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Environmental fate & pathways

Biodegradation in soil

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Description of key information

Initial rates of degradation in soil simulation tests ranged from 0.16 to 2.1% per month.

Key value for chemical safety assessment

Additional information

No soil simulation test data are available for 2,4,6,8 -tetramethylcylcotetrasiloxane. However, hydrolysis data (see 5.12.) indicate that this substance quickly hydrolyses in contact with water. The initial step is ring opening, followed by chains shortening, resulting in a mixture of progressively shortening alpha-omega methylsiloxanediols. The Si-H groups also hydrolyse but more slowly, ultimately resulting in methylsilanetriol.

Soil simulation studies, which are considered reliable, are available for the structural analogue dimethylsilanediol and/or for methylsilanetriol (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 2.1% 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.