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Environmental fate & pathways

Adsorption / desorption

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Reference
Endpoint:
adsorption / desorption
Remarks:
adsorption
Type of information:
calculation (if not (Q)SAR)
Remarks:
Migrated phrase: estimated by calculation
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
accepted calculation method
Qualifier:
no guideline followed
Principles of method if other than guideline:
An expert assessment was performed in order to determine the environmental adsorption of the substance. This assessment is based on EPI Suite and expert judgement.
GLP compliance:
no
Type of method:
other: An expert assessment was performed in order to determine the environmental adsorption of the substance.
Media:
other: soil, sediment and organic matter
Key result
Type:
log Koc
Value:
>= 1.5 - <= 2 dimensionless
Remarks on result:
other: Estimated using EPIsuite modelling system

Methods and results

The model was run for the three components, using in the first case measured water solubility and partition coefficient data for BPA 2EO and in the second case, letting the model estimate these endpoints from the structure alone. 

 

The physical properties (melting points, boiling point and vapour pressure) were entered manually in each case as the modelled data (suggestion solid form) was clearly incorrect.

 

Log Koc is estimated by two methods within the model; the MCI method (Molecular Connectivity Index) that looks at the functional groups of the substance and their interaction and the Kow method that uses the partition coefficient as a starting point. The Koc determined from the structure of the substance (MCI method) is not influenced by the user-input partition coefficient and will therefore be the same with or without the measured Kow.

 

Table 1

Results based on measured physico-chemical properties for BPA 2EO

 

 

BPA 2EO

Measured

BPA 1EO

Modelled

BPA 2EO

Modelled

BPA 3EO

Modelled

Melting point

- 20 C

 

-

 

Boiling point

350 C

 

-

 

Vapour pressure

< 0.00036 Pa

 

-

 

Water solubility

440 mg/L

1420 mg/L

-

385 mg/L

Log Kow

2.7

4.18

-

3.88

Log Koc

(MCI method)

-

3.8

3.2

3.1

Log Koc

 (Kow method)

-

2.0

1.6

1.5

 

Table 2

Results based on estimated water solubility / Log Kow properties for BPA 2EO

 

 

BPA 2EO

Measured

BPA 1EO

Modelled

BPA 2EO

Modelled

BPA 3EO

Modelled

Melting point

- 20 C

 

-

 

Boiling point

350 C

 

-

 

Vapour pressure

< 0.00036 Pa

 

-

 

Water solubility

-

54 mg/L

18 mg/L

9.0 mg/L

Log Kow

-

4.18

4.16

3.88

Log Koc

(MCI method)

-

3.8

3.2

3.1

Log Koc

 (Kow method)

-

2.8

2.4

2.2

 

 

Discussion

By running the model with and without user-input data, it is apparent that using structural activity only as a basis for estimation will result in an estimated lower water solubility and subsequently higher adsorption coefficient. However, even with the structure modelling alone (without user input data), the estimates based on Kow are significantly lower than those estimated by MCI. 

 

It is very likely that this modelling suite is estimating a higher Koc than is likely if measured. The estimated Kow in Table 2 for BPA 2EO is significantly higher than the measure Kow.

 

It is therefore proposed to report a Log Koc in the range of 1.5 – 2.0 obtained using the Kow Calculation and based on the user input water solubility and partition coefficient data.

Validity criteria fulfilled:
not applicable
Conclusions:
The assessment demonstrated a log Koc in the range of 1.5 – 2.0 based on the results modelled using the user-input water solubility and partition coefficient data. The Log Koc was calculated using the Kow method within the KCOWIN model of the EPIsuite modelling system. The substance is therefore expected to be weakly adsorbed to soils, sediments and organic matter.
Executive summary:

Bisphenol A ethoxylated with 2 moles Ethylene Oxide (BPA 2EO) has been assessed for the potential to adsorb to soils, sediments and organic matter in the environment. Due to the nature of the substance and from experience with the partition coefficient, obtaining an accurate figure from laboratory testing is likely to be difficult.

It is therefore considered acceptable to perform an assessment using EPISuite, which is a validated modelling system, to indicate the approximate adsorption potential for the substance.

Although it is expected that the substance will typically comprise of 2EO, it is likely to contain some traces of 1EO and 3EO; these have been assessed using the same model to provide an indication of the range of probable figures.

From the results of this assessment, with a Log Koc in the range of 1.5 – 2.0, the substance will be weakly adsorbed to soils, sediments and organic matter. 

Description of key information

The assessment demonstrated a log Koc in the range of 1.5 – 2.0 based on the results modelled using the user-input water solubility and partition coefficient data. The substance is expected to be weakly adsorbed to soils, sediments and organic matter.

Key value for chemical safety assessment

Koc at 20 °C:
100

Additional information

An assessment was conducted to determine the adsorption potential of the substance. The adsorption coefficient was estimated using the KOCWIN model, included in the EPIsuite modelling system. It was considered difficult to obtain an accurate figure from laboratory testing owing to the partition coefficient, and nature of the substance. The EPIsuite modelling system is a validated method for estimating selected physicochemical properties of substances. The adsorption coefficient (Koc) was estimated using the KOCWIN model included in the suite. The Log Koc was estimated by two methods within the model; the Molecular Connectivity Index (MCI) method that looks at the functional groups of the substance and their interaction, and the Kow method which uses the partition coefficient as a starting point. The assessment demonstrated a Log Koc in the range of 1.5 – 2.0 based on the results modelled using the user-input water solubility and partition coefficient data. The Log Koc was calculated using the Kow method within the KCOWIN model of the EPIsuite modelling system. The substance is therefore expected to be weakly adsorbed to soils, sediments and organic matter.

[LogKoc: 2.0]