Octanoic acid, monoester with 1,2-propanediol

Endpoint summary

Description of key information

Skin irritation /corrosion potential

In the report, the conclusion for all three main components for the skin irritation and corrosive potential, based on the results by the OECD toolbox, CASE Ultra and statistical method predictions, is inconclusive.

The reason for this conclusion is based on the weakness of the negative results/ predictions and not on any positive result.

 

However, the report conclusions for the educt substances 1,2/ 1,3-propanediol are clear negative and the for the caprylic acid clear positive. The latter is considered to be based on the short C-chain length and its pka of4,89.

 

Taken into account the very low water solubility, the natural pH of the skin and the good metabolization of the substance PGMC, the substance is finally concluded to be NON SKIN IRRITANT and NOT SKIN CORROSIVE.

 

 

Eye irritation /corrosion potential

In the report, the conclusion for the two monoester components for their eye irritation potential is inconclusive, while the third main component, the diester, is concluded to be negative, based on results and predictions coning from CASE Ultra, CASE Ultra Draize, Toxtree and OECD Toolbox.

The reason for this conclusion is based on the weakness of the negative results/ predictions and not on any reported positive result.

 

However, the report conclusions for the educt substances 1,2/ 1,3-propanediol are clear negative and the for the caprylic acid inconclusive, maybe slightly positive. This is concluded to be based on the short C-chain length and the pka of4,89.

 

Taken into account the very low water solubility, the natural pH of the skin and the good metabolization of the substance PGMC, the substance is finally concluded to be NON EYE IRRITANT.

Key value for chemical safety assessment

Skin irritation / corrosion

Link to relevant study records

Reference

Endpoint:

skin irritation / corrosion, other

Remarks:

QSAR

Type of information:

(Q)SAR

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification

Justification for type of information:

1. SOFTWARE
Various tools, inter alia CASE Ultra, DEREK Nexus, OECD Toolbox, ToxRead, Toxtree, VEGA

2. MODEL (incl. version number)

Model Version Approach
CASE Ultra 1.8.0.2 Statistical/Expert
DEREK Nexus 6.0.1 Expert
OECD (Q)SAR Toolbox 4.4.1 Expert/Read-across
ToxRead 0.23beta Read-across
Toxtree 3.1.0 Expert
VEGA 1.1.5_b36 Hybrid

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
Main components of the substance:

1) CCCCCCCC(=O)OCC(C)O
2) CCCCCCCC(=O)OC(C)CO
3) CCCCCCCC(=O)OCC(C)OC(=O)CCCCCCC

Impurities (=educts) of the substance
4) CC(O)CO
5) OCCCO
6) CCCCCCCC(=O)O

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
See attached QMRF/ QPRF Report

5. APPLICABILITY DOMAIN
See attached QMRF/ QPRF Report

6. ADEQUACY OF THE RESULT
See attached QMRF/ QPRF Report

Principles of method if other than guideline:

- Principle of test, short description of test conditions and Parameters analysed / observed
CASE Ultra Statistical/Expert
DEREK Nexus Expert
OECD (Q)SAR Toolbox Expert/Read-across
Toxtree Expert

GLP compliance:

no

Test system:

other: QSAR prediction

Remarks on result:

no indication of irritation

Remarks:

QSAR prediction

Compound	Method				Final Conclusion***
	Statistical / CASE Ultra		Rule-based
	Irritation	Corrosion	Toxtree	OECD Toolbox
2-hydroxypropyl octanoate	Inconclusive	Inconclusive	Irritating*	No alerts	Inconclusive
Propylene glycol 2-caprylate	Negative	Negative	Irritating*	No alerts	Inconclusive
Propylene-1,2-dioctanoate	Negative	Negative	Irritating*	No alerts	Inconclusive
1,2 propanediol	Inconclusive**	Inconclusive	Irritating*	No alerts	Negative
1,3 propanediol	Positive**	Inconclusive	Irritating*	No alerts	Negative
Caprylic acid	Positive	Positive	Irritating*	No alerts	Positive Corrosive

* Dismissed due to alerts out of context
** Negative study results in database

*** Expert opinion based on structures only, and not taking into account educt or other substance properties

Interpretation of results:

study cannot be used for classification

Conclusions:

PGMC is finally concluded to be NON SKIN IRRITANT and NOT SKIN CORROSIVE.

Executive summary:

Irritation and Corrosion

None of the query structures have an alert for skin and eye irritation from the rule-based expert system DEREK.

OECD Toolbox contains profiler for skin/eye irritation based on the exclusion/inclusion rules by BfR. The exclusion rules for eye/skin irritation/corrosion are based on physico-chemical cut-off values to identify chemicals that do not exhibit eye/skin irritation or corrosion potential. The parameters used for defining skin/eye irritation rules are: lipid solubility, surface tension (only skin), octanol water partition coefficient, aqueous solubility, melting point and molecular weight. Since none of the query structures met all the cut-off values Toolbox concluded the results to be undefined. The profiler with inclusion rules by BfR contains structural alerts which can be used for positive classification of chemicals causing irritation/corrosion. However, none of the query structures has such an alert or passed the exclusion rules. Additional read-across with OECD Toolbox failed because no structural similar chemicals with study results on irritation and corrosion could be obtained from the Toolbox database.

Almost the same physicochemical property limits and structural rules are used by the rule-based expert system Toxtree for estimating skin/eye irritation/corrosion (see,Table7). All query structures belong to Toxtree Group C (only molecules with CxHyOz) and have obviously not passed any the physicochemical limit values for being excluded from skin corrosion or skin irritation and are then considered to potentially cause skin corrosion or skin irritation (see,Table8)[1]. It has however to be noted that if any of the physicochemical parameter is missing, Toxtree will skip the physicochemical rules and only the structural alerts will be applied, which may result in a low quality prediction. This is in contrast to the inclusion and exclusion rules in OECD Toolbox, which consider physicochemical parameter and structural alert separately. Since no information were available for the query structures while all others were estimated using EpiSuite and US EPA Test software (see, appendix), the predictions by Toxtree are considered to be of low confidence. Moreover, the structural alerts between the OECD profiler and the structural classes of Toxtree are also different and therefore explaining the different results. 2-hydroxypropyl octanoate and propylene glycol 2-caprylate belong to the structural Toxtree class of C₁₀–C₂₀aliphatic alcohols which are considered potential skin irritants. This class is however not included in the inclusion rules of the OECD profiler. The Draft OECD SIDS Initial Assessment Report C6-22 primary aliphatic alcohols concludes that linear aliphatic alcohols in the range C6 – C11 are mild irritants, not anticipated to be corrosive. Aliphatic alcohols in the range C12 – C16 have a low degree of skin irritation potential; alcohols with chain lengths of C18 and above are non-irritant to skin. For the essentially linear alcohols, a differentiation in the irritation similar to that of the linear alcohols can be identified. For the alcohols in the C6- C11 range the skin irritation potential can be categorised as mild - irritant. The skin irritation potential for the higher members of the essentially linear alcohols in the range C12 – C16 is mild - essentially non-irritant. In addition, human data indicate that the irritation responses for the category of the linear alcohols are of a lower order than those observed in rabbits‎[12]. Therefore, the prediction by Toxtree does not validate well. Taking into account the absence of the structural class of aliphatic alcohols in the inclusion rules of the OECD Toolbox profiler, suggests no confidence in the prediction by Toxtree and the prediction are therefore dismissed. Taking into account the negative prediction by CASE Ultra for propylene glycol 2-caprylate and an inconclusive result for 2-hydroxypropyl octanoate (see,Table9), there no supporting evidence that skin irritation can be excluded, although the assessments in the OECD SIDS report suggests aliphatic alcohols to be only mild irritants.

Therefore, the outcome of the predictions for SKIN IRRITATIONof 2-hydroxypropyl octanoate and propylene glycol 2-caprylate can only be considered INCONCLUSIVE.

Toxtree assigned propylene-1,2-dioctanoate, 1,2 propanediol and 1,3 propanediol and caprylic acid to the structural class ethylene glycol ethers which are considered potential skin irritants. None of these structures is however a glycol ether. While an explanation including SMARTS definition could be obtained from the OECD Toolbox profiler (see,Figure8), the mapping in Toxtree indicates the structural alert not properly defined (see,Figure9). Overall, the structural alert of Toxtree is out of context and the predictions can therefore be dismissed.

However, the report conclusions for the educt substances 1,2/ 1,3-propanediol are clear negative and the for the caprylic acid clear positive. The latter is considered to be based on the short C-chain length and the pka of 4,89.

 

Taken into account the very low water solubility, the natural pH of the skin and the good metabolization of the substance PGMC, the substance is finally concluded to be NON SKIN IRRITANT and NOT SKIN CORROSIVE.

 

 

 

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not irritating)

Eye irritation

Link to relevant study records

Reference

Endpoint:

eye irritation: in vitro / ex vivo

Type of information:

(Q)SAR

Adequacy of study:

key study

Study period:

2021

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification

Justification for type of information:

1. SOFTWARE
Various tools, inter alia CASE Ultra, DEREK Nexus, OECD Toolbox, ToxRead, Toxtree, VEGA

2. MODEL (incl. version number)

Model Version Approach
CASE Ultra 1.8.0.2 Statistical/Expert
DEREK Nexus 6.0.1 Expert
OECD (Q)SAR Toolbox 4.4.1 Expert/Read-across
ToxRead 0.23beta Read-across
Toxtree 3.1.0 Expert
VEGA 1.1.5_b36 Hybrid

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
Main components of the substance:

1) CCCCCCCC(=O)OCC(C)O
2) CCCCCCCC(=O)OC(C)CO
3) CCCCCCCC(=O)OCC(C)OC(=O)CCCCCCC

Impurities (=educts) of the substance
4) CC(O)CO
5) OCCCO
6) CCCCCCCC(=O)O

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
See attached QMRF/ QPRF Report

5. APPLICABILITY DOMAIN
See attached QMRF/ QPRF Report

6. ADEQUACY OF THE RESULT
See attached QMRF/ QPRF Report

Reason / purpose for cross-reference:

reference to same study

Qualifier:

no guideline followed

Principles of method if other than guideline:

- Principle of test, short description of test conditions and Parameters analysed / observed
CASE Ultra Statistical/Expert
DEREK Nexus Expert
OECD (Q)SAR Toolbox Expert/Read-across
Toxtree Expert

GLP compliance:

no

Irritation parameter:

other: QSAR predictions

Remarks on result:

no indication of irritation

Other effects / acceptance of results:

OTHER EFFECTS:
- Visible damage on test system:

DEMONSTRATION OF TECHNICAL PROFICIENCY:

ACCEPTANCE OF RESULTS:
- Acceptance criteria met for negative control:
- Acceptance criteria met for positive control:
- Range of historical values if different from the ones specified in the test guideline:

 

Compound	Method				Final Conclusion **
	Statistical		Rule-based
	CASE Ultra	CASE Ultra Draize	Toxtree	OECD Toolbox
2-hydroxypropyl octanoate	Negative	Negative	unkown	No alerts	Inconclusive
Propylene glycol 2-caprylate	Negative	Inconclusive	unkown	No alerts	Inconclusive
Propylene-1,2-dioctanoate	Negative	Negative	NOT eye irritation R36	No alerts	Negative
1,2 propanediol	Negative	Negative	Serious lesions to the eye*	No alerts	Negative
1,3 propanediol	Negative	Negative	Serious lesions to the eye*	No alerts	Negative
Caprylic acid	Negative	Positive	unkown	No alerts	Inconclusive (is corrosive)

* Dismissed due to alerts out of context

** Expert opinion based on structures only, and not taking into account educt or other substance properties

Interpretation of results:

GHS criteria not met

Conclusions:

The substance PGMC is concluded to be NON EYE IRRITANT.

Executive summary:

No predictions results for eye irritation of 2-hydroxypropyl octanoate, propylene glycol 2-caprylate and caprylic acid were provided by Toxtree as (i) the structures did not match any of the structural alerts and (ii) the physicochemical properties did not pass the limits of being excluded from eye irritation. 2-hydroxypropyl octanoate was predicted negative for eye irritation by the two CASE Ultra models. This may suggest some confidence, however since both predictions was assigned low reliability and taking into account that the physicochemical properties did not pass the limits of being excluded from eye irritation, in our expert opinion there is not sufficient evidence to exclude eye irritation of 2-hydroxypropyl octanoate. The predictions of eye irritation for 2 -hydroxypropyl octanoate are therefore considered INCONCLUSIVE.

Propylene glycol 2-caprylate was predicted to be not irritating to eyes by the CASE Ultra model based on the Alarie test, while the prediction with Draize test model was considered inconclusive. Taking into account that the physicochemical properties did not pass the limits of being excluded from eye irritation, in our expert opinion there is not sufficient evidence to exclude eye irritation of propylene glycol 2-caprylate. The predictions of eye irritation fo rpropylene glycol 2-caprylateare therefore considered INCONCLUSIVE.

Propylene-1,2-dioctanoate was predicted negative for eye irritation by Toxtree and the two eye irritation models of CASE Ultra. Based on the results with a rule-based expert system two statistical-based models of two independent platforms, in our expert opinion there is evidence that propylene-1,2-dioctanoate can be considered NOT EYE IRRITANT.

1,2 propanediol and 1,3 propanediol were predicted negative for eye irritation by the two CASE Ultra models, while the result for 1,2 propanediol was substantiated by a negative study result[1]in the training set of Draize test model. Since water solubility and partition coefficient of 1,2 propanediol compares with 1,3 propanediol, their irritating properties can be considered the same. The structural alerts for 1,2 propanediol and 1,3 propanediol from Toxtree refers to aliphatic mono alcohols (see software printouts) indicates again the Toxtree structural class not well defined as both are not mono alcohols. It has also to noted that as in the case of skin irritation inclusion rules, alcohols are not considered in the BfR inclusion rules of the OECD Toolbox profiler for eye irritation. That makes the alerts and predictions by Toxtree out of context. In our expert opinion, the predictions by Toxtree can therefore be dismissed. Overall, based on the negative result from CASE Ultra predictions substantiated by a negative study result,1,2 propanediol and 1,3 propanediolcan be consideredNOT EYE IRRITANT.

Based on caprylic acid being reported and classified as CORROSIVE, contact with eyes has to be avoided in any caseand predictions of eye irritation are considered out of scope.

However, the report conclusions for the educt substances 1,2/ 1,3-propanediol are clear negative and the for the caprylic acid inconclusive, maybe slightly positive. This is concluded to be based on the short C-chain length and the pka of4,89.

 

Taken into account the very low water solubility, the natural pH of the skin and the good metabolization of the substance PGMC, the substance is finally concluded to beNOT EYE IRRITANT.

[1]See also OECD SIDS CAS 57-55-6: Studies demonstrate that propylene glycol is not irritating to skin or eye, nor does it cause sensitization by skin contact.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not irritating)

Respiratory irritation

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

The conclusion PGMC is not irritating is further assisted by the conclusion in the CIR Risk assessment (2014), reporting "There were no adverse effects reported, including irritation, in a skin test (n=5) of a sunless tanning preparation containing propylene glycol dicaprylate/dicaprate".