Dimethoxydimethylsilane

Endpoint summary

Additional information

Dimethoxy(dimethyl)silane (CAS No. 1112-39-6) hydrolyses rapidly in contact with water (DT50 < 0.6 h, pH 7, 25 °C, OECD 111, GLP) and forms the degradation products dimethylsilanediol (DMSD, CAS No. 1066-42-8) and methanol (CAS No. 67-56-1). Thus, the environmental fate assessment is based on the hydrolysis products dimethylsilanediol (DMSD) and methanol rather than the parent substance.

Dimethylsilanediol
The biodegradation of DMSD (dimethylsilanediol) in environmental matrices was investigated in soil and sediments in the presence of microorganisms that are likely to degrade DMSD (CES, 2016). Different sites known or expected to be contaminated with silanols were selected in order to maximize the probability to obtain samples with various organisms previously exposed and potentially adapted to silanols. Four types of environmental matrices were sampled (surface water, sludge, leachate and soil) and mixed together to obtain four groups with an initial microbial diversity which was as broad as possible. Eight different conditions that cover a range of environmentally relevant redox conditions were tested in duplicate. The reactors were incubated for more than one year and sacrifices were performed four times. This extensive study found no evidence for any significant degradation or conversion of DMSD in any of the aquatic or soil conditions representative of diverse environmental conditions.
In a PhD thesis, Fischer-Reinhard (2007) investigated the biodegradation of DMSD by microbial consortia (activated sludge from the wastewater treatment plant of a silicone oil producing plant, and a mix of several activated and digested industrial and municipal wastewater sludges) under aerobic, anoxic, sulfato-reducing and methanogenic conditions. There was no evidence for a significant conversion of DMSD to CO2 under these environmentally relevant conditions.
The biodegradability of dimethylsilanediol in soil has also been the subject of several earlier studies published in the scientific literature (Sabourin et al., 1996; Lehman et al., 1998; Sabourin et al., 1999). Various types of soil and test durations were applied. However, the biodegradation rate was no more than a few percent per month.
Overall, the available data suggest that biodegradation of dimethylsilanediol in water, soil or sediment is negligible. Thus, dimethylsilanediol can be regarded as persistent in the environment.

Additionally, further available evidence regarding biodegradation and persistence of organosilicon compounds is summarised in an attached document in Section 13 (PFA 2021).

Methanol
In contrast, the second hydrolysis product methanol is readily biodegradable based on the OECD SIDS report (OECD, 2004).

 

References
Fischer-Reinhard, M. (2007). Mikrobieller Abbau von Siliconölen, Siloxanen und Silanolen?, Ph.D. Thesis

Lehmann RG, Miller JR, Collins HP (1998). Microbial degradation of dimethylsilanediol in soil. Water Air and Soil Pollution 106: 111-122

OECD (2004). SIDS Methanol.

Sabourin CL, Carpenter JC, Leib TK, Spivack JL (1996). Biodegradation of dimethylsilanediol in soils. Applied and Environmental Microbiology 62: 4352-4360

Sabourin CL, Carpenter JC, Leib TK, Spivack JL (1999). Mineralization of dimethylsilanediol by microorganisms isolated from soil. Environmental Toxicology and Chemistry 18: 1913-1919

CES - Silicones Europe (2016). Fate of silanols in various aquatic / soil environments: Investigation of dimethylsilanediol (bio)degradation in microcosms.

PFA (2021): Background to persistence assessment of organosilicon compounds, Reference: PFA.923.001.001, February 2021.