Lactic acid

Partition coefficient

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

partition coefficient

Type of information:

other: Literature review

Adequacy of study:

supporting study

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Extrapolation from literature data; documentation of the methodology in the original references is scarce, complicating proper assessment of the reliability. Therefore, a Klimisch score of 4 is assigned. Nevertheless, in view of the overall consistency of the reported results the data can be used in a weight-of-evidence approach.

Qualifier:

no guideline required

Principles of method if other than guideline:

Extrapolation from literature data.

GLP compliance:

no

Type of method:

other: Extrapolation of literature data

Partition coefficient type:

octanol-water

Specific details on test material used for the study:

Lactic acid (CAS 50-21-5), i.e. the racemic mixture, was considered in this literature review. D-(-)-lactic acid is one of two possible enantiomers. Enantiomers are totally equivalent regarding physicochemical properties hence "read-across" from the racemic mixture (CAS 50-21-5) to the target molecule D-(-)-lactic acid is not restricted.

Type:

log Pow

Partition coefficient:

>= -0.72 - <= -0.62

Temp.:

20 °C

Remarks on result:

other: Range of values from the publications reviewed

Conclusions:

The log Kow of lactic acid as cited in the reviewed publications ranges between - 0.72 and - 0.62.

Executive summary:

An overview is given of literature data (measured values) for the log Kow of lactic acid. The reported values consistently range between -0.72 and -0.62. However, documentation of the methodology in the original references is scarce, complicating assessment of the reliability of the individual sources.

Reference 2

Endpoint:

partition coefficient

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Justification for type of information:

For details and justification of read-across please refer to the read-across report attached to IUCLID section 13.

Reason / purpose for cross-reference:

read-across source

GLP compliance:

no

Type:

log Pow

Partition coefficient:

-0.65

Temp.:

20 °C

Remarks on result:

other: QSAR calculation

Details on results:

The n-octonal/water coefficient is given in the EPIWIN modeling 1) of the EPA. The log KOW calculated within the KOWWIN module is –0.65.

Conclusions:

The log octanol-water partition coefficient of lactic acid, calculated by a QSAR method (KOWWin, EpiSuite), is -0.65.

Executive summary:

The log octanol-water partition coefficient of lactic acid, calculated by a QSAR method (KOWWin, EpiSuite), is -0.65.

In support of this calculation, publicly available values for lactic acid are quoted in the expert statement:

European HPV programme: logP_ow= -0.62

IPCS International program on Chemical Safety: logP_ow= -0.6

This information is used in a read-across approach in the assessment of the target substance.

For details and justification of read-across please refer to the attached report in section 13 of IUCLID.

Reference 3

Endpoint:

partition coefficient

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

For details and justification of read-across please refer to the read-across report attached to IUCLID section 13.

Reason / purpose for cross-reference:

read-across source

Key result

Type:

log Pow

Partition coefficient:

ca. -0.54

Temp.:

25 °C

pH:

7

It was found that n-octanol influences the enzyme reaction and that the tested UV-Vis spectrophotometric method involving enzymatic reactions is not a suitable method to determine the test substance concentration in samples taken from the partition coefficient (shake flask method) at low concentration levels.

Since an analytical method for the determination of L(+)-lactic acid concentrations in samples from the shake flask method and/or estimation method could not be developed, these methods are not applicable for the determination of log Pow of the test substance.

The HPLC method is also not applicable as it covers log Pow values in the range of 0 to 6, and because the calculation method indicated a log Pow value outside this range. Based on this, it was decided to report the result of the calculation method.

Conclusions:

A study was performed in accordance with EU method A.8 and OECD guideline 107 and in compliance with GLP. The Pow of the test substance was calculated to be 2.9E-01 (log Pow -0.54) using the Rekker calculation method.

Executive summary:

Due to the poor UV-absorption ability of the test item an enzymatic reaction in combination with UV-detection was performed. However, no suitable method for the detection of lactic acid in n-octanol and/or water in the required concentration range could be developed (technically not feasible). Therefore, the partition coefficient of the test substance was calculated using the Rekker calculation method by the software PrologP 6.0, module in Pallas 3.0, CompuDrug International, San Francisco, CA, USA.

The calculated log Pow is –0.54.

This information is used in a read-across approach in the assessment of the target substance.

For details and justification of read-across please refer to the attached report in section 13 of IUCLID.

Description of key information

All available evidence indicates that the octanol-water partition coefficient of lactic acid is significantly below 0. In a worst-case approach, and supported by weight of evidence from a range of published studies, the highest value of log P_ow= -0.54 (QSAR estimate) is selected.

Key value for chemical safety assessment

Log Kow (Log Pow):

-0.54

at the temperature of:

20 °C

Additional information

In a weight-of-evidence approach the partition coefficient of lactic acid is assessed to range between -0.72 and -0.54. Typically the racemic mixture (lactic acid) is referred to, but since enantiomers are optical antipodes they do not differ in their physicochemical properties.

Early publications claim to have measured the concentrations of lactic acid in n-octanol and water, either by titration against phenol red (Leonard et al., 1948), or, in most other cases, by an unspecified method. This limits the individual reliability of the reported values. However, all reported partition coefficients are consistent, and are supported by a recent QSAR calculation using the software PrologP 6.0 (Selditz, 2014; log P_ow= -0.54). Note that the QSAR estimate generated by KOWWin (EpiSuite) cannot be used since the experimental value by Leonard et al. (1948) is included in the training data set (autocorrelation).

In conclusion, adopting a worst-case approach (highest predicted distribution into biota, if any) the highest reported partition coefficient of log P_ow= -0.54 is selected as the key value for chemical safety assessment. The weight of evidence from all other identified literature sources indicates that this value is fully appropriate for risk assessment.