1-acetyl-4-(3-dodecyl-2,5-dioxo-1-pyrrolidinyl)-2,2,6,6-tetramethylpiperidine

Bioaccumulation: aquatic / sediment

Link to relevant study record(s)

Reference

Endpoint:

bioaccumulation in aquatic species: fish

Type of information:

(Q)SAR

Adequacy of study:

key study

Study period:

November 2017

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

Remarks:

Results from two relevant supporting models corroborate key model result.

Justification for type of information:

See attached QPRF and QMRF section "Attached justification".

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:

Model selection for BCF calculation was based on a recent publication by Gissi et al. (2015), evaluating and comparing several relevant QSAR models for BCF prediction under REACH based on a validated experimental data set of 851 compounds containing a subset of ionisable compounds (at least 131). Considering the outcome of this work as well as the specific properties of the submission substance, the following models were selected:
Key model: US EPA T.E.S.T v. 4.2.1, Consensus Method (see attached QMRF and QPRF);
Supporting model (1): Arnot & Gobas (2003) bioconcentration model including predicted metabolism;
Supporting model (2): log Kow based equations - Connell equation (recalculated from Connell and Hawker, 1988) recommended for compounds with log Kow values above 6.
For full details on a) rational for model selection; b) details on selected models with regard to comparative statistical evaluation by Gissi et al. (2015) and c) full literature references, see IUCLID section “Any other information on materials and methods incl. tables”!

GLP compliance:

no

Specific details on test material used for the study:

• CAS number: 106917-31-1
• EC number: 411-930-5
• IUPAC name / common name: 1-(1-Acetyl-2,2,6,6-tetramethylpiperidin-4-yl)-3-dodecylpyrrolidine-2,5-dione / Hostavin 3058
• Structural formula: C27-H48-N2-O3.
• Canonical SMILES: CCCCCCCCCCCCC1CC(=O)N(C1=O)C2CC(N(C(C2)(C)C)C(=O)C)(C)C
• Partition coefficient n-octanol water, log Kow: 7.439 (slow stirring method according to OECD 123; Noack, 2016) at 25°C and pH 5.7

Details on sampling:

Not applicabale

Details on preparation of test solutions, spiked fish food or sediment:

Not applicabale

Test organisms (species):

other: mostly lower trophic level fresh water fish species

Details on test organisms:

For the key model US EPA T.E.S.T. v. 4.2.1. the bioconcentration factor data set was compiled by researchers at the Mario Negri Istituto Di Ricerche Farmacologiche and based on Dimitrov et al. (2005). Fish experimental BCF values (two databases combined; experimental data obtained according to OECD 305 protocol; fish species: Cyprinus Carpio and salmonids) were obtained according to official protocols. Furthermore, as explained in the Literature (Zhao et al. 2008), all structures were checked one-by-one within the EC funded project CAESAR, by at least two scientists. Further high quality data were added from the Arnot & Gobas database as well as the EURAS Gold Standard Database.
The following relevant references are given in the User’s Guide on T.E.S.T. v. 4.2.:
- Dimitrov, S.; Dimitrova, N.; Parkerton, T.; Combers, M.; Bonnell, M.; Mekenyan, O. Base-line model for identifying the bioaccumulation potential of chemicals. SAR QSAR Environ. Res. 2005, 16, 531-554
- Arnot, J. A.; Gobas, F. A. P. C. A review of bioconcentration factor (BCF) and bioaccumulation factor (BAF) assessments for organic chemicals in aquatic organisms. Environ. Rev. 2006, 14, 257-297.
- EURAS. Establishing a bioconcentration factor (BCF) Gold Standard Database. http://www.euras.be/eng/project.asp?ProjectId=92 (accessed 5/20/09).
- Zhao, C. B., E.; Chana, A.; Roncaglioni, A.; Benfenati, E. A new hybrid system of QSAR models for predicting bioconcentration factors (BCF). Chemosphere 2008, 73, 1701-1707.

Route of exposure:

aqueous

Justification for method:

aqueous exposure method used for following reason: Recommended according to ECHA guidance R.7c (2017) if experimentally feasible

Test type:

other: Predominantly (94%) flow through according to Arnot and Gobas (2006) BCF database considering acceptable (category 1) data, only

Water / sediment media type:

other: Predominantly (80%) fresh water according to Arnot and Gobas (2006) BCF database considering acceptable (category 1) data, only

Hardness:

Not applicable

Test temperature:

Not applicable

pH:

Not applicable

Dissolved oxygen:

Not applicable

TOC:

Not applicable

Salinity:

Not applicable

Conductivity:

Not applicable

Details on test conditions:

Not applicable

Nominal and measured concentrations:

Not applicable

Reference substance (positive control):

not required

Details on estimation of bioconcentration:

For key model calculation via US EPA T.E.S.T. v.4.2.1. BCF Consensus Method, see attached QMRF and QPRF!
For supporting estimations via Arnot & Gobas (2003) bioconcentration model as well as BCF-calculation via the modified Connell equation, see below section "Any other information on materials and methods including tables"!

Lipid content:

>= 5 - <= 6 %

Remarks on result:

other: generally assumed lipid content for lower trophic fish

Key result

Type:

BCF

Value:

>= 26 - <= 447 L/kg

Basis:

whole body w.w.

Calculation basis:

other: QSAR

Remarks:

Actual result of BCF Consensus Method: 23 L/kg (range of 5 single models: 2.65-127.01 L/kg); upper limit (447 L/kg) externally calculated taking into account deviations of calculated from experimental values for similar compounds.

Remarks on result:

other: Key model: US EPA T.E.S.T. v. 4.2.1. BCF Consensus Method

Type:

BCF

Value:

193.06 L/kg

Basis:

whole body w.w.

Calculation basis:

other: QSAR

Remarks:

BCF derived for upper trophic level fish, 10.7% lipid content at 12°C env. Temp.

Remarks on result:

other: Supporting model: Arnot & Gobas (2003) bioconcentration model

Type:

BCF

Value:

266.15 L/kg

Basis:

whole body w.w.

Calculation basis:

other: QSAR

Remarks:

BCF derived for mid trophic level fish, 6.85% lipid content at 12°C env. Temp.

Remarks on result:

other: Supporting model: Arnot & Gobas (2003) bioconcentration model

Type:

BCF

Value:

293.7 L/kg

Basis:

whole body w.w.

Calculation basis:

other: QSAR

Remarks:

BCF derived for lower trophic level fish (standard experimental fish species), 5.98% lipid content at 12°C env. Temp.

Remarks on result:

other: Supporting model: Arnot & Gobas (2003) bioconcentration model

Type:

BCF

Value:

386 L/kg

Basis:

whole body w.w.

Calculation basis:

other: QSAR

Remarks:

BCF calculated based on experimentally determined log Kow of 7.439 (slow stirring method according to OECD 123)

Remarks on result:

other: Supporting model: Modified Connell equation

Details on kinetic parameters:

Not applicable

Metabolites:

Not applicable

Results with reference substance (positive control):

Not applicable

Details on results:

KEY MODEL RESULT: US EPA T.E.S.T. (version 4.2.1) BCF-Calculation
The T.E.S.T. Consensus Method estimates BCF based on the results of 5 sub-models (single models), taking into account the applicability domain of each method. At least predictions of 2 sub-models are required, otherwise the predicted value is deemed unreliable and not used. Sub-model results are integrated in the Consensus Method for BCF by averaging. Details on US EPA T.E.S.T. BCF model is given in the available QSAR Model Reporting Format (QMRF_BCF_TEST_v4-2-1) attached to this dossier.
The following results per sub-model were obtained and used within the T.E.S.T. Consensus method for BCF:
• Hierarchical clustering: BCF 127.01 L/kg wet weight
• Single model: BCF 23.38 L/kg wet weight
• Group contribution: BCF 2.65 L/kg wet weight
• FDA: BCF 30.06 L/kg wet weight
• Nearest neighbour: BCF 49.23 L/kg wet weight
• Consensus method:             BCF 26 L/kg wet weight (average over 5 single models); log BCF= 1.41

The BCF based on the estimate of the T.E.S.T. Consensus Method for the submission substance is given as a range to account for some uncertainty in the estimate apparent from analysis of calculated and experimental values for similar compounds as well as confidence ranges provided by 4 of the 5 sub-models integrated in the Consensus Method: taking as the lower value the actual estimate according to the Consensus Method (BCF 26 L/kg) and as the upper value the sum of (a) the highest absolute deviation between experimental and calculated value from analysis of similar substances (1.24 log units) and (b) the actual estimate (1.41 log units), resulting in 2.65 log units, i.e. BCF 447 L/kg wet weight.

FINAL RESULT relevant for PBT assessment and exposure and risk assessment:
BCF (US EPA T.E.S.T version 4.2.1): 26 to 447 L/kg whole body wet weight (range of 5 single models: 2.65-127.01 L/kg)
For further information please see corresponding methodological background on the model QMRF as well as QPRF attached to this dossier.

RESULTS SUPPORTING MODELS (1) ARNOT AND GOBAS (2003) BIOCONCENTRATION MODEL AND (2) MODIFIED CONNELL EQUATION
See sections "Any other information on results incl. tables" as well as "Overall remarks, attachments".

 Supporting Model 1: Arnot & Gobas (2003) Bioconcentration Model – results

Calculation and Results Tables for Upper and Lower Trophic Level Fish:

Table 1: The Arnot & Gobas (2003) model on bioconcentration for lower trophic level fish with 5.98% lipid content. Calculation was performed in MS Excel spreadsheet according to Arnot and Gobas(2003) with correction according to Arnot and Gobas (2006) where annotated. Formulas for calculation of the different kinetic constants and other parameters dependent from the input parameters are given together with their results. 

						Weights and lipid fraction of upper, mid and lower trophic fish
T=	12	°C		Temperature		Wup [kg]	1.53	LB_upper	0.107
W=	0.096	kg		Weight of Organism		Wmid [kg]	0.184	LB_mid	0.0685
LB=	0.0598			Lipid content of oranism		Wlow [kg]	0.096	LB_lower	0.0598
KM_N=	0.2234	metabolic transformation rate constant normalized to 10 g fish at 15°C - input from BCFBAF v. 3.01
KM=	0.12316478	dayE(-1)	kM,X = kM,N x (WX/WN)^(-0.25) x e^(0.01(TX–TN))
K1=	1/((0.01+1/Kow)*W^(0.4)=				255.323873		Uptake rate constant
k2=	k1/(LB*Kow)=				0.00015538		Elimination rate constant (via respiratory surface)
KD=	0.02*W^(-0.15)*e^(0.06*T)/(5.1*10^(-8)*Kow+2)=				0.01716802		Dietary uptake rate constant
KE=	0.125*kD=				0.002146		Fecal egestion rate constant
KG=	0.0005*W^(-0.2)=				0.00079894		Growth rate constant (growth dilution)
λPOC=	Concentration of particulate organic carbon=				0.0000005	g/ml	default
λDOC=	Concentration of dissolved organic caron=				0.0000005	g/ml	default
ɸ=	Fraction of freely dissolved chemical in water=				1/(1+λPOC*0.35*Kow+λDOC*0.08*Kow)=			0.14476028
						(second term corrected to "λDOC*0.08*Kow" according to Arnot & Gobas, 2006)
log Kow=	7.439		Kow=	27478941.5
BCF=	(1-LB)+(k1*ɸ/(k2+kE+KG+kM))=			293.663637		log BCF=	2.46785017

Table 2: The Arnot & Gobas (2003) model on bioconcentration for upper trophic level fish with 10.7% lipid content. Calculation was performed in MS Excel spreadsheet according to Arnot and Gobas(2003) with correction according to Arnot and Gobas (2006) where annotated. Formulas for calculation of the different kinetic constants and other parameters dependent from the input parameters are given together with their results.

						Weights and lipid fraction of upper, mid and lower trophic fish
T=	12	°C		Temperature		Wup [kg]	1.53	LB_upper	0.107
W=	1.53	kg		Weight of Organism		Wmid [kg]	0.184	LB_mid	0.0685
LB=	0.107			Lipid content of oranism		Wlow [kg]	0.096	LB_lower	0.0598
KM_N=	0.2234	metabolic transformation rate constant normalized to 10 g fish at 15°C - input from BCFBAF v. 3.01
KM=	0.06164267	dayE(-1)		kM,X = kM,N x (WX/WN)^(-0.25) x e^(0.01(TX–TN))
K1=	1/((0.01+1/Kow)*W^(0.4)=				84.3574307		Uptake rate constant
k2=	k1/(LB*Kow)=				2.8691E-05		Elimination rate constant (via respiratory surface)
KD=	0.02*W^(-0.15)*e^(0.06*T)/(5.1*10^(-8)*Kow+2)=				0.01133332		Dietary uptake rate constant
KE=	0.125*kD=				0.00141667		Fecal egestion rate constant
KG=	0.0005*W^(-0,2)=				0.00045923		Growth rate constant (growth dilution)
λPOC=	Concentration of particulate organic carbon=				0.0000005	g/ml	default
λDOC=	Concentration of dissolved organic caron=				0.0000005	g/ml	default
ɸ=	Fraction of freely dissolved chemical in water=				1/(1+λPOC*0.35*Kow+λDOC*0.08*Kow)=			0.14476028
						(second term corrected to "λDOC*0.08*Kow" according to Arnot & Gobas, 2006)
log Kow=	7.439		Kow=	27478941.5
BCF=	(1-LB)+(k1*ɸ/(k2+kE+KG+kM))=			193.058713		log BCF=	2.28568941

Results

The results of the calculation of bioconcentration for the submission substance according to the Arnot and Gobas (2003) Bioconcentration Model are:

Upper trophic level fish, 10.7% lipid content:

·      BCF = 193.06 L/kg wet-weight

·      log BCF = 2.29

 

Mid trophic level fish, 6.85% lipid content:

·      BCF = 266.15 L/kg wet-weight

·      log BCF = 2.43

 Lower trophic level fish (standard experimental fish species), 5.98% lipid content:

·      BCF = 293.70 L/kg wet-weight

·      log BCF = 2.47

 

Conclusion on results

As outlined above, results according to the Arnot and Gobas BCF-model proved to be of high sensitivity and accuracy (MCC) with regard to discrimination between bioaccumulative (B, BCF >2000) and not bioaccumulative (not B, BCF <2000) substances (Gissi et al., 2015). The actual bioconcentration model is independent from a “training”-data set and the data quality thereof, as it is based on several relatively simple mechanistically based assumptions relating on few environmental and organism specific parameters and the K_OW of the compound in question. It is therefore completely different from regression based models dependent on the empirical database used for the regression. Furthermore, as outlined by Arnot and Gobas (2003), regression based models tend to “arrive at an ‘average’ BCF value, allowing for a relatively large number of occurrences where the actual BCF is greater than the BCF predicted values”.

Taken into account the very different methodological approach and the results of the comparative evaluation of QSAR BCF models by Gissi et al (2015), BCF values derived via the Arnot and Gobas model are an important complementation of the key model used for BCF estimation (US EPA T.E.S.T.).

The following results were obtained depending on the fish trophic level:

·      Upper trophic level fish:  BCF = 193.06 L/kg wet-weight

·      Mid trophic level fish:      BCF = 266.15 L/kg wet-weight

·      Lower trophic level fish:  BCF = 293.70 L/kg wet-weight

Because experimental fish species normally are lower trophic level fish, and the result for lower trophic fish is highest, as a conservative approach the result for lower trophic level fish is deemed to be most relevant for the submission substance.

The BCF of (rounded) 294 L/kg wet weight compares very well with the result from key model T.E.S.T Consensus method (BCF: 26 – 447 L/kg wet-weight), and based on the fundamentally different methodological approach it is an important support for the result of the key model.

References:

Arnot, J.A.; Gobas, F.A.P.C. (2003)

A generic QSAR for assessing the bioaccumulation potential of organic chemicals in aquatic food webs

QSAR & Combinatorial Science, 22, 337-345

 

Arnot, J.A.; Gobas, F.A.P.C. (2006)

A review of bioconcentration factor (BCF) and bioaccumulation factor (BAF) assessments for organic chemicals in aquatic organisms

Environmental Reviews, 14, 257-297

Validity criteria fulfilled:

yes

Remarks:

with regard to OECD principles for (Q)SAR validation as well as ECHA guidance document R.6 (2008)

Conclusions:

The results of the key model (US EPA T.E.S.T. v. 4.2.1 BCF Consensus Method) and the supporting models (supporting model 1: Arnot & Gobas (2003) Bioconcentration Model; supporting model 2: Modified Connell Equation) conclusively demonstrate that:
• The submission substance is not bioaccumulative (BCF clearly below 2000 L/kg);
• The upper limit of the estimated BCF (447 L/kg) based on T.E.S.T. Consensus Method results (key model) will be sufficiently conservative as the relevant figure for chemical risk assessment.

Executive summary:

To conclude on a bioconcentration potential (BCF), three different models have been applied:

Key model: US EPA T.E.S.T. version 4.2.1 Consensus Method on BCF

The estimate for BCF according to T.E.S.T. is adequate for PBT/vPvB assessment (first tier) and risk assessment (first tier) for the submission substance because: (a) the model fulfils the OECD principles for QSAR models (algorithm and experimental data used for model building and validation are freely available) and (b) the submission substance is in the applicability domain of the model and evaluation of sufficiently similar compounds with experimental data increases the confidence in the estimated value for the submission substance according to ECHA guidance chapter R.6 (ECHA, 2008), section R.6.1.5.3.

All single model results integrated within the Consensus Method are far below the regulatory threshold for B (BCF 2000):

•       Hierarchical clustering:       BCF 127.01 L/kg wet weight

•       Single model:                     BCF 23.38 L/kg wet weight

•       Group contribution:            BCF 2.65 L/kg wet weight

•       FDA:                                 BCF 30.06 L/kg wet weight

•       Nearest neighbour:             BCF 49.23 L/kg wet weight

•       Consensus method:            BCF 26 L/kg wet weight (average over 5 single models); log BCF= 1.41

Based on available data for similar compounds, some uncertainty in the estimate should be accounted for (external to the calculation routine of the model):

Considering the highest absolute deviation between experimental and calculated value (Consensus Model) for the reported similar compounds of test and training set (-1.24 log units, i.e. underestimation of BCF), and adding this to the predicted value for the submission substance (1.24 + 1.41) yields an upper threshold log BCF value of 2.65, corresponding to a BCF of 447 L/kg (rounded).

Result Key model:

BCF (US EPA T.E.S.T version 4.2.1): 26 to 447 L/kg whole body wet weight (range of 5 single models: 2.65 -127.01 L/kg)

Supporting model results corroborate the result obtained from the key model:

Supporting model 1:

Arnot & Gobas (2003) bioconcentration model – result: BCF 294 L/kg wet weight.

This estimate is well within the range estimated by the T.E.S.T Consensus method (BCF: 26 – 447 L/kg wet-weight). The result from the mechanistically based Arnot & Gobas (2003) bioconcentration model therefore clearly supports the result of the key model.

 

Supporting model 2:

BCF estimated according to the modified Connell equation based on experimentally determined log Kow– result: BCF 386 L/kg wet weight.

Also this estimate is within the range estimated by the T.E.S.T Consensus method (BCF: 26 – 447 L/kg wet-weight). Given the high sensitivity as well as conservatism (no biotransformation assumed) of this method, the result from the modified Connell equation corroborates the key model result.

 

Taken together, it is safe to conclude that

·      The submission substance is not bioaccumulative (BCF clearly below 2000 L/kg);

·      Taking the upper limit of the estimated BCF (447 L/kg) as the relevant figure for chemical risk assessment will be sufficiently conservative.

Description of key information

BCF (US EPA T.E.S.T version 4.2.1): 26 to 447 L/kg whole body weight

Key value for chemical safety assessment

BCF (aquatic species):

447 L/kg ww

Additional information

No experimental data on bioaccumulation of the submission substance in fish are available. Considering ECHA guidance document R.7c (ECHA, 2017), section R.7.10.2 encouraging the use of alternative information at all supply levels, BCF was estimated by QSAR.

To conclude on a bioconcentration potential (BCF), three different models have been applied:

Key model: US EPA T.E.S.T. version 4.2.1 Consensus Method on BCF

The estimate for BCF according to T.E.S.T. is adequate for PBT/vPvB assessment (first tier) and risk assessment (first tier) for the submission substance because: (a) the model fulfils the OECD principles for QSAR models (algorithm and experimental data used for model building and validation are freely available) and (b) the submission substance is in the applicability domain of the model and evaluation of sufficiently similar compounds with experimental data increases the confidence in the estimated value for the submission substance according to ECHA guidance chapter R.6 (ECHA, 2008), section R.6.1.5.3.

All single model results integrated within the Consensus Method are far below the regulatory threshold for B (BCF 2000):

•       Hierarchical clustering:       BCF 127.01 L/kg wet weight

•       Single model:                     BCF 23.38 L/kg wet weight

•       Group contribution:            BCF 2.65 L/kg wet weight

•       FDA:                                 BCF 30.06 L/kg wet weight

•       Nearest neighbour:             BCF 49.23 L/kg wet weight

•       Consensus method:            BCF 26 L/kg wet weight (average over 5 single models); log BCF= 1.41

Based on available data for similar compounds, some uncertainty in the estimate should be accounted for (external to the calculation routine of the model):

Considering the highest absolute deviation between experimental and calculated value (Consensus Model) for the reported similar compounds of test and training set (-1.24 log units, i.e. underestimation of BCF), and adding this to the predicted value for the submission substance (1.24 + 1.41) yields an upper threshold log BCF value of 2.65, corresponding to a BCF of 447 L/kg (rounded).

Result Key model:

BCF (US EPA T.E.S.T version 4.2.1): 26 to 447 L/kg whole body wet weight (range of 5 single models: 2.65 -127.01 L/kg)

Supporting model results corroborate the result obtained from the key model:

Supporting model 1:

Arnot & Gobas (2003) bioconcentration model – result: BCF 294 L/kg wet weight.

This estimate is well within the range estimated by the T.E.S.T Consensus method (BCF: 26 – 447 L/kg wet-weight). The result from the mechanistically based Arnot & Gobas (2003) bioconcentration model therefore clearly supports the result of the key model.

 

Supporting model 2:

BCF estimated according to the modified Connell equation based on experimentally determined log Kow– result: BCF 386 L/kg wet weight.

Also this estimate is within the range estimated by the T.E.S.T Consensus method (BCF: 26 – 447 L/kg wet-weight). Given the high sensitivity as well as conservatism (no biotransformation assumed) of this method, the result from the modified Connell equation corroborates the key model result.

 

Taken together, it is safe to conclude that

·      The submission substance is not bioaccumulative (BCF clearly below 2000 L/kg);

·      Taking the upper limit of the estimated BCF (447 L/kg) as the relevant figure for chemical risk assessment will be sufficiently conservative.