Effect of hydrocarbon pollution on the microbial properties of a sandy and a clay soil

Environmental risk substances in soil on seed germination: Chemical species, inhibition performance, and mechanisms

Nowadays, numerous environmental risk substances in soil worldwide have exhibited serious germination inhibition of crop seeds, posing a threat to food supply and security. This review provides a comprehensive summary and discussion of the inhibitory effects of environmental risk substances on seed germination, encompassing heavy metals, microplastics, petroleum hydrocarbons, salinity, phenols, essential oil, agricultural waste, antibiotics, etc. The impacts of species, concentrations, and particle sizes of various environmental risk substances are critically investigated. Furthermore, three primary inhibition mechanisms of environmental risk substances are elucidated: hindering water absorption, inducing oxidative damage, and damaging seed cells/organelles/cell membranes. To address these negative impacts, diverse effective coping measures such as biochar/compost addition, biological remediation, seed priming, coating, and genetic modification are proposed. In brief, this study systematically analyzes the negative effects of environmental risk substances on seed germination, and provides a basis for the comprehensive understanding and future implementation of efficient treatments to address this significant challenge and ensure food security and human survival.

Simultaneous remediation of diesel-polluted soil and promoted ryegrass growth by non-thermal plasma pretreatment

The remediation of petroleum-polluted soil has garnered significant global attention. In this study, a pot-culture experiment was conducted to assess the feasibility of using non-thermal plasma (NTP) as an efficient and economic-friendly pretreatment method in the phytoremediation of diesel-polluted soil. The remediation effectiveness was evaluated via both the removal of diesel and the ryegrass growth. Specifically, at the 50th d of ryegrass growth, the increase of diesel removal efficiency with NTP pretreatment ranged from 16 % to 30 %. Moreover, both clean and diesel-polluted soils pretreated by NTP promoted the growth of ryegrass in shoot lengths and biomass especially after the 35th d. It was found that nitrate nitrogen fixed by NTP not only stimulated the nitrate reductase activities in leaves and promoted plant growth, but also was transformed to more ammonia nitrogen for organism life activity. Subsequent investigation proved that the related nitrogen-metabolism activities of microbes were enriched in rhizosphere soils with NTP pretreatment. Furthermore, NTP treatment increased the abundance of beneficial microbial communities in diesel soil rhizosphere on the 42nd d of growth period. In addition, changes in the proportions of soil dissolved organic matter indicated enhanced nutrient cycling in soils with NTP pretreatment. These promotional effects underscored the contribution of NTP pretreatment in rapidly detoxifying diesel-contaminated soil within 10 min and accelerated the establishment of ryegrass ecosystem. This study provides valuable insights into the role of nitrogen fixation and offers an efficient and promising advanced approach for the phytoremediation of diesel-polluted soil with NTP pretreatment.

Bacterial Diversity in Old Hydrocarbon Polluted Sediments of Ecuadorian Amazon River Basins

The Ecuadorian Amazon rainforest stands out as one of the world's most biodiverse regions, yet faces significant threats due to oil extraction activities dating back to the 1970s in the northeastern provinces. This research investigates the environmental and societal consequences of prolonged petroleum exploitation and oil spills in Ecuador's Amazon. Conducted in June 2015, the study involved a comprehensive analysis of freshwater sediment samples from 24 locations in the Rio Aguarico and Napo basins. Parameters such as water and air temperature, conductivity, soil pH, and hydrocarbon concentrations were examined. Total petroleum hydrocarbon (TPH) concentrations ranged from 9.4 to 847.4 mg kg-1, with polycyclic aromatic hydrocarbon (PAH) levels varying from 10.15 to 711.1 mg kg-1. The pristane/phytane ratio indicated historic hydrocarbon pollution in 8 of the 15 chemically analyzed sediments. Using non-culturable techniques (Illumina), bacterial analyses identified over 350 ASV, with prominent families including Comamonadaceae, Chitinophagaceae, Anaeromyxobacteraceae, Sphingomonadaceae, and Xanthobacteraceae. Bacterial diversity, assessed in eight samples, exhibited a positive correlation with PAH concentrations. The study provides insights into how microbial communities respond to varying levels of hydrocarbon pollution, shedding light on the enduring impact of oil exploitation in the Amazonian region. Its objective is to deepen our understanding of the environmental and human well-being in the affected area, underscoring the pressing need for remedial actions in the face of ongoing ecological challenges.

Accelerated deterioration corrosion of X70 steel by oxidation acid-producing process catalyzed by Acinetobacter soli in oil-water environment

Deterioration corrosion occurs between the external surface of oil pipelines and aerobic oil-degrading microorganisms in oil fields. Microorganisms with aerobic oil pollution remediation capabilities may catalyze more serious anaerobic microbial corrosion due to the carbon source supply. In this study, Acinetobacter soli strains were isolated from oil-contaminated environments, and their role in the deterioration corrosion behavior of X70 steel in an oil-water environment was investigated using the EDS multipoint scanning method. The presence of oil controls the deposition of carbon and phosphorus and diffusion of oxygen, leading to significant adhesion attraction and initial growth inhibition of biofilm on the metal surface. A. soli facilitates oxygen transfer and iron ion dissolution, thereby accelerating the pitting corrosion of X70 steel. This corrosion of the X70 steel, in turn, further accelerates the microbial degradation of oil, inhibiting the appearance of calcareous scale in the later stage of corrosion. The corrosion of X70 steel is influenced by microbial degradation, and the specific corrosion behaviors are related to the activity of A. soli in the petroleum environment. This study sheds light on the corrosion mechanisms of X70 steel by A. soli at different stages, providing insights into the interactions between microorganisms, oil pollution, and metal corrosion in oil fields.

Effect of crude oil exploration and exploitation activities on soil, water and air in a Nigerian community

The continuous degradation of environmental ecosystems (land, water and soil) resulting from crude oil exploration and exploitation activities continues to gain global attention. This study investigates the effects of crude oil exploration and exploitation activities on soil, water and air in the study area. Soil samples were collected in three replicates at depths of 0-15 and 15-30 cm at sampling distances of 20, 100 and 200 m a from core oil exploitation operation area and a control point. Water samples were also taken from within the study area and analyzed using standard procedures. Major pollutants concentrations of particulate matter (PM_2.5 and PM₁₀) of the air were also measured using Air Quality Index (AQI). The results reveal that the soil, water and air parameters measured mostly at 20 m from the core oil operation area compromise the allowable standards provided for healthy living. In the same manner, some results at 100 and 200 m were slightly higher than the recommended values in some cases of heavy metals and bacteria activities in the soil. The AQI at 20 m was far above the permissible limit provided by the Environmental Protection Agency while others are gradually drawing towards the limit given for each pollutant. To safeguard the health of the residents of the host community and oil field workers, there is a need for proper and frequent environmental monitoring and assessment by authorized regulatory bodies in Nigeria. This will prevent any future exposure which may endanger the lives of the dwellers.

Biostimulation of Petroleum-Contaminated Soil Using Organic and Inorganic Amendments

The most common approaches for the in-situ bioremediation of contaminated sites worldwide are bioaugmentation and biostimulation. Biostimulation has often proved more effective for chronically contaminated sites. This study examined the effectiveness of optimized water hyacinth compost in comparison with other organic and inorganic amendments for the remediation of crude oil-polluted soils. Water hyacinth was found to be rich in nutrients necessary to stimulate microbial growth and activity. An organic geochemical analysis revealed that all amendments in this study increased total petroleum hydrocarbon (TPH) biodegradation by ≥75% within 56 days, with the greatest biodegradation (93%) occurring in sterilized soil inoculated with optimized water hyacinth compost. This was followed by polluted soil amended with a combination of spent mushroom and water hyacinth composts (SMC + WH), which recorded a TPH biodegradation of 89%. Soil amendment using the inorganic fertilizer NPK (20:10:10) resulted in 86% TPH biodegradation. On the other hand, control samples (natural attenuation) recorded only 4% degradation. A molecular analysis of residual polycyclic aromatic hydrocarbons (PAHs) showed that the 16 PAHs designated by the US EPA as priority pollutants were either completely or highly degraded in the combined treatment (SMC + WH), indicating the potential of this amendment for the environmental remediation of soils contaminated with recalcitrant organic pollutants.

Physiological and microbiological hormesis in sedge Eleocharis palustris induced by crude oil in phytoremediation of flooded clay soil

Soil contamination with petroleum hydrocarbons affects plants and rhizospheric microorganisms. Microbial activity participates in important biochemical processes that stimulate, together with plants, the modification of toxic compounds for organisms. A nine-month experiment was set up to study the effect over time of oil on plant height (cm), formation of new plants, plant matter production (gravimetry), and population of rhizospheric microorganisms (serial dilution) in the sedge Eleocharis palustris. Removal of total petroleum hydrocarbons (soxhlet and gravimetry) from the soil was also evaluated. The means of the evaluated variables registered significant statistical differences (Duncan, p < 0.05) regarding the age of the plant and the amount of crude oil. There was a high correlation between oil and plant height (0.848) and with new plants (0.994). 60 mg oil dose promoted the greatest statistical difference in the amounts of roots and plant biomass (p < 0.05). E. palustris exposed to 60 and 75 mg of oil stimulated high densities of microalgae, actinomycetes, fungi, hydrocarbonoclastic bacteria and Pseudomonas spp; the overall ratio was 2:1 relative to natural attenuation. Plant and microorganism variables evaluated registered physiological and microbiological hormetic indices ≥1, showing a positive linear relationship. Natural attenuation was more efficient in removing crude oil. We conclude that E. palustris is tolerant to oil exposure. It is suggested to combine it with natural attenuation for the optimization of soils contaminated with crude oil.

Transport and targeted binding of Pluronic-coated nanoparticles in unsaturated porous media

The effectiveness of most in situ remedial technologies, including nanoremediation, lies on successful delivery of reagents to a subsurface target treatment zone. Targeted delivery of engineered nanoparticles (NPs) to treat petroleum hydrocarbons present in the unsaturated zone requires an understanding of their transport behaviour in these systems. A series of column experiments explored the effect of initial water saturation, flowrate, input dosage, and porous medium texture on the transport of iron oxide or cobalt ferrite NPs coated with an amphiphilic co-polymer, as well as their targeted attachment to a crude oil zone. As the initial water content increased with a concomitant reduction in air saturation, the degree of tailing present in the NP breakthrough curves (BTCs) reduced, and the mass of NPs recovered increased. Air saturation is positively correlated with the magnitude of air-water interfaces, which provide additional NP retention sites. At a lower injection flow rate, NP retention increased due to a longer residence time and comparatively high air saturation. NP transport behaviour was not sensitive to NP injection dose over the range tested. Increased retention and retardation of the NP BTC was observed in sediments with a higher clay and silt content. NPs coated with a lower concentration of a Pluronic block co-polymer to promote binding were preferentially retained within the crude oil zone. To simulate the asymmetrical NP breakthrough curves observed from the unsaturated systems required the use of a model that accounted for both mobile and immobile flow regions as well as NP attachment and detachment with nonlinear Langmuirian blocking. This model allowed examination of attachment and detachment rate coefficients which captured NP interaction with the porous medium and/or crude oil. It was found that the initial water saturation and flow rate did not have an appreciable impact on the NP attachment rate coefficient, while it increased by ~10× with increasing clay and silt content, and by ~100× in the presence of crude oil, indicating preferential NP attachment within the crude oil zone. As a result of the lower NP polymer concentration coating used to promote increased attachment to crude oil, higher retention was observed near the column inlet and was captured quantitatively by adding a depth-dependent straining term to the model. This retention behaviour represents a combination of irreversible attachment at the air-water interfaces and straining near the column inlet enhanced by the formation of NP aggregates. The detachment rate coefficient decreased with a lower initial water saturation and flowrate, but increased with higher clay and silt content. The findings from this study contribute to our understanding of the transport and binding behaviour of Pluronic-coated NPs in unsaturated conditions and, in particular, the role of initial water content, flowrate and porous medium texture. Demonstrated delivery of NPs to a target zone is an important step towards expanding the utility of NPs as treatment reagents.

Advances in Biochar and PGPR engineering system for hydrocarbon degradation: A promising strategy for environmental remediation

In soil, polycyclic aromatic hydrocarbons (PAHs) have resulted in severe environmental deterioration, compromised soil characteristics, and negatively affect all life forms, including humans. Developing appropriate and effective clean-up technology is crucial in solving the contamination issues. The traditional methods to treat PHAs contaminated soil are less effective and not ecofriendly. Bioremediation, based on bioaugmentation and biostimulation approaches, is a promising strategy for remediating contaminated soil. The use of plant growth-promoting rhizobacteria (PGPR) as a bioaugmentation tool is an effective technique for treating hydrocarbon contaminated soil. Plant growth-promoting rhizobacteria (PGPR) are group of rhizospheric bacteria that colonize the roots of plants. Biochar is a carbon-rich residue, which acts as a source of nutrients, and is also a bio-stimulating candidate to enhance the activities of oil-degrading bacteria. The application of biochar as a nutrient source to bioremediate oil-contaminated soil is a promising approach for reducing PHA contamination. Biochar induces polyaromatic hydrocarbons (PAHs) immobilization and removes the contaminants by various methods such as ion exchange electrostatic attractions and volatilization. In comparison, PGPR produce multiple types of biosurfactants to enhance the adsorption of hydrocarbons and mineralize the hydrocarbons with the conversion to less toxic substances. During the last few decades, the use of PGPR and biochar in the bioremediation of hydrocarbons-contaminated soil has gained greater importance. Therefore, developing and applying a PGPR-biochar-based remediating system can help manage hazardous PAH contaminated soil. The goal of this review paper is to (i) provide an overview of the PGPR mechanism for degradation of hydrocarbons and (ii) discuss the contaminants absorbent by biochar and its characteristics (iii) critically discuss the combined effect of PGPR and biochar for degradation of hydrocarbons by decreasing their mobility and bioavailability. The present review focuses on techniques of bioaugmentation and biostimulation based on use of PGPR and biochar in remediating the oil-contaminated soil.

Petroleum-contaminated soil: environmental occurrence and remediation strategies

Soil is an environmental matrix that carries life for all living things. With the rise of human activities and the acceleration of population, the soil has been exposed in part to pollution by the discharge of various xenobiotics and persistent pollutants into it. The disposal of toxic substances such as polycyclic aromatic hydrocarbons (PAHs) alters soil properties, affects microbial biodiversity, and damages objects. Considering the mutagenicity, carcinogenicity, and toxicity of petroleum hydrocarbons, the restoration and clean-up of PAH-polluted sites represents an important technological and environmental challenge for sustainable growth and development. Though several treatment methods to remediate PAH-polluted soils exist, interesting bacteria, fungi, and their enzymes receive considerable attention. The aim of the present review is to discuss PAHs' impact on soil properties. Also, this review illustrates physicochemical and biological remediation strategies for treating PAH-contaminated soil. The degradation pathways and contributing factors of microbial PAH-degradation are elucidated. This review also assesses the use of conventional microbial remediation compared to the application of genetically engineered microorganisms (GEM) that can provide a cost-effective and eco-friendly PAH-bioremediation strategy.

Bacterial community profile of the crude oil-contaminated saline soil in the Yellow River Delta Natural Reserve, China

Crude oil contamination greatly influence soil bacterial community. Proliferative microbes in the crude oil-contaminated soil are closely related to the living conditions. Oil wells in the Yellow River Delta Natural Reserve (YRDNR) region is an ideal site for investigating the bacterial community of crude oil-contaminated saline soil. In the present study, 18 soil samples were collected from the depths of 0-20 cm and 20-40 cm around the oil wells in the YRDNR. The bacterial community profile was analyzed through high-throughput sequencing to trace the oil-degrading aerobic and anaerobic bacteria. The results indicated that C₁₅-C₂₈ and C₂₉-C₃₈ were the main fractions of total petroleum hydrocarbon (TPH) in the sampled soil. These TPH fractions had a significant negative effect on bacterial biodiversity (Shannon, Simpson, and Chao1 indices), which led to the proliferation of hydrocarbon-degrading bacteria. A comprehensive analysis between the environmental factors and soil microbial community structure showed that Streptococcus, Bacillus, Sphingomonas, and Arthrobacter were the aerobic hydrocarbon-degrading bacteria; unidentified Rhodobacteraceae and Porticoccus were considered to be the possible facultative anaerobic bacteria with hydrocarbon biodegradation ability; Acidithiobacillus, SAR324 clade, and Nitrosarchaeum were predicted to be the anaerobic hydrocarbon-degrading bacteria in the sub-surface soil. Furthermore, large amount of carbon sources derived from TPH was found to cause depletion of bioavailable nitrogen in the soil. The bacteria associated with nitrogen transformation, such as Solirubrobacter, Candidatus Udaeobacter, Lysinibacillus, Bradyrhizobium, Sphingomonas, Mycobacterium, and Acidithiobacillus, were highly abundant; these bacteria may possess the ability to increase nitrogen availability in the crude oil-contaminated soil. The bacterial community functions were significantly different between the surface and the sub-surface soil, and the dissolved oxygen concentration in soil was considered to be potential influencing factor. Our results could provide useful information for the bioremediation of crude oil-contaminated saline soil.

Population dynamics and crude oil degrading ability of bacterial consortia of isolates from oil-contaminated sites in Nigeria

Application of bacterial consortium of hydrocarbon degraders to crude oil-contaminated site can enhance bioremediation. This study evaluated the population dynamics and crude oil degradation abilities of various consortia developed from bacterial strains isolated from crude oil-contaminated sites using crude oil-supplemented Bushnell Haas media. Each consortium consisted of three bacterial strains and was designated as Consortium A (Serratia marcescens strain N4, Pseudomonas aeruginosa strain N3R, Pseudomonas aeruginosa strain W11), B (Pseudomonas aeruginosa strain N3R, Pseudomonas aeruginosa strain W11, Pseudomonas protegens strain P7), C (Serratia marcescens strain N4, Pseudomonas aeruginosa strain W11, Pseudomonas protegens strain P7), and D (Pseudomonas aeruginosa strain W15, Providencia vermicola strain W8, Serratia marcescens strain W13). There was progressive decline in the populations of Serratia marcescens strains in the consortia as the incubation period progressed. This may have led to reduction in their synergistic contribution and, subsequently, total degradation ability of crude oil by the consortia. The gravimetric analyses showed that Consortium D produced the highest % crude oil degradation of 29.66% compared to Consortia A, B, and C with 23.73%, 11.86%, and 19.49% respectively. Based on gas chromatography-mass spectrometry analyses, Consortium D produced the highest percentage total petroleum hydrocarbon degradation of 73.65% compared to 68.24%, 68.94%, and 69.19% produced by Consortia A, B, and C respectively. The biodegradation potential of Consortium D also demonstrates the significance of using isolates from the same isolation site in development of consortium for bioremediation.

Stoichiometric characteristics of microbial biomass in oil-contaminated soil in the loess hilly region

Purpose

The present study envisaged the stoichiometry of microbial biomass in petroleum-contaminated soil, in order to study the influence of the petroleum-contaminated soil on the ecosystem stability.

Methods

A typical oil well area in the Northern Shaanxi was considered the research object and the oil pollution status was assessed by studying the physical, chemical, and microbiological characteristics of the soil in the area.

Results

From the measurement and analysis of the petroleum pollutants in the soil samples, it was observed that the concentration of the petroleum pollutants around all the oil well areas was higher than the critical value of 500 mg/kg. Furthermore, the C to N ratio of 8 soil samples around the oil wells (0.8:1~13.3:1) was lower than that of the control soil samples in most cases and could not reach the nutrient proportion level required by soil microorganisms. It was observed that the oil organic carbon content at 0~10 m from the wellhead was obviously higher than that in other areas, and decreased with an increase in the distance from the well. Based on the determination of soil organic carbon, total nitrogen, total phosphorus, and the soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN), and phosphorus content analysis, it was observed that only the soil organic carbon was significantly positively correlated to the oil pollutants in soil.

Conclusions

Imbalance in the C to N, SMBC, and SMBN ratio can lead to an acute shortage of the required nutrients than microorganisms, limit the soil microbial reproduction and growth, and thereby slow down the rate of indigenous microbial degradation of petroleum hydrocarbons, so as to reduce the impact of oil pollution on the stability of the entire ecosystem. Therefore, during the remediation of petroleum-contaminated soil in this study area, adequate nutrients need to be reasonably added to the soil.

Succession of microbial communities and synergetic effects during bioremediation of petroleum hydrocarbon-contaminated soil enhanced by chemical oxidation

Biotechnologies integrated with chemical techniques are promising in treating the soils contaminated by petroleum hydrocarbons. Experiments by applying the degrading consortium and the modified Fenton (MF) with the chelator sodium citrate simultaneously were carried out to investigate the effects of the MF reagents on the degradation of total petroleum hydrocarbons (TPHs), changes in enzyme activities and the succession of microbial communities at the 0, 20, 100 and 500 mmol/kg hydrogen peroxide concentration levels. The ratio between hydrogen peroxide, ferrous sulfate and sodium citrate in the MF reagents was 100:1:1. The results indicated that the degradation of TPHs conformed to first-order kinetics and MF treatments increased the total removal rates of TPHs (4.73-24.26%) and activated dehydrogenase and polyphenol oxidase activities. A shift in microbial communities from Proteobacteria to Bacteroidetes was observed during the enhanced bioremediation, and the predominant genus shifted from Pseudomonas with an average relative abundance (ARAs) of 76.61% at the beginning to Sphingobacterium with ARAs of 52.06% at the later stage. The MF reagents at the proper level could simplify the relationship among the community populations, alleviate their competition and strengthen their associations, which would optimize the removal efficiency.

Prokaryotic community diversity during bioremediation of crude oil contaminated oilfield soil: effects of hydrocarbon concentration and salinity

Crude oil extracted from oilfield reservoirs brings together hypersaline produced water. Failure in pipelines transporting this mixture causes contamination of the soil with oil and hypersaline water. Soil salinization is harmful to biological populations, impairing the biodegradation of contaminants. We simulated the contamination of a soil from an oilfield with produced water containing different concentrations of NaCl and crude oil, in order to evaluate the effect of salinity and hydrocarbon concentration on prokaryote community structure and biodegradation activity. Microcosms were incubated in CO₂-measuring respirometer. After the incubation, residual aliphatic hydrocarbons were quantified and were performed 16S rRNA gene sequencing. An increase in CO₂ emission and hydrocarbon biodegradation was observed with increasing oil concentration up to 100 g kg^-1. Alpha diversity decreased in oil-contaminated soils with an increase in the relative abundance of Actinobacteria and reduction of Bacteroidetes with increasing oil concentration. In the NaCl-contaminated soils, alpha diversity, CO₂ emission, and hydrocarbon biodegradation decreased with increasing NaCl concentration. There was an increase in the relative abundance of Firmicutes and Proteobacteria and a reduction of Actinobacteria with increasing salt concentration. Our results highlight the need to adopt specific bioremediation strategies in soils impacted by mixtures of crude oil and hypersaline produced water.

Metagenome Analysis of a Hydrocarbon-Degrading Bacterial Consortium Reveals the Specific Roles of BTEX Biodegraders

Environmental contamination by petroleum hydrocarbons is of concern due to the carcinogenicity and neurotoxicity of these compounds. Successful bioremediation of organic contaminants requires bacterial populations with degradative capacity for these contaminants. Through successive enrichment of microorganisms from a petroleum-contaminated soil using diesel fuel as the sole carbon and energy source, we successfully isolated a bacterial consortium that can degrade diesel fuel hydrocarbons. Metagenome analysis revealed the specific roles of different microbial populations involved in the degradation of benzene, toluene, ethylbenzene and xylene (BTEX), and the metabolic pathways involved in these reactions. One hundred and five putative coding DNA sequences were identified as responsible for both the activation of BTEX and central metabolism (ring-cleavage) of catechol and alkylcatechols during BTEX degradation. The majority of the Coding DNA sequences (CDSs) were affiliated to Acidocella, which was also the dominant bacterial genus in the consortium. The inoculation of diesel fuel contaminated soils with the consortium resulted in approximately 70% hydrocarbon biodegradation, indicating the potential of the consortium for environmental remediation of petroleum hydrocarbons.

Response of bacterial and fungal communities to high petroleum pollution in different soils

Petroleum pollution of soils is a major environmental problem. Soil microorganisms can decompose a significant fraction of petroleum hydrocarbons in soil at low concentrations (1-5%). This characteristic can be used for soil remediation after oil pollution. Microbial community dynamics and functions are well studied in cases of moderate petroleum pollution, while cases with heavy soil pollution have received much less attention. We studied bacterial and fungal successions in three different soils with high petroleum contents (6 and 25%) in a laboratory experiment. The proportion of aliphatic and aromatic compounds decreased by 4-7% in samples with 6% pollution after 120 days of incubation but remained unchanged in samples with 25% hydrocarbons. The composition of the microbial community changed significantly in all cases. Oil pollution led to an increase in the relative abundance of bacteria such as Actinobacteria and the candidate TM7 phylum (Saccaribacteria) and to a decrease in that of Bacteroidetes. The gene abundance (number of OTUs) of oil-degrading bacteria (Rhodococcus sp., candidate class TM7-3 representative) became dominant in all soil samples, irrespective of the petroleum pollution level and soil type. The fungal communities in unpolluted soil samples differed more significantly than the bacterial communities. Nonmetric multidimensional scaling revealed that in the polluted soil, successions of fungal communities differed between soils, in contrast to bacterial communities. However, these successions showed similar trends: fungi capable of lignin and cellulose decomposition, e.g., from the genera Fusarium and Mortierella, were dominant during the incubation period.

Use of Soil Enzymes as Indicators for Contaminated Soil Monitoring and Sustainable Management

Diagnosis of the risk of soil pollution and the performance of measures for the recovery of contaminated soil requires proper monitoring of the extent of soil function damage and its recovery process. Soil enzymes reveal ecosystem perturbations, are sensitive to management choices, and have been used as indicators of biogeochemical cycles, organic matter degradation, and soil remediation processes. Thus, enzymes can indicate, along with other physical or chemical properties, soil quality. In this paper, we review the effects of soil pollutants [toxic trace elements (TTE), and petroleum hydrocarbons (PHC)] on enzymatic activities and evaluate the usefulness of soil enzyme’s activity for monitoring recovery processes in contaminated soil. Soil enzymes can be said to be a powerful means of monitoring to properly indicate the degree of deterioration of soil quality caused by soil pollution and to diagnose the process of functional recovery of contaminated soil. Further research is needed to establish the quantitative relationships between the soil physico-chemical properties and enzyme activity and the effect of soil remediation on the functional recovery of soil-related to soil quality.

The possible role of toxigenic fungi in ecotoxicity of two contrasting oil-contaminated soils - A field study

Long-term field experiments were performed to evaluate the phytotoxic properties of fungal metabolites in oil-contaminated soil and to assess the impact of contamination on the allelopathic activity of soil mycobiota. Two contrasting soils of Northwest Russia (sandy and loamy podzols) exposed to oil contamination underwent changes in abundance and allelopathic activities of soil fungi. Shifts within the microbial community caused by oil contamination affected not only oil-decomposition rates but also ecotoxicity of contaminated soil. There were significant differences in soil toxicity dynamics between sandy and loamy podzols. Four years after contamination, ecotoxicity of loamy podzol decreased, whereas sandy podzol remained highly toxic even nine years after contamination. The abundance and allelopathic activity of fungi is correlated with hydrocarbon degradation dynamics. The soil fungal community demonstrated high allelopathic activity which decreased over time in fertile loamy podzolic soil, whereas in poor sandy podzolic soil it remained high over the nine-year monitoring period. The results illustrate how oil contamination may influence allelopathic interactions in soil and demonstrate the advantage of using fungal metabolite toxicity test for testing of oil-contaminated soil samples.

Copper accumulation in agricultural soils: Risks for the food chain and soil microbial populations

The long-term use of Cu-based fungicides at doses of several kilograms per hectare stimulated a wide debate about the human health and environmental risks of the progressive accumulation of Cu in agricultural soils. Here, the health risks due to copper accumulation in agricultural soils were evaluated with a survey in intensive agricultural land of the Campania region (Italy), aiming to evaluate Cu accumulation in food crops. The health risk due to dietary exposure was estimated by using the Hazard Quotient (HQ), calculated as the ratio between the average daily dose and the reference dose of copper, suggesting that when HQ > 1 there is a potential risk for consumers. According to a survey of soils with a Cu content up to 217 mg kg^-1, no foodstuffs showed dietary risks. Nevertheless, the contribution of Cu contained in these foodstuffs to the overall intake of Cu by consumers could increase health risks since such risks must be evaluated on the basis of the whole standard diet by quantifying the Cu content not only in vegetables and fruits but also in other sources, such as cereals, not cultivated in the study area and thus not considered in this paper. The environmental risks due to copper accumulation in agricultural soils were then evaluated with a field experiment in a soil characterized by a very high Cu concentration (up to 1700 mg kg^-1), aiming to study the impacts of Cu on native soil microorganisms. The study of the microbiota highlighted that the presence of Cu in soil did not reduce the total richness and diversity of microorganisms, which were not related to increasing concentrations of Cu in the soil. Nevertheless, Cu contamination was found to exert significant selection pressure on the soil microbiota, as shown by beta diversity and correlation analysis between taxa and Cu content.

Urease activity and microbial biomass of carbon in hydrocarbon contaminated soils. A case study of cheshmeh-khosh oil field, Iran

Crude oil contamination in soils may result in destructive effects on soil microorganisms and plants and act as a source of groundwater contamination. The objective of this study was to evaluate the biological activities for a better understanding of ecological risks. A couple of biological assays, including soil microbial biomass of carbon (SMBC) and urease activity (UA), were used to evaluate the microbial activities in soils. The chemical analysis demonstrated different values of total petroleum hydrocarbons (TPHs) concentrations (from 0.12 to 2.99 mg/kg of dry soil) and relatively high quantities of Nickel (from 32 to 136.8 mg/kg of dry soil) and cadmium (from 0 to 4 mg/kg of dry soil) in samples. UA and SMBC values were comparatively lower in close distances to oil wells, pipelines, and especially drilling sediments pool. The spatial variability maps using the interpolation module by GIS specified the line from northwest to the southeast of the area as a more affected area by TPHs and Ni + Cd.

Monitoring oil contamination in vegetated areas with optical remote sensing: A comprehensive review

The monitoring of soil contamination deriving from oil and gas industry remains difficult in vegetated areas. Over the last decade, optical remote sensing has proved helpful for this purpose. By tracking alterations in vegetation biochemistry through its optical properties, multi- and hyperspectral remote sensing allow detecting and quantifying crude oil and petroleum products leaked following accidental leakages or bad cessation practices. Recent advances in this field have led to the development of various methods that can be applied either in the field using portable spectroradiometers or at large scale on airborne and satellite images. Experiments carried out under controlled conditions have largely contributed to identifying the most important factors influencing the detection of oil (plant species, mixture composition, etc.). In a perspective of operational use, an important effort is still required to make optical remote sensing a reliable tool for oil and gas companies. The current methods used on imagery should extend their scope to a wide range of contexts and their application to upcoming satellite-embedded hyperspectral sensors should be considered in future studies.

Antifungal and Phytotoxic Activities of Essential Oils: In Vitro Assays and Their Potential Use in Crop Protection

(1) Background: The use of natural products based on essential oils (EO) is nowadays arousing great interest as an alternative method to control plant pathogens and weeds. However, EO possess low bioavailability and are highly volatile, and their encapsulation in hydroxypropyl-ß-cyclodextrin (HP-β-CD) could be a means to enhance their stability and maintain their bioactivity. Thus, the current study aims at investigating, in the presence and the absence of HP-β-CD, the antifungal and phytotoxic activities of nine EO, distilled from plant species belonging to Alliaceae, Apiaceae, and Cupressaceae families, with considerations for their chemical composition. (2) Methods: EO antifungal activity was assessed by direct contact and volatility assays against Fusarium culmorum, a major phytopathogenic fungi, while phytotoxic effects were evaluated against lettuce (Lactuca sativa L.) and rye-grass (Lolium perenne L.), by seedling’s emergence and growth assays. (3) Results: These EO inhibit fungal growth in both direct contact and volatility assays, with half-maximal inhibitory concentrations (IC50) ranging from 0.01 to 4.2 g L−1, and from 0.08 up to 25.6 g L−1, respectively. Concerning phytotoxicity, these EO have shown great potential in inhibiting lettuce (IC50 ranging from 0.0008 up to 0.3 g L−1) and rye-grass (IC50 ranging from 0.01 to 0.8 g L−1) seedlings’ emergence and growth. However, the EO encapsulation in HP-β-CD has not shown a significant improvement in EO biological properties in our experimental conditions. (4) Conclusion: All tested EO present antifungal and phytotoxic activities, with diverse efficacy regarding their chemical composition, whilst no increase of their biological effects was observed with HP-β-CD.

Remediation of hexavalent chromium contaminated soil by nano-FeS coated humic acid complex in combination with Cr-resistant microflora

A novel nano-composite material (CMC-FeS@HA) combining the advantages of humic acid (HA) and FeS was synthesized to remediate hexavalent chromium (Cr(VI)) contaminated soil along with chromium (Cr) resistant microflora. The characteristic analysis confirmed the successful synthesis of the nano-composite, which provided further mechanism evidence of its detoxification effect on polluted soil. Energy Dispersive System analysis proved the adsorption of the microbe consortium (MC) for Cr. After remediation, Cr(VI) in all treatments was dramatically reduced and the leachable Cr in soil treated by CMC-FeS@HA and MC decreased 89.14% compared with control. The result of BCR sequential extraction showed that Cr was stabilized, whose form changed to oxidizable and residual from HOAC-extractable. Besides, CMC-FeS@HA, as a sustained-release acid with high biocompatibility, could continuously decrease the pH of strongly alkaline soil and created a suitable micro-ecological environment for soil microorganisms. Moreover, CMC-FeS@HA dramatically improved soil physicochemical property, soil microbial activity (dehydrogenase, hydrolase, urease, and invertase activities), and soil microecological diversity. In total, this study provided a useful technology for soil remediation, which innovatively combined chemical remediation and microbial-remediation with a positive effect on soil quality, providing a good approach for the multiple technology combination in the environmental cause.

Monitoring of a long term phytoremediation process of a soil contaminated by heavy metals and hydrocarbons in Tuscany

The purpose of this study was to monitor and model indicators of soil contamination, organic matter evolution and biochemical processes involved in a long-term phytoremediation process. Populus nigra L., Paulownia tomentosa Steud., Cytisus scoparius L. and natural vegetation were used in differently contaminated areas (high, medium and low levels of contamination). Parameters indicating contamination (total petroleum hydrocarbons (TPH) and heavy metals) and agronomic (C, N and P) and functional (enzyme activities) soil recovery were monitored for 3.5 years. Three subareas with different levels of contamination (high, medium and low) were identified according to the Nemerow Index. A considerable decrease in TPH (52% on average) over time in the whole site was measured, while the metal reduction was only of about 22% at surface level. A stimulation in metabolic soil processes and improvement in the chemical quality of the soil was also observed throughout the experimental site. Statistical analysis modelling showed that the contaminant content decreased following a one-phase decay model, while the dramatic increase in enzyme activities could be represented by an exponential growth equation. On the basis of our data, it is possible to conclude that the initial contamination level affected neither the decontamination process nor the improvement in soil quality, which occurred similarly in the three different contaminated areas.

Ecological risk of combined pollution on soil ecosystem functions: Insight from the functional sensitivity and stability

Assessing the ecological risk of combined pollution, especially from a holistic perspective with the consideration of the overarching functions of soil ecosystem, is crucial and beneficial to the improvement of ecological risk assessment (ERA) framework. In this study, four soils with similar physicochemical properties but contrasting heavy metals contamination levels were selected to explore changes in the integrated functional sensitivity (MSI), resistance (MRS) and resilience (MRL) of soil microbial communities subjected to herbicide siduron, based on which the ecological risk of the accumulation of siduron in the four studied soils were evaluated. The results suggested that the microbial biomass carbon, activity of denitrification enzyme and nitrogenase were indicative of MSI and MRS, and the same three parameters plus soil basal respiration were indicative of MRL. Significant dose-effect relationships between siduron residues in soils and MSI, MRS and MRL under combined pollution were observed. Heavy metal polluted soils showed higher sensitivity and lower resistance to the additional disturbance of herbicide siduron due to the lower microbial biomass, while the resilience of heavy metal polluted soils was much higher due to the pre-adaption to the chemical stresses. The quantifiable indicator microbial functional stability was incorporated in the framework of ERA and the results showed that the accumulation of siduron in the studied soils could exhibit potential harm to the integrated functional stability of soil microbial community. Thus, this work provides insights into the application of integrated function of soil microbial community into the framework of ERA.

Progress in ultrasonic oil-contaminated sand cleaning: a fundamental review

Steady efforts in using ultrasonic energy to treat oil-contaminated sand started in the early 2000s until today, although pilot studies on the area can be traced to even earlier dates. Owing to the unique characteristics of the acoustic means, the separation of oil from sand has been showing good results in laboratories. This review provides the compilation of researches and insights into the mechanism of separation thus far. Related topics in the areas of oil-contaminated sand characterizations, fundamental ultrasonic cleaning, and cavitation effects are also addressed. Nevertheless, many of the documented works are only at laboratory or pilot-scale level, and the comprehensive interaction between ultrasonic parameters towards cleaning efficiencies may not have been fully unveiled. Gaps and opportunities are also presented at the end of this article.

Remediation potential of immobilized bacterial consortium with biochar as carrier in pyrene-Cr(VI) co-contaminated soil

Polycyclic aromatic hydrocarbons (PAHs) and potentially toxic trace elements (PTEs) soil contamination have become areas of concern. Bioaugmentation is regarded as an effective bioremediation method, however it is difficult to simultaneously degrade organic compounds and remove PTEs with individual microbial strains. Therefore, the objective of this study was to evaluate the feasibility of using immobilized microbial consortia, including two PAH-degrading bacterial strains (W1 and W2) and a Cr(VI)-reducing bacterium (Y2), for the remediation of pyrene-Cr(VI) co-contaminated soil. Three immobilization methods were investigated: (1) bacterial consortium adsorption onto biochar (BC), (2) bacterial consortium entrapment in alginate beads (AC), (3) bacterial consortium adsorption on biochar and sequential entrapment in alginate beads (BAC). In addition, a free bacterial consortium (FC) was also used for comparison. Ten treatments were designed to illustrate the bioremediation efficiency of the free and immobilized consortia. The results show that treatments AC and BAC resulted in more efficient Cr(VI) removal compared with BC and FC. Pyrene levels in AC and BAC microcosms were reduced from 42.33 ± 3.82 to 11.56 ± 1.37 and 7.48 ± 0.39 mg kg^-1, respectively. Bioavailable Cr (VI) in AC and BAC was significantly lower than that in other microcosms after 28 days' incubation. Both AC and BAC microcosms exhibited a higher level of dehydrogenase and fluorescein diacetate hydrolysis activity. Furthermore, soil microbial diversity was higher in AC and BAC microcosms compared with the others. Thus, the entrapped consortia may be useful for bioremediation of pyrene and Cr (VI) without compromising soil ecology.

Impact of Crude Oil on Functional Groups of Culturable Bacteria and Colonization of Symbiotic Microorganisms in the <i>Clitoria-Brachiaria</i> Rhizosphere Grown in Mesocosms

This research evaluated the changes on populations of culturable N-fixing free bacteria (NFFB) and P-solubilizing bacteria (PSB), as well as on the root nodulation by native rhizobia, the root colonization and spore number of arbuscular mycorrhizal fungi (AMF), in the rhizosphere of Clitoria ternatea and Brachiaria brizantha grown in mesocosms contaminated with crude oil (0, 3000, 6000, 9000, and 12000 mg kg-1), for 240 days. After 24 h of soil contamination, the highest populations of NFFB and PSB (5.5 and 4.9 LogUFC, respectively) were found in control, and the lowest populations were obtained at 12000 mg kg-1 (5.1 and 4.2 LogUFC, respectively). In contrast, at 60 and 240 days, the control showed lower populations of NFFB and PSB (5.4 and 4.8 LogUFC, respectively) than contaminated treatments. The highest number or root nodules in C. ternatea was quantified in control at 60 and 240 days (25 and 27 nodules, respectively) in comparison to those observed at the treatment with 12000 mg kg-1 (7 and 1 nodule, respectively). At 60 days, AMF colonization in both plant species, and the number of spores significantly decreased as the crude oil concentration increased; however, at 240 days, the highest number of AMF spores was recorded at treatments with 6000 and 12000 mg kg-1. The dry weight of both plant species significantly decreased as crude oil concentrations increased. Although C. ternatea was more susceptible to the toxic effects of crude oil, this plant species showed greater content of total chlorophyll than B. brizantha.

Microbial diversity and bioremediation of rhizospheric soils from Trindade Island - Brazil

Pristine environments may harbor complex microbial communities with metabolic potential for use in bioremediation of organic pollutants. This study aimed to evaluate crude oil biodegradation by microbial communities present in rhizospheric soils of Bulbostylis nesiotis and Cyperus atlanticus on Trindade Island and the compositional structure of these communities. After 60 days under aerobic conditions, Total Petroleum Hydrocarbon biodegradation ranged from 66 to 75%, depending on the plant species and the origin of the soil samples. There was no response of petroleum biodegradation to fertilization with N:P:K (80:160:80 mg dm^-3). Soil contamination with crude oil did not necessarily reduce microbial diversity. The richness and diversity increased in contaminated soils in some specific situations. We conclude that microbial communities from pristine soils have the ability to remove hydrocarbons through biodegradation and that Bulbostylis nesiotis and Cyperus atlanticus inhabiting Trindade Island harbor rhizospheric microbial communities with potential for application in rhizoremediation.

Production of rhamnolipids with different proportions of mono-rhamnolipids using crude glycerol and a comparison of their application potential for oil recovery from oily sludge

The use of efficient green cleaning agents, such as biosurfactants, is important in oil sludge treatment. Enhanced oil recovery from oily sludge by different rhamnolipids was comparatively evaluated. Using crude glycerol, the wild-type strain Pseudomonas aeruginosa SG and the recombinant strains P. aeruginosa PrhlAB and P. stutzeri Rhl produced 1.98 g L⁻¹, 2.87 g L⁻¹ and 0.87 g L⁻¹ of rhamnolipids, respectively. The three bacterial strains produced different rhamnolipid mixtures under the same conditions. The proportions of mono-rhamnolipids in the three rhamnolipid products were 55.92%, 94.92% and 100%, respectively. These rhamnolipid products also possessed different bioactivities. Emulsifying activity became higher as the proportion of mono-rhamnolipids increased. The three rhamnolipid products were stable at temperatures lower than 121 °C, pH values from 5–11 and NaCl concentrations from 0–15%. All three rhamnolipid products could recover oil from oily sludge, but oil recovery efficiency was positively related to the proportion of mono-rhamnolipids. Mono-rhamnolipids produced by the recombinant strain Rhl exhibited the best oil recovery efficiency (53.81%). The results reveal that mono-rhamnolipids are the most promising for oil recovery from oily sludge.

Oil recovery from oily sludge is positively related to the proportion of mono-rhamnolipids.

Petroleum Hydrocarbon-Degrading Bacteria for the Remediation of Oil Pollution Under Aerobic Conditions: A Perspective Analysis

With the sharp increase in population and modernization of society, environmental pollution resulting from petroleum hydrocarbons has increased, resulting in an urgent need for remediation. Petroleum hydrocarbon-degrading bacteria are ubiquitous in nature and can utilize these compounds as sources of carbon and energy. Bacteria displaying such capabilities are often exploited for the bioremediation of petroleum oil-contaminated environments. Recently, microbial remediation technology has developed rapidly and achieved major gains. However, this technology is not omnipotent. It is affected by many environmental factors that hinder its practical application, limiting the large-scale application of the technology. This paper provides an overview of the recent literature referring to the usage of bacteria as biodegraders, discusses barriers regarding the implementation of this microbial technology, and provides suggestions for further developments.

Antioxidant responses of Triticum aestivum plants to petroleum-derived substances

Winter common wheat (Triticum aestivum L.) plants were cultivated on petroleum products contaminated soils with and without using biopreparation ZB-01. We determined the impact of soil contamination with petrol, diesel fuel and engine oil on selected antioxidant enzymes and the levels of antioxidants in the leaves of winter wheat. The impact of petroleum products on selected morphological characteristics of the plants, levels of nutrients and heavy metals was also assessed. Winter wheat was relatively resistant to soil contamination with petroleum products, and did not show a significant impact on the morphological characteristics of the plants. The levels of nutrients and heavy metals in the plants depended on the type of pollutant and the analyzed component.‬ Biopreparation ZB-01 generally resulted in an increase in calcium levels in the plants.‬ The winter wheat plants growing in soil contaminated with engine oil were characterized by higher levels of zinc, lead, manganese and cadmium than the control plants.‬ Biopreparation applied to the soil contaminated with petrol resulted in a slight increase in the levels of lead and zinc in the plants.‬ The petroleum products affected the activity of antioxidant enzymes and the levels of antioxidants in the plants.‬ The general markers of soil contaminated with diesel fuel and petrol were POD activity and proline levels. Use of the ZB-01 biopreparation caused an increase in the levels of proline and -SH groups and an increase in the levels of carbon and calcium in the plants and had no effect on the morphological characteristics of plants.‬.

Toxicity assessment of fresh and weathered petroleum hydrocarbons in contaminated soil- a review

Soil contamination with total petroleum hydrocarbons (TPH) is widespread throughout the globe due to the massive production of TPH anthropogenically and its occurrence in the soil. TPH is toxic to beneficial soil organisms and humans and thus has become a serious concern among the public. Traditionally TPH toxicity in the soil is estimated based on chemical fractions and a range of bioassays including plants, invertebrates and microorganisms. There is a large inconsistency among ecotoxicology data using these assays due to the nature of TPH and their weathering. Therefore, in this article, we critically reviewed the weathered conditions of TPH, the potential fate in soil and the bioindicators for the assessment of the ecotoxicity. Based on the current research and the state-of-the-art problem, we also highlighted key recommendations for future research scope for the real-world solution of the ecotoxicological studies of hydrocarbons.

Bioprospecting for microbes with potential hydrocarbon remediation activity on the northwest coast of the Yucatan Peninsula, Mexico, using DNA sequencing

Coastal environments harbor diverse microbial communities, which can contain genera with potential bioremediation activity. Next-generation DNA sequencing was used to identify bacteria to the genus level in water and sediment samples collected from the open ocean, shoreline, wetlands and freshwater upwellings on the northwest coast of the Yucatan Peninsula. Supported by an extensive literature review, a phylogenetic investigation of the communities was done using reconstruction of unobserved states software (PICRUSt) to predict metagenome functional content from the sequenced 16S gene in all the samples. Bacterial genera were identified for their potential hydrocarbon bioremediation activity. These included generalist genera commonly reported in hydrocarbon-polluted areas and petroleum reservoirs, as well as specialists such as Alcanivorax and Cycloclasticus. The highest readings for bacteria with potential hydrocarbon bioremediation activity were for the genera Vibrio, Alteromonas, Pseudomonas, Acinetobacter, Burkholderia, Acidovorax and Pseudoalteromonas from different environments in the study area. Some genera were identified only in specific sites; for example, Aquabacterium and Polaromonas were found only in freshwater upwellings. Variation in genera distribution was probably due to differences in environmental conditions in the sampled zones. Bacterial diversity was high in the study area and included numerous genera with known bioremediation activity. Functional prediction of the metagenome indicated that the studied bacterial communities would most probably degrade toluene, naphthalene, chloroalkane and chloroalkene, with lower degradation proportions for aromatic hydrocarbons, fluorobenzoate and xylene. Differences in predicted degradation existed between sediments and water, and between different locations.

Catabolic Fingerprinting and Diversity of Bacteria in Mollic Gleysol Contaminated with Petroleum Substances

This study focused on the determination of both catabolic and genetic fingerprinting of bacteria inhabiting soil contaminated with car fuels. A surface layer (0–20 cm) of Mollic Gleysol was used for the experiment and was contaminated with car fuels—unleaded 95-octane petrol and diesel at a dose of 15 g per 10 g of soil. The experiment lasted 42 days and was performed at 20 °C. The metabolic potential of soil bacterial communities was evaluated using the Biolog EcoPlate system. The results demonstrated that petroleum substances influenced the structure of the microbial populations and their catabolic activity. The Arthrobacter, Paenibacillus, and Pseudomonas genera were found in diesel-contaminated soil, whilst Bacillus and Microbacterium were found in petrol-contaminated soil. Rhodococcus species were identified in both variants of impurities, suggesting the widest capability of car fuel degradation by this bacterial genus. The contamination with unleaded 95-octane petrol caused rapid inhibition of the metabolic activity of soil bacteria in contrast to the diesel treatment, where high metabolic activity of bacteria was observed until the end of the incubation period. Higher toxicity of petrol in comparison with diesel car fuel was evidenced.

Response of soil phosphatase activities to contamination with two types of tar oil

Tar oil is a complex mixture of hydrocarbon compounds obtained from high-temperature distillation of coal tar. It has been used for over 100 years from now to protect wood and has been applied to wood products, primary utility poles, and railroad ties by pressure methods. Composition of the tar oil depends on the source and typically consists of 85% polycyclic aromatic hydrocarbons (PAHs), 10% phenolic compounds, and 5% heterocyclic compounds. In this research, we performed the laboratory experiment to compare two types of tar oil: C and GX-Plus, and their effects on P-cycling enzymes (phosphatases) in sandy loam and loamy sand. Tar oil was applied to soil samples at the following doses: 2, 10, and 50 g kg^-1. Soil without tar oil was used as a control sample. The experiment showed that the contamination of soil with tar oil affects the enzyme activities measured and with this most probably the P-cycle in soil. Phosphomonoesterases were the most sensitive to the contamination of soil with both type of tar oil: typeC and type GX-Plus. Greater changes in the enzymatic activity were observed in the loamy sand. Moreover, the type C tar oil demonstrated higher toxicity for phosphatases than type GX-Plus.

Evaluation of the natural attenuation capacity of urban residential soils with ecosystem-service performance index (EPX) and entropy-weight methods

Soils provide the service of attenuating and detoxifying pollutants. Such ability, natural attenuation capacity (NAC), is one of the most important ecosystem services for urban soils. We improved the ecosystem-service performance index (EPX) model by integrating with entropy weight determination method to evaluate the NAC of residential soils in Beijing. Eleven parameters related to the soil process of pollutants fate and transport were selected and 115 residential soil samples were collected. The results showed that bulk density, microbial functional diversity and soil organic matter had high weights in the NAC evaluation. Urban socio-economic indicators of residential communities such as construction age, population density and property & management fee could be employed in kinetic fittings of NAC. It could be concluded urbanization had significant impacts on NAC in residential soils. The improved method revealed reasonable and practical results, and it could be served as a potential measure for application to other quantitative assessment.

Microbial functional gene patterns related to soil greenhouse gas emissions in oil contaminated areas

Linking microbial community structure to physiology and ecological processes is a critical focus of microbial ecology. To understand the microbial functional gene patterns related to soil greenhouse gas [carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O)] emissions under oil contamination, we used functional gene array (GeoChip 5.0) analysis and network methods to investigate the feedback responses of soil microbial functional gene patterns and identify keystone genes in Shengli Oilfield, China. The microbial functional gene number, relative abundance and diversity involved in carbon degradation and nitrogen cycling decreased consistently with the reduced CO₂ and N₂O flux in oil contaminated soils, whereas the gene number and relative abundance of methane-production related genes increased with contamination. Functional molecular ecological networks were built based on random matrix theory, where network structures and properties showed significantly variation between oil contaminated and uncontaminated soils (P<0.05). Network nodes, connectivity and complexity all reduced under oil contamination. The sensitive and the highest connective genes in the network were identified as keystone genes, based on Mann-Whitney U tests and network analysis. Our findings improved the understanding of the microbe-mediated mechanisms affecting soil greenhouse gas emissions.

The Impact of Diesel Oil Pollution on the Hydrophobicity and CO2 Efflux of Forest Soils

The contamination of soil with petroleum products is a major environmental problem. Petroleum products are common soil contaminants as a result of human activities, and they are causing substantial changes in the biological (particularly microbiological) processes, chemical composition, structure and physical properties of soil. The main objective of this study was to assess the impact of soil moisture on CO₂ efflux from diesel-contaminated albic podzol soils. Two contamination treatments (3000 and 9000 mg of diesel oil per kg of soil) were prepared for four horizons from two forest study sites with different initial levels of soil water repellency. CO₂ emissions were measured using a portable infrared gas analyser (LCpro+, ADC BioScientific, UK) while the soil samples were drying under laboratory conditions (from saturation to air-dry). The assessment of soil water repellency was performed using the water drop penetration time test. An analysis of variance (ANVOA) was conducted for the CO₂ efflux data. The obtained results show that CO₂ efflux from diesel-contaminated soils is higher than efflux from uncontaminated soils. The initially water-repellent soils were found to have a bigger CO₂ efflux. The non-linear relationship between soil moisture content and CO₂ efflux only existed for the upper soil horizons, while for deeper soil horizons, the efflux is practically independent of soil moisture content. The contamination of soil by diesel leads to increased soil water repellency.

Combining stable carbon isotope analysis and petroleum-fingerprinting to evaluate petroleum contamination in the Yanchang oilfield located on loess plateau in China

This study evaluated petroleum contamination in the Yanchang (Shaanxi Yanchang Petroleum (Group) Co., Ltd.) oilfield, located in the loess plateau region of northern Shaanxi, China. Surface soil and sediment samples were collected from the wasteland, farmland, and riverbed in this area to assess the following parameters: total petroleum hydrocarbon (TPH), n-alkanes, polycyclic aromatic hydrocarbons (PAHs), and carbon isotope ratios (δ¹³C). The results showed that TPH and PAH levels in the study area were 907-3447 mg/kg and 103.59-563.50 μg/kg, respectively, significantly higher than the control samples (TPH 224 mg/kg, PAHs below method quantification limit, MQL). Tests using δ¹³C to detect modified TPH (2238.66 to 6639.42 mg/kg) in the wastelands adjacent to the oil wells revealed more significant contamination than tests using extraction gravimetric analysis. In addition, "chemical fingerprint" indicators, such as low to high molecular weight (LMW/HMW) hydrocarbons, carbon preference index (CPI), and pristine/phytane (Pr/Ph), further confirmed the presence of heavy petroleum contamination and weathering. This has resulted in a nutrient imbalance and unsuitable pH and moisture conditions for microbial metabolic activities. This study evaluates petroleum contamination, which can inform contamination remediation on a case by case basis.

Synergistic action of rhizospheric fungi with Megathyrsus maximus root speeds up hydrocarbon degradation kinetics in oil polluted soil

This study was aimed at combining the potentials of plant and some rhizospheric fungal strains in remediation of crude-oil polluted soil. Four new rhizospheric fungi were identified from an aged crude-oil polluted site and used with Megathyrsus maximus (guinea grass) for a 90 day synergistic remediation experiment. Cultures of these strains were first mixed with spent mushroom compost (SMC), the mixture was then applied to a sterilized crude oil polluted soil at concentrations of 10%, 20%, 30% and 40% potted in three replicates. Soil with plant alone (0%₁) and soil with fungi-SMC alone (0%₂) served as controls. The soil's initial and final pH, nutrient, 16 EPA PAHs and heavy metal contents were determined, degradation rate, half-life and percentage loss of the total polyaromatic hydrocarbon (TPAH) were also calculated. Finally, the remediated soils were further screened for seed germination supporting index. The fungal strains were identified and registered at NCBI as Aspergillus niger asemoA (KY473958.1), Talaromyces purpurogenus asemoF (KY488463.1), Trichoderma harzianum asemoJ (KY488466.1) and Aspergillus flavus asemoM (KY488467.1). We observed for the first time that the synergistic mechanism improved the soil nutrient, reduced the heavy metal concentration and sped up hydrocarbon degradation rate. Using the initial and final concentrations of the TPAH, we recorded highest biodegradation rates (K₁) and half-life (t_1/2) in 30 and 40% treatments over controls, these treatments also had highest seed germination supporting index. This work suggests that the set-up synergistic remediation could be used to remediate crude oil polluted soil and this could be used in large scale.

Aerobic degradation of crude oil by microorganisms in soils from four geographic regions of China

A microcosm experiment was conducted for 112 d by spiking petroleum hydrocarbons into soils from four regions of China. Molecular analyses of soils from microcosms revealed changes in taxonomic diversity and oil catabolic genes of microbial communities. Degradation of total petroleum hydrocarbons (TPHs) in Sand from the Bohai Sea (SS) and Northeast China (NE) exhibited greater microbial mineralization than those of the Dagang Oilfield (DG) and Xiamen (XM). High-throughput sequencing and denaturing gradient gel electrophoresis (DGGE) profiles demonstrated an obvious reconstruction of the bacterial community in all soils. The dominant phylum of the XM with clay soil texture was Firmicutes instead of Proteobacteria in others (DG, SS, and NE) with silty or sandy soil texture. Abundances of alkane monooxygenase gene AlkB increased by 10- to 1000-fold, relative to initial values, and were positively correlated with rates of degradation of TPHs and n-alkanes C13-C30. Abundances of naphthalene dioxygenase gene Nah were positively correlated with degradation of naphthalene and total tricyclic PAHs. Redundancy analysis (RDA) showed that abiotic process derived from geographical heterogeneity was the primary effect on bioremediation of soils contaminated with oil. The optimization of abiotic and biotic factors should be the focus of future bioremediation of oil contaminated soil.

Cupriavidus pinatubonensis AEO106 deals with copper-induced oxidative stress before engaging in biodegradation of the herbicide 4-chloro-2-methylphenoxyacetic acid

BACKGROUND

Microbial degradation of phenoxy acid (PA) herbicides in agricultural soils is important to minimize herbicide leaching to groundwater reservoirs. Degradation may, however, be hampered by exposure of the degrader bacteria to toxic metals as copper (Cu) in the soil environment. Exposure to Cu leads to accumulation of intracellular reactive oxygen species (ROS) in some bacteria, but it is not known how Cu-derived ROS and an ensuing oxidative stress affect the degradation of PA herbicides. Based on the previously proposed paradigm that bacteria deal with environmental stress before they engage in biodegradation, we studied how the degradation of the PA herbicide 2-methyl-4-chlorophenoxyacetic acid (MCPA) by the model PA degrader Cupriavidus pinatubonensis AEO106 was affected by Cu exposure.

RESULTS

Exposure of C. pinatubonensis in batch culture to sublethal concentrations of Cu increased accumulation of ROS measured by the oxidant sensing probe 2,7-dichlorodihydrofluorescein diacetate and flow cytometry, and resulted in upregulation of a gene encoding a protein belong to the Ohr/OsmC protein family. The ohr/osmC gene was also highly induced by H₂O₂ exposure suggesting that it is involved in the oxidative stress response in C. pinatubonensis. The increased ROS accumulation and increased expression of the oxidative stress defense coincided with a delay in the catabolic performance, since both expression of the catabolic tfdA gene and MCPA mineralization were delayed compared to unexposed control cells.

CONCLUSIONS

The current study suggests that Cu-induced ROS accumulation in C. pinatubonensis activates a stress response involving the product of the ohr/osmC gene. Further, the stress response is launched before induction of the catabolic tfdA gene and mineralization occurs.