## 4 Discussion
### Carrying Out a Mercury-Contaminated Soil Remediation Treatment on the Pilot Site
Comparing the changes in mercury emissions values over time, it was observed that for 70% of the results, there was a reduction in mercury emissions in the contaminated area by 66 to 97%. One measurement point showed a 59% reduction in emissions and one a 27.9% reduction in emissions. Only at three measurement points was there an increase in emissions values of approximately 1%, 24%, and 58% observed (however, the measured emissions values at these three points were low and did not exceed emissions values of 85 ng/h/m\({}^{2}\)). The results of the control measurements carried out 90 days after the remediation procedure showed that the value of mercury emissions from the examined area does not exceed 50 ng/h/m\({}^{2}\). All measurement points showed a significant decrease in mercury emissions. Notably, the highest mercury emissions measurement result obtained in this series was less than the lowest emissions value recorded before the procedure. This result is also 40 times lower than the highest mercury emissions level recorded in the test area prior to the remediation procedure. As part of the works carried out, the degree of reduction of mercury emissions at individual measurement points was also assessed. It was found that at fourteen out of seventeen measurement points (82%), the mercury emissions decreased by 91.6% to as much as 99.3%. At the remaining three measurement points, a reduction in mercury emissions ranging from 60% to 88% was observed. These changes were noted at the measurement points where emissions after the remediation procedure did not exceed 22.8 ng/h/m\({}^{2}\). The results obtained using diffusion chambers (shown in Figure 4) also confirm the effectiveness of the remediation procedure. When immobilizing mercury in soil by means of ground sulfur, it is essential to periodically assess the effectiveness of this procedure. Relying solely on direct methods for determining the total mercury content in the soil is insufficient for evaluating the effectiveness of metallic mercury stabilization in the form of HgS. To accurately assess the effectiveness of mercury immobilization in soil, it is necessary to use a speciation method that can differentiate between the mercury permanently bonded as HgS and unbound mercury with the potential to emit. A laboratory method based on speciation measurements of metallic mercury content in the soil, using an indirect method of measuring mercury emissions with gold sensors in flasks, can be employed to assess the mercury emissions levels and thus evaluate the effectiveness of the laboratory tests for using sulfur as a stabilizing agent in mercury-contaminated soils [18; 31]. To estimate the amount of mercury capable of being emitted from the soil under field conditions, methods using a passive sensor of its own design and diffusion chambers can be used. The latter two methods were used to assess the effectiveness of the remediation procedure. Additionally, it should be noted that the effectiveness of the mercury immobilization method not only reduced its emissions into the air but also decreased its solubility in water. Studies of water extracts from the soil samples taken from the contaminated area before and after treatment showed that mercury bound as HgS is less soluble in water. Specifically, after immobilization with sulfur, the content of soluble mercury forms ranged from 0.017 to 0.1 mg/kg dry matter. This stabilization with sulfur resulted in a tenfold decrease in the leaching of mercury from the soil.