Sodium azide

Adsorption / desorption

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

adsorption / desorption: screening

Remarks:

Batch Equilibrium Method

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2016-11-17 to 2017-07-05

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.18 (Adsorption / Desorption Using a Batch Equilibrium Method)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

sediment

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source and lot/batch no.of test material: BCBQ6197V
- Expiration date of the lot/batch: July 2021

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: Store at a cool place. Keep container tightly closed at a dry, well ventilated place. Avoid every contact of the product with water. Do not store together with acids. Access denied to unauthorized persons.

TREATMENT OF TEST MATERIAL PRIOR TO TESTING
- None

OTHER SPECIFICS:
CAS RN: 26628-22-8
Purity (certified): 100.2 %
Molecular formula: NaN3
Molecular weight: 65.01 g/mol
Water solubility: 65 g/L at 20 °C
Appearance: White, crystalline powder

Radiolabelling:

no

Test temperature:

20 ± 2 °C

Details on study design: HPLC method:

not applicable

Analytical monitoring:

yes

Remarks:

GC-MS/MS

Details on sampling:

Sample volumes used for derivatisation
Sludge Hildesheim: 9.0 mL 9.0 mL (tier 1 and 2) 4.0 mL (tier 3)
Sludge Hannover: 9.0 mL 9.0 mL (tier 1 and 2) 4.0 mL (tier 3)
Sediment Rössingbach: 9.0 mL 9.0 mL (tier 1 and 2) 4.5 mL (tier 3)
LUFA 2.3: 9.0 mL (tier 1, 2, and 3)
LUFA 2.4: 9.0 mL (tier 1, 2, and 3)

Preparation of standards: Stock solutions of 500 mg test item/L in HPLC water were prepared and diluted to 6 concentrations with matrix-conditioned CaCl2 solution. The organic extracts were measured directly.

Preparation of fortified samples: The fortified samples were prepared in matrix-conditioned and filtrated CaCl2 solution by spiking at LOQ level with the test item. Blank samples were prepared in matrix-conditioned and filtrated CaCl2 solution but without spiking with the test item. All fortified samples and blank samples were derivatized as described in “Details on analytical methods” under 'Derivatisation'. The organic extracts were measured directly.

Preparation aqueous samples: The aqueous phase was derivatized as described in “Details on analytical methods” under 'Derivatisation' after separation from the solid phase by centrifugation (5 min, 10000 rpm). Samples were diluted to calibration with matrix-conditioned CaCl2 solution prior to derivatization, if necessary. The organic extracts were measured directly.

Extraction of solid matrices: After removal of the aqueous phases, soil samples were extracted with HPLC water. Therefore, 20 mL HPLC water were added to the solid matrix followed by shaking on a rotary shaker for 30 minutes and ultrasound treatment for 10 sec. Afterwards, samples were centrifuged for five minutes at the respective centrifugation force (described above) and the supernatant was transferred to a 50-mL measuring flask. Extraction, ultrasound and centrifugation was repeated with additional 20 mL HPLC water and the measuring flask was filled up to 50 mL with HPLC water. Samples were derivatized as described in “Details on analytical methods” under 'Derivatisation'. The organic extracts were measured directly. 'Fresh spikes' I freshly spiked samples were prepared as described above after spiking the solid matrix after removal of aqueous phase. During Tier 1, additional experiments using 0.01 M CaCl2 solution or buffered aqueous solutions were conducted using an equivalent procedure.

Sample storage: All samples were stored at 6 ± 2 °C prior and after analysis, if necessary.

Evaluations: Quantification of the test item was calculated by peak area based on the external standard.

Matrix no.:

#1

Matrix type:

other: Silty sand (LUFA 2.3)

% Clay:

8.6

% Silt:

29.3

% Sand:

62.1

% Org. carbon:

0.412

pH:

7

CEC:

4.9 other: mval/100g

Matrix no.:

#2

Matrix type:

other: LUFA 2.4 (batch F2.44116)

% Clay:

25.2

% Silt:

29.3

% Sand:

62.1

% Org. carbon:

1.74

pH:

7.7

CEC:

22 other: mval/100g

Matrix no.:

#2

Matrix type:

other: LUFA 2.4 (batch F2.42116)

% Clay:

27.5

% Silt:

44.2

% Sand:

28.3

% Org. carbon:

2.07

pH:

7.7

CEC:

26 other: mval/100g

Matrix no.:

#2

Matrix type:

other: LUFA 2.4 (batch F2.41016)

% Clay:

27.6

% Silt:

43.3

% Sand:

29.1

% Org. carbon:

2.07

pH:

7.7

CEC:

24 other: mval/100g

Matrix no.:

#3

Matrix type:

other: Sediment Rössingbach

% Clay:

17.9

% Silt:

71

% Sand:

11.1

% Org. carbon:

4.5

pH:

7.5

CEC:

19 other: mval/100g

Matrix no.:

#4

Matrix type:

other: Sewage sludge from Hildesheim

% Org. carbon:

40

pH:

5.5

Matrix no.:

#5

Matrix type:

other: Sewage sludge from Hannover

% Org. carbon:

39

pH:

5.1

Details on matrix:

Test system: Standard LUFA soils 2.3 and 2.4, two types of sludge (returned sludge) from two different sewage treatment plants as well as one sediment in contact to 0.01 M CaCl2 were used for this study. These matrices have varying adsorption capacities in relation to their content of organic matter, clay, pH and cation exchange capacity (CEC). The soils were dried and sieved to a maximum particle size of 2 mm (by LUFA Speyer) prior to start of the adsorption and desorption experiments. The sediment was also sieved to a maximum particle size of 2 mm and freeze-dried. The returned sludge was prepared following guideline OPPTS 835.1110. The content of organic matter, the content of clay, silt and sand (if feasible) and the cation exchange capacity were determined (externally, non-GLP). The pH was determined during the course of the study for each matrix.


Origin of sediment:
Sediment Rössingbach, 31171 Rössing, Germany (52°11 '03.6"N, 9°49'13.4"E)


Reason for the selection: Two types of soil, two types of sludge, and one sediment in contact to 0.01 M CaCl2 were used for this study. The reasons for including two sewage sludge samples are (i) the use pattern of sodium azide not leading to direct release to soil but potentially to wastewater, and (ii) the ex ante expected low adsorption potential of the substance, prompting inclusion of sediment and sewage sludge of additional, potentially more relevant matrices. The matrices vary considerably in their sorption relevant physico-chemical properties. Therefore, these matrices are suitable for the conduction of the study because all parameters with impact on the adsorption/desorption behaviour of a chemical substance are considered.

Origin of soil/sediment/sludge:
Sewage treatment plant, Kanalstrasse 50, 31137 Hildesheim, Germany
Sewage treatment plant, Dünenweg 20, 30419 Hannover, Germany


Only two soils were tested. The reasons for this deviation are (i) the use pattern of sodium azide not leading to direct release to soil, and (ii) the ex ante expected low adsorption potential of the substance, prompting inclusion of sediment and sewage sludge of additional, potentially more relevant matrices. The matrices vary considerably in their sorption relevant physico-chemical properties. Therefore, these matrices are suitable for the conduction of the study because all parameters with impact on the adsorption/desorption behaviour of a chemical substance are considered.

Origin of soil:
LANDWIRTSCHAFTLICHE UNTERSUCHUNGS- UND FORSCHUNGSANSTALT LUFA SPEYER, Obere Langgasse 40, 67346 Speyer, Germany

Details on test conditions:

TEST SYSTEM
- Type, size and further details on reaction vessel: Disposable centrifugation tubes
- Amount of soil/sediment/sludge and water per treatment (if simulation test): Tier 1 and Tier 2: 500 μg/L Additional concentrations for Tier 3: 50 μg/L - 200 μg/L - 2000 μg/L - 5000 μg/L
- Sediment/water ratio (if simulation test): Sediment was 1:40 ratio
- Sludge/water ratio (if simulation test): Sludge was 1:30 ratio.
- Soil/water ratio (if simulation test): LUFA 2.3 was 1:1 ratio, LUFA 2.4 was 1:5 ratio.
- Number of reaction vessels/concentration: Duplicates
- Measuring equipment: Standard laboratory glassware
- Test performed in closed vessels due to significant volatility of test substance: No data
- Test performed in open system: No data
- Method of preparation of test solution: Aqueous stock solutions of sodium azide were prepared. 1 % (v/v) of these stock solutions, related to the volume of the aqueous phase in the matrix suspensions, were used for spiking.
- Matrix samples (conditioning): The matrices were weighed into the test vessels and an appropriate volume of 0.01 M CaCl2-solution was added. After agitation overnight (12 h minimum), the samples were used for adsorption experiments.
- Samples for adsorption experiments: 1 % (v/v) of the test item stock solutions, related to the volume of the aqueous phase in the matrix suspensions, were added in order to adjust the test concentrations. Afterwards, the samples were agitated.
- Samples for desorption experiments: Samples after 48 h adsorption were used for this purpose. After completion of the adsorption experiment the test vessels were centrifuged and the supernatant was replaced by fresh 0.01 M CaCl2-solution. Then the test vessels were agitated again and sampled at defined sampling points to investigate the desorption behavior of the test item.
- Samples for analysis: After agitation, the matrix suspensions were centrifuged at 10000 rpm to separate the phases, followed by analysing the concentration of Sodium azide in the aqueous phase and in soil extracts. For analysis of the matrix, the aqueous phase was decanted and the matrix was extracted followed by analysis.

CONTROLS:
- Controls: CaCl2-solution was conditioned with the matrix followed by separation of the aqueous phase by centrifugation and filtration, if necessary. Then the aqueous phase was fortified acc. to the concentrations used for the test item samples and agitated as long as the test item sample with the longest agitation period.
- Replicates: Duplicates
- Blanks: Blank samples were prepared for all matrices as described for the test item samples but without fortification with the test item. The samples were agitated as long as the samples with the longest agitation period.
- Replicates: Duplicates (Tier 1), single (Tier 2 and Tier 3)

Computational methods:

See "Freundlich Adsorption for Sodium azide in Different Matrices table" in "Any other information on results incl. tables" section for the following parameters:
- Adsorption and desorption coefficients (Kd); Freundlich adsorption and desorption coefficients; slope of Freundlich adsorption/desorption isotherms; adsorption coefficient per organic carbon (Koc); regression coefficient of Freundlich equation.

Sample No.:

#1

Type:

Kd

Value:

2.21 L/kg

pH:

7

Temp.:

20 °C

Matrix:

Soil LUFA 2.3

% Org. carbon:

0.412

Key result

Sample No.:

#1

Type:

Koc

Value:

535 L/kg

pH:

7

Temp.:

20 °C

Matrix:

Soil LUFA 2.3

% Org. carbon:

0.412

Sample No.:

#2

Type:

Kd

Value:

7.69 L/kg

pH:

7.7

Temp.:

20 °C

Matrix:

Soil LUFA 2.4

% Org. carbon:

1.96

Key result

Sample No.:

#2

Type:

Koc

Value:

442 L/kg

pH:

7.7

Temp.:

20 °C

Matrix:

LUFA 2.4

% Org. carbon:

1.96

Remarks on result:

other: Mean % org. carbon calculated from 3 values

Sample No.:

#3

Type:

Kd

Value:

24.8 L/kg

pH:

7.5

Temp.:

20 °C

Matrix:

Sediment Rössingbach

% Org. carbon:

4.5

Key result

Sample No.:

#3

Type:

Koc

Value:

551 L/kg

pH:

7.5

Temp.:

20 °C

Matrix:

Sediment Rössingbach

% Org. carbon:

4.5

Sample No.:

#4

Type:

Kd

Value:

131 L/kg

pH:

5.5

Temp.:

20 °C

Matrix:

Sludge Hildesheim

% Org. carbon:

40

Key result

Sample No.:

#4

Type:

Koc

Value:

328 L/kg

pH:

5.5

Temp.:

20 °C

Matrix:

Sludge Hildesheim

% Org. carbon:

40

Sample No.:

#5

Type:

Kd

Value:

103 L/kg

pH:

5.1

Temp.:

20 °C

Matrix:

Sludge Hannover

% Org. carbon:

39

Key result

Sample No.:

#5

Type:

Koc

Value:

264 L/kg

pH:

5.1

Temp.:

20 °C

Matrix:

Sludge Hannover

% Org. carbon:

39

Details on results (HPLC method):

not applicable

Adsorption and desorption constants:

Freundlich adsorption constants:
Sediment Rössingbach: 0.0027
Sewage Sludge Sludge Hildesheim: 0.00075
Sewage Sludge Hannover: 0.0039

Recovery of test material:

Recovery rate after 48 hours related to nominal concentration:
Sediment Rössingbach: 86 %
Sewage Sludge Sludge Hildesheim: 61 %
Sewage Sludge Hannover: 71 %

Concentration of test substance at end of adsorption equilibration period:

Absolute amount [µg] in the matrix; concentration at the end of the adsorption equilibrium period not available.
Sediment Rössingbach: 4.76 µg
Sewage sludge Sludge Hildesheim: 12.1 µg
Sewage sludge Hannover: 11.5 µg

Concentration of test substance at end of desorption equilibration period:

Tier 3 - Desorption kinetics:
Desorption experiments were conducted exemplarily for LUFA 2.4 - see BPR Annex point 10.2.4. Since sodium azide is not stable in the aqueous test medium over time, the calculated concentrations of the test item in the remaining pore water were higher than the actually measured concentrations after desorption. This led to calculated negative desorption values. Since the adsorption of the test item to soil is low even when a high matrix/solution ratio is used, and with regard to the instability of the test item in aqueous environment, the desorption was not determined for the other matrices.

Sample no.:

#1

Duration:

48 h

% Adsorption:

68

Remarks on result:

other: Soil LUFA 2.3 % mass balance

Sample no.:

#2

Duration:

48 h

% Adsorption:

59

Remarks on result:

other: Soil LUFA 2.4 % mass balance

Sample no.:

#3

Duration:

48 h

% Adsorption:

38

Remarks on result:

other: Sediment Rössingbach % mass balance

Sample no.:

#4

Duration:

48 h

% Adsorption:

80

Remarks on result:

other: Sewage sludge Hildesheim % mass balance

Sample no.:

#5

Duration:

48 h

% Adsorption:

76

Remarks on result:

other: Sewage sludge Hannover % mass balance

Transformation products:

not measured

Details on results (Batch equilibrium method):

PRELIMINARY TEST
- Sample purity: 100.2 %
- Weighed soil: The dry weight of each matrix was determined in triplicate at 105 °C, the following are mean values of three weights: Sediment Rössingbach = 98.9 %, Soil LUFA 2.3 = 95.9 %; soil LUFA 2.4 = 97.7 % (batch F2.42116), 93.1 % (F2.44116); Hildesheim sludge = 94.1 %; Hannover sludge = 94.8 %.
- Volume of CaCl2 solution: 0.01 M (molar concentration, not volume)
- Initial test substance concentration: 50 μg/L and 5000 μg/L
- Test substance concentration in final solution: 50, 200, 500 and 5000 μg/L

MAIN TEST: PERFORMANCE
- Test material stability during adsorption/desorption phase: The test item control samples showed stability of the test item for 24 h.
- Experimental conditions maintained throughout the study: Yes
- Buffer/test substance interactions affecting sorption: None
- Further chemical interactions: None
- Buffer-catalyzed degradation of test substance: None
- Anomalies or problems encountered (if yes): None
- Other observations: None

Overall results:

Freundlich adsorption for sodium azide in different matrices Applied concentrations, test item [μg/L]: 50, 200, 500, 2000, 5000
Matrix Type	Soil LUFA 2.3	Soil LUFA 2.4	Sediment Rössingbach	Sewage sludge Hildesheim	Sewage sludge Hannover
Matrix/ solution ratio	1:1	1:1	1:2	1:7	1:7
R²	0.9941	0.8273	0.9907	0.9927	0.9617
1/n	0.86	0.59	0.76	0.83	0.58
K^adsF	0.0013	0.0016	0.003	0.00075	0.0039
K^OCF	0.31	0.094	0.060	0.0019	0.010
Kd (50 µg/L, 0.5 h)	0.90	0.41	2.4	3.5	5.7
KOC (50 µg/L, 0.5 h)	217	24	54	9	15
Kd (5000 µg/L, 0.5 h)	0.50	0.030	0.62	1.6	0.79
KOC(5000 µg/L, 0.5 h)	122	2	14	4	2
Mobility according to McCall	high-medium high	very high	very high-high	very high	very high
Mobility according to McCallet al.(1980): KOC: 0–50: very high KOC: 50–150: high KOC: 150–500: medium KOC: 500–2000: low KOC: 2000–5000: slight KOC: > 5000: immobile
n: regression constant K^adsF: Freundlich adsorption coefficient [μg^1–1/n(mL)^1/ng^–1] K^OCF: Freundlich adsorption coefficient normalized to content of organic carbon  [μg^1–1/n(mL)^1/ng^–1]

Validity criteria fulfilled:

yes

Conclusions:

The results indicate that the test item has a very high mobility in sediment. Since the adsorption of the test item to sediment is low even if a high matrix/solution ratio is used and with regard to the instability of the test item in aqueous environment, the desorption was not determined.

Executive summary:

The adsorption/desorption characteristics of sodium azide was studied in two soils, two sewage sludges and one sediment in a batch equilibrium experiment in accordance with the OECD guideline 106 and EC method C.18, and in compliance with GLP, with the following specifics:

Medium type	Source	pH	% organic carbon	K^adsF	Koc
Soil LUFA 2.3	Landwirtschaftliche Untersuchungs- und Forschungsanstalt LUFA Speyer, Obere Langgasse 40, 67346 Speyer, Germany	7.0	0.412	0.0013	535 mL/g
Soil LUFA 2.4		7.7	1.96 (mean of 3)	0.0016	442 mL/g
Rossingbach Sediment	Sediment Rössingbach, 31171 Rössing, Germany (52°11 '03.6"N, 9°49'13.4"E)	7.5	4.50	0.0027	551 mL/g
Hildesheim Sewage sludge	Sewage treatment plant, Kanalstr. 50, 31137 Hildesheim, Germany	5.5	4.0	0.00075	328 mL/g
Hannover Sewage sludge	Sewage treatment plant, Dünenweg 20, 30419 Hannover, Germany	5.1	39	0.0039	264 mL/g

The adsorption phase of the study was carried out by equilibrating soil, sediment and sludge with sodium azide using the following test concentrations: 500 µg/L (Tier 1 and Tier 2) and 50, 200, 2000, 5000 µg/L (Tier 3) at 20 °C for 48 hr.  The adsorption of the test item decreased with increasing nominal concentration. The equilibrating solution used was 0.01 M CaCl₂/other, with a soil/solution ratio of 1:1 or 1:5 (soils), 1:40 (sediment), 1:30 (sludges). 

The soil suspensions were centrifuged after agitation followed by analysing the concentration of sodium azide in soil extracts and in the aqueous phase. Analytical evaluation of sodium azide was carried out via GC-MS/MS after derivatisation of the test item with pentafluorobenzyl bromide to pentafluorobenzyl azide, residues were analysed by GC-MS/MS.  The adsorption parameters were calculated using the Freudlich adsorption isotherm.

Since the adsorption of the test item to soil is low even if a high matrix / solution ratio is used and with regard to the instability of the test item in aqueous environment, the desorption was not determined.  The mass balance at the end of adsorption phase was 68, 59, 38, 80, and 76 %, for the soils, sediment and sludge, respectively.

After 48 h of equilibration, the recovery rate after 48 hours related to nominal concentration: Soil LUFA 2.3: 35 %, soil LUFA 2.4: 88 %, sediment Rössingbach: 86 %, sewage sludge Hildesheim: 61 %, and sewage sludge Hannover: 71 %. The adsorption Koc values were soil LUFA 2.3: 535 mL/g, soil LUFA 2.4: 442 mL/g, sediment Rössingbach: 551 mL/g, sewage sludge Hildesheim: 328 mL/g, and sewage sludge Hannover: 264 mL/g.

Results synopsis:

Medium type	Kd	Koc	% adsorption
Soil LUFA 2.3	2.21 mL/g	5.35 mL/g	68
Soil LUFA 2.4	7.69 mL/g	442 mL/g	59
Rössingbach sediment	24.8 mL/g	551 mL/g	38
Hildesheim sewage sludge	131 mL/g	328 mL/g	80
Hannover sewage sludge	103 mL/g	264 mL/g	76

Study acceptability:  This study is classified acceptable and satisfies the guideline requirement for an adsorption/desorption study in soil, sediment and sewage sludge.

Reference 2

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

3 (not reliable)

Rationale for reliability incl. deficiencies:

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

Principles of method if other than guideline:

batch equilibrium adsorption and continuous
column adsorption of hydrazoic acid

GLP compliance:

no

Type of method:

other: adsorption of hydrazoic acid from aqueous solution by macroreticular resin

Media:

other: adsorption of hydrazoic acid from aqueous solution by macroreticular resin

Specific details on test material used for the study:

Obtained from Fluka Chemical Co. (microelectronic grade)

Radiolabelling:

no

Analytical monitoring:

yes

Matrix type:

other: Macroreticular resin, stable polymer of styrene/divinyl- benzene

% Clay:

0

% Silt:

0

% Sand:

0

% Org. carbon:

0

CEC:

1.4 other: meq/ mL wet resin

Bulk density (g/cm³):

1.11

Details on matrix:

"The macroreticular resin employed in this study was the Dowex SAR, as obtained from Dow Chemical Company (Midland, MI, USA). It was a stable polymer of styrene/divinyl-benzene. According to the manufacturer, the Cl-type, strong base anion SAR resin had an average diameter of 0.3–1.2 mm (over 90%), a cation exchange capacity (CEC) of 1.4 meq/ml wet resin and a density of 1.11. For pretreatment, the resin was washed alternately several
times with acetone and deionized water to remove all impurities on its surfaces. It was then rinsed with hexane a few times. Finally, it was dried at 60◦C in an electric oven for over 24 h and put in a desiccator for cooling."

Details on test conditions:

BATCH EQUILIBRIUM TEST
TEST CONDITIONS
- other: batch equilibrium tests were run for 6 hours

TEST SYSTEM
- Type, size and further details on reaction vessel: a 500 ml Erlenmeyer flask was placed in a constant temperature bath for temperature control. About 250 ml of the stock solution were put in the flask and 0.5 g of pretreated Dowex resin was added. The flask was sealed. The speed of the constant temperature shaker was set at 100 cycle/mm and the temperature was maintained at 25 ± 0.25 °C.
- Water filtered (i.e. yes/no; type of size of filter used, if any):
- Amount of water per treatment (if simulation test): 250 mL and 0.5 g macroreticular resin
- Soil/sediment/sludge-water ratio (if simulation test): 2:1
- Number of reaction vessels/concentration: not reported
- Measuring equipment: GBC UV–VIS 916, GBC Scientific Equipment Private Ltd., Melbourne, Australia
- Test performed in closed vessels due to significant volatility of test substance: sealed flask
- Test performed in open system: no
- Method of preparation of test solution: The stock hydrazoic acid solution was prepared gravimetrically using NaN3 obtained from Fluka Chemical Co. (microelectronic grade). The hydrazoic acid concentrations of the stock solution and all samples during the experimental tests were measured using an ultraviolet spectrophotometer (GBC UV–VIS 916, GBC Scientific Equipment Private Ltd., Melbourne, Australia).

COLUMN ADSORPTION TEST
TEST CONDITIONS/ TEST SYSTEM
- Type, size and further details on reaction vessel: The adsorption column (see Figure 1) was a pyrex glass tube of 1.6 cm i.d. and 20 cm high. It was equipped with a water jacket for temperature control. The adsorption column was randomly packed with 10 g of the pretreated Dowex resin.
- Amount of soil/sediment/sludge and water per treatment (if simulation test): 10 g Macroreticular resin,
- Soil/sediment/sludge-water ratio (if simulation test): In each test run, the stock solution containing no more than 1000 mg/l hydrazoic acid was fed using a feed pump to the top of the adsorption column and its flow rate was regulated by a precision flow meter. After a test run was started, the exiting aqueous solution was sampled periodically and the hydrazoic acid concentration determined. The column adsorption tests were conducted for various feed flow rates of 10, 20 and 30 ml/min and inlet hydrazoic acid concentrations of 400, 600 and 800 mg/L.
- Number of reaction vessels/concentration: 1
- Method of preparation of test solution: The stock hydrazoic acid solution was prepared gravimetrically using NaN3 obtained from Fluka Chemical Co. (microelectronic grade). The hydrazoic acid concentrations of the stock solution and all samples during the experimental tests were measured using an ultraviolet spectrophotometer (GBC UV–VIS 916, GBC Scientific Equipment Private Ltd., Melbourne, Australia).

Sample No.:

#1

Duration:

2 h

Initial conc. measured:

250 other: mg/L

Temp.:

25 °C

Remarks:

Equilibrium adsorption method

Type:

other: adsorption isotherm

Value:

ca. 100 other: mg HN3 / g resin

Temp.:

25 °C

Matrix:

macroreticular resin

"In the present study, the Dowex SAR resin was tested in batch and continuous processes to remove hydrazoic acid from the aqueous solution. Theoretical models were adopted for representing the equilibrium and column adsorption processes. Based on the experimental and theoretical investigations, the following conclusions were drawn. 1. Test results revealed that monolayer isotherms were inadequate for describing the equilibrium adsorption of hydrazoic acid. Instead, multilayer, three-parameter modified Langmuir isotherm or that of Jossens et al. represents the equilibrium adsorption data quite well.

2. Theoretical column model based on nonlinear adsorption mechanisms was successfully developed for predicting the hydrazoic acid concentration in the exit aqueous solution. The two model parameters involved can be readily determined by a complete breakthrough curve. With properly identified parameters, the column adsorption model represents the breakthrough curves quite well. The theoretical column model offers a convenient means for accurate estimation of the breakthrough times.

3. The exhausted Dowex resin can be efficiently regenerated by 10 % (w/w) sodium chloride solution. Test runs showed that approximately 14 BV of sodium chloride solution yield very good results. Repeat adsorption tests showed that the regeneration process is very efficient with negligible loss of the resin adsorption capacity."

Validity criteria fulfilled:

not applicable

Conclusions:

Dowex SAR resin is a possible resin to remove sodium azide from aquatic solutions.

Executive summary:

In the present study, the Dowex SAR resin was tested in batch and continuous processes to remove hydrazoic acid from aqueous solution, simulating a contaminated aquatic bodies. Theoretical models were adopted for representing the equilibrium and column adsorption processes, as well as showing that 10 % (w/w) NaCl is an efficient regenerant for the resin.

Reference 3

Endpoint:

adsorption / desorption

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

other: Handbook data lacking methodological details

Media:

soil

Executive summary:

Sodium azide is hardly adsorbed by mineral soils, but is adsorbed by muck soils and by activated charcoal. It may be converted to hydrazoic acid in acid soils, and both the sodium azide and hydrazoic acid are readily leachable.

Description of key information

The adsorption/desorption characteristics of sodium azide were studied in two soils, two sewage sludges and one sediment in a batch equilibrium experiment in accordance with the OECD guideline 106 and EC method C.18, and in compliance with GLP. The results are presented in table 1 below:

 

Table1: Experimentally determined Kd, Koc and % adsorption values for different matrices

Medium type	Kd [mL/g]	KOC [mL/g]	Adsorption [%]
Soil LUFA 2.3	2.21	535	68
Soil LUFA 2.4	7.69	442	59
Rössingbach sediment	24.8	551	38
Hildesheim sewage sludge	131	328	80
Hannover sewage sludge	103	264	76

 

The organic carbon/water partition coefficient (Koc) is low in all matrices investigated. The arithmetic mean Koc is calculated from the five matrix-specific determinations as 424 mL/g and is set as key value.

 

Key value for chemical safety assessment

Koc at 20 °C:

424

Additional information

Two studies are added to the dossier as supportive material. One study by Sheng and Cheng (2001) assessed the ability of a resin in batch and continuous processes to remove hydrazoic acid from aqueous solution. Theoretical models were adopted for representing the equilibrium and column adsorption processes, as well as showing that 10 % (w/w) NaCl is an efficient regenerant for the resin.

In the Herbicide Handbook from the Weed Science Society of America (1983) it is stated that sodium azide is hardly adsorbed by mineral soils, but is adsorbed by muck soils and by activated charcoal. It may be converted to hydrazoic acid in acid soils, and both the sodium azide and hydrazoic acid are readily leachable.