Synthetic amorphous silica
MAK Value Documentation, addendum – Translation of the German version from 2023
Andrea Hartwig1 (Chair of the Permanent Senate Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area, Deutsche Forschungsgemeinschaft)MAK Commission2
1 Institute of Applied Biosciences, Department of Food Chemistry and Toxicology, Karlsruhe Institute of Technology (KIT), Adenauerring 20a, Building 50.41, 76131 Karlsruhe, Germany
2 Permanent Senate Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area, Deutsche Forschungsgemeinschaft, Kennedyallee 40, 53175 Bonn, Germany
Abstract
The German Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area (MAK Commission) has re-evaluated the occupational exposure limit value (maximum concentration at the workplace, MAK value) of synthetic amorphous silica [7631-86-9] considering all toxicological end points. Relevant studies were identified from a literature search and also unpublished study reports were used. The critical effects are the inflammatory effects in the lungs. A NOAEC cannot be established for these effects. In a 90-day study, one form of nanoscale synthetic amorphous silica induced inflammatory effects in the lungs of rats at the lowest concentration tested of 0.5 mg/m3 and above. Based on this LOAEC, a maximum concentration at the workplace (MAK value) of 0.02 mg/m3 has been derived for the respirable fraction and the substance has been classified in Peak Limitation Category II with an excursion factor of 8. The NOAEL for developmental or perinatal toxicity in rats was 1000 mg/kg body weight and day after gavage; this corresponds to concentrations of 1750 or 2450 mg/m3 at the workplace. As the margins between these values and the MAK value are sufficiently large, synthetic amorphous silica has been assigned to Pregnancy Risk Group C. Studies in animals did not show a carcinogenic potential of synthetic amorphous silica, which is relevant for humans. Synthetic colloidal amorphous silica is not mutagenic in vitro or in vivo. The DNA strand breaks and micronuclei that were observed in vitro were not confirmed by the results in vivo. Synthetic colloidal amorphous silica is not absorbed through the skin in toxicologically relevant amounts and there is no evidence that it induces contact sensitization.
