Assessment of cytotoxicity of an original industrial aerosol containing a high percentage of amorphous silica in the nanometer range

Introduction. At the current stage of hygienic evaluation, the substantiation of at least approximate safe concentrations in the ambient air of populated areas for nanoparticles is an up-to-date challenge. Its persistence dissolves the guidelines for risk management and divests the supervisory bodies of legal support. A comparative toxicological evaluation of the studied substance and its chemical analogue is one of the guidelines for the academic substantiation of the hygienic standards for the permissible content of hazardous substances in the air. It already has previously defined exposure standards.

Materials and methods. To investigate the cytotoxicity of the studied particles, a shift of the cellular composition of the bronchoalveolar lavage fluid (BALF) was used. Also, some biochemical measurements of the BALF supernatant were investigated. Outbred female rats were instilled with a suspension of particles in the volume of 1 ml of various concentrations in the form of an intratracheal suspension. Distilled water was used as a solvent. Statistical analysis of the data obtained was performed using the Student’s t-test.

Results. The comparative assessment of the cytotoxicity of an original industrial aerosol containing 72% amorphous silica with an average particle size of 90 nm (SiO₂ IA) was performed. It also included engineered particles of amorphous silica with an average size of 43 nm (SiO₂ NPs), a commercial, an industrial sample of 100% amorphous silica with a particle size of 5 to 60 nm (amorphous SiO₂), and a reference sample of standard quartz DQ₁₂ in a volume of 1 ml of water suspension. Under the findings of changes in the cellular composition of the bronchoalveolar lavage fluid 24 hours after the intratracheal instillation of these particles, it was revealed that the biological power (in terms of the NL/AM ratio) of both SiO₂ NPs and amorphous SiO₂ is statistically much higher than the industrial aerosol under study. It is also higher than the standard quartz dust DQ₁₂. In this regard, the cytotoxicity of SiO₂ IA may be explained by the predominant content of amorphous silica nanoparticles in it.

Conclusion. Under the obtained results, the appropriateness of using indicative safe exposure levels (ISEL) of 0.02 mg/m³ for amorphous silica needs to be reviewed. The safe reference level of impact guideline does not contain data concerning the particle size and the percentage of amorphous SiO₂ in the aerosol. Nevertheless, it is impossible to pollute the ambient air with an aerosol containing only this substance. 

Contribution:

Solovyеva S.N. — collection and processing of material;

Sutunkova M.P. — the concept and design of the study, writing;

Kuzmin S.V. — the concept and design of the study;

Privalova L.I. — the concept and design of the study, editing;

Gurvich V.B. — the concept and design of the study;

Katsnelson B.A. — concept and design of the study.

All authors are responsible for the integrity of all parts of the manuscript and approval of the manuscript final version.

Conflict of interest. The authors declare no conflict of interest.

Acknowledgement. The study had no sponsorship.