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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:
other: Well performed batch equilibrium experiment.
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)
GLP compliance:
not specified
Remarks:
study published in peer reviewed scientific literature
Type of method:
batch equilibrium method
Media:
soil
Radiolabelling:
no
Test temperature:
not reported
Analytical monitoring:
yes
Details on sampling:
Samples of supernatant (filtered 0.45 µm) were taken after 24 h.
Details on matrix:
16 different Australian soils were used.
Soils were pooled samples from the top 0-15 cm of the soil profile, air-dried at 25°C, passed through 2 mm sieve.
Soil properties reported in supplementary information.
Details on test conditions:
- Soil:solution ratio = 1:10 m/v (50 g soil and 500 mL solution)
- Spiking rates: 9.14 µmol Ce+III/kg from Ce(NO3)3 or 9.14 µmol Ce+IV/kg from (NH4)2Ce(NO3)6
- Soil suspension shaken end over end during 24 h (2 mM KNO3)
- 0.45 µm filtrates of supernatant solution were analysed after 24 h of shaking
Computational methods:
Kp values were calculated by dividing Ce concentration in soil (calculated from Ce added and Ce in solution after 24 h) by Ce concentration in filtered supernatant (L/kg).
Phase system:
soil-water
Type:
log Kp
Value:
3.58 L/kg
Remarks on result:
other: median for Ce+III
Phase system:
soil-water
Type:
log Kp
Value:
2.95 L/kg
Remarks on result:
other: 25th percentile for Ce+III
Phase system:
soil-water
Type:
log Kp
Value:
3.78 L/kg
Remarks on result:
other: 75th percentile for Ce+III
Phase system:
soil-water
Type:
log Kp
Value:
3.26 L/kg
Remarks on result:
other: median for Ce+IV
Phase system:
soil-water
Type:
log Kp
Value:
2.53 L/kg
Remarks on result:
other: 25th percentile for Ce+IV
Phase system:
soil-water
Type:
log Kp
Value:
3.63 L/kg
Remarks on result:
other: 75th percentile for Ce+IV
Details on results (Batch equilibrium method):
Kp values increased with increasing CEC (cation exchange capacity).
Adsorption of Ce+III and Ce+IV by metal oxides and clays and interchanges between Ce+III and Ce+IV explain the similarity of their respective Kp values.
Statistics:
Kp values for Ce+III and Ce+IV were not significantly different from each other (paired t-test, p < 0.05).
Conclusions:
In this study, adsorption of Ce+III (added as Ce(NO3)3) and Ce+IV (added as (NH4)2Ce(NO3)6) on 16 Australian soils was studied in batch equilibrium experiments. Median log Kp values were reported to be 3.58 and 3.26 L/kg for Ce+III and Ce+IV, respectively. There was no significant difference between the Kp values of Ce+III and Ce+IV, most likely due to the fact that there are interchanges between Ce+III and Ce+IV during the experiment and because both adsorb on metal oxides and clays.
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 batch equilibrium experiment.
Qualifier:
equivalent or similar to
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:
20°C
Analytical monitoring:
yes
Details on sampling:
After 20 days of equilibration, the suspension was centrifuged at 4500 rpm.
Details on matrix:
Soil samples taken from a pine plantation (Pinus sylvestris, ca. 50 yrs of age), located in Northern Bavaria, 2.5 km north of the village Altenschwand on an almost plain plateau, 400 m above mean sea level. The soil is classified as podzol, consisting of a black partially decomposed forest litter (O-horizon, 0-5 cm) over a gray layer of silty sand (E-horizon, 0-8 cm). Soil samples were air dried, sieved (2 mm) and mixed.
- pH (CaCl2): 3.1 (O), 3.3 (E)
- CaCO3: 0%
- Loss on ignition: 82% (O), 7% (E)
- Total N: 1.1% (O), 0.1% (E)
- Clay: 0% (O), 3% (E)
- Silt: 0% (O), 17% (E)
- Sand: 0% (O), 80% (E)
- CEC: 750 me/kg (O), 125 me/kg (E)
- Ca: 72 me/kg (O), 11 me/kg (E)
- K: 9 me/kg (O), < 1 me/kg (E)
- Mn: 30 mg/kg (O), 1 mg/kg (E)
- Fe: 1240 mg/kg (O), 360 mg/kg (E)
Details on test conditions:
- Soil:solution ratio = 10 g soil and 25 mL water (1:2.5)
- Equilibration time: 20 days
- Concentration of individual metal ions added to solution was always < 6E-08 mol/L
- Four replicate experiments were performed with each soil sample
Computational methods:
The amount sorbed was calculated from initial and final activity of each radionuclide in the solution. Kp was calculated by dividing amount of ion sorbed per kg air-dry soil by amount of ion per L of soil solution.
Phase system:
soil-water
Type:
log Kp
Value:
>= 2.18 - <= 2.88 L/kg
Temp.:
20 °C
Remarks on result:
other: in O-horizon
Phase system:
soil-water
Type:
log Kp
Value:
>= 2.2 - <= 2.88 L/kg
Temp.:
20 °C
Remarks on result:
other: in E-horizon
Phase system:
soil-water
Type:
log Kp
Value:
2.5 L/kg
Temp.:
20 °C
Remarks on result:
other: median in O-horizon
Phase system:
soil-water
Type:
log Kp
Value:
2.49 L/kg
Temp.:
20 °C
Remarks on result:
other: median in E-horizon
Conclusions:
In this study, batch equilibrium experiments were performed using samples from the O- and E-horizon of a podzol soil. Radionuclide 141Ce was added as chloride. After 20 days of equilibration, remaining activities were measured in the supernatant. Log Kp values for O-horizon were calculated to be 2.18 to 2.88 L/kg (median 2.5 L/kg). For E-horizon, log Kp values ranged from 2.2 to 2.88 L/kg, the median being 2.49 L/kg (which is very similar).
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:
other: Well performed study. Reliable with restrictions (Klimisch 2) because data were taken from figures.
Qualifier:
no guideline followed
Principles of method if other than guideline:
Sediment and filtered water samples were taken from several locations along the Sava River (affected by the Chernobyl accident) and analysed for 144Ce.
GLP compliance:
not specified
Type of method:
other: field study
Media:
sediment
Test temperature:
not reported
Analytical monitoring:
yes
Details on sampling:
Sediments were collected with a grab sampler. Sediments were dried in an oven at 105°C to a constant weight. Caked sediments were then finely ground.
Water samples were collected with plastic bottles and acidified with 0.1N HNO3. Water samples were filtered and evaporated under infrared lamps.
Details on matrix:
no details reported
Details on test conditions:
field study
Computational methods:
The partitioning coefficient was calculated dividing the concentration in the sediment by the concentration in the water (L/kg).
Phase system:
sediment-water
Type:
log Kp
Value:
ca. 3.25 L/kg
Remarks on result:
other: taken from figure
Conclusions:
In this study, sediment and filtered water samples were taken from the Sava River (affected by the Chernobyl accident) and analysed for 144Ce. A log Kpsediment-water value was reported of ca. 3.25 L/kg (taken from figure).
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 study.
Qualifier:
equivalent or similar to
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:
2.6 L/kg
Remarks on result:
other: untreated soil
Adsorption and desorption constants:
Log Kp soil in untreated soil was 2.60.
Log Kp soil in treated soil (CaCO3 or both CaCO3 and organic matter removed) was 4.42.
Details on results (Batch equilibrium method):
Adsorption of lanthanides is concluded to be largely determined by oxides and silicate clays rather than CaCO3 and organic matter, because the values of lanthanides on both treated soils (CaCO3 and/or organic matter removed) are either greater or equal to those for untreated soil.
Conclusions:
In this study, adsorption of Ce was investigated using cultivated Chinese soil and radiolabeled Ce. After 2 h contact time in a batch equilibrium experiment, a log Kp of 2.60 L/kg was obtained.
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:
other: Well performed field study. However, for calculation of the Kpsuspended matter-water, the detection limit was used as aquatic Ce concentration since Ce was not detectable in the water phase. This reduces the reliability of this value.
Qualifier:
no guideline followed
Principles of method if other than guideline:
Sediment, pore water, suspended matter, and water samples were taken in the Forsmark area, Baltic Sea, and analysed for Ce.
GLP compliance:
not specified
Type of method:
other: field study
Media:
other: sediment and suspended matter
Radiolabelling:
no
Test temperature:
between 2.3 and 12.3°C during sampling
Analytical monitoring:
yes
Details on sampling:
- Location and timing: all samples collected between 12-20 April 2005 in the bay between the north side of the islands of Stor and Lill-Tixlan, between the Forsmark nuclear power station and the town of Öregrund, NW Baltic Proper.
- Integrated water samples (10 L) collected from 0-4 m depth using a metal-free pump.
- Particulate organic matter in the water column was sampled through filtration of the water samples.
- Sediment: Kajak cores were taken at 7-8 m depth and sliced into two sections (0-3 cm and 3-6 cm).
- Pore water was extracted by centrifugation (20 min at 4500 rpm) from sediment samples.
Details on matrix:
no details reported
Details on test conditions:
field test
Computational methods:
Partitioning coefficients were calculated by dividing Ce concentration in solid phase by Ce concentration in water (L/kg).
Kpsuspended matter-water was calculated as well as Kpsediment-pore water for upper layer (0-3 cm) and lower layer (3-6 cm).
Phase system:
suspended matter-water
Type:
log Kp
Value:
6.52 L/kg
Remarks on result:
other: concentrations in filtered water and particulate organic matter used, Ce concentration in water phase was below detection limit, therefore, the detection limit was used as aquatic Ce concentration
Phase system:
solids-water in sediment
Type:
log Kp
Value:
3.41 L/kg
Remarks on result:
other: concentrations in sediment and pore water of upper sediment layer (0-3 cm) used
Details on results (Batch equilibrium method):
For the lower sediment layer (3-6 cm), a log Kpsediment-pore water of 4.96 L/kg was obtained.
Conclusions:
In this study, water, suspended matter, sediment, and pore water samples were taken in the Forsmark area, Baltic Sea, and analysed for Ce. The log Kpsuspended matter-water was calculated to be 6.52 L/kg, using the detection limit as aquatic Ce concentration since Ce was not detectable in the water phase. The log Kpsediment-pore water for the upper sediment layer (0-3 cm) was determined to be 3.41 L/kg.
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 batch equilibrium experiment.
Qualifier:
equivalent or similar to
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:
25°C
Analytical monitoring:
yes
Details on sampling:
Adsorption
- Samples taken after 0.17, 0.5, 1, 5, 10, 30 or 60 min.
- Centrifugation at 4000 rpm for 5 min.
Desorption
- Samples taken after 2 h of agitation.
Details on matrix:
Four types of soils that are common in China have been used. Soil samples were air dried and ground to < 0.28 mm.
Fluvio-aquic soil from north of China:
- Order: Alfisol
- pH: 8.32
- Organic matter: 16 g/kg
- Clay: 364 g/kg
- CEC: 10.32 cmol(+)/kg
Red earth from Jiangxi Province, south of China:
- Order: Oxisol
- pH: 5.54
- Organic matter: 11.2 g/kg
- Clay: 895 g/kg
- CEC: 6.55 cmol(+)/kg
Black soil from Heilongjiang Province, northeast of China:
- Order: Mollisol
- pH: 6.0
- Organic matter: 53.8 g/kg
- Clay: 599 g/kg
- CEC: 17.29 cmol(+)/kg
Loess soil from Shaanxi Province, southwest of China:
- Order: Aridisol
- pH: 7.91
- Organic matter: 16.2 g/kg
- Clay: 579 g/kg
- CEC: 10.39 cmol(+)/kg
Details on test conditions:
Adsorption
- 1 g soil and 20 mL solution (1:20 soil:solution ratio)
- Three Ce+III concentrations: 20, 40, 80 µg Ce/mL
- Centrifuge tubes laid horizontally on reciprocation shaker and agitated continuously at 240 cycles/min
- Seven agitation times: 0.17, 0.5, 1, 5, 10, 30 and 60 min
- All treatments replicated three times
Desorption
- Similar procedures, but only agitation for 2 h
Computational methods:
Amounts of Ce(III) sorbed by the soil samples were calculated from the reduction of Ce(III) in solution. Kp values calculated from data shown in Table 3 in the publication (amount sorbed after 60 min).
Phase system:
soil-water
Type:
log Kp
Value:
>= 3.7 - <= 4.5 L/kg
Temp.:
25 °C
% Org. carbon:
>= 1.6 - <= 5.4
Remarks on result:
other: for four Chinese soils after 60 min
Details on results (Batch equilibrium method):
ADSORPTION
The initial contents of Ce(III) in stock solutions at 20, 40 and 80 µg/mL were 400, 800 and 1600 µg. After 0.5 min of the adsorption experiment, 396 to 399 µg of Ce(III) were adsorbed to the soil in treatment corresponding to the concentration of 20 µg/mL, 792 to 798 µg in the treatment corresponding to the concentration of 40 µg/mL and 1585 to 1594 in the treatment corresponding to the concentration of 80 µg/mL. There is no difference regardless the kind of soil. The Ce(III) adsorption reaction was thus nearly complete and very rapid.

DESORPTION
The results obtained on a same soil but with different concentrations being of the same order of magnitude, the highest concentration (i.e. 80 µg/mL) was retained for further interpretations. The amounts of Ce(III) remaining in soil after the desorption experiment were about 210, 10, 5 and 4 µg for red, fluvo-aquic, loess and black soils, respectively (graphically determined from the publication). Desorption was thus quasi-complete for the three last soils and partial for red earth. The equilibria were reached after 10 to 30 min for the four soil types; with a decreasing order of equilibration time being the following : red earth > fluvo-aquic soil > loess soil > black soil. This means the longer the desorption time took before approaching the equilibrium, the less the desorption rate was. Furthermore, it was found that the desorption equilibrium times were relatively longer and the Ce(III) amounts remaining in soil were higher when the soil CEC (Cations Exchange Capacity) was low.
Conclusions:
In this study, batch equilibrium experiments were performed with 4 Chinese soils and adding 141Ce-labeled Ce(NO3)3. Sorption was very rapid and nearly complete. Using the data for the 60 min sampling point, log Kp values of 3.7 to 4.5 L/kg were obtained. Depending on the soil type, it took 10 to 30 min for desorption to be nearly complete.
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:
other: Well performed study, however, reliable with restrictions (Klimisch 2) because samples were taken from a polluted area and because precipitation processes may have been involved in the sediment, resulting in higher log Kp values.
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 Ce.
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 Ce concentration in sediment by Ce concentration in pore water (L/kg).
Phase system:
solids-water in sediment
Type:
log Kp
Value:
>= 5.15 - <= 7.18 L/kg
% Org. carbon:
>= 1.2 - <= 10.6
Remarks on result:
other: range for all paired samples, precipitation processes may have been involved
Details on results (Batch equilibrium method):
Organic matter seemed to have the most important effect on sediment Ce concentrations.
Conclusions:
In this study, samples of sediment and pore water were taken along two rivers receiving wastewater from Hanoi, Vietnam, and analysed for Ce. Log Kpsediment-pore water values of 5.15 to 7.18 L/kg were reported. However, reliability is restricted, because precipitation processes may have been involved in sediment next to sorption processes, yielding overestimated partitioning coefficients. Suggest using only the lowest boundary for further data analysis.
Endpoint:
adsorption / desorption, other
Remarks:
field study and lab study using field samples
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Acceptable, well documented publication which meets basic scientific principles. However, a Klimisch 2 score (reliable with restrictions) was assigned because paired concentrations are not reported and adsorption coefficients are calculated using medians.
Qualifier:
no guideline followed
Principles of method if other than guideline:
Field study in which Ce concentrations were determined in both surface water, pore water, sediment, and suspended matter. Samples were taken from 6 sampling locations in the Rhine-Meuse estuary in the Netherlands. Further, also a lab study was performed using field samples.
GLP compliance:
not specified
Type of method:
other: both field study and lab study using field samples
Media:
other: sediment and suspended matter
Radiolabelling:
no
Test temperature:
Field sampling: no temperature range given.
Lab experiment: 15 °C
Analytical monitoring:
yes
Details on sampling:
Field sampling:
- Surface-water samples, suspended solids, and sediments (through 25-cm-deep, box-core sampling) were collected during June and July 1997 at six locations in the Rhine-Meuse estuary.
- Sampling locations: Nieuwe Maas, Nieuwe Maas, First Petroleum Harbour, Botlekhaven, Northsea Loswal Noord, and Northsea Terheide 30. Locations 1,2,6 are relatively clean. Locations 3,4 are directly influenced by industrial discharges, and location 5 is a disposal site for sediments that are contaminated through industrial discharges.
- Surface water samples were 0.45 µm filtered.
- Pore water samples were obtained by positive-pressure filtration (0.45 µm).
Lab study (location 2 sediment and water):
- Samples taken after 10 days.
Details on matrix:
- Sampling: see above.
- Organic carbon (%) median (range): 5.9 (4.0-24.2) in suspended solids of the six locations, 1.94 (0.08-3.82) in sediments of the six locations, 2.13 (0.88-2.81) for the sediments used in the lab study.
Details on test conditions:
Field study: no specific test conditions.
Lab study:
For every assay, two acid-rinsed polystyrene aquaria (replicates) were filled with sediments (1750 g wet weight) and seawater (4 L) from the appropriate location (2). Standard conditions: pH = 8.1, salinity 30 g/L, no addition of complexing agents, exposure time 10 d.
Further assays were conducted with diversified conditions:
- varying pH: 7.1, 7.7, 8.1 and 8.5;
- varying salinity: 10, 20 and 30 g/L
- addition of complexing agents: 500 mg H(PO4)2-, 400 µg F-
Computational methods:
Indicative adsorption coefficients could only be calculated using the median Ce concentrations reported for the six locations and the lab study in pore water, surface water, sediments and suspended solids.
Phase system:
sediment-water
Type:
log Kp
Value:
ca. 3.13 L/kg
Remarks on result:
other: calculated using median values for field samples
Phase system:
solids-water in sediment
Type:
log Kp
Value:
ca. 2.86 L/kg
Remarks on result:
other: calculated using median values for field samples
Phase system:
suspended matter-water
Type:
log Kp
Value:
ca. 3.3 L/kg
Remarks on result:
other: calculated using median values for field samples
Phase system:
sediment-water
Type:
log Kp
Value:
ca. 2.68 L/kg
Remarks on result:
other: calculated using median values for lab study samples
Phase system:
solids-water in sediment
Type:
log Kp
Value:
ca. 2.02 L/kg
Remarks on result:
other: calculated using median values for lab study samples
Adsorption and desorption constants:
see above
Statistics:
Median values used for Kp calculation, hence Kp values only indicative. Paired values for aqueous and solid phase not reported.
Conclusions:
In this study, cerium concentrations were determined in surface water, pore water, sediment and suspended solids of six locations in the Rhine-Meuse estuary (the Netherlands) as well as in a lab study using field samples of one of the six locations. Only medians and ranges were reported, therefore, only indicative adsorption coefficients could be calculated using the median values. Overall, log Kp values for sediment-surface water, sediment-pore water and suspended solids-surface water varied from 2.02 to 3.30 L/kg.
Endpoint:
adsorption / desorption
Remarks:
field study and lab experiment with field samples
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
other: Acceptable, well documented publication/study report which meets basic scientific principles. Reliability not assignable because original publication not available.
Qualifier:
no guideline followed
Principles of method if other than guideline:
The concentration of Ce 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 lab 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 lab 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:
6.31 L/kg
Remarks on result:
other: field
Phase system:
sediment-water
Type:
log Kp
Value:
5.78 L/kg
Remarks on result:
other: lab
Phase system:
solids-water in sediment
Type:
log Kp
Value:
5.93 L/kg
Remarks on result:
other: field
Phase system:
solids-water in sediment
Type:
log Kp
Value:
4.94 L/kg
Remarks on result:
other: lab

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 Ce to sediment was evaluated by determining Ce 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 lab. The obtained log Kp sediment values were 4.94 and 5.93 L/kg when based on pore water concentrations in lab and field, respectively, and 5.78 and 6.31 L/kg when based on surface water concentrations in lab and field, 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 study.
Qualifier:
equivalent or similar to
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:
4.43
Temp.:
25 °C
% Org. carbon:
1.72
Remarks on result:
other: calcareous soil
Phase system:
soil-water
Type:
log Kp
Value:
2.6
Temp.:
25 °C
% Org. carbon:
3.28
Remarks on result:
other: red earth
Conclusions:
In this multitracer study, the adsorption of Ce to two Chinese soils, a calcareous soil and a sandy red earth, was investigated in a batch equilibrium experiment. Log Kp values were 4.43 and 2.60 L/kg for the calcareous soil and red earth, respectively.
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:
other: Well performed field study.
Qualifier:
no guideline followed
Principles of method if other than guideline:
Water and suspended matter samples were collected from 54 Czech rivers at 119 sampling locations and analysed for Ce.
GLP compliance:
not specified
Type of method:
other: field study
Media:
suspended matter
Radiolabelling:
no
Test temperature:
not reported
Analytical monitoring:
yes
Details on sampling:
Samples taken from 54 Czech rivers at 119 localities over the whole state territory in summers 1997 and 1998 under stable hydrological conditions.
- Water samples: filtered (0.4 µm) and unfiltered samples taken. Acidification by adding 1 mL of HNO3 1:1 purified by sub-boiling distillation on the day of collection, to attain a pH of about 1.5.
- Sediment samples: 200 mL water was generally filtered, and the SPM deposited on the filters was dried at 105°C.
Details on matrix:
The river waters had a mean pH of 7.74 (6.9-8.8), ionic strength (I) 7.8 mmol/L, specific conductance 538 µS/cm at 25°C, alkalinity 1.9 mmol/L, and moderate mean contents of SPM 9.9 mg/L (1.0-124 mg/L).
Details on test conditions:
Field study.
Computational methods:
Log Kp suspended matter was calculated dividing concentrations in SPM (suspended particulate matter) (mg/kg) by concentrations in water (mg/L). The Kp values for which log values were reported in the publication were different because they divided the concentrations in SPM (mg/kg) by concentrations in water in µg/L.
Phase system:
suspended matter-water
Type:
log Kp
Value:
5.54 L/kg
Remarks on result:
other: calculated from median reported Ce concentrations in SPM (mg/kg) and aqueous phase (mg/L)
Phase system:
suspended matter-water
Type:
log Kp
Value:
5.52 L/kg
Remarks on result:
other: reported median Kp suspended matter value, but corrected for using aqueous Ce concentrations in mg/L instead of µg/L
Concentration of test substance at end of adsorption equilibration period:
Median Ce concentration in aqueous phase: 0.20 µg/L.
Median Ce concentration in suspended matter: 69 mg/kg.
Conclusions:
In this study, samples of suspended matter and water were taken from Czech rivers and analysed for Ce. Log Kp suspended matter was reported to be 5.52 L/kg (median of all samplings), and was 5.54 L/kg when calculated using median concentrations in water and suspended matter.
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:
other: Well performed field study, however, a Klimisch 2 score (reliable with restrictions) was assigned because data for Kp sediment calculation was only given in figures.
Qualifier:
no guideline followed
Principles of method if other than guideline:
Sediment, pore water, and surface water samples were taken at five locations in The Netherlands. These samples were analysed for Ce.
GLP compliance:
not specified
Type of method:
other: field study
Media:
sediment
Radiolabelling:
no
Test temperature:
Temperature at sampling occasions between 18 and 21°C.
Analytical monitoring:
yes
Details on sampling:
Five locations in The Netherlands, four of them in highly industrialised region around city of Rotterdam. All sampling sites in catchment of Rhine and Meuse rivers. 1. Veluwemeer, 2. Botlekpark, 3. Kralingse Plas, 4. Nieuwe Maas, 5. Charlois.
Samples were taken in August and September 2000.
Surface water samples (n=3) 0.45 µm filtered.
Pore water samples (n=3) were extracted in situ using Rhizon soil moisture samplers (MOM type, Eijkelkamp Agrisearch Equipment, Giesbeek, The Netherlands).
Sediment samples (n=3) were collected with a bottom sampler according to Ekman-Birge (Hydro-bios, Kiel, Germany).
Details on matrix:
Average pH of sampling locations at time of sampling was between 7.30 and 8.72. Quite similar for pore water.
No characteristics given for sediment.
Details on test conditions:
Field study.
Computational methods:
Kp sediment values were calculated dividing concentration in sediment (mg/kg) by concentrations in either surface water or pore water (mg/L).
Phase system:
sediment-water
Type:
log Kp
Value:
>= 4.9 - <= 5.6 L/kg
Remarks on result:
other: range derived from Figure 11
Phase system:
solids-water in sediment
Type:
log Kp
Value:
>= 5.4 - <= 5.9 L/kg
Remarks on result:
other: range derived from Figure 12
Conclusions:
In this study, sediment, surface water, and pore water samples were taken at five locations in the Netherlands in the Rhine-Meuse catchment. Ce was determined in all samples and log Kp sediment-surface water was reported (in figures) to range from 4.9 to 5.6 L/kg, whereas the log Kp sediment-pore water was reported (also in figures) to range from 5.4 to 5.9 L/kg.
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 study.
Qualifier:
equivalent or similar to
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 Ce 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. Ce remaining in solution was then calculated. Soil:solution ratio was taken into account.
Phase system:
soil-water
Type:
log Kp
Value:
>= 3.54 - <= 4.46 L/kg
Temp.:
20 °C
% Org. carbon:
>= 1.35 - <= 36.4
Remarks on result:
other: range
Phase system:
soil-water
Type:
log Kp
Value:
4.13 L/kg
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 Ce was studied in 4 Chinese soils using a batch equilibrium method (solutions spiked with Ce(NO3)3). Log Kp values ranged from 3.54 to 4.46 L/kg, and the average log Kp was 4.13 L/kg. Desorption was also studied, and indicated the effect of pH on desorption (higher at low pH, lower at high pH).
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:
other: Well performed field study, however, a Klimisch 2 score (reliable with restrictions) was assigned 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 REEs 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 Ce concentration in the soil under consideration (mg/kg) by the minimum and maximum of the range of water soluble Ce reported in figures (mg/kg).
Phase system:
soil-water
Type:
log Kp
Value:
>= 2.04 - <= 4.25 L/kg
% Org. carbon:
>= 0.39 - <= 6.76
Remarks on result:
other: range for all nine soils
Phase system:
soil-water
Type:
log Kp
Value:
3.25 L/kg
% 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 Ce concentrations determined in the laboratory. This resulted in a range of Kp soil values of 2.04 to 4.25 L/kg, the average being 3.25 L/kg.
Endpoint:
adsorption / desorption, other
Remarks:
other: microcosm study
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Well performed study, however a Klimisch 2 score (reliable with restrictions) was assigned because data for Kp sediment calculation could only be derived from figures.
Qualifier:
no guideline followed
Principles of method if other than guideline:
A microcosm study was performed in which concentrations of Ce 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 +/- °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. 0.5 g 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.
pH 6.5-6.8.
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:
2.9 L/kg
Temp.:
22 °C
Remarks on result:
other: value after 16 days
Details on results (Batch equilibrium method):
Distribution of Ce was 92.48% in sediment, 7.06% in water, and 0.46% in biota.
Conclusions:
In this microcosm study, water and sediment Ce concentrations were monitored for up to 16 days. Based on the concentrations reported for 16 days, a log Kp sediment of 2.9 L/kg could be calculated. Data were taken from figures.
Endpoint:
adsorption / desorption, other
Remarks:
partitioning between water, suspended matter, sediment, and soil
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Justification for type of information:
The endpoint adsorption/desorption is covered by a series of read across studies, among which several field studies (in which cerium was analysed in field samples) as well as laboratory studies performed with water soluble cerium salts other than cerium ammonium nitrate (e.g., Ce(NO3)3, CeCl3, as well as a multitracer solutions containing non-specified cerium salts). The rationale for read across is described to detail in the read across document attached to IUCLID Section 13. One study (Cornelis et al., 2011) was performed with cerium ammonium nitrate (next to Ce(NO3)3). For completeness the results of all these studies have been included in the derivation of the key partitioning coefficients presented here below.
Reason / purpose:
read-across source
Reason / purpose:
read-across source
Reason / purpose:
read-across source
Reason / purpose:
read-across source
Reason / purpose:
read-across source
Reason / purpose:
read-across source
Reason / purpose:
read-across source
Reason / purpose:
read-across source
Reason / purpose:
read-across source
Reason / purpose:
read-across source
Reason / purpose:
read-across source
Reason / purpose:
read-across source
Reason / purpose:
read-across source
Reason / purpose:
read-across source
Key result
Phase system:
suspended matter-water
Type:
log Kp
Value:
5.12 L/kg
Remarks on result:
other: mean log Kp value for suspended matter-water
Key result
Phase system:
sediment-water
Type:
log Kp
Value:
5.15 L/kg
Remarks on result:
other: median log Kp value for sediment-water
Key result
Phase system:
soil-water
Type:
log Kp
Value:
3.54 L/kg
Remarks on result:
other: median log Kp value for soil-water

Description of key information

A total of fifteen studies was used in a weight of evidence approach to cover the endpoint. Data were available for soil, suspended matter, and sediment. The following final key values were retained: a log Kp of 5.12 L/kg for suspended matter-water, a log Kp of 5.15 L/kg for sediment-water, and a log Kp of 3.54 L/kg for soil-water. Adsorption to sediment and suspended matter appears to be more pronounced than adsorption to soil for cerium.

Key value for chemical safety assessment

Other adsorption coefficients

Type:
log Kp (suspended matter-water)
Value in L/kg:
5.12

Other adsorption coefficients

Type:
log Kp (sediment-water)
Value in L/kg:
5.15

Other adsorption coefficients

Type:
log Kp (soil-water)
Value in L/kg:
3.54

Additional information

In total, 15 studies were selected as useful for covering the adsorption/desorption endpoint using a weight of evidence approach. Data were available for soil, sediment, and suspended matter and will be further discussed below. Adsorption/desorption is evaluated on an elemental basis, lumping information from field studies as well as laboratory studies performed with trivalent or tetravalent cerium compounds. A study of Cornelis et al. (2011) compared the adsorption capacity of Ce+3 and Ce+4, however no difference was noted. Therefore it seems justified to lump data for Ce+3 compounds with data for Ce+4 compounds. Anyhow, according to the Pourbaix diagram (see read across justification document attached to IUCLID Section 13), Ce+4 is not stable in aqueous media at environmentally relevant conditions. Depending on the conditions, either a reduction to Ce+3 occurs or Ce+4 disappears from solution as CeO2. Therefore, any cerium in solution (water column, sediment or soil pore water), available for adsorption to particulate matter, is expected to be present as trivalent cerium. Although no information is available on how fast speciation equilibrium is reached, the results of the study of Cornelis et al. (2011) - i.e., no significant difference in adsorption capacity of Ce+3 and Ce+4 - suggest that equilibrium is relatively rapidly reached.

For suspended matter three studies were identified as useful. From the study of Veselý et al. (2001), an average (arithmetic mean) log Kp of 5.53 L/kg is obtained for a series of samplings along Czech rivers. Moermond et al. (2001) analysed samples from several locations along the Rhine-Meuse estuary. Based on cerium concentrations measured in suspended matter and water, a log Kp of 3.3 L/kg was calculated. Finally, Kumblad and Bradshaw (2008) reported a log Kp value of 6.52 L/kg, based on cerium concentrations measured in water and suspended matter sampled in the Forsmark area, Baltic Sea. Because there is a limited amount of values available, the average (arithmetic mean) log Kp of 5.12 L/kg for these three studies is selected as key value for characterising distribution between suspended matter and water.

For sediment seven studies were included in the weight of evidence approach. Based on data from the study of Moermond et al. (2001) for sediment, surface water and pore water, log Kp values could be calculated ranging from 2.02 to 3.13 L/kg. Sneller et al. (2000) reported log Kp values obtained by Stronkhorst and Yland (1998) of 4.94 to 6.31 L/kg for samples taken from the field and a laboratory study using field samples. Weltje et al. (2002) investigated cerium distribution between sediment and surface water or pore water in samples taken along the Rhine-Meuse catchment (the Netherlands) and reported log Kp values of 4.90 to 5.60 L/kg for sediment-surface water and 5.40 to 5.90 L/kg for sediment-pore water. Drndarski and Golobocanin (1995) obtained a log Kp value of ca. 3.25 L/kg for samples taken from the Sava River, an environment which was affected by the Chernobyl accident and in which 144Ce is present. 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 5.15 and 7.18 L/kg. 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. Kumblad and Bradshaw (2008) reported a log Kp for upper sediment of 3.41 L/kg based on results for samples taken in the Forsmark area, Baltic Sea. Finally, the microcosm study of Yang et al. (1999) yielded a log Kp sediment of 2.90 L/kg 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. Pore water-based and surface water-based data were however not lumped, individual average values (arithmetic mean) were retained for this. The 10th, 50th and 90th percentile of the retained values was 2.85, 5.15 and 5.73 L/kg, respectively. The median of 5.15 L/kg was taken as key log Kp.

For soil, seven studies were included in the weight of evidence approach. Wen et al. (2006) gathered samples of nine Chinese soils and analysed total and water soluble cerium concentrations in the laboratory, which resulted in a range of log Kp values of 2.04 to 4.25 L/kg. Based on data from Du et al. (1998), in which adsorption of cerium was investigated using cultivated Chinese soil and radiolabeled cerium, a log Kp of 2.6 L/kg could be obtained. This study also indicated that cerium sorption is rather determined by the presence of oxides and silicate clays than by CaCO3 and organic matter. Another batch equilibrium experiment with Chinese soils yielded log Kp values of 3.50 to 4.22 L/kg (Wen et al., 2002). Bunzl and Schimmack (1989) performed batch equilibrium experiments using samples from the O- and E-horizon of a podzol soil and 141Ce radiolabeled CeCl3. Log Kp values for O-horizon were calculated to be 2.18 to 2.88 L/kg (median 2.5 L/kg). For E-horizon, log Kp values ranged from 2.2 to 2.88 L/kg, the median being 2.49 L/kg (which is very similar). In the multitracer study of Tao et al. (2000), the adsorption of cerium to two Chinese soils, a calcareous soil and a sandy red earth, was investigated in a batch equilibrium experiment. Log Kp values were 4.43 and 2.60 L/kg for the calcareous soil and red earth, respectively. Cornelis et al. (2011) studied the adsorption of Ce+III (added as Ce(NO3)3) and Ce+IV (added as (NH4)2Ce(NO3)6) on 16 Australian soils in batch equilibrium experiments. Median log Kp values were reported to be 3.58 and 3.26 L/kg for Ce+III and Ce+IV, respectively. There was no significant difference between the Kp values of Ce+III and Ce+IV, most likely due to the fact that there are interchanges between Ce+III and Ce+IV during the experiment and because both adsorb on metal oxides and clays. And finally, Li et al. (2001) performed batch equilibrium experiments with 4 Chinese soils and 141Ce-labeled Ce(NO3)3. Based on their data, log Kp values of 3.7 to 4.5 L/kg were obtained. Sorption was reported to be very rapid and nearly complete. To determine a final key value for adsorption of cerium to soil, a single value (arithmetic mean) was retained for each soil in each study. The 10th, 50th and 90th percentile of the retained values was 2.52, 3.54 and 4.28 L/kg, respectively. The median value of 3.54 L/kg was taken as key log Kp for soil.

Overall, the obtained adsorption coefficients were similar as for many other metals. Adsorption to soil appears to be mild, however a stronger adsorption of cerium to suspended matter and sediment seems to occur.