Triethoxy(3-isocyanatopropyl)silane

Endpoint summary

Additional information

There are no reliable data for toxicity of the registration substance to aquatic organisms. The isocyanate functional group of triethoxy(3-isocyanatopropyl)silane (CAS 24801-88-5) undergoes a very rapid hydrolysis reaction (half-life <5 minutes at pH 7) to form the intermediate hydrolysis product 3-aminopropyl(triethoxy)silane (CAS 919-30-2). A second rapid hydrolysis step then follows (half-life 8.5 hours at pH 7) to produce 3-aminopropylsilanetriol.

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.

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.

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.

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.

To support the available reliable short-term toxicity tests results with 3-aminopropyl(triethoxy)silane (CAS 919-30-2), 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 <5 minutes 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 hours 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). 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 4.8 of IUCLID). The same alkoxysilane to silanol hydrolysis reaction and potential for condensation reactions also occur 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.

The registration substance, triethoxy(3-isocyanatopropyl)silane, was not toxic to waste water (activated sludge) bacteria at or below a loading rate of 10 mg/l (NOEC). This was determined in a reliable study conducted according to an appropriate test protocol (OECD 209), and in compliance with GLP.

Data waivers are applicable to long-term toxicity data for fish and the toxicity to sediment organisms.