2-benzyl-4-methyl-4a,5,6,7,8,8a-hexahydro-4H-benzo[d][1,3]dioxine

Short-term toxicity to aquatic invertebrates

Description of key information

QSAR model, iSafeRat , key study, validity 1:

48h-EC50 = 6.4 mg/L (95% CL: 5.7 - 7.1 mg/L).

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Dose descriptor:

EC50

Effect concentration:

6.4 mg/L

Additional information

To assess the short-term toxicity of the registered substance to aquatic invertebrates, two data are available.

 

The first data (QSAR-KREATiS, 2021) is assessed as the key study and is a QSAR. This QSAR prediction (iSafeRat daphnEC50 ) was performed on the registered substance, to assess the acute toxicity of the substance to daphnids. This QSAR has been validated to be compliant with the OECD recommendations for QSAR modelling (OECD, 2004) and predicts the endpoint value which would be expected when testing the substance under experimental conditions in a laboratory following OECD Guideline 202. The immobility of the daphnids was determined using a validated QSAR model for the Mechanism of Action (MechoA) in question (MechoA 1.1, i.e. non-polar narcosis) (Bauer et al., 2018). The QSAR model is based on validated data for a training set of 58 chemicals derived from 48-hour test on daphnids, for which the concentrations of the test item had been determined by chemical analyses over the test period. The test item falls within the applicability domain. The 48-h EC50 based on mobility was determined to be 6 mg/L with 95%-Confidence Limit between 5.7 and 7.1 mg/L.

 

The second data (phytosafe, 2012) is an experimental study assessed as not realiable . A Study was performed according to OECD Guideline 202 with GLP statement, to determine the treatment concentrations liable to immobilize 50 % of the daphnids (EC50) after 24 and 48 h exposure of the test item to Daphnia magna, under static conditions.A 48 h range-finding test was conducted and the percent immobilization was 0, 0, 20, 0, 100, 100 and 100 % at 0.01, 0.1, 1.0, 9.9 and 98.8 mg/L, respectively.

 

No immobilization was observed throughout the test period for the water and solvent control. The percentage of immobilization was 20 % as a maximum for the 0.01 and 0.1 mg/L test item treatments, at 1.0 mg/L 40 % of the daphnids were immobilized after 24 h of standing and then 100 % after 48 h of testing. At both 9.9 and 98.8 mg/L all the daphnids were immobilized after 24 h of testing. The measured concentrations of florenthene as percent nominal value were 109.8, 96.1, 94.7, 95.3 and 102.4 % at initial medium while 100.9, 97.3, 96.4, 95.7 and 98.6 % at final medium in definitive test. The test item treatments were satisfactorily maintained between 80-120 % of the nominal values throughout the test period.

 

Under the test conditions, 48h-EC50 (Daphnia magna) = 0,38 mg/L (95% CL: 0,12-1,20 mg/L) based on analytically confirmed nominal concentrations (recovery of the substance at the end of the test: 95.7-100.9 %).

 

However, this study is not reliable due to high concentration of solvent used. Indeed, a large quantity of acetone was used as solvent in this study. Because of the potential for interaction with the test chemical resulting in an altered response in the test, solvent use should be restricted to situations where no other acceptable method of test solution preparation is available. The use of solvent is not the best method at the time being. Then, the concentration/quantity of solvent used in the treatment solutions was 5 mL/L, corresponding to 3.95 g/L (with a density of 0.79), which is 50 times higher than the recommended maximum level of solvent (below 0.1 mL/L; OECD 23) and represent almost half of the EC50 of acetone (which was reported in the ECHA disseminated dossier at 8.8 g/L). Acetone is suspected to have affected the definitive results. Some solvent/substance interactions may have occurred in this study with this high concentration of acetone.

 

In conclusion, the experimental range-finding tests performed on the registered substance supports the key prediction data. Therefore, the 48h-EC50 value was considered to be 6,4 mg/L.