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Environmental fate & pathways

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Hexachlorodisilane hydrolyses very rapidly to give hexahydroxydisilane and HCl. Further hydrolysis of the Si-Si bonds in hexahydroxydisilane is expected to happen rapidly and produces monosilicic acid.

Monosilicic acid exists only in dilute aqueous solutions and readily condenses at concentrations above approximately 100 -150 mg/l as SiO2 to give a dynamic equilibrium between monomer, oligomers and insoluble amorphous polysilicic acid.

Hexahydroxydisilane is also likely to form condensation products (polyhydroxy-polysilanes).

These hydrolysis products are inorganic substances which are ubiquitous in the environment and are expected to

enter natural biogeochemical cycles.

A comparison of the total flux of dissolved silica into rivers can be compared with the input from manufacture and use of hexachlorodisilane (refer to Section 9), and indicates that the input is considered negligible in comparison with the natural flux of silica/silicic acid in the environment.

Therefore, it is not appropriate to calculate Predicted Environmental Concentrations (PECs) for the ultimate silanol hydrolysis product, monosilicic acid.

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