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Adsorption / desorption

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Description of key information

The assessment is based on Kd values derived from monitoring data for elemental Sr concentrations in streamwater and corresponding sediments. The partition coeffient for soil was derived in a weight of evidence approach using published Kd values. 

Key value for chemical safety assessment

Other adsorption coefficients

Type:
log Kp (solids-water in sediment)
Value in L/kg:
2.96

Other adsorption coefficients

Type:
log Kp (solids-water in soil)
Value in L/kg:
1.81

Additional information

Partitioning in sediment

Published data:

Kd valuesof strontium in the sediment are available from five published and peer-reviewed studies raning from 13 to 108 L/kg (median). These data are used in a weight of evidence approach to determine a median sediment Kd value of 39 L/kg (geo. mean) as follows:

Table: Median Kd sediment-water values of different studies

Reference

Kd value (median)

Log Kd

Bunde et al. (1997)

53

1.72

Bunde et al. (1998)

39

1.59

Hemming et al. (1997)

13

1.10

Kaplan et al. (2000)

27

1.43

Liszewski et al. (2000)

108

2.03

 Median

39

1.59

Additionally, 2 Kd values for two different marine sediments were determined ranging from 35 to 164 L/kg with a median of 100 L/kg.

Geochemical background data

In the FOREGS-database, geochemical background concentrations are available for strontium in of stream water and sediment for EU-28 countries plus Norway. Data from sampling locations with similar coordinates were selected to match stream water with stream sediment samples. A total of 757 paired samples were analysed to derive the European-specific median value (50th percentile) of stream water/sediment Kd for strontium of 915 L/kg that is applied in the CSA.

The assessment of the partitioning of strontium in freshwater sediments media is based on Kp values derived from monitoring data for elemental strontium concentrations in water and corresponding sediments provided by the FOREGS Geochemical Baseline Mapping Programme that aimed to provide high quality, multi-purpose homogeneous environmental geochemical baseline data for Europe. A total of 745 paired samples, i.e. samples with the same coordinates for the sampling location of stream water (filtered to < 0.45 µm) and sediment (wet sieved in the field to <0.15 mm) were processed (Salminen et al. 2005) with results corresponding to steady-state conditions of Sr independent of Sr speciation.

Sampled stream water and sediments cover a wide range of environmental conditions. Water parameters such as pH, hardness and organic carbon concentrations cover several magnitudes. Strontium concentrations of sediments range from 31 mg/kg to 1352 mg/kg with a 50thand 90thpercentile of 122 mg/kg and 280 mg/kg, respectively, whereas dissolved strontium concentrations in the water column of European stream waters range from 0.1 µg/L to 13.6 mg/L with the 50thand 90thpercentiles amounting to 0.11 and 0.5 mg/L, respectively.

Partitioning in soil

Published data:

Reported Kd values from several published and peer-reviewed studies are available for the soil compartment. The results range from 27.5 to 310 L/kg (median). A weight of evidence approch resulted in an overall median soil Kd value of 65 L/kg that is applied in the CSA.

Table: Median Kd soil-water values of different studies

Reference

Kd value (median)

Log Kd

Bunzl and Schimmack (1989)

92

1.96

Kamei-Ishikawa et al (2008)

310

2.49

Twinning et al. (2004)

45

1.65

Wang and Staunton (2005)

27.5

1.44

Sheppard and Thibault (1990)

65

1.81

Median

65

1.81

Partitioning in stream water: Geochemical background data

Regarding the partitioning of strontium in the water column, stream water/sediment partition coefficients range from 38.64 L/kg to > 10000 L/kg. Since FOREGS sampled on a grid aiming to equally represent geochemical baseline concentrations across Europe, a European median log Kp value of 2.96 is derived for sediment-water partitioning.