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Environmental fate & pathways

Biodegradation in soil

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No soil simulation test data are available for 1,1,3,3-tetramethyldisiloxane (H2-L2). However, hydrolysis data indicate that this substance quickly hydrolyses in contact with water; the intitial step is the hydrolysis of the siloxane (Si-O-Si) group to form dimethylsilanol, with subsequent hydrolysis of the Si-H bond to form dimethylsilanediol.

Soil simulation studies, which are considered reliable, are available for dimethylsilanediol (Lehmann et al. (1994), Lehmann et al. (1998), Sabourin et al. (1996a and b)).

These studies were conducted according to generally accepted scientific principles, and are used as weight of evidence that degradation in soil does occur but not to a significant extent. Initial rates of soil degradation from these studies are considered to be the data of most use, and most representative of field conditions, as rates tended to slow over the course of the experiments. Initial rates of degradation ranged from 0.16 to 6.8% per month. The decrease in rates of degradation over the course of the experiments may be due to some form of binding of organosilane compounds to soil, as indicated by HPLC analysis of HCl-extractable fractions from the soil in some of the studies.