Priority Substances List Assessment Report for Ammonia in the Aquatic Environment

2.0 Summary of Information Critical to Assessment of "Toxic" Under CEPA 1999 (Continued)

2.4 Effects characterization

Two types of biotic effects, direct and indirect, will be discussed in this section. Direct toxic effects from ammonia are those that directly impact on an individual -- typically, death, reduced growth rate or reduced reproductive success. Indirect effects are those that typically affect ecosystems by altering the nutritional regime, in the case of eutrophication, or by altering some other physical parameter, like pH in the case of acidification. Negative effects on ecosystems usually take the form of shifts in dominant organisms, usually to ones more capable of exploiting the nutritional regime or withstanding altered physical parameters. In these cases, toxicity to organisms comes about indirectly but is still ultimately traceable to deposition of ammonia in some form. Abiotic effects mediated through the atmosphere -- i.e., destruction of stratospheric ozone, formation of ground-level ozone and enhancing the greenhouse effect -- are also discussed.

2.4.1 Effects on terrestrial plants

The toxicity of atmospheric ammonia to plants is a very active research area, with the wide-scale importance of the problem being recognized only in the late 1980s and early 1990s. Ammonia was found to be a contributor to forest decline and soil acidification in Europe only after the effects of sulphur and nitrogen oxides were fairly well known. The effects of ammonia stood apart from those of the other atmospheric pollutants because they were seen in lowlands and near livestock production. It is now well documented that visible effects and dieback within metres to kilometres of large livestock operations can be the result of NH₃ emissions.

Ecological effects of NH₃ deposition are most likely to be associated with nitrogen-poor settings, where plants adapted to low nitrogen supply are dominant (Heil and Diemont, 1983; Schjoerring et al., 1998). Alpine and boreal regions may be most susceptible (Boxman et al., 1988; Aber et al., 1989; Bobbink et al., 1992). Soils with low pH buffer capacity and a tendency to be acidic may be susceptible because of the acidifying effects of nitrification of NH₄⁺ to nitrate (Schuurkes et al., 1986). Also, the addition of ionic NH₄⁺ may disrupt cation balances.

Short-term (<1 day) acute toxicity values for plants are not readily available; however, Van der Eerden (1982) published a graph of mass concentrations versus exposure time for the effects of ammonia on terrestrial plants from published literature values. Some terrestrial plants (deciduous and coniferous trees and crops like buckwheat, cauliflower, tomato and sunflower) were adversely affected (leaf necrosis, increased sensitivity to cold) after an hour-long exposure to air concentrations ranging from 25 to 50 mg/m³ (25 000 - 50 000 µg/m³).

2.4.2 Acute effects on freshwater organisms

Concentrations of ammonia that are toxic to aquatic organisms are generally expressed as un-ionized ammonia (NH₃), because NH₃ and not NH₄⁺ has been demonstrated to be the principal toxic form of ammonia in the environment, with few exceptions.

Although a sizeable body of knowledge exists on acute, chronic and sublethal effects of ammonia on fish, there is less literature available on its effects on invertebrate species and benthic organisms. Data on concentrations of NH₃ that are toxic to freshwater phytoplankton and vascular plants, although limited, indicate that freshwater plant species are appreciably more tolerant of NH₃ than invertebrates or fish.

2.4.2.1 Algae

Experimental data on the toxicity of ammonia to freshwater phytoplankton and vascular plant communities are limited and contradictory, although that may be the result of variation in response from different species. Most studies reported total ammonia concentrations and did not report pH and temperature, so that it was not possible to calculate un-ionized ammonia concentrations. At relatively high concentrations (compared with exposure levels for fish), some algae and most aquatic macrophytes can use ammonia as a nutrient. At concentrations between 2 and 5 mg total ammonia/L, growth inhibition occurred in Chlorella vulgaris, whereas complete growth inhibition occurred at 5.5 mg/L and 50% lethality occurred around 9 mg/L for a 120-hour exposure (Przytocka-Jusiak, 1976). Bretthauer (1978) reported that a concentration (assuming pH 6.5 and 30°C) of 0.6 mg NH₃/L killed Ochromonas sociabilis and that development of the population was reduced at 0.3 mg/L (duration of tests not reported). Concentrations of 0.06-0.15 mg NH₃/L had an insignificant effect on growth, and concentrations of 0.015-0.03 mg NH₃/L enhanced growth. Studies have shown that ammonia at concentrations exceeding 2.5 mg NH₃/L inhibited photosynthesis and growth in the algal species Scenedesmus obliquus and inhibited photosynthesis in the algae Chlorella pyrenoidosa, Anacystis nidulans and Plectonema boryanum (Abeliovich and Azov, 1976).

2.4.2.2 Fish

Symptoms of acute toxicity of ammonia in fish are loss of equilibrium, hyperexcitability, increased breathing, cardiac output and oxygen uptake, and, eventually, convulsions, coma and death.

Fish can tolerate high concentrations of unionized ammonia over a period of hours. As the exposure period extends, tolerance diminishes. Early studies with rainbow trout (Oncorhynchus mykiss) and coho salmon (O. kisutch) (Grindley, 1946; Downing and Merkins, 1955; Lloyd and Herbert, 1960; Ball, 1967; Department of Scientific and Industrial Research, 1967; Brown et al., 1969; Buckley, 1978; Thurston et al., 1981a,b) reported the hours to 50% mortality for various exposure conditions. The relationship developed using the data from these studies describes the time to 50% mortality (LT₅₀) for a given exposure concentration (x, in mg NH₃/L) as:

LT₅₀ = 4.7942 * x ^-1.7681 hours

Conversely, for a given exposure period (x, in hours), the LC₅₀ (concentration of un-ionized ammonia producing 50% mortality) can be determined:

LC₅₀ = 1.7928 * x ^-0.3573 mg NH₃/L

These relationships are valid for exposure periods between 30 minutes and 24 hours, since they are developed from a narrow range of high concentrations in water and a limited number of studies.

A few of the above studies have also reported the slope of the response relationships such that the LC₁₀ could be estimated (Craig, 1999). Studies by Ball (1967), Brown et al. (1969) and Buckley (1978) demonstrate that between 3 and 48 hours, the LC₁₀ is about 10% of the LC₅₀ , as calculated by the above equation. As the duration of exposure increases, the percentage increases to about 70%, as illustrated by Broderius and Smith (1979) and reported by Lloyd (1961).

The species mean LC₅₀ values for fish found in Canadian waters were calculated from data taken from Table 1 of the U.S. EPA (1985) water quality criteria document. Most of the acute tests were conducted in laboratories where concentrations were maintained at a constant level, and after 48--96 hours mortality would not change. The species acute mean un-ionized ammonia concentrations are the geometric mean of LC₅₀ s reported for respective species in the U.S. EPA (1985) document. The resulting values are presented in Table 4 along with the number of studies used to calculate the species mean LC₅₀ and the minimum and maximum LC₅₀ reported among the studies for that species. Species that are reported in Table 4 of U.S. EPA (1985) but are not indigenous to Canada have been excluded from Table 4.

Table 4 Mean LC₅₀s for un-ionized ammonia in Canadian fish species

Common name	Species name	LC50 1 (mg NH3/L)	No. of studies	Minimum LC50 (mg NH3/L)	Maximum LC50 mg NH3/L)
White perch	Morone americana	0.279	2	0.150	0.520
Mountain whitefish	Prosopium williamsoni	0.289	3	0.143	0.473
Chinook salmon	Oncorhynchus tshawytscha	0.442	3	0.399	0.476
Rainbow trout	Oncorhynchus mykiss	0.481	112	0.158	1.090
Pumpkinseed	Lepomis gibbosus	0.489	4	0.140	0.860
Coho salmon	Oncorhynchus kisutch	0.520	8	0.272	0.880
Cutthroat trout	Oncorhynchus clarki	0.642	4	0.520	0.800
Brown trout	Salmo trutta	0.657	3	0.597	0.701
Mountain sucker	Catostomus platyrhynchus	0.685	3	0.668	0.819
Walleye	Stizostedion vitreum	0.706	4	0.510	1.100
Golden shiner	Notemigonus crysoleucas	0.720	1
Golden trout	Oncorhynchus aguabonita	0.755	1
Brook trout	Salvelinus fontinalis	1.005	2	0.962	1.050
Smallmouth bass	Micropterus dolomieu	1.105	4	0.690	1.780
Largemouth bass	Micropterus salmoides	1.304	2	1.000	1.700
Fathead minnow	Pimephales promelas	1.344	45	0.240	3.440
White sucker	Catostomus commersoni	1.349	7	0.760	2.220
Mottled sculpin	Cottus bairdi	1.390	1
Bluegill	Lepomis macrochirus	1.406	15	0.260	2.970
Spotfin shiner	Cyprinella spiloptera	1.479	3	1.200	1.620
Channel catfish	Ictalurus punctatus	1.707	14	0.500	4.200
Stoneroller	Comostoma anonalum	1.720	1
Green sunfish	Lepomis cyanellus	1.860	6	0.590	2.110

¹LC₅₀ is the geometric mean when more than one study result is reported.

Species mean LC₅₀ values range from 0.28 mg NH₃/L for white perch (Morone americana) to 1.86 mg NH₃/L for green sunfish (Lepomis cyanellus). Certain sensitive species are localized, such as white perch, which are usually found in brackish waters on the Atlantic coast but have also been reported in Lake Ontario and the Bay of Quinte (Scott and Crossman, 1973). Mountain whitefish (Prosopium williamsoni) are also restricted to western Alberta and are widespread in British Columbia (Scott and Crossman, 1973). Salmonids are widespread and represent the next most sensitive group of species.

2.4.2.3 Invertebrates

A number of invertebrate acute lethality studies are also referenced in the U.S. EPA (1985) water criteria document and presented in Table 5; concentrations are similar to those found for fish.

The species mean LC₅₀ values for invertebrates range from 1.2 mg NH₃/L for the cladoceran species and fingernail claim (Musculium transversum) to as high as 10.2 mg NH₃/L reported for caddisfly larvae. The more sensitive invertebrates appear to be the pelagic cladocerans, while the epibenthic and benthic organisms appear more tolerant. The sensitivity of invertebrates to ammonia as a group overlaps with the median of most tolerant fish species.

Table 5 Mean LC₅₀ s for un-ionized ammonia in invertebrate species

Common name	Species name	LC50 1 (mg NH3/L)	No.of studies	Minimum LC50 (mg NH3/L)	Maximum LC50 (mg NH3/L)
Daphnid	Daphnia pulicaria	1.160	1
Cladoceran	Simocephalus vetulus	1.185	2	0.613	2.29
Fingernail clam	Musculium transversum	1.191	3	0.93	1.29
Flatworm	Dendrocoelum lacteum	1.400	1
Daphnid	Daphnia magna	1.613	12	0.53	4.94
Mayfly	Callibaetis sp.	1.800	1
Snail	Physa gyrina	1.961	5	1.59	2.49
Stonefly	Arcynopteryx parallela	2.030	2	2.00	2.06
Scud	Crangonyx pseudogracilis	2.316	5	1.63	5.63
Worm	Tubifex tubifex	2.700	1
Snail	Helisoma trivolvis	2.760	1
Crayfish	Orconectes nais	3.150	1
Mayfly	Callibaetis skokianus	4.829	3	3.86	5.88
Isopod	Asellus racovitzai	4.950	1
Beetle	Stenelmis sexilneata	8.000	1
Caddisfly	Philarctus quaeris	10.200	1

¹LC₅₀ is the geometric mean when more than one study result is reported.