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Physical & Chemical properties

Partition coefficient

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Endpoint:
partition coefficient
Type of information:
(Q)SAR
Adequacy of study:
weight of evidence
Reliability:
1 (reliable without restriction)
Guideline:
other: ECHA Guidance on Information Requirements and Chemical Safety Assessment. Chapter R. 6: QSARs and grouping of chemicals
Version / remarks:
2008
Guideline:
other: ECHA Practical guide How to use and report (Q)SARs
Version / remarks:
2016
Principles of method if other than guideline:
The kinetics of disintegration of Step 2 catalyst saturated with water (2-phase system) is fast. In a reliable study (Tenn, W.J., 2017) a pseudo-first order rate constant of 0.0194 /min was determined, corresponding to a half-life in water (aerobic) of 35.7 minutes. After degradation of Step 2 catalyst, the remaining aromatic phosphites and phosphates continue to react quickly to afford aryl alcohols, phosphorous and phosphoric acids. The final aromatic reaction products resulting from phosphites initially present in Step 2 catalyst solution will therefore be LHP-fin1 and LHP-fin2 as well as phosphoric and phosphorous acid.
Because of this, the partition coefficient n-octanol-water (Pow) cannot be determined for Step 2 catalyst experimentally. The only scientifically sound solution is to estimate Pow for the final stable products of transformation by hydrolysis / oxidation, namely LHP-fin1 and LHP-fin2, and to use the results in a weight of evidence for bioaccumulation assessment and classification and labelling.
Type of method:
other: QSAR
Partition coefficient type:
octanol-water
Key result
Type:
log Pow
Partition coefficient:
2.34
Temp.:
20 °C
Remarks on result:
other: OPERA V1.5 model for Pow
Remarks:
Inside AD; local AD index: 0.96; confidence level: 0.92
Type:
log Pow
Partition coefficient:
2.3
Temp.:
20 °C
Remarks on result:
other: Experimental result according to Hansch et al., 1995
Remarks:
Available over US EPA Chemistry Dashboard: PhysPropNCCT, referencing to SRC PhysProp database
Details on results:
The experimental value of log Pow 2.3 is available over US EPA Chemistry Dashboard: PhysPropNCCT, with the following information awailable:
"The PHYSPROP data sets are the publicly available data files underpinning the EPISuiteTM prediction models. The data were curated by NCCT using a combination of manual and automated processing routines with only the highest quality data reported."
From the SRC PhysProp database the following reference is available:
Hansch, C.; Leo, A.; Hoekman, D. (1995). Exploring QSAR. Hydrophobic, Electronic, and Steric Constants.
ACS Professional Reference Book. Washington, DC, American Chemical Society

Please see IUCLID section "Executive Summary" below for further details.

Endpoint:
partition coefficient
Type of information:
(Q)SAR
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Guideline:
other: ECHA Guidance on Information Requirements and Chemical Safety Assessment. Chapter R. 6: QSARs and grouping of chemicals
Version / remarks:
2008
Guideline:
other: ECHA Practical guide How to use and report (Q)SARs
Version / remarks:
2016
Principles of method if other than guideline:
The kinetics of disintegration of Step 2 catalyst saturated with water (2-phase system) is fast. In a reliable study (Tenn, W.J., 2017) a pseudo-first order rate constant of 0.0194 /min was determined, corresponding to a half-life in water (aerobic) of 35.7 minutes. After degradation of Step 2 catalyst, the remaining aromatic phosphites and phosphates continue to react quickly to afford aryl alcohols, phosphorous and phosphoric acids. The final aromatic reaction products resulting from phosphites initially present in Step 2 catalyst solution will therefore be LHP-fin1 and LHP-fin2 as well as phosphoric and phosphorous acid.
Because of this, the partition coefficient n-octanol-water (Pow) cannot be determined for Step 2 catalyst experimentally. The only scientifically sound solution is to estimate Pow for the final stable products of transformation by hydrolysis / oxidation, namely LHP-fin1 and LHP-fin2, and to use the results in a weight of evidence for bioaccumulation assessment and classification and labelling.
Type of method:
other: QSAR
Partition coefficient type:
octanol-water
Key result
Type:
log Pow
Partition coefficient:
7.32
Temp.:
20 °C
Remarks on result:
other: log Kow by consensus modelling according to UFZ (2017)
Remarks:
Overall inside AD; inside AD for three constituting methods (Hou and Xu, 2003; Marrero and Gani, 2002; ALOGP); outside AD for one constituting method (Dubost et al., 2005)
Type:
log Pow
Partition coefficient:
7.82
Temp.:
20 °C
Remarks on result:
other: According to Hou and Xu (2003) as implemented in ChemProp V.6.6
Remarks:
Part of UFZ consensus model
Type:
log Pow
Partition coefficient:
7.05
Temp.:
20 °C
Remarks on result:
other: According to Marrero and Gani (2002) as implemented in ChemProp V.6.6
Remarks:
Part of UFZ consensus model
Type:
log Pow
Partition coefficient:
7.09
Temp.:
20 °C
Remarks on result:
other: According to ALOGP (Ghose et al, 1998) as implemented in ChemProp V.6.6
Remarks:
Part of UFZ consensus model
Type:
log Pow
Partition coefficient:
7.11
Temp.:
20 °C
Remarks on result:
other: According to Klopman et al. (1994) as implemented in ChemPropV.6.6
Remarks:
Supporting model
Type:
log Pow
Partition coefficient:
7.9
Temp.:
20 °C
Remarks on result:
other: According to LSER model (Platts et al. and Abraham et al.) as implemented in ChemPropV.6.6
Remarks:
Supporting model
Details on results:
Key model is the consensus model for log Kow by UFZ (2017). The model calculates Pow from 4 individual models. The consensus is always made from the logarithmic values. In the default mode (which was applied), the arithmetic mean value of all individual results is calculated. In the output, the number of valid results and the difference between the maximum and minimum individual result (+/- 0.77) is shown in addition.
LHP-fin2 was overall inside the applicability domain (AD). It was inside AD for three constituting methods (Hou and Xu, 2003; Marrero and Gani, 2002; ALOGP) and outside the AD for one constituting method (Dubost et al., 2005).
The range of results contributing to the final value of 7.32 according to the consensus model is log Pow 7.05 to log Pow 7.82.

The result of the valid key model (consensus model according to UFZ) of log Pow 7.32 (+/- 0.77) is corroborated by two supporting models implemented in ChemPropV.6.6, i.e. the method according to Klopman (1994) and a LSER based method (according to Platts et al. and Abraham et al.), giving results for logP of 7.11 and 7.9, respectively.

Please see IUCLID section "Executive Summary" below for further details.

Endpoint:
partition coefficient
Data waiving:
study technically not feasible
Justification for data waiving:
the study does not need to be conducted because the substance decomposes

Description of key information

Due to fast disintegration of Step 2 catalyst by hydrolysis / oxidation (half-life 35.7 minutes), no experimental determination of Pow is possible.

QSAR was performed for the final hydrolytic reaction products LHP-fin1 and LHP-fin2. In a WoE approach the decisive value for classification, hazard and risk assessment is based on results for the higher molecular weight and more hydrophobic compound LHP-fin2:

log Kow (log Pow) = 7.32 (+/- 0.77)

Key value for chemical safety assessment

Log Kow (Log Pow):
7.32
at the temperature of:
20 °C

Additional information

The kinetics of disintegration of Step 2 catalyst saturated with water (2-phase system) is fast. In a reliable study (Tenn, W.J., 2017) a pseudo-first order rate constant of 0.0194 /min was determined, corresponding to a half-life in water (aerobic) of 35.7 minutes. After degradation of Step 2 catalyst the remaining aromatic phosphites and phosphates continue to react quickly to afford aryl alcohols, phosphorous and phosphoric acids. The final aromatic reaction products resulting from phosphites initially present in Step 2 catalyst solution will therefore be LHP-fin1 and LHP-fin2 as well as phosphoric and phosphorous acid.

Because of this, the partition coefficient n-octanol-water (Pow) cannot be determined for Step 2 catalyst experimentally. The only scientifically sound solution is to estimate Pow for the final stable products of transformation by hydrolysis / oxidation, namely LHP-fin1 and LHP-fin2, and to use the results in a weight of evidence for hazard and risk assessment under REACH (including PBT assessment) as well as classification and labelling according to GHS.

For LHP-fin1, the n-octanol-water partition coefficient was calculated by “OPERA-model for Octanol-water partition coefficient”, V1.5. The model is freely accessible via the US EPA Chemistry Dashboard (https://comptox.epa.gov/dashboard). The model fulfils the OECD principles for QSAR models with algorithm and used experimental data for model build and validation being freely available. A QSAR Model Reporting Format is published and available from the JRC QSAR Model Database and attached to the robust study summary.

LHP-fin1 was within the global applicability domain and both, the local applicability domain index as well the confidence level index were high (0.96 and 0.92 - theoretical maximum for both values is 1.0). In addition, predicted and calculated results for the 5 nearest neighbours used for the prediction were checked and matched closely. One of the 5 nearest neighbours turned out to be the query compound itself, i.e. LHP-fin1. The experimental value of log Pow 2.3 for LHP-fin1 was determined by Hansch et al. (1995) and is available from SRC PhysProp database. In conclusion, the estimated value of log Pow of 2.34 resulting from the “OPERA-model for Octanol-water partition coefficient” V1.5 is judged to be reliable.

For the second final hydrolysis product of Step 2 catalyst, LHP-fin2, QSAR was also applied for estimation of Pow. Chemical Properties Estimation Software System (ChemProp) version 6.6 (UFZ, 2017) was used for calculation. ChemProp includes different methods for calculation of Pow. It includes applicability domain checks specific for the respective models. Based on these checks, not all implemented models for Pow calculation could be used for LHP-fin2.

The implemented models fulfil the OECD principles for QSAR models with algorithm and used experimental data for model build and validation being freely available. A QSAR Model Reporting Format and QSAR Prediction Reporting format is attached to the robust study summary. Key model is the "Consensus model for log Kow" by UFZ (2017). The model calculates Pow from 4 individual models. The consensus is always made from the logarithmic values. In the default mode (which was applied), the arithmetic mean value of all individual results is calculated.

LHP-fin2 was overall inside the applicability domain (AD) of the consensus model. It was inside AD for three constituting methods (Hou and Xu, 2003; Marrero and Gani, 2002; ALOGP) and outside the AD for one constituting method (Dubost et al., 2005). The result of the consensus model (UFZ) for log P was 7.32 (+/- 0.77). The range of results of single models contributing to the final value of 7.32 according to the consensus model is log Pow 7.05 to log Pow 7.82. The result of the valid key model (consensus model according to UFZ) is corroborated by two supporting models implemented in ChemPropV.6.6, i.e. the method according to Klopman (1994) and a LSER based method (according to Platts et al. and Abraham et al.), giving results for logPow of 7.11 and 7.9, respectively.

In the WoE approach, the following results are integrated:

Final organic hydrolysis products of Step 2 catalyst are LHP-fin1 and LHP-fin2, which will form in a molar ratio of 4 : 1.

log Pow for LHP-fin 1: 2.34;

log Pow for LHP-fin 2: 7.32.

In spite of the fact that LHP-fin2 will arise only in one fourth of the concentration of LHP-fin1, for a cautious assessment the log Pow of 7.32 for LHP-fin2 will be used for hazard and risk assessment under REACH (including PBT assessment) as well as classification and labelling according to GHS.

Reference:

UFZ Department of Ecological Chemistry 2017. ChemProp 6.6 http://www.ufz.de/ecochem/chemprop