Scanning electron microscopic investigations of root structural modifications arising from growth in crude oil-contaminated sand

Comparative analysis of remediation efficiency and ultrastructural translocalization of polycyclic aromatic hydrocarbons in Medicago sativa, Helianthus annuus, and Tagetes erecta

Polycyclic aromatic hydrocarbons (PAHs) are semi-volatile anthropogenic contaminants that can damage soil fertility and threaten the environment due to their hazardous effects on various ecological parameters. The experimental objective was divided into two parts because PAHs are always present in mixtures. The toxicity of anthracene, phenanthrene, pyrene, and fluoranthene was examined and investigated the potential of three phytoremediator plants species viz Tagetes erecta, Helianthus annuus, and Medicago sativa for remediation and translocation of individual PAH. PAHs were shown to have inhibitory or stimulating effects on growth, antioxidant properties, and impact on the structure of plant cells. The result showed that M. sativa significantly enhances the removal rate of PAHs in the soil. The dissipation rate reached 96.2% in M. sativa planted soil, followed by H. annuus and T. erecta. Among the plant species, M. sativa exhibited the highest root and shoot concentrations (314.37 and 169.55 mg kg-1), while the lowest concentration was 187.56 and 76.60 mg kg-1 in T. erecta. SEM-EDX and fluorescence micrographs confirmed that pyrene altered plant tissue's ultrastructure and cell viability and was found to be the most toxic and resistant. M. sativa was proven to be the most effective plant for the mitigation of PAHs.

Influence of Bacteria of the Genus Pseudomonas on Leguminous Plants and Their Joint Application for Bioremediation of Oil Contaminated Soils

The modern approach to the creation of biological products to stimulate plant growth is based on the study of specific inter-bacterial interactions. This study describes the impact that the introduction of strains of the genus Pseudomonas has on annual and perennial leguminous plants and the ecosystem of the leguminous plant-the indigenous microbial community. The objects of research under the conditions of vegetation experiments were plants of field peas (Pisum sativum L.), white lupine (Lupinus albus L.), chickpea (Cicer arietinum L.), alfalfa (Medicago sativa subsp. varia (Martyn) Arcang.), and white sweet clover (Melilotus albus Medik.). For the treatment of plant seeds, a liquid culture of strains of growth-stimulating bacteria Pseudomonas koreensis IB-4, and P. laurentiana ANT 17 was used. The positive effect of the studied strains on the germination, growth and development of plants was established. There was no inhibitory effect of inoculants on rhizobia; on the contrary, an increase in nodule formation was observed. The possibility of recultivation of oil-contaminated soil using chickpea and alfalfa as phytomeliorants and growth-stimulating strains P. koreensis IB-4, P. laurentiana ANT 17 as inoculants was evaluated. It is proved that seed treatment improved the morphological parameters of plants, as well as the efficiency of oil destruction.

Optimization of Phytoremediation of Nickel by Alocasia puber Using Response Surface Methodology

The contamination of water by heavy metals is a worldwide environmental problem. Phytoremediation and constructed wetlands have become increasingly popular as more sustainable and environmentally friendly techniques of removing heavy metals from the wastewater. This study, therefore, investigated the phytoremediation of nickel by Alocasia puber (A. puber) in a constructed wetlands (CW) microcosm. This study identified the optimum conditions for nickel (Ni) removal from wastewater using response surface methodology (RSM) with central composite design (CCD). Two operational variables were assessed: exposure time and initial Ni concentration. The optimum conditions for the maximum removal of Ni from water were an exposure time of 10 days and 99.76 mg/L initial Ni concentration. The results indicated that 95.6% removal was achieved under the optimized conditions, with a high correlation coefficient (R2 = 0.97) between the statistical model and the experimental data. Field emission scanning electron microscopy images showed anatomical changes in the A. puber samples due to Ni exposure, and transmission electron microscopy images revealed some internal damages in the A. puber, but visual Ni toxicity symptoms, such as necrosis and chlorosis, were not observed in the A. puber. This study demonstrated that A. puber planted in a constructed wetland microcosm was able to remediate wastewater contaminated with Ni.

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.

Estimating persistent oil contamination in tropical region using vegetation indices and random forest regression

The persistence of soil contamination after cessation of oil activities remains a major environmental issue in tropical regions. The assessment of the contamination is particularly difficult on vegetated sites, but promising advances in reflectance spectroscopy have recently emerged for this purpose. This study aimed to exploit vegetation reflectance for estimating low concentrations of Total Petroleum Hydrocarbons (TPH) in soils. A greenhouse experiment was carried out for 42 days on Cenchrus alopecuroides (L.) under realistic tropical conditions. The species was grown on oil-contaminated mud pit soils from industrial sites, with various concentrations of TPH. After 42 days, a significant decrease in plant growth and leaf chlorophyll and carotenoid contents was observed for plants exposed to 5-19 g kg^-1 TPH in comparison to the controls (p < 0.05). Conversely, pigment contents were higher for plants exposed to 1 g kg^-1 TPH (hormesis phenomenon). These modifications proportionally affected the reflectance of C. alopecuroides at leaf and plant scales, especially in the visible region around 550 and 700 nm. 33 vegetation indices were used for linking the biochemical and spectral responses of the species to oil using elastic net regressions. The established models indicated that chlorophylls a and b and β-carotene were the main pigments involved in the modifications of reflectance (R² > 0.7). The same indices also succeeded in estimating the concentrations of TPH using random forest regression, at leaf and plant scales (RMSE = 1.46 and 1.63 g kg^-1 and RPD = 5.09 and 4.44, respectively). Four out of the 33 indices contributed the most to the models (>75%). This study opens up encouraging perspectives for monitoring the cessation of oil activities in tropical regions. Further researches will focus on the application of our approach at larger scale, on airborne and satellite imagery.

Stomatal Response of Maize (Zea mays L.) to Crude Oil Contamination in Soils

In this study, maize plant was cultured in soil contaminated with different levels of crude oil. The purpose was to investigate the change of soil properties, leaf physiological and chemical parameters, and phenanthrene content in the leaf. Results showed that soil water content significantly increased when the levels of total petroleum hydrocarbons were 3700–17,800 mg/kg in soil, and soil electrical conductivity significantly increased compared with the control. In maize leaf, stomatal length and density, as well as K and Na contents decreased in contaminated treatments compared with the control. Stomatal length has a significant positive correlation with K content in leaf (r = 0.92, p < 0.01), while stomatal density was negatively correlated to the crude oil level in soil (r = −0.91, p < 0.05). Accumulation of phenanthrene in maize leaf was mainly through the foliar uptake pathway. Phenanthrene concentrations of maize leaf in oil-treated soil were less than that of the control, which exhibited a significant positive relationship with stomatal length (r = 0.98, p < 0.01). This study demonstrated that the stomata structure of maize could be influenced by crude oil and thus possibly controlling the accumulation of polycyclic aromatic hydrocarbons in aerial tissues. Based on these results, controlling stomata movement will be beneficial to phytoremediation of contaminated soil.

Application of PROSPECT for estimating total petroleum hydrocarbons in contaminated soils from leaf optical properties

Recent advances in hyperspectral spectroscopy suggest making use of leaf optical properties for monitoring soil contamination in oil production regions by detecting pigment alterations induced by Total Petroleum Hydrocarbons (TPH). However, this provides no quantitative information about the level of contamination. To achieve this, we propose an approach based on the inversion of the PROSPECT model. 1620 leaves from five species were collected on a site contaminated by 16 to 77 g.kg^-1 of TPH over a 14-month period. Their spectral signature was measured and used in PROSPECT model inversions to retrieve leaf biochemistry. The model performed well for simulating the spectral signatures (RMSE < 2%) and for estimating leaf pigment contents (RMSE ≤ 2.95 μg.cm^-2 for chlorophylls). Four out of the five species exhibited alterations in pigment contents when exposed to TPH. A strong correlation was established between leaf chlorophyll content and soil TPH concentrations (R² ≥ 0.74) for three of them, allowing accurate predictions of TPH (RMSE =3.20 g.kg^-1 and RPD = 5.17). The accuracy of predictions varied by season and improved after the growing period. This study demonstrates the capacity of PROSPECT to estimate oil contamination and opens up promising perspectives for larger-scale applications.

Differentiation between physical and chemical effects of oil presence in freshly spiked soil during rhizoremediation trial

Petroleum contamination and its remediation via plant-based solutions have got increasing attention by environmental scientists and engineers. In the current study, the physiological and growth responses of two diesel-tolerant plant species (tolerance limit: 1500-2000 mg/kg), Italian ryegrass (Lolium multiflorum) and Birdsfoot trefoil (Lotus corniculatus), have been investigated in vegetable oil- and diesel oil-amended soils. A long-term (147-day) greenhouse pot experiment was conducted to differentiate the main focus of the study: physical and chemical effects of oil (vegetable and diesel) in freshly spiked soils via evaluating the plant performance and hydrocarbon degradation. Moreover, plant performance was evaluated in terms of seed germination, plant shoot biomass, physiological parameters, and root biomass. Addition of both diesel oil and vegetable oil in freshly spiked soils showed deleterious effects on seedling emergence, root/shoot biomass, and chlorophyll content of grass and legume plants. Italian ryegrass showed more sensitivity in terms of germination rate to both vegetable and diesel oil as compared to non-contaminated soils while Birdsfoot trefoil reduced the germination rate only in diesel oil-impacted soils. The results of the current study suggest that both physical and chemical effects of oil pose negative effects of plant growth and root development. This observation may explain the phenomenon of reduced plant growth in aged/weathered contaminated soils during rhizoremediation experiments.

Assessing Soil Contamination Due to Oil and Gas Production Using Vegetation Hyperspectral Reflectance

The remote assessment of soil contamination remains difficult in vegetated areas. Recent advances in hyperspectral spectroscopy suggest making use of plant reflectance to monitor oil and gas leakage from industrial facilities. However, knowledge about plant response to oil contamination is still limited, so only very few imaging applications are possible at this stage. We therefore conducted a greenhouse experiment on three species long-term exposed to either oil-contaminated or water-deficient soils. Reflectance measurements were regularly performed at leaf and plant scale over 61 days of exposure. Results showed an increase of reflectance in the visible (VIS), the red-edge and the short-wave infrared (SWIR) under both oil and water-deficit stress exposure. A contrasted response in the near-infrared (NIR) was also observed among species. Spectra underwent transformations to discriminate species' responses to the different treatments using linear discriminant analysis (LDA) with a stepwise procedure. Original and transformed spectra enabled to discriminate the plants' responses to the different treatments without confusion after 61 days. The discriminating wavelengths were consistent with the spectral differences observed. These results suggest differential changes in plant pigments, structure and water content as a response to various stressors, and open up promising perspectives for airborne and satellite applications.

A comprehensive guide of remediation technologies for oil contaminated soil - Present works and future directions

Oil spills result in negative impacts on the environment, economy and society. Due to tidal and waves actions, the oil spillage affects the shorelines by adhering to the soil, making it difficult for immediate cleaning of the soil. As shoreline clean-up is the most costly component of a response operation, there is a need for effective oil remediation technologies. This paper provides a review on the remediation technologies for soil contaminated with various types of oil, including diesel, crude oil, petroleum, lubricating oil, bitumen and bunker oil. The methods discussed include solvent extraction, bioremediation, phytoremediation, chemical oxidation, electrokinetic remediation, thermal technologies, ultrasonication, flotation and integrated remediation technologies. Each of these technologies was discussed, and associated with their advantages, disadvantages, advancements and future work in detail. Nonetheless, it is important to note that no single remediation technology is considered the best solution for the remediation of oil contaminated soil.

CAPSULE

This review provides a comprehensive literature on the various remediation technologies studied in the removal of different oil types from soil.

The effect of U speciation in cultivation solution on the uptake of U by variant Sedum alfredii

In the present study, five plant species were screened for uranium uptake using a hydroponic experimental set-up. The effect of the U concentration, pH, as well as the presence of carbonates, phosphates, and organic acids (lactic acid, malic acid, citric acid) on the uptake of U by variant S. alfredii (V S. alfredii) and wild S. alfredii (W S. alfredii) were investigated. Results showed that V S. alfredii exhibited higher U content in the roots than the other four plants and with the increase of U concentration in the solution, the U uptake by V S. alfredii and W S. alfredii increased. The results also showed that different U speciation in different cultivation solution took an important role on the uptake of U in variant Sedum alfredii: at pH 6.5, U hydrolysis species (UO2)3(OH)5 (+)is predominant and the U concentrations in V S. alfredii roots reached a maximum value (3.7 × 10(4) mg/kg). U complexation with carbonates, phosphates, and some organic acids in the solution resulted in a decrease in the U content in the roots except for lactic acid. Our researches highlight the correlations between U speciation and the uptake on V S. Alfredii, which will be helpful for improved removal of U from the groundwater using phytoremediation method.

Responses of tall fescue (Festuca arundinacea) to growth in naphthalene-contaminated sand: xenobiotic stress versus water stress

The adaptations of tall fescue (Festuca arundinacea) arising from growth in naphthalene-contaminated sand (0.8 g kg(-1) sand dry weight (dw)) were investigated in the contexts of xenobiotic stress and water stress. The transfer of polycyclic aromatic hydrocarbons (PAHs) across the root endodermis was investigated using the hydrophobic Nile red stain as a PAH homologue. Nile red was applied to the epidermis of a living root to visualise uptake into the root through the transpiration stream, and the distance travelled by the stain into the root tissues was investigated using epi-fluorescence microscopy (Nikon Eclipse 90i). The results showed that the Nile red applied to the roots grown in naphthalene-contaminated sand was unable to penetrate the roots beyond the endodermis, whereas those grown in 'clean' sand showed evidence of uptake into the xylem vessels beyond the endodermis. Furthermore, partial collapse was observed in the cortex of naphthalene-treated roots, suggesting drought stress. Interestingly, the treated plants showed visual resilience to drought stress whilst the leaves of the control plants showed signs of wilting.