Hexanedioic acid, di-C16-18 (even numbered) alkyl esters

Biodegradation in water: screening tests

Description of key information

Readily Biodegradable: 89% in 29 d (OECD 301B)

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

One experimental study is available assessing the ready biodegradability of Hexanedioic acid, di-C16-18 alkyl esters (CAS 92969-90-9) in an aerobic aqueous medium. The study was performed according to OECD Guidelines for Testing of Chemicals (1992) No. 301B, "Ready Biodegradability; CO2 Evolution Test" referenced as Method C.4 -C of Commission Regulation (EC) No. 440/2008. The test item, at a concentration of 15.5 mg/L, was exposed to activated sewage sludge microorganisms with mineral medium in culture vessels in the dark at 21.7 - 23.0 °C for 29 days. The biodegradation of the test item was assessed by the determination of carbon dioxide produced. Control solutions with inoculum and the reference item, sodium acetate, together with a toxicity control were used for validation purposes. The relative biodegradation values calculated from the measurements performed during the test period revealed 88% and 90% biodegradation of Hexanedioic acid, di-C16-18 alkyl esters, for bottle A and B (mean 89%), respectively (based on ThCO2) after 29 days. In the toxicity control, more than 25% biodegradation occurred within 14 days (28%, based on ThCO2). Therefore, the test item was assumed not to inhibit microbial activity. In this study, the 10-day window criterion was not met. 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 of structurally similar chemicals should be evaluated carefully. A sequential biodegradation might have led to a prolonged lag-phase and therefore a slower biodegradation period although the test substance was biodegraded in a large amount within 29 d. In this case the pass level can be applied at 29 d and the substance is therefore considered to be readily biodegradable (89% after 29 d).