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Environmental fate & pathways

Adsorption / desorption

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Reference
Endpoint:
adsorption / desorption, other
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
For details on endpoint specific justification please see read-across report in section 13 or find a link in cross-reference “assessment report”.
Reason / purpose for cross-reference:
assessment report
Reason / purpose for cross-reference:
read-across source
Media:
other:
Type:
Kd
Remarks:
#1
Value:
14
Temp.:
20 °C
Remarks on result:
other: L/kg
Type:
Kd
Remarks:
#2
Value:
714
Temp.:
20 °C
Remarks on result:
other: L/kg
Type:
Kd
Remarks:
#3
Value:
490
Temp.:
20 °C
Remarks on result:
other: L/kg
Type:
Kd
Remarks:
#4
Value:
134
Temp.:
20 °C
Remarks on result:
other: L/kg
Type:
Kd
Remarks:
#5
Value:
152
Temp.:
20 °C
Remarks on result:
other: L/kg
Adsorption and desorption constants:
See "any other information on results incl. tables", table 1
Concentration of test substance at end of adsorption equilibration period:
Please see table 2, section "Any other information on results including tables"!
Transformation products:
no
Details on results (Batch equilibrium method):
Results on read-across source substance HMD are directly applicable to target substance MPMD: Independently of molecular weight (which indeed is identical), for calculation of the distribution coefficient Kd, the ratio of (1) the amount of the substance adsorbed on the soil at adsorption equilibrium (µg/g) and (2) the mass concentration of the substance in the aqueous phase at adsorption equilibrium (µg/cm^3) is decisive.

Table 1: Determined adsorption constants for source substance HMD:


































Parameter



Unit



Soil I



Soil II



Soil III



Soil IV



Soil V



Kd_ads



[mL/g]



14



714



490



134



152



Koc_ads



[mL/g]



2‘023



43‘004



12‘164



11‘253



14‘754




While Koc-values are given, calculated adsorption and desorption distribution coefficients were independent of the organic carbon content. Therefore, any environmental fate assessment should preferably be based on Kd_ads or Kd_des values.


 


Table 2: Kinetics test: Distribution of source substance HMD between the aqueous phase and soil after 48 hours of adsorption at the soil/solution ratio of 4/100 or 1/100. Each sample contained 179 µg HMD



























































































































































































Soil



Sample



Ratio



m



Vo



m(ads)s



m(ads)aq



Kd_ ads



Kd· ratio



KOC_ ads



[g]



[mL]



[µg]



[µg]



[mL/g]



 



[mL/g]



Soil I
Speyer 2.1



Sample A



4:100



4



100



60.65



118.22



13



1



1'894



Sample B



4



100



65.85



113.02



15



1



2'151



Mean



 



 



63.25



115.62



14



1



2'023



Soil II
Speyer 6S



Sample A



1:100



1



100



156.17



22.70



716



7



43'145



Sample B



1



100



156.04



22.83



712



7



42'863



Mean



 



 



156.10



22.76



714



7



43'004



Soil III
Empingham



Sample A



1:100



1



100



147.95



30.91



486



5



12'070



Sample B



1



100



148.34



30.52



494



5



12'257



Mean



 



 



148.15



30.72



490



5



12'164



Soil IV
Mechtildshausen



Sample A



1:100



1



100



100.35



78.52



134



1



11'255



Sample B



1



100



100.33



78.54



134



1



11'250



Mean



 



 



100.34



78.53



134



1



11'253



Soil V
River Sediment



Sample A



1:100



1



100



104.19



74.68



141



1



13'657



Sample B



1



100



110.58



68.29



163



2



15'852



Mean



 



 



107.39



71.48



152



2



14'754



 


Table 3: Stability of read-across source substance HMD in 0.01 M CaCl2 solution during the experiment at an initial test item concentration of about 1.8 mg/L


 
































































Control
% of initial



Adsorption time (hours)



2



5



24



48



52



72



96



168



Glas



 



 



 



 



 



 



 



 



Sample A



102.5



92.4



100.6



97.3



101.2



95.2



92.2



104.7



Sample B



98.2



99.6



98.9



97.2



94.3



98.2



98.7



101.1



Mean



100.4



96.0



99.8



97.2



97.8



96.7



95.5



102.9


Validity criteria fulfilled:
yes
Conclusions:
A Batch Equilibrium test (according to OECD 106, compliant to GLP; 2013) was performed using the following soil and sediment types:
Speyer 2.1 (soil I, sand), Speyer 6S (soil II, clay), Empingham (soil III, clay loam), Mechtildshausen (soil IV, loam) and sediment of the River Rhine (soil V, sandy loam).
The following results were obtained for the source substance 1,6-hexane diamine (HMD; CAS No. 124-09-4):
Sorption was strongest to the clay soil (soil II) and weakest to the sand soil (soil I). With the exception of the river sediment (Soil V), sorption increased with increasing clay content. No correlation of sorption and the soil properties pH value, cation exchange capacity and organic carbon content was observed. The sorbed fraction of analyte increased with the amount of soil used in the batch systems. Apparent equilibrium distribution was reached within 48h. Accordingly, the adsorption coefficients (Kd) were calculated after 48h of adsorption:

Kd range soil: 14 (soil I) to 714 (soil II) L/kg; average Kd: 338 L/kg (log Kd: 2.53); corresponding to average log Koc = 4.23 (based on a default OC content of soil of 2% according to ECHA guidance document R.16);
Kd sediment: Kd = 152 L/kg (log Kd: 2.18); corresponding to log Koc = 3.18 (based on a default OC content of suspended matter of 10% according to ECHA guidance document R.16);

The calculated adsorption and desorption distribution coefficients were independent of the organic carbon content. Therefore, any environmental fate assessment should preferably be based on Kd_ads values.
Executive summary:

The study used as source investigated the distribution coefficients for adsorption (Kd) for four soils and one sediment according to OECD TG 106 (Batch Equilibrium Test; 2000).


The study results of the source compound were considered applicable to the target compound. No adaption of results obtained on the source substance to the target substance were required: independently of molecular weight (which indeed is identical), for calculation of the distribution coefficient Kd, the ratio of (1) the amount of the substance adsorbed on the soil at adsorption equilibrium (µg/g) and (2) the mass concentration of the substance in the aqueous phase at adsorption equilibrium (µg/cm^3) is decisive. The Justification and applicability of the read-across approach (structural analogue) is outlined in the read-across report in section 13 or find a link in cross-reference “assessment report”.

Description of key information

A Batch Equilibrium test (according to OECD 106, compliant to GLP; 2013) was performed using the following soil and sediment types:
Speyer 2.1 (soil I, sand), Speyer 6S (soil II, clay), Empingham (soil III, clay loam), Mechtildshausen (soil IV, loam) and sediment of the River Rhine (soil V, sandy loam).
The following results were obtained for the source substance 1,6-hexane diamine (HMD; CAS No. 124-09-4):
Sorption was strongest to the clay soil (soil II) and weakest to the sand soil (soil I). With the exception of the river sediment (Soil V), sorption increased with increasing clay content. No correlation of sorption and the soil properties pH value, cation exchange capacity and organic carbon content was observed. The sorbed fraction of analyte increased with the amount of soil used in the batch systems. Apparent equilibrium distribution was reached within 48h. Accordingly, the adsorption coefficients (Kd) were calculated after 48h of adsorption:


Kd range soil: 14 (soil I) to 714 (soil II) L/kg; average Kd: 338 L/kg (log Kd: 2.53); corresponding to average log Koc = 4.23 (based on a default OC content of soil of 2% according to ECHA guidance document R.16);
Kd sediment: Kd = 152 L/kg (log Kd: 2.18); corresponding to log Koc = 3.18 (based on a default OC content of suspended matter of 10% according to ECHA guidance document R.16);


The calculated adsorption and desorption distribution coefficients were independent of the organic carbon content. Therefore, any environmental fate assessment should preferably be based on Kd_ads values.

Key value for chemical safety assessment

Other adsorption coefficients

Type:
log Kp (solids-water in effluent sewage sludge)
Value in L/kg:
2.18
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in activated sewage sludge)
Value in L/kg:
2.18
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in settled sewage sludge)
Value in L/kg:
2.18
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in raw sewage sludge)
Value in L/kg:
2.18
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in suspended matter)
Value in L/kg:
2.18
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in soil)
Value in L/kg:
2.53
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in sediment)
Value in L/kg:
2.18
at the temperature of:
20 °C

Additional information

The study used as source investigated the distribution coefficients for adsorption (Kd) for four soils and one sediment according to OECD TG 106 (Batch Equilibrium Test; 2000). The following results were obtained:
























Para-meter



Unit



Soil I



Soil II



Soil III



Soil IV



Sed (soil V)



Kd



[mL/g]



14



 


714


 

490



134



152



 


The following values are used for risk assessment:


Soil: (arithmetic mean over all four soils) Kd: 338 L/kg (log Kd: 2.53);


Sediment: Kd = 152 L/kg (log Kd: 2.18).


Indicative Koc values can be calculated from the Kd values, following Gustafson (1989; Groundwater ubiquity score: A simple method for assessing pesticide leachability; Environmental Toxicology and Chemistry, 8, 339-357): mean Kd for soil is divided by the generic organic carbon content of European soils as given in REACH guidance R. 16 (weight fraction organic carbon in soil solids = 2%). Proceeding the same way for sediment (division of Kd by generic weight fraction organic carbon in suspended matter of 10% as given in R.16 - for local assessment of sediment suspended matter is used instead of sediment according to R.16 and EUSES / ECETOC TRA), the following indicative log Koc value can be derived from the Kd value:


 


Soil (average):  log Koc = 4.23;


Sediment:         log Koc = 3.18.


 


The study results of the source compound were considered applicable to the target compound. No adaption of results obtained on the source substance to the target substance were required: independently of molecular weight (which indeed is identical), for calculation of the distribution coefficient Kd, the ratio of (1) the amount of the substance adsorbed on the soil at adsorption equilibrium (µg/g) and (2) the mass concentration of the substance in the aqueous phase at adsorption equilibrium (µg/cm^3) is decisive. The Justification and applicability of the read-across approach (structural analogue) is outlined in the read-across report in IUCLID section 13.