The influence of heavy metals on the enzyme activity within the soils of the nature recreation zone in Perm (Model Experiment)

The aim of this study was to assess the change in enzyme activity (catalase, urease, and invertase) in soddy-eluvozem and dark humus soil under simulated contamination with Cd, Cu, Zn, and Pb. Enzyme activity serves as one of the indicators of metal toxicity in soils. Appropriate levels of pollution were established in preserved media using solutions of acetic acid salts of Cd, Cu, Zn, and Pb with concentrations of 0 (control), 2.5, 5, 10, 25, 50, 100, 250, 500, 1000, and 1500 mg/kg. Based on genetic properties, dark humus soils exhibit greater resistance to pollutants compared to soddy-eluvozem. The average organic matter content in dark humus soil reaches 7.0%, with nearly neutral pH, while the granulometric composition varies from heavy loamy to medium clayey, and sod-eluvozem is characterized by light loamy texture, acidity, and a lower humus content. The assessment of the critical pollution threshold, indicated by the activity levels of catalase, urease, and invertase, demonstrates the enhanced stability of dark humus soil. Among the indicators studied, the urease activity emerged as the most sensitive indicator of heavy metal pollution in both types of soil; it decreased in sod-eluvozem with the introduction of Cd and Cu starting at 100 mg/kg and higher, while in dark humus soil, the decline occurred with the introduction of Cd starting at 100 mg/kg and higher and Cu starting at 1000 mg/kg and higher. The negative impact of Pb was observed only in dark humus soil, where urease activity decreased under pollution levels of 250 mg/kg and greater. The enzyme activity remained consistent when the soil was contaminated with Zn, with a decrease in the indicator observed only at elevated doses (1500 mg/kg). A notable feature of catalase and invertase activity in both soils was their increase under higher levels of contamination, which is presumably due to a decrease in microbial activity. When analyzing the comparative toxicity of metals, it was found that Cu, despite its biogenic significance, exhibited a greater ecotoxicological effect when compared to Zn and Cd; the introduction of Pb had the minimal effect on enzyme activity.