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Environmental fate & pathways

Hydrolysis

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Silicon is more susceptible to hydrolysis (more soluble) in neutral and alkaline solutions than in acidic solutions. The ionic composition (e. g. Cl) and higher ionic strength of solvents seems to clearly increase the hydrolysis rates.

In the OECD T/Dp screening test solutions very small quantities of elements were released from the particle mass in both pH 6 and 8 media. In total, only a very small portion (less than 0.2%) of the loaded amount of particles sized less than 1 mm of Si HG, Si LG and PCS was released/dissolved upon the 24hour exposure to the OECD T/Dp test media. In comparison synthetic media pH 7.4 dissolved even more than 10% of test material in 24 hours. More than 50% of PCS material was transformed/dissolved in 168 hours.

In addition, the full 7 and 28 day T/Dp tests revealed that the elements that were analysed were only present in very low concentrations, and similar to the screening tests, Si was only present at a concentration of 0.2-0.3 % of the initial amount loaded.