Assessment of hydrophobic properties of oil-contaminated soils using the «Water Spot» method

Abstract

The aim of the study was to assess the hydrophobicity degree of oil-contaminated soils using the Water Spot method.

Location and time of the study. The study was carried out in 2024 in laboratory conditions with typical chernozem and gray forest soil.

Methods. The sieved (2 mm, air-dried and milled soil samples were amended with oil in amounts needed to established the chosen concentration (0, 0,2, 0,5, 1, 3 and 5% on the mass basis). Then hexane and distilled water were added to reduce oil viscosity and increase soil moisture, respectively. After two days of incubating soil, sodium fluorescein solution was added onto the sample surface to visualize spot boundaries. The images were taken in a dark place under the ultraviolet light.

To determine the effectiveness of chitosan (as a natural sorbent), a second series of experiments was performed in the same setup, but with chitosan addition, followed with two days incubation. Sodium fluorescein was then applied, and the area of the resulting spot was imaged. The resulted images were processed using the CorelDRAW software and the Microsoft Excel analysis package.

Results. Oil contamination of soils usually disturbs the water regime. Increase in petroleum products content from 0,5 to 5% leads to decrease in absorbency and the area of the water spot on the soil surface. After treating the contaminated soil samples with 0,1% chitosan solution, the water spot area increased on average by 43% on the gray forest soil, and by 6% on typical chernozem. With a twofold increase in the concentration of chitosan solution, the water spot area increased on the gray forest soil by an average of 48% and by 46% on typical chernozem. Thus chitosan solution can be used as a sorbent when soil is contaminated with oil products.

Conclusions. The water spot method is reproducible, simple, and can be used to assess soil contamination with petroleum products. The results show that with an increase in the degree of pollution, a decrease in the area of the water spot on the soil is observed.