Experimental thawing events enhance petroleum hydrocarbons attenuation and enzymatic activities in polluted temperate soils

Polluted soils in temperate regions are frequently exposed to seasonal freezing and thawing events during which the soil biological properties are expected to change in response to the associated temperature variations. In this study, we investigated the influence of freeze-thaw events on enzymatic activities and natural attenuation of petroleum hydrocarbons in temperate soils with varying pollution profiles. Four soils [clean natural, Diesel amended (DAS), Crude-oil amended (COAS), and aged oil polluted] were subjected to ten freeze-thaw temperature regimes ranging from - 20 to + 20 degrees C for 45 days. The soil enzymatic activities and fractional petroleum hydrocarbon analysis were conducted using spectrophotometry and gas chromatography-mass spectrometry, respectively. After the incubation period, freezing resulted in decreased enzyme (lipase and dehydrogenase) activities in both clean and polluted soils, while thawing events compensated for the enzymatic losses that occurred during the preceding freezing phase. Fractional hydrocarbon analysis revealed that there was a switch from active removal of light- to medium-chain hydrocarbons (C10-C23) in the short-term polluted soils (DAS and COAS) during the freezing phase to rapid degradation of the heavier nonvolatile hydrocarbon fractions (C23-C34) during the thawing phase, and the long-term polluted soil had lower hydrocarbon removal rates than the short-term polluted soils. The relationship between the natural attenuation of hydrocarbons in the oil polluted soils and incubation temperatures was linear in the short- and long-term petroleum polluted soils.

Automated summary

Polluted soils in temperate regions are exposed to seasonal freezing and thawing events, which influence enzymatic activities and natural attenuation of petroleum hydrocarbons. Freeze-thaw cycles impact enzyme activities and the degradation of different hydrocarbon fractions in polluted soils with varying pollution profiles.