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Ecotoxicological information

Endpoint summary

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Reliable short-term toxicity test results are available for freshwater invertebrates (Daphnia magna) and algae (Pseudokirchneriella subcapitata) for the registration substance 2,4,6,8-tetramethylcyclotetrasiloxane (HD4, CAS 2370-88-9). The relevant short-term values are:

Daphnia: EC50 (48 h): >100 mg/l nominal concentration.

Algae: EC50 (72 h): >100 mg/l; NOEC: ≥100 mg/l nominal concentration.

 

2,4,6,8-Tetramethylcyclotetrasiloxane (HD4, CAS 2370-88-9) hydrolyses rapidly and, at low concentrations, the final hydrolysis product is methylsilanetriol (see IUCLID Section 4.1.1.1). However, at high concentrations unspecified polymeric species are expected to dominate and short-term aquatic toxicity tests with Daphnia and algae at 100 mg/l found low concentrations of dissolved carbon (≤5 mg/l) in the test media. The EC50s were found to be >100 mg/l and the NOECs ≥100 mg/l based on nominal concentrations. Therefore, due to the instability of the substance and that of its breakdown products, it is not considered appropriate to conduct further testing. In addition, the substance is only used in industrial settings in closed systems under controlled conditions and emissions to surface waters are unlikely.

Data have been read across from substances which rapidly hydrolyse to methylsilanetriol. Reliable short-term toxicity tests results are available for freshwater fish (Danio rerio), invertebrates (Daphnia magna) and algae (Pseudokirchneriella subcapitata) read across from triethoxy(methyl)silane (CAS 2031-67-6). The relevant short-term values are:

 

Fish: LC50 (96 h): >500 mg/l nominal concentration or >264 mg/l expressed in terms of concentration of the hydrolysis product, methylsilanetriol.

Daphnia: EC50 (48 h): >500 mg/l nominal concentration or >264 mg/l expressed in terms of concentration of the hydrolysis product, methylsilanetriol.

Algae: EC50 (72 h): >500 mg/l; NOEC: ≥500 mg/l nominal concentration or >264 mg/l and ≥264 mg/l, respectively, expressed in terms of concentration of the hydrolysis product, methylsilanetriol.

 

Reliable data for long-term toxicity to Daphnia magna are available with methylsilanetriol. In this test the 21 day NOEC for survival and reproduction was found to be ≥10 mg/l based on the mean measured concentration.

 

An activated sludge respiration inhibition 3 hour NOEC value of 32 mg/l, read across from a structurally-related substance dichloro(methyl)silane (CAS 75-54-7), has been determined in a reliable study.

 

The rapid hydrolysis of triethoxy(methyl)silane (CAS 2031-67-6 ) (half-life 5.5 h at pH 7 and 20-25 °C) and the test preparation method (overnight stirring of test solutions prior to addition of test organisms) means it is likely that the test organisms in each test were exposed primarily to the hydrolysis products, methylsilanetriol and ethanol. 

 

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.