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Adsorption / desorption

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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 for suspended matter-water, a log Kp of 5.15 for sediment-water, and a log Kp of 3.54 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

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

Other adsorption coefficients

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

Other adsorption coefficients

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

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.

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 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 was calculated. Finally, Kumblad and Bradshaw (2008) reported a log Kp value of 6.52, 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 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. Sneller et al. (2000) reported log Kp values obtained by Stronkhorst and Yland (1998) of 4.94 to 6.31 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 for sediment-surface water and 5.40 to 5.90 for sediment-pore water. Drndarski and Golobocanin (1995) obtained a log Kp value of ca. 3.25 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. 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 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 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, respectively. The median of 5.15 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. 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 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 (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 (median 2.5). For E-horizon, log Kp values ranged from 2.2 to 2.88, the median being 2.49 (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 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 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 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, respectively. The median value of 3.54 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.