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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Biodegradation in water (screening tests): 0.7% in 28 days (OECD 301D; EU Method C4-E), read-across from an analogous/structurally related substance. 

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

Trimethylsilane is expected to hydrolyse in water within the timescale of the ready biodegradation study (half-life of about 3 days 24.7°C in well water) to form trimethylsilanol and hydrogen.

There are no reliable ready biodegradation data available for the registration substance trimethylsilane (CAS No: 993-07-7), therefore good quality data for the silanol hydrolysis product, tetramethylsilane (CAS No: 75 -76 -3) has been used to assess this endpoint.


Hydrogen is an inorganic gas and biodegradation study is therefore not relevant.


Trimethylsilane (CAS No 993 -07 -7) and tetramethylsilane (CAS No. 75-76-3) are within an analogue group of substances within which, in general, there is no evidence of any significant biodegradation once hydrolysis and subsequent biodegradation of alkoxy/acetoxy groups has been taken into account. In this case, neither substance contains such a group.

This analogue group for the ready biodegradability endpoint consists of a number of sub-classes of substances (based on structure/functionality) with different main codes (used to represent the different sub-classes). However, read-across is carried out between substances with the same main code in most cases.

The table below presents ready biodegradation data for substances within the sub-class[I-1] of silanes.Trimethylsilane (CAS No 993 -07-7) and tetramethylsilane (CAS No. 75-76-3) are members of this class.

It is therefore considered valid to read-across the results for tetramethylsilane (CAS No. 75-76-3) to fill the data gap for the registered substance. Additional information is given in a supporting report (PFA, 2013f) attached in Section 13.

Table: Ready biodegradation data for substances within the relevant sub-class [I-1] of chemicals



Readily biodegradable? Yes/no

Result: Biodegradation after 28 day


Test type

Klimisch code

Corrected % biodegradation once alkoxy/acetoxy biodegradation is accounted for













0ECD 301C





In the study with tetramethylsilane (CAS No. 75-76-3), 0.7% biodegradation was observed in 28 days.

No significant biodegradation is expected for the silanol hydrolysis product.

The study was conducted according to OECD 301D and is considered reliable. This is selected as the key study.

The study is considered to be reliability 1 (reliable without restrictions); the read across of the result is considered to be reliability 2 (reliable with restrictions).



PFA, 2013f, Peter Fisk Associates, Biodegradation Main Analogue Group report, PFA.300.005.007