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Partition coefficient

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Endpoint:
partition coefficient
Data waiving:
study technically not feasible
Justification for data waiving:
other:
Justification for type of information:
JUSTIFICATION FOR DATA WAIVING :

The substance is a complex mixture only partially known and its physical state leads to difficulties for physico-chemical testing: It is described as a viscous liquid.

GLP studies according to OECD 117 have been conducted on other substances belonging to the same group of substance (UVCB sub-type 3, where the source is biological and the process is refinement, such as: exudates, resinoids and concretes that are well-known to be very difficult to analytically assess). These studies show that this method is not appropriate for such complex substances (the study lead to one peak or to a significant part of the substance with a log Kow < 0.3 while the substance is not soluble in water). In addition, % Area is not necessarily correlated to absolute concentration in the substance if UV detection is used. Therefore we cannot guarantee the repartition of the logPow in the composition of the substance and that the results obtained by HPLC/UV-DAD are representative of the whole substance.

Moreover the physical state and the limited knowledge on the composition of such substances lead to technical issues to quantify the substance dissolved in water or in octanol media (HPLC or GC/FID do not allow to detect the totality of the test item constituents). Then OCDE 107 and 123 are also considered as not appropriate.

Finally conventional standard tests for partition coefficient endpoint intended for single substances are considered as not appropriate for such complex substances.

That is why the test has been waived for the registered substance.
Endpoint:
partition coefficient
Type of information:
(Q)SAR
Adequacy of study:
supporting study
Study period:
run on 2018
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a valid (Q)SAR model and falling into its applicability domain, with limited documentation / justification
Justification for type of information:
QSAR prediction : The values obtained on known constituents of the substance are not experimental results, however the QSAR model is recommended by the ECHA guidance document on information requirements, is well documented with regard to validation parameters according to OECD principles. Moreover, the constituents of the substance are fully characterised towards the applicability domain.
Reason / purpose:
reference to other study
Principles of method if other than guideline:
QSAR estimation
Partition coefficient type:
octanol-water
Type:
log Pow
Partition coefficient:
>= 6.96 - <= 7.94
Remarks on result:
other: Temperature and pH not provided (QSAR estimation)
Remarks:
Range of logKow estimated on the known constituents of the substance

Temperature and pH values are not considered in this model.

The estimation is based on the non-ionised form of the molecule.

No Experimental Value Adjustment was made.

The molecular weight of the constituents are between 256.43 and 284.484g/mol, hence within the estimation domain of the validation set (27.03 -991.15 g/mol), all the functional groups are included in the list of descriptors, and, the occurence of each fragment is below the maximum number in the training/validation sets (Appendix D), such as:

 

 

TRAINING SET

VALIDATION SET

LOGKOW FRAGMENT DESCRIPTION        

COEFF

MAX

NUMBER

MAX

Number

-CH3 [aliphatic carbon]

0.5473

13

1401

20

7413

-CH2-   [aliphatic carbon]

0.4911

18

1083

28

7051

-COOH  [acid, aliphatic attach]         

-0.6895

3

126

3

672

=CH- or =C< [olefinc carbon]            

0.3836 

10

239

10

1847

Executive summary:

When the constituents of the substance were sufficiently known and were within the applicability domain (MW, descriptors), the partition coefficient of the known constituents of the substance were estimated using the recommended QSAR model KOWWIN v1.68, based on Atom/Fragment Contribution (AFC) method.

Log Kow of these constituents were estimated to be between 6.96 and 7.94 (estimated by QSAR) but this range is not representative of all the substance.

Description of key information

No range of logKow representative of the test item can be determined (neither with an experimental approach nor with an estimation approach)

Key value for chemical safety assessment

Additional information

The substance is a complex mixture only partially known and its physical state leads to difficulties for physico-chemical testing: It is described as a viscous liquid.

GLP studies according to OECD 117 have been conducted on other substances belonging to the same group of substance (UVCB sub-type 3, where the source is biological and the process is refinement, such as : exudates, resinoids and concretes that are well-known to be very difficult to analytically assess). These studies showed that this method was not appropriate for such complex substances (the study lead to one peak or to a significant part of the substance with a log Kow < 0.3 while the substance was not soluble in water). In addition, % Area is not necessarily correlated to absolute concentration in the substance if UV detection is used. Therefore we cannot guarantee the repartition of the logPow in the composition of the substance and that the results obtained by HPLC/UV-DAD are representative of the whole substance.

Moreover, the physical state, limited knowledge on the composition of the substance and the diverse nature of the constituents of the substance (proteins, fatty acids...) lead to technical issues to quantify the substance dissolved in water or in octanol media (HPLC do not allow to detect the totality of the test item constituents). Then OCDE 107 and 123 are also considered as not appropriate.

Finally as reported in the EU/OECD guidelines and in Chapter R.7a,  v6.0, July 2017,R.7.1.8.3, the high performance liquid chromatography (HPLC) is applicable when the log Pow value falls within range 0 to 6 and the flask method is applicable when the log Pow value falls within range -2 to 4. Considering QSAR estimations on known constituents of the substance (EpiSuite estimations of logKow are above 6), we anticipate that a part of the constituents of the substance will be outside the applicability domain of the standard methods.

Therefore conventional standard tests for partition coefficient endpoint intended for single substances are considered as not appropriate for such complex substances.

That is why the test has been waived for the registered substance.

 

Note that even if only a range of logKow on a limited part of the composition of the substance, not representative of the whole substance, can be calculated using QSAR estimations, calculated values were provided on known constituents of the substance, when possible.

However it is considered that no range logKow representative of the whole test item can be determined (neither with an experimental approach nor with an estimation approach).