3,5,5-trimethylhexanoic acid

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Remarks:

adsorption

Type of information:

calculation (if not (Q)SAR)

Adequacy of study:

key study

Study period:

2019

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Scientifically accepted estimation method

Reason / purpose for cross-reference:

other: log Pn input parameter for the calculation

Reason / purpose for cross-reference:

other: pKa input parameter for the calculation

Qualifier:

no guideline followed

Principles of method if other than guideline:

Calculation method determining the Koc for charged molecules according to Franco & Trapp (2008), Franco, Fu and Trapp (2009) and additional information via personal communication from A. Franco (2010).

GLP compliance:

no

Type of method:

other: calculation of log Koc for ionized molecule

Media:

soil

Radiolabelling:

no

Test temperature:

not applicable, calculation

Details on study design: HPLC method:

not applicable, calculation

Analytical monitoring:

not required

Details on sampling:

not applicable, calculation

Details on matrix:

not applicable, calculation

Details on test conditions:

not applicable, calculation

Computational methods:

The following input parameters were used for the calculation:
1. Test substance is an acid.

2. Octanol-water partition coefficient for the neutral molecule, Pn= Kow (neutral). This value was determined in a reliable study (OECD 117) at acidic pH (pH 3.0), such that nearly 100% of molecules were in the neutral, non-dissociated state.
log Kow (neutral) = logPn = 3.2

3. Dissociation constant
pKa was determined in a reliable study (OECD 112, titration method) to be 4.8.
pKa = 4.8

For further details, see IUCLID section "Any other information on materials and methods incl. tables".

Sample No.:

#1

Type:

Koc

Value:

79.5 L/kg

pH:

8

Temp.:

20 °C

Matrix:

Soil

Sample No.:

#2

Type:

Koc

Value:

92.9 L/kg

pH:

7

Temp.:

20 °C

Matrix:

Soil

Key result

Sample No.:

#5

Type:

Koc

Value:

122.9 L/kg

pH:

6.5

Temp.:

20 °C

Matrix:

Soil

Sample No.:

#3

Type:

Koc

Value:

200.6 L/kg

pH:

6

Temp.:

20 °C

Matrix:

Soil

Sample No.:

#4

Type:

Koc

Value:

620.4 L/kg

pH:

4.5

Temp.:

20 °C

Matrix:

Soil

Details on results (HPLC method):

not applicable, calculation

Statistics:

not applicable, calculation

Validity criteria fulfilled:

not applicable

Remarks:

estimation method

Conclusions:

The Koc for 3,5,5-trimethylhexanoic acid was estimated by calculation as a function of soil pH using the method of Franco, Fu and Trapp (2009), with the following results (OXEA, 2019):
pH 8.0: 79.5 L/kg
pH 7.0: 92.9 L/kg
pH 6.5: 122.9 L/kg
pH 6.0: 200.6 L/kg
pH 4.5: 620.4 L/kg

Executive summary:

The Koc for 3,5,5-trimethylhexanoic acid was estimated by calculation as a function of soil pH using the method of Franco, Fu and Trapp (2009).

The model considers as the main parameters governing adsorption the log Kow of the neutral compound (logPn = 3.2, determined experimentally) as well as the dissociation degree, characterized by pKa (4.8, determined experimentally) and the prevailing soil pH. As such, adsorption of a compound to soil is broken down into the sum of adsorption of the neutral species multiplied by the non-dissociated fraction and the adsorption of the ionized species multiplied by the dissociated (ionized) fraction at a given soil pH. The model allows calculation of Koc as a function of soil pH, with the following results obtained for 3,5,5-trimethylhexanoic acid (OXEA, 2019):

pH 8.0:               79.5 L/kg

pH 7.0:               92.9 L/kg

pH 6.5:               122.9 L/kg

pH 6.0:               200.6 L/kg

pH 4.5:               620.4 L/kg

For environmental exposure and risk assessment, the value of (rounded) 123 L/kg obtained for Koc at soil pH 6.5 is regarded to be most relevant, because European soils are predominantly of neutral to slightly acidic pH.

Description of key information

The Koc for 3,5,5-trimethylhexanoic acid was estimated by calculation as a function of soil pH using the method of Franco, Fu and Trapp (2009), with the following results (OXEA, 2019):

pH 8.0:       79.5 L/kg

pH 7.0:       92.9 L/kg

pH 6.5:       122.9 L/kg - key value for agricultural soils in Europe

pH 6.0:       200.6 L/kg

pH 4.5:       620.4 L/kg

Key value for chemical safety assessment

Koc at 20 °C:

123

Additional information

The Koc for 3,5,5-trimethylhexanoic acid was estimated by calculation as a function of soil pH using the method of Franco, Fu and Trapp (2009).

The model considers as the main parameters governing adsorption the log Kow of the neutral compound (logPn = 3.2, determined experimentally) as well as the dissociation degree, characterized by pKa (4.8, determined experimentally) and the prevailing soil pH. As such, adsorption of a compound to soil is broken down into the sum of adsorption of the neutral species multiplied by the non-dissociated fraction and the adsorption of the ionized species multiplied by the dissociated (ionized) fraction at a given soil pH. The model allows calculation of Koc as a function of soil pH, with the following results obtained for 3,5,5-trimethylhexanoic acid (OXEA, 2019):

 

pH 8.0:               79.5 L/kg

pH 7.0:               92.9 L/kg

pH 6.5:               122.9 L/kg

pH 6.0:               200.6 L/kg

pH 4.5:               620.4 L/kg

 

For environmental exposure and risk assessment, the value of (rounded) 123 L/kg obtained for Koc at soil pH 6.5 is regarded to be most relevant, because European soils are predominantly of neutral to slightly acidic pH.