Petroleum Hydrocarbon Concentrations Research Articles

Shaping the concentration of petroleum hydrocarbon pollution in soil: A machine learning and resistivity-based prediction method

A new method relying on machine learning and resistivity to predict concentrations of petroleum hydrocarbon pollution in soil was proposed as a means of investigation and monitoring. Currently, determining pollutant concentrations in soil is primarily achieved through costly sampling and testing of numerous borehole samples, which carries the risk of further contamination by penetrating the aquifer. Additionally, conventional petroleum hydrocarbon geophysical surveys struggle to establish a correlation between survey results and pollutant concentration. To overcome these limitations, three machine learning models (KNN, RF, and XGBOOST) were combined with the geoelectrical method to predict petroleum hydrocarbon concentrations in the source area. The results demonstrate that the resistivity-based prediction method utilizing machine learning is effective, as validated by R-squared values of 0.91 and 0.94 for the test and validation sets, respectively, and a root mean squared error of 0.19. Furthermore, this study confirmed the feasibility of the approach using actual site data, along with a discussion of its advantages and limitations, establishing it as an inexpensive option to investigate and monitor changes in petroleum hydrocarbon concentration in soil.

Distribution and abundance of oil-degrading bacteria in seawater of the Yellow Sea and Bohai Sea, China

Petroleum hydrocarbons are widespread in seawater. As an important sea area in northern China, the content and distribution of petroleum hydrocarbons in seawater need our attention because of the high toxicity and lasting polluting effects on the ecological environment of the Yellow Sea and Bohai Sea. In addition, there are few reports comparing the diversity of oil-degrading bacteria before and after enrichment. Therefore, we collected surface seawater from 10 sites in the Yellow Sea and Bohai Sea in the autumn of 2020 to study the distribution characteristics of total petroleum hydrocarbons (TPH) and the diversity of oil-degrading bacteria. The concentration of TPH was 81.65 μg/L-139.55 μg/L at ten sites in the Bohai Sea and the Yellow Sea, which conformed to the China Grade II water quality standard (GB3097–1997). Moreover, the pristine/phytane (PR/PH) value of most sites was close to 1, indicating that the area was obviously polluted by exogenous petroleum hydrocarbons. We found that oil-degrading bacteria in the seawater of the Yellow Sea and the Bohai Sea had a good degradation effect on C11-C14 short chain alkanes (degradation rate of 59.19–73.22 %) and C1-C4 phenanthrene (degradation rate of 48.19–60.74 %). In terms of the diversity of oil-degrading bacteria, Gammaproteobacteria and Alphaproteobacteria dominated the enriched bacterial communities. Notably, the relative abundance of Alcanivorax changed significantly before and after enrichment. We proposed that surface seawater in the Bohai Sea and Yellow Sea could form oil-degrading bacteria mainly composed of Alcanivorax, which had great potential for oil pollution remediation.

Experimental Study and Parameter Optimization of Oily Sludge Treatment Through Ozonation Technology

AbstractOily sludge contains a large number of hydrocarbons, heavy metals, and other toxic and harmful substances, which not only pose a significant threat to human health but also severely impact the stability and sustainability of the ecological environment. Therefore, the development of a clean and efficient production process is urgently needed. The ozonation technology is a promising treatment method with high efficiency and no secondary pollution. In this study, ozonation technology was used to degrade the pollutants in the oily sludge, and the impact of different influencing factors on the treatment effect was discussed, and the operational parameters were optimized. Additionally, we investigated the mechanism of ozonation for oily sludge to provide a basis for a deeper understanding. The results demonstrated that after treatment, the total petroleum hydrocarbon content in the oily sludge was significantly reduced, and the residual oil rate decreased to 1.04 %, indicating the enormous potential of ozonation technology for oily sludge treatment.

Correction method of the fluorescence intensity of petroleum hydrocarbons in different soil types based on resonance scattering spectroscopy

Soil types has an obvious impact influence on the fluorescence intensity of soil petroleum hydrocarbons. To reduce the interference caused by soil types, this paper proposes a calibration method using resonance scattering spectroscopy. To establish the correction method, 100 g/kg crude oil samples from six soil types were prepared. The mission and resonance scattering spectrum under 280 nm excitation were measured for all samples. The results showed that the fluorescence spectra and resonance scattering spectra of soil crude oil vary with different soil types. And the fluorescence peak intensity and the resonance scattering peak intensity at 360 nm of soil petroleum hydrocarbons are highly correlated in different soil types. The fluorescence peak intensity at 360 nm was divided by the resonance scattering light intensity at 360 nm to obtain the corrected fluorescence intensity, which can effectively reduce the influence of soil type on fluorescence intensity. The feasibility of correction method was further verified for different types and concentrations of soil crude oil. The results showed better linearity between the fluorescence intensity and the concentration of Petroleum Hydrocarbons after the correction (with a correlation coefficient R2 of 0.96) than before the correction (with R2 of 0.72), the mean relative prediction error of all samples decreased from 31.92 % to 4.71 % after correction. The research can provide theoretical basis and technical support for the accurate and rapid detection of Petroleum Hydrocarbons in soil by fluorescence spectroscopy.

HYDROCARBON CONTAMINATION IMPACT ON SANDY SOILS WITHIN THE DZUNBAYAN OIL FIELD (EASTERN MONGOLIA)

The data are presented on the particle-size distribution, content of hydrocarbons, n-alkanes in their composition and the number of microorganisms in the soils of Dzunbayan oil production area (Mongolia, the Eastern Gobi desert steppe). The soils studied are characterized by the dominance of sand and fluid fraction (99.50–99.8%) with particles of 2–20 μm. The soils show alkaline reaction (pH 8.2–8.7), they are slightly saline in the control areas and highly saline (water extract salinity 0.13–2.34‰) near the production well. The content of petroleum hydrocarbons (HC) in soils of the study area varied from 9 to 60 mg/kg, with a maximum near the well. The study of the molecular composition of n-alkanes revealed the dominance of long-chain homologues (66.3–79.2% of the total n-alkanes), occurring at various stages of physicochemical and microbiological weathering. According to a number of features, the microbial community of soils is characterized by a high degree of adaptation to the conditions of the arid zone, salinity, and high pH values; at the same time, these conditions limit the development of typical representatives of soil microbiocenoses, i.e., actinomycetes and, to a greater extent, microscopic fungi. The total number of heterotrophic bacteria (HBGs) in the studied soil samples varied within 1.22–3.49 million CFU/g of soil. The proportion of oil-oxidizing bacteria (NOB) was 12.6–18.9% OBA, which corresponded to the high adaptive capacity of the community to hydrocarbons. Specific climatic conditions, features of soil composition, as well as oil with a predominance of heavy paraffin fractions of the Dzunbayan deposit, characterize the low potential ability of soils to self-purify under the oil pollution.

Comparative study of bioremediation of crude oil spillage using Cissus populnea stem and root as bio-sorbents

The total petroleum hydrocarbon concentration decrease at the initial and final bioremediation across different variable and the comparative effect of roots and stem of Cisuss populnea biosorbent were studied. 25 g of soil was weighed into different plate, contaminated with about 10 ml of crude oil, the plate was labeled as BI, CI DI, BF, CF and DF (stem), (root) across 3 g, 6 g, and 9 g variables and A (soil and crude oil mixture) as control for initial and final bioremediation. 1 g of each contaminated soil sample was extracted using mechanical shaker at room temperature and the extracts were analyzed using GC/MS the results showed that the initial treatment of stem biosorbent were 358.47455 ppm, 248.02045 ppm, 249.97273 ppm respectively and the final treatment after 4 weeks of biodegradation were 173.40636 ppm, 70.44364 ppm, 45.60818 ppm and control 757.39864 ppm. The total effect removal of Total petroleum hydrocarbon obtained were 51.6%, 75.2% and 81.8%, while the initial treatment of the root biosorbent were 366.72762 ppm, 347.75909 ppm, 337.04227ppm, after 4 weeks of biodegradation, the Total petroleum hydrocarbon concentration decreases to 143.6982 ppm, 60.05455 ppm, 52.21045 ppm and control 757.39864 ppm and the effect removal were 60.8%, 82.7% and 84.5%.

Response of the soil microbial community to petroleum hydrocarbon stress shows a threshold effect: research on aged realistic contaminated fields.

Microbes play key roles in maintaining soil ecological functions. Petroleum hydrocarbon contamination is expected to affect microbial ecological characteristics and the ecological services they provide. In this study, the multifunctionalities of contaminated and uncontaminated soils in an aged petroleum hydrocarbon-contaminated field and their correlation with soil microbial characteristics were analyzed to explore the effect of petroleum hydrocarbons on soil microbes. Soil physicochemical parameters were determined to calculate soil multifunctionalities. In addition, 16S high-throughput sequencing technology and bioinformation analysis were used to explore microbial characteristics. The results indicated that high concentrations of petroleum hydrocarbons (565-3,613 mg•kg-1, high contamination) reduced soil multifunctionality, while low concentrations of petroleum hydrocarbons (13-408 mg•kg-1, light contamination) might increase soil multifunctionality. In addition, light petroleum hydrocarbon contamination increased the richness and evenness of microbial community (p < 0.01), enhanced the microbial interactions and widened the niche breadth of keystone genus, while high petroleum hydrocarbon contamination reduced the richness of the microbial community (p < 0.05), simplified the microbial co-occurrence network, and increased the niche overlap of keystone genus. Our study demonstrates that light petroleum hydrocarbon contamination has a certain improvement effect on soil multifunctionalities and microbial characteristics. While high contamination shows an inhibitory effect on soil multifunctionalities and microbial characteristics, which has significance for the protection and management of petroleum hydrocarbon-contaminated soil.

Diversity and Biotic Index of Wild Pioneer Plants as Potential Bioindicators of Crude Oil-Contaminated Soil in Siak Regency, Riau Province, Indonesia

This study aims to determine the spatial variations in the diversity of wild pioneer plants along the gradation of crude oil-polluted soils and to analyze their biotic potential as a bioindicator of crude oil-contaminated soils in Siak Regency. Sampling was done in three oil wells using a purposive sampling method (center, edge, far from the well) measuring 1 x 1 m2. The soil at each contamination gradation was composited and analyzed for Total Petroleum Hydrocarbon (TPH) content. Vegetation data were analyzed using biotic indices such as density, Shannon-Wiener distribution index, species richness, rate of endemism, and importance value index. Potential bioindicator was analyzed by regression analysis, biplot, and IndVal. The results showed spatial variations in colonization, diversity, and structure of pioneer plants along the gradation of oil contamination. Species from the Cyperaceae, notably Scleria sumatrensis, Cyperus rotundus, and Fimbristylis ovata, were found in the center of the contamination area and resistant to oil contamination. The regression and biplot analysis revealed that along with the increasing soil TPH, the species richness and diversity index tended to decline, but the rate of endemism increased. IndVal analysis showed that C. rotundus and S. sumatrensis showed a potential bioindicators of oil-contaminated soils with TPH content of 2,700 to 3,300 ppm, while F. ovata, Panicum repens, and Imperata cylindrica was potential for TPH 692 to 851 ppm. Mimosa pudica was a sensitive plant and found on the soil TPH 73 ppm.

Diversity and Biotic Index of Wild Pioneer Plants as Potential Bioindicators of Crude Oil-Contaminated Soil in Siak Regency, Riau Province, Indonesia

This study aims to determine the spatial variations in the diversity of wild pioneer plants along the gradation of crude oil-polluted soils and to analyze their biotic potential as a bioindicator of crude oil-contaminated soils in Siak Regency. Sampling was done in three oil wells using a purposive sampling method (center, edge, far from the well) measuring 1 x 1 m2. The soil at each contamination gradation was composited and analyzed for Total Petroleum Hydrocarbon (TPH) content. Vegetation data were analyzed using biotic indices such as density, Shannon-Wiener distribution index, species richness, rate of endemism, and importance value index. Potential bioindicator was analyzed by regression analysis, biplot, and IndVal. The results showed spatial variations in colonization, diversity, and structure of pioneer plants along the gradation of oil contamination. Species from the Cyperaceae, notably Scleria sumatrensis, Cyperus rotundus, and Fimbristylis ovata, were found in the center of the contamination area and resistant to oil contamination. The regression and biplot analysis revealed that along with the increasing soil TPH, the species richness and diversity index tended to decline, but the rate of endemism increased. IndVal analysis showed that C. rotundus and S. sumatrensis showed a potential bioindicators of oil-contaminated soils with TPH content of 2,700 to 3,300 ppm, while F. ovata, Panicum repens, and Imperata cylindrica was potential for TPH 692 to 851 ppm. Mimosa pudica was a sensitive plant and found on the soil TPH 73 ppm.

Bioremediation of crude oil spillage using Cisuss populnea leave as bio-sorbent

The total petroleum hydrocarbon concentration decrease at the initial and final bioremediation across different variable of cisuss populnea leave biosorbent. 25 g of soil was weighed into different plate, contaminated with about 10 ml of crude oil, the plate was labeled as BI, CI DI, BF, CF and DF (leave) across 3 g, 6 g, and 9 g variables and A (soil and crude oil mixture) as control for initial and final bioremediation. 1 g of each contaminated soil sample was extracted using mechanical shaker at room temperature and the extracts were analyzed using GC/MS the results showed that the initial treatment of leave biosorbent were 706.4482 ppm, 544.2509 ppm, 347.75909 ppm respectively. After 4 weeks of biodegradation, the concentration decreases to 310.4318 ppm, 117.8105 ppm, 60.05455pmm and control 757.39864 ppm respectively. The Total removal efficiencies of Total petroleum hydrocarbon were 56.2%, 78.4%, and 82.7% for the treatments of 3 g, 6 g, and 9 g of leaves sorbent

Remediation of petroleum hydrocarbon-contaminated groundwater by biochar-based immobilized bacteria

It is essential to research the technology for effective remediation of petroleum hydrocarbon-contaminated groundwater because the petroleum hydrocarbon contamination of groundwater is becoming more and more serious. The petroleum hydrocarbon-degrading bacteria screened in this experiment were identified as Pseudomonas spp. by 16 S rDNA sequencing. Using wheat straw biochar as the carrier, a highly stable immobilized bacteria integrating adsorption and degradation was prepared by microbial immobilization technology. The results of scanning electron microscopy and Fourier transform infrared spectroscopy analysis showed that the microorganisms were adsorbed on the biochar. Degradation of petroleum hydrocarbon by immobilized bacteria conformed to the second-order kinetic model. For the manufacture of immobilized bacteria, the following immobilization parameters worked best: immobilization pH of 7 and immobilization time of 24 h. Finally, the produced immobilized bacteria were added to four groundwater samples with various initial concentrations of petroleum hydrocarbon, and it was found that all of the petroleum hydrocarbon degradations were above 95%. The study can serve as a useful resource for groundwater petroleum hydrocarbon remediation technology since the immobilized bacteria can successfully adapt to the groundwater petroleum hydrocarbon environment and significantly reduce the concentration of petroleum hydrocarbon.

Comparative Study of Heavy Metals and Total Petroleum Hydrocarbon Concentrations in Remediated and Non-Remediated Crude Oil Contaminated Soil

Abstract: The discharge of crude oil products to the environment (soil, water and air) has great negative impacts on the ecosystem. Most of these effects are from heavy metals, total petroleum hydrocarbons (TPH), polyaromatic hydrocarbons (PAH) among others. The aim of this research is to assess the effectiveness of the remediation on impacted soil through comparative analysis, and provide a recent data base on the pollution status of the soil. A stratified and random method of sample collection was adopted. From the three locations in Nkelleoken community, the result from the remediated soil showed that the greater amount of almost all the metals are bounded to F4 and F5 which are non-bioavailable to plants. Meanwhile the one from non- remediated soil is the opposite. The total petroleum hydrocarbon (TPH) results from the non-remediated soil samples were comparatively larger than that of the remediated soil (from 418.30±42.13 to 502.68 mg/kg). Whereas the TPH values from remediated site ranged from 193.65±37.20 to 207.0.4±70.14. Compared to the WHO standard (100-300 mg/kg) the TPH in the remediated soil were below the background limit. Microplasma Atomic Emission Spectroscopy and Total Petroleum Hydrocarbon Analyzer were used for the quantification of the inorganic and organic pollutants.

Hierarchical electronic nose detection and assessment technology for the reusage of land contaminated with petroleum hydrocarbons

Soil contamination with petroleum hydrocarbons is becoming increasingly serious. Efficient detection and assessment of contamination is conducive to rational land use and precise remediation. In this paper, a hierarchical framework for petroleum hydrocarbon pollution detection and soil assessment based on electronic nose is proposed. The proposed framework includes four independent and collaborative functional modules: petroleum hydrocarbon pollution detection module, pollution level identification module, petroleum hydrocarbon content analysis module and organic matter content analysis module. The experimental results show that the proposed framework can realize pollution detection, level recognition, petroleum hydrocarbon content analysis and organic matter analysis at the same time. The pollution recognition rate reached 98.99%, and the pollution level recognition rate reached 97.67%. The goodness of fit of quantitative analysis of petroleum hydrocarbon content and organic matter content were 0.97 and 0.87 respectively. The hierarchical petroleum hydrocarbon pollution detection and soil assessment framework proposed in this paper can comprehensively reflect the soil information status and provide accurate decision support for land use decision and soil remediation.

COMPOSITION OF BACTERIAL COMMUNITIES IN OIL-CONTAMINATED BOTTOM SEDIMENTS OF THE KAMENKA RIVER

The Kamenka River ows through the territory of the Kokuyskoye gas and oil eld located in the Perm Territory. Despite the absence of oil-producing facilities in the immediate vicinity of the river, oil hydrocarbons were found in the waters and bottom sediments at a concentration of 2445-25800 mg/kg. The composition of microbial communities of bottom sediments of the Kamenka River, located at the source and along the river, was studied. Using the methods of high-performance sequencing and bioinformatic data processing, it was established that the main share of microbial communities is represented by bacteria of the phylum Proteobacteria (16.7-30.3%), as well as the phyla Actinobacteriota, Bacteroidota, Bdellovibrionota, Campilobacterota, Chloro exi, Cyanobacteria, Deferribacterota, Desulfobacterota, Firmicutes, Gemmatimonadota, Methylomirabilota, Myxococcota, Nitrospirota, Patescibacteria, Planctomycetota, Spirochaetota, Synergistota, Thermotofota and Verrucomicrobiota. The values of the Shannon index for the studied communities are directly correlated with the concentration of petroleum hydrocarbons in bottom sediments. The phylum Proteobacteria in communities is represented by the classes Alphaproteobacteria and Gammaproteobacteria, among which representatives of the families Rhodobacteriaceae and Comamonadaceae dominate. When identifying to the genus, it was found that in the Comamonadaceae family, the main share is made up of bacteria of the genus Hydrogenophaga. It should be noted that bacteria of the genus Pseudomonas (class Gammaproteobacteria) were found only in the microbiocenosis of bottom sediments, characterized by the highest concentration of petroleum hydrocarbons.

Hyperspectral Characteristic Band Selection and Estimation Content of Soil Petroleum Hydrocarbon Based on GARF-PLSR.

With continuous improvements in oil production, the environmental problems caused by oil exploitation are becoming increasingly serious. Rapid and accurate estimation of soil petroleum hydrocarbon content is of great significance to the investigation and restoration of environments in oil-producing areas. In this study, the content of petroleum hydrocarbon and the hyperspectral data of soil samples collected from an oil-producing area were measured. For the hyperspectral data, spectral transforms, including continuum removal (CR), first- and second-order differential (CR-FD, CR-SD), and Napierian logarithm (CR-LN), were applied to eliminate background noise. At present, there are some shortcomings in the method of feature band selection, such as large quantity, time of calculation, and unclear importance of each feature band obtained. Meanwhile, redundant bands easily exist in the feature set, which seriously affects the accuracy of the inversion algorithm. In order to solve the above problems, a new method (GARF) for hyperspectral characteristic band selection was proposed. It combined the advantage that the grouping search algorithm can effectively reduce the calculation time with the advantage that the point-by-point search algorithm can determine the importance of each band, which provided a clearer direction for further spectroscopic research. The 17 selected bands were used as the input data of partial least squares regression (PLSR) and K-nearest neighbor (KNN) algorithms to estimate soil petroleum hydrocarbon content, and the leave-one-out method was used for cross-validation. The root mean squared error (RMSE) and coefficient of determination (R2) of the estimation result were 3.52 and 0.90, which implemented a high accuracy with only 8.37% of the entire bands. The results showed that compared with the traditional characteristic band selection methods, GARF can effectively reduce the redundant bands and screen out the optimal characteristic bands in the hyperspectral data of soil petroleum hydrocarbon with the method of importance assessment, which retained the physical meaning. It provided a new idea for the research of other substances in soil.

Rapid Determination of the Total Petroleum Hydrocarbon Content of Soils by Handheld Fourier Transform Near-Infrared Spectroscopy.

For successful soil remediation and hydrocarbon exploration operations, determining the total petroleum hydrocarbon (TPH) content of soils is an indispensable process step. This paper reports on the performance of a handheld Fourier transform near-infrared (FT-NIR) spectrometer for rapid and quantitative determination of TPH content of soils from two different sites by diffuse reflection measurements. For rapid decisions for exploration work or environmental site assessment projects, a quick─preferably on-site─determination of TPH content is valuable. Diffuse reflection NIR spectra were recorded from soil samples of two different sites with TPH reference values ranging from 350 to 30,000 ppm, as determined by capillary gas chromatography and flame ionization detection with hydrocarbon fingerprinting C1-C44. However, this paper not only addresses the development of site-specific partial-least squares (PLS) calibrations but also demonstrates the locally-weighted PLS (LW-PLS) technique, which can be used to develop global, site-independent PLS calibrations without significant penalty in calibration performance. As a first step, the diffuse reflection spectra were used to develop conservative, site-specific PLS calibration models with root-mean-square calibration/cross-validation errors (RMSEC/RMSECV) of 1043/1106 and 741/785 ppm TPH, respectively, and the average absolute prediction errors for samples not contained in the calibration set were 451 and 293 ppm for the two sites, respectively. In a further step, significant degradation of the RMSE values of a conservative PLS model based on the NIR spectra of both sites was then compared to the application of the LW-PLS method, with only a slight loss of the prediction accuracy relative to the site-independent models. This study confirms the ability of next-generation portable FT-NIR spectrometers to predict low TPH levels in various soil types through both─soil-specific and site-independent─calibrations, giving these spectrometers the potential to become rapid screening tools in the field.

МНОГОЛЕТНЯЯ ДИНАМИКА СОДЕРЖАНИЯ НЕФТЯНЫХ УГЛЕВОДОРОДОВ В ВОДАХ КОЛЬСКОГО ЗАЛИВА БАРЕНЦЕВА МОРЯ

Long-term dynamics of petroleum hydrocarbons content in the seawater of the Kola Bay (the Barents Sea) and in the area of the water station in the commercial port of Murmansk is analyzed. The study is based on the data from the state observation system for the period of 2011-2021. A variation range of petroleum hydrocarbons concentrations in the seawater is estimated; the average, minimum, and maximum values are analyzed and compared. Maps of concentrations and variability of hydrocarbons in the southern, northern, and central bends of the Kola Bay until 2014 inclusive are constructed. A necessity of resuming studies of the petroleum hydrocarbons content across the Kola Bay is substantiated.

Microbe-Assisted Rhizoremediation of Hydrocarbons and Growth Promotion of Chickpea Plants in Petroleum Hydrocarbons-Contaminated Soil

The present work aimed to develop and investigate microbial consortia for petroleum hydrocarbons (PHCs) detoxification and plant growth improvement in hydrocarbons-contaminated soil. Here, we isolated several bacteria from PHCs-contaminated soils to make bacterial consortia and two of the best consortia were tested in a pot experiment to evaluate their potential for PHCs removal and chickpea growth promotion in PHCs-contaminated soil. Results demonstrated that the PHCs exerted considerable phytotoxic effects on chickpea growth and physiology by causing a 13–29% and a 12–43% reduction in agronomic and physiological traits, respectively. However, in the presence of bacterial consortia, the phytotoxicity of PHCs to chickpea plants was minimized, resulting in a 7.0–24% and a 6.0–35% increase in agronomic and physiological traits, respectively over un-inoculated controls. Bacterial consortia also boosted nutrient uptake and the antioxidant mechanism of the chickpea. In addition, chickpea plants alone phytoremediated 52% of initial PHCs concentration. The addition of bacterial consortia in the presence of chickpea plants could remove 74–80% of the initial PHCs concentration in soil. Based on our research findings, we suggest that the use of multi-trait bacterial consortia could be a sustainable and environmentally friendly strategy for PHCs remediation and plant growth promotion in hydrocarbons in contaminated soil.

Effects of Dispersant on the Petroleum Hydrocarbon Biodegradation and Microbial Communities in Seawater from the Baltic Sea and Norwegian Sea.

Dispersants have been used in several oil spill accidents, but little information is available on their effectiveness in Baltic Sea conditions with low salinity and cold seawater. This study investigated the effects of dispersant use on petroleum hydrocarbon biodegradation rates and bacterial community structures. Microcosm experiments were conducted at 5 °C for 12 days with North Sea crude oil and dispersant Finasol 51 with open sea Gulf of Bothnia and coastal Gulf of Finland and Norwegian Sea seawater. Petroleum hydrocarbon concentrations were analysed with GC-FID. Bacterial community structures were studied using 16S rDNA gene amplicon sequencing, and the abundance of genes involved in hydrocarbon degradation with quantitative PCR. The highest oil degradation gene abundances and oil removal were observed in microcosms with coastal seawater from the Gulf of Bothnia and Gulf of Finland, respectively, and the lowest in the seawater from the Norwegian Sea. Dispersant usage caused apparent effects on bacterial communities in all treatments; however, the dispersant's effect on the biodegradation rate was unclear due to uncertainties with chemical analysis and variation in oil concentrations used in the experiments.

Legacy Effects of Phytoremediation on Plant-Associated Prokaryotic Communities in Remediated Subarctic Soil Historically Contaminated with Petroleum Hydrocarbons.

Phytoremediation of petroleum hydrocarbons in subarctic regions relies on the successful establishment of plants that stimulate petroleum-degrading microorganisms, which can be challenging due to the extreme climate, limited nutrients, and difficulties in maintaining sites in remote locations. A long-term phytoremediation experiment was initiated in Alaska in 1995 with the introduction of grasses and/or fertilizer to petroleum hydrocarbon (PHC)-contaminated soils that were subsequently left unmanaged. In 2011, the PHC concentrations were below detection limits in all soils tested and the originally planted grasses had been replaced by volunteer plant species that had colonized the site. Here, we sought to understand how the original treatments influenced the structure of prokaryotic communities associated with plant species that colonized the soils and to assess the interactions between the rhizospheric and endophytic communities of the colonizing vegetation 20 years after the experiment was established. Metataxonomic analysis performed using 16S rRNA gene sequencing revealed that the original type of contaminated soil and phytoremediation strategy influenced the structure of both rhizospheric and endophytic communities of colonizing plants, even 20 years after the treatments were applied and following the disappearance of the originally planted grasses. Our findings demonstrate that the choice of initial phytoremediation strategy drove the succession of microorganisms associated with the colonizing vegetation. The outcome of this study provides new insight into the establishment of plant-associated microbial communities during secondary succession of subarctic areas previously contaminated by PHCs and indicates that the strategies for restoring these ecosystems influence the plant-associated microbiota in the long term. IMPORTANCE Subarctic ecosystems provide key services to local communities, yet they are threatened by pollution caused by spills and disposal of petroleum waste. Finding solutions for the remediation and restoration of subarctic soils is valuable for reasons related to human and ecosystem health, as well as environmental justice. This study provides novel insight into the long-term succession of soil and plant-associated microbiota in subarctic soils that had been historically contaminated with different sources of PHCs and subjected to distinct phytoremediation strategies. We provide evidence that even after the successful removal of PHCs and the occurrence of secondary succession, the fingerprint of the original source of contamination and the initial choice of remediation strategy can be detected as a microbial legacy in the rhizosphere, roots, and shoots of volunteer vegetation even 2 decades after the contamination had occurred. Such information needs to be borne in mind when designing and applying restoration approaches for PHC-contaminated soils in subarctic ecosystems.