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Key value for chemical safety assessment

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Data usable for read-across purposes have been collected on the toxicokinetics of silica and silicates, which can be used for read-across purposes have been collected. There is no need to generate specific data related to Si/FeSi silicate.

 

Release tests in different synthetic biological fluids show that compared to the total amount of particles loaded, between 0.06 and 10% of the Si/FeSi silicate particles sized less than 0.05 mm were dissolved/released as silicon. Significantly higher quantities of silicon were dissolved/released in Gamble's fluid (<10%) than in gastric fluid (<2%) and in phosphate-buffered saline, artificial sweat, or artificial lysosomal fluid (<0.2%) after 168 hours of exposure.

After ingestion, amorphous silicon dioxide seems to have insignificant effects on tissue or urinary silicon levels. Since silicon in different forms is ubiquitous in the environment, various foods, drinking water and beverages contain silicon. Our normal dietary intake of silicon is between 20-50 mg Si/day, and the silicon in the diet seems to be in highly bioavailable form as shown as a high proportion of dietary silicon excreted in the urine. The differences in dietary intake are likely to explain the variability in urine levels of silicon among different individuals. Although in neutral solutions, elemental silicon and amorphous silicon dioxide is slowly dissolved, in acidic solutions the dissolution of silicon and amorphous silicon dioxide is significantly impaired. Thus, e. g., in the stomach, the release of silicon from silicon particles is likely to be low, which is likely to affect the absorption from the gastrointestinal tract.

After inhalation of synthetic amorphous silicon dioxide, the lung silicon content reaches a plateau level at which elimination equates with deposition. After the cessation of exposure amorphous silica is rapidly eliminated from the lung tissue.

No significant deposition into the lymph nodes has been seen in prolonged rat exposure during the first 40 days, but after 120 days, the retention was about 31% of total deposited (and 1.5 - 2% of theoretically deposited) silica. This suggests that the involvement of lymphatic elimination is not relevant in short exposure periods/lower body burdens.