Assessment of soil tolerance toward contamination with black oil in the south of Russia on the basis of soil biological indices: A model experiment

The effect of soil contamination with black oil added in amounts of 0.1, 0.5, 1.0, 2.5, 5, 10, 25, and 50% of the soil mass on the biological properties of ordinary and leached vertic chernozems, brown forest soils, and gray sands in the south of Russia was studied in a model laboratory experiment. It was shown that the soil contamination causes a drop in the catalase and dehydrogenase activities, the cellulolytic capacity, the number of Azotobacter bacteria, and the characteristics of the plant germination. The ordinary and vertic chernozems were more tolerant toward the contamination than the gray sands and brown forest soils. The changes in the biological soil properties in dependence on the degree of the soil contamination differed considerably for the soils with different properties (the chernozems, brown forest soil, and gray sands) and were similar for the soils with similar properties (the ordinary and vertic chernozems). One soil (the brown forest soil) could be more tolerant toward the contamination than another soil (the gray sands) at a given concentration of black oil (2.5%). The ecologically safe levels of the soil contamination with black oil do not exceed 0.7% in the ordinary chernozems, 0.3% in the compact chernozems, 0.1% in the brown forest soils, and 0.06% in the gray sands.