2,4,6-trimethyl-2,4,6-tris(3,3,3-trifluoropropyl)cyclotrisiloxane

Long-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

long-term toxicity to aquatic invertebrates

Data waiving:

study technically not feasible

Justification for data waiving:

other:

Description of key information

Long-term toxicity to invertebrates: 21-d NOEC <2.6 µg/L (single concentration tested; significantly exceeds solubility limit) (OECD 210 with significant methodological adaptations). The test result is not suitable for use in hazard assessment and is included for completeness only.

Additional information

A long-term (21-d) flow-through toxicity limit test (OECD TG 211) was performed with Daphnia magna. The nominal concentration was 20 µg/L (which is far above water solubility of 1.3E-06 mg/L). A solvent (acetone) was used, and a solvent control was included in the study. The measured concentrations at days 0, 7, 14, and 21 were 0.51, 6.1, 0.79, and 3.1 µg/L with a mean of 2.6 µg/L.

The NOEC (mortality, adult length) ≥2.6 µg/L; the NOEC (reproduction, offspring/female) <2.6 µg/L and the LOEC for mortality and body length >2.6 µg/L.

In view of the exposure regime and based on evidence from the study report it is likely that the test organisms were exposed to a mixture of dissolved and undissolved parent substance, dissolved and undissolved hydrolysis products and precipitated oligomers. The study is not suitable for use in hazard assessment. The following considerations were taken into account in this conclusion: - Solubility was exceeded. - The test system was regularly cleaned due to biofilms forming. Both the biofilms and cleaning stress may have contributed to effects observed in the test. - Analytical recoveries were very poor and extremely variable, consistent with partially dissolved and condensed material being included in the samples. - The control culture performed unusually well, making sensitivity interpretation more difficult.

In summary, various factors may have contributed to effects observed in this study so that effects cannot reliably be attributed to the registration substance. It is not possible to accurately interpret whether any intrinsic toxicity occurred below the limit of solubility of the registration substance. The formation of precipitates, biofilms and stress from additional cleaning procedures would be expected to have contributed.

A data waiver is in place for long-term toxicity to aquatic invertebrates. Testing is not required for the following reasons:

- It is technically not feasible to conduct an aquatic study due to the very low water solubility of the substance (1.3E-06 mg/l) and very high log K_ow (9), as confirmed by the attempted long-term Daphnia study. These values indicate that maintaining stable aqueous test solutions will be extremely difficult. Furthermore, once dissolved, the substance will have the tendency to adsorb onto the glassware under experimental conditions and onto dissolved organic matter in the natural environment.

- Above a log K_ow of 6.0 short-term toxicity effects are not expected to occur, because the very limited aqueous solubility prevents toxic concentrations being achieved in exposure media. Similarly, above log K_ow of 8, long-term toxicity effects are not expected; The very high log K_ow and very low limit of solubility in water mean the substances have very low bioavailability and uptake of the substance is limited. For substances with these properties, chronic aquatic ecotoxicity is unlikely to be of concern.

- The physicochemical properties and very high value of K_oc (6) means that if the substance could enter a wastewater treatment plant in influent waste waters, it would partition mainly to sludge (a small proportion may be volatilised), with a negligible amount passing to water. The result is that exposure of freshwater or marine aquatic compartments is negligible.

- The substance is not manufactured or used as such in the EU and is registered in accordance with the REACH Regulation (Article 6) in order to support import of polymers. Residual unbound monomer in polymer is very low and the substance is of extremely low water solubility, such that unintentional release to the aquatic environment from end use of the polymers is negligible.