Spatial distribution, composition, and source analysis of petroleum pollutants in soil from the Changqing Oilfield, Northwest China

Quantitative expression of LNAPL pollutant concentrations in capillary zone by coupling multiple environmental factors based on random forest algorithm

The capillary zone plays a crucial role in migration and transformation of pollutants. Light nonaqueous liquids (LNAPLs) have become the main organic pollutant in soil and groundwater environments. However, few studies have focused on the concentration distribution characteristics and quantitative expression of LNAPL pollutants within capillary zone. In this study, we conducted a sandbox-migration experiment using diesel oil as a typical LNAPL pollutant, with the capillary zone of silty sand as the research object. The variation characteristics of LNAPL pollutants (total petroleum hydrocarbon) concentration and environmental factors (moisture content, electrical conductivity, pH, and oxidationreduction potential) were essentially consistent at different locations with the same height. These characteristics differed within range of 10.0-50.0 cm and above 60.0 cm from groundwater. A model for quantitative expression of concentrations was constructed by coupling multiple environmental factors of 968 sets-7744 data via random forest algorithm. The goodness of fit (R2) for both training and test sets was greater than 0.90, and the mean absolute percentage error (MAPE) was less than 16.00 %. The absolute values of relative errors in predicting concentrations at characteristic points were less than 15.00 %. The constructed model can accurately and quantitatively express and predict concentrations in capillary zone.

Remediating petroleum hydrocarbons in highly saline-alkali soils using three native plant species

Phytoremediation of total petroleum hydrocarbons (TPHs) contamination is a process that uses the synergistic action of plants and rhizosphere microorganisms to degrade, absorb and stabilize pollutants in the soil, and has received increasing attention in recent years. However, this technology still has some challenges under certain conditions (e.g., highly alkaline and saline environments). The present study was selected three native plant species (alfalfa, tall fescue, and ryegrass) to remediate petroleum pollutants in greenhouse pot experiments. The results indicate that TPH contamination not only inhibited plant growth, soil chemical properties and soil fertility (i.e. lower plant biomass, chlorophyll, pH, and electrical conductivity), but also increased the malondialdehyde, glutathione, and antioxidant enzyme activities (catalase and polyphenol oxidase). Further, correlation analysis results illustrated that TPH removal was strongly positively correlated with chlorophyll, soil fertility, and total organic carbon, but was negatively correlated with dehydrogenase, polyphenol oxidase, pH, and electrical conductivity. The highest TPHs removal rate (74.13%) was exhibited by alfalfa, followed by tall fescue (61.79%) and ryegrass (57.28%). The degradation rates of short-chain alkanes and low rings polycyclic aromatic hydrocarbons (PAHs) were substantially higher than those of long-chain alkanes and high rings PAHs. The findings of this study provide valuable insights into petroleum decontamination strategies in the highly saline - alkali environments.