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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Adsorption of Chromium (III) is stronger in alkaline conditions.  There are no proprietary studies investigating the adsorption/desorption of the substance. The estimation methods given in the main Technical Guidance document for determining adsorption coefficients for soil, sediment and suspended sediment are not applicable to chromium compounds. Measured values are avaiolable in the EU RAR for a number of soil and sediment types. 
In general, Chromium (III) is more strongly absorbed than Chromium (VI). Adsorption is pH dependant. Adsorption of Chromium (III) is stronger in alkaline conditions.

Key value for chemical safety assessment

Additional information

Discussion of adsorption coefficients for chromium

The table below summarises the published values for Kpwater-solids for both freshwater and marine environments. The values are reported according to a variety of methods and may not be directly comparable; however, they do give a general indication of the partitioning of chromium (VI) in the environment relative to that of total chromium and/or chromium (III) for several environmental compartments. In general, chromium (III) is more likely to partition to solids in the sediment and soil.

Summary of measured partition coefficients (Kp) for chromium

Phase

Kp (l/kg)

Comments

Reference

Total Cr

Cr(VI)

Cr(III)

Suspended sediment partition coefficients

Kpsusp

250-50,000

25,000-800,000

Freshwater and saltwater
 Netherlands estimate

Braunschweiler et al. (1996)

126,000-786,000
median 290,000

Freshwater, based on routine water quality data from The Netherlands

Van Der Kooij et al. (1991)

30,100-1,059,600; mean 322,400

Freshwater River suspended sediments, United States - based on monitoring data

Young et al. (1987)

324,000

Saltwater (0.1-0.5‰), based on routine water quality data from The Netherlands

Van Der Kooij et al. (1991)

306,000-320,000

Saltwater (1-5‰), based on routine water quality data from The Netherlands

228,000

Saltwater (>10‰), based on routine water quality data from The Netherlands

140,000-570,000

Freshwater (Rhine-Meuse delta)

Golimowski et al. (1990)

29,200-200,000

Saltwater (Tyrrhenian Sea), silty-clay sediment, organic carbon content 1.6%, salinity 3.8‰, pH 8.2-8.3.

Ciceri et al. (1992)

Sediment-water partition coefficients

Kpsed

940a

34,000

Saltwater, organic matter content ~2%, pH 7.8-8.0

Wang et al. (1997)

2,300a

Saltwater, organic matter content ~10%, pH 7.8-8.0

25,600-32,800

Freshwater, pH 8.3, organic carbon content 2.65%

Young et al. (1987)

60-44,800; mean 7,100

Freshwater River sediments, United States -based on monitoring data

11,000

Freshwater, pH=4.5

Young et al. (1992)

120,000

Freshwater, pH >6

Soil-water partition coefficients

Kpsoil

524-24,217

Dutch field soils, pH~3.8-7.9; 2-21.8% organic matter

Janssen et al. (1997)

13-40

298-788

Loam; pH 6; 1.92% organic carbon

Hassan and Garrison (1996)

1-6.1

2,823-15,382

Loam; pH >6; 1.92% organic carbon

45.4-52.3

Loess; pH6; 0.11% organic carbon

1.5-12.1

19,716-55,918

Loess; pH>6; 0.11% organic carbon

17-44.6

330-27,151

Clay; pH7; 3.75% organic carbon

1.4-2.0

Clay; pH>7; 3.75% organic carbon

0.35-17.4b

12-27

Sand, pH 4-8

Pérez et al. (1988)

21-197

Sandy soil, pH 4-8, 0.77% organic matter

6.6-18.4b

116-608

Sandy loam, pH 4-8, 1.62% organic matter

Chromium (III) appears to be strongly adsorbed to soils and sediments. The adsorption of chromium (III) onto soil follows the pattern typical of cationic metals and increases with increasing pH (lowering pH results in increased protonation of the adsorbent leading to fewer adsorption sites for the cationic metal) and the organic matter content of the soil and decreases when other competing (metal) cations are present. Certain dissolved organic ligands may also reduce the adsorption of chromium (III) to the solid phase by forming complexes which enhance the solubility of chromium (III) in the aqueous phase. Based on the available measured values for the adsorption coefficients the values indicated below will be used in the risk assessment. These values are not taken directly from specific tests, but have been chosen by the Rapporteur to be representative for acidic-neutral and neutral-alkaline environments. The values do not correspond to any specific individual test results, nor are they derived statistically from the available data (since these are insufficient to allow meaningful values to be derived). Instead they were selected by inspection of the data to reflect the available information under the two sets of conditions and to reflect the differences between these. Acid-neutral environments are considered to be those at pH 5 and below; neutral-alkaline environments are taken to be those at pH 6 and above.

Chromium (III)                      Acid conditions                           Alkaline conditions

                                               Kpsusp = 30,000 l/kg                   Kpsusp = 300,000 l/kg

                                               Kpsed = 11,000 l/kg                     Kpsed = 120,000 l/kg

                                               Kpsoil = 800 l/kg                          Kpsoil = 15,000 l/kg

The equivalent values for the dimensionless form of the partition coefficient using the methods given in the Technical Guidance document are:

Chromium (III)                     Acid conditions                                 Alkaline conditions

                                               Ksusp-water = 7,500 m3/m3       Ksusp-water = 75,000 m3/m3

                                               Ksed-water = 5,500 m3/m3         Ksed-water = 60,000 m3/m3

                                               Ksoil-water = 1,200 m3/m3          Ksoil-water = 22,500 m3/m3

Cr(VI) data are also retrieved from the EU RAR(2005) and reported in the CSR.