Soil Polycyclic Aromatic Hydrocarbons Pollution Research Articles

Effects of Chinese “double carbon strategy” on soil polycyclic aromatic hydrocarbons pollution

Polycyclic aromatic hydrocarbons (PAHs) and carbon dioxide primarily originate from the combustion of fossil fuels and biomass. The implementation of the Chinese “double carbon strategy” is expected to impact the distribution of PAH emissions, consequently influencing the spatial distribution trend of PAHs in surface soil. Therefore, it is crucial to quantitatively evaluate the effectiveness of the Chinese “double carbon strategy” on soil PAH pollution for the purpose of “the reduction of pollution and carbon emissions”. This study utilized 15,088 individual PAH concentration data from 943 soil samples collected between 2003 and 2020 in China, in conjunction with PAH emissions at a 10 km resolution, for meta-analysis. The calculated PAH emissions in this study are in line with the global PAH emission inventory (PKU-PAH-2007), with a relative standard deviation at the provincial level of less than 25 %. Subsequently, a novel method was developed using emission density and Kow of PAHs to predict PAH concentrations in surface soil based on a least-squares regression model. Compared to other environmental models, the method established in this study significantly reduced the percent sample deviation to less than 70 %. Furthermore, energy consumption data for China were simulated based on the implementation plan of the “double carbon strategy” to project PAH emissions and soil PAH levels for the years 2030 and 2060. The predicted PAH emissions in China were estimated to decrease to 41,300 t in 2030 and 10,406.5 t in 2060 from 78,815 t in 2020. Moreover, the heavily contaminated areas of soil PAHs (i.e., total PAH concentrations in soil exceeding 1000 μg kg−1) were projected to decrease by 45 % and 82 % in 2030 and 2060, respectively, compared to levels in 2020. These findings suggest that the implementation of the “double carbon strategy” can fundamentally reduce the pollution of PAHs in surface soil of China.

Spatiotemporal distribution, sources, and ecological risk of soil polycyclic aromatic hydrocarbons in Chinese urban agglomerations from 2000 to 2020

To investigate the spatial and temporal distribution, sources, and ecological risk of soil polycyclic aromatic hydrocarbons (PAHs) in China’s urban agglomerations from 2000 to 2020, a comprehensive search strategy was employed using the keywords “soil”, “PAHs”, and “city”. A total of 122 relevant studies that provided information on individual PAH content during the specified time period were collected. These studies encompassed 20 urban agglomerations in China, which were further categorized into two distinct periods: 2000 to 2010 and 2011 to 2020. The diagnostic ratio method and principal component analysis were employed to identify the sources of PAHs, and a risk quotient model was used to evaluate the soil ecological risk. The results revealed the average PAH content in the 20 urban agglomerations in China from 2011 to 2020 was 2,439 ± 4,633 ng·g-1, which exceeded the severe pollution level cut-off (> 1,000 ng·g-1). The soil PAH content in the period from 2011 to 2020 decreased by 28% compared to the soil PAH content in the period from 2000 to 2010. Soil PAH pollution was more severe in the northern urban agglomerations than in the southern urban agglomerations. Diagnostic ratios and principal component analysis demonstrated that the principal sources in most urban agglomerations in China were traffic and coal combustion. GeoDetector found that coal and fuel oil consumption were the main factors affecting the spatial differentiation of PAHs. The ecological risk quotient showed that approximately 80% of the urban agglomerations were at a medium-high ecological risk from 2000 to 2010, compared with 72% from 2011 to 2020. Thus, it is necessary to deepen energy structure reform to alleviate the threat of serious pollution caused by coal and fuel oil in urban agglomerations.

Pollution Characteristics and Risk Assessment of Polycyclic Aromatic Hydrocarbons in Soils of Guangzhou

In order to comprehensively study the pollution characteristics of polycyclic aromatic hydrocarbons （PAHs） in soils of Guangzhou， 222 topsoil samples were collected and analyzed. The ecological risk of soil PAHs pollution was evaluated using the effect interval low/median method （ERL/ERM） and the （BaP） toxicity equivalent method， and the health risk of soil PAHs pollution was evaluated using the lifelong cancer risk increment model. The source of PAHs was analyzed using the characteristic compound ratio method and PMF model. The results indicated that： the content of surface soil （∑16PAHs） in Guangzhou was 38-11 115 μg·kg-1， with an average of 526 μg·kg-1， and 16 types of polycyclic aromatic hydrocarbon monomers showed strong variation. There was a certain degree of ecological risk of PAHs in Guangzhou， and there was already a significant ecological risk of PAHs pollution in individual sampling points， which were generally in a state of mild pollution. Based on the results of the health risk assessment， the contribution rates of total cancer risk in both adults and children were presented as follows： skin contact > ingestion of soil > respiratory intake. The health risk of children was greater than that of adults， and the overall health risk was within an acceptable range. Source analysis showed that the main sources of soil PAHs in Guangzhou were coal （37.1%）； diesel （32%）； coking （17.3%）； and mixed sources of traffic emissions， biomass combustion， and petrochemical product volatilization （13.6%）. The overall source of soil PAHs belonged to mixed sources. The research results have enriched our understanding of the pollution status of PAHs in the surface soil of Guangzhou and are helpful in promoting soil pollution prevention and control actions.

Transfer and Degradation of PAHs in the Soil-Plant System: A Review.

Polycyclic aromatic hydrocarbons (PAHs) are highly toxic, persistent organic pollutants that threaten ecosystems and human health. Consistent monitoring is essential to minimize the entry of PAHs into plants and reduce food chain contamination. PAHs infiltrate plants through multiple pathways, causing detrimental effects and triggering diverse plant responses, ultimately increasing either toxicity or tolerance. Primary plant detoxification processes include enzymatic transformation, conjugation, and accumulation of contaminants in cell walls/vacuoles. Plants also play a crucial role in stimulating microbial PAHs degradation by producing root exudates, enhancing bioavailability, supplying nutrients, and promoting soil microbial diversity and activity. Thus, synergistic plant-microbe interactions efficiently decrease PAHs uptake by plants and, thereby, their accumulation along the food chain. This review highlights PAHs uptake pathways and their overall fate as contaminants of emerging concern (CEC). Understanding plant uptake mechanisms, responses to contaminants, and interactions with rhizosphere microbiota is vital for addressing PAH pollution in soil and ensuring food safety and quality.

Contamination and source-specific health risk assessment of polycyclic aromatic hydrocarbons in soil from a mega iron and steel site in China

The iron and steel industry has always been a key and difficult point of environmental pollution control. In the present study, 493, 175, 153, 72, and 42 soil samples were collected from the soil depths of 0–0.5, 0.5–2, 2–3, 3–4, and 4–5 m (herein called the layers) of the Shougang Steel site, respectively. Compared with the evaluation criteria, the Shougang Steel surface soil was severely polluted by polycyclic aromatic hydrocarbons (PAHs). Inverse distance-weighted interpolation and the Kruskal-Wallis H test revealed that the soil PAH pollution in the iron-making area, especially the coking area, was severer than those in other areas. The PAH concentrations first decreased, and then, increased with the increase of depth. With the increase in depth, the contributions of 2- and 3-ring PAHs increased, while those of 4-, 5-, and 6-ring PAHs decreased. The bivariate local indicators of spatial association (LISA) analysis was used to identify the areas prone to soil PAH pollution due to atmospheric deposition of industrial waste gas and traffic emissions. The method could be used to analyze the impact of anthropogenic activities on soil's PAH pollution for other contaminated sites. Three main pollution sources of soil PAHs, the backfill source, the combustion of coal, and the traffic emissions, were identified based upon three diagnostic ratios, positive matrix factorization and the bivariate LISA analysis, and accounted for 53.8%, 23.5%, and 22.7%, respectively. The combination of bivariate LISA analysis and other source analysis methods could improve the accuracy of source analysis. Benzo[a]pyrene contributed the most to the total health risk among sixteen PAHs. The health risks related to the three pollution sources decreased in the order of backfill sources > coal combustion > traffic emissions. The incremental life-time carcinogenic risks were all below 10−4, indicating negligible or acceptable risks.

Content, Distribution, Source Analysis, and Risk Assessment of PAHs in Arable Soils of Taiyuan

PAHs (polycyclic aromatic hydrocarbons) accumulated in arable soils have significant impacts on farmland quality and human health, which has attracted wide attention from scientists and the public. A total of 22 arable soil samples were collected from Taiyuan, an old industrial city, including three districts (industrial zones, hilly areas, and sewage irrigation area), and the contents of 21 PAHs were detected using the GC-MS method. The sources of PAHs in soils were analyzed using the diagnostic ratios (DRs) method and positive matrix factorization (PMF) model, and the soil health risks were analyzed using the incremental lifetime cancer risk (ILCR) model. The results indicated that the average concentrations of Σ21PAHs and Σ16PAHs in arable soils of Taiyuan were 934.6 ng·g-1 and 787.7 ng·g-1, respectively, which were lower than the soil pollution risk screening value of agricultural land stipulated in GB 15168-2018. 3-5 rings PAHs were the dominant components, accounting for~90% of the Σ21PAHs. Approximately 60% of sites in industrial zones, 13% in hilly areas, and 33% in the sewage irrigation area had high PAHs contents larger than 1000 ng·g-1. The spatial distribution of PAHs showed that more severe PAHs pollution in the soil occurred in industrial areas than that in the other two districts. The DRs suggested that the combustion of coals, bio-masses, and traffic emissions were the dominant sources for PAHs pollution in arable soils in Taiyuan. The simulation results of the PMF model indicated that the sources and contribution rates of PAHs in cultivated soils were coal and biomass burning sources (59%), traffic sources (22%), and coking sources (19%). The risk assessment confirmed that the arable soils in Taiyuan had high potential carcinogenic risks; thus, more attention should be paid to the PAHs pollutions in arable soils.

Spatial distribution characteristics, source analysis and risk assessment of polycyclic aromatic hydrocarbons in topsoil of a typical chemical industry park

Polycyclic aromatic hydrocarbons (PAHs) are widely distributed in soil and are difficult to degrade, posing a great threat to the ecological environment and human health. Therefore, research on the distribution characteristics and risks of PAHs is of great significance to protect human and ecosystem health. Taking a typical chemical industry park in Chongqing as an example, the spatial distribution characteristics of PAHs content in 54 topsoil samples in the typical area were analyzed, and the soil PAHs pollution was evaluated by incremental models such as single-factor index and Nemerow comprehensive index. A factor decomposition model Positive Definite Matrix Factorization (PMF) was used to analyze the sources of PAHs. The results showed that 16 kinds of optimally controlled PAHs were detected, and the content of ΣPAHs in the topsoil ranged from ND to 16.07 mg/kg, with an average value of 1.78 mg/kg; spatially, pollutant levels are higher in the south and southwest of the park as well as in the center; source analysis showed that Chongqing The PAHs pollution in this typical chemical industry park in the city is from coke combustion sources, traffic emission sources, biomass combustion sources, oil sources, coal combustion sources and oil leakage sources, and the contribution rates to PAHs are 10.7%, 35.2%, 20.7%, and 5.0%, 24.6%, and 3.7%; respectively. The health risk assessment of soil PAHs shows that there is no potential carcinogenic risk of PAHs in different age groups in this area, and the main exposure route of adults is dermal > ingestion > inhalation, and the main exposure route of children is ingestion > dermal > inhalation.

Contrasting response strategies of microbial functional traits to polycyclic aromatic hydrocarbons contamination under aerobic and anaerobic conditions

PAHs (Polycyclic aromatic hydrocarbons) are widely distributed in soil ecosystems, but our knowledge regarding the impacts of PAHs effects on soil microbial functional traits is limited. In this study, we evaluated the response and regulating strategies of microbial functional traits that are associated with the typical C, N, P, S cycling processes in a pristine soil under aerobic and anaerobic conditions after the addition of PAHs. Results revealed that indigenous microorganisms had strong degradation potential and adaptability to PAHs especially under aerobic conditions, while anaerobic conditions favored the degradation of high molecular weight PAHs. PAHs exhibited contrasting effects on soil microbial functional traits under different aeration conditions. It would probably change microbial carbon source utilization preference, stimulate inorganic P solubilization and strengthen the functional interactions between soil microorganisms under aerobic conditions, while might cause the increase of H2S and CH4 emissions under anaerobic conditions. This research provides an effective theoretical support for the ecological risk assessment of soil PAHs pollution.

Investigation of relationship between polycyclic aromatic hydrocarbons and human activities in urban soils of China using machine learning methods

Clarifying the impact of human activities on polycyclic aromatic hydrocarbons (PAHs) in soil can provide a scientific basis to reduce PAHs pollution and formulate control measures to manage soil PAHs pollution, which are important to reduce global warming and support China's implementation of carbon neutrality goals. Here, we characterize the PAHs in 1055 samples of urban soil collected in China from 2000 to 2020. The total concentration of PAHs ranged from 2.75 to 38,865 ng g−1. PAHs concentrations in the Yangtze River Delta (YangtzeD) and Pearl River Delta exhibited an inverted U-shaped curve over time, and PAHs concentrations in Beijing have decreased. Air pollution prevention policies and vehicle emission standards in these regions reduced PAHs in the soil. We measured PAHs in soils of 18 major cities in YangtzeD, representing a typical area. Total concentration of PAHs was 3.88–2153 ng g−1 in YangtzeD, with 40.5%, 36.3%, and 23.2% of PAHs coming from industry and transportation, coal combustion, and biomass combustion, respectively by Positive matrix factorization (PMF) model. To explore how human activities affect the PAH concentrations, we screened three machine learning models and selected SHapley Additive explanation-extreme gradient boosting (XGB-SHAP) as the best model. The results of XGB-SHAP (R2 = 0.64) show that the main human activities affecting PAHs were carbon emissions, population size, and economic development (MAS = 709.1) and industrial waste gas emissions (MAS = 577.1), and these were positively correlated with PAHs. Therefore, effective ways to reduce PAHs may largely rely on industrial co-control. With the prevention and control of air pollution, clean energy, and green and low-carbon development policies constantly being implemented, PAH concentrations will continue to be reduced in the future.

Status assessment and probabilistic health risk modeling of polycyclic aromatic hydrocarbons (PAHs) in surface soil across China

Polycyclic aromatic hydrocarbon (PAH) accumulation in topsoil is getting particular concern with the rapid development of urbanization and industrialization, while the overall pollution status and related risk posed by PAHs received limited attentions at the national scale. This study conducted an overview of published data on 16 priority control PAHs by USEPA on the related peer-reviewed 207 research papers between 2000 and 2020 in 30 provinces of China. Based on that, the pollution levels, composition status, spatial distribution pattern, ecological risk, and human health risk posed by soil PAHs were evaluated. Monte Carlo simulation was adopted to model the probabilistic health risk and identify the contributor of such risks. Results demonstrated the concentrations of ∑16PAHs in soil varied from “undetected” to 261 μg g−1 with a mean value of 0.63 μg g−1, indicating the obvious accumulation of PAHs in topsoil of most provinces in China compared with the guideline value (0.2 μg g−1). The concentrations of ∑16PAHs in surface soil of China has obvious regional characteristics. Higher concentrations of soil PAHs are mainly distributed in north, northwest, and eastern regions, especially in Xinjiang, Shandong, Jiangsu, Sichuan, and Guangxi Province. Risk assessment indicates potential ecological and human health risk were posed by soil PAHs, therefore, reducing soil PAHs concentration and exposure frequency are the most effective pathways to protect human health. Despite the fact that risks posed by soil PAHs are generally low, concentrations of PAHs in some sites are relatively high. It is necessary to take effective measures to remediate soil PAHs pollution in certain areas to reduce concentration and associated risks.

Toxicity and Risks Assessment of Polycyclic Aromatic Hydrocarbons in River Bed Sediments of an Artisanal Crude Oil Refining Area in the Niger Delta, Nigeria

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants that possess serious risks to human health and the environment. Forty riverbed sediments samples were collected in mangrove river bed sediments where artisanal refining of crude oil takes place in the Niger Delta of Nigeria. The concentration, occurrence, distribution, toxicity and health risk of sixteen priority PAHs (16PAHs) were analysed in the samples. Apart from Nap, Acy, BkF, InP and DbE, all the other PAHs were present in all the sampled points of the studied area with BbF and BaA recording the highest mean values. The range and mean of the total PAHs (∑16PAHs) of this study are 23.461–89.886 mg/kg and 42.607 ± 14.30 mg/kg dry weight (dw), which is classified as heavily contaminated when compared to the European classification of PAHs pollution in soil (>1.0 mg/kg). The range of the effect range factors used to assess the risk of PAHs in an ecosystem (Effect rang-low (ER-L) and Effect range-median ER-M) of this study is from 0.953 to 8.80 mg/kg. PAHs below ER-L (4.0 mg/kg) indicate no toxic effect, but values above ER-M (44.79 mg/kg) indicate toxic effects to the sediments, its resources and, ultimately, the public that consumes the resources thereof; hence, the study area falls within the contaminated category. The occurrence of the high molecular weight (HMW) PAHs (73.4%) supersedes those of the lower molecular weight (LMW) PAHs (26.6%). The diagnostic ratios and principal component analysis suggest that the main contributors of PAHS into the sediments are the combustion of biomass, fossil fuel (crude oil) and pyrogenic sources. The toxic equivalent quotient (TEQ) and mutagenic equivalent quotient (MEQ) of PAHs ranged from 2.96 to 23.26 mgTEQ/kg dw and 4.47 to 23.52 mgMEQ/kg dw, and the total mean toxic equivalency quotient (∑TEQ) (15.12 ± 8.4 mg/kg) is also greater than the safe level of 0.6 mg/kg, which indicates high toxicity potency. The mean incremental lifetime cancer risks (ILCRs) of human exposure to PAHs shows that both adults TotalILCR adults (6.15 × 10−5) and children TotalILCR children (2.48 × 10−4) can be affected by dermal contact rather than ingestion and inhalation. Based on these findings, the appropriate regulatory bodies and other organs of government in the region should enforce outright stoppage of the activities of these illegal artisans who do not have control mechanisms for loss control at the site and carry out appropriate clean-up of the area.

Advances in bioremediation of polycyclic aromatic hydrocarbons contaminated soil

Polycyclic aromatic hydrocarbons (PAHs) are a class of persistent pollutants that are widely distributed in the environment. Due to their stable structure and poor degradability, PAHs exhibit carcinogenic, teratogenic, and mutagenic toxicity to the ecological environment and organisms, thus increasing attentions have been paid to their removals and remediation. Green, safe and economical technologies are widely used in the bioremediation of PAHs-contaminated soil. This article summarizes the present status of PAHs pollution in soil of China from the aspects of origin, migration, fate, and pollution level. Meanwhile, the types of microorganisms and plants capable of degrading PAHs, as well as the underlying mechanisms, are summarized. The features of three major bioremediation technologies, i.e., microbial remediation, phytoremediation, and joint remediation, are compared. Analysis of the interaction mechanisms between plants and microorganisms, selection and cultivation of stress-resistant strains and plants, as well as safety and efficacy evaluation of practical applications, are expected to become future directions in this field.

Concentration, distribution, source apportionment, and risk assessment of surrounding soil PAHs in industrial and rural areas: A comparative study

Polycyclic aromatic hydrocarbons (PAHs) are one of the important environmental pollutants that are mainly originated from industrial activities, vehicle emissions, biomass combustion, etc. Nowadays, the surrounding environment of the abandoned industrial area may still have potential health effects on the population, but current researches have paid less attention to this issue. Therefore, we report a comparative investigation focusing on the concentration, distribution, source identification, and risk assessment of PAHs in soils from surrounding areas of an abandoned industrial district and an ecological village in Zhejiang Province, China. Our findings are as follows: the levels of ∑16PAHs ranged from 150.2 to 83096 ng·g−1 with an average concentration of 7680.4 ng·g−1 in industrial area, whereas 49.4 to 778.2 ng·g−1 with an average concentration of 213.5 ng·g−1 in rural area. Although high molecular weight PAHs were both dominant contaminants in study areas, the composition profiles of 16 priority PAHs in soils from the two sampling sites had large differences. Source identification analysis verified that fossil fuel burning and vehicle emissions were the main sources of PAHs in industrial area, while the primary sources were biomass burning and vehicle emission in rural area. The incremental lifetime cancer risk results demonstrated that dermal contact was the most influential factor for all groups, and adults might face higher potential health risk than children in both industrial and rural areas. Moreover, the overall ecological risk of soil PAH pollution was low in rural area, but some individual samples were still high in the abandoned industrial area. Our research is of great significance for the management of the surrounding environment of abandoned industrial areas.

Spatial Distribution Characteristics and Source Apportionment of Soil PAHs in Shizuishan City Based on GIS and PMF Model

With the acceleration of urbanization and industrialization, the content and pollution of polycyclic aromatic hydrocarbons (PAHs) in urban soils have been sources of widespread concern. Taking Shizuishan City as an example, the spatial distribution characteristics of PAHs in 156 surface soil samples (0-20 cm) from eight urban functional areas were analyzed. Single factor and Nemero composite indices, as well as a lifetime cancer risk increment model were used to evaluate PAHs pollution in soils. The sources of PAHs were analyzed using the positive matrix factorization (PMF) model. The results showed that the mean value of PAHs in the surface soil of Shizuishan City was 489.82 ng·g-1 and the coefficient of variation of 15 PAHs except for Pyr were more than 100%, indicating strong variation. The PAH contents of urban surface soils in different functional areas showed the following:traffic area (1217.61 ng·g-1) > industrial area (809.58 ng·g-1) > park (273.66 ng·g-1) > cultural and educational area (268.18 ng·g-1) > commercial area (240.05 ng·g-1) > agricultural area (226.81 ng·g-1) > medical area (211.90 ng·g-1) > residential area (183.49 ng·g-1). The Nemero composite index showed that 82.58% of the samples had no pollution, and the proportion of slight, mild, and moderate pollution were 6.45%, 4.52%, and 0.65%, respectively. Only 5.8% of the samples had serious pollution. The results of health risk assessment showed that skin contact and ingestion were the main routes of PAH exposure in soil, and the health risk was acceptable. Source analysis showed that the main sources of PAHs in Shizuishan City were traffic emissions, coal combustion, mixed biomass/heavy oil combustion, and oil sources, with contribution rates of 10.5%, 36.6%, 50.3%, and 2.6% respectively, and most of the high values were distributed in industrial or coal production areas. These results could provide reference for the study of soil pollution in industrial cities, and play an important role in preventing soil pollution, ensuring the environmental quality of the soil and human health and safety.

El hongo Lewia sp. mitiga el estrés oxidante en F. arundinacea durante la fitorremediación de hidrocarburos asistida por endófitos

Due to their mutagenic and carcinogenic effects, polycyclic aromatic hydrocarbons (PAH) have gathered significant environmental concern. Endophyte-assisted phytoremediation is a feasible alternative to reduce PAH pollution in soils more efficiently than plants or microorganisms individually. Endophytes can improve the growth, fitness, and antioxidant system of their hosts, especially under stress, including contamination. In this context, this study aimed to assess the influence of Lewia sp. on antioxidant defense and the hydrocarbon removal by F. arundinacea during 45 days of exposure to a hydrocarbon mixture. Plant growth and lipid peroxidation (LPO), as well as superoxide dismutase (SOD), peroxidase (POD) and glutathione S-transferase (GST) activities were determined in a kinetic assay. The association significantly improved the hydrocarbon removal over a 45-day period, while promoting plant growth and controlling oxidative damage, particularly in the roots. The root antioxidant system in F. arundinacea is itself effective in counteracting the phytotoxicity of direct contact with hydrocarbons. However, Lewia sp. controls LPO in the roots, which may be a consequence of the fungus's own antioxidant system, involving the coordinated activity of SOD and POD. Once the endophytic association is established, it can be applied to phytoremediate PAH-polluted soils during a minimum period of 45 days.

Formation mechanism of soil PAH distribution: High and low urbanization

Urbanization is an important driving force for the distribution of polycyclic aromatic hydrocarbons (PAHs) in urban soils. Research on factors affecting PAH distribution in urban soils has focused on analyses of statistical relationships, and quantitative models are not available in the literature. Accordingly, we chose the urban area of Nanjing (high urbanization), and Dingshu (low urbanization), and then comprehensively utilized soil sample test analyses, multivariate statistics, and other technical means to (1) study the concentration and sources of PAHs in urban soils, and (2) identify the main controlling factors that affect urban soil PAH distribution. We found that the population density and black carbon (BC) components were the critical factors of soil PAH distribution in Nanjing, yet BC components and leaf area index in Dingshu. We then constructed a quantitative relationship model of urban soil PAH distribution in different levels of urbanization. Using this model, we conducted a preliminary analysis of the formation mechanism of urban soil PAHs under different urbanization levels. This research provides a basis for finely controlling regional urban soil PAH pollution.

Distribution, sources and influence factors of polycyclic aromatic hydrocarbon at different depths of the soil and sediments of two typical coal mining subsidence areas in Huainan, China

The coal mining subsidence area in Huainan is a specific but common ecosystem in China. Not a lot of researches focusing on persistent organic pollutants like polycyclic aromatic hydrocarbons (PAHs) in this area have been done. In order to investigate the concentrations, sources, environmental fate of PAHs and its distribution factors, Yangzhuang and Xieqiao coal mining subsidence areas in Huainan, China were determined as the object of the research, where samples from different depths of soil and sediments were collected to detect and analyze PAHs with Gas Chromatography-Mass Spectrometry. The result showed that the 16 PAH compounds were all detected with a detection rate of 100%. The concentrations of PAHs at different depths of the soil and sediments of Yangzhuang were in the range of 42.1–22149.0 and 44.0–7644.2 ng/g, respectively, and in Xieqiao which were in the range of 17.8–1617.7 and 35.7–264.6 ng/g, respectively. Through comparing the results about spatial interpolation analyses of two subsidence areas, we found that PAHs pollution in soil was heavier than that in sediments of the subsidence areas with relatively small man-made interference. Man-made pollution had a great influence on the vertical distribution of PAHs in the subsidence areas. The PAHs with three or four rings dominated in the areas. Using diagnostic ratios, we found PAHs came from mixed pollutions including the combustion of coal and traffic pollution. As for the influence factors, based on regression analysis and Pearson correlation analysis, the increase of organic matters (OM) and total organic carbon (TOC) favored the deposition of PAHs and had a positive impact on the vertical distribution of PAHs.

Soil Polycyclic Aromatic Hydrocarbons Across Urban Density Zones in Shenzhen, China: Occurrences, Source Apportionments, and Spatial Risk Assessment

Urbanization may cause increased exposure levels to polycyclic aromatic hydrocarbons (PAHs) and associated health risks for over half of the world's population living in cities, but little evidence has shown a direct spatial relationship between urbanization and soil PAH pollution. Based on the monitored PAH concentrations in 188 topsoil (0–5 cm) samples in Shenzhen, the most rapidly developing city in China, in recent decades, we applied geographical demarcation to determine the occurrences, source apportionments, and spatial ecological risks of soil PAHs across five zones of varying urban densities. Mean concentrations of the 16 US Environmental Protection Agency (EPA) priority PAHs (∑16PAHs) and the 7 carcinogenic PAHs (∑7CarPAHs) both followed the order: Zone D (60%–80% constructive land density (CLD)) > Zone E (80%–100% CLD) > Zone C (40%–60% CLD) > Zone B (20%–40% CLD) > Zone A (0%–20% CLD), suggesting that the highest PAH levels occurred in the suburban-urban center transitional zone (Zone D) rather than the urban center zone (Zone E) in Shenzhen. There were significant correlations of ∑16PAHs to TOC and sampling altitude across all samples but not within highly-urbanized regions (Zones D and E), implying a considerable disturbance of urbanization to the soil PAH pool. Source apportionments suggested that soil PAHs of all zones were mainly derived from fossil fuel combustion, with Zone E showing the highest contribution from oil sources among different zones. Spatial ecological risk analysis showed that the contaminated area (467 km2; 23.9% of total area; toxic equivalency quotients > 33 ng g−1) had a higher contribution from the highly-urbanized regions (Zones D and E) than the uncontaminated area (42.3% vs. 18.1%). Overall, our study highlighted a strong spatial relationship between urbanization and soil PAH pollution.

Response of bacterial pdo1, nah, and C12O genes to aged soil PAH pollution in a coke factory area.

Soil pollution caused by polycyclic aromatic hydrocarbons (PAHs) is threatening human health and environmental safety. Investigating the relative prevalence of different PAH-degrading genes in PAH-polluted soils and searching for potential bioindicators reflecting the impact of PAH pollution on microbial communities are useful for microbial monitoring, risk evaluation, and potential bioremediation of soils polluted by PAHs. In this study, three functional genes, pdo1, nah, and C12O, which might be involved in the degradation of PAHs from a coke factory, were investigated by real-time quantitative PCR (qPCR) and clone library approaches. The results showed that the pdo1 and C12O genes were more abundant than the nah gene in the soils. There was a significantly positive relationship between the nah or pdo1 gene abundances and PAH content, while there was no correlation between C12O gene abundance and PAH content. Analyses of clone libraries showed that all the pdo1 sequences were grouped into Mycobacterium, while all the nah sequences were classified into three groups: Pseudomonas, Comamonas, and Polaromonas. These results indicated that the abundances of nah and pdo1 genes were positively influenced by levels of PAHs in soil and could be potential microbial indicators reflecting the impact of soil PAH pollution and that Mycobacteria were one of the most prevalent PAHs degraders in these PAH-polluted soils. Principal component analysis (PCA) and correlation analyses between microbial parameters and environmental factors revealed that total carbon (TC), total nitrogen (TN), and dissolved organic carbon (DOC) had positive effects on the abundances of all PAH-degrading genes. It suggests that increasing TC, TN, and DOC inputs could be a useful way to remediate PAH-polluted soils.

Fate estimation of polycyclic aromatic hydrocarbons in soils in a rapid urbanization region, Shenzhen of China

Our previous study indicated that the current level of polycyclic aromatic hydrocarbons (PAHs) in Shenzhen soil is in the low-end of world soil PAH pollution. In this study, the fate of PAHs in the soil of Shenzhen was investigated. The mass inventories of Σ(27)PAHs and Σ(15)PAHs (defined as the sum of the 27 or 15 PAH compounds sought) in topsoil of Shenzhen were ∼204 and ∼152 metric tons, respectively. Fate estimation of Σ(15)PAHs shows that air-soil gaseous exchange is the primary environmental process with ∼10,076 kg/year diffusing from soil to air. Rain washing (∼1131 kg/year from air to soil) is the most important input pathway followed by wet (∼17 kg/year) and dry deposition (∼8 kg/year) to soils in Shenzhen. The transport of Σ(15)PAHs by soil erosion is a crucial loss process for soil PAHs in Shenzhen (1918 kg/year for water runoff and 657 kg/year for solid runoff from soil). Moreover, degradation is not ignorable at present (95 kg/year). Comparison of inventory and residue (defined as Σ(15)PAHs left in topsoils after all environmental loss processes) suggested that input and loss of high molecular weight PAHs for Shenzhen's soil reached apparent equilibrium. Soil PAH pollution in Shenzhen will stay in a quasi-steady state for a long period and the natural environmental processes can not significantly reduce the pollution.