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Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)
GLP compliance:
not specified
Type of method:
batch equilibrium method
Media:
soil
Radiolabelling:
yes
Test temperature:
not reported
Analytical monitoring:
yes
Details on sampling:
Referred to previous papers (Yin et al., 1966; Du et al., 1996a, 1996b; Tao et al., 1996a, 1996b).
Contact time was 2 h.
Details on matrix:
Calcareous, sierozen soil, samples taken from top layer (0-20 cm) of cultivated land of Yuzhong county in the middle Gansu province, China.
Details on test conditions:
Experiments were conducted with untreated soil, treated soil to remove CaCO3, and treated soil to remove both CaCO3 and organic matter.
Ratio of solution to soil was 12.5 g/L.
Contact time 2 h.
Computational methods:
Kp calculations based on change in activity in aqueous solution before and after adsorption.
If the activity in the supernatant after adsorption was lower than the minimum detectable activity of the detector, Kp was roughly estimated from the activity before adsorption and the minimum detectable activity.
Phase system:
soil-water
Type:
log Kp
Value:
4.72
Remarks on result:
other: untreated soil
Adsorption and desorption constants:
Log Kp soil in untreated soil was 4.72.
Log Kp soil in treated soil (CaCO3 or both CaCO3 and organic matter removed) was 3.97.
Details on results (Batch equilibrium method):
In this study, the log Kp for yttrium in a soil-water system was determined to be 4.72 (untreated soil). Since the log Kp obtained in soil treated to remove CaCO3 or both CaCO3 and organic matter was 3.97, it was concluded that adsorption of yttrium is not only determined by the oxides and silicates but that CaCO3 also affects adsorption.
Conclusions:
In this study, adsorption of Y was investigated using cultivated Chinese soil and radiolabeled Y. The log Kp in untreated soil was determined to be 4.72.
Endpoint:
adsorption / desorption, other
Remarks:
field study
Type of information:
experimental study
Adequacy of study:
weight of evidence
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:
Sediment and pore water samples were collected from two rivers which receive wastewater from urban Hanoi (Vietnam) and analysed for Y.
GLP compliance:
not specified
Type of method:
other: field study
Media:
sediment
Radiolabelling:
no
Test temperature:
not reported
Analytical monitoring:
yes
Details on sampling:
- Sediment samples collected from To Lich and Kim Nguu rivers, both of which receive wastewater from urban Hanoi, Vietnam. Samples collected from three sites in both rivers with a stainless steel Kajak core sediment sampler equipped with a polymethylmethacrylat inner liner with an inner diameter of 46 mm. Three replicates were collected from each site. Core samples were subdivided into sections 0-10cm, 10-20cm, 20-30cm. Sediment samples were dried at 45°C until constant weight, passed through a 2 mm stainless steel sieve and pulverised in an agate mortar.
- Pore water was extracted from sediment samples: sediment from 0-10cm depth was transferred to polypropylene büchner funnel with 25 µm mesh nylon filter and a minimum of 15 mL pore water was extracted under suction of 10 kPa. Pore water was filtered through a 0.45 µm nylon filter (Millipore) and acidified with 0.1 mL 70% HNO3 (Baker Instra-Analysed).
Details on matrix:
- % organic carbon: 1.2-5.3% in To Lich river samples, 1.8-10.6% in Kim Nguu rivers
- pH of pore water was 7.4-8.1
- redox potential of pore water was -257 to -185 mV
Details on test conditions:
field study
Computational methods:
Partitioning coefficients were calculated by dividing Y concentration in sediment by Y concentration in pore water (L/kg).
Phase system:
solids-water in sediment
Type:
log Kp
Value:
>= 5.04 - <= 6.57
% Org. carbon:
>= 1.2 - <= 10.6
Remarks on result:
other: range for all paired samples, precipitation processes may have been involved
Remarks:
actual range reported was 5.04 to > 6.57
Details on results (Batch equilibrium method):
The upper boundary of the range of log Kp values reported in the publication was represented by an unbounded value (> 6.57) because the yttrium pore water concentration was below the limit of detection
.
The organic carbon concentration had a significant effect on the sediment Y concentrations, indicating that organic carbon is important for retention controlled by sorption processes.
Conclusions:
In this study, samples of sediment and pore water were taken along two rivers receiving wastewater from Hanoi, Vietnam, and analysed for Y. Log Kpsediment-pore water values of 5.04 to > 6.57 were reported. However, reliability is restricted, because precipitation processes may have been involved in sediment next to sorption processes, yielding overestimated partitioning coefficients. The unbound value should not be used for further data analysis.
Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)
GLP compliance:
not specified
Type of method:
batch equilibrium method
Media:
soil
Radiolabelling:
yes
Test temperature:
ca. 25°C
Analytical monitoring:
yes
Details on sampling:
After shaking for 2 h, the two phases were separated by centrifugation at 4000 rpm for 30 min.
Details on matrix:
1. Calcareous soil: irrigating soil, surface 0-20 cm, cultivated land in Jiuquan county of the Gansu corridor, China. pH 8.30, 1.72% oc, 13.5% CaCO3, CEC 5.94 meq./100 g soil, 10.4% clay.
2. Red earth: coastal sandy soil, from the coast of Da-Ya Bay of Guangdong province, China. pH 6.4, 3.28% oc, no CaCO3, CEC 6.82 meq./100 g soil, 2.0% clay.
Details on test conditions:
Batch equilibrium experiments at ca. 25°C.
50 mg soil and 4.0 mL aqueous solution containing 2.0 mL of multitracer solution and 2.0 mL of compound solution in a polyethylene test tube.
Test tubes shaken for 2 h.
Computational methods:
Values of Kp calculated from the difference in activities measured before and after sorption in the aqueous solution. If not detectable, minimum detectable activities were used for Kp calculation.
Phase system:
soil-water
Type:
log Kp
Value:
4.67
Temp.:
25 °C
% Org. carbon:
1.72
Remarks on result:
other: calcareous soil
Phase system:
soil-water
Type:
log Kp
Value:
4.76
Temp.:
25 °C
% Org. carbon:
3.28
Remarks on result:
other: red earth
Conclusions:
In this multitracer study, the adsorption of Y to two Chinese soils, a calcareous soil and a sandy red earth, was investigated in a batch equilibrium experiment. Log Kp values were 4.67 and 4.76 for the calcareous soil and red earth, respectively.
Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)
GLP compliance:
not specified
Type of method:
batch equilibrium method
Media:
soil
Radiolabelling:
no
Test temperature:
ca. 20°C
Analytical monitoring:
yes
Details on sampling:
Soils:
Four Chinese cultivated soils were collected from Jiangxi Province, southern China (Yingtan soil), Beijing, northern China (Beijing soil), and Heilongjiang Province, northeastern China (Tongjiang and Haerbin soil). All samples taken from surface layer 0-20 cm. Air dried, ground, 1-mm sieved.
Experiment:
Sampling after 1 or 20 weeks of incubation.
Samples filtered 0.45 µm.
Details on matrix:
- Yingtan: ultisol, 19.5% sand, 35.2% silt, 45.3% clay, CEC 14.24 cmol/kg, pH 5.43, 1.53% oc.
- Beijing: mollisol, 37.6% sand, 51.6% silt, 10.8% clay, CEC 15.71 cmol/kg, pH 8.28, 1.35% oc.
- Tongjiang: mollisol, 16.3% sand, 65.5% silt, 18.2% clay, CEC 15.20 cmol/kg, pH 7.16, 5.28% oc.
- Haerbin: mollisol, 9.8% sand, 62.8% silt, 27.4% clay, CEC 26.00 cmol/kg, pH 7.23, 36.40% oc.
Details on test conditions:
Batch equilibrium method.
50.0 mg soil and 10 mL of solution added to 25-mL polypropylene vials.
Final Y concentration in solution initially 1.0 mmol/L, in a background electrolyte solution of 10 mmol/L Ca(NO3)2.
pH values adjusted to 6.0 by adding small amount of Ca(OH)2 solution.
Samples shaken for 24 h at 20°C, and then incubated for either 1 or 20 weeks.
Computational methods:
Kp values were calculated starting from reported values of metal sorbed at the end of the sorption phase. Y remaining in solution was then calculated. Soil:solution ratio was taken into account.
Phase system:
soil-water
Type:
log Kp
Value:
>= 3.61 - <= 4.47
Temp.:
20 °C
% Org. carbon:
>= 1.35 - <= 36.4
Remarks on result:
other: range
Phase system:
soil-water
Type:
log Kp
Value:
4.16
Temp.:
20 °C
% Org. carbon:
>= 1.35 - <= 36.4
Remarks on result:
other: average
Adsorption and desorption constants:
Desorption kinetics were described using three models, first-order, two site first-order, and log-normal distribution first-order kinetics models. The latter two resulted in excellent fits.
Conclusions:
In this study, sorption of Y was studied in 4 Chinese soils using a batch equilibrium method. Log Kp values ranged from 3.61 to 4.47, and the average log Kp was 4.16. Desorption was also studied, and indicated the effect of pH on desorption (higher at low pH, lower at high pH).
Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Remarks:
Reliable with restrictions because data needed for Kp calculation were taken from figures.
Qualifier:
no guideline followed
Principles of method if other than guideline:
Water soluble and total rare earth elements (including yttrium) were determined in nine Chinese soils.
GLP compliance:
not specified
Type of method:
other: study using sequential extraction on field samples
Media:
soil
Radiolabelling:
no
Test temperature:
not reported
Analytical monitoring:
yes
Details on sampling:
Soils:
- Nine Chinese cultivated soils collected from Jiangxi Province (Yingtan soil), Beijing, northern China (Beijing soil), Hubei Province, central China (Wuhan soil), Shandong Province, eastern China (Rongcheng soil), Heilongjiang Province, northeastern China (Heilongjiang soil), Guizhou Province, southeast China (Anshun soil), Shanghai, east China (Shanghai soil), Fujian Province, southeast China (Chaozhou soil), and Shanxi Province, northern China (Changzhi soil).
- Samples taken from cultivated surface layer (0-20 cm), air dried, ground, and 1-mm sieved.
Details on matrix:
- Beijing: mollisol, 37.6% sand, 51.6% silt, 10.8% clay, CEC 15.7 cmol/kg, pH 6.90, 0.78% oc.
- Yingtan: ultisol, 19.5% sand, 38.7% silt, 42.4% clay, CEC 14.2 cmol/kg, pH 4.56, 0.89% oc.
- Helongjiang: mollisol, 9.8% sand, 62.8% silt, 27.4% clay, CEC 26.0 cmol/kg, pH 7.35, 3.71% oc.
- Rongcheng: mollisol, 89.7% sand, 3.91% silt, 6.40% clay, CEC 9.82 cmol/kg, pH 6.08, 0.39% oc.
- Wuhan: alfisol, 52.9% sand, 21.4% silt, 25.7% clay, CEC 22.8 cmol/kg, pH 6.73, 1.72% oc.
- Anshun: cambisol, 37.2% sand, 32.8% silt, 30.1% clay, CEC 51.3 cmol/kg, pH 6.29, 6.76% oc.
- Shanghai: luvisol, 21.4% sand, 65.5% silt, 13.2% clay, CEC 36.6 cmol/kg, pH 5.53, 3.02% oc.
- Chaozhou: ferralisol, 29.6% sand, 33.7% silt, 36.7% clay, CEC 18.1 cmol/kg, pH 5.96, 1.81% oc.
- Changzhi: luvisol, 24.6% sand, 52.3% silt, 18.1% clay, CEC 21.9 cmol/kg, pH 7.29, 4.12% oc.
Details on test conditions:
Water-soluble REEs were obtained by shaking 1.0 g of dried soil with 5.0 mL of deionised distilled water in 50 mL polypropylene centrifuge tubes for 24 h. After centrifuging at 4000g for 30 min, the supernatant was filtered with 0.45 µm membrane.
Next to water-soluble REEs, total REEs were determined.
Computational methods:
A range of Kp values was obtained by dividing total Y concentration in the soil under consideration (mg/kg) by the minimum and maximum of the range of water soluble Y reported in figures (mg/kg).
Phase system:
soil-water
Type:
log Kp
Value:
>= 2.42 - <= 3.87
% Org. carbon:
>= 0.39 - <= 6.76
Remarks on result:
other: range for all nine soils
Phase system:
soil-water
Type:
log Kp
Value:
3.12
% Org. carbon:
>= 0.39 - <= 6.76
Remarks on result:
other: average for all nine soils
Conclusions:
In this study, nine Chinese soils were sampled and total and water soluble Y concentrations determined in the laboratory. This resulted in a range of log Kp soil values of 2.42 to 3.87, the average being 3.12.
Endpoint:
adsorption / desorption, other
Remarks:
microcosm study
Type of information:
experimental study
Adequacy of study:
weight of evidence
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:
A microcosm study was performed in which concentrations of Y in water and sediment were also monitored.
GLP compliance:
not specified
Type of method:
other: microcosm study
Media:
sediment
Radiolabelling:
no
Test temperature:
Water temperature 22 +/- 1°C
Analytical monitoring:
yes
Details on sampling:
- Water and sediment sampled at 12 and 24 h and 2, 4, 8, 12 and 16 d.
- Water was filtered 0.45 µm.
- Sediment samples were washed with deionised water and dried by air. Then 0.5 g of dried sample was digested with Na2O2 at 700°C and passed through cation-exchange columns.
- Final solutions of all samples brought to 5 mL with 7% HCl.
Details on matrix:
Sediment from eutrophic lake (Xuanwu Lake, Nanjing, China).
Sediment samples were dried by air before adding into aquarium.
Details on test conditions:
Microcosm study using water and sediment from a typical eutrophic lake - Xuanwu Lake in Nanjing, China.
Organisms: duckweeds (Sperollela polyrrhiza), crustaceans (Daphnia magna), goldfish (Carassius auratus), shellfish (Bellamya aeruginosa).
After the system has equilibrated for 1 week, the experiment was initiated by spiking mixed REEs stock solutions (a mixture of five REEs with 1.00 mg/mL each: La(NO3)3.6H2O, CeCl3.7H2O, SmCl3.nH2O, Gd2O3 and Y2O3) into the aquarium to 1 mg/L.
The pH was kept at 6.5-6.8 because rare earth elements would precipitate under alkaline conditions.
Computational methods:
Kp sediment values were calculated dividing concentrations in sediment (mg/kg) by concentrations in water (mg/L).
Phase system:
sediment-water
Type:
log Kp
Value:
3.48
Temp.:
22 °C
Remarks on result:
other: Value after 16 days
Details on results (Batch equilibrium method):
Distribution of Y was 87.80% in sediment, 11.69% in water, and 0.51% in biota.
Conclusions:
In this microcosm study, water and sediment Y concentrations were monitored for up to 16 days. Based on the concentrations reported for 16 days, a log Kp sediment of 3.48 could be calculated. Data were taken from figures.
Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: In this study, Kp values were determined for Zr using a water soluble Zr compound (ZrOCl2) and two different soils.
Remarks:
The Kp values were determined using a batch equilibrium experimental setup similar to that described in the corresponding OECD guideline. The experiments seem to be well performed and a suitable method of analysis was used. A Klimisch 2 reliability score was assigned to this study because not all results were presented and because total recovery of the added Zr was not discussed.
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)
GLP compliance:
not specified
Type of method:
batch equilibrium method
Media:
soil
Radiolabelling:
no
Test temperature:
20°C
Analytical monitoring:
yes
Details on sampling:
- Concentrations: a single concentration of 9.12 µg/L Zr was used (50 mL of a 0.1 µM ZrOCl2 dilute suspension in a 0.1 M KNO3 ionic buffer)
- Sampling interval: contact time ranged from 5 min to 48 h
Details on matrix:
COLLECTION AND STORAGE
- Geographic location: two agricultural soils were sampled close to the underground research laboratory (Meuse/Haute Marne, France) of the National Agency for management of radioactive wastes (Andra)
- Sampling depth (cm): top soils 0-20 cm
- Soil preparation (e.g.: 2 mm sieved; air dried etc.): air-dry soils were crushed and sieved under 2 mm

PROPERTIES
Soil A (acidic sandy clayey loamy)
- % sand: 31.9
- % silt: 48.7
- % clay: 19.4
- pH: 5.45
- Organic carbon (%): 31.8
- CEC (meq/100 g): 9.0 cmol/kg
- Background Zr content: 417.4 mg/kg dw
Soil B (clayey calcareous soil)
- % sand: 10.7
- % silt: 50.7
- % clay: 38.6
- pH: 8.3
- Organic carbon (%): 33.6
- CEC (meq/100 g): 10.02 cmol/kg
- Background Zr content: 164 mg/kg dw
Details on test conditions:
TEST CONDITIONS
- Buffer: a 0.1 M KNO3 ionic buffer
- pH: at soil pH
- Suspended solids concentration: 200 mg soil (on a dry weight basis)

TEST SYSTEM
- Type, size and further details on reaction vessel: polypropylene tubes
- Amount of soil/sediment/sludge and water per treatment (if simulation test): 200 mg soil (on a dry weight basis)
- Soil/sediment/sludge-water ratio (if simulation test): 4:1 (50 mL solution)
- Number of reaction vessels/concentration: not reported
Computational methods:
[Zr]adsorbed by soil = V ([Zr]initial - [Zr]solution)/Msoil
Kp in L/kg = [Zr]adsorbed by soil / [Zr]solution
The calculated Zr adsorbed by soil could afterwards be compared to the cumulative concentration desorbed by extraction with CaCl2, DTPA and NaPP
Phase system:
soil-water
Type:
Kp
Value:
6 000 L/kg
Temp.:
20 °C
Matrix:
Soil A
% Org. carbon:
31.8
Phase system:
soil-water
Type:
Kp
Value:
30 000 L/kg
Temp.:
20 °C
Matrix:
Soil B
% Org. carbon:
33.6
Adsorption and desorption constants:
Kp = 6000 L/kg dw for soil A.
Kp = 30000 L/kg dw for soil B.
Details on results (Batch equilibrium method):
Kinetic experiments showed that Zr is retained on soil components in few minutes.
The curves can be described by a first order kinetic model:
[Zr]adsorbed = [Zr]sat (1-e^-kt)
Saturated Zr adsorbed concentrations were 0.002 mg Zr/g dry soil for soil A.
Saturated Zr adsorbed concentrations were 0.00215 mg Zr/g dry soil for soil B.
At equilibrium, Zr concentrations measured in solution are lower for soil B (10^-9 M) than for soil A (4x10^-9 M).
Soil B has a higher affinity for Zr than soil A.
Conclusions:
In this study, batch equilibrium experiments were conducted with ZrOCl2 solutions and two different soils (an acidic sandy clayey loamy soil and a clayey calcareous soil). The Kp values resulting from this study are 6000 L/kg (dw) for the acidic soil and 30000 L/kg (dw) for the calcareous soil.
Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: In this study, Kp values were determined for Zr using a water soluble Zr compound (ZrOCl2) and two different soils.
Remarks:
The Kp values were determined using a batch equilibrium experimental setup similar to that described in the corresponding OECD guideline. Additionally, desorption experiments were conducted with the soils used in the adsorption experiments. The experiments seem to be well performed and a suitable method of analysis was used. A reliability score of Klimisch 2 was assigned to this study because total recovery of the added Zr was not discussed and because the results may have been affected by the very low soil:solution ratio.
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)
GLP compliance:
not specified
Type of method:
batch equilibrium method
Media:
soil
Radiolabelling:
no
Test temperature:
20°C
Analytical monitoring:
yes
Details on sampling:
Adsorption experiments
- Concentrations: a single concentration of 9.12 µg/L Zr was used (50 mL of a 0.1 µM ZrOCl2 dilute suspension in a 0.1 M KNO3 ionic buffer)
- Sampling interval: contact time ranged from 5 min to 48 h
Desorption experiments:
- Sampling interval: contact time ranged from 5 min to 48 h
Details on matrix:
COLLECTION AND STORAGE
- Geographic location: two agricultural soils were sampled close to the underground research laboratory (Meuse/Haute Marne, France) of the National Agency for management of radioactive wastes (Andra)
- Sampling depth (cm): top soils 0-20 cm
- Soil preparation (e.g.: 2 mm sieved; air dried etc.): air-dry soils were crushed and sieved under 2 mm

PROPERTIES
Soil A (acidic sandy clayey loamy)
- % sand: 31.9
- % silt: 48.7
- % clay: 19.4
- pH: 5.45
- Organic carbon (%): 31.8
- CEC (meq/100 g): 9.0 cmol/kg
- Background Zr content: 417.4 mg/kg dw
Soil B (clayey calcareous soil)
- % sand: 10.7
- % silt: 50.7
- % clay: 38.6
- pH: 8.3
- Organic carbon (%): 33.6
- CEC (meq/100 g): 10.02 cmol/kg
- Background Zr content: 164 mg/kg dw
Details on test conditions:
TEST CONDITIONS
- Buffer: a 0.1 M KNO3 ionic buffer
- pH: at soil pH
- Suspended solids concentration: 200 mg soil (on a dry weight basis) in 50 mL solution

TEST SYSTEM
- Type, size and further details on reaction vessel: polypropylene tubes
- Amount of soil/sediment/sludge and water per treatment (if simulation test): 200 mg soil (on a dry weight basis)
- Soil/sediment/sludge-water ratio (if simulation test): 1:250 (50 mL solution)
- Number of reaction vessels/concentration: two + one control without soil
- In the desorption experiments, dried soil used in the adsorption experiments were mixed with milliQ water. All other test conditions as mentioned above.
Computational methods:
Adsorbed Zr in soil was determined by mass balance calculations using the initial concentration in solution and those measured in solution after certain contact periods.
Kp in L/kg = [Zr]adsorbed by soil / [Zr]solution (taking into account soil:solution ratio).
Phase system:
soil-water
Type:
Kp
Value:
6 000 L/kg
Temp.:
20 °C
Matrix:
Soil A
% Org. carbon:
31.8
Phase system:
soil-water
Type:
Kp
Value:
30 000 L/kg
Temp.:
20 °C
Matrix:
Soil B
% Org. carbon:
33.6
Adsorption and desorption constants:
Kp = 6000 L/kg dw for soil A.
Kp = 30000 L/kg dw for soil B.
Recovery of test material:
not reported
Details on results (Batch equilibrium method):
ADSORPTION
Kinetic experiments showed that Zr is retained on soil components in few minutes.
The curves can be described by a first order kinetic model:
[Zr]adsorbed = [Zr]sat (1-e^-kt)
With
- [Zr]adsorbed = mg Zr/kg dry soil
- [Zr]sat = concentration of Zr sorbed at saturation (mg Zr/kg dry soil)
- k = adsorption constant (min^-1)
- t = contact time (min)
The time constants (T = 1/k) were 3 min for soil A and 2.5 min for soil B.
Saturated Zr adsorbed concentrations were 2.09 mg Zr/kg dry soil for soil A.
Saturated Zr adsorbed concentrations were 2.2 mg Zr/kg dry soil for soil B.
At equilibrium, Zr concentrations measured in solution are lower for soil B (10^-9 M; 0.091 µg/L) than for soil A (4x10^-9 M; 0.365 µg/L).
Soil B has a higher affinity for Zr than soil A.

DESORPTION
At desorption equilibrium, the Zr concentrations in solution were 0.365 µg/L in soil A and 0.219 µg/L in soil B.
Statistics:
not reported

- Soil B (the calcareous soil) had more affinity for Zr than soil A (the acidic soil) and sorption also occurred faster in soil B. This may be explained by the fact that the H+ ions present in the acidic soil enter in competition with Zr ions for adsorption to available sites on the solid phase.

- The very low soil:solution ratio used in this study was necessary because at higher ratios the concentrations of Zr in solution would be below the detection limit of the available method of analysis. However, such low soil:solution ratios favor adsorption and therefore the Kp values may have been affected by these experimental conditions.

- The method of Kp determination does not allow to distinguish between the different solid forms of Zr in the experiment (adsorbed to iron oxides, adsorbed to organic matter, precipitated as hydroxydes or carbonates). According to formerly obtained results, the authors mention that adsorption to iron oxides may be the predominant process in soil.

- The desorption experiments indicate that the concentrations of Zr in soil remain largely unaffected, suggesting that non-reversible processes are involved such as inner sphere complexation or surface precipitation.

Conclusions:
In this study, batch equilibrium experiments were conducted with ZrOCl2 solutions and two different soils (an acidic sandy clayey loamy soil and a clayey calcareous soil). These experiments indicate very fast adsorption of Zr to soil (time constants (1/k) = 2.5-3 min). The Kp values resulting from this study are 6000 L/kg (dw) for the acidic soil and 30000 L/kg (dw) for the calcareous soil. Very low soil to solution ratios were used because otherwise concentrations in solution would become unquantifiable. Such low soil to solution ratios however favor adsorption. This should be kept in mind when using the Kp values resulting from this study. Desorption experiments indicated very limited desorption suggesting that non-reversible adsorption processes such as inner sphere complexation or surface precipitation are involved.
Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Well performed field study. The results can be considered reliable with restrictions, keeping in mind that log Kp values were calculated based on average concentrations of Zr in water and suspended particulate matter.
Qualifier:
no guideline available
Principles of method if other than guideline:
Paired samples of (filtered) water and suspended particulate matter were taken monthly during one year at two locations along the St. Lawrence River: 1) at a municipal water filtration plant located near the mouth, and 2) at the Montreal City purification plant (treated urban effluents). Zr concentrations were determined in both filtered water and suspended particulate matter.
GLP compliance:
no
Type of method:
other: field study
Media:
other: suspended particulate matter
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
- All sample material was acid washed before use.
- 0.45 µm polycarbonate membrane filters were used for filtering water samples.
- Monthly sampling between July 2000 and July 2001 at the Lévis municipal water filtration plant located near the mouth of the St. Lawrence River and at the Montreal City purification plant (treated urban effluent, samples taken during 24 h proportionally to flow rate).
- Filtrate was acidified with ultrapure nitric acid to pH 2.
- Filters with residu were frozen until further treatment.
- Filters and their contents were oven-dried at 65°C for 12 h, digested with 2 mL of concentrated nitric acid and 1 mL of concentrated hydrofluoric acid first for 12 h at ambient air temperature and then for 1 h in an oven at 125°C, acids were then evaporated and residues diluted with 15 mL of 0.1 N nitric acid.
Details on test conditions:
Suspended matter concentrations varied between 16 and 27 mg/L during the sampling period.
Computational methods:
Concentration Zr in SPM (mg/kg) / concentration Zr in filtered river water (mg/L) = Kp.
Phase system:
suspended matter-water
Type:
log Kp
Value:
6.26
Matrix:
St. Lawrence River
Phase system:
suspended matter-water
Type:
log Kp
Value:
5.51
Matrix:
Effluent from Montreal City purification
Adsorption and desorption constants:
Average log Kp in St. Lawrence River water = 6.26 (mean Zr concentration in filtered water and SPM = 7.2 ng/L and 13.1 mg/kg, respectively).
Average log Kp in effluent from Montreal City purification plant = 5.51 (mean Zr concentration in filtered water and SPM = 22 ng/L and 7.13 mg/kg, respectively).
Statistics:
Average Zr concentrations were reported and used for Kp calculation.
Conclusions:
In this study, paired samples of (filtered) water and suspended particulate matter were taken monthly during one year at two locations along St. Lawrence River. At one location river water was sampled and at the other location effluent of the Montreal waste water treatment plant was sampled. Based on average concentrations of Zr in filtered water and suspended particulate matter, log Kp values of 6.26 and 5.51 were calculated for these locations, respectively.
Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Well performed field study reporting paired measurements of Zr concentrations in filtered water and sediment samples from 20 sites along the Blesbokspruit, as well as the range of Kp values obtained from these measurements.
Qualifier:
no guideline available
Principles of method if other than guideline:
In this study, Zr concentrations were determined in paired samples of filtered water and sediment from 20 sites along the Blesbokspruit, South Africa. Based on the reported Zr concentrations, Kp values can be calculated for the individual sites.
GLP compliance:
no
Type of method:
other: field study
Media:
sediment
Radiolabelling:
no
Test temperature:
Between 5.7 and 24.2°C.
Analytical monitoring:
yes
Details on sampling:
- Paired samples of water and sediment were taken at 20 randomly chosen sites along the Blesbokspruit (both upstream and downstream of a liming plant and the site where mine water from Grootvlei Gold Mine is discharged).
- Surface water samples were filtered through a 0.45 µm nylon membrane filter using a hand-held vacuum pump.
- One of two filtered samples was acidified with 3 M HNO3 to a pH < 2 to prevent metal precipitation.
- Water samples were stored in plastic bottles pre-rinsed with HNO3 and deionized water. Bottles were sealed and stored at 4°C.
- Sediment samples were taken close to the sediment-water interface by inserting 50-mL polypropylene centrifuge vials.
- Vials were capped without leaving headspace and stored under anoxic conditions on ice.
- Digestion of sediment samples: 50 mg dried sediment + 4 mL of a 4:1 mixture of 28M HF and 14M HNO3, digested for 48 h at 50-60°C. After evaporation to dryness, 2 mL of 14M HNO3 was added repeatedly for digestion at 50-60°C until complete dissolution, followed by evaporation to dryness at 75°C. After cooling, samples were diluted 1000 times with an internal standard.
Details on matrix:
Sediment characteristics were reported in Table 3. Generally:
- % gravel: 0-44
- % sand: 11-85
- % silt: 8-73
- % clay: 4-43
- % organic carbon: 0.5-9.0
Some trends are reported in the results section.
Details on test conditions:
Chemistry of surface water samples:
- pH: 7-9.2
- dissolved oxygen: 2.5-10.8 mg/L
- conductivity: 521-2400 µS/cm
- Cl: 28-161 mg/L
- SO4: 73-702 mg/L (outlier 4194 mg/L)
- Na: 69-855 mg/L
- Ca: 21-195 mg/L
- Mg: 9-56 mg/L
- K: 9-32 mg/L
Computational methods:
Zr concentration in sediment (mg/kg) / Zr concentration in filtered water (mg/L) = Kp.
Phase system:
sediment-water
Type:
log Kp
Value:
5.47
Matrix:
Sediments from sites along the Blesbokspruit.
Remarks on result:
other: average
Phase system:
sediment-water
Type:
log Kp
Value:
5.12 - 5.92
Matrix:
Sediments from sites along the Blesbokspruit.
Remarks on result:
other: range
Adsorption and desorption constants:
Log Kp between 5.12 and 5.92, average value 5.47.
Zr concentrations in filtered water were between 0.1 and 0.5 µg/L.
Zr concentrations in sediment were between 26.5 and 175.7 mg/kg.
Statistics:
Separate values can be calculated, average Kp and Kp range reported.
Conclusions:
In this study, paired samples of filtered water and sediment were taken from 20 sites along the Blesbokspruit. Based on Zr concentrations in these filtered water and sediment samples, an average log Kp of 5.47 could be calculated, the range being 5.12-5.92.
Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Well performed field study, reporting mean Kp values for elements determined in paired samples of (filtered) water and suspended particulate matter.
Qualifier:
no guideline available
Principles of method if other than guideline:
Field study in which paired samples were taken from water and suspended particulate matter (through 0.4 µm filtration) from 54 Czech rivers at 119 localities. Analysis of the metal under consideration was done in the laboratory in both filtered water and suspended particulate matter.
GLP compliance:
no
Type of method:
other: field study
Media:
other: suspended particulate matter
Radiolabelling:
no
Test temperature:
not reported (samples taken during summers of 1997 and 1998)
Analytical monitoring:
yes
Details on sampling:
- 54 Czech rivers, 119 sites
- During summers of 1997 and 1998
- Paired samples were taken at each location of water and suspended matter.
- Suspended particulate matter was sampled by filtration (volume of water filtered: 200 mL, filters used: perforated polycarbonate filters 0.4 µm).
- Treatment of (filtered) water samples: acidification using HNO3, cooled storage in vessels cleaned with 10% HNO3 for at least 2 days.
- Treatment of filters before use: boiled with distilled water acidified by HNO3 for 10 min before use, dried at 105°C, weighed.
- Treatment of used filters: dried at 105°C and weighed.
- Filtration system: Antlia hand pump filter system (Schleicher & Schnell), air pressure of 5.3 kg/cm2 (regularly washed with 0.01 M HNO3 and distilled water before filtration in the field).
Details on matrix:
Mean % particulate organic matter in suspended particulate matter = 47%.
Using a factor of 2.0 for conversion of POM to particulate organic carbon results in 23.5% (range = 5.9-43%).
Details on test conditions:
Field study - paired samples of water and SPM
- Mean contents of SPM = 9.9 mg/L (range = 1.0-124 mg/L)
- Mean pH river waters = 7.74 (range = 6.9-8.8)
- Mean ionic strength river waters = 7.8 mM
- Mean specific conductance river waters = 538 µS/cm at 25°C
- Mean alkalinity river waters = 1.9 mM
Computational methods:
Concentration Zr in SPM / concentration Zr in filtered river water = Kp.
Phase system:
suspended matter-water
Type:
log Kp
Value:
3.23
Remarks on result:
other: median value
Adsorption and desorption constants:
Median log Kp = 3.23 (median Zr concentration in filtered water = 0.07 mg/L, median Zr concentration in SPM = 109 mg/kg).
Statistics:
Medians were reported (for log Kp) because this allows taking into account sites where element concentration was below detection limits in filtered water and to eliminate the effect of several strongly polluted rivers.
Conclusions:
In this study, paired samples of filtered water and suspended particulate matter were taken from 119 sites along 54 Czech rivers and element concentrations were determined in both filtered water and suspended particulate matter. The suspended matter-water partition coefficient Kp was calculated by taking the ratio of the element concentration in suspended particulate matter to the element concentration in filtered water. The median log Kp for Zr was reported to be 3.23.
Endpoint:
adsorption / desorption, other
Remarks:
field study and lab study with field samples
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
secondary literature
Qualifier:
no guideline followed
Principles of method if other than guideline:
The concentration of Y in water and sediment at state of equilibrium was measured in laboratory tests and in the field and Kp values were calculated.
GLP compliance:
no
Type of method:
other: field study and laboratory experiment with field samples
Media:
sediment
Radiolabelling:
no
Test temperature:
no data
Analytical monitoring:
yes
Details on sampling:
Samples of sediment, pore water and surface water were taken at Nieuwe Maas, Rhine estuary, the Netherlands.
Samples in the laboratory study were taken after 10 days.
All water samples 0.45 µm filtered.
Details on matrix:
- Details on collection location: Nieuwe Maas , Rhine estuary, The Netherlands, three different collection times.
- pH at time of collection: 8-8.5
- Organic carbon (%): 0.88, 2.17 and 2.77 % at different sample collection times
Details on test conditions:
Lab experiment: duration time 10 d
Computational methods:
Kp sediment-surface water and Kp sediment-pore water distribution coefficients were calculated using measured concentrations in solid and aqueous phase.
Phase system:
sediment-water
Type:
log Kp
Value:
5.18
Remarks on result:
other: laboratory (sediment and surface water)
Phase system:
sediment-water
Type:
log Kp
Value:
6.04
Remarks on result:
other: field (sediment and surface water)
Phase system:
solids-water in sediment
Type:
log Kp
Value:
4.65
Remarks on result:
other: laboratory (sediment and pore water)
Phase system:
solids-water in sediment
Type:
log Kp
Value:
5.35
Remarks on result:
other: field (sediment and pore water)

Sneller et al. stated, that the differences between the laboratory and the field derived data are probably due to disturbance and subsequent oxidation of the sediments in the laboratory experiments, causing relatively high concentrations in the pore water. In addition, increased decay of organic material in the disturbed sediments, involving reduction-processes, may contribute to release of REEs from sediment. For these reasons, field derived partition coefficients are preferred over laboratory derived values for calculation of MACs (maximum acceptable concentrations).

Furthermore, when evaluating the partitioning data one must keep in mind that pH, the presence of negative counterions and the concentration of dissolved organic carbon (DOC) in the (pore-) water strongly influence the concentration of REEs in solution. When pH, DOC concentrations and negative counterion concentrations are high, a large part of the total dissolved REE concentrations may not represent ´true´ partitioning.

Conclusions:
In this study, adsorption of Y to sediment was evaluated by determining Y in sediment, pore water, and surface water sampled in the field and after 10 days of using sediment/water samples in a study in the laboratory. The obtained log Kp sediment values were 4.65 and 5.35 when based on sediment and pore water concentrations in laboratory and field, respectively, and 5.18 and 6.04 when based on sediment and surface water concentrations in laboratory and field, respectively.
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:
Yttrium zirconium oxide is anticipated to have a limited water solubility and therefore only minor amounts of free metal ion (yttrium and zirconium) are expected to be released to the aquatic part of the environmental compartment under consideration. Any released yttrium or zirconium will be subjected to adsorption processes. Individual data on the adsorption capacity of zirconium and yttrium is included in this dossier. For zirconium, a total of five studies was used in a weight of evidence approach to cover the endpoint (Veselý et al., 2001; Gobeil et al., 2005; Roychoudhury and Starke, 2006; Ferrand, 2005; Ferrand et al., 2006). For yttrium, a total of 7 studies was used in a weight of evidence approach (Du et al., 1998; Tao et al., 2000; Wen et al., 2002, 2006; Marcussen et al., 2008; Sneller et al., 2000; Yang et al., 1999).
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
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read-across source
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read-across source
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read-across source
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Phase system:
suspended matter-water
Type:
log Kp
Value:
5 L/kg
Remarks on result:
other: zirconium
Phase system:
sediment-water
Type:
log Kp
Value:
5.47 L/kg
Remarks on result:
other: zirconium
Phase system:
soil-water
Type:
log Kp
Value:
4.13 L/kg
Remarks on result:
other: zirconium
Phase system:
sediment-water
Type:
log Kp
Value:
4.78 L/kg
Remarks on result:
other: yttrium
Phase system:
soil-water
Type:
log Kp
Value:
3.59 L/kg
Remarks on result:
other: yttrium

Description of key information

Assessment of this endpoint and derivation of adsorption coefficients are element-based (i.e., not substance-based). Yttrium zirconium oxide is anticipated to have a limited water solubility. Consequently, only minor amounts of free metal ion (yttrium and zirconium) can be expected to be released to the aquatic part of the environmental compartment under consideration. Therefore, adsorption is considered to be a less important process determining the fate and behaviour of the substance in the environment. 
Any released yttrium or zirconium will however be subjected to adsorption processes. Individual data on the adsorption capacity of zirconium and yttrium is included in this dossier. For zirconium, a total of five studies was used in a weight of evidence approach to cover the endpoint (Veselý et al., 2001; Gobeil et al., 2005; Roychoudhury and Starke, 2006; Ferrand, 2005; Ferrand et al., 2006). Reliable data were available for soil, suspended matter, and sediment. The following final key values were retained: a log Kp of 5.00 for suspended matter-water, a log Kp of 5.47 for sediment-water, and a log Kp of 4.13 for soil-water. Adsorption to sediment and suspended matter appears to be slightly more pronounced than to soil for zirconium. For yttrium, a total of 7 studies was used in a weight of evidence approach (Du et al., 1998; Tao et al., 2000; Wen et al., 2002, 2006; Marcussen et al., 2008; Sneller et al., 2000; Yang et al., 1999). No reliable data were available for suspended matter. A log Kp of 4.78 and 3.59 was retained for sediment-water and soil-water, respectively. Here too, strong adsorption is observed, being however slightly less pronounced in soil.

Key value for chemical safety assessment

Additional information

Information on zirconium

Adsorption of zirconium compounds (as such) to particles of suspended matter, sediment, or soil, is not expected to occur. It is rather the zirconium cation (or potentially other cationic zirconium species) that will adsorb to particulate matter. Therefore, the assessment of adsorption capacity and the derivation of adsorption coefficients is element-based (and not substance-based).

In total, five studies were identified containing relevant information on adsorption of zirconium to particulate matter. These studies were considered reliable and were used in a weight of evidence approach. Data were available for soil, sediment, and suspended matter and will be further discussed below.

For suspended matter, two studies were identified as useful. Veselý et al. (2001) reported a median log Kp of 3.23 for a series of samplings along Czech rivers. Gobeil et al. (2005) analysed samples from several locations along the St. Lawrence river, at one location river water was sampled and at the other location effluent of the Montreal waste water treatment plant was sampled. Based on average concentrations of zirconium in filtered water and suspended particulate matter, log Kp values of 6.26 and 5.51 were calculated for these locations. Because there is a limited amount of values available, the average log Kp (arithmetic mean) of 5.00 for these two studies is selected as key value for characterising distribution between suspended matter and water.

For sediment, only one reliable study is available (Klimisch score of 2). In this study, zirconium concentrations were determined in paired samples of filtered water and sediment from 20 sites along the Blesbokspruit, South Africa. Based on data from this study (Roychoudhury and Starke, 2006) an average log Kp value (arithmetic mean) of 5.47 was calculated, the range being 5.12-5.92.

For soil, two reliable studies were retained for the determination of the key value. Ferrand (2005) (see also Ferrand et al., 2006) conducted batch equilibrium experiments with ZrOCl2 solutions and two different soils (acidic sandy clayey loamy soil and a clayey calcareous soil). The Kp values resulting from this study were 6,000 L/kg (dw) (or log Kp of 3.78) for the acidic soil and 30,000 L/kg (dw) for the calcareous soil (or log Kp of 4.48). The average log Kp value (arithmetic mean) of 4.13 was taken as key log Kp for soil.

Overall, strong adsorption of zirconium to particulate matter is observed, whether soil, sediment, or suspended matter.

For adsorption to occur however, free zirconium has to end up in the aqueous phase of the environmental compartment under consideration (water column, or pore water in sediment/soil).

Information on yttrium

In total, four studies were identified containing relevant information on adsorption of yttrium to soil. These studies were considered reliable and were used in a weight of evidence approach. Wen et al. (2006) gathered samples of nine Chinese soils and analysed total and water soluble yttrium concentrations in the laboratory, which resulted in a range of log Kp values of 2.42 to 3.87. Based on data from Du et al. (1998), in which adsorption of yttrium was investigated using cultivated Chinese soil and radiolabeled yttrium, a log Kp of 4.72 could be obtained for untreated soil. Another batch equilibrium experiment with Chinese soils yielded log Kp values of 3.61 to 4.47 (Wen et al., 2002). In the multitracer study of Tao et al. (2000), the adsorption of yttrium to two Chinese soils, a calcareous soil and a sandy red earth, was investigated in a batch equilibrium experiment. Log Kp values were 4.67 and 4.76 for the calcareous soil and red earth, respectively. To determine a final key value for adsorption of yttrium to soil, a single value (arithmetic mean) was retained for each soil in each study. Based on those data, the 10th, 50th and 90th percentile of the retained values was 2.73, 3.59 and 4.70, respectively. The median value of 3.59 was taken as key log Kp for soil.

For sediment, three studies were included in a weight of evidence approach. Sneller et al. (2000) reported log Kp values obtained by Stronkhorst and Yland (1998) of 4.65 to 6.04 for samples taken from the field and a laboratory study using field samples. Marcussen et al. (2008) sampled sediment and pore water along two rivers receiving wastewater from Hanoi, Vietnam. Log Kpsediment-pore water values for these samples were reported to be between 5.04 and > 6.57. However, because precipitation processes may have been involved in sediment next to sorption processes, partitioning coefficients may have been overestimated. Therefore only the lower boundary of the reported range was included in the calculation of a key value for partitioning between sediment and water. Finally, the microcosm study of Yang et al. (1999) yielded a log Kp sediment of 3.48 when using the data for the 16-d sampling point. To determine a final key value, a single average (arithmetic mean) log Kp value was retained for each study. For studies reporting results for both pore water and surface water, separate average values were determined for the pore water-based data and the surface water-based data. Based on the study-specific averages, an overall average (arithmetic mean) log Kp of 4.78 was obtained.

No data were identified on yttrium adsorption to suspended matter. Overall, the obtained adsorption coefficients were similar as for many other metals. Adsorption to sediment appears to be stronger than to soil particles.

Conclusion on yttrium zirconium oxide

Yttrium zirconium oxide has a limited solubility in water. Consequently, only minor amounts of free metal ion (yttrium and zirconium) can be expected to be released to the aquatic part of the environmental compartment under consideration. Therefore, adsorption is considered to be a less important process determining the fate and behaviour of the substance in the environment. Individual data on the adsorption capacity of zirconium and yttrium is given above. Log Kp values for zirconium were determined to be 5.0, 5.47 and 4.13 for suspended matter, sediment and soil, respectively, whereas for yttrium, log Kp values of 4.78 and 3.59 were obtained for sediment and soil, respectively (no data for suspended matter). Yttrium and zirconium both strongly adsorb to particles, adsorption to soil particles being however somewhat less strong than adsorption to suspended matter and sediment particles.