PAH Composition Research Articles

Torrefied and pyrolyzed pellets and their environmental impact in household heating

The transition from original feedstock to torrefied and pyrolyzed biofuels was investigated on a small-scale automatic pellet boiler. Thermal treatment significantly improves fuel quality; however, several technological difficulties were encountered. The entrainment of unburnt fuel particles led to severe CO, TOC and PM emissions as well as a drop in power output. All these issues were exacerbated when firing herbaceous biomass. It was found that most of the emitted particles are smaller than 1 μm in aerodynamic diameter, which necessitates additional flue gas filtering. Furthermore, 16 selected PAHs were individually monitored to evaluate the effect of thermal treatment on PAHs emissions and composition. On average, the most abundant PAH was naphthalene (4135 μg·kgfuel−1), followed by phenanthrene (246 μg·kgfuel−1), acenaphthylene (145 μg·kgfuel−1), fluoranthene (97 μg·kgfuel−1) and pyrene (95 μg·kgfuel−1). Benzo(a)pyrene contributed minimally to the total PAHs emissions (on average 16.6 μg·kgfuel−1). The 16 selected PAHs constitute only about 0.1–1.1 % of the total organic carbon emitted from solid biofuel combustion.

Study the Concentration of PAHS in Al-Rumayth River Water-Iraq

This study’s goals were to look into PAH concentrations and compositions as well as chemical and physical water characteristics. In Al –Rumaytha river. This study was conducted out during from November 2021 to October 2022. According to the results, sixteen PAHs compounds were found in the water, including According to the results, water contained sixteen different PAHs components including Acenaphthene and Acenaphthylene ranged between (47.1-91.5, 24.9-55.7) ppm, The values Anthracene, Naphthalene, phenanthene and fluorine results ranged (14.9-48.9 ppm,18.9 -68.7ppm,8.9-41.7 ppm,8.5-41 ppm) respectively, the minimum and maximum concentrations of Benzo[A]anthracen, Benzo[B]fluoranthene, Benzo [K] fluorantyene, Benz [G,H] perylen, Benz [A] Pryene, Chrysene, Dibenzo [A,H] Anthracene, Anthracene, Fluoranthene, Indeno and Pryene was 4.1-20.6 ppm, 20.1-69.7ppm, 30.1-97.4 ppm,4.1-36.9 ppm,0.29-1.6ppm 10.5-40.8 ppm, 8.9-36.9 ppm, 6.5-33.4 ppm,2.5-10.2 ppm,1.3-10.4 ppm. The results show that the Al-Rumaytha River is PAH-polluted, with human activities having the greatest negative effects on the river’s water quality and health.

Linking PAHs concentration, risk to PAHs source shift in soil and water in epikarst spring systems, Southwest China

A systematic assessment of the variations in the ecological risk of PAHs and the key emission sources controlling the variations is of great importance to human health and aquatic organisms. PAH concentrations, composition, source, and ecological risk in soils and water in two different periods (2010–2011 and 2019) of three typical epikarst springs in Southwest China were investigated. Results showed that PAH concentrations in soil and water have an overall downward trend (a reduction of 57 % and 93 %, respectively) in the past 10 years, which is consistent with the downward trend in the relative contribution rate of raw coal production (a 66 % reduction). In terms of composition, the proportion of low-ring PAHs decreased, medium-ring and high-ring PAHs increased in the soil profile. The proportion of low-ring PAHs did not change obviously, the proportion of medium-ring PAHs increased, and the proportion of high-ring PAHs decreased in epikarst springs. The source of PAHs changed remarkably over time, the relative contribution of coal combustion to PAHs decreased from 38 % to 20 %, and the vehicle contribution of PAHs increased from 31 % to 44 % in soils. The relative contribution rate of unburned oil and coke oven and biomass combustion change is less. Furthermore, the ecological risk of PAHs in the soils was reduced from moderate risk 2 to moderate risk 1, the risk in epikarst spring was reduced from high risk to moderate risk 2 after 10 years. This study demonstrates that substituting petroleum and coal with green energies can reduce PAH concentrations and risk.

Urbanization affects the composition, source, and risk of soil PAHs in lakeside residential area of the Yangtze River Delta, China

Urbanization affects the composition, source, and risk of soil PAHs in lakeside residential area of the Yangtze River Delta, China

FEATURES OF THE DISTRIBUTION AND COMPOSITION OF ORGANIC COMPOUNDS IN WATER AND BOTTOM SEDIMENTS CHERNAVKA RIVER FLOWING INTO ELTON LAKE

Organic compounds: Corg, lipids, hydrocarbons (HCs) – aliphatic (AHCs) and polycyclic aromatic (PAHs) in suspended particulate matter of surface waters and in bottom sediments of the shallow Chernavka River, which flows into a self-sustaining Elton Lake were studied. High concentrations of organic compounds were found in surface waters: in averaged 692, 80 and 0.79 µg/L for lipids, AHCs, and PAHs respectively. The composition of alkanes in the aqueous suspension corresponded to the weathered oil hydrocarbons. HC transformation occurs here not in the course of sedimentation, but at the water–bottom sediment interface. As a result, the AHC composition of the sediments differed from that of the particulate matter in the presence of planktonogenic low molecular weight homologues of n C15–C17 and a sharp increase in the series of odd high molecular weight alkanes, while the PAH composition differed in the increase in the proportion of naphthalene.

Hydrocarbons and suspended matter in the atmosphere-water boundary layer in the Barents and Kara Seas

The concentrations and composition of hydrocarbons - HCs (aliphatic - AHCs and polycyclic aromatic hydrocarbons - PAHs) in the Barents and Kara Seas (cruises 80, 83 and 89 of the R/V «Akademik Mstislav Keldysh», August 2020, June 2021, September 2022 respectively) are analyzed in the paper. The concentrations of the HC dissolved and suspended forms were measured in the surface microlayer (SML, 100–1000 μm thick), melting ice and surface waters. Higher concentration of HCs in SML was found in suspended particulate matter (SPM). AHC concentration in SPM in the Barents Sea were lower (31–96, on average 68 μg/L) than in the Kara Sea in June 2021 (187–1051, 573 μg/L on average), where the studies were carried out in the early summer season. The concentrations of AHCs in the SPM in the SML of the Kara Sea were 3.6 times higher than in the dissolved form (127–217, on average 187 μg/L), and they were almost 15 times higher than those in the surface waters. The accumulation of organic compounds also occurs in ice, but to a lesser extent than in the SML. The composition of alkanes in SML and melting ice mainly indicates the slight influence of autochthonous processes shaping HCs. The average content of PAHs in SPM was also 4.8 times higher than that in the dissolved form. According to the markers, the influence of combustion products of marine fuel was traced in the composition of PAHs. In September 2022, AHC and PAH concentrations in the Kara Sea were lower than in June 2021: on average, 159 μg/L and 492 ng/L accordingly, that is due to a decrease in the content of SPM from an average of 1.89 to 1.21 mg/L.

HYDROCARBONS IN THE SURFACE MICROLAYER AND ICE OF THE KARA SEA

Concentrations and composition of hydrocarbons – HCs (aliphatic – AHCs and polycyclic aromatic hydrocarbons – PAHs) in the Kara Sea (cruise 83 of the R/V Academic Mstislav Keldysh, June 2021) in the sea surface microlayer – SML (about 300 µm thick), ice and surface waters weree defined. The concentration of AHCs in SML occurs in suspended particulate matter (SPM), where their content varied in the range of 197–1051 µg/l, on average 621 and was almost 4 times higher than in the dissolved form: 89–270, on average 158 µg/l, and according to compared with the suspended form of surface waters – almost 22 times higher (on average 33 µg/l). The accumulation of organic compounds also occurs in ice, but to a lesser extent than in the SML. According to the composition of alkanes, the influence of autochthonous processes on the formation of AHCs in surface microlayer and melting ice is mostly insignificant, and this distinguishes their behavior from the ice that forms. The content of PAHs in surface microlayer in SPM was also 4.8 times higher on average than in the dissolved form. Despite the different sources of these hydrocarbon classes, for all samples taken, a dependence was observed in the distribution of AHCs and PAHs in SPM (r = 0.79, n = 52, at p 0.01). In the composition of PAHs, according to the markers, the influence of combustion products of marine fuel is traced, since, in addition to phenanthrene, fluoranthene and pyrene dominated in all samples.

Urban and suburban variations in emission sources and quality-adjusted life year loss of PM2.5-bound PAHs in Beijing, China

Urban and suburban variations in PM2.5-bound PAH compositions, sources and their potential health risk in terms of quality-adjusted life year (QALY) loss were explored, taking Haidian and Fangshan as urban and suburban representatives in Beijing. The annual mean total concentration of 16 priority PAHs in Fangshan (26.95 ng/m3) was higher than that in Haidian (12.59 ng/m3). The concentration of PAHs was much higher during the heating season, with four-ring PAHs as the dominant species. The PMF-PSCF-CPF integrated source apportionment method identified the same three sources in both areas; however, the mass contribution of traffic emissions in Haidian (64.2%) was larger than that in Fangshan (54.7%), while the source of coal and natural gas combustion and the source of biomass combustion, petroleum volatilization and coke oven contributed less (26.4% and 9.3%) than those in Fangshan (32.1% and 13.2%). Potential risk contribution of vehicle emissions (Haidian: 2943.39 QALYs, 91.36%; Fangshan: 6360.58 QALYs, 83.25%) was much greater than its mass contribution because its emission contained more PAH species with high toxicity, such as BaP. QALY loss covers the content of mental health, integrates noncarcinogenic and carcinogenic effects, and can more comprehensively reflect the health loss of affected people, thus being a suitable indicator for determining priority control sources.

An analysis of PAH soil contamination in south east England: A case study leading to an evidence-based portfolio and process route map

Through the regulatory planning process, UK local government has detailed information on contaminants for most of their development (predominantly brownfield) sites, dating back to 2000. The soil data collected includes information on polycyclic aromatic hydrocarbons, PAH, a group of potentially carcinogenic chemicals. This paper describes how an evidence-based portfolio of PAH contamination has been generated from this site measured dataset and developed into a process route map to facilitate PAH data analyses in other regions.The PAH data, site history and borehole information were extracted from 1990 to 2019 records of 120 brownfield sites in Elmbridge Borough, a suburban region southwest of London. The data were interrogated using spatial and depth analysis, diagnostic ratios and chemical composition analysis. Elevated PAH concentrations were predominantly found within Made Ground and indicated that the major source was anthropogenic deposition. The results from the diagnostic ratios indicated a pyrogenic, non-traffic related source for 90% of the samples. Statistical analysis showed low median concentration values with a few high outliers for all PAHs studied. Most soil samples had a similar PAH composition, irrespective of site history or soil sample description. This PAH composition was found on residential sites, where the likely source was coal-based burning. The data thus suggested a coal-based source for most of the PAH contamination in the study area.The results for PAH contamintation on brownfield sites in suburban Surrey were similar to a UK study for a UK coal-based industrial area. The PAH concentrations found were significantly higher than those reported in other international studies, however this was partly due to different sampling techniques. A process route map is proposed which incorporates both the analytical processes and the evidence-based portfolio of key findings. This route map is portable to different regions and consequently can be used as a platform for the analysis of PAH data to inform developers and regulators of potential sources and distribution in a region.

Ammonia in urban atmosphere can be substantially reduced by vehicle emission control: A case study in Shanghai, China

To investigate the impact of emission controls on ammonia (NH3) pollution in urban atmosphere, observation on NH3 (1 hr interval) was performed in Shanghai before, during and after the 2019 China International Import Expo (CIIE) event, along with measurements on inorganic ions, organic tracers and stable nitrogen isotope compositions of ammonium in PM2.5. NH3 during the CIIE period was 6.5±1.0 µg/m3, which is 41% and 32% lower than that before and after the event, respectively. Such a decrease was largely ascribed to the emission controls in nonagricultural sources, of which contribution for measured NH3 in control phase abated by ∼20% compared to that during uncontrol period. Molecular compositions of PAHs and hopanes further suggested a dominant role of the reduced vehicle emissions in the urban NH3 abatement during the CIIE period. Our results revealed that vehicle exhaust emission control is an effective way to mitigate NH3 pollution and improve air quality in Chinese urban areas.

The polycyclic aromatic hydrocarbons in the water of the Black Sea studied during the research cruise no. 114 aboard the r/v “Professor Vodyanitsky” in 2020

The content and composition of polycyclic aromatic hydrocarbons have been studied in the water column (surface layer, thermocline layer, at a depth of 500 m and the bottom layer) of the deep-water areas of the Black Sea near the Crimean Peninsula and the Caucasian coast, and the results are presented. The identified PAHs included naphthalene, 2-methylnaphthalene, phenanthrene, anthracene, fluoranthene, pyrene, triphenylene, chrysene, benz (b) fluoranthene, benz(k)fluoranthene, benz(a)pyrene, dibenz(a,h)anthracene, benzo(g,h,i)perylene. The concentrations of the total PAHs detected near the capes Sarych and Chauda were the highest, 532 and 593 ng/L, respectively. The distribution of PAHs over the horizons did not have a clear pattern. The composition of PAHs was dominated by 2-nuclear compounds, namely, naphthalene and 2-methylnaphthalene, their share on average accounted for 63 % of the total of the PAHs identified. The most dangerous nuclear PAHs containing 5 and 6 aromatic rings (benzo(b)fluoranthene, benz(k)fluoranthene, benzo(a)pyrene, dibenz(a,h)anthracene) accounted for less than 0.5 % in all the analyzed water samples. According to the calculated indices of technogenicity and pyrogenicity, PAHs of naphthydogenic origin predominated in almost all analyzed water samples. PAHs of technogenic oil origin prevailed in the water samples taken in the zone of shipping lanes to the port of Novorossiysk.

Characterization of PAHs contamination from unconventional bitumen derived synthetic crude oil in soil microcosms: composition, ecotoxicity and loss rate

The increasing exploitation of the unconventional bitumen-derived oils from Alberta (Canada) have raised new environmental concerns because they are inherently different than conventional oils. Previous studies mainly focused on diluted bitumen, but the Synthetic Crude Oil (SCO) which takes 35% of market share (of bitumen oils) has not been well studied. The main purpose of this study was to characterize PAHs in the SCO, since they are usually high-risk contaminants that often being prioritized in environmental monitoring practices. The obtained PAHs profile of SCO was also compared to that from a common benchmark oil, the Texas intermediate crude. PAH composition and eco-toxicity (based on Escherichia coli, Eisenia andrei and Lactuca sativa) were studied by spiking the oil in soil microcosms. Results showed a sharp difference in relative abundance of PAH between SCO spiked soil (SCO-soil) and Texas-soil. SCO-soil were characterized by a significantly higher fraction of heavy PAHs (with 3- to 6-rings), 85% versus 36% of relative abundance in Texas-soil. The two soils were also characterized by contrasted PAH-loss rates (82% for SCO-soil and 93% for Texas-soil) likely resulting from their contrasted composition. As for the eco-toxicity, SCO had generally lower toxicity of than Texas. This could attribute to the lower total PAHs concentration and the lower bioavailability of heavy PAHs more abundant in SCO than Texas. This study also suggests that evaluations of oil contamination in soil using selected regulated PAHs would be incomplete and biased for SCO that contains a large fraction of unregulated alkylated PAHs.

Changes in the content of polycyclic aromatic hydrocarbons in tundra peatlands with increasing natural temperatures

A model experiment was carried out to assess the temporal changes in the composition of poly cyclic aromatic hydrocarbons extracted from peat samples of the seasonally thawed layer of tundra peatland at the Barents Sea coast under the conditions of the temperature rising to 5 ± 1 °C. The data obtained indicate constant variation in the PAH composition throughout the experiment. Changes in the molar fraction of PAHs can be described by a sinusoidal curve with several maxima and minima. The molar fraction of naphthalene, which dominated in the composition of peat PAHs, changed similarly to the changes in the total content of polyarenes. The total proportion of heavy polyarenes increased regularly throughout the experiment. The presence of extema in the PAH content and recombination of their composition during the experiment is explained by the fact that in the absence of light hydrocarbons readily available for decomposition microorganisms began to decompose heavier structures, or, as their content decreases, more complex organic substances of peat.

Polycyclic aromatic hydrocarbons in permafrost peatlands

The concentrations of 15 individual PAHs in 93 peat cores have been determined by using high-performance liquid chromatography methods. In the profile the qualitative and quantitative composition of PAHs was non-uniform estimated in a wide range: from 112 to 3673 ng/g with mean 1214 ± 794 ng/g. Among 15 identified individual PAHs, the main contribution to their total amount was made by heavy highly condensed PAHs in the Eastern European peat plateaus, in particular, 6-nuclear benzo[ghi]perylene (1021 ± 707 ng/g), whereas in West Siberian permafrost peatlands, light PAHs were dominating, mostly naphthalene and phenanthrene (211 ± 87 and 64 ± 25 ng/g, respectively). The grass-equisetum peat contained the maximum of heavy PAHs and the dwarf shrub-grass—the minimum. In grass-dwarf shrub, grass-moss and moss peat, the share of 2-nuclear PAHs was most significant: naphthalene and fluorene, as well as 6-nuclear benzo[ghi]perylene. The presence of benzo[ghi]perylene in the entire peat strata, including its permafrost layer, was a marker of the anaerobic conditions that persisted throughout the Holocene and they were necessary for the synthesis of this compound.

The chemical composition and toxicological effects of fine particulate matter (PM2.5) emitted from different cooking styles

The mass, chemical composition and toxicological properties of fine particulates (PM2.5) emitted from cooking activities in three Hong Kong based restaurants and two simulated cooking experiments were characterized. Extracts from the PM2.5 samples elicited significant biological activities [cell viability, generation of reactive oxygen species (ROS), DNA damage and inflammation effect (TNF-α)] in a dose-dependent manner. The composition of PAHs, oxygenated PAHs (OPAHs) and azaarenes (AZAs) mixtures differed between samples. The concentration ranges of the Σ30PAHs, Σ17OPAHs and Σ4AZAs and Σ7Carbonyls in the samples were 9627–23,452 pg m−3, 503–3700 pg m−3, 33–263 pg m−3 and 158 – 5328 ng m−3, respectively. Cell viability caused by extracts from the samples was positively correlated to the concentration of benzo[a]anthracene, indeno[1,2,3-cd]pyrene and 1,4-naphthoquinone in the PM2.5 extracts. Cellular ROS production (upon exposure to extracts) was positively correlated with the concentrations of PM2.5, decaldehyde, acridine, Σ17OPAHs and 7 individual OPAHs. TNF-α showed significant positive correlations with the concentrations of most chemical species (elemental carbon, 16 individual PAHs including benzo[a]pyrene, Σ30PAHs, SO42−, Ca2+, Ca, Na, K, Ti, Cr, Mn, Fe, Cu and Zn). The concentrations of Al, Ti, Mn, Σ30PAHs and 8 individual PAHs including benzo[a]pyrene in the samples were positively correlated with DNA damage caused by extracts from the samples. This study demonstrates that inhalation of PM2.5 emitted from cooking could result in adverse human health effects.

Status, Sources and Potential Risk of Polycyclic Aromatic Hydrocarbons in Soils from Hexi Corridor in Northwest China.

The Hexi Corridor is the main commodity grain base in northwest China and plays a special role in ensuring food security in northwest China. However, the multiple pollution transport pathways of PAHs and complex and co-existing potential pollution sources around the study areas require a combination of pollution status, source identification, and risk assessment to explore pollution distribution and potential risks. In this study, the total PAHs concentration (∑18PAHs) in soils ranged from 69.6 to 1300ng/g. Spatially, the higher content of PAHs was detected in the Jinchang, followed by Jiayuguan, Jiuquan, Wuwei, and Zhangye, indicating a remarkable influence of different industrial activities. Although high-molecular-weight PAHs were predominated, the compositions of PAHs in most of the soil samples were varied. The isomer ratios of PAHs and principal component analysis were also revealed the PAHs probably originate from the sources different significantly. The total health risk values indicated a low health risk.

Remediation of Oily Waste using Soil Organic Nutrient Stimulant

Aims: This present study aim at assessing the efficacy of soil-organic nutrient stimulant in the remediation of oily waste.
 Study design: Preparation of Soil-goat dung mix was used as stimulant for the remediation of oily waste. 
 Place and duration of study: The study was carried out at the Department of Microbiology University of Uyo, Uyo, Akwa Ibom state, Nigeria in the dry season months of January - March
 Methodology: Remediation of oily waste using soil - organic (goat dung) nutrient stimulant was assessed for 12 weeks using standard culture-dependent microbiological, chemical and enzyme activity assay procedures.
 Results: The results indicate increased counts of hydrocarbon utilizing bacteria, fungi and actinomycetes with remediation time. Microorganisms belonging to the genera Bacillus, Pseudomonas, Acinetobacter, Alcaligenes, Serratia, Penicillium, Aspergillus, Cladosporium, Rhodococcus, Nocardia and Streptomyces were recovered from the remediated waste. The pH of the soil-goat dung treatment ranged from 6.5 ± 0.02 to 7.1 ± 0.05. Enzyme activity by dehydrogenase and urease were higher than phenol oxidase with time. PAHs were below detectable limits (< 0.01) and reduction in total petroleum hydrocarbon was 99.3% for the remediated waste.
 Conclusion: Overall, enhanced microbial activities correlated positively with reduction in Total Petroleum Hydrocarbon and PAH composition which resulted in ecofriendly waste product. Soil-goat dung stimulant can therefore serve as a cheap alternative in the management of oily waste.

Efficiencies of selected biotreatments for the remediation of PAH in diluted bitumen contaminated soil microcosms.

Unconventional oils such as diluted bitumen from oil sands differs from most of conventional oils in terms of physiochemical properties and PAHs composition. This raises concerns regarding the effectiveness of current remediation strategies and protocols originally developed for conventional oil. Here we evaluated the efficiency of different biotreatment approaches, such as fungi inoculation (bioaugmentation), sludge addition (bioaugmentation/biostimulation), perennial grasses plantation (phytoremediation) and their combinations as well as natural attenuation (as control condition), for the remediation of soil contaminated by synthetic crude oil (a product of diluted bitumen) in laboratory microcosms. We specifically monitored the PAHs loss percentage (alkylated PAHs and unsubstituted 16 EPA Priority PAHs), the residue of PAHs and evaluated the ecotoxicity of soil after treatment. All treatments were highly efficient with more than ~ 80% of ∑PAHs loss after 60days. Distinctive loss efficiencies between light PAHs (≤ 3 rings, ~ 96% average loss) and heavy PAHs (4-6 rings, ~ 29% average loss) were observed. The lowest average PAHs residue (0.10 ± 0.02mg·kg-1, for an initial concentration of 0.29 ± 0.12mg·kg-1) was achieved with the "sludge-plants (grasses)" combination. Sludge addition was the only treatment that achieved significantly lower ecotoxicity (3% ± 4% of growth inhibition of L. sativa) than the control (natural attenuation, 13% ± 4% of inhibition). Sludge addition, grasses plantation and "sludge-fungi combination" treatments could result in lower PAH exposure (than other treatments) in post-treated soil when using the Canadian Soil Quality Guidelines for the protection of environmental and human health for potentially carcinogenic and other PAHs.

Time-resolved study of mixing and reaction in an aero-engine model combustor at increased pressure

In this study, we experimentally investigate large-scale vortex structures, fuel-air mixing and reaction processes, which occur in a partially premixed swirl-stabilized ethylene/air flame in a laboratory-scale gas turbine model combustor. Time-resolved stereo-PIV, OH-PLIF, and acetone/PAH-PLIF systems with a repetition rate of 10 kHz are used to investigate the flame behavior at 3 bar pressure and an equivalence ratio of Φ=1.2. For isothermal conditions, the results strongly indicate that vortex-induced roll-up of fuel is a main driver of the mixing process. For the reacting case, a precessing vortex core (PVC) and a double helical vortex (DHV), both co-rotating with the swirl direction and occurring simultaneously in the inner and outer shear layer, respectively, are identified by using proper orthogonal decomposition (POD) and phase-averaging techniques. Acetone-PLIF measurements show that the fuel exhibits a motion that resembles a strong axial flapping at the frequency of the DHV at reacting conditions when considering the measurement plane. The measurements show that the PVC and DHV cause a regular sequence of flame roll-up, mixture of burned and unburned gases, and the subsequent ignition of this mixture. The pockets of rich burned gas formed by mixing and reaction can eventually be oxidized by OH-rich lean burned gas regions that have the potential to prevent soot formation; however, this process strongly depends on intermittent motion within the inner recirculation zone. Based on the additional visualization of PAH-PLIF distributions, the present study further reveals for the first time the complete sequence of formation of rich burned gas, PAH and soot in a GT combustor. It is shown that soot forms only in certain regions of the high-PAH rich burned gas pockets. This indicates that other factors, such as the detailed composition of PAHs or local temperatures, which cannot be resolved here, likely also play an important role in soot formation.

Bacterial community and PAH-degrading genes in paddy soil and rice grain from PAH-contaminated area

The significance of the bacterial communities and PAH-degrading genes (PDGs) in PAH-contaminated soil has received extensive attention, however, little attention was focused on those in plants grown on contaminated farmland soil. This study aimed to dissect the interactive relationships among PAHs, PDGs, and bacterial communities in the rhizosphere soil and rice grain. Although the concentrations and compositions of PAHs varied greatly, PAHs was the most critical factor in shifting of community in the soil and rice grain. Diversity of the potential PAH-degrading bacteria (PDB) in the rhizosphere soil was higher than that in the rice grain; however, the relative and absolute abundances of PDB in the rhizosphere soil were lower than those in the rice grain. Abundances of four PDGs in the soil were higher than those in the rice grain, and many species of bacteria, including Pseudomonas, Sphingomonas, and so on, which may harbor PDGs were detected. Bacteria in the soil had stronger relationships and were more centrally clustered within the network compared to bacteria in the rice grain. The keystone species (Actiobacteria, Betaproteobacteria, and Chloroflexi) in the soil were different from those (Pseudomonas, Sphingomonas, and Comamonadaceae) in the rice grain. Pseudomonas and Sphingomonas in the rice grain seemed to be the most important bacteria associated with PAH degradation. Overall, these findings provided novel insights into bacterial communities and PDGs in both the soil and plant from the PAH-contaminated paddy soil.