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Short-term toxicity to aquatic invertebrates

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No reliable toxicity to aquatic invertebrates data are available for 1,3,5-trimethyl-1,1,3,5,5-pentaphenyltrisiloxane (CAS 3390-61-2).

A short-term toxicity to invertebrates test has been carried out with the registration substance. A 48-hour EL50 value of >100 mg/l and NOEC of 1 mg/l were determined for the effects of the test substance on mobility of Daphnia magna based on nominal test substance loading rate. A corresponding EC50 value of >1.4 mg/l was determined on the basis of the measured concentration of Dissolved Organic Carbon (DOC) in the test medium. However, concentrations used in this test far exceeded the limit of solubility of the test substance. Formation of an emulsion was probable and the filtration was not adequate for emulsions. For these reasons, this test has been disregarded.

Testing is not required for the following reasons:

- It is technically not feasible to conduct an aquatic study due to the insolubility of the substance (predicted water solubility of 9.0E-11 mg/l) and very high log Kow (9). 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 Kow of 6 short-term toxicity effects are not expected, because the very limited aqueous solubility prevents toxic concentrations being achieved in exposure media.

- The physicochemical properties and very high value of Koc (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.