Response of soil microorganisms to radioactive oil waste: results from a leaching experiment

[摘要] Oil wastes produced in large amounts in the processes of oil extraction,refining, and transportation are of great environmental concern because oftheir mutagenicity, toxicity, high fire hazardousness, and hydrophobicity.About 40% of these wastes contain radionuclides; however, the effects ofoil products and radionuclides on soil microorganisms are frequently studiedseparately.

The effects on various microbial parameters of raw waste containing 575 g oftotal petroleum hydrocarbons (TPH) kg⁻¹ waste, 4.4 of²²⁶Ra, 2.8 of ²³²Th, and 1.3 kBq kg⁻¹ of⁴⁰K and its treated variant (1.6 g kg⁻¹ of TPH, 7.9of ²²⁶Ra, 3.9 of ²³²Th, and 183 kBq kg⁻¹ of⁴⁰K) were examined in a leaching column experiment to separate theeffects of hydrocarbons from those of radioactive elements. The raw wastesample (H) was collected from tanks during cleaning and maintenance, and atreated waste sample (R) was obtained from equipment for oil wastetreatment. Thermal steam treatment is used in the production yard to reducethe oil content.

The disposal of H waste samples on the soil surface led to an increase inthe TPH content in soil: it became 3.5, 2.8, and 2.2 times higher in theupper (0–20 cm), middle (20–40 cm), and lower (40–60cm) layers,respectively.

Activity concentrations of ²²⁶Ra and ²³²Th increased in soilsampled from both H- and R- columns in comparison to their concentrations incontrol soil. The activity concentrations of these two elements in samplestaken from the upper and middle layers were much higher for the R-columncompared to the H-column, despite the fact that the amount of waste added tothe columns was equalized with respect to the activity concentrations ofradionuclides.

The H waste containing both TPH and radionuclides affected the functioningof the soil microbial community, and the effect was more pronounced in theupper layer of the column. Metabolic quotient and cellulase activity werethe most sensitive microbial parameters as their levels were changed 5–1.4times in comparison to control ones. Changes in soil functionalcharacteristics caused by the treated waste containing mainly radionuclideswere not observed. PCR-SSCP (polymerase chain reaction – single strandconformation polymorphism) analysis followed by MDS (metric multidimensionalscaling) and clustering analysis revealed that the shifts in microbialcommunity structure were affected by both hydrocarbons and radioactivity.Thus, molecular methods permitted to reveal the effects on soil microbialcommunity not only from hydrocarbons, which significantly altered functionalcharacteristics of soil microbiome, but also from radioactive elements.

[学科分类] 地球化学与岩石