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Read across approach

Few data were available on aluminium ammonium sulfate (AlNH4(SO4)2.12H2O). However, this salt instantaneously dissociates in water in its two components salts, aluminium sulfate (Al2(SO4)3) and ammonium sulfate ((NH4)2SO4, and further to the ions aluminium, ammonium and sulfate. Therefore, the hazard of this salt for the aquatic environment can be assessed by the effects of its dissociation products in a read across approach. The detailed justification of the read across approach can be found in the discussion field of the Ecotoxicological information section.

Aluminium toxicity

The toxicity of aluminium to organisms has been subject of numerous reviews, including WHO (1997); INERIS (2005) or Environment Canada (2010). The fate and behaviour of aluminium in the aquatic environment and thereby the toxic effect is largely dependent on the speciation of aluminium. The latter is affected by a wide range of environmental parameters such as pH; temperature, dissolved organic carbon (DOC) and numerous other ligands . Interactions with pH and DOC are, however, of primary importance. DOC will complex aluminium in water, forming aluminium-organic complexes and thus reducing concentrations of monomeric forms of aluminium with its complexing capacity increasing as pH increases. Furthermore, aluminium is relatively insoluble in the neutral pH-range of 6.0-8.0. Al3+is mainly present at low pH values and rising pH results in a series of less soluble or insoluble hydroxide complexes e.g. Al(OH)2+.

Ammonia toxicity

The toxicity of ammonium sulfate to organisms has been assessed at the OECD level and is reported in the OECD SIDS (2004) report. In aqueous solution, ammonium sulfate is completely dissociated into the ammonium ion (NH4+) and the sulfate anion (SO42-). Depending on pH, ammonia (NH3) exists in equilibrium with the ammonium ion (NH4+), according to the following relationship:

NH4++ H2O → NH3+ H3O+

It is the un-ionized ammonia which is generally considered to be the primary cause of toxicity in aquatic systems. Un-ionized ammonia is more toxic to aquatic organisms than the ammonium ion because the un-ionized form is readily soluble in the lipid of the cell membrane and is rapidly absorbed by the gill. In contrast, the charged ion is not easily passed through the charged-line hydrophobic space in the membrane. Under most environmental conditions, the un-ionized ammonia concentration is the primary driver of toxicity. In general, as pH increases, the fraction of the total ammonia which is un-ionized increases. For example, at pH 6.5 (and 5 °C), 0.0395 % of the total ammonia is present as NH3 increasing the pH from 6.5 to 8.5 will increase the un-ionized ammonium by a factor of approximately 100. Increasing the temperature will also increase the percentage of unionized ammonium. The toxicity of ammonia to aquatic organisms is therefore highly dependent on physicochemical factors, most notably pH but also to a lesser degree by temperature, carbon dioxide, dissolved oxygen, and salinity.

 

Within this dossier, the aquatic hazard assessment of aluminium and ammonia is focused on the environmental relevant pH-range (6-8), exclusively. An overview of all data available is shown in the Table 1 below. All results in this Table 1 are expressed in terms of AlNH4(SO4)2.12H2O concentrations.

Aquatic toxicity dataset

Two standardized test on Al2(SO4)3and two non standardized tests on (NH4)2SO4and AlNH4(SO4)2were performed on two different freshwater fish species and one marine water fish species. The greatest sensitivity observed was related to aluminium toxicty at pH ranging between 4.8-5. The lowest reliable LC50(96h) correspond to 158 mg/L of AlNH4(SO4)2.12H2O. Two standardized test on Al2(SO4)3and two non standardized tests on (NH4)2SO4 and AlNH4(SO4)2were performed on the same species (Daphnia magna). The greatest sensitivity was related to aluminium toxicty at pH ranging between 6.5-7.5. The lowest EC50(48h) correspond to 72.2 mg/L of AlNH4(SO4)2.12H2O. In both cases, the result on the toxicity of the salt confirms the result on the dissociation products reinforcing the read across approach reliability. One standardized test on aluminium chloride hydroxide sulfate (AlOHClSO4) and one non standardized tests on (NH4)2SO4were performed on two freshwater algae species. The greatest sensitivity was related to aluminium toxicty at pH ranging between 7.1-8.4. The lowest toxicity values correspond at an ErC(50)= 32.9, an ErC10(72h)=7.2 and a NOECr= 2.4 mg/L AlNH4(SO4)2.12H2O.

To complete the dataset, chronic studies are available on fish and aquatic invertebrates.

For fish trophic level, two non standard tests are availaible to assess the chronic toxicty of Al2(SO4)3 on the same freshwater fish and the lowest toxicity value is a NOEC on weight (60d) converted into 1.14 mg/L AlNH4(SO4)2.12H2O at pH 5.6 -5.7.

For aquatic invertebrates trophic level, one valid standard test is available to assess the inhibition effect of Aluminium powder on the reproduction of the fresh water crustacean Daphnia magna. The test animals were exposed of the aqueous medium from a transformation/dissolution (T/D) test of aluminium powder. Based on measured concentrations, the test showed that NOEC (21 days) based on reproduction and immobilisation were 76 µg Al/L and 137 µg Al/L, respectively. These values corresponds to 1.28 mg/L and 2.30 mg/L of AlNH4(SO4)2.12H2O.

These results show that the hazard of aluminium ammonium sulfate to the aquatic environment is drove by the hazard of aluminium and is largely dependent on the pH.

Table 1: Aquatic toxicity endpoints from read across converted in AlNH4(SO4)2.12H2O concentrations (mg/L)

Species

Effect, mg AlNH4(SO4)2.12H2O /L

Conditions

Test material

Reliability/Flag

Reference

Acute

Algae

Pseudokirchneriella subcapitata

Growth rate

EC50 (72h)= 32.9

EC10 (72h)= 7.2

NOEC (72h)= 2.4

pH=7.1-8.4.

AlSO4OHCl

2/W

Bouwman, 2010

Chlorella vulgaris

Cell count

EC50 (18 d)= 18528

Growth rate

NOEC (18d) = 16184

pH= 7

(NH4)2SO4

4/W

Tam and Wong, 1996

Invertebrates

Daphnia magna

Mobility

EC50 (48h)=1001.3

pH=7.6

Hardness= 240 mg/l (CaCO3)

AlNH4(SO4)2

4/W

Khangarot and Ray, 1989.

Daphnia magna

Mobility

EC50 (48h)= 72,2

 

pH= 6.5 -7.5

Al2(SO4)3

2/W

Schafers, 2003.

Daphnia magna

Mobility

EC50 (48h)> 242

pH= 7.5-8.0

 

Al2(SO4)3

2/W

Schafers C, 2003

Daphnia magna

LC50 (96h)> 172 mg

pH= 6.5-8.5

Temperature= 20 +/- 1 °C

(NH4)2SO4

4/W

Ewell et al.,1986

Fish

Fundulus heteroclitus

(Marine water)

Mortality

LC50 (96h)= 60.5 at 6.6 ppt salinity

 

LC50 (96h)= 461.4 at 17 ppt salinity

pH not controlled

4< pH< 7.4

 

AlNH4(SO4)2

4/ W

Dorfman D, 1977.

Danio rerio

Mortality

LC50 (96h)= 158

LC10 (96h)= 147.8

NOEC (96h)= 121

 

pH not adjusted

4.8 < pH < 5

Al2(SO4)3

2/W

Schafers C, 2003.

Danio rerio

Mortality

NOEC (96h)≥1444.8

7.4 < pH < 8

Al2(SO4)3

2/W

Schafers C, 2003.

Salmo gairdneri

Mortality

LC50 (96 h)= 924

pH= 7.9-8

Temperature= 12-4-12.5 °C

(NH4)2SO4

2/W

Thurston and Russo, 1983

Chronic

Fish

Salvelinus fontinalis

Weight

NOEC (60d)= 1.14

 

Weight

NOEC (60d)= 1.48

 

pH 5.6 to 5.7

DOC= 1.8 mg/L

 

 

pH 6.5 to 6.6

DOC= 1.9 mg/L

 

Al2(SO4)3. 12H2O

2/ K

Cleveland L et al., 1989.

Salvelinus fontinalis

Length and Weight of fry

LOEC (61 d)= 128

NOEC (61 d)= 64

pH= 6.3-6.5.

(NH4)2SO4

2/K

Rice and Bailey, 1980

Invertebrates

Daphnia magna

Reproduction

NOEC (21d) = 1.28

 

Immobilisation

NOEC (21d) =2.30

pH 7.6-8.1

DOC = 7.12-9.30 ppm

 Al powder

2/K

Torsten Källqvist, 2000.