Zirconium dichloride 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

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.

Reference 2

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.

Reference 3

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:

Read across from several studies reporting on adsorption of zirconium to particulate matter. The read across justification document is attached in IUCLID Section 13.

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

Key result

Phase system:

sediment-water

Type:

log Kp

Value:

5.47

Remarks on result:

other: Key log Kp sediment-water for Zr based on the read across study from Roychoudhury and Starke (2006).

Key result

Phase system:

suspended matter-water

Type:

log Kp

Value:

5

Remarks on result:

other: Key log Kp suspended matter-water for Zr based on the read across studies from Veselý et al. (2001) and Gobeil et al. (2005).

Two other studies from Thibault et al. (1990) and Drndarski and Golobocanin (1995) were also available. The first study predicted Kp values for 4 different types of soil based on a previously reported plant to soil concentration factor. The log Kp values for sandy, loamy, clay and organic soil were calculated to be 2.76, 3.31, 3.49 and 3.86, respectively. Since this plant to soil concentration factor was also a predicted value and no information was reported on the applicability and accuracy of the regression equation used for prediction of Kp values, the reliability of the study is considered not high enough. This study was not used for the derivation of the final Kp value for soil but was considered a supporting study.

The other study from Drndarski and Golobocanin (1995) investigated a series of sampling sites along the Sava River. Analyses of zirconium concentrations in both filtered water and sediment yielded a log Kp of approximately 3.1, which was only reported in a figure, and therefore cannot be considered reliable. The result was used as supporting information.

Description of key information

Assessment of this endpoint and derivation of adsorption coefficients are element-based (i.e., not substance-based). A total of five studies was used in a weight of evidence approach to cover the endpoint. Two studies were added as supportive, but the data were not used to derive the key adsorption coefficients. 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 for soil for zirconium. Based on these Kp values, zirconium clearly has a strong potential for adsorption to particulate matter. For adsorption to occur however, zirconium has to end up in the aqueous phase of the environmental compartment under consideration (water column, or pore water in sediment/soil). 

Key value for chemical safety assessment

Other adsorption coefficients

Type:

log Kp (solids-water in suspended matter)

Value in L/kg:

5

Other adsorption coefficients

Type:

log Kp (solids-water in sediment)

Value in L/kg:

5.47

Other adsorption coefficients

Type:

log Kp (solids-water in soil)

Value in L/kg:

4.13

Additional information

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, seven studies were identified containing relevant information on adsorption of zirconium to particulate matter. Five of 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 (artihmetic mean) of 4.13 was taken as key log Kp for soil.

Two other studies from Thibault et al. (1990) and Drndarski and Golobocanin (1995) were also available. The first study predicted Kp values for 4 different types of soil based on a previously reported plant to soil concentration factor. The log Kp values for sandy, loamy, clay and organic soil were calculated to be 2.76, 3.31, 3.49 and 3.86, respectively. Since this plant to soil concentration factor was also a predicted value and no information was reported on the applicability and accuracy of the regression equation used for prediction of Kp values, the reliability of the study is considered not high enough. This study was not used for the derivation of the final Kp value for soil but was considered a supporting study.

The other study from Drndarski and Golobocanin (1995) investigated a series of sampling sites along the Sava River. Analyses of zirconium concentrations in both filtered water and sediment yielded a log Kp of approximately 3.1, which was only reported in a figure, and therefore cannot be considered reliable. The result was used as supporting information.

Overall, strong adsorption of zirconium to particulate matter is observed, whether soil, sediment, or suspended matter. For adsorption to occur however, zirconium has to end up in the aqueous phase of the environmental compartment under consideration (water column, or pore water in sediment/soil).