AUTHOR=Krug Harald F. 

TITLE=A Systematic Review on the Hazard Assessment of Amorphous Silica Based on the Literature From 2013 to 2018

JOURNAL=Frontiers in Public Health

VOLUME=Volume 10 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/public-health/articles/10.3389/fpubh.2022.902893

DOI=10.3389/fpubh.2022.902893

ISSN=2296-2565

ABSTRACT=Background: Nanomaterials are suspected of causing health problems, as published studies on nanotoxicology indicate. On the other hand, several of these materials, such as nanostructured pyrogenic and precipitated synthetic amorphous silica and silica gel (SAS), have been used for decades, without safety concerns in industrial, commercial and consumer applications. However, in addition to many in vivo and in vitro studies that have failed to demonstrate intrinsic toxicity of SAS, papers periodically emerge in which biological effects of concern have been described. Even though most of these studies do not meet high quality standards and not always using the equivalent test materials or standardized test systems, these results often trigger a substance re-evaluation. In order to put these results into perspective, an extensive literature study was carried out and the example of amorphous silica will be used to try to unravel the reliable from the unreliable results.
Methods: A systematic search of studies on nanotoxicological effects has been performed covering the years 2013 to 2018. The identified studies have been evaluated for their quality regarding material and methods details and the data have been curated and put into a data collection. This review deals only with the investigations on amorphous silica.
Results: From 18’162 publications 1’217 have been selected with direct reference to experiments with synthetically produced amorphous silica materials. The assessment of these studies based on defined criteria leads to further reduction to 316 studies which have been included in this systematic review. Screening for quality with well-defined quantitative criteria following the GUIDEnano concept reveals only 27.3% of acceptable quality. Overall, the in vitro and in vivo data showed low or no toxicity of amorphous silica. The data shown do not support the hypothesis of a dependency of biological effects on primary particle size of the tested materials.
Conclusion: This review demonstrates the relatively low quality of most studies published on nanotoxicological issues in this case of amorphous silica. Moreover, mechanistic studies are often passed off or considered as toxicological studies. In general, standardized methods or the OECD guidelines are rarely used for toxicological experiments.