PC D75-F, PC WD-881, or FT LCG-R except with 90-dph fish (Table 3).

Ammonia, Nitrate, Nitrite

Estimated un-ionized ammonia concentrations at the 96-h LC50 for the five fire-control chemicals are given in Table 4. Comparison of the regression equations for each water type and formulation indicated that both FT GTS-R and PC D75-F had similar slopes [26]. The slopes indicated the ammonia percentage of the formulation, i.e., that approx. 20 to 23% of both FT GTS-R and PC D75-F was ammonia, whereas FT LCG-R was only 10 to 12% ammonia.

Table 4. Range of estimated un-ionized ammonia concentrations (mg/L) at the 96-h median lethal concentration (LC50) for the five rainbow trout life stages tested with five fire-fighting chemical formulations in ASTM^a soft and hard water.

Un-ionized ammonia ranges at the 96-h LC50 were similar for the three fire retardants (FT GTS-R, 0.41-4.30 mg/L; FT LCG-R, 0.24-2.44 mg/L; and PC D75-F, 0.03-3.12 mg/L) excluding NH₃ estimates for the eyed-egg tests. Fire-Trol GTS-R had a higher pH range than FT LCG-R and PC D75-F in all but two cases, which contributed to its greater amount of un-ionized ammonia. In these two cases, embryo-larvae exposures to PC D75-F in hard and soft water had a higher pH than those in FT GTS-R. Due to extremely low concentrations of NH₃-N in PC WD-881 and Silv-Ex, further analysis of NH ₃ concentrations at the 96-h LC50 was not completed.

Estimated nitrate-nitrogen (NO₃^--N) and nitrite-nitrogen (NO ₂^--N) concentrations at the 96-h LC50 for four life stages, and measured for the swim-up fry stage, are given in Table 5. Fire-Trol LCG-R had substantially more nitrate and nitrite than either FT LCG-R or PC D75-F. Nitrite concentrations were 21- to 26-fold higher than nitrate in FT GTS-R, whereas they were 10- to 19-fold higher than nitrate in FT LCG-R. In contrast, nitrite concentrations were three- to fivefold lower than nitrate in PC D75-F. Nitrate-nitrogen concentrations ranged from 0.17 to >5.4 mg/L in FT GTS-R and from 2.0 to >60 mg/L in FT LCG-R. Measured concentrations of nitrate-nitrogen in PC D75-F were between those in FT GTS-R and FT LCG-R. Estimated nitrite-nitrogen concentrations at the LC50 ranged from 3.6 to >113 mg/L in FT GTS-R and from 38 to >540 mg/L in FT LCG-R. Measured concentrations of nitrite-nitrogen in PC D75-F were <1 mg/L.

Table 5. Range of estimated nitrate (mg/L NO^--N) and nitrite (mg/L NO^-₂-N) concentrations at the 96-h median lethal concentration (LC50) for the five life stages of rainbow trout tested with five fire-fighting chemical formulations in ASTM^a soft and hard water.