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.

Forest ecosystems perform important forestry and ecological functions. However, mining and processing companies cause significant soil contamination by heavy metals, in particular, copper (Cu). The resistance of nine types and subtypes of forest soils of the dry and humid subtropics in the Greater Caucasus region to Cu contamination at concentrations of 100, 1000, and 10,000 mg/kg was evaluated for the first time following the most sensitive and informative biological (microbiological, biochemical, and phytotoxic) indicators via a laboratory simulation study. Contamination was simulated under laboratory conditions. The series of forest soils was established following their resistance to Cu pollution: brown leached soils (Haplic Cambisols Eutric) = brown typical soils (Haplic Cambisols Eutric) > brown carbonate soils (Haplic Cambisols Eutric) = sod-carbonate typical soils (Rendzic Leptosols Eutric) ≥ yellow soils (Albic Luvisols Abruptic) ≥ leached sod-carbonate soils (Rendzic Leptosols Eutric) > brown forest slightly unsaturated soils (Haplic Cambisols Eutric) > acid brown forest soils (Haplic Cambisols Eutric) > acid brown forest podzolized soils (Haplic Cambisols Eutric). Regional environmentally safe standards for the Cu content in forest soils of the dry and humid subtropics of the Greater Caucasus were proposed: for brown typical soils, brown leached soils, brown carbonate soils, brown forest slightly unsaturated soils, sod-carbonate typical soils, leached sod-carbonate soils, and yellow soils, the rMPC was 100 mg/kg; for acid brown forest soils and acid brown forest podzolized soils, the rMPC was 70 mg/kg.

Bacteria are a sensitive marker of the state of soils contaminated with oil and petroleum products. Introduction of ameliorants leads to the changes in the