3-(trimethoxysilyl)propyl isocyanate

Endpoint summary

Additional information

Reliable data for short-term toxicity of the registration substance to fish and invertebrates are available. The isocyanate functional group of 3-(trimethoxysilyl)propyl isocyanate (CAS 15396-00-6) undergoes a very rapid hydrolysis reaction (half-life <5 minutes at pH 7, estimated based on read-across) to initially produce 3-(trimethoxysilyl)propylamine (CAS 13822-56-6). A second rapid hydrolysis step then follows (half-life 2.6 h at pH 7, QSAR) which produces 3-aminopropylsilanetriol (CAS 58160-99-9) and methanol (CAS 67-56-1).

The rapid hydrolysis means it is likely that the test organisms in each test were exposed primarily to the hydrolysis products, 3-aminopropylsilanetriol and methanol.

The studies used a single stock solution at 100 mg/L in limit studies and no serial dilution took place. The DOC analysis shows the test substance to be in solution within 20% of nominal, while some loss of the test substance was measured (6 to 12%). However models would suggest that the irreversible condensation is unlikely for these silanol hydrolysis products at the concentrations relevant to the studies (PFA, 2016am). It is assumed that the dosing method used by the laboratory was adequate to prevent undesirable cross-reactions of the isocyanate group.

 

The relevant short-term values are:

Fish: LC₅₀ (96 h): >100 mg/l or >67 mg/L expressed in terms of concentration of the hydrolysis product, 3-aminopropylsilanetriol.

Daphnia: EC₅₀ (48 h): >100 mg/l or >67 mg/L expressed in terms of concentration of the hydrolysis product, 3-aminopropylsilanetriol.

 

Reliable short-term toxicity test results are also available with an aminopropyltrialkoxysilane, 3-aminopropyl(triethoxy)silane (CAS 919-30-2), which is a close analogue of 3-(trimethoxysilyl)propylamine (CAS 13822-56-6), the amine which is formed when the registered substance comes into contact with water/moisture. 3-Aminopropyl(triethoxy)silane (CAS 919-30-2) also reacts in water to the same final silanol hydrolysis product as the registration substance, 3-aminopropylsilanetriol (half-life of 8.5 hours at pH 7 and 25 °C).

The prolonged test solution preparation time (18-24 hours) and the pH of the test solutions (initial pH >7.5) means it is likely that the test organisms in each test were exposed primarily to the hydrolysis products, 3-aminopropylsilanetriol and ethanol (CAS 64-17-5).

 

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.

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

Acartia tonsa: LC₅₀ (48 h): 580 mg/L or 360 mg/L expressed in terms of concentration of the hydrolysis product, 3-aminopropylsilanetriol.

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

Algae: Marine water: ErC₅₀ (72 h): 863 mg/L and NOEC 40 mg/L or 535 mg/L and 25 mg/L respectively, expressed in terms of concentration of the hydrolysis product, 3-aminopropylsilanetriol.

 

Results for 3-(trimethoxysilyl)propylamine (CAS 13822-56-6) are available from a secondary source for which no reliability can be assigned.

 

A reliable long-term toxicity to aquatic invertebrates result is available for a structural analogue of the registration substance, trichloro(ethyl)silane (CAS 115-21-9).

 

The relevant result is: 21-day NOEC of =100 mg/L based on survival and reproduction of Daphnia magna. The hydrolysis half-lives of the registration substance and trichloro(ethyl)silane indicate that, under conditions relevant to ecotoxicity assessment, both will hydrolyse to similar hydrolysis products 3-aminopropylsilanetriol and ethylsilanetriol (CAS 5651-16-1), respectively, over the course of the test. The result is therefore equivalent to =66 mg/L when expressed in terms of silanol hydrolysis product.

 

There are no reliable data for toxicity of the substance to sewage treatment plant microorganisms. A 3 hour ASRI NOEC value of 10 mg/L (nominal) has been read-across from the structurally-related substance triethoxy(3-isocyanatopropyl)silane (CAS 24801-88-5). Both substances hydrolyse very rapidly and share the same silanol hydrolysis product, 3-aminopropylsilanetriol.

 

Data waivers are applicable to long-term toxicity data for fish. 

Refer to IUCLID Section 6 endpoint summary (CSR Section 7.0) for further discussion of the approach to chemical safety assessment and justification for read across.