Trichloro(propyl)silane

Endpoint summary

Additional information

No data are available for the registration substance, trichloro(propyl)silane (CAS 141-57-1). However, data are available for the structurally related substance, trimethoxy(propyl)silane (CAS 1067-25-0). Both substances rapidly hydrolyse to the same silanol containing hydrolysis product propylsilanetriol. Reliable short-term toxicity tests results are available for freshwater fish (Danio rerio, tested as Brachydanio rerio), invertebrates (Daphnia magna) and algae (Desmodesmus subspicatus, tested as Scenedesmus subspicatus). The relevant short-term values are:

Fish: LC₅₀ (96 h): >746 mg/l expressed in terms of measured concentrations of Dissolved Organic Carbon (DOC).

Daphnia: EC₅₀ (48 h): >816 mg/l expressed in terms of measured concentrations of Dissolved Organic Carbon (DOC).

Algae: EC₅₀ (72 h): >913 mg/l; NOEC: ≥913 mg/l expressed in terms of measured concentrations of Dissolved Organic Carbon (DOC).

 

The rapid hydrolysis of trimethoxy(propyl)silane (CAS 1067-25-0) (half-life 2.6 h at pH 7 and 20-25 °C) means it is likely that the test organisms in each test were exposed primarily to the hydrolysis products, propylsilanetriol and methanol.

 

These short-term aquatic toxicity studies used stock solutions at a nominal concentration of 1000 mg/l. At this concentration the silanol hydrolysis product (which is formed in significant quantities over the time-scale of the media preparation) can undergo condensation reactions to give siloxane and siloxanol dimers, oligomers and polymers. If these are present in significant quantities as insoluble materials they have the potential to cause physical effects on test organisms.

At dilute concentrations polymerisation is understood to be a reversible process, resulting in test organisms being exposed to the hydrolysis products of this substance in solution.

The stock solutions used to prepare the test media for the tests with the structurally analogous substance were filtered and no condensation products were observed. After filtration, the measured DOC (dissolved organic carbon) concentration in the stock solutions were in the range 823-975 mg/l, indicating that not significant quantities of undissolved or condensed test material had been removed (<20%). However, some polymerisation products such as oligomers could still have been present in the stock solutions if they were able to pass through the filter membrane. Therefore, while the stock solution preparation was not carried out under ideal conditions for this substance, the studies do indicate that the structurally analogous substance is of low short-term toxicity to the tested organisms.

 

Reliable data for long-term toxicity to Daphnia magna are available for the read-across substance, trichloro(ethyl)silane (CAS 115-21-9). In this test the 21-day NOEC for survival and reproduction was found to be ≥100 mg/l, nominal concentration. The test substance very rapidly hydrolyses to ethylsilanetriol and hydrochloric acid. The NOEC expressed in terms of the silanol hydrolysis product, ethylsilanetriol, is ≥66 mg/l.

 

An activated sludge respiration inhibition 3 hour EC₁₀ value of >100 mg/l (nominal) was determined in a reliable study read-across from an appropriate structural analogue trimethoxy(methyl)silane (CAS 1185-55-3). Both the registration substance and the read-across substance hydrolyse to structurally related silanol hydrolysis products propylsilanetriol and methylsilanetriol, respectively.