2-Butenedioic acid, 2-methyl-, 1,4-bis(2-ethylhexyl) ester, (2Z)-

Endpoint summary

Additional information

There are two valid experimental studies conducted on acute aquatic toxicity, even if the extremely limited water solubility of the test substance is taken into account.

The algal toxicity test conducted according to OECD 201 and EC C.3 under GLP indicates that the test substance exhibited no toxic effects at the saturation concentration. The reported 72 h EC50 values are > 100 % (v/v) and statistically determined NOECs based on growth inhibition and yield were 100 % v/v saturated nominal concentration (p >= 0.05). In addition, the OECD Guidance Document on Aquatic Toxicity Testing of Difficult Substances and Mixtures (OECD 2000) was followed and two preparatory tests conducted prior to the definitive test. Also the concentrations were analytically determined in the test solution at the beginning and end of the definitive test. As all validation criteria were met, the test result is considered as reliable (Klimisch 1). The study is selected as the key on acute aquatic toxicity.

In daphnids, the experimentally observed acute aquatic toxicity (EC50 48-h) was > 100% of the saturated solution in a non-GLP screening test (OECD 202). The nominal concentrations were 0.1, 1, 10 and 100 mg/L at 20 oC. Concentrations were not analytically measured and the substance is very poorly soluble in water. The results are therefore rated as reliable with restrictions (Klimisch 2). The experimental screening study is selected as a supporting.

An ECOSAR v 1.1 QSAR modelling was performed using experimentally determined water solubility and log P values. The model gave five estimates (i - v) for three classes: esters, methacrylates and neutral organics (baseline toxicity).The methacrylate estimates for five endpoints were selected to be reported in this dataset as the most conservative, but disregarded as not reliable (Klimisch 3) due to the applicability domain of the acute toxicity estimates and and limited chronic data:

i) The ECOSAR QSAR estimate for acute aquatic toxicity LC50 (96 h) on fish was 0.007 mg/L based on mortality. As the experimental Log P (7.63) used for modelling is out of applicability domain of the model (maximum 5.0 for fish acute toxicity), the result is rated as not reliable (Klimisch 3).

ii) The ECOSAR QSAR estimate for acute aquatic toxicity LC50 (48 h) on daphnids was 0.007 mg/L based on mortality. As the experimental Log P (7.63) used for modelling is out of applicability domain of the model (maximum 5.0), and the data set is very limited, the result is rated as not reliable (Klimisch 3).

iii) The most conservative ECOSAR QSAR estimate for chronic toxicity ChV of methacrylates on fish was 0.000418 mg/L based on acute/chronic ratio 1/10. Even if log P of the test substance 7.63 is within the applicability domain of the chronic model (< 8), the estimate is derived from acute fish toxicity results, where the log P is out of the descriptor domain. The result is therefore rated as not reliable (Klimisch 3).

iv) The most conservative ECOSAR QSAR estimate for chronic toxicity ChV of methacrylates on daphnids was 0.000943 mg/L based on acute/chronic ratio 1/10. Even if log P of the test substance 7.63 is within the applicability domain of the chronic model (< 8), the estimate is derived from acute fish toxicity results, where the log P is out of the descriptor domain. The result is therefore rated as not reliable (Klimisch 3).

v) The ECOSAR QSAR estimates for acute aquatic toxicity EC50 (96 h) on green algae was 0.0018 mg/L, and for chronic toxicity ChV was 0.01 mg/L. As there are extremely limited acute and chronic toxicity data on algae, the result is rated as not reliable. Furthermore, log P of the test substance 7.63 is out of the domain of the acute descriptors (maximum 5). The results are therefore rated as not reliable (Klimisch 3).

Conclusion: the two experimental acute toxicity tests conducted on algae and daphnids both indicate that the test substance is not acutely toxic to daphnids and algae at saturation (76 h and 24 h EC50 values > 100 % v/v saturated nominal concentration). For algae, the derived chronic NOEC value is also 100 % v/v saturated nominal concentration, indicating that there are no chronically toxic effects at the saturation concentration. The ECOSAR 1.1 QSAR modelling results are disregarded.