Features of the processes of detoxification and self-restoration of oil-contaminated soils — a field study.

Purpose: The aim of the research was to study the direction, dynamics, and features of the restoration of the main ecological functions of different podzolic soils disturbed by oil pollution. Materials and methods: Soil contamination with crude oil was carried out in field experiments at two sites near St. Petersburg, Russia. Loamy soddy-podzolic soil (Umbric Albeluvisol) and sandy illuvial-ferruginous podzol (Podzol), the most common in the region, were the objects of study. Key indicators were used to investigate the dynamics of self-purification processes of oil-contaminated soils: (1) the rate of carbon dioxide emission by the soil, which quantitatively characterizes the mineralization of petroleum hydrocarbons by microorganisms, was determined by the absorption method in laboratory conditions; (2) toxicological rate of soils and water extracts from them was determined by eluate and substrate bioassay; (3) the value of aboveground biomass and the projective vegetation cover were determined by direct weighing out and visually. Content of petroleum products in soils was determined by infrared spectrometry. Results and discussion: Self-purification and self-recovery dynamics in the oil-contaminated soils differed significantly depending on the soil type. The rate and intensity of oil biodegradation in the sandy podzol due to the activity of microorganisms, as well as the rate and degree of restoration of vegetation cover, were significantly lower compared to the soddy-podzolic soil, despite the same level of oil pollution. Podzol was characterized both by a higher degree of toxicity and a lower rate of its decline compared to the soddy-podzolic soil. The soddy-podzolic soil at the maximum level of pollution restored the disturbed basic ecological functions in 4 years. In podzol, with a comparable high pollution level, by the end of the fifth year, acute toxicity remained and there was practically no vegetation. Conclusions: The factors affecting the rate of oil degradation should be associated primarily with the chemical and microbiological parameters of soils and the characteristics of the vegetation growing on them. Different levels of stability of the loamy soddy-podzolic soil and sandy podzol in conditions of oil pollution, and the peculiarities of the processes of their natural recovery, should be taken into account in environmental regulations, when determining the maximum permissible residual oil concentrations in soils, as well as in the development of effective methods for their reclamation. [ABSTRACT FROM AUTHOR]