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

Short-term toxicity to fish

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

short-term toxicity to fish

Type of information:

experimental study

Adequacy of study:

key study

Study period:

From August 31, 1992 to September 4,1992

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Deficiences are i) use of an emulsifier, ii) lack of analytical confirmation of test substance and iii) use of a static design. Each of these is discussed, along with the rationale as to why the study is still considered valid and reliable, in the section "overall remarks".

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 203 (Fish, Acute Toxicity Test)

GLP compliance:

yes

Specific details on test material used for the study:

Roche No: Ro 01-8915/000
Lot No: 202471
Purity: 91.4 % (sum of isomers)
Composition: 60.2% iso-alpha, 2.6% iso-beta, 21.5% n-alpha, 7.1% n-beta isomer

Analytical monitoring:

no

Vehicle:

yes

Remarks:

Polysorbat 80 (Tween 80)

Details on test solutions:

The various test concentrations of the test substance were prepared by adding the test substance dispersed in Polysorbat 80 (Tween 80) at the appropriate amount. The test substance concentrations were 0 mg/L (control), 7.8 mg/L, 10.9 mg/L, 15.3 mg/L, 21.4 mg/L and 30 mg/L. The amount of vehi-cle in the control and each test item solution was 10 mg/L, except for the 7.8mg/L treatment group where the test substance and vehicle concentration were both present at 7.8 mg/L.

Test organisms (species):

Oncorhynchus mykiss (previous name: Salmo gairdneri)

Test type:

static

Water media type:

freshwater

Total exposure duration:

96 h

Nominal and measured concentrations:

Nominal: 0 mg/L (control), 7.8 mg/L, 10.9 mg/L, 15.3 mg/L, 21.4 mg/L and 30 mg/L.

Reference substance (positive control):

no

Key result

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

10.9 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Details on results:

- The percentage mortality rate (after 96 hours) was 0%, 80%, 100%, 100% and 100% for respectively the 7.8 mg/L, 10.9 mg/L, 15.3 mg/L, 21.4 mg/L and 30 mg/L nominal test concentration.
- The mortality in the control (0mg/L test substance + 10mg/L vehicle) was 0%. Thus the test is considered valid and any toxicity observed in the treatment groups attributed to the test item.
- Based on visual inspection of the data the LC50 is expected to be > 7.8mg/L and < 10.9 mg/L.
- By plotting the log of the various nominal test concentrations against percent mortality, the LC50 value for the test substance was determined by fitting a linear least squares regression line to the data. The LC50 for Isoraldein 70 was determined to be 10.9 mg/L.

Conclusions:

In a guideline study, conducted according to GLP, the exposure of rainbow trout to Isoraldein 70 resulted in a 96 hour LC50 of 10.9 mg/L based on nominal concentrations.

This value is being used in to read-across to 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” (see target endpoint record).

Reference 2

Endpoint:

short-term toxicity to fish

Type of information:

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

Adequacy of study:

key study

Justification for type of information:

A detailed read-across justification in-line with the ECHA RAAF guidelines is provided as an attached document in this IUCLID endpoint record. In summary, the read-across is based on the hypothesis that the target and source substance have similar ecotoxicological properties as a result of structural similarity, the same expected mode of action and similar physicochemical properties. The target and source substance 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 registered substance (target) is a multi-constituent substance consisting of 1-(2,6,6-trimethyl-1-cyclohexen-1-yl)pent-1-en-3-one (beta-n-methylionone, concentration range 10-50%) and 1-(2,6,6-trimethyl-2-cyclohexen-1-yl)pent-1-en-3-one (alpha-n-methylionone 30-77%). These two constituents were present in the source test item at 7.1 and 21.5%. The source substance also has the alpha-iso-methylionone isomer as a main constituent (approximately 60%). All of the aforementioned isomers have the same functional group chemistry (vinyl ketones). The only structural difference between them is the position of the double bond associated with the cyclohexyl ring and/or the position of the methyl group in the side chain (see generic structure, attached in illustration section of this IUCLID endpoint record). These slight differences will not affect the mode of action. This is supported by the OECD QSAR toolbox aquatic toxicity profiles which are identical for all these isomers. Given also the similar lipophilicity of the isomers (as modelled by log Kow), it is expected that all individual isomers will exhibit a similar strength of aquatic toxicity and that any variation in the ratio of isomers between substances will not significantly influence the aquatic toxicity properties. Any minor components present in either the target or source substance are also methyl ionone structural isomers and thus will not impact the prediction.

Reason / purpose for cross-reference:

read-across source

Key result

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

10.9 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

read-across / source substance: Isoraldeine 70

Basis for effect:

mortality (fish)

Remarks on result:

other: read-across from Isoraldeine 70

Conclusions:

A valid short-term fish study exists for related substance; Isoraldeine 70. The study is GLP compliant, conducted to OECD 203 guidelines, covered the required exposure duration of 96 hours and included sufficient dose levels to enable the relevant determination of potency. The LC50 value was determined to be 10.9 mg/L based on nominal concentrations - see source study summaries for details.

The detailed information provided in the attached read-across justification document indicates that the aquatic ecotoxicity of target and source substance are expected to be similar as a result of structural similarity. Both the target and source substances are made up of various methyl ionone isomers, which are expected to exhibit a similar strength of aquatic toxicity based on the same expected mode of action and similar lipophilicity. This is supported by daphnia and algae data for other related source substances (see endpoints 6.1.3 and 6.1.5 respectively), which show that this family of isomeric substances exhibit similar aquatic toxicity irrespective of the isomer ratios present.

Therefore, the above fish LC50 result is considered to give a reliable estimate of short term toxicity to fish of the registered 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.

Description of key information

Based on a valid short-term fish study, based on OECD guideline No. 203 for the closely related substance Isoraldeine 70, the fish 96 hour LC50 for 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 estimated to be 10.9 mg/L.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

10.9 mg/L

Additional information

A study to assess the short-term toxicity to fish is not available for the registration substance. However, a valid short-term fish study does exist for the related substance; Isoraldeine 70. Read-across from this source substance is considered to give a reliable estimate of the short-term toxicity of 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 to fish and is justified based on the hypothesis that the target substance and source substance will have similar ecotoxicological properties. Both the target and source substances are made up of various methyl ionone isomers, which have the same expected mode of action for aquatic toxicity and similar physicochemical properties relevant for the read-across ecotoxicological endpoint. A detailed justification for the proposed read-across in-line with the ECHA RAAF guidelines is provided in the target endpoint record.

The study performed on Isoraldeine 70 (Study Report Number: B-161751, Schlienger 1992) employed a static design. It is GLP compliant, conducted to OECD guideline 203 and using test material (approximately 60% iso-alpha-methyl ionone, 91.4% total of all isomers) which is representative of the source substance. The study design covered the required exposure duration of 96 hours and included sufficient dose levels to enable the relevant determination of potency. Analytical confirmation was not performed and results were based on nominal concentrations. However, studies performed on related substances and included in this REACH dossier confirm that the “methyl ionone” group of substances are chemically stable over periods of 24 hours (Raldeine A GD, semi-static daphnia study no 2469-FF, Ward 2003), 48 hours (Methyl Ionone Alpha Iso 60, daphnia study no AT/N51/02, Unilever 1994) and 72 hours (Raldeine A GD, stability sample in algal inhibition study no 2470-FF, Ward 2003). 

Loss due to volatility cannot be excluded from the fish test as it is not specified whether the glass aquaria were covered. If losses due to volatility were to have occurred these are expected to be at worst approximately 80%. The latter is based on losses seen in the algae studies of Methyl Ionone Alpha Iso 60 (Study No AL/N51/02) and Methylionon 70 (Study No 60E0397/093104) included in this REACH dossier. Final measured concentrations at 72h were respectively, 14-25% and 20.8-25.2% of the initial. In these algae studies, as well as losses due to volatility, adsorption to the growing algae biomass may also have contributed to the decrease in measured concentrations after 72 hours. Thus an estimated loss of 80% in an acute fish study is worst-case and conservative. Adjusting the LC50 of 10.9 mg/L based on nominal for a similar loss would at worst give an LC50 of 2.2mg/L. Since this is in the same range as EC50 values for other aquatic toxicity endpoints (key daphnia 48 EC50 value = 2.65mg/L; Key algae 72h ErC50 value = 7.47 mg/L); the fish study for Isoraldeine 70 is considered reliable with restrictions (Reliability 2) and the results adequate for the purpose of classification and labelling and/or risk assessment.

The original LC50 value of 10.9 mg/L has been selected as the key result for the chemical safety assessment since the above discussion on losses due to volatility is speculative and in reality may not have occurred (i.e. the glass aquaria may have been covered but not specified in the report).