Contamination, Sources, and Health Risks Associated with Soil PAHs in Rebuilt Land from a Coking Plant, Beijing, China

Increasing contamination of polycyclic aromatic hydrocarbons in Chinese soils

China is facing a serious threat PAHs contaminated soil. To better understand the current state of soil PAH pollution in China and contribute to the development of feasible prevention and control measures and policies in the future. This study examines the spatiotemporal distributions of soil Polycyclic Aromatic Hydrocarbons (PAHs) pollution in China since 2000, and investigates the key factors influencing changes in levels of soil PAHs. The results of the survey on soil PAHs concentration levels in 716 areas were analyzed by visualization of ArcGIS pro data, correlation analysis and linear regression analysis, it was found that the increase in soil PAH pollution in China is concerning. The analysis indicates significant regional disparities, with pollution levels in the north being higher than in the south. Over the 20-year period, the median level of PAHs in soil increased by 476.8 μg/kg. Construction land areas that heavily rely on fossil fuels and industrial activities exhibit significantly higher concentrations of polycyclic aromatic hydrocarbons (PAHs) compared to other land use types. The study identifies key socio-economic factors linked to rising PAH levels, including energy consumption (notably coal and oil), industrial and domestic waste production. Coal consumption is highlighted as the leading factor in PAH concentration changes in 18 provinces, followed by industrial waste in 6 provinces. Future projections up to 2030 suggest continued influence of these factors on soil PAH levels. The research emphasizes the urgent necessity for comprehensive soil management policies to address the growing PAH pollution, offering insights into its dynamics and contributing factors in China.

Spatial distribution, environmental behavior, and health risk assessment of PAHs in soils at prototype coking plants in Shanxi, China: Stable carbon isotope and molecular composition analyses

To investigate the environmental behavior of and carcinogenic risk posed by 16 priority-controlled polycyclic aromatic hydrocarbons (PAHs), soil samples and air samples from the coke oven top were collected in two prototype coking plants (named PF and JD). The PF soils contained more PAHs than the JD soils because the PF plant employed the side-charging technique and had a lower coke oven height. The soils from both plants contained enough PAHs to pose a carcinogenic risk, and this risk was higher in the PF plant. Data were collected on the source characteristic spectrum of stable carbon isotopic composition (δ13C) of PAHs emitted from the coke oven top (δ13C values of -36.02‰ to -32.05‰ for gaseous PAHs and -34.09‰ to -25.28‰ for particulate PAHs), and these data fill a research gap and may be referenced for isotopic-technology-based source apportionment. Diagnostic ratios and isotopic technology revealed that the coking plant soils were mainly influenced by the coking process, followed by vehicle exhaust; the soils near the boundary of each plant were slightly affected by C3 plant burning. For most PAHs [excluding fluoranthene, benzo(k)fluoranthene, indeno(1,2,3-c,d)pyrene, and dibenzo(a,h)anthracene], the dominant migration process was the net volatilization of PAHs from soil to air. In the PF plant, 13C was depleted in gaseous PAHs during volatilization.

The occurrence characteristics, removal efficiency, and risk assessment of polycyclic aromatic hydrocarbons in sewage sludges from across China

Sewage sludge is considered to be an important sink for polycyclic aromatic hydrocarbons (PAHs) in wastewater treatment plants and the potential risks from sludge contaminated with PAHs during land application has attracted attention. To identify the priority PAHs for control and enhance their removal from sludge, the occurrence characteristics, removal efficiency, and risk assessment of PAHs in sewage sludges from across China were analyzed. Data collection was from 2001 to 2023. Results showed that 16 PAHs were widely detected in Chinese sewage sludge with total amounts (∑16PAHs) between 0.06 and 34.93 mg kg dw-1. Fossil fuel, coal, and biomass combustion are main anthropogenic sources of PAHs in China. In general, phenanthrene (PHE), anthracene (ANT), fluorescein (FL), chrysene (CHR), pyrene (PYR), and benzo[b]fluoranthene (BbF) are regarded as the main components and PAHs with 3-5 rings dominate (84.01%-91.53%) sewage sludge in China. Although aerobic composting and anaerobic treatment significantly improve ∑16PAHs removal, sludge stabilization treatment only reduced the risk by a small amount, especially for high-molecular-weight (HMW) PAHs. The benzo[a]anthracene (BaA), benzo[a]pyrene (BaP), and dibenzo[a,h]anthracene (DahA) are proposed as the priority control contaminants for sewage sludge in China because they have consistently high-risk quotient (RQ) values of 2.42-7.47, 1.28-3.16, 1.06-1.83 before and after sludge stabilization, respectively. More attention should be paid to BaA, BbF, benzo[k]fluoranthene (BkF), BaP, DahA, and indeno[1,2,3-cd]pyrene (IcdP) in Beijing; ANT, BaA, and BaP in Shanghai; and BaA and BaP in Guanghzou. Although the toxic equivalent quotient (TEQ) for PAHs met the limit concentration requirements of the national standard, the potential health risks due to long-term exposure to HMW PAHs cannot be ignored because the incremental lifetime cancer risk (ILCR) was consistently in the risk threshold range (>1 × 10-6). Some suggestions on enhanced treatment approaches and land use standards are proposed to further alleviate the risk from HMW PAHs.

Spatial distribution and risk assessment of polycyclic aromatic hydrocarbons in soils from contaminated sites in Eastern China

A total of 16 polycyclic aromatic hydrocarbons (PAHs) were measured in 28 soil column samples from two contaminated industrial sites in Eastern China. The total concentration of 16 PAHs (∑PAHs) in the surface soil (0-20 cm) was measured up to 52,600 ng/g (dry weight basis) with a remarkable spatial difference in the studied contaminated sites. The concentrations of the ∑PAHs in soils decreased with the increase in soil depth (0-10 m). The surface and subsurface soil presented a tenfold higher concentration than the soil with depth greater than 4 m. Additionally, the vertical migration tendency of the PAHs was found to be correlated significantly with their hydrophobicity (R2 = 0.79, P < 0.01). Naphthalene (with lowest octanol-water partition coefficient among the studied PAHs) showed the greatest average soil depth at which its peak concentration occurred. Furthermore, risk quotient analysis by using benzo[a]pyrene as reference compound showed that 71.4% of the samples exhibited high ecological risk for soil. Moreover, the total carcinogenic risk of the PAHs in the surface soil samples was assessed at 5.61 × 10-5-1.28 × 10-4 and 4.41 × 10-6-9.43 × 10-5 for male and female workers, respectively, in which 67.9%-71.4% of the samples showed potential risk. Generally, these results suggest a further consideration of ecological and health risks associated with PAHs in contaminated sites in Eastern China.

The past 40 years' assessment of urban-rural differences in Benzo[a]pyrene contamination and human health risk in coastal China

China has implemented many environmental regulations to battle against polycyclic aromatic hydrocarbon (PAH) contamination since the 1990s. It remains unclear how the exposure levels of PAHs changed quantitatively since reform and opening up in 1978 in China, whether the human health risks decreased or not, and how about the discrepancy between urban and rural areas. Here, taking Benzo[a]pyrene (BaP) in the rapidly urbanized Bohai region of China as a case, we used the improved Berkeley-Trent-Urban-Rural model to simulate the multimedia concentrations of BaP from 1980 to 2020 based on BaP emissions at a regional scale. The total emission of BaP in 1990 was the highest, with a value of 240 t, while the urban emission peaked in 2010. The BaP emissions from rural areas were two to seven times higher than urban areas, and the differences became smaller over time. Despite this, the average modeled BaP concentrations in urban air and soil were two to tens fold higher than in rural areas, particularly in highly urbanized or industrialized cities. Mostly, the concentrations of BaP in rural areas peaked in 1990, while those in urban areas peaked in 1990 or 2010. Early urbanized Beijing and Tianjin were the hot-spot cities of BaP contamination before 2000, while after 2010, higher concentrations were found in late industrialized Shandong and Hebei. BaP posed potential cancer risks to local residents, and air inhalation accounted for more than 80 % of the total risk. Under the stronger implementation of environmental regulations since the 1990s, it showed great health benefits, particularly for the urban residents in Beijing and Tianjin. The biggest decline in cancer risk was found in the period 2010-2020, and the average decreasing rates were 61.4 % and 57.4 % for urban and rural areas, respectively.

Application of magnetic-nanoparticle functionalized whole-cell biosensor array for bioavailability and ecotoxicity estimation at urban contaminated sites

The bioavailability and ecotoxicity of pollutants are important for urban ecological systems and human health, particularly at contaminated urban sites. Therefore, whole-cell bioreporters are used in many studies to assess the risks of priority chemicals; however, their application is restricted by low throughput for specific compounds and complicated operations for field tests. In this study, an assembly technology for manufacturing Acinetobacter-based biosensor arrays using magnetic nanoparticle functionalization was developed to solve this problem. The bioreporter cells maintained high viability, sensitivity, and specificity in sensing 28 priority chemicals, seven heavy metals, and seven inorganic compounds in a high-throughput manner, and their performance remained acceptable for at least 20 d. We also tested the performance by assessing 22 real environmental soil samples from urban areas in China, and our results showed positive correlations between the biosensor estimation and chemical analysis. Our findings prove the feasibility of the magnetic nanoparticle-functionalized biosensor array to recognize the types and toxicities of multiple contaminants for online environmental monitoring at contaminated sites.

Non-target and target analysis to identify and characterize thiophenes in soil from an abandoned coking plant

There is concern about the large amounts of aromatic compounds emitted during coking. Previous studies of coking emissions have been focused on polycyclic aromatic hydrocarbons, dioxin-like compounds, phenols, and volatile organic compounds, but previously unidentified compounds produced during coking may also harm human health. Here, the main pollutants in 69 soil samples from an abandoned coking plant were identified by non-target screening using two-dimensional gas chromatography time-of-flight mass spectrometry. Polycyclic aromatic hydrocarbons, long-chain alkanes, and thiophenes were dominant. High concentrations of thiophenes (benzothiophenes, dibenzothiophenes, and benzonaphtholthiophenes) were found. Quantitative analysis of 12 thiophenes (selected because of their concentrations and detection frequencies) was performed, and the concentrations were 0.03-647 μg/g dry weight, which were extremely high compared with concentrations in soil from uncontaminated sites and other industrial sites. Dibenzothiophene and benzo[b]naphtho[2,1-d]thiophene were dominant, accounting for 69% of the total thiophene concentration. Thiophene profiles in very contaminated areas were different from the profile in coal but similar to the profile in tar. Thiophenes in soil at the coking plant may have been supplied in tar leaks, wastewater, coke oven gases, and exhaust gases. A toxicity assessment indicated a strong likelihood of oxidative stress being induced by exposure to multiple thiophenes at the coking plant. The results suggest that thiophene emissions from coking plants should attract more attention than currently.

Ecotoxicological evaluation of oxidative stress-mediated neurotoxic effects, genetic toxicity, behavioral disorders, and the corresponding mechanisms induced by fluorene-contaminated soil targeted to earthworm (Eisenia fetida) brain

Fluorene is a commonly identified PAH pollutant in soil and exhibits various worrisome hazardous effects to soil organisms. Currently, the toxicity profiles of fluorene on earthworm brain are rare, and the mechanisms and their corresponding pathways involved in fluorene-triggered neurotoxicity, genotoxicity, and behavior changes have not been reported hitherto. Herein, earthworm (Eisenia fetida) brain was chosen as targeted receptor to explore the neurotoxic effects, genetic toxicity, behavioral disorders, and related mechanisms caused by fluorene-induced oxidative stress pathways. The results showed excess fluorene initiated the release of excessive quantities of ROS in earthworm brain, which have caused oxidative stress and accompanied by serious oxidative effects, including LPO (lipid peroxidation) and DNA injury. To minimize the damage effects, the antioxidant defense mechanisms (antioxidant enzymes and non-enzymatic antioxidants) were activated, and entailed a decrease of the antioxidant capacity in E. fetida brain, which, in turn, causes further ROS-induced ROS release. Exposure of fluorene induced the abnormal mRNA expression of genes relevant to oxidative stress (e.g., GST, SOD, CAT, GPx, MT, and Hsp70) and neurotoxicity (e.g., H02, C04, D06, and E08) in E. fetida brain. Specifically, fluorene can bind directly to AChE, destroying the conformation of this protein, and even affecting its physiological functions. This occurrence caused the inhibition of AChE activity and excess ACh accumulation at the nicotinic post-synaptic membrane, finally triggering neurotoxicity by activation of pathways related to oxidative stress. Moreover, the avoidance responses and burrowing behavior were obviously disturbed by oxidative stress-induced neurotoxicity after exposure to fluorene. The results form IBR suggested more severe poisoning effects to E. fetida brain initiated by high-dose and long-term exposure of fluorene. Among, oxidative stress injury and genotoxic potential are more sensitive endpoint than others. Collectively, fluorene stress can provoke potential neurotoxicity, genotoxicity, and behavioral disturbances targeted to E. fetida brain through the ROS-mediated pathways involving oxidative stress. These findings are of great significance to estimate the detrimental effects of fluorene and the corresponding mechanisms on soil eco-safety.

Characteristics and Risk Assessment of PAH Pollution in Soil of a Retired Coking Wastewater Treatment Plant in Taiyuan, Northern China

We analyzed the soil at the site of a former coking wastewater treatment plant on redeveloped land in Taiyuan, northern China, in an attempt to detect the presence of 16 types of priority polycyclic aromatic hydrocarbons (PAHs) listed by the United States Environmental Protection Agency (US EPA) and evaluate the potential pollution risks. The results show that the total proportion of PAHs in the surface soil of the redeveloped land ranged from 0.3 to 1092.57 mg/kg, with an average value of 218.5 mg/kg, mainly consisting of high-ring (5-6 rings) components. Characteristic ratio analysis indicated that the pollution was mainly related to the combustion of petroleum, coal, and biomasses. The wastewater treatment units operated according to the following treatment train: advection oil separation tank, dissolved air flotation tank, aerobic tank, secondary sedimentation tank, and sludge concentration tank. Our study found that pollution resulting from low-ring PAHs mainly appeared in the advection oil separation tank during the pre-wastewater treatment stage, while medium-ring PAH contamination mainly occurred in the dissolved air floatation tank, aerobic tank, and secondary sedimentation tank during the middle stages of wastewater treatment. High-ring PAH contamination primarily appeared in the sludge concentration tank in the latter stage of wastewater treatment. Based on our assessment of the ecological risk using the Nemerow Comprehensive Pollution Index and the toxicity equivalent factor (TEF) method, we determined that individual PAHs in the study area exceeded acceptable levels and the total amount of pollution was potentially harmful to the ecological environment. In addition, the comprehensive lifetime cancer risk for different populations resulting from exposure to the soil in the study area was determined to be within acceptable limits based on the average PAH concentrations.

Application of a hybrid GEM-CMB model for source apportionment of PAHs in soil of complex industrial zone

Accurate source apportionment is essential for preventing the contamination of pervasive industrial zones. However, a limitation of traditional receptor models is their negligence of transmission loss, which consequently reduces their accuracy. Herein, chemical mass balance (CMB) and generic environmental model (GEM) was fused into a new method, which was employed to determine the traceability of polycyclic aromatic hydrocarbons (PAHs) in a complex zone containing three coking plants, two steel plants, and one energy plant. Five categories of fingerprints comprising various compounds were established for the six plant sources where seven PAHs with low-high rings were screened as the best. Considering volatilization, dry deposition, and advective and dispersive transport, the GEM model generated 232 "compartments" in multimedia to capture subtle variations of PAHs during transmission. More than 90 % of the transmission of the seven PAHs varied between 0.4 % and 6.0 %. Over pure CMB model, acceptable results and best-fit results improved by 1.6-44.4 % and 0.3-80.8 % in the GEM-CMB model. Additionally, the coking, steel, and energy industries accounted for 36.4-56.1 %, 25.6-41.7 %, and 18.3-23.6 % of PAHs sources at four receptor points, respectively. Furthermore, quantifying contaminant loss rendered the traceability results more realistic, judged by distances and discharge capacities. Accordingly, these outcomes can help in precisely determining soil contamination.

Spatial distribution, source identification, and human health risk assessment of PAHs and their derivatives in soils nearby the coke plants

The coking industry can generate large amounts of polycyclic aromatic hydrocarbons (PAHs) and their derivatives, which may negatively impact the environment and human health. In this study, soils nearby a typical coking plant were sampled to assess the impact of coke production on the surrounding residential areas and human health. The mean concentration of PAHs and their derivatives in residential area soils nearby the coke plant was 4270 ng/g dw, which was 1 order of magnitude higher than that observed in areas far from the coke plant and approximately 4 times lower than that revealed the coke plant. In addition, the results showed that coking processing area was the most contaminant area of the coke plant (mean: 74.4 μg/g dw), where was also the main source of pollutants in residential areas. In terms of vertical soils in coking plant, the maximum levels of chemicals (mean: 205 μg/g dw) were presented at the leakage of underground pipelines, where were much higher than those in surface soils, and decreased with the increase of depth. The analysis of variance (ANOVA) results showed obvious differences in the concentrations of 6-nitrochrysene between the plant, residential areas and control areas. Meanwhile, 6-nitrochrysene had potential cancer risk (CR) for human in the coking site. Thus, 6-nitrochrysene was the most noteworthy PAH derivatives. Furthermore, the CR (mean: 5.94 × 10^-5) and toxic equivalent quantities (TEQs) (mean: 14.8 μg·TEQ/g) of PAHs and their derivatives was assessed in this study. This finding suggested that PAHs and their derivatives especially those extremely toxic chemicals (Nitro-PAHs (NPAHs) and Br/Cl-PAHs (XPAHs)) might pose a potential health risk to residents nearby the coke plant. The current study provides further insights into the pollution characteristics of PAHs and their derivatives in coke plants and potential risks to the workers and surrounding residents.

Correlation of soil microbiome with crude oil contamination drives detection of hydrocarbon degrading genes which are independent to quantity and type of contaminants

The impacts of crude oil contamination on soil microbial populations were explored in seven different polluted areas near oil and gas drilling sites and refineries of Assam, India. Using high-throughput sequencing techniques, the functional genes and metabolic pathways involved in the bioconversion of crude oil contaminants by the indigenous microbial community were explored. Total petroleum hydrocarbon (TPH) concentrations in soil samples ranged from 1109.47 to 75,725.33 mg/kg, while total polyaromatic hydrocarbon (PAH) concentrations ranged from 0.780 to 560.05 mg/kg. Pyrene, benzo[a]anthracene, naphthalene, phenanthrene, and anthracene had greater quantities than the maximum permitted limits, suggesting a greater ecological risk, in comparison to other polyaromatic hydrocarbons. According to the metagenomic data analysis, the bacterial phyla Proteobacteria, Actinobacteria, Acidobacteria, and Bacteroides were the most prevalent among all polluted areas. The most prominent hydrocarbon degraders in the contaminated sites included Burkholderia, Mycobacterium, Polaromonas, and Pseudomonas. However, the kinds of pollutants and their concentrations did not correlate with the abundances of respective degrading genes for all polluted locations, as some of the sites with little to low PAH contamination had significant abundances of corresponding functional genes for degradation. Thus, the findings of this study imply that the microbiome of hydrocarbon-contaminated areas, which are biologically involved in the degradation process, has various genes, operons and catabolic pathways that are independent of the presence of a specific kind of contaminant.

Effect of Normalization Methods on Accuracy of Estimating Low- and High-Molecular Weight PAHs Distribution in the Soils of a Coking Plant

Mapping spatial distribution of soil contaminants at contaminated sites is the basis of risk assessment. Hotspots can cause strongly skewed distribution of the raw contaminant concentrations in soil, and consequently can require suitable normalization prior to interpolation. In this study, three normalization methods including normal score, Johnson, and Box-Cox transformation were performed on the concentrations of two low-molecular weight (LMW) PAHs (i.e., acenaphthene (Ace) and naphthalene (Nap)) and two high-molecular weight (HMW) PAHs (i.e., benzo(a)pyrene (BaP) and benzo(b)fluoranthene (BbF)) in soils of a typical coking plant in North China. The estimating accuracy of soil LMW and HMW PAHs distribution using ordinary kriging with different normalization methods was compared. The results showed that all transformed data passed the Kolmogorov-Smirnov test, indicating that all three data transformation methods achieved normality of raw data. Compared to Box-Cox-ordinary kriging, normal score-, and Johnson-ordinary kriging had higher estimating accuracy of the four soil PAHs distribution. In cross-validation, smaller root-mean-square error (RMSE) and mean error (ME) values were observed for normal score-ordinary kriging for both LMW and HMW PAHs compared to Johnson- and Box-Cox-ordinary kriging. Thus, normal score transformation is suitable for alleviating the impact of hotspots on estimating accuracy of the four selected soil PAHs distribution at this coking plant. The findings can provide insights into reducing uncertainty in spatial interpolation at PAHs-contaminated sites.

Seasonal variation and source apportionment of inorganic and organic components in PM2.5: influence of organic markers application on PMF source apportionment

PM_2.5 samples collected over a 1-year period in a Chinese megacity were analyzed for organic carbon (OC), elemental carbon (EC), water-soluble ions, elements, and organic markers such as polycyclic aromatic hydrocarbons (PAHs), hopanes, steranes, and n-alkanes. To study the applicability of organic markers in source apportionment, the relationship between organic and inorganic components was analyzed, and four scenarios were implemented by incorporating different combinations of organic and inorganic tracers. The consistent temporal variations trend of 4-ring PAHs and SO₄^2- prove that coal burning directly emits a portion of sulfate. The concentrations of ∑5-7-ring PAHs, NO₃^-, and NO₂ show a trend of simultaneous increase and decrease, implying collective impacts from the vehicle source. The concentrations of OC and EC positively correlate with the 5-7-ring PAHs and Cu and Zn, which proves that part of Cu and Zn comes from vehicle emissions. Five factors were identified by incorporating only conventional components, including secondary source (SS, 30%), fugitive dust (FD, 14%), construction dust (CD, 4%), traffic source (TS, 19%), and coal combustion (CC, 14%). Six factors were identified by incorporating conventional components and PAHs, including SS (28%), FD (15%), CD (4%), CC (13%), gasoline vehicles (GV, 12%), and diesel vehicles (DV, 10%). Eight factors were identified by incorporating conventional components, PAHs, hopanes, and n-alkanes, including SS (26%), FD (17%), CD (3%), GV (14%), DV (8%), immature coal combustion (ICC, 5%), mature coal combustion (MCC, 10%), and biogenic source (BS, 1%).

Spatial Distribution, Potential Sources, and Health Risk of Polycyclic Aromatic Hydrocarbons (PAHs) in the Surface Soils under Different Land-Use Covers of Shanxi Province, North China

Polycyclic aromatic hydrocarbons (PAHs) are widespread in the environment and pose a serious threat to the soil ecosystem. In order to better understand the health risks for residents exposed to PAH-contaminated soil, 173 surface soil samples were collected in Shanxi Province, China, to detect the levels of 16 priority PAHs. The spatial distribution patterns of PAHs were explored using interpolation and spatial clustering analysis, and the probable sources of soil PAHs were identified for different land-use covers. The results indicate that the soil Σ16 PAH concentration ranged from 22.12 to 1337.82 ng g^-1, with a mean of 224.21 ng g^-1. The soils were weakly to moderately contaminated by high molecular weight PAHs (3-5 ring) and the Taiyuan-Linfen Basin was the most polluted areas. In addition, the concentration of soil PAHs on construction land was higher than that on other land-use covers. Key sources of soil PAHs were related to industrial activities dominated by coal burning, coking, and heavy traffic. Based on the exposure risk assessment of PAHs, more than 10% of the area was revealed to be likely to suffer from high carcinogenic risks for children. The study maps the high-risk distribution of soil PAHs in Shanxi Province and provides PAH pollution reduction strategies for policy makers to prevent adverse health risks to residents.

Source identification and toxicity apportionment of polycyclic aromatic hydrocarbons in surface soils in Beijing and Tianjin using a PMF-TEQ method

Beijing and Tianjin are two of the largest cities in northern China with high population densities and highly developed manufacturing industries. In the past decade, some authors have reported their PAH concentrations in surface soils, identified their sources and quantitatively reported their health risks. However, the contributions of different PAH sources to their toxicity have not been reported thus far. In this study, we reviewed the PAH concentrations, contributions of different sources to the toxicity, and cancer risks in soils from different land use types found within Beijing and Tianjin from data gathered by 41 studies. The total PAH concentration varied in the range of 175.7–1989.0 ng g-1 with a higher median PAH concentration detected in urban soils (789.7 ng g-1), followed by suburban soils (647.3 ng g-1) and rural soils (390.8 ng g-1). Source identification using diagnostic ratios and principal component analysis (PCA) suggested that the PAHs in all three land use types mainly originated from biomass and coal combustion, vehicular emissions, and petrogenic processes with contributions varying from 13% to 62%. Furthermore, results from a positive matrix factorization (PMF) model suggested that vehicular emissions and coal combustion in urban soils, and the vehicular emissions, coal combustion and biomass combustion in suburban and rural soils dominated the total PAH concentrations (>85%). These results were consistent with those of the PCA model. Results of the additional toxicity apportionment performed using the PMF model suggested that vehicular emissions and coal combustion contributed the most to the toxic equivalent quantity for Benzo(a)Pyrene (BaPTEQ) and, by extension, to the carcinogenic potencies. The incremental lifetime cancer risk (ILCR) values suggested a low risk level for adults exposed to PAHs in the different land use types found within Beijing and Tianjin.

Pilot-scale bioaugmentation of polycyclic aromatic hydrocarbon (PAH)-contaminated soil using an indigenous bacterial consortium in soil-slurry bioreactors

Soil-slurry bioreactor based bioremediation of polycyclic aromatic hydrocarbons (PAHs) contaminated soil was studied through laboratory and pilot-scale trials, in which the degradation mechanism was explored. Indigenous PAH-degrading consortium was firstly screened out and it degraded 80.5% of total PAHs in lab-scale bioreactors. Then a pilot-scale trial lasting 410 days was conducted in two bioreactors of 1.5 m³ to examine the operating parameters and validate the optimum running conditions. During the initial 200 days, the crucial running parameters affecting PAH removal were evaluated and selected. Subsequently, an average PAH removal rate of 93.4% was achieved during 15 consecutive batches (210 days) under the optimum running conditions. The kinetic analysis showed that the reactor under optimum conditions achieved the highest PAH degradation rate of 0.1795 day^-1 and the shortest half-life of 3.86 days. Notably, efficient mass transfer of PAHs and high biodegradation capability by bioaugmented consortia in soil-slurry bioreactors were two key mechanisms for appreciable PAH removal performance. Under the optimal operating conditions, the degradation rate of low-molecular-weight (LMW) PAHs was significantly higher than high-molecular-weight (HMW) PAHs; when the mass transfer was limited, there was no significant difference between their degradation behaviors. Both microbial co-metabolism and collaborative metabolism might occur when all PAHs demonstrated low degradation rates. The findings provide insightful guidance on the future assessment and remediation practices of PAH-contaminated sites.

Mycolicibacterium sp. strain PAM1, an alfalfa rhizosphere dweller, catabolizes PAHs and promotes partner-plant growth

This research was focused on the isolation and characterization of a PAH-catabolizing mycobacterial strain from the petroleum hydrocarbon-contaminated rhizosphere of alfalfa, as well as on revealing some points of interaction between the microorganism and the plant. Mycolicibacterium sp. PAM1, a pyrene degrader isolated from the niche of interest to us, can catabolize fluoranthene, anthracene, fluorene, and phenanthrene. On the basis of curves of PAM1 growth with different PAHs as the sole carbon sources and on the basis of PAH-degradation rates, we found that pollutant availability to the strain decreased in the sequence phenanthrene > fluorene > fluoranthene ∼ pyrene > anthracene. For each PAH, the catabolic products were identified. PAM1 was found to have the functional genes nidA and nidB. New data modeling the 2D and 3D structures, intrinsic structural disorder, and molecular dynamics of the nidA and nidB gene products were obtained. The identified genes and intermediates of pyrene degradation indicate that PAM1 has a PAH catabolic pathway that is peculiar to known mycobacterial pyrene degraders. PAM1 utilized some components of alfalfa root exudates as nutrients and promoted plant growth. The use of mycobacterial partners of alfalfa is attractive for enhancing the phytoremediation of PAH-contaminated soils.

A review on analysis methods, source identification, and cancer risk evaluation of atmospheric polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) have gained attention because of their environmental persistence and effects on ecosystems, animals, and human health. They are mutagenic, carcinogenic, and teratogenic. The review provides background knowledge about their sources, metabolism, temporal variations, and size distribution in atmospheric particulate matter. The review article briefly discusses the analytical methods suitable for the extraction, characterization, and quantification of nonpolar and polar PAHs, addressing the challenges. Herein, we discussed the molecular diagnostic ratios (DRs), stable carbon isotopic analysis (SCIA), and receptor models, with much emphasis on the positive matrix factorization (PMF) model, for apportioning PAH sources. Among which, DRs and PCA identified as the most widely employed method, but their accuracy for PAH source identification has received global criticism. Therefore, the review recommends compound-specific isotopic analysis (CSIA) and PMF as the best alternative methods to provide detailed qualitative and quantitative source analysis. The compound-specific isotopic signatures are not affected by environmental degradation and are considered promising for apportioning PAH sources. However, isotopic fractions of co-eluted compounds like polar PAHs and aliphatic hydrocarbons make the PAHs isotopic fractions interpretation difficult. The interference of unresolved complex mixtures is a limitation to the application of CSIA for PAH source apportionment. Hence, for CSIA to further support PAH source apportionment, fast and cost-effective purification techniques with no isotopic fractionation effects are highly desirable. The present review explains the concept of stable carbon isotopic analysis (SCIA) relevant to PAH source analysis, identifying the techniques suitable for sample extract purification. We demonstrate how the source apportioned PAHs can be applied in assessing the health risk of PAHs using the incremental lifetime cancer risk (ILCR) model, and in doing so, we identify the key factors that could undermine the accuracy of the ILCR and research gaps that need further investigation.

Source apportionment and risk assessment for polycyclic aromatic hydrocarbons in soils at a typical coking plant

Polycyclic aromatic hydrocarbons (PAHs) are widely present in the environment. The coking industry is an important industrial source of PAHs. Coke production in China accounts for 67.44% of total global coke production. Tangshan, a coastal city on the Bohai Rim, contains the largest cluster of coking plants in China. Extremely high PAH emissions in Tangshan may cause long-distance cross-border pollution problems. In this study, the concentrations and sources of 16 priority PAHs in soil at a coking plant in Tangshan were determined and the risks posed by the PAHs were assessed. The PAH concentrations were generally higher in surface soil than subsurface soil, particularly near the coke oven, crude benzol, and coal blending areas. The dibenz[a,h]anthracene (DBA) concentrations were higher than the risk screening value (1500 ngg^-1) but lower than the control value (15,000 ngg^-1) for type II land defined in Chinese standard (GB36600-2018). The main sources of PAHs were coal combustion, the coke oven, and traffic. The PAH concentrations were higher in the ammonium sulfate, boiler room, coal blending, and coke oven areas than in the other areas. Toxic equivalent concentrations were calculated to assess the toxic and carcinogenic risks posed by PAHs. The toxic equivalent concentrations were relatively high in the boiler, crude benzol, and coal blending areas, where the toxic equivalent concentrations for the sums of seven highly carcinogenic PAHs contributed 95% of the toxic equivalent concentrations for the sums of the 16 PAHs that were analyzed. The carcinogenic risks posed to humans were therefore assessed using the concentrations of the seven highly carcinogenic PAHs. Dermal contact was found to be an important exposure pathway leading to carcinogenic risks. The carcinogenic risk posed by DBA was > 1 × 10^-6 but < 5 × 10^-6, indicating that DBA concentrations at the study site monitored closely.

Human Health Assessment of Sixteen Priority Polycyclic Aromatic Hydrocarbons in Contaminated Soils of Northwestern Algeria

BACKGROUND

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental organic contaminants generated by incomplete combustion of organic materials that are widely distributed in soils.

OBJECTIVES

This study represents the first attempt to examine the health toxicity of 16 detected PAHs in contaminated soil, via different exposure pathways to populations in northwestern Algeria.

METHODS

The toxicity equivalency quotients (TEQ) of PAHs were evaluated. The carcinogenic risk assessment of incremental lifetime cancer risk (ILCR) from ingestion, inhalation, and dermal exposure pathways to each PAH in soil are described.

RESULTS

Incremental lifetime cancer risk values were in the upper limit of the tolerable range (10^-6-10^-4) for adults and children. The total cancer risk of PAH-contaminated soils for children, adolescents and adults was 2.48×10^-5, 2.04×10^-5 and 3.12×10^-5mg.kg^-1d^-1, respectively. The highest potential cancer risks were identified for adults and children, with adolescents having the lowest risks. Across exposure pathways, the dermal contact and ingestion pathways had the greatest contributions to the carcinogenic risk of human exposure to PAHs.

CONCLUSIONS

Further research and guidelines are needed for risk assessments of PAHs in agricultural, residential/urban, and industrial areas, and further risk assessments should include risks posed by exposure through air.

COMPETING INTERESTS

The authors declare no competing financial interests.

Rhizosphere assisted bioengineering approaches for the mitigation of petroleum hydrocarbons contamination in soil

The high demand for petroleum oil has led to hydrocarbon contamination in soil, including agricultural lands, and many other ecosystems across the globe. Physical and chemical treatments are effective strategies for the removal of high contamination levels and are useful for small areas, although with concerns of cost-effectiveness. Alternatively, several bacteria belonging to the Phylum: Proteobacteria, Bacteroidetes, Actinobacteria, Nocardioides, or Firmicutes are used for biodegradation of different hydrocarbons - aliphatic, polyaromatic hydrocarbons (PAH), and asphaltenes in the oil-contaminated soil. The rhizoremediation strategy with plant-microbe interactions has prospects to achieve the desired result in the field conditions. However, adequate biostimulation, and bioaugmentation with the suitable plant-microbe combination, and efficiency under a toxic environment needs to be evaluated. Modifying the microbiomes to achieve better biodegradation of contaminants is an upcoming strategy popularly known as microbiome engineering. In this review, rhizoremediation for the successful removal of the hydrocarbons have been critically discussed, with challenges for making it a feasible technology.HIGHLIGHTSPetroleum hydrocarbon contamination has increased around the globe.Rhizoremediation has the potential for the mitigation of pollutants from the contaminated sites.An accurate and detailed analysis of the physio-chemical and climatic conditions of the contaminated sites must be focused on.The suitable plant and bacteria, with other major considerations, may be employed for in-situ remediation.The appropriate data should be obtained using the omics approach to help toward the success of the rhizoremediation strategy.

The occurrence and distribution of polycyclic aromatic hydrocarbons, bisphenol A and organophosphate flame retardants in indoor dust and soils from public open spaces: Implications for human exposure

Global concern exists regarding human exposure to organic pollutants derived from public open spaces and indoor dust. This study has evaluated the occurrence of 18 polycyclic aromatic hydrocarbons (PAHs), 11 organophosphorus flame retardants (OPFRs) and bisphenol A (BPA). To achieve this, a new simple, efficient and fast multi-residue analytical method based on a fully automated pressurised liquid extraction (PLE) and subsequent quantification by gas chromatography coupled to electron ionization-mass spectrometry (GC-EI-MS) in selected ion monitoring (SIM) mode was developed. The developed method was applied to indoor dust (12 sampling households) and soil derived from two public open spaces (POSs). Among all compounds studied, PAHs were the most ubiquitous contaminants detected in POS soils and indoor dust although some OPFRs and BPA were detected in lower concentrations. An assessment of the incremental lifetime cancer risk (ILCR) was done and indicated a high potential cancer risk from the POS sites and some of the indoor dust sampled sites. However, key variables, such as the actual exposure duration, frequency of contact and indoor cleaning protocols will significantly reduce the potential risk. Finally, the ingestion of soils and indoor dust contaminated with OPFRs and BPA was investigated and noted in almost all cases to be below the USEPA reference doses.

Microbial diversity and co-occurrence patterns in deep soils contaminated by polycyclic aromatic hydrocarbons (PAHs)

Numerous studies have enriched our knowledge of the microbial community composition and metabolic versatility of contaminated soil. However, there remains a substantial gap regarding the bioassembly patterns of the indigenous microbial community distribution in contaminated deep soils. Herein, the indigenous microbial community structure diversity, function, and co-occurrence relationships in aged PAH-contaminated deep soil collected from an abandoned chemical facility were investigated using high-throughput sequencing. The results showed that the dominant phyla in all samples were responsible for PAH degradation and included Proteobacteria (20.86%-81.37%), Chloroflexi (2.03%-28.44%), Firmicutes (3.06%-31.16%), Actinobacteria (2.92%-11.91%), Acidobacteria (0.41%-12.68%), and Nitrospirae (0.81%-9.21%). Eighty biomarkers were obtained by linear discriminant analysis of effect size (LEfSe), and most of these biomarkers were PAH degraders. Functional predictions using Tax4Fun indicated that the aged contaminated soil has the potential for PAH degradation. Statistical analysis showed that in contrast with the PAH concentration, edaphic properties (nutrients and pH) were significantly correlated (r > 0.25, P < 0.01) with the bacterial community and functional composition. Co-occurrence network analysis (modularity index of 0.781) revealed non-random assembly patterns of the bacterial communities in the PAH-contaminated soils. The modules in the network were mainly involved in carbon and nitrogen cycles, organic substance degradation, and biological electron transfer processes. Microbes from the same module had strong ecological linkages. Additionally, SAR202 clade, Thermoanaerobaculum, Nitrospira, and Xanthomonadales, which were identified as keystone species, played an irreplaceable role in the network. Overall, our results suggested that environmental factors such as nutrients and pH, together with ecological function, are the main factors driving the assembly of microbial communities in aged PAH-contaminated deep soils.

Mapping the Finer-Scale Carcinogenic Risk of Polycyclic Aromatic Hydrocarbons (PAHs) in Urban Soil-A Case Study of Shenzhen City, China

The high-precision mapping of urban health risk is a difficult problem due to the high heterogeneity of the urban environment. In this paper, the spatial distribution characteristics of the Polycyclic Aromatic Hydrocarbon (PAH) content in the urban soil of Shenzhen City were analyzed through a field investigation. We propose an approach for improving the accuracy and spatial resolution of PAH carcinogenic risk assessment by integrating the pollutant distribution and Location Based Service (LBS) data. The results showed that the concentration of PAHs in the high-density urban area was 271.67 ng g⁻¹, which was 27.2% higher than that in the green area. Although the average carcinogenic risk of PAHs in the surface soil of Shenzhen city was less than 10⁻⁶, the maximum carcinogenic risk at some sample sites exceeded 10⁻⁶, which indicates a potential health risk. The LBS data were effective for high-precision mapping of the population distribution. According to the combination relationship between the risk threshold of pollutants and the population density, four types of risk zones were proposed. Among them, 6.9% of the areas had a high-risk and high population density and 15.8% of the areas were high-risk with a low population density. These two kinds of zones were the critical areas for controlling risk. The fine-scale risk mapping approach for determining the carcinogenic risk of soil PAHs integrating pollutant distribution and location based service data was demonstrated to be a useful tool for explicit spatial risk management. This tool could provide spatial insights and decision support for urban health-risk management and pollution prevention.

Desorption process and morphological analysis of real polycyclic aromatic hydrocarbons contaminated soil by the heterogemini surfactant and its mixed systems

Surfactant-enhanced remediation (SER) is an efficient and low-cost technology for polycyclic aromatic hydrocarbons (PAHs) contaminated sites. This study assessed the desorption processes and effects of Heterogemini surfactant (Dodecyldimethylammonium bromide/tetradecyldimethylammonium bromide, DBTB), two traditional surfactants (Hexadecyl trimethyl ammonium bromide, CTAB; Sorbitan monolaurate, Span 20) and their mixed systems on the real PAHs-contaminated soil from an abandoned coking plant, as well they were analyzed micro morphologically. DBTB had greater desorption capability for PAHs and favorable interaction with the traditional surfactants confirmed by reaction parameters β^m and Gibbs. Whether for total PAHs (TPAHs) or different molecular weight PAHs, the mixed system Span 20/DBTB had larger molar solubilization ratio (MSR) and partition coefficient (K_m) than CTAB/DBTB, the highest desorption rate for TPAHs reaching 68.83%. Additionally, microscopic morphology showed micelles of Span 20/DBTB were more dispersed and formed strings easily, explaining its good desorption capability. What resulted demonstrated the feasibility of DBTB, a novel Heterogemini surfactant, and its mixed systems remediating PAHs-contaminated soil of abandoned industrial site.

Post relocation of industrial sites for decades: Ascertain sources and human risk assessment of soil polycyclic aromatic hydrocarbons

As a persistent organic pollutant, polycyclic aromatic hydrocarbons (PAHs) may still residually pollute industrial sites after relocation. This study investigated the contamination status of PAHs in the topsoils of three industrial legacy sites (the Shougang industrial ruins, the original Beijing coking plant area, and an abandoned gas station) that relocated more than 10 years ago from downtown Beijing. The sources of PAHs in the soil were qualitatively and quantitatively analyzed, and health risks were evaluated for different groups of people. The total concentration of 16 PAHs in the study area ranged from 371.1 ng g^-1 to 4073.9 ng g^-1. The pollution levels of the three study areas were abandoned gas station > Beijing coking plant > Shougang ruins. In terms of composition, low-ring aromatics accounted for the majority of the detected PAHs, and in the dry season, low-ring aromatics accounted for a higher proportion in the three areas than in the wet season. The comparison of the PAH diagnostic ratio and PMF model verification showed that the sources of PAHs in the Shougang ruins and the Beijing coking plant area were mainly those of biomass and coal combustion, accounting for 66.3% and 56.1% of the total detected PAHs, respectively; the PAH sources of the abandoned gas station storage tank area were largely that of petrol (33.9%) and diesel combustion (23.8%). Since these industrial sites were located in urban centers, this study also conducted a health risk assessment of the topsoil. The total carcinogenic risk range of the three contaminated sites was 1.41E-06 to 2.47E-05. Abandoned industrial sites have potential carcinogenic risks to human health. The government needs to conduct comprehensive risk assessments and remedial measures on soils of industrial legacy sites to achieve land reuse.

Distribution, Origins and Hazardous Effects of Polycyclic Aromatic Hydrocarbons in Topsoil Surrounding Oil Fields: A Case Study on the Loess Plateau, China

The Loess Plateau has one of the most vulnerable ecological environments in the world, but it also contains abundant oil and gas resources that are regularly exploited, which has resulted in serious environmental problems. Therefore, it is important to analyze the polycyclic aromatic hydrocarbons (PAHs) present in the topsoil of this region. The ∑16PAHs concentrations between 1980–1999 and 2000–2019 ranged from 1134.20–15871.04 and 1010.67–18,068.80 µg kg⁻¹, with average values of 5021.30 and 5662.82 µg kg⁻¹. All samples displayed heavy pollution levels according to European soil quality standards. In addition, among the measured physicochemical properties, the soil organic carbon (SOC) had the greatest influence on PAHs, while soil particle size distribution had the smallest effect. Source apportionment indicated that the two main sources were petroleum source (37.57%) and vehicular traffic source (25.88%). Lastly, an assessment of the carcinogenic risks illustrated that more focus should be placed on the dermal pathway in which the human body is exposed to soil PAHs. Overall, the carcinogenic risks in different populations did not exceed 10⁻⁴, but there was still a potential carcinogenic risk in some age groups, especially in adult women.

Eight Elements in Soils from a Typical Light Industrial City, China: Spatial Distribution, Ecological Assessment, and the Source Apportionment

Contamination with the eight elements, Hg, As, Cr, Cu, Ni, Pb, Zn, and Cd, is a serious concern in Zhongshan, which is a typical light industrial city, China. 60 surface soil samples were collected to investigate the concentrations, spatial distribution, human health risk, and sources of these elements in the soils in Zhongshan. The concentrations of the eight elements were analyzed while using ordinary kriging analysis, pollution load index (PLI), potential ecological risk index (RI), human health risk, correlation analysis, and factor analysis. The mean concentrations of the tested elements, excluding Pb and As, were higher than the soil background values in the Pearl River Delta. The spatial distribution of the tested elements revealed a zonal distribution pattern and high values in several areas. The mean PLI and RI indicated slight and moderate risk levels. Health risk assessment demonstrates that both children and adults were more exposed to Cu than to Cr, As, and Cd. However, the associated carcinogenic risk is acceptable. Hg that originated from human activities; As, Cr, Cu, Ni, and Cd originated from industrial activities; and, Pb and Zn originated from transportation activities. Cd was the main pollutant in the study area and it was present at higher concentrations when compared with those of the other elements. Therefore, Zhongshan should encourage enterprises to conduct industrial transformation to control the ecological risk.