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Biodegradation in water: screening tests

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Description of key information

The test compound was found to be poorly and partially biodegradable according to OECD criteria.

Key value for chemical safety assessment

Additional information

The ready biodegradability of the tested substance was measured to be 4 respectively 5 % according to a Modified Sturm Test (OECD-Guideline No. 301 B, CIBA-GEIGY 850178, 1985).

Additional QSAR calculations with Catalogic v5.11.19, Catalogic 301C v09.13 revealed a degradation of 2% after 28d. The main metabolite was identified as 3-(3,5-ditert-butyl-4-hydroxy-phenyl)propanoic acid.

The identification of the degradation products of CAS 6683-19-8 was conducted with Catalogic v5.11.19, CATALOGIC 301C v.09.13 in compliance with Annex XI, paragraph 1.3 of Regulation (EC) No 1907/2006. The respective QMRF and QPRF documents are attached.

In Article 13 of Regulation (EC) No 1907/2006, it is laid down that information on intrinsic properties of substances may be generated by means other than tests, provided that the conditions set out in Annex XI (of the same Regulation) are met.

According to Annex XI, paragraph 1.3 results of (Q)SAR may be used instead of testing when the following conditions are met:

-      results are derived from a (Q)SAR model whose scientific validity has been established,

-      the substance falls within the applicability domain of the (Q)SAR model,

-      results are adequate for the purpose of classification and labelling and/or risk assessment, and

-      adequate and reliable documentation of the applied method is provided.

The CATALOGIC 301C v.09.13 model implemented in Catalogic v5.11.19 is a highly-established model for estimating the aerobic biodegradation under MITI I (OECD 301 C) test conditions. The training set contains BOD data from 1986 chemicals from the MITI I database [1], 769 chemicals were provided by the NITE, Japan [2] and 472 proprietary chemicals were provided by NITE, Japan. The training set includes 544 readily biodegradable and 1442 not readily biodegradable chemicals.  Another training database of catabolic pathways for 551 organic compounds, new proprietary observed metabolites for 68 proprietary chemicals provided by NITE and expert knowledge were used to determine the principal transformations and to train the system to simulate aerobic catabolism of training chemicals. The documented pathways of microbial catabolism were collected from scientific papers, monographs and databases accessible over the Internet. Details on the mathematical formalism of the model can be reviewed in [3, 4].

The endpoint is the percentage of the theoretical biological oxygen demand on 28thday. The model consists of a metabolism simulator and an endpoint model. It provides results for the BOD (%), primary half-life (days), ultimate half-life (days), quantities of parents and biodegradation products, and details on the applicability domain. Detailed information about the validity of the model can be found in the QMRF document attached to this document.

Regarding the applicability domain, the model uses a stepwise approach to define the applicability domain [5]. It consists of the following sub-domain levels.

-      General parametric requirements – includes ranges of variation of logKow and MW,

-      Structural domain – based on atom-centered fragments

-      Domain of simulator of metabolism – determines the reliability of the simulated metabolism.

CAS 6683-19-8 falls within all three sub-domains of the model which makes the prediction highly reliable. Details can be found in the attached QPRF document.

As the model incorporates a metabolism simulator the results are regarded as adequate for the identification of degradation products as requested by ECHA. Detailed information about the model and the prediction can be found in the QMRF and QPRF documents attached to this response.

In summary, the conditions listed in Annex XI, paragraph 1.3 are clearly met and the results of the model can be used instead of testing to identify the degradation products of CAS 6683-19-8.

In total, the model identified 23 metabolites or degradation products, respectively. This can be regarded as clear worst case as the model lists the complete degradation map which also contains metabolites at very low quantities as well as metabolites that are subject to further degradation. The main metabolite was metilox acid (CAS 20170-32-5) which was also identified by the ECB PBT working group (PBT List No 77) in the available PBT assessment of CAS 6683-19-8. The PBT working group identified two potential degradation products.

(1)  benzenepropanoic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxy- (metilox acid; CAS 20170-32-5)

(2)  pentaerythritol (CAS 115-77-5)

The assumed formation of these degradation products is based on data on a structural analogue (CAS 2082-79-3). They are in line with the before-mentioned results of CATALOGIC which predicted metilox acid to be the main metabolite as well. Concerning pentaerythritol CATALOGIC assumed that this compound is subject to further degradation processes and therefore its quantity is rather low. The detailed assessment of the ECB PBT working group on CAS 6683-19-8 is attached in IUCLID section 13.

Identified degradation products (Catalogic 301C)

Quantity [%] mol/mol parent

LogKow

Remarks

Smiles

4.01

19.60

Parent (CAS 6683-19-8)

CC(C)(C)c1cc(CCC(=O)OCC(COC(=O)CCc2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)(COC(=O)CCc2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)COC(=O)CCc2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)cc(C(C)(C)C)c1O

230.20

4.77

Metabolite (Metilox acid; CAS 20170-32-5)

CC(C)(C)c1cc(CCC(O)=O)cc(C(C)(C)C)c1O

10.38

13.91

Metabolite (triester of CAS 6683-19-8)

CC(C)(C)c1cc(CCC(=O)OCC(CO)(COC(=O)CCc2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)COC(=O)CCc2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)cc(C(C)(C)C)c1O

0.00

18.1342

Metabolite

CC(C)(C)c1cc(CCC(=O)OCC(COC(=O)CCc2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)(COC(=O)CCc2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)COC(=O)CCc2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)cc(C(C)(C)CO)c1O

0.37

18.06

Metabolite

CC(C)(C)c1cc(CCC(=O)OCC(COC(=O)CCc2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)(COC(=O)CCc2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)COC(=O)CC(O)c2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)cc(C(C)(C)C)c1O

6.48

3.31

Metabolite

CC(C)(C)c1cc(CCC(O)=O)cc(C(C)(C)CO)c1O

24.37

8.62

Metabolite (diester of CAS 6683-19-8)

CC(C)(C)c1cc(CCC(=O)OCC(CO)(CO)COC(=O)CCc2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)cc(C(C)(C)C)c1O

0.00

18.1095

Metabolite

CC(C)(C)c1cc(CCC(=O)OCC(COC(=O)CCc2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)(COC(=O)CCc2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)COC(=O)CCc2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)cc(C(C)(C)C=O)c1O

1.63

3.24

Metabolite

CC(C)(C)c1cc(C(O)CC(O)=O)cc(C(C)(C)C)c1O

0.51

12.77

Metabolite

CC(C)(C)c1cc(CCC(=O)OCC(CO)(COC(=O)CCc2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)COC(=O)CC(O)c2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)cc(C(C)(C)C)c1O

25.77

3.93

Metabolite

CC(C)(C)c1cc(CCC(=O)OCC(CO)(CO)CO)cc(C(C)(C)C)c1O

0.00

3.285

Metabolite

CC(C)(C)c1cc(CCC(O)=O)cc(C(C)(C)C=O)c1O

0.73

18.00

Metabolite

CC(C)(C)c1cc(CCC(=O)OCC(COC(=O)CCc2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)(COC(=O)CCc2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)COC(=O)CCc2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)cc(C(C)(C)C(O)=O)c1O

0.86

3.98

Metabolite

CC(O)c1cc(C(C)(C)C)c(O)c(C(C)(C)C)c1

2.38

7.08

Metabolite

CC(C)(C)c1cc(CCC(=O)OCC(CO)(CO)COC(=O)CC(O)c2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)cc(C(C)(C)C)c1O

0.00

-1.767

Metabolite (Pentaerythritol; CAS 115-77-5)

OCC(CO)(CO)CO

15.28

2.59

Metabolite

CC(C)(C)c1cc(CCC(O)=O)cc(C(C)(C)C(O)=O)c1O

1.03

12.30

Metabolite

CC(C)(C)c1cc(CCC(=O)OCC(CO)(COC(=O)CCc2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)COC(=O)CCc2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)cc(C(C)(C)C(O)=O)c1O

0.07

2.9235

Metabolite

CC(O)c1cc(C(C)(C)CO)c(O)c(C(C)(C)C)c1

0.00

-1.7917

Metabolite

OCC(CO)(CO)C=O

0.49

1.12

Metabolite

CC(C)(CO)c1cc(CCC(O)=O)cc(C(C)(C)C(O)=O)c1O

4.76

7.02

Metabolite

CC(C)(C)c1cc(CCC(=O)OCC(CO)(CO)COC(=O)CCc2cc(C(C)(C)C)c(O)c(C(C)(C)C)c2)cc(C(C)(C)C(O)=O)c1O

25.69

-1.54

Metabolite

OCC(CO)(CO)C(O)=O

0.00

-0.7557

Metabolite

OCC(CO)CO

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existing chemicals based on the CSCL Japan, Chemical Industry Ecology-Toxicology &

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Chemical Substances Control Law, http://www.safe.nite.go.jp/english/db.html

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