Polysulfides, bis[3-(triethoxysilyl)propyl]

Long-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

long-term toxicity to aquatic invertebrates

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Reason / purpose for cross-reference:

reference to other study

Reason / purpose for cross-reference:

reference to other study

Reason / purpose for cross-reference:

reference to other study

Reason / purpose for cross-reference:

reference to other study

Reason / purpose for cross-reference:

reference to other study

Reason / purpose for cross-reference:

reference to other study

Additional information

Testing for long-term toxicity to aquatic invertebrates is not considered necessary because:

No data are available for the registered substance, which has a hydrolysis half-life of 40-80 hours, 40-110 hours and 40-130 hours at pH 7 and 20-25°C for the S2, S3 and S4 constituents, respectively to form (3-{[3-(trihydroxysilyl)propyl]disulfanyl}propyl)silanetriol, (3-{[3-(trihydroxysilyl)propyl]trisulfanyl}propyl)silanetriol and [3-({[3-(trihydroxysilyl)propyl]disulfanyl}disulfanyl)propyl]silanetriol and ethanol. Due to this moderate hydrolysis rate, the assessment entity for the aquatic compartment is the parent substance. Long-term aquatic toxicity testing for the silanol hydrolysis product is therefore not appropriate. Long-term aquatic toxicity testing for the parent substance, bis[3-(triethoxysilyl)propyl]polysulfides (CAS 211519-85-6, EC 915-673-4), is not required for the following reasons:

In accordance with Column 2 of REACH Annex IX, there is no need to further investigate the effects of this substance in a long-term aquatic toxicity to aquatic invertebrates study because, as indicated in guidance R.7.8.4.3 (ECHA 2017), the quantitative chemical safety assessment (conducted according to Annex I of REACH) indicates that the Risk Characterisation Ratio is well below 1, even with due consideration of contributing uncertainties, and therefore the risk is already adequately controlled and further testing is not justifiable. The parent substance has a low solubility in water, is not bioaccumulative (based on BCF = ≤ 188 to 511 (mean: 244, see IUCLID Section 5.3 for further details) and there is no reason to expect any specific mechanism of toxicity beyond narcosis. Therefore, the occurrence of toxic effects that were not expressed at, or below the limit of solubility (that were not attributed to physical effects of undissolved test substance or precipitated by-products) would be considered unlikely. Based on the short-term aquatic data set for the parent substance, the most sensitive trophic level is algae, which has a 72-hour EL₅₀ value of 700 mg/l. This value is above the limit of solubility for the parent substance (0.01 mg/l at 20°C), however a PNEC has been derived for the purpose of chemical safety assessment, using this value as a starting point. An assessment factor of 1000 was applied to derive the freshwater PNEC. For a narcotic chemical without a specific mode of toxic action, it is unlikely that the aquatic PNEC would be significantly over-estimated using this method.

Based on the highest freshwater RCR available for the parent substance, bis[3-(triethoxysilyl)propyl]polysulfides (0.012), with a corresponding Predicted Environmental Concentration (PEC) of 0.00812 mg/l, the PNECaquatic (freshwater) value would need to be ≤0.00812 mg/l to result in RCR values ≥1. This value is 86.2 times lower than the current PNECaquatic (freshwater), based on the short-term dataset (0.7 mg/l). A PNECaquatic (freshwater) value of ≤0.00812 mg/l would correspond to a long-term EC₁₀ or NOEC value of ≤0.406 mg/l when applying an assessment factor of 50, indicating high toxicity which was not observed in the short-term dataset.

Additionally, the parent substance is highly insoluble and any effects observed in the short-term aquatic dataset are attributable to physical effects of undissolved test substance or precipitated by-products, rather than intrinsic toxicity. The test media preparation is extremely difficult for this substance, due to the low water solubility of the substance, its potential to hydrolyse and the condensation of the hydrolysis products to insoluble oligomers. As a consequence, there is the likelihood that in long-term aquatic tests, dissolved and undissolved phases of the parent substance will be present simultaneously potentially causing physical effects and that hydrolysis product will also be present. Additionally, preparation of a test medium containing a pre-hydrolysed form of the substance for testing is not technically achievable due to the formation of different chemical species and different phases, and this would not assess the parent substance.

Overall it is concluded that the risk characterisation conclusion is sufficiently conservative in respect of any uncertainties and therefore further testing is not considered necessary. Details on how the PNEC and the risk characterisation ratio have been derived can be found in IUCLID Section 6, CSR Section 7.0 and Chapters 9 and 10 of the Chemical Safety Report, respectively.