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Short-term toxicity to aquatic invertebrates

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The assessment entity “Ammonium (NH4+)” is a natural and common component of the environment andof all living organisms(OECD SIDS, 2004).In aquatic and terrestrial environments, ionic ammonium (NH4+) is in equilibrium with ammonia (NH3), and the respective speciation is influenced by various parameters, including temperature, pH, salinity and ionic strength. The main factors, however, that influence the equilibrium between un-ionized and ionized ammonia are pH and temperature (Environment Canada 2010 and references therein). Raising pH by one unit can cause the un-ionized ammonia concentration to increase nearly tenfold, while a 5 °C temperature increase can cause an increase of 40-50% (Environment Canada 2010 and references therein). The ionic strength of the water is also an important influence on the un-ionized ammonia concentration. As the ionic strength increases in hard or marine waters, there is a decrease in the un-ionized NH3 concentration (Environment Canada 2010 and references therein). Ammonia (NH3) and ionic ammonium (NH4+) are referred to as total ammonia nitrogen (TAN). Ammonia is essential for many biological processes and serves as a precursor for amino acid and nucleotide synthesis. Most ammonia is produced by bacteria in water and soil as an end product of plant and animal waste decomposition. It is found in soil, air, and water and provides a source of nitrogen for plants. As part of the natural nitrogen cycle, ammonia is biochemically transformed in soils and water.

The endpoint is addressed with publicly available data on ammonium (NH4+) and if relevant ammonia (NH3), including the OECD SIDS Assessment Report for ammonium chloride (2004).

A registration dossier shall contain information on the environmental hazard assessment (Regulation 1907/2006, Article 10). For the environmental hazard assessment of ammonium (NH4+), the standard testing regime set out in Annexes VII and VIII is adapted in accordance with Section 1.2 and 1.3 of Annex XI so that “testing does not appear to be scientifically necessary” as follows:

 

(I) The ecotoxic potential of ammonium is assumed to be negligible since ammonium is generally not considered to represent a risk to the environment. According to the OECD SIAR for ammonium chloride (2004), the log Kow, that cannot be experimentally determined, is expected to be very low. Moreover, ammonium (NH4+) is rapidly degraded. Hence, is not likely to accumulate in the environment or living organisms (OECD SIDS, 2004). Ammonium “has a low inherent hazard potential for the environment” (OECD SIDS, 2004).

(II) Ammonia,used asfeed additive, represents a significant portion of the normal daily diet of aquatic organisms (OECD SIDS, 2004) and is thus not expected to be hazardous to members of lower trophic levels.

(III) Free ammonia with effect concentrations ranging from 0.39 to 22.84 mg NH3/L for invertebrates is known to be the most toxic ammonia species since it passes biological membranes more easily (Fent, 2007). However, predominating pH conditions in aquatic systems typically shift the equilibrium towards the less toxic, ionic species NH4+. At a solution pH < 9.26 (pKa = 9.26), NH4+ is more dominant whereas NH3 is favoured at a pH > 9.26. Thus, the majority (i.e. 80 - 100 %) of ammonia in fresh and saltwater will be in the less toxic ammonium form at acidic, neutral and slightly basic conditions.

(IV) The acute aquatic toxicity of ammonium in the form of ammonia chloride was tested at different trophic levels (algae, invertebrates and fish). A 48-LC50 value of 34.1 mg/L and a 10-d EC50 value of 14.2 mg/L were obtained for Daphnia magna and the bivalve Mulinia lateralis, respectively, indicating that bivalves may be somewhat sensitive (OECD SIDS, 2004). The EC/LC50 values reported for aquatic invertebrates are well above classification criteria for acute (short-term) hazard of Regulation (EC) No 1272/2008 (CLP Regulation).

 

Table 1:Acute and chronic toxicity endpoints foraquatic invertebratesand ammonium chloridereviewed byOECD SIDS (2004)

Species

Endpoint [mg NH4+ /L]#

Test conditions

Reference*

Acute toxicity

.

.

.

Daphnia magna

48h-LC50 = 34.1

pH 8.4 - 8.6

19.5 - 20.5 °C

static

Gersich and Hopkins, 1986

Mulinia lateralis

10d-LC50 = 28.0

10d-EC50 = 14.2

(growth: weight)

pH 7.79

21.8 °C

Semi-static

Huber et al., 1997

Chronic toxicity

.

.

.

Daphnia magna

NOEC = 4.9

LOEC = 10.2

(reproduction)

pH 8.3 - 8.6

19.5 - 20.0 °C

Semi-static

Gersich and Hopkins, 1986

# based on measured concentrations; * See references in OECD SIDS (2004)

(V) The chronicaquatictoxicity of ammonium in the form of ammonia chloride was also tested at different trophic levels (algae, invertebrates and fish) (OECD SIDS, 2004). The 28-d NOEC reported for the reproduction of Daphnia magna amounts to 4.9 mg NH4+ /L and is thus well above classification criteria for long-term hazard of Regulation (EC) No 1272/2008 (CLP Regulation).

In summary, ammonium is expected to possess a low toxic potential for aquatic invertebrates. Based on acute (and chronic) effect concentrations, bivalves appear to be somewhat sensitive. However, ammonium is a natural component of the environment, represents a significant portion of the normal daily diet of aquatic organisms, is rapidly degraded and therefore not expected to accumulate in the environment.Hence, from a scientific point of view, further tests on the short-term toxicity of ammonium to aquatic invertebrates are not considered to be required.

 

References:

Environment Canada (2010) Ammonia. Canadian Water Quality Guidelines for the Protection of Aquatic Life.

Fent, K. (2007). Ökotoxikologie: Umweltchemie – Toxikologie -Ökologie, Thieme Verlag, 3rd Edition, p. 338

OECD SIDS (2004). Ammonium Chloride CAS No: 12125-02-9, SIDS Initial Assessment Report for SIAM 17, UNEP Publications, Arona, Italy, p. 92

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