Acute Toxicity of Firefighting Chemical Formulations to Four Life Stages of Fathead Minnow

Results

Dissolved oxygen was maintained at greater than 40% saturation, as recommended by ASTM 1989, in all but one test. Sixty-DPH juveniles exposed to PC D75-F in soft water had a dissolved oxygen of 34% saturation at 48 hr; however, the live fish in the test demonstrated no overt signs of oxygen deprivation. Ten tests had dissolved oxygen readings below 60% saturation at 48 hr (range, 42 - 59), and four tests at 96 hr (range 52 - 59).

The 96-hr LC₅₀ values determined for the four life stages tested with the five firefighting chemicals in two water types are presented in Table 3. There was no mortality in any control exposures at any life stage in four control exposures in hard water and in four control exposures in soft water. The LC₅₀ values for each 24-hr observation period are given in Gaikowski (1994). Most mortality in fish tests occurred in the initial 24 hr of exposure, whereas in egg tests, most mortality was delayed until 48 hr of exposure or later (Gaikowski, 1994). Applying the Friedman test (Conover, 1980) to the 96-hr LC₅₀s derived for each life stage and water quality resulted in the following rank order of most toxic to least toxic 96-hr LC₅₀s: PC WD-881 > Silv-Ex > FT GTS-R > PC D75-F > FT LCG-R (Table 3).

Table 3. Acute Toxicity (96-hr LC₅₀; mg/Liter; 95% Confidence Interval in Parentheses) of Five Firefighting Chemical Formulations to Fathead Minnow Exposed in ASTM Soft and Hard Water at Four Life Stages.

Formulation	Water type	Life stage
Formulation	Water type	Egg	Fry	30 DPH	60 DPH
FT GTS-R	Soft	787^a,*	233^b,*	494^c,*	605^a,c,*^,†
	Soft	(529-1025)	(184-301)	(432-573)	(470-780)
	Hard	363^a,*^,‡	135^b,*	193^c,*	320^a,*
	Hard	(280-470)	(105-165)	(153-235)	(252-392)
FT LCG-R	Soft	2317^a,*	1080^b	1676^c,†	1797^a,c,
	Soft	(1802-2830)	(880-1353)	(1300-2160)	(1466-2247)
	Hard	6705^a,*	519^b	1181^c	1676^c,†
	Hard	(5720-8281)	(389-654)	(937-1584)	(1300-2160)
PC D75-F	Soft	2250^a,*	420^b,*	572^b,c*	612^c
	Soft	(1736-2748)	(320-532)	(455-780)	(444-770)
	Hard	1569^a,*	168^b,*	237^c,*	490^d
	Hard	(1255-1924)	(136-207)	(194-296)	(378-597)
PC WD-881	Soft	32^a,‡	14^b	22^a,*^,†	22^a,*^,†
	Soft	(10-47)	(11-17)	(17-28)	(17-28)
	Hard	26^a	14^b	13^b,*^,†	13^b,*^,†
	Hard	(21-33)	(11-17)	(10-17)	(10-17)
Silv-EX	Soft	32^a	22^b,†	20^b	22^b,†
	Soft	(25-39)	(17-28)	16-25	(17-28)
	Hard	28^a	20^a,b	19^b	22^a,b†
	Hard	(23-37)	(16-25)	(15-24)	(17-28)

Note. Asterisks denote a significant difference (P = 0.05) between soft and hard water for a test formulation. Letters in common denote no significant difference(P = 0.05) among life stages within a test formulation and water quality.
† No partial kills; 95% confidence interval: lower limit, highest test concentration with 0% mortality; upper limit, lowest test concentration with 100% mortality.
‡ LC₅₀ calculated using the binomial test.

The fire-suppressant foams, PC WD-881 and Silv-Ex, were substantially more toxic than fire-retardant formulations tested. For a given life stage and water type, PC WD-881 and Silv-Ex were 10 - 258 times more toxic than FT LCG-R, FT GTS-R, and PC D75-F (Table 3).

Life Stage and Water Type

Life stage and water type influenced the toxicity of the five firefighting chemicals. Based on the Friedman test, the rank order of the life stages tested in both water types from most sensitive to least sensitive was: fry = 30 DPH > 60 DPH > egg. In only one case were eggs more sensitive than another life stage; eggs tested with FT GTS-R in hard water were more sensitive than 30- and 60-DPH juveniles tested in soft water (Table 3). In 7 of 10 tests the magnitude of difference in sensitivity between the most sensitive life stage and the least sensitive was 3-fold or less. The greatest difference was a 13-fold difference between eggs and fry exposed to FT LCG-R in hard water, followed by a 9-fold difference between eggs and fry exposed to PC D75-F in hard water.

Water type influenced the toxicity of the firefighting chemicals. In 19 of 20 tests, the chemicals were less toxic in soft water tests than in hard water tests (Table 3). In 10 of the tests the difference was significant. The only test where toxicity was greater in soft water than in hard water was eggs exposed to FT LCG-R. Based on the Wilcoxon signed rank test, only the overall toxicity of FT GTS-R and PC D75-F was significantly influenced by water type.

Ammonia, Nitrate, Nitrite

Estimated un-ionized ammonia concentrations at the 96-hr LC₅₀ for the five fire-control chemicals are given in Table 4. Comparison of the slopes of the chemicals indicatated that FT GTS-R had a higher percentage of NH₃-N (21%) than PC D75-F (18%) or FT LCG-R (10%) (Gaikowski, 1994). Un-ionized ammonia ranges at the 96-hr LC₅₀s were similar for the three retardants (FT LCG-R, 0.33 - 7.01 mg/liter; FT GTS-R, 0.43 - 4.51 mg/liter; PC D75-F, 0.10 - 4.58 mg/liter). Phos-Chek D75-F had the greatest variance in pH readings with an average of 0.93 units between the low and high pH, whereas FT LCG-R and FT GTS-R had average differences of only 0.30 units between low and high pH. Consequently, the ranges of un-ionized ammonia concentrations were wider for PC D75-F than for FT LCG-R and FT GTS-R.

Table 4. Range of Un-ionized Ammonia concentrations (mg/Liter) at the 96-hr LC₅₀ for the Four Life Stages of Fathead Minnow Tested with Five Firefighting Chemical Formulations in ASTM Soft and Hard Water.

Formulation	Water type	Life stage
Formulation	Water type	Egg	Fry	30 DPH	60 DPH
FI GTS-R	Soft	2.40-2.95	0.69-1.27	1.81-3.80	1.87-2.41
FI GTS-R	Hard	1.71-4.51	0.43-0.80	1.23-3.46	1.58-3.94
FT LCG-R	Soft	1.18-1.73	0.64-1.02	1.19-1.76	1.22-1.28
FT LCG-R	Hard	2.62-7.01	0.33-0.74	0.86-3.22	0.95-2.77
PC D75-F	Soft	0.25-1.56	0.15-1.04	0.28-1.93	0.27-1.51
PC D75-F	Hard	0.23-3.16	0.10-1.02	0.33-3.08	0.46-4.58
PC WD-881	Soft	0.05^a	0.04^a	0.03^a	0.04^a
PC WD-881	Hard	0.03^a	0.03^a	0.04^a	0.07^a
Silv-Ex	Soft	0.29^a	0.23^a	0.15^a	0.22^a
Silv-Ex	Hard	0.27^a	0.18^a	0.18^a	0.22^a
^a Concentration given as mg/liter NH₃-N.

Measured nitrate-nitrogen (NO₃^--N) and nitrite-nitrogen (NO₂^--N) concentrations at the 96-hr LC₅₀ for the fry life stage, and estimated for the three other stages, are given in Table 5. Fire-Trol LCG-R had substantially more nitrate and nitrite than either FT GTS-R or PC D75-F. Nitrate-nitrogen concentrations in FT GTS-R ranged from 0.12 to 0.27 mg/liter, in FT LCG-R from 2.6 to 26 mg/liter, and in PC D75-F from 0.60 to 10 mg/liter. Nitrite-nitrogen concentrations in FT GTS-R ranged from 2.9 to 14 mg/liter, in FT LCG-R from 21 to 642 mg/liter, and in PC D75-F from 0.16 to 0.21 mg/liter. Nitrite concentrations were 24- to 51-fold higher than nitrate in FT GTS-R, whereas they were 8- to 25-fold higher than nitrate in FT LCG-R. In contrast, nitrite concentrations were 35- to 43-fold lower in tests with eggs and 4- to 15-fold lower in tests with fish than nitrate in PC D75-F.

Table 5. Range of Nitrate (mg/Liter NO₃^--N) and Nitrite (mg/Liter NO₂^--N) Concentrations at the 96-hr LC₅₀ for Four Life Stages of Fathead Minnow Tested with Five Firefighting Chemical Formulations in ASTM Soft and Hard Water.

Formulation	Water type	Life stage
Formulation	Water type	Egg	Fry	30 DPH	60 DPH
Nitrate
FT GTS-R	Soft	0.27	0.14	0.21	0.23
FT GTS-R	Hard	0.17	0.12	0.14	0.16
FT LCG-R	Soft	9.1	4.56	6.81	7.25
FT LCG-R	Hard	26	2.56	5.01	6.81
PC D75-F	Soft	10	1.80	2.54	2.73
PC D75-F	Hard	7.3	0.60	0.94	2.14
Nitrite
FT GTS-R	Soft	14	4.52	9.46	9.46
FT GTS-R	Hard	6.7	2.86	3.83	5.96
FT LCG-R	Soft	110	49	78	84
FT LCG-R	Hard	642	21	54	78
PC D75-F	Soft	0.23	0.17	0.18	0.18
PC D75-F	Hard	0.21	0.17	0.16	0.17
^a Measured values.

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