2-(1-(3',3'-dimethyl-1'-cyclohexyl)ethoxy)-2-methyl propyl propanoate

Endpoint summary

Description of key information

Two terrestrial long term toxicity studies, covering two trophic levels, soil microorganisms and earthworms, were conducted on the registered substance further to a request from the European authorities.

 

The long-term toxicity study of the registered substance on nitrogen transformation activity of soil microorganisms was performed according to the OECD Guideline 216 and EU Test Method C.21 with GLP statement (Fraunhofer, 2018). The inhibitory effect of the registered substance on nitrogen transformation was assessed by the determination of nitrate concentration in the soil samples and compared to data obtained from control soil samples. The registered substance was incubated, in a single application, in loamy sand soil over a period of 28 days in nominal concentrations of 62.5, 125, 250, 500 and 1000 mg/kg dry mass soil. Based on the results of this study, there was a concentration-effect relationship due to the test substance for the relative content of nitrate compared to the control after 28 days of incubation. The EC10 value for nitrogen transformation was determined at 161 (95% CL = 122 - 190) mg/kg dry soil, based on nominal concentrations.

The long-term toxicity study of the registered substance on survival rate, biomass, and reproduction of adult earthworms of the species Eisenia andrei was performed according to the OECD Guideline 222 with GLP statement (Fraunhofer, 2019). The worms were placed in a defined artificial soil substrate containing the registered substance, in a single application, in different nominal concentrations: 15.6, 31.3, 62.5, 125 and 250 mg/kg dry mass soil. The effects on survival rate and biomass were determined after 28 days, and the effects on reproduction were determined after 56 days. As the registered substance degrades into a transformation product at a ratio of 78 -80% of degradation product, an alcohol, and ca. 20% Propionic acid with this latter ultimately mineralizing) in a ready biodegradation test (OECD 301C, Yokohama Lab, 2009), it was decided to include supplementary analytical measurements of the relevant transformation product (non-GLP), along with the measurements of the parent substance (GLP) in the soil samples at the same sampling points. According to the analytical results, the registered substance, as expected, degraded very rapidly. This rapid loss of parent substance is completely in line with the expected degradation profile of an ester. Esters are rapidly metabolised to an alcohol and an acid, but the acid moiety is extremely small and not expected to contribute to the observed toxicity (furthermore, as in the biodegradation test, a complete mineralization of the Propionic acid moiety was observed the propionic acid would be expected to biodegrade rapidly in soil too). The concentrations of the relevant transformation product (the residual alcohol) increased at a rate inversely proportional to the loss of the parent substance and then itself diminished until both substances were no longer analytically measurable. The peak of concentrations of the transformation product was measured at day 3 -7. The reproductive toxicity of the registered substance to earthworms was based on initial concentrations of the test substance (measured at 17.5, 26.4, 58.5, 85.3 and 234.9 mg test item/kg dry mass soil) as this was the parent substance under review, and as the parent substance represented an acute dose at the beginning of the experiment which could account for the effects found. Use of a time weighted average for either the parent and transformation product was considered inappropriate as a means to measure chronic toxicity due to the prolonged absence of the parent and transformation product over a large portion of the study period and as the relevant transformation product, which is the residual alcohol of the registered substance, is a non-polar narcotic (MechoA 1.1) and is expected to be less toxic than the ester (the registered substance).

No decreased survival rate when compared to the control worms and no significant effect on weight change were found up to and including the highest tested concentration. However, due to maximum effects of 9 -13% reduction of weight change in the two highest treatment levels, a slight concentration-effect relationship was observed and an EC10 value was determined at 170.1 mg/kg soil (initial concentration). Regarding reproduction effects, a significant decrease in reproduction was found starting at an initial concentration of 58.5 mg test item/kg dry mass soil. The EC10 value was determined at 61.8 (CL 95%: 42.5 – 78.3) mg/kg dry mass soil (initial concentration).

In conclusion, chronic effects on terrestrial organisms were observed for the registered substance. The lowest EC10 value, determined at 61.8 mg/kg dry mass soil for reproduction of Eisenia andrei, was chosen as key value for the chemical safety assessment.

Based on a conservative estimation from Chesar, further testing on terrestrial effects does not need to be conducted as the chemical safety assessment does not indicate a need for further investigation.