Ecological, Geochemical, and Microbiological Evaluation of Soil Properties in the Territory of Smelovsky Oil Field, Russia

Soils in areas undergoing oil production require regular comprehensive monitoring due to exposure to dangerous ecotoxicants, primarily petroleum hydrocarbons and heavy metals. The ecological and functional state of 82 soil samples from the territory of the Smelovsky oil field in the Saratov region, Russian Federation, were analyzed using environmental, geochemical, and microbiological indicators. The atomic absorption spectroscopy method determined the concentrations of mobile forms of copper, zinc, lead, chromium, nickel, and cadmium. Mobile form concentrations of Ni (13.51–20.75 mg kg−1 of soil) and Cu (4.82–8.35 mg kg−1 of soil) exceeded the maximum permissible concentration (MPC) of 4.0 mg kg−1 of soil and 3.0 mg kg−1 of soil, respectively, throughout the territory. Mobile form concentrations of Pb (0.51–9.76 mg kg−1 of soil) exceeded the MPC (6.0 mg kg−1 of soil) in 23 samples. The total pollution coefficient (Zc) varied between 0.97 and 15.73, and all 82 soil samples were considered to be within acceptable contamination levels (Zc = 0–16). Mass concentration of petroleum products ranged from 120 to 640 mg kg−1 of soil, not exceeding the approximate permissible concentration (APC) (1000 mg kg−1 of soil). Soil microbiological analysis and significant positive correlations between specialized ecological and physiological microbial groups (heterotrophic microorganisms, hydrocarbon-oxidizing microorganisms, obligate methylotrophic microorganisms, and sulfur-oxidizing microorganisms) indicated hydrocarbon contamination. These identified peculiarities in soil properties on the territory of the Smelovsky oil field could lead to the development of soil environmental monitoring methods for oil-producing areas, thereby reducing the risk of soil contamination.