Aluminium nitride

Hydrolysis

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1999

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: non-guideline, non-GLP study, but scientifically robust

Qualifier:

no guideline followed

Principles of method if other than guideline:

Test item was diluted with water and stirred. pH-time profiles were measured. Hydrolysis was investigated by using XRD, DRIFT and the zeta potentials were measured.

GLP compliance:

not specified

Radiolabelling:

not specified

Analytical monitoring:

yes

Duration:

10 h

Initial conc. measured:

ca. 2 other: % (w/w) of AlN in water

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

No.:

#4

Remarks on result:

not measured/tested

The study confirmed that the main hydrolysis products of AlN are Al(OH)3, AlOOH and NH3.

Validity criteria fulfilled:

not applicable

Remarks:

Non-guideline study, but scientifically robust result published in peer-reviewed article.

Conclusions:

Main hydrolysis products of AlN are Al(OH)3, AlOOH and NH3.

Executive summary:

The AlN powder was mixed with water to a 2 % (w/w) AlN solution and subsequently pH and temperature were measured. Degradation products were measured using XRD and DRIFT. The study confirmed that the main hydrolysis products of AlN are Al(OH)3, AlOOH and NH3.

Reference 2

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1990

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Non-guideline, non-GLP study but scientifically robust

Qualifier:

no guideline followed

Principles of method if other than guideline:

Degradation of AIN powder was investigated in excess water at room temperature for up to 24 h. Samples were characterised by various techniques (IR; XRD; SEM, XPS; C, H, N analysis; surface area, particle size, and weight change measurements).

GLP compliance:

not specified

Radiolabelling:

no

Analytical monitoring:

yes

Duration:

24 h

pH:

7

Temp.:

25

Initial conc. measured:

ca. 200 g/L

Positive controls:

no

Negative controls:

no

Preliminary study:

Hydrolysis and reaction rate constants are described only qualitatively. Final result is that after 24 h ca. 80 % of AlN are transformed by hydrolysis.

Transformation products:

yes

No.:

#1

No.:

#2

Remarks on result:

not measured/tested

Details on results:

Hydrolysis and reaction rate constants are described only qualitatively. Final result is that after 24 h ca. 80 % of AlN are transformed by hydrolysis.

Validity criteria fulfilled:

not applicable

Remarks:

Non-guideline study, but scientifically robust result published in peer-reviewed article.

Conclusions:

AlN powder in excess H2O at room temperature reacts initially to give amorphous layers of AlOOH. After ca. 16 h this layer is transformed into a crystalline hydroxide, which is bayerite Al(OH)3. The kinetics of the reaction are well described by an unreacted core model where the chemical reaction at the product layer/unreacted core interface controls the reaction rate. The AlN consumption is first order and the corresponding reaction rate is linear.
After 24 h in water ca. 80 % of the AlN powder was transformed.
AlN transformed to bayerite is not necessarily correlating with the existence of ions dissolved in the aqueous solution, because the transformation product is not water soluble.

Executive summary:

The degradation of AIN powder in excess H20 at room temperature for up to 24 h was investigated. Samples were characterized by various techniques (IR XRD; SEM, XPS; C, H, N analysis; surface area, particle size, and weight change measurements). The reaction rate was found to be significant, with 80 % of the AIN being consumed in 24 h. The initial reaction product was found to be a porous, amorphous, hydrated alumina with stoichiometry near AIOOH. After -16 h a crystalline phase, bayerite AI(OH), was detected which became the predominant phase after 24-h contact. The kinetics of the AIN consumption were found to be first order and the reaction rate linear. The kinetic data fitted an unreacted core model with a porous product layer where the surface chemical reaction controlled the overall kinetics.

Reference 3

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2000

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Non-guideline, non-GLP study, but scientifically robust

Qualifier:

no guideline followed

Principles of method if other than guideline:

AlN powder was immersed in deionised water, HCl aq, NaOH aq and H3PO4 aq to investigate its hydrolysis behaviour at 283 to 373 K.

GLP compliance:

not specified

Radiolabelling:

no

Analytical monitoring:

yes

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

Remarks on result:

not measured/tested

The hydrolysis at the higher temperature was different from at the lower. Below 351 K a crystalline bayerite was produced on the surface of AlN particle, while crystalline boehmite was produced at higher than 351 K.

Validity criteria fulfilled:

not applicable

Remarks:

Non-guideline study, but scientifically robust result published in peer-reviewed article.

Conclusions:

The hydrolysis at the higher temperature was different from at the lower. Below 351 K a crystalline bayerite was produced on the surface of AlN particle, while crystalline boehmite was produced at higher than 351 K.

Executive summary:

AlN powder and bulk substrate were immersed in deionized water and in various acidic and basic solutions. The reaction behaviour of AlN with water yielded the following results. 1) Higher temperature and larger surface area of AlN caused more efficient acceleration of the hydrolysis. 2) The hydrolysis behaviour changed at 351 K. Below 351 K crystalline bayerite and NH3 were produced, while crystalline boehmite and NH3 were produced a above 351 K. 3) The hydrolysis of AlN powder was accelerated in NaOH aq and HCl aq in comparison with in deionized water while H3PO4 aq restrained the hydrolysis of AlN powder.

Reference 4

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2013-10-07 to 2014-05-05

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: OECD Series on Testing and Assessment No. 29

GLP compliance:

no

Remarks:

according to OECD Series on Testing and Assessment No. 29, thus in principle testing physical and chemical properties

Radiolabelling:

no

Analytical monitoring:

yes

Details on test conditions:

The water used for this test was purified with a Pure Lab Ultra water purification system from ELGA LabWater, Celle, Germany.
The applied chemicals were of the following quality:
Nitric acid Rotipuran® - “Supra®” quality (supplied by Carl Roth, Karlsruhe, Germany)
Hydrochloric acid - “instar analyzed” quality (supplied by J. T. Baker, Griesheim, Germany)
Other chemicals used for the preparation of media were at least of pro analysis grade.

Duration:

28 d

pH:

8

Temp.:

21.5 °C

Initial conc. measured:

ca. 1 mg/L

Duration:

7 d

pH:

8

Temp.:

21.5 °C

Initial conc. measured:

ca. 10 mg/L

Duration:

7 d

pH:

8

Temp.:

21.5 °C

Initial conc. measured:

ca. 100 mg/L

Positive controls:

not specified

Negative controls:

not specified

Preliminary study:

see "any other information on results!

Test performance:

see "any other information on results!

Transformation products:

yes

No.:

#1

No.:

#2

Details on hydrolysis and appearance of transformation product(s):

see "any other information on results!

Remarks on result:

not measured/tested

Details on results:

see "any other information on results!

The acute endpoint (7 days) was determined at sample loadings of 1, 10 and 100 mg/L; the chronic endpoint was determined from the extension of the 1 mg/L loading test to 28 days. The results of the study documented aluminum release measurements of 202.9 ± 14.8 µg Al/L, 366.0 ± 11.4 μg Al/L and 1087.1 ± 69.6 μg Al/L for 1, 10 and 100 mg/L sample loading, respectively. Therefore, aluminum nitride is considered to be slightly soluble in water.

Al concentrations for the loading of 1 mg/L

 

				within			between	variation
		meanpervessel	SD pervessel	vessel	meanall	SDall	vessel	between
sample	targetpH	Alconc.	Alconc.	variation	Alconc.	Alconc.	variation	sampling
		µg/L	µg/L	%	µg/L	µg/L	%	intervals
								%
1672h	8	188.7	0.4	0.2
2672h	8	199.0	0.5	0.3
3672h	8	221.1	0.0	<0.1	202.9	14.8	7.3	3.5

 

NH3 concentrations for the loading of 1 mg/L

 

				within			between	variation
		meanpervessel	SD pervessel	vessel	meanall	SDall	vessel	between
sample	targetpH	NH3conc.	NH3conc.	variation	NH3conc.	NH3conc.	variation	sampling
		µg/L	µg/L	%	µg/L	µg/L		intervals
							%	%
1672h	8	129.8	2.4	1.8
2672h	8	152.3	5.9	3.9
3672h	8	156.5	2.4	1.5	146.2	13.2	9.02	2.6

 

 

Validity criteria fulfilled:

yes

Conclusions:

The transformation dissolution test is described in the weight of evidence approach to illustrate the transformation processes of AlN in aqueous solution. It cannot be clearly distinguished between water solubility and hydrolysis because AlN hydrolyses in water, resulting in several different transformation products including boehmite and bayerite. In the present study the concentration of free aluminium ions in water was tested with ICP-OES. The other studies used for this weight-of-evidence approach determined the intermediate products of hydrolysis.
The other studies in this weight-of-evidence approach revealed that AlN is almost quantitavely transformed into its hydrolysis products (i.e. mainly bayerite and boehmite) within a time frame of a few days at room temperature, but the concentration of free Al3+ ions or otherwise dissolved aluminium was only measured in the present Fraunhofer study.

Executive summary:

A transformation/dissolution (T/D) test in accordance with OECD Series on Testing and Assessment No. 29 was carried out to study the potential of aluminum nitride to release metal ions into the environment. A 24-hour screening test to determine the pH of maximum aluminium release was performed at pH 6 and 8 and a loading rate of 100 mg/L. The pH screening test showed aluminium releases of 981.7 ± 12.9 µg Al/L at pH 8, while the mean release of Al at pH 6 was 76.4 ± 1.1 μg Al/L. Therefore, the full T/D test was conducted at pH 8. The acute endpoint (7 days) was determined at sample loadings of 1, 10 and 100 mg/L; the chronic endpoint was determined from the extension of the 1 mg/L loading test to 28 days. The results of the study documented aluminum release measurements of 202.9 ± 14.8 µg Al/L, 366.0 ± 11.4 μg Al/L and 1087.1 ± 69.6 μg Al/L for 1, 10 and 100 mg/L sample loading, respectively. Therefore, aluminum nitride is considered to be slightly soluble in water.

Reference 5

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2007

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: non-guideline, non-GLP study, but scientifically robust

Qualifier:

no guideline followed

Principles of method if other than guideline:

AlN powder was hydrolysed in water and the reaction products were analyzed using XRD, TEM, SEM and pH measurements.

GLP compliance:

not specified

Radiolabelling:

no

Analytical monitoring:

yes

Duration:

150 min

Temp.:

90

Initial conc. measured:

ca. 3 other: % (w/w) AlN in water

Duration:

150 min

Temp.:

80

Initial conc. measured:

ca. 3 other: % (w/w) AlN in water

Duration:

150 min

Temp.:

70

Initial conc. measured:

ca. 3 other: % (w/w) AlN in water

Duration:

150 min

Temp.:

60

Initial conc. measured:

ca. 3 other: % (w/w) AlN in water

Duration:

150 min

Temp.:

50 °C

Initial conc. measured:

ca. 3 other: % (w/w) AlN in water

Duration:

150 min

Initial conc. measured:

ca. 3 other: % (w/w) AlN in water

Duration:

150 min

Temp.:

40 °C

Initial conc. measured:

ca. 3 other: % (w/w) AlN in water

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

Remarks on result:

not measured/tested

AlN powder was hydrolysed in water and the reaction products were analysed using XRD, TEM, SEM and pH measurements. The study confirmed that the main hydrolysis products of AlN are Al(OH)3, AlOOH and NH3.

Validity criteria fulfilled:

not applicable

Remarks:

non-guideline study, but scientifically solid result published in peer-reviewed article

Conclusions:

Main hydrolysis products of AlN are Al(OH)3, AlOOH and NH3.

Executive summary:

The hydrolysis tests were carried out in dilute suspensions containing 3 % (w/w) of AlN in water. The water was heated under constant stirring to RT, 40, 50, 60, 70, 80 and 90 °C and AlN was added. pH was measured during the study. XRD, SEM and TEM was used to identify hydrolysis products. The study confirmed that the main hydrolysis products of AlN are Al(OH)3, AlOOH and NH3.

Reference 6

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2011

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

no guideline followed

Principles of method if other than guideline:

The temperature-dependent conversion of the AlN powder in water was recorded using a thermogravimetric (TG) analysis by calculating the mass ratio between aluminium hydroxide and aluminium nitride which forms the basis for determination of hydrolysis kinetics.

GLP compliance:

no

Remarks:

This study is a scientifically robust peer-reviewed journal publication.

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

- Sampling intervals for the parent/transformation products: ca. 10 min.
- Sampling method: Filtration, washing
- Sampling intervals/times for pH measurements: ca. 10 min.
- Sample storage conditions before analysis: at 80 °C for 24 h and then stored in plastic, airtight containers for subsequent analysis.

Buffers:

water suspensions of 3 mass-% AlN powder were used

Duration:

1 000 min

Initial conc. measured:

ca. 30 g/L

Positive controls:

no

Negative controls:

no

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

No.:

#4

No.:

#5

Details on hydrolysis and appearance of transformation product(s):

Three different stages of hydrolysis for AlN have been identifed.

STAGE ONE OF HYDROLYSIS - INDUCTION PERIOD
The first stage was called "induction period" and is characterized by the presence of a thin layer on the surface of the AlN particles. There was no incubation time observed in this first stage. pH raises immediately after AlN is added to water. It is assumed that during the induction period, the OH− ion, as a reactant, arrives at the AlN surface and attacks the Al–N bond, which then decomposes. In this way the Al3+ ion is released and ammonia is formed. In the following the increasing pH has influence on the formed hydroxylated species/complexes.

STAGE TWO OF HYDROLYSIS - GROWTH OF BOEHMITE (AlO(OH))
The induction period ended and the hydrolysis was accelerated mafter 180 min at 22 °C and after 5–10 min at 50 °C. This is the predominant step at accelerated temperatures. The second stage of the hydrolysis presumably starts when the critical concentration of [Al(OH)4]− in the suspension (at the expense of the dissolution of the aluminum amorphous hydroxide gel) is achieved, which results in the nucleation and growth of porous lamellar-like particles comprising a product shell on the surface of the AlN particles. It is assumed that this layer is composed of amorphous, porous, mono-hydroxide particles, with a stoichiometry close to boehmite, according to an X-ray photoelectron spectroscopy (XPS) analysis.

STAGE THREE - GROWTH OF BAYERITE (Al(OH)3)
During this last step of the hydrolysis the bayerite phase was formed, according to the SAED pattern.

pH:

5

Temp.:

22 °C

Hydrolysis rate constant:

>= 0 s-1

DT50:

ca. 1 320 min

Remarks on result:

other: R2 = 0.999

pH:

5.5

Temp.:

50 °C

Hydrolysis rate constant:

>= 0 s-1

DT50:

ca. 30 min

Remarks on result:

other: R2 = 0.999

pH:

5.5

Temp.:

90 °C

Hydrolysis rate constant:

>= 0.001 s-1

DT50:

ca. 3.5 min

Remarks on result:

other: R2 = 0.998

Other kinetic parameters:

The degradation of AlN powder in water is a heterogeneous reaction of a solid particle in a fluid.

Details on results:

TEST CONDITIONS
- pH and temperature were not maintained throughout the study, but changes in pH and temperature were observed over time. pH changed because hydroxide ions were formed and temperature changed because the process is exothermic.

MAJOR TRANSFORMATION PRODUCTS
- Ammonia, hydroxide, boehmite (AlO(OH)/γ-AlOOH) and bayerite (α-Al(OH)3)

Time-dependent conversion for a 3 wt-% AlN powder suspension in water at 22 °C, 50 °C and 90 °C was for all temperatures finally over 90 %; with different time-frames respectively.

VOLATILIZATION (at end of study)
- ammonia concentrations were not measures in this study
- pH and temperature was measured

Estimated rate-controlling steps with corresponding rate constants, k, and regression coefficients, R², for the second stage of the hydrolysis of a 3 % (w/w) AlN powder in water in a temperature range 22–90 °C.

Temperature [°C]	K=1/τ[s^-1]	R²
22	2.87E-06	0.999
50	1.84E-04	0.999
60	3.34E-04	0.997
70	8.99E-04	0.996
90	1.048E-03	0.998

Validity criteria fulfilled:

not applicable

Remarks:

Non-guideline study, but scientifically robust result published in peer-reviewed article.

Conclusions:

After adding AlN to water the hydrolysis starts immediately. At room temperature (22 °C) the half life time was determined to be ca. 1320 min. Time-dependent conversion for a 3 wt-% AlN powder suspension in water at 22 °C, 50 °C and 90 °C was for all temperatures finally over 90 %; with different time-frames respectively. The measured half-life time of AlN in aqueous solution does not directly result in free aluminum ions because
the predominant resulting aluminium species was bayerite (Al(OH)3) which is not water-soluble.

Executive summary:

A study was performed using powder X-ray diffraction (XRD), TEM images and selected-area electron diffraction (SAED) to determine the reaction kinetics of the hydrolysis of the test substance aluminium nitride (AlN) at different temperatures. For the hydrolysis tests, water suspensions of 3 % (w/w) AlN powder were prepared and water was blown through with nitrogen in order to minimize the dissolution of CO₂. Resulting intermediates were washed with 2-propanol, dried and subsequently analyzed with XRD, TEM, SAED and thermogravimetry. pH, temperature and particular reaction products were measured or identified. At room temperature (22 °C) the half life time of AlN was determined to be about 1320 min. At this temperature over 90 % of the test item was hydrolysed after 2000 min.

Reference 7

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2004

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: non-guideline, non-GLP study, but scientifically robust

Qualifier:

no guideline followed

Principles of method if other than guideline:

A dilute suspension of AlN (2 % w/w) in water was prepared; slurries stirred; analysis by X-ray, SEM, TEM.

GLP compliance:

not specified

Radiolabelling:

not specified

Analytical monitoring:

yes

Duration:

1 000 min

Initial conc. measured:

ca. 2 other: % (w/w) of AlN in water

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

No.:

#4

No.:

#5

Remarks on result:

not measured/tested

Remarks on result:

not measured/tested

Dried settled hydrolysis products were analysed using X-ray, TEM and SEM. The study confirmed that the main hydrolysis products of AlN are Al(OH)3, AlOOH and NH3.

Validity criteria fulfilled:

not applicable

Remarks:

Non-guideline study, but scientifically robust result published in peer-reviewed article.

Conclusions:

Main hydrolysis products of AlN are Al(OH)3, AlOOH and NH3.

Executive summary:

A dilute suspension containing 2 % (w/w) of AlN in deionised water was prepared by stirring. The slurries were stirred for 1–20 h at room temperature, 40 and 70 °C. pH and temperature were monitored during the hydrolysis. The concentration of ammonia released during the reaction were calculated from the measured pH. Dried settled hydrolysis products were analysed using X-ray, TEM and SEM.

The study confirmed that the main hydrolysis products of AlN are Al(OH)3, AlOOH and NH3.

Reference 8

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Non-GLP, non-guideline study in peer-reviewd journal, scientifically robust

Qualifier:

no guideline followed

Principles of method if other than guideline:

AlN particles were exposed to water; analysis was performed using FT-IR, various conditions were tested, including comparison between H3PO4 "protected" and pure AlN particles.

GLP compliance:

not specified

Radiolabelling:

no

Analytical monitoring:

not specified

Duration:

7 h

Temp.:

25 °C

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

No.:

#4

No.:

#5

Remarks on result:

other: no hydrolysis rate constant or half-life reported

The study revealed that AlN powder/particles are rapidly transformed into intermediate transformation products and finally into Al(OH)3 and NH3. The presence of H3PO4 drastically reduced the transformation speed, probably due to adsorption-based mechanisms.

Validity criteria fulfilled:

not applicable

Remarks:

Non-guideline study, but scientifically robust result published in peer-reviewed article.

Conclusions:

The study revealed that AlN powder/particles are rapidly transformed into intermediate transformation products and finally into Al(OH)3 and NH3. The presence of H3PO4 drastically reduced the transformation speed, probably due to adsorption-based mechanisms.

Executive summary:

A study was performed to investigate and control the hydrolysis and dispersion mechanisms of AlN powders in aqueous media. The test item was exposed to water and the formation of NH4+ was analytically monitored. Additionally, XRD patterns and FT-IR measurements were performed to investigate the hydrolysis of AlN over different time frames.

Description of key information

After adding AlN to water hydrolysis starts immediately. At room temperature (22 °C) the half life time was determined to be ca. 1320 min. Time-dependent conversion for a 3 % (w/w) AlN powder suspension in water at 22 °C, 50 °C and 90 °C was finally over 90 % at all temperatures, with different time-frames, respectively. The measured half-life time of AlN in aqueous solution does not directly result in free aluminium ions because the predominant resulting aluminium species was bayerite (Al(OH)3) which is not water-soluble.

Key value for chemical safety assessment

Half-life for hydrolysis:

1 320 min

at the temperature of:

22 °C

Additional information

Aluminium nitride (AlN) is hydrolytically degraded, and various poorly soluble aluminium salts, predominantly bayerite Al(OH)3 and boehmite AlO(OH) are formed. The nitride fraction is transformed into ammonia (NH3). Studies identifying and quantifying the degradation of aluminium nitride are summarised as follows:

Kocjan et al. (2011) found that the half-life time of AlN at room temperature (22 °C) was about 1320 min. More than 90 % of the test item was hydrolysed after 2000 min at this temperature.

Bowen et al. (1990) determined the hydrolysis rate of AlN in water: after 24 h ca. 80 % of the AlN powder was transformed.

The study by Oliveira et al. (2003) revealed that AlN powder/particles are rapidly transformed into intermediate transformation products and finally into Al(OH)3 and NH3. The presence of H3PO4 reduced the rate of transformation drastically due to the protective action of the insoluble aluminium phosphate formed at the surface.

The studies of Kocjan et al. (2007) and Krnel et al. (2004; 1999) confirmed that the main hydrolysis products of AlN are Al(OH)3, AlOOH and NH3. In addition, the study of Krnel et al. (1999) determined the reactivity of AlN powder in diluted inorganic acids by measuring pH and temperature during hydrolysis.

Fukumoto et al. (2000) found out that the formation of hydrolysis products from AlN is temperature dependent. Below 351 K (ca. 78 °C) a crystalline bayerite was produced on the surface of AlN particle, while crystalline boehmite was produced at temperatures higher than 351 K.

Under REACH (cf. ECHA guidance on CSA and information requirements, chapter R.7B), the term „hydrolysis“refers to the decomposition or degradation of a chemical by reaction with water, as a function of pH where relevant (i.e. abiotic degradation). Aluminium can participate in hydrolysis reactions, thereby forming a number of monomeric and polymeric Al-hydroxides and this process is highly dependent on pH. However, aluminium persists in the environment irrespective of the chemical species formed as a result of hydrolysis, although this may result in insoluble aluminium hydroxides that precipitate from the solution. Characterisation of aluminium in environmental media is typically based on total aluminium concentrations (including all specific chemical forms or species). Since hydrolysis changes only the chemical form of aluminium but does not decompose the substance and since characterisation of total aluminium take into account all chemical forms, the concept of degradation of aluminium by hydrolysis is not relevant in the consideration of environmental fate.

The hydrolysis of AlN is assessed in a weight-of-evidence approach to illustrate the transformation processes of AlN in aqueous media. The different studies show that distinguishing between water solubility and hydrolysis is not possible for this test item. AlN hydrolysis results in several poorly soluble transformation products including boehmite and bayerite, which are practically insoluble in the neutral pH range (5–7). For this reason, the transformation/dissolution test (T/D) performed for AlN (see Klawonn, 2014) was additionally included in the WoE. AlN was found to release low amounts of soluble Al during hydrolysis (Al concentrations at maximum 1 mg/L). These results in combination indicate that AlN is almost quantitatively transformed after exposure to water, but the concentration of free aluminium ions is low.