Reaction mass of 1-(2,6,6-trimethyl-1-cyclohexen-1-yl)pent-1-en-3-one and 1-(2,6,6-trimethyl-2-cyclohexen-1-yl)pent-1-en-3-one

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

From August 02, 2012 to October 15,2012

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

This information is used for read-across to reaction mass of 1-(2,6,6-trimethyl-1-cyclohexen-1-yl)pent-1-en-3-one and 1-(2,6,6-trimethyl-2-cyclohexen-1-yl)pent-1-en-3-one.

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)

Deviations:

yes

Remarks:

An optional toxicity control as suggested by OECD guideline 301F was not performed. The validity of the study is not adversely affected.

Qualifier:

according to guideline

Guideline:

EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)

Qualifier:

according to guideline

Guideline:

EPA OPPTS 835.3110 (Ready Biodegradability)

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Lot #: SC00003617
Purity: isomer n-alpha 51%, isomer n-beta 10%, isomer iso-alpha 20% and isomer iso-beta 6%

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): sludge from a biological WWTP of the city of Geneva treating predominatly domestic sewage
- Dry weight of suspended solids: 3.56 g/l, diluted to 1.53 g/l

Duration of test (contact time):

54 d

Initial conc.:

20 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST CONDITIONS
- Test temperature: 21.4 °C - 22.6°C
- pH: 7.48 - 8.06

Reference substance:

benzoic acid, sodium salt

Remarks:

purity: min 99.0%

Test performance:

Everyday the oxygen consumption of each flask is recorded and correct temperature and stirring are checked.
At the end of the test period (normally 28 days), the pH of each flask is measured again.

Key result

Parameter:

% degradation (O2 consumption)

Value:

81

Sampling time:

28 d

Parameter:

% degradation (O2 consumption)

Value:

80

Sampling time:

54 d

Details on results:

The 10-day window criterion is fulfilled (21% biodegradation on day 4 and 74% on day 14). The biodegradation achieved after 28 days was 81%.
The test was extended beyond the standard 28 days to 54 days. The degradation level remained at approximately 80%.
Methylionantheme 100% did not inhibit the intrinsic respiration of the inoculum at the test concentration and was therefore considered to be non-toxic to the inoculum at the test concentration.

Validity criteria fulfilled:

yes

Remarks:

Degradation of reference substance exceeded 60% after 14d verifying activity of inoculum and the difference between replicates was less than 20%.

Interpretation of results:

readily biodegradable

Conclusions:

Methylionantheme 100% undergoes 81% biodegradation after 28 days in the test conditions. The 10-day window criterion is also fulfilled. Thus, methylionantheme 100% should be regarded as readily biodegradable according to this test.

Methylionantheme 100% did not inhibit the intrinsic respiration of the inoculum at the test concentration and was therefore considered to be non-toxic to the inoculum at the test concentration.

Methylionantheme 100% is a mixture of isomers. ECHA guidance (version 3.0, June 2017, section R.11.4.2.2.3) states that “If the selected test item consists of sufficiently similar structures and is shown to meet the stringent ultimate ready biodegradation test criterion (>60% in 28 days), it can be concluded that the underlying constituents comprising the complex substance are not expected to be persistent”. Thus Methylionantheme 100% and its underlying isomeric constituents are considered to be readily biodegradable and not persistent in the environment.

The ready biodegradability result of Methylionantheme 100% along with two other source substances is being used to support the biodegradation assessment of the registration substance, Reaction mass of 1-(2,6,6-trimethyl-1-cyclohexen-1-yl)pent-1-en-3-one and 1-(2,6,6-trimethyl-2-cyclohexen-1-yl)pent-1-en-3-one. The study for Methylionantheme 100% has been chosen as the key study because the isomeric composition for this analogue most closely matches that of the registered substance. The two main constituents of the registered substance are present at 30-77% and 10-50% respectively. These isomers are commonly known as n-alpha methyl ionone and n-beta methyl ionone. The test item, Methylionantheme 100%, is described in the biodegradation study report as having a purity of isomer n-alpha (51%) and isomer n-beta (10%). The other components and impurities are other methyl ionone isomers.

The other source substances are included as supporting studies as their isomeric composition is predominantly iso-methyl ionone isomers (see other endpoint record for details). The fact that all three source substances pass the stringent criteria of a ready biodegradability screening test indicates all methyl ionone isomers are readily biodegradable. Therefore, read-across to the target substance is justified and the substance and its underlying constituents can be regarded as readily biodegradable and not persistent.

Executive summary:

The ready biodegradability of Methylionantheme 100% was determined by the manometric respirometry test.

Methylionantheme 100% undergoes 81% biodegradation after 28 days (80% after 54 days) in the test conditions. The 10day window criterion is also fulfilled (21% biodegradation on day 4 and 74% on day 14).

Methylionantheme 100% did not inhibit the intrinsic respiration of the inoculum at the test concentration and was therefore considered to be non-toxic to the inoculum at the test concentration.

Thus, Methylionantheme 100% should be regarded as readily biodegradable according to this test.

Reference 2

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

A detailed justification is provided in the attached document.

In summary, the read-across is based on the hypothesis that the target and three source substances have similar biodegradation properties as a result of structural similarity. The target and three source substances consist of methyl ionone isomers (C14H22O, MW 206.33). The substances differ in the ratio of the isomers present and whether individual isomers are considered as constituents (≥10%) or impurities (<10%) under the REACH naming convention. The individual isomers are structurally very similar, i.e. the arrangements of atoms (or carbon skeleton) and chemical functionality (ketone) are comparable – see figure of generic methyl ionone attached.

The only structural difference between these isomers is the position of the double bond associated with the cyclohexyl ring and/or the position of the methyl group in the side chain. Changes in the position of the double bond are not expected to significantly affect biodegradation properties. However, the position of the methyl group may have an impact since increased branching is known to hinder biodegradation. Thus, in theory, the iso-methyl ionone isomers may be less easily biodegraded than the n-methyl ionone isomers.

Three studies were chosen for inclusion in the registration dossier; 1) a study on Methylionantheme 100% because this substance has a composition that most closes matches that of the registration substance “Reaction Mass of 1-(2,6,6-trimethyl-1-cyclohexen-1-yl)pent-1-en-3-one and 1-(2,6,6-trimethyl-2-cyclohexen-1-yl)pent-1-en-3-one”; 2) a study on Isoraleine Cetone alpha because this is a mono-constituent substance made up of the potentially less easily degraded isomer and 3) a study on Isoraldeine 70 because its composition contains, as main components, a mixture of the n-methyl and iso-methyl ionones.

The experimental data show that this family of isomeric substances exhibit similar biodegradation profiles irrespective of the isomer ratios present. The fact that all three source substances pass the stringent criteria of a ready biodegradability screening test indicates that all isomers present in this family of materials are readily biodegradable. Therefore, read-across to the target substance is justified and the substance and its underlying constituents can be regarded as readily biodegradable and not persistent.

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Key result

Parameter:

% degradation (O2 consumption)

Value:

81

Sampling time:

28 d

Remarks on result:

other: read-across from Methylionantheme 100%

Parameter:

% degradation (O2 consumption)

Value:

76

Sampling time:

28 d

Remarks on result:

other: read-across from Isoraldeine 70

Parameter:

% degradation (O2 consumption)

Value:

71

Sampling time:

28 d

Remarks on result:

other: read-across from Isoraldeine Cetone Alpha

Details on results:

The 10 day window was met in all three studies.

Validity criteria fulfilled:

yes

Remarks:

Read across rationale is provided according the Annex XI criteria

Interpretation of results:

readily biodegradable

Conclusions:

Reaction mass of 1-(2,6,6-trimethyl-1-cyclohexen-1-yl)pent-1-en-3-one and 1-(2,6,6-trimethyl-2-cyclohexen-1-yl)pent-1-en-3-one is readily biodegradable based on read across from three source substances. The target and three source substances consist of methyl ionone isomers (C14H22O, MW 206.33). The substances differ in the ratio of the isomers present and whether individual isomers are considered as constituents (≥10%) or impurities (<10%) under the REACH naming convention. The fact that all three source substances passed the stringent criteria of a ready biodegradability screening test, indicates that all isomers present in this family of materials are readily biodegradable. Therefore, read-across to the target substance is justified and the substance and its underlying constituents can be regarded as readily biodegradable and not persistent.

Description of key information

Reaction mass of 1-(2,6,6-trimethyl-1-cyclohexen-1-yl)pent-1-en-3-one and 1-(2,6,6-trimethyl-2-cyclohexen-1-yl)pent-1-en-3-one

is readily biodegradable based on read across from three analogue substances.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Type of water:

freshwater

Additional information

The registered substance is a multi-constituent substance, Reaction mass of 1-(2,6,6-trimethyl-1-cyclohexen-1-yl)pent-1-en-3-one and 1-(2,6,6-trimethyl-2-cyclohexen-1-yl)pent-1-en-3-one. Other components present are isomers which are described as impurities in the REACH registration because they are typically present at < 10%. The total content of the isomers is > 93% to > 99% (based on identified components present at ≥ 1%, see GCMS data in section 1.4 of this IUCLID REACH dossier).

A study to assess the ready biodegradability of the registered substance is not available. However, valid ready biodegradability studies exist for three analogue substances; Methylionantheme 100% (Key Study, Givaudan Study Number 12 -E166), Isoraldeine 70 (Supporting study, Givaudan Study Number 00-E024) and Isoraldeine Cetone Alpha (Supporting Study, Givaudan Study Number 12 -E010). 

Read-across is based on the hypothesis that the target and three source substances have similar biodegradation properties as a result of structural similarity. The target substance and three source substances all consist of related isomers. The study for Methylionantheme 100% has been chosen as the key study because the isomeric composition for this analogue most closely matches that of the registered substance. As mentioned above the two main isomeric components of the registered substance are 1-(2,6,6-trimethyl-1-cyclohexen-1-yl)pent-1-en-3-one and 1-(2,6,6-trimethyl-2-cyclohexen-1-yl)pent-1-en-3-one. These are commonly known as n-alpha methyl ionone and n-beta methyl ionone. The concentration range for these two components in the registered substance is 30-77% and 10-50% respectively. The test item, Methylionantheme 100%, is described in the biodegradation study report as having a purity of isomer n-alpha (51%), isomer n-beta (10%), isomer iso-alpha (20%) and isomer iso-beta (6%). Methylionantheme 100% has been tested in the OECD 301F Manometric Respiratory Test and achieved a biodegradation level of 81% after 28 days. The 10-day window criterion was also fulfilled. Thus, Methylionantheme 100% is regarded as readily biodegradable according to this test.

The other two source substances contain higher levels of the iso-methyl ionone isomers. ISORALDEINE 70 (supporting Study,Givaudan Study Number 00-E024) is composed of isomer iso-alpha 60-70%, n-alpha 20-30% and n-beta 0-10% while Isoraldeine Cetone Alpha (Supporting Study, Givaudan Study Number 12 -E010) is a mono constituent substance, containing (E)-3-methyl-4-(2,6,6-trimethylcyclohex-2-en-1-yl)but-3-en-2-one (isomer iso-alpha) as its major constituent and having a total iso-methyl ionone content of >98%. Both of these substance have been tested in an OECD 301F study and achieved biodegradation levels of 76% and 71% respectively after 28 days. The 10-day window criterion was also fulfilled. Thus, ISORALDEINE 70 and Isoraldeine Cetone Alpha are regarded as readily biodegradable.

The individual isomers present in the registered substance and source substances are expected to exhibit similar biodegradation profiles as a result of similar chemical functionality (unsaturated aliphatic ketones) and similar carbon skeletons (i.e. arrangement of atoms). The only structural difference between them is the position of the double bond associated with the cyclohexyl ring (denoted by the terms alpha and beta) and/or the position of the methyl group in the side chain (denoted by the prefixes iso- and n-) - see generic structure in attachment. Changes in the position of the double bond are not expected to significantly affect biodegradation properties. However, the position of the methyl group may have an impact on biodegradation potential with the iso-methyl ionone isomers being potentially less easily biodegraded than the n-methyl ionone isomers due to the increased branching of the side chain. The fact that all test substances passed the stringent criteria of a ready biodegradability screening test indicates that both groups of isomers are readily biodegradable.

ECHA guidance (version 3.0, June 2017, section R.11.4.2.2.3) states that “If the selected test item consists of sufficiently similar structures and is shown to meet the stringent ultimate ready biodegradation test criterion (>60% in 28 days), it can be concluded that the underlying constituents comprising the complex substances are not expected to be persistent”. Thus based on the studies of the three analogue substances, the registered substance and its underlying isomeric constituents are considered to be readily biodegradable and not persistent in the environment.