Influence of Soil Moisture on Bioaccumulation, Growth, and Recruitment of Folsomia candida Exposed to Phenanthrene-Polluted Soil

Bioremediation of petroleum-contaminated soil based on both toxicity risk control and hydrocarbon removal-progress and prospect

Petroleum contamination remains a worldwide issue requiring cost-effective bioremediation techniques. However, establishing a universal bioremediation strategy for all types of oil-polluted sites is challenging. This difficulty arises from the heterogeneity of soil textures, the complexity of oil products, and the variations in local climate and environment across different oil-contaminated regions. Several factors can impede bioremediation efficacy: (i) differences in bioavailability and biodegradability between aliphatic and aromatic fractions of crude oil; (ii) inconsistencies between hydrocarbon removal efficiency and toxicity attenuation during remediation; (iii) varying adverse effect of aliphatic and aromatic fractions on soil microorganisms. This review examines the ecotoxicity risk of petroleum contamination to soil fauna and flora. It also discusses three primary bioremediation strategies: biostimulation with nutrients, bioaugmentation with petroleum degraders, and phytoremediation with plants. Based on current research and state-of-the-art challenges, we highlighted future research scopes should focus on (i) exploring the ecotoxicity differentiation of aliphatic and aromatic fractions of crude oil, (ii) establishing unified risk factors and indicators for evaluating oil pollution toxicity, (iii) determining the fate and transformation of aliphatic and aromatic fractions of crude oil using advanced analytical techniques, and (iv) developing combined bioremediation techniques that improve petroleum removal and ecotoxicity attenuation.

Uptake of polycyclic aromatic hydrocarbons (PAHs) from PAH-contaminated soils to carrots and Chinese cabbages under the greenhouse and field conditions

Polycyclic aromatic hydrocarbons (PAHs) with the properties of structural stability, semi-volatility, and hydrophobicity are toxic and persistent in environments; thus, their transport and fate in agroecosystems is essential for reducing PAH accumulation in the edible parts of crops. Here, we cultivated cabbages (Brassica pekinensis L.) and carrots (Daucus carota L.) in PAH-contaminated soils under the greenhouse and field conditions. After harvesting, we observed a 9.5-46% reduction in soil ∑PAH concentrations. There were 37% of bioconcentration factors (BCFbs) > 1 and 93% of translocation factors (TFab) > 1, while low-molecular-weight (LMW) PAHs had higher BCFbs than high-molecular-weight (HMW) PAHs. The PAH concentrations showed significant and positive correlations among soils, the belowground parts, and the aboveground parts. The toxicity equivalent concentration (TEQBaP) followed the order of cabbage (greenhouse) > cabbage (field) > carrot (greenhouse) > carrot (field), suggesting potentially higher health risks in cabbage relative to carrot and vegetables under the greenhouse relative to field condition. Our study suggested growing carrots under field conditions as a management strategy for reducing the risks of vegetables grown in PAH-contaminated soils.

Low soil Moisture Slows Uptake and Elimination Rates of Phenanthrene in Springtails

This study investigated the influence of soil water status on the toxicokinetics of phenanthrene in the springtail Folsomia candida allowing estimation of uptake and elimination rates at two contrasting soil water potentials. Fitting a three-phase model to the observations showed that uptake rate (ku) was almost two times higher in moist soil (-2 kPa) than in dry soil (-360 kPa). During the first days of the exposure, elimination rate (ke) was not significantly different in moist and dry soil, but after eight days ke had increased significantly more in moist soil than in dry soil. Our results confirm the general notion that the exposure route via soil pore water is important. Understanding the significance of soil moisture in exposure and effects of contaminants on soil invertebrates is crucial for assessing the ecological risks associated with soil pollution in a changing climate.

Soil drying legacy does not affect phenanthrene fate in soil but modifies bacterial community response

Alteration of the structure of soil microbial communities following the elimination of hydrophobic organic pollutants (e.g., polycyclic aromatic hydrocarbons, PAHs) is generally assessed using DNA-based techniques, and soil is often required to dry prior to pollutant addition, to facilitate a better mix when establishing microcosms. However, the drying practice may have a legacy effect on soil microbial community structure, which would in turn influence the biodegradation process. Here, we used ¹⁴C-labeled phenanthrene to examine the potential side effects of precedent short-term drought events. The results indicate that the drying practice had legacy effects on soil microbial community structure, illustrated by irreversible shifts in the communities. The legacy effects had no significant impact on phenanthrene mineralization and non-extractable residue formation. However, they altered the response of bacterial communities to PAH degradation, leading to a decrease in the abundance of potential PAH degradation genes plausibly attributed to moderately abundant taxa. Based on a comparison of the varied effects of different drying intensity levels, an accurate description of microbial responses to phenanthrene degradation strongly relies on the establishment of stable microbial communities before PAH amendment. Concurrent alterations in the communities resulting from environmental perturbation could greatly mask minor alterations from the degradation of recalcitrant hydrophobic PAH. In practice, to minimize the legacy effects, a soil equilibration step with a reduced drying intensity is indispensable.