Lead (Pb) is one of the most common environmental pollutants. Lead has an acute toxic effect on soil biotas and the enzymatic system of soils. The objective of this study is to carry out enzymatic diagnostics of soil health in the European part of Russia after Pb contamination. As a part of the simulation experiment, Pb (at maximum permissible concentrations (MPCs) of 1, 10, and 100) was used to contaminate 12 types of soils in the south and center of the European part of Russia, which differed in their physical and chemical properties. To assess soil health, the activity of oxidoreductases (catalase, dehydrogenases, and cysteine reductase) and hydrolases (invertase, urease, and phosphatase) was studied. Most enzymes were inhibited with increased Pb dosage. The most sensitive soils to Pb contamination, assessed by enzyme activity, are soils of semi-deserts and dry steppes. Cysteine reductase is considered the most sensitive enzyme to Pb contamination. The most informative indicators for Pb contamination were phosphatase, cysteine reductase, and invertase. The P (phosphatase) cycle and the redox enzyme (catalase) also have instability in Pb-contaminated soils. The C (invertase and dehydrogenases) and N (urease) cycles do not change significantly when contaminated with lead. The results of this study can be used for the diagnostics of the condition of soils in different natural areas after Pb contamination.

One of the most modern and effective methods of soil restoration after pollution is the use of bioremediation. In recent years, special attention has been paid to the use of biochar. However, the ecological state after the introduction of biochar into petroleum-hydrocarbons-contaminated soils at different levels of pollution has been little studied. The work objective was to study the effect of biochar (10% of the soil mass) on the ecological statement of Haplic Chernozem contaminated with different levels of oil, from 0.1 to 50% of the soil mass. To assess the state of Haplic Chernozem after remediation with biochar, indicators of the biological activity of soils were studied. The maximum information content in the case of oil pollution and remediation with biochar was established by the activity of dehydrogenases (r = −0.90) and the total number of bacteria (r = −0.98). When applying biochar, the maximum stimulations of the integral indicator of the biological state (IIBS) relative to the background, by 62, 76, and 72%, were noted in samples with oil at concentrations of 0.5, 25, and 50%, respectively. The results of the study should be used for biodiagnostics and monitoring of the state of oil-contaminated Haplic Chernozem at different levels of contamination after remediation with biochar.