Neodymium oxide

Adsorption / desorption

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

15 August 2007 - 13 August 2008

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Study conducted to GLP in compliance with agreed protocols, with no or minor deviations from standard test guidelines and/or minor methodological deficiencies, which do not affect the quality of the relevant results. Study read-across from similar substance.

Justification for type of information:

The data on the read-across substance is considered representative.

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

no

Test temperature:

20 ± 2 °C

Analytical monitoring:

yes

Details on sampling:

- Concentrations:
Preliminary test: Three soil-to-solution ratios = 1/50, 1/25, 1/5; one test item concentration = 0.64 mg/L
Screening test: One soil-to-solution ratio = 1/50; one test item concentration = 1.29 mg/L

- Sampling interval:
Preliminary test: 48 hours
Screening test: adsorption phase: 2, 5, 24 and 48 hours; desorption phase: 2, 4, 24 and 48 hours
- Sample storage before analysis: before analyses all samples were stabilised by adding 0.5 mL nitric acid to 5 mL supernatant.

Details on matrix:

COLLECTION AND STORAGE
- Geographic location:
Soil I (SI): Hanhofen (Speyer, Rheinland-Pfalz, Germany; latitude 49°19’N, longitude 08°20’E). The sampling side was a meadow in the sampling year and at least 4 former years.
Soil II (SII): Attenschwiller (68220 Attenschwiller, France, latitude 47°34’N, longitude 7°27’E). The field cover at the time of sampling consisted of weeds.
Soil III (SIII): Siebeldingen (Speyer, Rheinland-Pfalz, Germany, latitude 49°12’N, longitude 08°03’E). The sampling site was uncultivated in the sampling year and at least 4 years before.
- Collection procedures: Sampling and handling of the soils were performed under consideration of ISO 10381-6 “(Soil Quality-Sampling-Guidance on the collection, handling and storage of soil for the assessment of microbial processes in the laboratory)”.
- Sampling depth (cm): The three soils were sampled from the top 20 cm layer.
- Storage conditions and length: no data except that SI, SII and SIII were sampled on August 2006, March 2007 and September 2006, respectively.
- Soil preparation: The soils, sieved to 2 mm, were air-dried at room temperature and homogenised. Disaggregation was performed with minimal force, so that the original texture of the soil was changed as little as possible. In order to eliminate microbial degradation of the test material, the soils were sterilised before use by γ-irradiation (Studer Hard, 4658 Däniken / Switzerland). Thereafter, the soil samples were pre-equilibrated with 50 % of the targeted volume of the aqueous phase by shaking for at least 20 hours at 20 °C prior to application of the test material.

PROPERTIES
- Soil texture
% sand: SI = 79.1, SII = 11.8, SIII = 21.9.
% silt: SI = 13.5, SII = 72.8, SIII = 36.0.
% clay: SI = 7.9, SII = 15.4, SIII = 42.
- Horizon: no data.
- Soil taxonomic classification: SI = Loamy sand, SII = Silt loam, SIII = Clay.
- Soil classification system: The soil types above mentioned were determined according to USDA (United States Department of Agriculture).
- Soil series and order: no data.
- pH: SI = 5.6, SII = 7.4, SIII = 7.0.
- Organic carbon (%): SI = 2.36, SII = 0.99, SIII = 1.89.
- CEC (meq/100 g): SI = 11.0, SII = 10.2, SIII = 20.0.
- Nitrogen content (%): SI = 0.21, SII = 0.11, SIII = 0.21.
- Organic matter (%): SI = 4.07, SII = 1.71, SIII = 3.26.
- C/N-ratio: SI = 11.2, SII = 9.0, SIII = 9.0
- Moisture (in g per 100 g dry soil): SI = 0.95, SII = 1.02, SIII = 5.78.
- Other: None of the soils had been fertilised or treated with pesticides for at least 12 months prior to sampling.
No further data.

Details on test conditions:

TEST CONDITIONS
- Buffer: none.
- pH: The pH of the aqueous phase was measured before and after contact with the soil at the soil-to-solution ratio of 1/50. The pH of the CaCl2-solution was 7.05 before contact with the soil and 6.79, 6.90 and 6.87 after contact with soil I to III, respectively.
- Suspended solids concentration: no data.

TEST SYSTEM
- Type, size and further details on reaction vessel: The study was performed in Teflon centrifuge tubes (preliminary test) or glass bottles (screening test).
- Water filtered: No.
- Number of reaction vessels/concentration: All experiments including controls were performed in duplicate.
- Measuring equipment: The concentration of the test material in the samples was determined by analysis of dissolved lanthanum using inductively coupled plasma mass spectroscopy (ICP-MS).
- Test performed in closed vessels (due to significant volatility of test substance) or in open system: No data.

- Method of preparation of test solution, incubation conditions and study conduct:
1) Preparation of the application solution:
Preliminary test: An application solution (AS1) was prepared for the preliminary test by weighing 1.21 mg of the test material and diluting it in 350 mL 0.01 M CaCl2 solution. Its final concentration was calculated to be 0.0034 mg/mL, taking into account the purity of the test material. The application solution was thoroughly mixed before use.
Screening test: An application solution (AS2) was prepared for the screening test in the same way as for the preliminary test only using an amount of 5.05 mg test material in 1500 mL 0.01 M CaCl2 solution. Its final concentration, corrected for purity, was calculated to be 0.0034 mg/mL.

2) Application: After pre-equilibration of the soil with 0.01 M CaCl2 solution, aliquots of the corresponding application solutions were added on the surface of the supernatant using a pipette as described in the table reported in the field “Any other information on materials and methods incl. tables”. Besides the treated samples, controls (duplicates, without soil) and blanks (duplicates, without test material) were subjected to precisely the same steps as the test samples. The control samples checked the stability of the test material in CaCl2 solution whereas the blanks served as a background control during the analysis to detect interfering compounds or contaminated soils. Analysis was only performed for the longest interval (48 hours). All test tubes were shaken briefly by hand, and then mechanically shaken on a rotary shaker in a temperature-controlled room.

3) Test concentrations: for the different parts of the adsorption/desorption test, the following test concentrations were measured by ICP/MS:
Preliminary test: 0.64 mg/L.
Screening test: 1.29 mg/L.

4) Conditions for adsorption/desorption:
Adsorption: All test tubes were shaken horizontally on a rotary shaker at about 150 strokes per minute. The agitation device kept the soil in suspension during shaking. After shaking, the samples were centrifuged (10 minutes at about 2800 or 3000 rpm) and the supernatants decanted into tarred, labelled sample containers. The volumes of the supernatants were determined gravimetrically. At the different sampling intervals, the samples were removed for ICP/MS analysis for determination of the test material concentration. The equilibrium concentration of the test material, and its total amount in the aqueous phase, were calculated based on the results of the analyses. The amount of test material adsorbed onto soil particles was obtained from the difference between the initial and final amount of test material in the aqueous phase.
Desorption: After separation of the soil from the adsorption solution, the same volume of 0.01 M CaCl2 as removed after the adsorption step was added. Thereafter, the mixtures were agitated in the same way as for the adsorption part. The samples were centrifuged and the supernatant analysed by ICP/MS at the different shaking intervals. The desorption equilibrium concentration of the test material, and its total amount in the aqueous phase, were calculated based on the results of the ICP/MS analyses. The remaining soil water in all samples was determined gravimetrically, and the mass of the test material left over from the adsorption equilibrium and the desorption step, respectively, was calculated.

5) Study conduct:
Preliminary test: The preliminary test was conducted using the three soils and three soil-to-solution ratios (1/50, 1/25 and 1/5) in order to select the optimal soil/solution ratio (for the subsequent screening test), to determine the adsorption of the test material onto the surfaces of the test vessels and the stability of the test material during the test period. A test material concentration of 0.64 mg/L and a sampling time of 48 hours were used. After 48 h, duplicate tubes were sampled and the supernatants analysed by ICP/MS for the test material concentration. Based on the results of the preliminary test, the soil-to-solution ratio of 1/50 was selected for the subsequent screening test.
Mass balance: The mass balance was carried out on all soils directly after the 48-hour adsorption step in the screening test at the soil-to-solution ratio of 1/50 (two tubes per soil). After sampling, the supernatant was removed and the soil was extracted three times, each using 5 mL nitric acid (10 %). The extracts resulting from the same tube were combined and analysed by ICP/MS.
Screening test: The adsorption kinetics were studied using the same soils as used for the preliminary test at the soil-to-solution ratio of 1/50 and a test material concentration of 1.29 mg/L. Additionally, the distribution coefficients Kd and Koc were determined after 48 hours of adsorption. After 2, 5, 24 and 48 hours of shaking during the adsorption phase, duplicate tubes were sampled and the supernatants analysed by ICP/MS. In order to determine whether the test material is readily desorbed from soil or not, a desorption experiment was performed directly after the adsorption step using sampling times at 2, 4, 24 and 48 hours.

Computational methods:

The following parameters were calculated using a commercially available Excel computer program:
- A: Percentage of substance adsorbed
- Kd: Distribution coefficient
- D: Percentage of substance desorbed
- Kdes: Desorption coefficient
- Koc: Organic carbon normalised adsorption/desorption coefficient

Type:

Koc

Value:

5 480 283 L/kg

Type:

log Koc

Value:

6.36 dimensionless

Adsorption and desorption constants:

Adsorption: The Kd values amounted to 5451, 46861 and 216905 mL/g for soils I to III, respectively, with corresponding Koc values of 230978, 4733400 and 11476472 mL/g, respectively.
Desorption: The Kd des values were 15203, 2641, 30858 mL/g for soils I to III, respectively, with corresponding Koc des of 644212, 266724 and 163702 mL/g, respectively.

Recovery of test material:

The mass balance showed overall recoveries of 62.0, 79.1 and 75.9 % of the initial amount applied for soils I to III, respectively. Most of the applied test material was found in soil (62 to 79 %). Insignificant amounts (0.1 % of applied or less) were detected in the supernatant.

Concentration of test substance at end of adsorption equilibration period:

After addition of 64.5 μg of test material, 63.9 to 64.5 μg were adsorbed to the soils, with only 0.01 to 0.59 μg detected in the supernatant.

Concentration of test substance at end of desorption equilibration period:

The amount of test material desorbed remained low and constant with time, with <0.1 to 3.3 % of the adsorbed amount desorbed for all three soils within the 48-hour desorption experiment.
After 48 hours of shaking in the desorption experiment 0.28, 1.23 and 0.54 μg was recovered in the desorption solution of soils I to III. In the soils, between 63.20 and 63.95 μg were recovered after the desorption step.

Sample no.:

#1

Duration:

48 h

% Adsorption:

62

Sample no.:

#2

Duration:

48 h

% Adsorption:

79.1

Sample no.:

#3

Duration:

48 h

% Adsorption:

75.9

Sample no.:

#1

Duration:

48 h

% Desorption:

0.4

Sample no.:

#2

Duration:

48 h

% Desorption:

1.9

Sample no.:

#3

Duration:

48 h

% Desorption:

0.8

Transformation products:

no

Details on results (Batch equilibrium method):

See Tables 1 and 2 below

Statistics:

All calculations were done using the program VALIDATA 3.0 according to DIN 38402-part51.

Table 1: Concentration of the Test Material in the Solid and Liquid Phases at the end of Adsorption Equilibration Period (Mean ± S.D.)

Concentration (mg/L)	Soil 1 (loamy sand)			Soil 2 (silt loam)			Soil 3 (clay)
	On soil (µg)	In solution (µg a.i./mL)	% Adsorbed	On soil (µg)	In solution (µg a.i./mL)	% Adsorbed	On soil (µg)	In solution (µg a.i./mL)	% Adsorbed
Control*	1.238 µg a.i./mL in solution; 96.0 % adsorbed
1.29	63.92	0.0117	99.1	64.43	0.001	99.9	64.49	0.0003	100.0

*Control = without soil

 

Table 2: Concentration of the Test Material in the Solid and Liquid Phases at the end of Desorption.

Concentration (mg/L)	Soil 1 (loamy sand)			Soil 2 (silt loam)			Soil 3 (clay)
	On soil (µg)	In solution (µg)	% Desorbed as % of the Adsorbed	On soil (µg)	In solution (µg)	% Desorbed as % of the Adsorbed	On soil (µg)	In solution (µg)	% Desorbed as % of the Adsorbed
1.29	63.67	0.28	0.4	63.20	1.23	1.9	63.95	0.54	0.8

Validity criteria fulfilled:

yes

Conclusions:

The test material was strongly adsorbed to soil.

Executive summary:

The adsorption/desorption behaviour of the test material on soil was determined using three soils and the batch equilibrium method in accordance with the standardised guideline OECD 106.

Initially, a preliminary test was performed in order to investigate the adsorption behaviour of the test material. For this purpose, three soils, a test concentration of 0.64 mg/L and three soil (dry weight) to aqueous phase ratios: 1/50 (1 g/50 mL), 1/25 (1 g/25 mL) and 1/5 (5 g/25 mL) were used. Very high adsorption was observed for all three ratios. After 48 hours of agitation, virtually all of the initial amount of test material was adsorbed (≥ 99 %).

Therefore, for the subsequent screening test, the maximum soil-to-solution ratio of 1/50 was selected together with a test material concentration of 1.29 mg/L and the same three soils. The adsorption/desorption kinetics of the test material were determined after 2, 4 or 5, 24 and 48 hours of agitation. After 2 hours of agitation, adsorption represented 96, 100 and 100 % for soils I to III, respectively. Only low desorption was observed during the 48-hour desorption period (maximum of 3 % of test material desorbed for all three soils).

The mass balance was performed during the screening test at the soil to solution ratio of 1/50. The amount of applied test material recovered from the samples represented 62, 79 and 76 % for soils I to III, respectively. Most of the applied amount was extracted from the soils, with only ≤0.5 % of applied detected in the supernatants. The mass balance results confirmed the strong adsorption of the test material to soil.

The following adsorption/desorption distribution coefficients were obtained for the soils at the selected ratio of 1/50:

- Mean Koc value: 5480283

- Mean Koc, des value: 358213

Reference 2

Endpoint:

adsorption / desorption: screening

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Justification for type of information:

The data on the read-across substance is considered representative.

Reason / purpose for cross-reference:

read-across source

Type:

Koc

Value:

5 480 283 L/kg

Type:

log Koc

Value:

6.36 dimensionless

Conclusions:

The test material was strongly adsorbed to soil.

Executive summary:

The adsorption/desorption behaviour of the test material on soil was determined using three soils and the batch equilibrium method in accordance with the standardised guideline OECD 106.

Initially, a preliminary test was performed in order to investigate the adsorption behaviour of the test material. For this purpose, three soils, a test concentration of 0.64 mg/L and three soil (dry weight) to aqueous phase ratios: 1/50 (1 g/50 mL), 1/25 (1 g/25 mL) and 1/5 (5 g/25 mL) were used. Very high adsorption was observed for all three ratios. After 48 hours of agitation, virtually all of the initial amount of test material was adsorbed (≥ 99 %).

Therefore, for the subsequent screening test, the maximum soil-to-solution ratio of 1/50 was selected together with a test material concentration of 1.29 mg/L and the same three soils. The adsorption/desorption kinetics of the test material were determined after 2, 4 or 5, 24 and 48 hours of agitation. After 2 hours of agitation, adsorption represented 96, 100 and 100 % for soils I to III, respectively. Only low desorption was observed during the 48-hour desorption period (maximum of 3 % of test material desorbed for all three soils).

The mass balance was performed during the screening test at the soil to solution ratio of 1/50. The amount of applied test material recovered from the samples represented 62, 79 and 76 % for soils I to III, respectively. Most of the applied amount was extracted from the soils, with only ≤0.5 % of applied detected in the supernatants. The mass balance results confirmed the strong adsorption of the test material to soil.

The following adsorption/desorption distribution coefficients were obtained for the soils at the selected ratio of 1/50:

- Mean Koc value: 5480283

- Mean Koc, des value: 358213

Reference 3

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

15 August 2007 - 17 September 2008

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Study conducted to GLP in compliance with agreed protocols, with no or minor deviations from standard test guidelines and/or minor methodological deficiencies, which do not affect the quality of the relevant results. Study read-across from similar substance.

Justification for type of information:

The data on the read-across substance is considered representative.

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

no

Test temperature:

20°C +/- 2°C

Analytical monitoring:

yes

Details on sampling:

- Concentrations:
Preliminary test : Three soil-to-solution ratios = 1/50, 1/25, 1/5; one test item concentration = 0.89 mg/l
Screening test : one soil-to-solution ratio = 1/50; one test item concentration = 1.23 mg/l

- Sampling interval:
Preliminary test : 48 hours
Screening test : adsorption phase: 2, 5, 24 and 48 hours ; desorption phase: 2, 4, 24 and 48 hours
- Sample storage before analysis: before analyses all samples were stabilized by adding 0.5 ml nitric acid to 5 ml supernatant.

Details on matrix:

COLLECTION AND STORAGE
- Geographic location:
Soil I (SI): Hanhofen (Speyer, Rheinland-Pfalz, Germany; latitude 49°19'N, longitude 8°20'E). The sampling side was a meadow in the sampling year and at least 4 former years.
Soil II (SII): Attenschwiller (68220 Attenschwiller, France, latitude 47°34'N, longitude 7°27'E). The field cover at the time of sampling consisted of weeds.
Soil III (SIII): Siebeldingen (Speyer, Rheinland-Pfalz, Germany, latitude 49°12'N, longitude 08°03'E). The sampling site was uncultivated in the sampling year and at least 4 years before.
- Collection procedures: Sampling and handling of the soils were performed under consideration of ISO 10381-6 (Soil Quality-Sampling-Guidance on the collection, handling and storage of soil for the assessment of microbial processes in the laboratory).
- Sampling depth (cm): The three soils were sampled from the top 20 cm layer.
- Storage conditions and length: no data except that SI, SII and SIII were sampled on August 2006, March 2007 and September 2006, respectively.
- Soil preparation: The soils, sieved to 2-mm, were air-dried at room temperature and homogenized. Disaggregation was performed with minimal force, so that the original texture of the soil was changed as little as possible. In order to eliminate microbial degradation of the test item, the soils were sterilized before use by irradiation (Studer Hard, 4658 Däniken / Switzerland). Thereafter, the soil samples were pre-equilibrated with 50% of the targeted volume of the aqueous phase by shaking for at least 20 hours at 20 °C prior to application of the test item.

PROPERTIES
- Soil texture
% sand: SI = 79.1, SII = 11.8, SIII = 21.9.
% silt: SI = 13.5, SII = 72.8, SIII = 36.0.
% clay: SI = 7.9, SII = 15.4, SIII = 42.
- Horizon: no data.
- Soil taxonomic classification: SI = Loamy sand, SII = Silt loam, SIII = Clay.
- Soil classification system: The soil types above mentioned were determined according to USDA (United States Department of Agriculture).
- Soil series and order: no data.
- pH: SI = 5.6, SII = 7.4, SIII = 7.0.
- Organic carbon (%): SI = 2.36, SII = 0.99, SIII = 1.89.
- CEC (meq/100 g): SI = 11.0, SII = 10.2, SIII = 20.0.
- Nitrogen content (%): SI = 0.21, SII = 0.11, SIII = 0.21.
- Organic matter (%): SI = 4.07, SII = 1.71, SIII = 3.26.
- C/N-ratio: SI = 11.2, SII = 9.0, SIII = 9.0
- Moisture (in g per 100 g dry soil): SI = 0.95, SII = 1.02, SIII = 5.78.
- Other: None of the soils had been fertilised or treated with pesticides for at least 12 months prior to sampling.
No further data.

Details on test conditions:

TEST CONDITIONS
- Buffer: none.
- pH: The pH of the aqueous phase was measured before and after contact with the soil at the soil-to-solution ratio of 1/50. The pH of the CaCl2-solution was 7.05 before contact with the soil and 6.59, 6.85 and 6.89 after contact with soil I to III, respectively.
- Suspended solids concentration: no data.

TEST SYSTEM
- Type, size and further details on reaction vessel: The study was performed in Teflon centrifuge tubes (preliminary test) or glass bottles (screening test).

- Water filtered: No.
- Number of reaction vessels/concentration: All experiments including controls were performed in duplicate.
- Measuring equipment: The concentration of Cerium Carbonate 99.9 Humide in the samples was determined by analysis of dissolved cerium using inductively coupled plasma mass spectroscopy (ICP-MS).
- Test performed in closed vessels (due to significant volatility of test substance) or in open system: No data.

- Method of preparation of test solution, incubation conditions and study conduct:
1) Preparation of the application solution:
Preliminary test: An application solution (AS1) was prepared for the preliminary test by weighing 1.66 mg of the test item and diluting it in 350 mL 0.01 M CaCl2 solution. Its final concentration was calculated to be 0.0036 mg/mL, taking into account the purity of the test item (76.7 %, Section 3.1). The application solution was thoroughly mixed before use.
Screening test: An application solution (AS2) was prepared for the screening test in the same way as for the preliminary test only using an amount of 10.22 mg test item in 1500 mL 0.01 M CaCl2 solution. Its final concentration, corrected for purity, was calculated to be 0.0052 mg/mL.

2) Application: After pre-equilibration of the soil with 0.01 M CaCl2 solution, aliquots of the corresponding application solutions were added on the surface of the supernatant using a pipette as described in the table reported in the field "Any other information on materials and methods incl. tables". Besides the treated samples, controls (duplicates, without soil) and blanks (duplicates, without test item) were subjected to precisely the same steps as the test samples. The control samples checked the stability of the test item in CaCl2 solution whereas the blanks served as a background control during the analysis to detect interfering compounds or contaminated soils. Analysis was only performed for the longest interval (48 hours). All test tubes were shaken briefly by hand, and then mechanically shaken on a rotary shaker in a temperature-controlled room.

3) Test concentrations: for the different parts of the adsorption/desorption test, the following test concentrations were measured by ICP/MS:
Preliminary test: 0.89 mg/L.
Screening test: 1.23 mg/L.

4) Conditions for adsorption/desorption:
Adsorption: All test tubes were shaken horizontally on a rotary shaker at about 150 strokes per minute. The agitation device kept the soil in suspension during shaking. After shaking, the samples were centrifuged (10 minutes at about 2800 or 3000 rpm) and the supernatants decanted into tarred, labelled sample containers. The volumes of the supernatants were determined gravimetrically. At the different sampling intervals, the samples were removed for ICP/MS analysis for determination of the test item concentration. The equilibrium concentration of the test item, and its total amount in the aqueous phase, were calculated based on the results of the analyses. The amount of test item adsorbed onto soil particles was obtained from the difference between the initial and final amount of test item in the aqueous phase.
Desorption: After separation of the soil from the adsorption solution, the same volume of 0.01 M CaCl2 as removed after the adsorption step was added. Thereafter, the mixtures were agitated in the same way as for the adsorption part. The samples were centrifuged and the supernatant analyzed by ICP/MS at the different shaking intervals. The desorption equilibrium concentration of the test item, and its total amount in the aqueous phase, were calculated based on the results of the ICP/MS analyses. The remaining soil water in all samples was determined gravimetrically, and the mass of the test item left over from the adsorption equilibrium and the desorption step, respectively, was calculated.

5) Study conduct:
Preliminary test: The preliminary test was conducted using the three soils and three soil-to-solution ratios (1/50, 1/25 and 1/5) in order to select the optimal soil/solution ratio (for the subsequent screening test), to determine the adsorption of the test item onto the surfaces of the test vessels and the stability of the test item during the test period. A test item concentration of 0.89 mg/L and a sampling time of 48 hours were used. At each sampling interval, duplicate tubes were sampled and the supernatants analyzed by ICP/MS for the test item concentration. Based on the results of the preliminary test and in order to obtain adsorption greater than 50 % for any soil (which enables accurate measurements of the test item in the aqueous phase), soil-to-solution ratio of 1/50 was selected for the subsequent screening test.
Mass balance: The mass balance was carried out on all soils directly after the 48-hour adsorption step in the screening test at the soil-to-solution ratio of 1/50 (two tubes per soil). After sampling, the supernatant was removed and the soil was extracted three times, each using 5 mL nitric acid (10%). The extracts resulting from the same tube were combined and analyzed by ICP/MS.
Screening test: The adsorption kinetics were studied using the same soils as used for the preliminary test at the soil-to-solution ratio of 1/50 and a test item concentration of 1.23 mg/L. Additionally, the distribution coefficients KD and KOC were determined after 48 hours of adsorption. After 2, 5, 24 and 48 hours of shaking during the adsorption phase, duplicate tubes were sampled and the supernatants analyzed by ICP/MS. In order to determine whether Cerium Carbonate 99.9 Humide is readily desorbed from soil or not, a desorption experiment was performed directly after the adsorption step using sampling times at 2, 4, 24 and 48 hours.

Computational methods:

The following parameters were calculated using a commercially available Excel computer program:
- A: Percentage of substance adsorbed
- Kd: Distribution coefficient
- D: Percentage of substance desorbed
- Kdes: Desorption coefficient
- Koc: Organic carbon normalized adsorption/desorption coefficient

Type:

Koc

Value:

3 940 404 L/kg

Type:

log Koc

Value:

6.6 dimensionless

Adsorption and desorption constants:

Adsorption: The Kd values amounted to 11784, 59264 and >100843 mL/g for soils I to III, respectively, with corresponding Koc values of 499332, 5986256 and >5335623 mL/g, respectively.
Desorption: The Kd des values were 10147, 102180, > 225268 mL/g for soils I to III, respectively, with corresponding Koc des of 429968, 10321193 and >11918936 mL/g respectively.

Recovery of test material:

The mass balance showed overall recoveries of 83.6 %, 100.9 % and 87. % of the initial amount applied for soils I to III, respectively. Most of the applied test item was found in soil (83.2 to 100.8 %). Insignificant amounts (0.4 % of applied or less) were detected in the supernatant.

Concentration of test substance at end of adsorption equilibration period:

After addition of 61.6 µg Cerium Carbonate 99.9 Humide, 61.33 to 61.56 µg were adsorbed to the soils, with only <0.03 - 0.27 µg detected in the supernatant.

Concentration of test substance at end of desorption equilibration period:

The amount of test item desorbed remained low and constant with time, with <0.02 % to 1.9 % of the adsorbed amount desorbed for all three soils within the 48-hour desorption experiment.
After 48 hours of shaking in the desorption experiment 0.31 µg, 0.03 µg and <0.01 µg was recovered in the desorption solution of soils I to III . In the soils, between 61.03 µg and >61.55 µg were recovered after the desorption step.

Sample no.:

#1

Duration:

48 h

% Adsorption:

83.6

Sample no.:

#2

Duration:

48 h

% Adsorption:

100.9

Sample no.:

#3

Duration:

48 h

% Adsorption:

87.4

Sample no.:

#1

Duration:

48 h

% Desorption:

0.5

Sample no.:

#2

Duration:

48 h

% Desorption:

0.05

Sample no.:

#3

Duration:

48 h

% Desorption:

< 0.02

Transformation products:

no

Details on results (Batch equilibrium method):

see below table 1 and 2

Statistics:

All calculations were done using the program VALIDATA 3.0 according to DIN 38402-part51.

Table 1: Concentration of  test item in the solid and liquid phases at the end of adsorption equilibration period (mean ± s.d.)

Concentration	Soil 1 (loamy sand)			Soil 2 (silt loam)			Soil 3 (clay)
	on soil (µg)	In solution (µg a.i./mL)	% adsorbed	on soil (µg)	In solution (µg a.i./mL)	% adsorbed	on soil (µg)	In solution (µg a.i./mL)	% adsorbed
Control*	1.215  µg a.i./mL in solution ; 98.7% adsorbed
Conc. (1.23 mg/l)	61.33	0.0053	99.6	61.54	0.0012	99.9	61.56	0.0006	99.9

* control = without soil

Table 2: Concentration of test item in the solid and liquid phases at the end of desorption.

Concentration	Soil 1 (loamy sand)			Soil 2 (silt loam)			Soil 3 (clay)
	on soil (µg)	in solution (µg)	% desorbed as % of the adsorbed	on soil (µg)	in solution (µg)	% desorbed as % of the adsorbed	on soil (µg)	in solution (µg)	% desorbed as % of the adsorbed
Conc. (1.23 mg/l)	61.03	0.31	0.5	61.51	0.03	0.05	> 61.55	< 0.01	< 0.02

Validity criteria fulfilled:

yes

Conclusions:

Dicerium tricarbonate was strongly adsorbed to soil.

Executive summary:

The adsorption/desorption behaviour of the test item, dicerium tricarbonate, on soil was determined using three soils and the batch equilibrium method according to OECD Guideline 106.

Initially, a preliminary test was performed in order to investigate the adsorption behaviour of dicerium tricarbonate. For this purpose, three soils, a test concentration of 0.89 mg/L and three soil (dry weight) to aqueous phase ratios: 1/50 (1 g/50 mL), 1/25 (1 g/25 mL) and 1/5 (5 g/25 mL) were used. Very high adsorption was observed for all three ratios. After 48 hours of agitation, virtually all of the initial amount of test item was adsorbed (>99 %).

Therefore, for the subsequent screening test, the maximum soil-to-solution ratio of 1/50 was selected together with a test item concentration of 1.23 mg/L and the same three soils. The adsorption/desorption kinetics of dicerium tricarbonate were determined after 2, 4 or 5, 24 and 48 hours of agitation. After 2 hours of agitation, adsorption represented 95 %, 100 % and 100 % for soils I to III, respectively. Only low desorption was observed during the 48-hour desorption period (maximum of 2 % of test item desorbed for all three soils).

The mass balance was performed during the screening test at the soil to solution ratio of 1/50. The amount of applied test item recovered from the samples represented 83.6 %, 100. 9% and 87.4 % for soils I to III, respectively. Most of the applied amount was extracted from the soils, with only <0.4 % of applied detected in the supernatants. The mass balance results confirmed the strong adsorption of dicerium tricarbonate to soil.

The following adsorption/desorption distribution coefficients were obtained for the soils at the selected ratio of 1/50:

- Mean Koc value: 3940404

- Mean Koc, des value: 7556699

Reference 4

Endpoint:

adsorption / desorption: screening

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Justification for type of information:

The data on the read-across substance is considered representative.

Reason / purpose for cross-reference:

read-across source

Type:

Koc

Value:

3 940 404 L/kg

Type:

log Koc

Value:

6.6 dimensionless

Conclusions:

Dicerium tricarbonate was strongly adsorbed to soil.

Executive summary:

The adsorption/desorption behaviour of the test item, dicerium tricarbonate, on soil was determined using three soils and the batch equilibrium method according to OECD Guideline 106.

Initially, a preliminary test was performed in order to investigate the adsorption behaviour of dicerium tricarbonate. For this purpose, three soils, a test concentration of 0.89 mg/L and three soil (dry weight) to aqueous phase ratios: 1/50 (1 g/50 mL), 1/25 (1 g/25 mL) and 1/5 (5 g/25 mL) were used. Very high adsorption was observed for all three ratios. After 48 hours of agitation, virtually all of the initial amount of test item was adsorbed (>99 %).

Therefore, for the subsequent screening test, the maximum soil-to-solution ratio of 1/50 was selected together with a test item concentration of 1.23 mg/L and the same three soils. The adsorption/desorption kinetics of dicerium tricarbonate were determined after 2, 4 or 5, 24 and 48 hours of agitation. After 2 hours of agitation, adsorption represented 95 %, 100 % and 100 % for soils I to III, respectively. Only low desorption was observed during the 48-hour desorption period (maximum of 2 % of test item desorbed for all three soils).

The mass balance was performed during the screening test at the soil to solution ratio of 1/50. The amount of applied test item recovered from the samples represented 83.6 %, 100. 9% and 87.4 % for soils I to III, respectively. Most of the applied amount was extracted from the soils, with only <0.4 % of applied detected in the supernatants. The mass balance results confirmed the strong adsorption of dicerium tricarbonate to soil.

The following adsorption/desorption distribution coefficients were obtained for the soils at the selected ratio of 1/50:

- Mean Koc value: 3940404

- Mean Koc, des value: 7556699

Reference 5

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

8 January 2013 to 15 April 2013

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Study conducted to GLP in compliance with agreed protocols, with no or minor deviations from standard test guidelines and/or minor methodological deficiencies, which do not affect the quality of the relevant results. Study read-across from similar substance.

Justification for type of information:

The data on the read-across substance is considered representative.

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

Principles of method if other than guideline:

With the exception of the acidic soil type 7, definitive results of distribution coefficients (Kd) and organic carbon normalised adsorption coefficients (Koc) were calculated from the initial sampling time-point, employing an adsorption equilibration period of 2 hours, at which the recovery of the dissolved neodymium content of soil-less control solutions was maximised.
This was concluded not to impact on the validity of the distribution coefficient and adsorption coefficient values obtained. With reference to the European Commission Health and Consumer Protection Directorate guidance document SCP/KOC/002, a batch equilibrium method with a reduced equilibrium time was detailed as the preferred method for substances shown to generate unstable aqueous solutions. The guidance document states that a large fraction of the adsorption onto the soil phase occurs within the first 30 minutes, and therefore any underestimation of the adsorption coefficient values by an amended procedure using a 30 minute incubation period to be less than a factor of two, i.e. negligible when considered in the more common logarithmic scale. Any systematic error would therefore be further reduced by the use of at least a 2 hour incubation period, as used in calculation of the adsorption characteristics of this test material.

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

no

Test temperature:

25 ± 2 °C

Analytical monitoring:

yes

Details on sampling:

- Concentrations: saturated solution in 0.01 M calcium chloride solution
- Sampling interval: 2, 5, 24 and 48 hours

Details on matrix:

All soils were stored air dried, in the dark, at ambient temperature. Organic carbon content, CEC and pH were re-analysed at least every 3 years.

SOIL TYPE 2
- USDA soil class: Loam
- Particle size: 50 µm to 2 mm: 35.9 %; 2 to 50 µm: 37.1 %; <2 µm: 27.0 %
- pH, 1:5 soil to 0.01 M CaCl2 ratio: 7.3
- Cation exchange capacity (meq/100 g): 34.7
- Organic carbon content (%): 4.10
- Total nitrogen content (%): 0.44
- Moisture content (% w/w): 18.0
- Geographical location: South Witham, Lincolnshire, UK, SK 921191
- Land usage: Undisturbed, previously arable land, adjacent to quarry. No pesticide use since at least 1995.
- Date of sampling: 28/10/2008
- Depth of sampling: 5 to 20 cm

SOIL TYPE 3
- USDA soil class: Silt loam
- Particle size: 50 µm to 2 mm: 12.3 %; 2 to 50 µm: 68.1 %; <2 µm: 19.6 %
- pH, 1:5 soil to 0.01 M CaCl2 ratio: 6.2
- Cation exchange capacity (meq/100 g): 15.1
- Organic carbon content (%): 2.47
- Total nitrogen content (%): 0.27
- Moisture content (% w/w): 4.84
- Geographical location: Chelmorton, Derbyshire, UK, SK 104691
- Land usage: Permanent dairy pasture. Localised pesticide spraying, but not to the sampling site.
- Date of sampling: 13/06/2003
- Depth of sampling: 10 to 20 cm

SOIL TYPE 4
- USDA soil class: Silt loam
- Particle size: 50 µm to 2 mm: 28.4 %; 2 to 50 µm: 51.8 %; <2 µm: 19.8 %
- pH, 1:5 soil to 0.01 M CaCl2 ratio: 5.1
- Cation exchange capacity (meq/100 g): 14.2
- Organic carbon content (%): 3.89
- Total nitrogen content (%): 0.36
- Moisture content (% w/w): 4.26
- Geographical location: Middleton, Derbyshire, UK, SK 179618
- Land usage: Permanent dairy pasture. No pesticide application.
- Date of sampling: 11/01/2011
- Depth of sampling: 10 to 20 cm

SOIL TYPE 5
- USDA soil class: Loamy sand
- Particle size: 50 µm to 2 mm: 81.8 %; 2 to 50 µm: 11.4 %; <2 µm: 6.8 %
- pH, 1:5 soil to 0.01 M CaCl2 ratio: 5.8
- Cation exchange capacity (meq/100 g): 9.2
- Organic carbon content (%): 1.01
- Total nitrogen content (%): 0.13
- Moisture content (% w/w): 1.46
- Geographical location: Ingleby, Derbyshire, UK, SK 34636 26943
- Land usage: Permanent pasture. No pesticide application to sampling site.
- Date of sampling: 06/06/2008
- Depth of sampling: 15 to 20 cm

SOIL TYPE 7
- USDA soil class: Loamy sand
- Particle size: 50 µm to 2 mm: 85 %*; 2 to 50 µm: 10 %*; <2 µm: 5 %*
- pH, 1:5 soil to 0.01 M CaCl2 ratio: 3.1
- Cation exchange capacity (meq/100 g): 49.8
- Organic carbon content (%): 22.7
- Total nitrogen content (%): 0.59
- Moisture content (% w/w): 17.1
- Geographical location: Lindholme, South Yorkshire, UK, SE 674064
- Land usage: Topsoil stock pile from former quarry works. No pesticide application.
- Date of sampling: 01/07/2003
- Depth of sampling: 0 to 20 cm

* No definitive experimental determination was possible due to the high humus content of the soil. Therefore the values presented are typical, historic values.

Details on test conditions:

The optimal soil to solution ratio was identified through preliminary testing at nominal soil to solution ratios of 1:5, 1:25 and 1:100. This indicated that testing would be optimised at a nominal ratio of 1:100, whilst remaining within the recommendations of the method guidelines.
Due to limited aqueous solubility of the test material and the irrelevance of organic co-solvents to inorganic test materials, stock solutions were prepared by shaking saturated solutions of test material in 0.01 M calcium chloride solution overnight, at ambient laboratory temperature.

PROCEDURE
Aliquots of soil and 0.01 M calcium chloride solution were taken in FEP/ETFE centrifuge tubes. Aliquots of 0.01 M calcium chloride solution required for soil-less blanks and soil-less controls were also taken in these test vessels. Due to the capacity of the available apparatus, the procedure was initially performed using soil type 2, soil type 3 and soil type 4. The procedure was then completed on a separate occasion using soil type 5 and soil type 7.

PREPARATION OF STOCK SOLUTIONS
An aliquot of test material (0.2546 g for testing of soil type 2, soil type 3 and soil type 4, and 0.2554 g for testing of soil type 5 and soil type 7) was diluted with 500 mL of 0.01 M calcium chloride solution. Each solution was shaken overnight on a flatbed shaker, at ambient temperature, to saturate. Following saturation, each stock solution was filtered through 0.45 µm filters to eliminate undissolved test material prior to use.

ADDITION OF TEST MATERIAL INTO SAMPLES
Relevant stock solution (2 mL) was added to all soil samples and all soil-less control solutions. An aliquot (2 mL) of 0.01 M calcium chloride solution was added to all soil blanks and all soil-less blanks. The addition of 2 mL to the existing 25 mL already present resulted in a stock solution addition of 7.4 % v/v.

ADSORPTION PROCEDURE
Each sample and soil-less control was agitated at 25 ± 2 °C, in the dark, for the relevant adsorption period.
All soil-less blanks and soil blanks were removed after 48 hours agitation to provide maximum opportunity for interfering species to leach out into solution.

DATA HANDLING
ADSORPTION DATA
The percentage of neodymium adsorbed (A) was calculated using the following equation:
A = [(Ccont - Ceq) / Ccont] x 100
where:
Ccont = mean soil-less control neodymium concentration (mg/L)
Ceq = neodymium concentration remaining in solution on analysis after completion of equilibration period (mg/L)

The distribution coefficient (Kd) was calculated using the following equation:
Kd = [Aeq / (100 - Aeq)] x (Vo / m-soil)
Where:
Kd = distribution coefficient (cm³/g)
Aeq = percentage of test material adsorbed (%)
Vo = volume of the aqueous phase in contact with the soil (cm³)
m-soil = quantity of the soil phase, expressed in dry mass of soil (g)

The organic carbon normalised adsorption coefficient (Koc) was calculated using the following equation:
Koc = Kd x (100 / %oc)
where:
Koc = organic carbon normalised adsorption coefficient (cm³/g)
%oc = percentage of organic carbon in the soil type (%)

Type:

Kd

Value:

>= 1 380 - <= 6 100 other: cm^3/g

Temp.:

25 °C

Remarks on result:

other: The overall Kd range was 1380 to at least 6100 at 25 ± 2 °C

Type:

Koc

Value:

>= 13 300 - <= 239 000 other: cm^3/g

Temp.:

25 °C

Remarks on result:

other: The overall Koc range was 13300 to at least 239000 at 25 ± 2 °C

Type:

log Koc

Value:

>= 4.12 - <= 5.38 dimensionless

Temp.:

25 °C

Remarks on result:

other: The overall log10 Koc range was 4.12 to at least 5.38 at 25 ± 2 °C

Adsorption and desorption constants:

The mean Kd values (cm³/g) were as follows:
- Soil type 2: 6.10 x 10³
- Soil type 3: ≥5.90 x 10³
- Soil type 4: 3.25 x 10³
- Soil type 5: 1.38 x 10³
- Soil type 7: 3.01 x 10³

The mean Koc values (cm³/g) were as follows:
- Soil type 2: 1.49 x 10⁵
- Soil type 3: ≥2.39 x 10⁵
- Soil type 4: 8.35 x 10⁴
- Soil type 5: 1.37 x 10⁵
- Soil type 7: 1.33 x 10⁴

Details on results (Batch equilibrium method):

The neodymium concentration (mg/L) of test material analysed in each solution, the solution pH and the percentage of test material adsorbed are shown in table 1. For soil type 2, 3, 4 and 5, the percentage of test material adsorbed has been calculated with respect to the relevant adsorption period mean soil-less control concentration. For soil type 7, the percentage of test material adsorbed has been calculated with respect to the theoretical dosed concentration, confirmed from analysis of the relevant stock solution.

The data required for the calculation of the distribution coefficient (Kd) and the organic carbon normalised adsorption coefficient (Koc) are shown in Table 2. Calculations have been completed from data generated at the 2 hour adsorption period time-point for soil type 2, 3, 4 and 5, and from the 5 hour adsorption period time-point for soil type 7.

The calculated distribution coefficients (Kd) and organic carbon normalised adsorption coefficients (Koc) for the neodymium content of the test material at 25 ± 2 °C, including the mean for each soil type, are shown in Table 3.

DISCUSSION
On analysis of the total dissolved neodymium concentration of the soil-less control solutions, the percentage recoveries with respect to the theoretical dosed concentration (from stock solution analysis) were low and declined with time. It could not be confirmed if losses were through adsorption to the test vessels, which were already optimised for low adsorption properties, or through precipitation followed by sedimentation on centrifugation; the control solutions being treated identically to the sample solutions.

However, irrespective of the fate of the decrease in neodymium concentration within the soil-less control solutions, the total dissolved neodymium concentration of the soil containing sample solutions decreased much more significantly and rapidly, such that this loss could be attributed confidently to interaction with the soil present.

Percentage adsorption calculations have been performed using the respective mean analysed soil-less control concentration at the 2 hour time-point. This therefore assumed the same degree of vessel adsorption and/or precipitation within the soil containing samples as for the soil-less controls. However, the strong affinity the test material has demonstrated for soils may have resulted in the soil active sites outcompeting any other underlying mechanism to strip the neodymium from solution and as such underestimated the actual adsorption onto the soils. To assess for the potential impact of this scenario on the study outcome, the distribution coefficient (Kd) and the organic carbon normalised adsorption coefficient (Koc) were recalculated against the theoretical dosed sample solution (calculated from stock solution analysis). This therefore assumed all decreases in the neodymium concentration of the sample solutions was due to soil adsorption alone. The results are summarised in Table 4.
This confirmed that the maximum possible deviation originating from the use of analysed soil-less control concentrations in calculation was equivalent to only 0.2 units as log10 Koc. Therefore, the decreases observed in the 2 hour soil-less control solutions on analysis did not impact significantly on the validity of the study, nor significantly skew the resulting quantified adsorption characterisation values obtained for soil types 2, 3, 4 and 5.

For the soil type 7, potentially due to the acidic nature of the soil/solution mixture promoting aqueous solubility, equilibrium was not evident at 2 hours. However consistent replicates were obtained following 5 hours equilibration and therefore these data were used for calculation of the distribution coefficient (Kd) and the organic carbon normalised adsorption coefficient (Koc) values. In addition, again due to the acidic pH promoting solubility of the neodymium content of the test material, for soil type 7 only, adsorption calculations have been performed from the theoretical dosed concentration confirmed from analysis of the relevant stock solution. This was since losses from the approximately neutral pH soil-less control solutions, attributed to adsorption and/or precipitation over time, were expected to be greatly reduced at an acidic pH. Therefore ( for the case of this soil type only) all reductions in the neodymium concentration of the aqueous phase on analysis have been attributed to adsorption on to the soil phase.

On analysis of the un-dosed soil blanks, low background concentrations of neodymium were detected. Due to the high percentage adsorption observed for the test material in the presence of all soil types, these blank concentrations were subsequently considered significant. Therefore prior to calculation of adsorption data, all sample solution concentrations were corrected for the relevant mean analysed soil blank concentration. The mean analysed soil blank neodymium concentrations were 6.0 x 10^-4 mg/L, 1.64 x 10^-3 mg/L, 1.04 x 10^-3 mg/L, 2.54 x 10^-3 mg/L and 8.16 x 10^-3 mg/L for soil types 2, 3, 4, 5 and 7 respectively. No significant neodymium concentration was detected in the matrix blanks or soil-less (solvent) blanks on analysis.

For soil type 3, 2 hour replicate B, and soil type 7, 48 hour replicates A and B, no detectable concentration of neodymium remained in the aqueous phase on analysis. These three samples have therefore been reported as greater than 99.0 % adsorption.

It was evident from the data generated that organic carbon normalised adsorption coefficient (Koc) values should be used with caution in any further environmental modelling of this test material. The adsorption properties (as distribution coefficients) observed for the dissolved neodymium content of the sample solutions showed no significant correlation to the organic carbon content of the soils evaluated.

From the soil type 7 results obtained, pH was evidently a very significant soil/solution criterion for the behaviour of this inorganic ion in soil. Even though soil type 7 presented both the highest organic carbon content and cation exchange capacity of the five soils investigated (22.7 % and 49.8 meq/100 g, respectively), the resultant distribution coefficient (Kd) value was the second lowest of the five soils investigated. Such a result was inversely proportional to the expectations of the methodology, predominantly aimed at organic compounds, as the acidic nature of this soil promoted aqueous solubility of the metal cation and therefore reduced the proportion partitioning on to the soil phase. Only soil type 5 resulted in a lower distribution coefficient (Kd) value. Soil type 5 presented both the lowest organic carbon content and cation exchange capacity of the five soils investigated (1.01 % and 9.2 meq/100 g, respectively). Therefore on comparison of soil type 5 and soil type 7, it can be observed that both the influence of an approximately 20 fold increase in organic carbon content and an approximately 5 fold increase in cation exchange capacity were negated by the decrease in the aqueous phase solution pH.

Table 1 Neodymium Concentration, pH and Percentage Adsorption

Soil Type	Solution	Nd Concentration (mg/L)*	Solution pH	Percentage Adsorption (%)	Mean Percentage Adsorption (%)
2	2 hour, Sample A	2.49E-03	6.4	98.4	98.0
	2 hour, Sample B	3.91E-03	6.4	97.5
	5 hour, Sample A	3.78E-03	6.4	96.9	97.5
	5 hour, Sample B	2.28E-03	6.6	98.1
	24 hour, Sample A	2.64E-03	6.4	95.3	93.0
	24 hour, Sample B	5.24E-03	6.5	90.7
	48 hour, Sample A	2.74E-03	6.4	95.9	96.1
	48 hour, Sample B	2.41E-03	6.3	96.4
3	2 hour, Sample A	2.75E-03	5.6	98.3	≥98.3
	2 hour, Sample B	None detected	5.7	>99.0
	5 hour, Sample A	2.28E-03	6.1	98.1	97.9
	5 hour, Sample B	2.72E-03	6.2	97.8
	24 hour, Sample A	1.03E-03	6.2	98.2	97.0
	24 hour, Sample B	2.40E-03	6.2	95.7
	48 hour, Sample A	1.21E-03	6.1	98.2	98.6
	48 hour, Sample B	5.91E-04	6.3	99.1
4	2 hour, Sample A	4.57E-03	5.8	97.1	96.9
	2 hour, Sample B	5.17E-03	5.4	96.7
	5 hour, Sample A	4.56E-03	5.5	96.2	95.7
	5 hour, Sample B	5.80E-03	5.3	95.2
	24 hour, Sample A	2.42E-03	5.2	95.7	95.6
	24 hour, Sample B	2.53E-03	5.2	95.5
	48 hour, Sample A	4.20E-03	5.3	93.7	95.3
	48 hour, Sample B	2.01E-03	5.4	97.0
5	2 hour, Sample A	8.41E-03	6.1	92.2	93.1
	2 hour, Sample B	6.51E-03	6.0	94.0
	5 hour, Sample A	6.20E-03	6.4	87.1	83.2
	5 hour, Sample B	9.92E-03	6.0	79.3
	24 hour, Sample A	4.51E-03	6.5	94.5	94.7
	24 hour, Sample B	4.26E-03	6.5	94.8
	48 hour, Sample A	2.44E-03	6.2	95.5	96.3
	48 hour, Sample B	1.57E-03	6.3	97.1
7	2 hour, Sample A	9.22E-03	3.3	94.4	92.0
	2 hour, Sample B	1.72E-02	3.3	89.6
	5 hour, Sample A	7.45E-03	3.2	95.5	96.1
	5 hour, Sample B	5.41E-03	3.2	96.7
	24 hour, Sample A	1.06E-02	3.5	93.6	96.2
	24 hour, Sample B	1.87E-03	3.5	98.9
	48 hour, Sample A	None detected	3.4	>99.0	>99.0
	48 hour, Sample B	None detected	3.4	>99.0

*Corrected for mean soil blank concentration on analysis

 

Table 2 Data Required for the Calculation of the Distribution Coefficient (Kd) and the Organic Carbon Normalised Adsorption Coefficient (Koc)

Soil Type	Sample Identity	Dry Mass of Soil (g)	Volume of Aqueous Phase (cm³)	Percentage Adsorption at Equilibrium (%)
2	A	0.2268	27	98.4
	B	0.2273	27	97.5
3	A	0.2601	27	98.3
	B	0.2593	27	>99.0
4	A	0.2647	27	97.1
	B	0.2626	27	96.7
5	A	0.2641	27	96.2
	B	0.2712	27	94.0
7	A	0.2306	27	95.5
	B	0.2252	27	96.7

 

Table 3 Distribution Coefficient (Kd) and Organic Carbon Normalised Adsorption Coefficient (Koc) Values

Soil Type	Sample Identity	Kd (cm³/g)	Mean / Overall Kd (cm³/g)	Koc (cm³/g)	Mean / Overall Koc (cm³/g)
2	A	7.48 x 10³	6.10 x 10³	1.83 x 10⁵	1.49 x 10⁵
	B	4.71 x 10³		1.15 x 10⁵
3	A	5.90 x 10³	≥5.90 x 10³	2.39 x 10⁵	≥2.39 x 10⁵
	B	>1.03 x 10⁴		>4.17 x 10⁵
4	A	3.44 x 10³	3.25 x 10³	8.85 x 10⁴	8.35 x 10⁴
	B	3.05 x 10³		7.85 x 10⁴
5	A	1.21 x 10³	1.38 x 10³	1.20 x 10⁵	1.37 x 10⁵
	B	1.56 x 10³		1.54 x 10⁵
7	A	2.48 x 10³	3.01 x 10³	1.09 x 10⁴	1.33 x 10⁴
	B	3.54 x 10³		1.56 x 10⁴

 

Table 4 Distribution Coefficient (Kd) and Organic Carbon Normalised Adsorption Coefficient (Koc) Values Derived from Analysed and Theoretical Soil-less Control Concentrations

Soil Type	Mean / Overall Kd (cm³/g)		Mean / Overall Koc (cm³/g)
	Calculated from Analysed Control Concentrations	Calculated from Theoretical Dosed Concentration	Calculated from Analysed Control Concentrations	Calculated from Theoretical Dosed Concentration
2	6.10 x 10³	7.85 x 10³	1.49 x 10⁵	1.92 x 10⁵
3	≥5.90 x 10³	≥7.59 x 10³	≥2.39 x 10⁵	≥3.07 x 10⁵
4	3.25 x 10³	4.19 x 10³	8.35 x 10⁴	1.08 x 10⁵
5	1.38 x 10³	2.17 x 10³	1.37 x 10⁵	2.15 x 10⁵

Validity criteria fulfilled:

yes

Conclusions:

Under the conditions of this study, the overall Kd range was 1.38 x 10³ to at least 6.10 x 10³, the overall Koc range was 1.33 x 10⁴ to at least 2.39 x 10⁵ and the overall log10 Koc range was 4.12 to at least 5.38.

Executive summary:

The adsorption characteristics of the test material were determined using a batch equilibrium method in accordance with the standardised guidelines OECD 106 and EU Method C.18 under GLP conditions.

The distribution coefficient (Kd) and the organic carbon normalised adsorption coefficient (Koc) for the neodymium content of the test material were determined for five soil types at 25 ± 2 °C. The soils were: soil type 2, loam (pH 7.3); soil type 3, silt loam (pH 6.2); soil type 4, silt loam (pH 5.1); soil type 5, loamy sand (pH 5.8); and soil type 7, loamy sand (pH 3).

Due to limited aqueous solubility of the test material and the irrelevance of organic co-solvents to inorganic test materials, stock solutions were prepared by shaking saturated solutions of test material in 0.01 M calcium chloride solution overnight, at ambient laboratory temperature.

With the exception of the acidic soil type 7, definitive results were calculated from the initial sampling time-point, employing an adsorption equilibration period of 2 hours, due to an inherent instability of the dissolved neodymium content of the soil-less control solutions as a function of time. For the soil type 7, potentially due to the acidic nature of the soil/solution mixture promoting aqueous solubility, equilibrium was not evident at 2 hours. However consistent replicates were obtained following 5 hours equilibration and therefore this data were used for calculation of the distribution coefficient (Kd) and the organic carbon normalised adsorption coefficient (Koc) values.

 

The adsorption properties (as distribution coefficients) observed for the dissolved neodymium content of the sample solutions showed no significant correlation to the organic carbon content of the soils evaluated.

From the soil type 7 results obtained, pH was evidently a very significant soil/solution criterion for the behaviour of this inorganic ion in soil. Even though soil type 7 presented both the highest organic carbon content and cation exchange capacity of the five soils investigated (22.7 % and 49.8 meq/100 g, respectively), the resultant distribution coefficient (Kd) value was the second lowest of the five soils investigated. Such a result was inversely proportional to the expectations of the methodology, predominantly aimed at organic compounds, as the acidic nature of this soil promoted aqueous solubility of the metal cation and therefore reduced the proportion partitioning on to the soil phase. Only soil type 5 resulted in a lower distribution coefficient (Kd) value. Soil type 5 presented both the lowest organic carbon content and cation exchange capacity of the five soils investigated (1.01 % and 9.2 meq/100 g, respectively). Therefore on comparison of soil type 5 and soil type 7, it can be observed that both the influence of an approximately 20 fold increase in organic carbon content and an approximately 5 fold in cation exchange capacity were negated by the decrease in the aqueous phase solution pH.

 

Under the conditions of this study, the overall Kd range was 1.38 x 10³ to at least 6.10 x 10³, the overall Koc range was 1.33 x 10⁴ to at least 2.39 x 10⁵ and the overall log10 Koc range was 4.12 to at least 5.38.

Reference 6

Endpoint:

adsorption / desorption: screening

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Justification for type of information:

The data on the read-across substance is considered representative.

Reason / purpose for cross-reference:

read-across source

Type:

Kd

Value:

>= 1 380 - <= 6 100 other: cm^3/g

Temp.:

25 °C

Remarks on result:

other: % organic carbon not specified.

Type:

Koc

Value:

>= 13 300 - <= 239 000 other: cm^3/g

Temp.:

25 °C

Remarks on result:

other: % organic carbon not specified.

Type:

log Koc

Value:

>= 4.12 - <= 5.38 dimensionless

Temp.:

25 °C

Remarks on result:

other: % organic carbon not specified.

Description of key information

The following adsorption/desorption distribution coefficients were obtained for the analogous test materials lanthanum oxide and cerium carbonate at the soil-to-solution ratio of 1/50:
- Mean Koc value: 5480283, 3940404
As a representative value, the lower mean value was used as the key value.
The results of the later study conducted on dineodymium tricarbonate were consistent with this. 

Key value for chemical safety assessment

Koc at 20 °C:

3 940 404

Additional information

The adsorption/desorption behaviour of the read-across test materials on soil was determined using three soils (seven soils for dineodymium tricarbonate) and the batch equilibrium method in accordance with the standardised guideline OECD 106.

Lanthanum oxide

Adsorption: The Kd values amounted to 5451, 46861 and 216905 mL/g for soils I to III, respectively, with corresponding Koc values of 230978, 4733400 and 11476472 mL/g, respectively. The mean value was 5480283 ml/g Desorption: The Kd des values were 15203, 2641, 30858 mL/g for soils I to III, respectively, with corresponding Koc des of 644212, 266724 and 163702 mL/g, respectively.

Cerium carbonate

Adsorption: The Kd values amounted to 11784, 59264 and >100843 mL/g for soils I to III, respectively, with corresponding Koc values of 499332, 5986256 and >5335623 mL/g, respectively. Desorption: The Kd des values were 10147, 102180, > 225268 mL/g for soils I to III, respectively, with corresponding Koc des of 429968, 10321193 and >11918936 mL/g respectively.

Dineodymium tricarbonate

The distribution coefficient (Kd) and the organic carbon normalised adsorption coefficient (Koc) for the neodymium content of the test material were determined for five soil types at 25 ± 2 °C. The soils were: soil type 2, loam (pH 7.3); soil type 3, silt loam (pH 6.2); soil type 4, silt loam (pH 5.1); soil type 5, loamy sand (pH 5.8); and soil type 7, loamy sand (pH 3).

Under the conditions of this study, the overall Kd range was 1.38 x 10³ to at least 6.10 x 10³, the overall Koc range was 1.33 x 10⁴to at least 2.39 x 10⁵ and the overall log10 Koc range was 4.12 to at least 5.38.

[LogKoc: 6.6]