Ammonia, anhydrous

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.001 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

0.008 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.001 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

no hazard identified

Sediment (freshwater)

Hazard assessment conclusion:

no hazard identified

Sediment (marine water)

Hazard assessment conclusion:

no hazard identified

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

0.022 mg/kg soil dw

Assessment factor:

10

Extrapolation method:

assessment factor

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

The substance is gaseous - in the environment it will become associated with water or moisture and will be therefore predominantly exist as aqueous ammonia.

Ammonia is naturally present in the environment as a consequence of the presence of decaying plant or animal matter or from animal excreta. Industrial activity may potentially cause local and regional elevations in emission and atmospheric concentrations.

In the aqueous environment, ammonia will be present as ammonia (NH3) or ammonium ion (NH4+); the relative proportions of the two chemical species are dependent on pH and (to a lesser extent) temperature. At environmentally relevant pH values of 5- 8, the predominant form will be NH4+. At higher pH values the proportion of ammonia (NH3) increases. The background concentration of ammonia in surface water varies regionally and seasonally. Survey data for total ammonia have reported average concentrations of < 0.18 mg/litre in most surface waters, and around 0.5 mg/litre in waters near large metropolitan areas. In ground water, ammonia levels are usually low as a consequence of the strong adsorption of the ammonium ion on clay minerals, or bacterial oxidation to nitrate, both processes which limit mobility in soil. Ammonia in soil is in dynamic equilibrium with nitrate and other substrates in the nitrogen cycle.

Ammonium is readily converted by bacterial species to nitrate, via the process of nitrification. The primary stage of nitrification, the oxidation of ammonium to nitrite (NO2-) is performed by Nitrosomonas (among other) species. Other bacterial species (including Nitrobacter) are responsible for the subsequent oxidation of nitrite to nitrate (NO3-). Nitrification is important in preventing the persistence or accumulation of high ammonia levels in waters receiving sewage effluent or agricultural runoff. Other mechanisms may also act to limit the concentration of ammonia in natural waters: ammonia is readily assimilated by aquatic algae and macrophytes for use as a nitrogen source. Ammonia in the aqueous environment may also be transferred to sediments by adsorption on particulates, or to the atmosphere by volatilisation at the air-water interface. Both processes have been described as having measurable effects on ammonia levels in water; however, the relative significance of each will vary according to specific environmental conditions.

In soil, ammonia is converted by a variety of bacteria, actinomycetes and fungi to ammonium (NH4+) by the process of ammonification or mineralization. Ammonium is then converted to nitrate. Nitrate is subsequently taken up and utilised by plants or returned to the atmosphere following denitrification; the metabolic reduction of nitrate into nitrogen or nitrous oxide (N2O) gas. The most likely fate of ammonium ions in soils is conversion to nitrates by nitrification.

It should be noted that the hazard assessment was based on NH3 - the form which is considered to be the toxic form of total ammonia (NH3 + NH₄ ⁺). NH₄ ⁺is considered to be non- or significantly less toxic. In order to use the results from this hazard assessment for the risk assessment, the pH and the temperature of the assessed compartment need to be considered.

As example: in freshwater with a pH of 8.5 and a temperature of 28°C (values which might be considered realistic worst case scenarios for streams, see "Verordnung zum Schutz der Oberflächengewässer (Oberflächengewässerverordnung - OGewV, 20 June 2016", attached to this endpoint summary) , about 18% of the total ammonium is present as NH3. Hence the PNEC for total ammonium concentration is about 5.5 times higher than the PNEC based on NH3. An Excel-spreadsheet for the conversion of NH3 to total ammonia based on the pH and temperature is attached to this endpoint summary.

Conclusion on classification

The substance is classified as very toxic to the environment (H400) due to the effects on fish. 

In accordance with the 2^ndATP to the CLP {Table: 4.1.0 b (II) } the classification of ammonia anhydrous should also consider the long – terms effect on the aquatic compartment. Based on the lowest NOEC value for chronic toxicity to fish (0.0135 mg/L), the substance is also classified as Aquatic chronic  2 (H411).

The large amount of data available for the aquatic toxicity of ammonia, does not facilitate direct comparison of individual studies, as various temperature and pH conditions were used in individual tests – both of these factors influence the relative proportion of ammonia present in the (more toxic) non-ionised form and consequently also the toxicity. The US EPA (1999) has extensively re-evaluated the existing data on ammonia toxicity by adjusting toxicity values to reflect the temperature and pH- conditions of individual tests, thereby allowing analysis of comparability. Available valid acute toxicity data, were recalculated after adjustment to pH 8, in order to take into account the fact that un-ionised NH₃exists in the aquatic environments and that this proportion increases with pH and/or temperature. It is well known that toxicity to aquatic organisms has been attributed to un-ionised ammonia (NH₃) species, and NH₄⁺is considered to be non- or significantly less toxic. In the normalisation process the temperature dependence was not considered, since temperature effects are negligible for acute toxicity of ammonia. The pH- and temperature adjusted (and therefore directly comparable) results of all literature data were averaged to species mean acute(chronic) values and genus mean values. A mean species value of 0.89 mg/l un-ionised ammonia was derived for Oncorhyncus mykiss. This value supports an M-factor of 1 for classification.