Registration Dossier

Ecotoxicological information

Endpoint summary

Administrative data

Description of key information

Additional information

2,4,6-Trimethyl-2,4,6-tris(3,3,3-trifluoropropyl)cyclotrisiloxane (CAS 2374-14-3, F-D3) has an extremely low water solubility (1.3E-06 mg/l) and very high log Kow (9). These values indicate that the equilibrium between dissolved substance in soil interstitial water and adsorbed substance on soil solids will be significantly in favour of the adsorbed (non-bioavailable) form. At equilibrium, the solids:water weight ratio is such that exposure via the interstitial water would be very low in absolute terms and also as a fraction of the total applied to soil. The substance is susceptible to hydrolysis with a half-life of 6 days at pH 7 and 25°C, and while the reaction products (fluorinated siloxanediols) in principle have higher water solubility than F-D3, preliminary evidence from the long-term Daphnia test suggests that precipitation of insoluble oligomers occurs at loading rates above the solubility of the test substance (refer to IUCLID Sections 4 and 5.1.2). However, the registered substance has a high adsorption potential, and once adsorbed, hydrolysis may not occur.

In addition:

- The physicochemical properties and very high value of Koc 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. WWTP sludge from all sites handling the substance is incinerated, therefore the result is that exposure of the terrestrial compartment is negligible.

- The high volatilisation potential of F-D3, as indicated by a very high Henry’s Law Constant (2.96E+10 Pa m3mol-1 at 25°C) and high air-soil partition coefficient (Kair-soil = 4.9 at 25°C) indicates that testing the substance would not be technically feasible because the substance would not be kept in soil under the experimental conditions of the test.

Furthermore, 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.