2-Butenedioic acid (E)-, di-C16-18-alkyl esters

Biodegradation in water: screening tests

Description of key information

Readily biodegradable: 60-70% based on CO2 evolution and oxygen consumption, read across

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

As no study is available for assessing the biodegradability of 2-Butenedioic acid (E)-, di-C16-18-alkyl esters (CAS 68921-52-8), in accordance to Regulation (EC) No. 1907/2006 Annex XI, 1.5 Grouping of substances, a read-across to the structurally related category members Didodecyl fumarate (CAS 2402-58-6, MW 453 g/mol), Ditetradecyl fumarate (CAS 10341-03-4, MW 509 g/mol) and 2-Butenedioic acid (E)-, di-C18-22-alkyl esters (CAS 68921-53-9, MW 621-733 g/mol) was conducted. 2-Butenedioic acid (E)-, di-C16-18-alkyl esters (CAS 68921-52-8) exhibits a molecular weight range of 565 - 621 g/mol. Thus, the read across is covered by interpolation for this substance. The read across is justified due to a) the structural similarity of the category members and b) similar physico-chemical properties resulting in a similar environmental fate and ecotoxicity profile.

Further justification is given within the endpoint summary 6.1 and within the category justification section 13.

The study with Didodecyl fumarate (CAS 2402-58-6) was conducted according to ISO guideline 10708 (BODIS test) under aerobic conditions using non-adapted activated sludge as inoculum (Börner, 1995). An initial test concentration of 100 mg/L (COD) was applied. Based on O2 consumption a mean degradation of 67% was observed after 28 days. The 14-day window was not passed. Hence, the substance is not readily biodegradable according to OECD criteria. Nevertheless, as the overall pass level of 60% O2 consumption for a BODIS test was passed within the 28 day exposure period, the substance is determined to be “readily biodegradable, but failing 10 window”.

The study with Ditetradecyl fumarate (CAS 10341-03-4) was conducted according to OECD 301B under aerobic conditions using non-adapted activated sludge as inoculum (Schwarz, 2012). An initial test concentration of 20 mg/L (TOC) was applied. Based on CO2 evolution a mean degradation of 71% was observed after 28 days. The 10-day window was not passed. Hence, the substance is not readily biodegradable according to OECD criteria. Nevertheless, as the overall pass level of 60% CO2 evolution for an OECD 301B test was passed within the 28 day exposure period, the substance is determined to be “readily biodegradable, but failing 10 window”. In addition, the test was enhanced up to 60 days resulting in a high overall biodegradation of 90%.

The study with 2-Butenedioic acid (E)-, di-C18-22-alkyl esters (CAS 68921-53-9) was conducted according to OECD 301B under aerobic conditions using non-adapted activated sludge as inoculum (Schwarz, 2013). An initial test concentration of 20 mg/L (TOC) was applied. Based on CO2 evolution a mean degradation of 62 % was observed after 28 days. According to “OECD Guidelines for the testing of chemicals – Revised introduction to the OECD guidelines for testing of chemicals, Section 3 – Part 1: Principles and strategies related to the testing of degradation of organic chemicals degradation” published by OECD (2006) the ready biodegradability data for mixtures should be evaluated carefully. For substances with different chain lengths the 10-day window should not be used for the interpretation of the results. It is possible that a sequential biodegradation occurred which might have led to a prolonged lag-Phase and therefore a slower biodegradation period. In this case only the pass level at 28 days has to be applied. Hence, the test substance is determined to be readily biodegradable according to OECD criteria.

In addition, the test was enhanced up to 60 days resulting in high overall biodegradation rates of 82-91 % biodegradation, showing that complete and ultimate will occur for this substance.

Due to the structural and property similarities with the tested category member Didodecyl fumarate (CAS 2402-58-6), Ditetradecyl fumarate (CAS 10341-03-4) and 2-Butenedioic acid (E)-, di-C18-22-alkyl esters (CAS 68921-53-9), the results are applicable to read across to 2-Butenedioic acid (E)-, di-C16-18-alkyl esters (CAS 68921-52-8).

 

Conclusion:

2-Butenedioic acid (E)-, di-C16-18-alkyl esters (CAS 68921-52-8) is a substance of variable composition (UVCB). For these substances, the 10 window criterion for ready biodegradability is not applicable and the 28 day pass level can be used for assessing the biodegradability of the substance in question. Based on the fact that in all tests presented above, the respective pass level was reached (i.e. > 60% CO2 evolution or oxygen consumption), 2-Butenedioic acid (E)-, di-C16-18-alkyl esters (CAS 68921-52-8) is regarded as readily biodegradable. Therefore, the substance will not be persistent, but will in fact be rapidly removed from the environment.