## 3 Results
### Enzymatic Activity  
Silver oxide in small concentrations did not significantly differ from the pure soil (day 10) and caused weak stimulation of catalase activity (days 30 and 90) (Figure 4). With an increase in the concentration of silver oxide to 30 PPC, decrease was established only on the 10 th day by 26-45%. On the 30 th day, only at a concentration of 10 and 30 PPC, decrease of catalase activity was established by 12 and 16%. On the 90 th day, regardless of the concentration of silver, catalase in soil did not differ from the pure soil and was stimulated. Nitrate of silver on the 10 th day caused decrease of enzymatic activity by 21%, and on the 30 th and 90 th days, it did not differ from the pure soil. On the 10 th day, with an increase in the concentration 1-30 PPC of nitrate of silver, activity decrease was 34-51%. After 30 days of the experiment, 1-30 PPC inhibited catalase activity by only 10-16% relative to the pure soil. After another 60 days, catalase activity decreased 3-30 PPC of nitrate of silver by 8-14%. Bismuth oxide at 0.5 PPC only on the 30 th day caused decrease of enzymatic activity by 11%, and on the 90 th had a stimulating effect (15% relative to the pure soil). On the 10 th day, only in soil with 10 and 30 PPC of bismuth oxide, decrease of activity was found by 37 and 43%. On the 30 th day, enzymatic activity at concentrations of 1-30 PPC varied in the range of 13-22% relative to the pure soil. On the 90 th day, there were no significant differences from the pure soil. Starting on the 10 th day, nitrate of bismuth had an inhibitory effect on catalase activity 0.5-30 PPC by 27-40%. On the 30 th day, activity was restored, and the process of its decrease was established with concentrations of 10 and 30 PPC by 14 and 18%. On the  
Figure 4: Catalase activity in soil after contamination of silver, bismuth, tellurium, and thallium, % of the pure soil. 90 th day, activity stimulation at 0.5 and 1 PPC of nitrate of bismuth was established, and at 3-30 PPC, no significant differences from the pure soil were revealed. Thallium oxide at 0.5 PPC on the 10 th day inhibited catalase activity by 16% relative to the pure soil, and on the 30 th and 90 th days, activity stimulation of soil enzyme was established by 7 and 11%. At concentrations 1-30 PPC of thallium oxide on the 10 th day, activity decrease was 39-54% relative to the pure soil. At the same time, on the 30 th day, decrease was established in the concentration range 3-30 PPC-12-21%, and on the 90 th day only at a concentration of 30 PPC by 10% relative to the pure soil. Nitrate of thallium at 0.5 PPC was highly toxic on the 10 th day--30% below the pure soil, as well as with an increase in the nitrate concentration 1-30 PPC by 36-76% relative to the pure soil. On the 30 th day, at a concentration of 3-30 PPC of nitrate of thallium, catalase activity was inhibited by 25-69% relative to the pure soil. On the 90 th day, activity decrease was established at a concentration of 10 and 30 PPC of nitrate of thallium by 17 and 56%. Tellurium oxide at 0.5 PPC inhibited catalase activity on the 10 th and 30 th days by 13 and 11% relative to the pure soil. On the 10 th day, with an increase in the concentration 1-30 PPC of tellurium oxide, catalase activity decrease was 20-53%, and on the 30 th day at the same concentrations, it was 19-27%. On the 90 th day, catalase activity decrease was found only at 30 PPC 9% lower than the pure soil. Nitrate of tellurium at 0.5 PPC on the 10 th and 30 th days inhibited enzyme activity by 24 and 12%. With an increase in the concentration of nitrate of tellurium on the 10 th day 1-30 PPC, catalase activity was inhibited by 25-75% relative to the pure soil, and on the 30 th day at concentrations 1-30 PPC, it was inhibited by 19-80% lower than the pure soil. On the 90 th day, nitrate of tellurium at 1-30 PPC caused decrease of enzyme activity by 10-57% relative to the pure soil.