1-(5,5-dimethyl-1-cyclohexen-1-yl)pent-4-en-1-one

Endpoint summary

Description of key information

Two experimental studies of reliability 1 (based on international guidelines and GLP compliance) and three QSAR results (ECOSAR v1.11 QSAR model) are available to assess the aquatic toxicity of the registered substance to the three aquatic trophic levels: aquatic invertebrates, algae and fish.

Experimental acute studies, assessed as key studies and performed on the registered substance, are available on the aquatic invertebrates, Daphnia magna and on the freshwater green algae, Pseudokirchneriella subcapitata. The 48h-EC50 value on aquatic invertebrates was determined at 1.7 mg/L and the 72h-ErC50 value on algae was determined at 3.4 mg/L. Also, the 72h-ErC10 value on algae was determined at 1.7 mg/L.

No experimental study is available on fish but a valid QSAR prediction was provided to fulfil the endpoint. This QSAR (ECOSAR v1.11 available from the U.S. EPA), assessed as a key data for the acute fish endpoint, was performed on the registered substance. The estimated 96h-LC50 value was determined at 1.90 mg/L.

This QSAR model was also used, as supporting information, to predict the acute toxicity of the substance to daphnid and green algae. Similar results or results slightly more conservative were predicted with the QSAR model, validating the model for use with this substance, for the acute fish endpoint.

In conclusion, the most sensitive species in acute conditions is the aquatic invertebrates, Daphnia magna, with a 48h-EC50 value at 1.7 mg/L.

As the registered substance is biodegraded totally in the environment to form two degradation products: succinic acid (degraded also and mineralized completely) and 3,3 -dimethyl cyclohexanone (DMCH). The aquatic toxicity of the relevant degradation product of the registered substance, DMCH, to the three trophic levels were estimated using the same QSAR model presented above, ECOSAR v1.11. The estimated endpoint values (E(L)C50) were all greater than 40 mg/L. Therefore, the relevant degradation product of the registered substance, DMCH, is presumably not Toxic (T) in the PBT assessment context.

In addition, no experimental study was performed on the registered substance to assess the toxicity to microorganisms. However, a study was performed on a read-across substance, to assess the effect of the test substance on the respiration rate of activated sludge after a contact time of 3 hours, according to OECD Guideline 209 with GLP statement. This source substance is a mixture of two isomers: 1-(5,5-Dimethyl-1-cyclohexen-1-yl)-4-penten-1-one, present as the major constituent at ca. 66% in the mixture, and corresponding to the registered/target (mono-constituent) substance, and 1-(3,3-Dimethyl-1-cyclohexen-1-yl)-4-penten-1-one, present at ca. 30% as second constituent.

According to this study, no statistically significant inhibition of the respiration rate of the sludge was recorded at a loading rate of 46 mg/L. At higher loading rates the inhibitory effect of test substance on aerobic waste water (activated sludge) bacteria increased with increased loading rate, ranging from 22% inhibition at 100 mg/L to 47% at 1000 mg/L. In conclusion, the test substance is considered not toxic to waste water bacteria (activated sludge) at a loading rate of 46 mg/L (NOEL). Based on structural/composition similarity, comparing physicochemical and environmental properties and ecotoxicological profile, both substances (the source and the target substances) are not expected to be significantly different in terms of their activated sludge respiration inhibition. Therefore, the same conclusion applies on the registered/target substance.