Environmental Health Standards of Arid Soils in Southern Russia under Pollution by Oil and Oil Products

Under the influence of pollution by petroleum hydrocarbons, soils from different natural zones have different physical, chemical, and biological indicators of the soil condition. Biological indicators are the most sensitive to soil pollution and changes in the ecological state. Arid zone soils, compared to other types of soils, due to the soil formation conditions and the physical and biological properties, are very unstable to pollution by petroleum hydrocarbons. In this regard, it is important to standardize the content of petroleum hydrocarbons taking into account the response of enzyme activity and microbiological indicators, and an assessment of soil phytotoxicity. Such standards serve as parameters for the health of soils in a region when contaminated with oil and oil products. The aim of this study is to assess the environmental health standards of arid soils in southern Russia when contaminated with oil and oil products. It has been established that, with an increase in the concentration of oil and oil products, the biological indicators of soils are suppressed. The ecological standard for oil in brown semi-desert soil (0.1%) is the lowest compared to solonchak (1.0%) and chestnut soil (0.2%). The permissible content of fuel oil in chestnut soil (0.4%) is less than in solonchak (1.0%) and brown semi-desert soil (0.5%). The content of diesel fuel in chestnut and brown semi-desert soils is the same (0.2%), and in solonchak it is three times higher (0.6%). The maximum difference in standards among the studied soil types was established for oil: between solonchak and chestnut and brown semi-desert soils, it is five and ten times. Chestnut and brown semi-desert soils are more sensitive to oil pollution than saline soils. Among the biological indicators, the greatest sensitivity to pollution by oil and oil products is the abundance of bacteria of the genus Azotobacter and the total number of bacteria, and the lowest, the activity of catalase and dehydrogenases and the length of roots. The most informative indicators for contamination of arid soils with oil and oil products are the activity of catalase and dehydrogenases and the length of roots, while the least informative indicators are the total number of bacteria and the activity of urease. The most resistant soil to pollution by petroleum hydrocarbons is the salt marsh, and the least resistant are brown semi-desert (oil and diesel fuel) and chestnut (fuel oil and gasoline) soils. The results of this study can be used in the development of environmental standards for the health of arid soils contaminated with oil and oil products.