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OECD 106 14C-HYEQS Adsorption Desorption test

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 primary as well as 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 below lists the Kdand Kocat that concentration which allows to judge the sorption behaviour without a calculation excerise using the Freundlich isotherm.

 

Table 5.4       Sorption behaviour of HYEQS 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   22.8 474    
    3.7   28   22.8 459    
Cranfield 277   2.7   57   8.3 6685    
    2.7   37   8.3 7081    
Cranfield 299   2.9   26   14.9 3875    
    2.9   26   14.9 4092    
mean   3.1   34   15.3 3778   121860
median   2.9   28   14.9 3875   133621
                   
SEDIMENT                  
SW   11.1   35   47.3 4529    
    11.1   35   47.3 4618    
mean   11.1   35   47.3 4574   41203
                   
SLUDGE                  
primary   47.1   54   147 1933    
    47.1   54   147 1850    
mean   47.1   54   147 1892   4016
                   
secondary (activated)   39.0   64   129 1420    
    39.0   64   129 1368    
mean   39.0   64   129 1394   3574

The Koc values from the OECD 106 study were used in the Environmental exposure assessment of HYEQS carried out with the EUSES model. As EUSES assigns certain OC % values to the different compartments Kd values for EUSES were calculate from the available Koc as given in the table below.

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 12608      
Cranfield 277 2.7 254926      
Cranfield 299 2.9 137362      
mean 3.0 132580 2 2535 SOIL
           
SEDIMENT          
SW 11.1 41203 5 2060 SEDIMENT
           
SLUDGE          
primary 47.1 4016 30 1205 RAW SEWAGE
     
secondary (activated) 39.9 3574 37 1322 ACTIV. SLUDGE

Henry’s Law Constant (HLC)

The HLC of HYEQS 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*10-4Pa*m3*mol-1at 25 degree C to 1.5*10 -4 Pa*m3*mol-1at the environmental temperature of 12 degree C. The dimensionless air-water partitioning coefficient is calculated to 6.2*10-8 m3/m3. The HLC shows that volatilisation of HYEQS from aqueous solutions is very low.