Phthalic anhydride

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Reason / purpose for cross-reference:

read-across: supporting information

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)

Principles of method if other than guideline:

Method: other (measurement): modified OECD-Guideline 106

GLP compliance:

no

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

no

Analytical monitoring:

yes

Matrix no.:

#1

Matrix type:

Podzol

% Clay:

2.6

% Silt:

8.2

% Sand:

89.2

% Org. carbon:

4.85

pH:

2.8

CEC:

15.1 meq/100 g soil d.w.

Matrix no.:

#2

Matrix type:

Alfisol

% Clay:

15.9

% Silt:

14.4

% Sand:

69.7

% Org. carbon:

1.25

pH:

6.7

CEC:

12.3 meq/100 g soil d.w.

Matrix no.:

#3

Matrix type:

other: Sediment

% Clay:

35.7

% Silt:

58.8

% Sand:

5.5

% Org. carbon:

1.58

pH:

7.1

CEC:

13.4 meq/100 g soil d.w.

Details on matrix:

PROPERTIES

1.- Soil texture: Prodzol
- Carbonate as CaCO3:0

2.- Soil texture: Alfisol
- Carbonate as CaCO3:0.4

3.- Soil texture: Sediment
- Carbonate as CaCO3:38.9

Type:

Koc

Value:

31 dimensionless

Remarks on result:

other: Podzol

Type:

Koc

Value:

2 dimensionless

Remarks on result:

other: Alfisol (agricultural soil)

Type:

Koc

Value:

2 dimensionless

Remarks on result:

other: sediment (Lake Constance)

Transformation products:

not measured

 The sorption equilibrium was reached within 16 hours.
 The mass balance  resulted in a recovery of > 80 %.

Sorption coefficient Koc determined for different soils:

- Podzol : 31
- Alfisol (agricultural soil): 2
- sediment (Lake Constance) : 2

Executive summary:

Von Oepen (1991) investigated the sorption capacity of three different soils by batch equilibrium studies for phthalic acid similar to the OECD TG 106 . The soils used for testing were an acidic forest soil, an agricultural soil and a sublimnic soil. The sorption equilibrium was reached within 16 hours. Sorption coefficients between 2 and 31 were determined (Von Oepen, 1991).

Description of key information

The highest measured Koc value of 31 of the hydrolysis product phthalic acid is used to describe the adsorption potential of phthalic anhydride (Von Oepen, 1991).

Key value for chemical safety assessment

Koc at 20 °C:

31

Additional information

During the ICCA HPV Chemicals Initiative, the distribution of phthalic 
anhydride and the hydrolysis product phthalic acid between the organic 
phase of soil or sediments and the porewater was calculated by using 
QSAR with the PCKOC program (v 1.66). A Koc of 11 for phthalic anhydride
(Bayer Industry Services, 2004a) and of 73 for phthalic acid was calculated.
 As any decomposition of the substance in water (e.g. due to hydrolysis,
 photolysis) is not taken into account by the program, 
the value for phthalic anhydride is only of theoretical intrest.
 As estimations methods for Koc are not appropriate for ionisable 
substances, the value for phthalic acid is also only of theoretical intrest. 
Phthalic acid is a weak dibasic acid whose pka1 is 2.76 and pKa2 is 5.43 at 25°C,
 indicating that the substance exists predominately in its dissociated 
form at environmentally relevant pH. This property is not incorporated
 by the program. 
Von Oepen (1991) investigated the sorption capacity of three different 
soils by batch equilibrium studies for the hydrolysis product phthalic acid 
similar to the OECD TG 106. The soils used for testing were an 
acidic forest soil, an agricultural soil and a sublimnic soil. 
The sorption equilibrium was reached within 16 hours. 
Sorption coefficients between 2 and 31 were determined. 
The experimental Koc values suggest that phthalic acid has a high
mobility in soil.