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[14C]-C22 ATQ Adsorption Desorption test according OECD 106

Cationic surfactants do not only sorb via van der Waal forces but also by ionic interactions (e.g ion pair formation, cation exchange). So far no mechanistic model exists to estimate the sorption behaviour of these substances. Therefore measurements are warranted to address the sorption to solid phases reliably. Sorption was measured in three different soils, one sediment and one secondary sludge. The Freundlich isotherms for the different matrices are non-linear (1/n < 1). As the lowest tested concentration is used for the exposure assessment Table 5.4-1 below lists the Kd and Koc at that concentration which allows to judge the sorption behaviour without a calculation excerise using the Freundlich isotherm.

  

Table 5.4       Sorption behaviour of [14C]-C22 ATQ to different solid matrices

 

  

SOIL

 

% OC

 

% Clay

 

CEC
(Meq/100g)

Kd (L/kg)
lowest conc.
Measured

 

Koc (L/kg)
lowest conc.
Measured

Cranfield 164

 

3.7

 

28

 

22.8

2028

 

 

 

 

3.7

 

28

 

22.8

1856

 

 

Cranfield 277

 

2.7

 

57

 

8.3

12326

 

 

 

 

2.7

 

37

 

8.3

17013

 

 

Cranfield 299

 

2.9

 

26

 

14.9

3670

 

 

 

 

2.9

 

26

 

14.9

5295

 

 

mean

 

3.1

 

34

 

15.3

7031

 

226807

median

 

2.9

 

28

 

14.9

4483

 

154569

SEDIMENT

 

 

 

 

 

 

 

 

 

SW

 

11.1

 

35

 

47.3

1178

 

 

 

 

11.1

 

35

 

47.3

2449

 

 

mean

 

11.1

 

35

 

47.3

1814

 

29250

SLUDGE

 

 

 

 

 

 

 

 

 

secondary (activated)

 

39.0

 

64

 

129

267

 

 

 

 

39.0

 

64

 

129

281

 

 

mean

 

39.0

 

64

 

129

274

 

731

 

 The Koc values from the OECD 106 study were used in the Environmental exposure assessment of C20/22 ATQ carried out with the EUSES model. As EUSES assigns certain percentages of organic carbon (OC) to the different compartments, Kd values for EUSES were calculate from the available Koc as given in the table 5.4-2

  

Table 5.4-2    Recalculation of Sorption constants for C22 ATQ to values which can be used in the EUSES Exposure assessment

 

 

OECD106 results

at 10 µg/L HYEQS

EUSES STANDARD VALUES %OC

and Kd related to Koc

SOIL

 

 

 

 

 

 

% OC

Koc (L/kg) average
lowest conc.
Measured

% OC
EUSES

Kd (L/kg) EUSES
based on EUSES OC

EUSES Term for
Compartment

Cranfield 164

3.7

52486

 

 

 

Cranfield 277

2.7

543315

 

 

 

Cranfield 299

2.9

309138

 

 

 

mean

3.1

226807

2

4536

SOIL

SEDIMENT

 

 

 

 

 

SW

11.1

29258

5

1463

SEDIMENT

SLUDGE

 

 

 

 

 

secondary (activated)

39.9

731

37

270

ACTIV. SLUDGE

 

  

Henry’s Law Constant (HLC)

The HLC of C20/22 ATQ can be calculated from vapour pressure (IUCLID Section 4.6) water solubility (IUCLID Section 4.8). The Exposure assessment tool EUSES 2.1 recalculates the HLC of 3.6*E-3 Pa*m3*mol-1at 25 degree C to 1.7*E-3 Pa*m3*mol-1at the environmental temperature of 12 degree C. The dimensionless air-water partitioning coefficient is calculated to 7.4*E-7 m3/m3. The HLC shows that volatilisation of C20/22 ATQ from aqueous solutions is very low.

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