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Reliable short-term toxicity tests conducted with 3-aminopropyl(triethoxy)silane (CAS 919-30-2) are available for species of freshwater fish (Brachydanio rerio), freshwater invertebrate (Daphnia magna) and fresh and marine water algae (Scenedesmus subspicatus and Skeletonema costatum, respectively) and are taken as key or weight of evidence data.

 

The hydrolysis rate of 3-aminopropyl(triethoxy)silane (CAS 919-30-2) (half-life 8.5 hours at pH 7 and 20-25 °C) and test media preparation methods and pH values mean it is likely that the test organisms in each test were exposed primarily to the hydrolysis products, 3-aminopropylsilanetriol and ethanol.

 

The relevant short-term values are:

Fish: LC50 (96 h): >934 mg/l or >579 mg/l expressed in terms of concentration of the hydrolysis product, 3-aminopropylsilanetriol (Evonik, 1994).

Invertebrates: Daphnia, freshwater: EC50 (48 h): 331 mg/l or 205 mg/l expressed in terms of concentration of the hydrolysis product, 3-aminopropylsilanetriol.

Invertebrates: Copepod, marine water: LC50 (48 h): 580 mg/l or 359 mg/l expressed in terms of concentration of the hydrolysis product, 3-aminopropylsilanetriol.

Algae: Freshwater: ErC50 (72 h): >1000 mg/l or >620 mg/l expressed in terms of concentration of the hydrolysis product, 3-aminopropylsilanetriol; ErC10: 321 mg/l or 199 mg/l expressed in terms of concentration of the hydrolysis product, 3-aminopropylsilanetriol (Hüls, 1993).

Algae: Marinewater: ErC50 (72 h): 863 mg/l, or 535 mg/l expressed in terms of concentration of the hydrolysis product, 3-aminopropylsilanetriol; NOEC for growth rate: 40 mg/l or 25 mg/l, expressed in terms of concentration of the hydrolysis product, 3-aminopropylsilanetriol (Evonik, 2005).

 

A study of long-term toxicity to Daphnia magna is read-across to the registration data set from N-(3-(trimethoxysilyl)propyl)ethylenediamine (CAS 1760-24-3). The substance hydrolyses rapidly to produce N-(3-(trihydroxysilyl)propyl)ethylenediamine, which is a structural analogue of the silanol hydrolysis product of the registered substance, and methanol. A 21 day NOEC value of =1 mg/l (nominal concentration, highest concentration tested) was determined for the effects of the test substance on survival and reproduction of Daphnia magna (Dow Corning, 1980).

 

To support the available reliable short-term toxicity tests results with the registration substance, data are read across from an analogous isocyanatopropyl trialkoxysilane, 3-(trimethoxysilyl)propyl isocyanate (CAS 15396-00-6), which undergoes a very rapid hydrolysis reaction (half-life <1 minute at pH 7) to form 3-(trimethoxysilyl)propylamine (CAS 13822-56-5) as an intermediate hydrolysis product, with subsequent rapid hydrolysis to 3-aminopropylsilanetriol (half-life 2.6 h at pH 7 and 25°C). This substance is therefore a relevant supporting substance.

Reliable short-term toxicity tests conducted with 3-(trimethoxysilyl)propyl isocyanate (CAS 15396-00-6) are available for species of freshwater fish (rainbow trout) and invertebrate (Daphnia magna) (IBACON, 2003). LC50 or EC50 values for the two organisms were >100 and >100 mg/L, respectively. These limit values are taken as supporting data. The test substance is susceptible to rapid hydrolysis and it is therefore likely that the test organisms were primarily exposed to the hydrolysis products of the substance.

The registration substance is susceptible to hydrolysis reactions (trialkoxysilane to silanetriol) and to potential condensation reactions (described in section 5.1.2 and 4.8 of IUCLID). The same alkoxysilane to silanol hydrolysis reaction and potential for condensation reactions also occurs with the read-across substance, 3-(trimethoxysilyl)propyl isocyanate (CAS 15396-00-6) where the isocyanate to amino reaction is very rapid. It is assumed that no undesirable cross-reactions of the isocyanate group would occur. The alkoxysilane to silanol hydrolysis reaction is faster under equivalent conditions, the ultimate silanol hydrolysis product and potential for condensation reactions are both the same as for the registration substance.

Toxicity to microorganisms data are available with the registered substance and a structural analogue, triethoxy(3-isocyanatopropyl)silane (CAS 24801-88-5).

 

The relevant key value is a 5.75 hour EC50 of 43 mg/l and EC10 of 13 mg/l for the effects of the registration substance on respiration inhibition of Pseudomonas putida (Schoberl, 1994).

 

This result is supported by data with triethoxy(3-isocyanatopropyl)silane (CAS 24801-88-5). This read-across substance undergoes a very rapid hydrolysis reaction (half-life <1 minute at pH 7) to form 3-aminopropyl(triethoxy)silane (CAS 919-30-2) as an intermediate hydrolysis product, with subsequent rapid hydrolysis to 3-aminopropylsilanetriol. A 3 hour EC50 value of 180 mg/l, a NOEC value of 10 mg/l and an EC10 value of 17 mg/l were determined for the effects of triethoxy(3-isocyanatopropyl)silane (CAS 24801-88-5) on respiration inhibition of waste water (activated sludge) bacteria (Desmares-Koopmans, 2013).

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