(E)-3-methyl-4-(2,6,6-trimethylcyclohex-2-en-1-yl)but-3-en-2-one

Biodegradation in water: screening tests

Description of key information

Based on the key study the registered substance is considered to be readily biodegradable for the chemical safety assessment.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

Two commercial qualities of the registration substance have been tested in the OECD 301F Manometric Respiratory Test: Isoraldeine Cetone Alpha (Key Study, Kreutzer 2012) and Isoraldeine 95 (Supporting Study, Rudio 1997). The level of biodegradation achieved after 28 days was 71% and 77% respectively. The 10-day window was fulfilled in the key study (34% on day 7; 66% on day 17) and only 1% below the pass limit in the supporting study (5% on day 5, 59% on day 15). The test concentrations employed in the two studies were 30 mg/L and 100 mg/L respectively. The latter is significantly higher than the water solubility of Isoraldeine 95, which has been determined to be 23.1 mg/L. This means that the biodegradation rate will be controlled by the dissolution rate and likely explains why the 10-day window in the study performed at 100mg/L was not quite met. For this reason the biodegradation study on Isoraldeine 95 (Rudio 1997) was considered reliability with restrictions and used only as a supporting study. Based on the key study and given that environmentally relevant concentrations will be significantly lower than even the 30mg/L test concentration used in this study, the registration substance is considered to be readily biodegradable.

For the purposes of the PBT assessment, the impurities present in the registered substance have also been considered. These are isomers of the main constituent having the same molecular formulae (C14H12O), same chemical functionality (ketone) and identical/similar arrangement of atoms (i.e. carbon skeleton). For two impurities (CAS 51703-99-2 and CAS 138506-81-7), the only structural difference compared to the main constituent is the position of the double bond associated with the cyclohexyl ring, which is not expected to significantly affect biodegradation properties. For the third impurity (CAS 93303-56-8), the C5 alkyl side chain is linear (“pent-1-en-3-one”) as opposed to branched (“3-methyl-but-3-en-2-one") which is expected to improve the biodegradability profile of this impurity. Therefore, given that the registered substance has passed the stringent criteria of a ready biodegradability screening test and that any impurities present are isomers of the main constituent with expected similar or more easily biodegradable profiles, it can be concluded that the all underlying components of the registered substance are readily biodegradable and not persistent.

An inhibition control was included in the supporting study (Rudio, 1997). At the concentration used in the test (100 mg/l), Isoraldeine 95 was not inhibitory to the micro-organisms. This concentration can be considered as a NOEC for the toxicity to STP microorganisms.