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Environmental fate & pathways

Adsorption / desorption

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Reference
Endpoint:
adsorption / desorption
Remarks:
adsorption
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
REPORTING FORMAT FOR THE ANALOGUE APPROACH

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
This read-across is based on the hypothesis that source and target substances have similar toxicological properties because
• they are manufactured from similar or identical precursors under similar conditions
• they share structural similarities with common functional groups: quaternary ammonium and saturated or unsaturated alkyl chains with comparable length (corresponding to scenario 2 of the read-across assessment framework)

The read-across hypothesis is based on structural similarity of target and source substances. Based on available experimental data, including key physicochemical properties and data from acute toxicity, irritation, sensitization (human) and genotoxicity studies, the read-across strategy is supported by a quite similar toxicological profile of all substances.

Therefore, read-across from the existing ecotoxicity, environmental fate and toxicity studies conducted with the source substances is considered as an appropriate adaptation to the standard information requirements of the REACH Regulation for the target substance, in accordance with the provisions of Annex XI, 1.5 of the REACH Regulation.

A justification for read-across is attached to IUCLID section 13.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
See justification for read-across attached to IUCLID section 13.

3. ANALOGUE APPROACH JUSTIFICATION
See justification for read-across attached to IUCLID section 13.

4. DATA MATRIX
See justification for read-across attached to IUCLID section 13.
Reason / purpose:
read-across source
Reason / purpose:
read-across source
Reason / purpose:
read-across: supporting information
Media:
sediment
Phase system:
solids-water in soil
Type:
Kp
Value:
10 000 L/kg
Phase system:
solids-water in sediment
Type:
Kp
Value:
10 000 L/kg
Phase system:
solids-water in suspended matter
Type:
Kp
Value:
16 800 L/kg
Transformation products:
not specified
Details on results (Batch equilibrium method):
Adsorption of long-chain QAC’s to EPA and river sediments was extensive relative to other organic chemicals such as polyaromatic hydrocarbons, substituted polycyclic compounds, and different detergent chemicals (Table 2). Equilibrium adsorption coefficients (Kd) for the three QAC’s tested were considerably higher than values for the other chemicals surveyed, with the relative strength of binding decreasing in the order STAC>CTAB>DSDMAC. Adsorption coefficients for the strongest binding QAC (STAC) to river sediments were comparable to values determined for raw wastewater solids and activated sludge and desorption experiments indicated that strong binding of this material occurred to both organic and inorganic particulate matter. Kinetic studies also indicated that adsorption was rapid, reaching equilibrium values within a few hours. In general, the QAC’s that were tested had a high affinity for particulate matter and were capable of strongly binding to a variety of environmentally relevant sorbents.
Statistics:
No details given
Validity criteria fulfilled:
not specified
Conclusions:
In the following exposure assessment, a value of 10,000 l/kg dw is chosen for both Kpsed and Kpsoil.
With an assumed Kpsusp of 10,000 l/kg and a concentration of 15 mg suspended matter per litre river water, about 87% of the DHTDMAC would remain in the water phase. In river water on average 27% of the DHTDMAC is adsorbed onto suspended matter (average concentration 22 mg/l). From these values, the Kpsusp is calculated to 16,800 l/kg. As the latter value has a better empirical basis, it is used in the exposure calculation.

Description of key information

Key value for chemical safety assessment

Koc at 20 °C:
10 000

Other adsorption coefficients

Type:
log Kp (solids-water in soil)
Value in L/kg:
4
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in sediment)
Value in L/kg:
4
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in suspended matter)
Value in L/kg:
4.22
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in raw sewage sludge)
Value in L/kg:
2.48
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in settled sewage sludge)
Value in L/kg:
2.48
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in activated sewage sludge)
Value in L/kg:
2.48
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in effluent sewage sludge)
Value in L/kg:
2.48
at the temperature of:
20 °C

Additional information

No experimental data are available for the target substance Di-C12-18 alkyldimethyl ammonium chloride. Based on structural similarities, a read-across from DODMAC and DHTDMAC is considered to be appropriate. A justification for read-across is attached to IUCLDI section 13.

 

Adsorption of quaternary ammonium compounds seems (QAC) to occur mainly by an ion-exchange mechanism and depends on cation-exchange capacity of the sorbent and variety of other parameters. An estimation of Koc using using EpiSuite v4.11, KOCWIN v2.00 is not reliable, since the training set for the Koc estimation of this program did not include any QACs. Therefore, the Koc estimate is outside the program's prediction domain.

 

DHTDMAC adsorbs onto both the mineral and the organic fraction of soil and sediments. Kappeler (1982) found that on average 27% of the DHTDMAC in river water is adsorbed onto suspended matter (mean 22 mg/L suspended solids). The Kpsusp is calculated to 16,800 L/kg from these values.

This demonstrates that DHTDMAC can be bound very strongly by some minerals, while in others relatively small distribution constants were estimated. Under environmental conditions, the sorption properties of DHTDMAC probably vary in a wide range depending on the nature of the adsorbant.

 

For exposure assessment purpose, a value of 10,000 L/kg dw is chosen for both Kpsed and Kpsoil.

With an assumed Kpsusp of 10,000 l/kg and a concentration of 15 mg suspended matter per litre river water, about 87% of the DHTDMAC would remain in the water phase. Kappeler (1982) found that in river water on average 27% of the DHTDMAC is adsorbed onto suspended matter (average concentration 22 mg/L). From these values, the Kpsusp is calculated to 16,800 L/kg. As the latter value has a better empirical basis, it is used in the exposure calculation.

[LogKoc: 4.0]