## 5 Conclusions  
The clays used in DGR as safety barriers were found to be able to act as sources of microflora and biogenic elements, which may have a negative effect on the DGR safety. The clay microbial complex contained primarily aerobic and anaerobic organotrophic bacteria due to secondary contamination at the plants. Microbial processes in clay barriers may be stimulated by the clay's organic matter, hydrogen of radiolytic origin, and release of biogenic elements (iron, potassium, sulfur, phosphorus, etc.) from the barriers. Microbial processes occurring in clay materials result in their partial dissolution and release of cations into the solution, impairing their sorption properties and favoring liquid diffusion. Formation of biogenic gases, including hydrogen sulfide, was observed in activated microbial complexes from the samples with high content of sulfur and organic carbon (bentonite from Zyryanskoye deposit); it may result in corrosion of steel RW containers. A positive correlation of the rates of microbial processes was found with the levels of sulfur, phosphorus, and iron in clays; both the elemental and mineral composition of the samples, as well as with their morphological properties, affected the development of microbial processes. An approach to ranking the bentonite and kaolin clay materials according to the safety of their application in engineered barriers was proposed based on a combination of factors.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app12041843/s1](https://www.mdpi.com/article/10.3390/app12041843/s1)]([https://www.mdpi.com/article/10.3390/app12041843/s1](https://www.mdpi.com/article/10.3390/app12041843/s1)), Table S1: title Experimental design and measurements techniques description.  
Conceptualization, E.Z. and A.S.; methodology, A.S.; validation, E.A., N.P. and G.A.; formal analysis, V.Z.; investigation, E.A., N.P., G.A. and V.Z.; writing--original draft preparation, A.S., E.A. and N.P.; writing--review and editing, A.S., E.A. and N.P.; visualization, N.P. and E.A.; supervision, A.S. All authors have read and agreed to the published version of the manuscript.  
This work was supported by state assignments from The Ministry of Science and Higher Education of the Russian Federation (#AAAA-A16-11611091001).  
Not applicable.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Parameters** & & **B-1** & **B-2** & **B-3** & **B-4** & **B-5** & **K-1** & **K-2** \\ \hline \multirow{4}{*}{Biogenic elements in clays} & Fe & 4 & 4 & 4 & 2 & 5 & 1 & 1 \\  & S & 3 & 3 & 1 & 2 & 5 & 1 & 1 \\  & C & 2 & 3 & 1 & 2 & 5 & 4 & 1 \\  & N & 1 & 1 & 1 & 1 & 3 & 2 & 1 \\  & P & 1 & 1 & 1 & 2 & 4 & 2 & 1 \\  & Acid leachate \(\Sigma\) & & 5 & 3 & 3 & 3 & 4 & 3 & 1 \\ \hline \multirow{4}{*}{Bioleachates} & Kl & 5 & 1 & 2 & 1 & 3 & 3 & 5 \\  & Si. & 3 & 1 & 1 & 2 & 5 & 3 & 2 \\  & Al. & 2 & 1 & 1 & 1 & 5 & 3 & 3 \\  & Ca. & 3 & 1 & 2 & 1 & 5 & 4 & 1 \\  & Fe. & 5 & 1 & 1 & 2 & 1 & 1 & 1 \\  & Na. & 2 & 1 & 4 & 1 & 2 & 5 & 4 \\ \hline MTInit & & 3 & 1 & 2 & 1 & 1 & 5 & 5 \\  & MTTox & 1 & 1 & 3 & 1 & 5 & 2 & 3 \\  & MTanox & 2 & 2 & 5 & 1 & 5 & 1 & 5 \\  & H\({}_{2}\)S & & 1 & 1 & 1 & 3 & 5 & 3 & 2 \\  & Total & 43 & 26 & 33 & 26 & 63 & 43 & 37 \\ \hline \hline \end{tabular}
\end{table}
Table 9: Overall safety prediction for clay materials.  
Data Availability Statement: Data is contained within the article.  
This work was performed using the equipment of the Core Facilities Center of IPCE RAS (CKP FMI IPCE RAS).  
The authors declare no conflict of interest.