Abstract:ObjectivePolycyclic aromatic hydrocarbons (PAHs) have carcinogenic, teratogenic, and mutagenic effects, and soil PAH pollution has become a world-wide problem. However, ecological soil screening and controlling levels (Eco-SSCLs) for PAHs in China have not yet been established. Thus, soil ecological security risk assessment is still unsubstantiated.MethodHere, we systematically investigated the research outcomes in related fields at home and aboard, and screened out 248 toxicity data (Effect concentration10, EC10 and No observed effect concentration, NOEC) of 16 pri-control PAHs listed in USEPA. The species sensitivity distributions were developed by a series of cumulative distribution functions, and were successfully used to derive soil environmental criteria of each PAH (PAH-SEC) for ecological security under different land use types.ResultThe PAH-SEC values under different land use types were 1.00-10.60 mg·kg-1 (natural reserve and agricultural land), 1.03-25.44 mg·kg-1 (parkland), 1.12-51.00 mg·kg-1(residential land), 1.20-68.41 mg·kg-1 (commercial service and industrial land).ConclusionThe results can provide data support for the formulation of soil environmental quality standards for ecological security, and offer bases for ecological risk assessment of PAHs polluted soil.

Abstract:Objective Polycyclic aromatic hydrocarbons (PAHs) are a kind of persistent organic pollutants that exist widely in various environmental media. As one of the most important ways to eliminate PAHs pollution in the environment, microbial degradation has been widely studied in the past few decades. Many of the polluted environmental media may undergo anaerobic states or remain in anaerobic states, e.g. paddy soils, bottom soils, wetlands, sediments, water. However, existing studies mainly focused on the aerobic environment and paid less attention to the anaerobic environment. Considering the current situation, this study systematically and comprehensively illustrates the research status of anaerobic microbial degradation of PAHs.Method The core collection database of Web of Science was used as the data source to conduct a bibliometric analysis of published literature in this field, with the aid of two pieces of software, VOSviewer and CiteSpace. The main contents of the bibliometric analysis included the year of publication, disciplines, keywords frequencies, keywords co-occurrence and most cited papers. In addition, by classifying different electron acceptors based on their reducing sequence, this paper discussed the research progress regarding anaerobic microbial degradation of PAHs in denitrification, metal ion reducing, sulfate reducing and methanogenesis conditions, respectively, with a focus on typical degrading microbes and mechanisms. On this basis, the existing theoretical gaps and future development trends in the field of PAHs anaerobic microbial degradation in the soil were discussed emphatically.Result The results showed that since 1991, the number of studies in this field showed the trend of fluctuating growth but was still relatively small on the whole, and most of them only focused on low-ring PAHs, especially naphthalene. Among the four different reducing systems, denitrification and sulfate reducing systems were studied more extensively, while less attention was paid to metal ion reducing and methanogenesis systems. Most significantly, the majority of mechanical studies remained at a relatively superficial level, without exposing the biological mechanisms of PAHs anaerobic microbial degradation and the interactions between functional microbes. Emerging technologies have not been commonly used in this field. Most studies were based on pure culture or environmental media such as water and sediment, but few were based on soil system.Conclusion As a result, there are still many theoretical gaps in the understanding of anaerobic microbial degradation of PAHs in the soil at present. Soil is the main site for the confluence and accumulation of PAHs in the environment. In the future, researchers should try to combine Compound-specific Stable Isotope Analysis (CSIA), DNA-stable isotope probing(DNA-SIP), Omics and other emerging technologies with traditional research methods to explore the mechanisms of PAHs anaerobic microbial degradation in the soil from a variety of different aspects, and verify the applicability of existing theories and experience to the soil, so as to fill the current theoretical gaps and promote the microbial remediation of PAHs pollution in anaerobic soil.

Abstract:In order to understand in depth the global status and frontier dynamic of the researches on polycyclic aromatic hydrocarbons (PAHs) in soil and to reflect scientific capabilities and influences of relevant countries, institutions and individuals objectively, a bibliometric analysis has been conducted of related literatures published in the period of 1900–2014 and included in the citation database Web of Science of the ISI Web of Knowledge. Results show that the number of related publications displayed a rapidly and steadily rising trend. In terms of number of articles, total citation and H index, the United States ranks first, and China second, but not in average citation per paper. Among the research institutions the world over, the Chinese Academy of Sciences and the University of Lancaster in England are on top of the list in number of articles and H index, and the University of Massachusetts in the United States is the top most one in average citation per paper. Among individuals, Prof. Jones, K. C. of the University of Lancaster is in the lead in number of articles and in H index, too, while Prof. Hawthorne, S. B. of the University of North Dakota is in average citation per paper. Prof. Tao Shu of the Beijing University and Prof. Zhu Lizhong of the Zhejiang University are the most influential scholars in China. In this academic field the journals of “Environmental Science & Technology”, “Chemosphere”, and “Environmental Pollution”, are the leading ones. The researches in this field are mostly focused on degradation and bioremediation of PAHs in the soil, dissolution and adsorption of PAHs in various media, and source apportionment of PAHs. Researches related to “China” hold an important position in the recent 5 years.

Abstract:Polycyclic aromatic hydrocarbons (PAHs) with highly mutagenic and carcinogenic properties are commonly found in the soil environment. Soil contamination by PAHs has become a major health risk issue. PAHs are widespread and occur at high concentrations (hundreds of mg kg-1) in soils of many countries. Since natural and xenobiotic PAHs present in soil may be absorbed by plants, PAHs can enter human and animal bodies through the food chain/web. Because of the health hazards of PAHs, understanding the distribution of PAH residues in rhizospheric soils is of crucial importance for risk assessment of PAH-contaminated areas. The distribution of PAHs in the rhizosphere affects their fate in the soil-plant system. After diffusion into rhizosphere soil, root exudates gradually disappear as a result of radial dilution and microbial consumption. Because these root exudates are ready carbon and energy sources to bacteria, a bacterial gradient is observed with a greater number of heterotrophs and PAH-degrading bacteria closest to the roots, which may generate a gradient of PAH degradation between the rhizosphere and bulk soil. Recently, it was reported that the residual concentrations of PAHs showed a rising gradient from the rhizoplane to the loosely adhering soil after 40 and 50 d, and were significantly and negatively correlated with the amount of root exudates in the rhizosphere. This was further supported by an in situ observation that concentrations of 11 EPA-priority PAHs in rhizosphere soils increased with the distance (0~9 mm) from the root surface. However, the documented gradient distributions in rhizosphere soils are overwhelmingly about the total concentrations of PAHs as well as other organic compounds. The International Union of Pure and Applied Chemistry (IUPAC) definition reserves the term of bound residues for the parent compound and its metabolites that cannot be extracted from soil using organic solvents. Bound residues have a direct effect on long-term partitioning behavior, bioavailability, and toxicity of the organic contaminants in soil. The formation of bound residue is considered to act as a soil detoxification process by permanently binding compounds into soil matrices, and the bioavailability of bound residues is the final endpoint for risk assessment and regulatory management of organic chemicals in the soil environment. However, there is little information available on the distribution of their bound residues in the rhizosphere. Therefore investigations were made of rhizospheric gradient distribution of bound-PAH residues (reference to parent compounds) in soils on a field scale. In Moleplant ( Euphorbia lathyris L.) and wood sorrel ( Oxalis corniculata L.) fields of yellow brown earth near a petrochemical plant, rhizosphere soils of the plants were sampled including the rhizoplane, strongly adhering soil, and loosely adhering soil, for analysis of content and gradient distribution of PCBR (Parent compound of bound residue) in the rhizosphere. Results show that PCBRs of the ten EPA-priority PAHs were detected in both the rhizosphere and non-rhizosphere soils, about 3.31 mg kg-1 in concentration in the latter, much higher than in the former (1.07~1.82 mg kg-1). The concentration of PCBRs increased with the distance (0~9 mm) from the root surface. It is feasible to use rhizosphere effect (R, in percent) to measure the proportion of the decrement of PCBRs in concentration in the rhizosphere as against that in the non-rhizosphere soil, R decreased with increasing distance from the root. Rof the total PCBRs of PAHs in three continuous layers of rhizosphere reached 45.15%~67.66%. R of two-ringed PAHs was the highest (61.18%~93.50%), while R of four- and five-ringed PAHs the lowest (2.39%~6.31%), which indicates that the PCBRs of PAHs with fewer rings are more liable to transformation in the rhizosphere. R of the PCBRs in the rhizosphere of moleplants was found to be relatively higher than that of wood sorrels, suggesting that the rhizosphere of moleplants was more favorable to transformation of PCBRs. The gradient distribution of PCBRs in the rhizosphere is closely related to that of root exudates, while type of PAHs and rhizosphere environment affect significantly distribution of PCBRs. The findings of this work provide some important information on fate of PAHs in the soil environment and are useful in risk assessment of PAHs-contaminated soils and development of strategies for remediation of contaminated areas.

Abstract:Five soil profiles were selected in typical epikarst spring catchments in Nanchuan District, Chongqing Municipality as objects of the study on rules and controlling factors of the vertical migration of 16 kinds of polycyclic aromatic hydrocarbons (PAHs) in the soils. Soil samples were collected from every soil layers, 10 cm thick each, of the soil profiles for quantitative analysis of the PAHs with gas chromatography-mass spectrometry (GC-MS). Results show that all the 16 PAHs were detected in all the 5 soil profiles, varying in the range of 161~3 285 ng g-1, and averaging 987 ng g-1 in concentration. In the soil profile at the Hougou epikarst catchment, high-ring PAHs were in dominancy, while in the soil profile at the paddy field of the Lanhuagou spring catchment and at the Shuifang spring catchment, low-ring PAHs were. However, in the soil profiles in pine forests at the Baishuwan and Lanhuagou spring catchments, high-ring PAHs dominated the 0~2 cm soil layers, but low-ring PAHs did the soil layers below 2 cm. From the contents of PAHs and changes in composition along the profiles, it could be inferred that low-ring PAHs migrate easily. But in soil profiles with a thin surface soil layer, artificial disturbance, like plowing, make it easy for high-ring PAHs to migrate. Among the five soil profiles, only the one in the Shuifang spring catchment witnesses the highest mobility of PAHs. As in karst areas, the surface soil layers are generally thin, PAHs migrate easily, thus polluting epikarst spring water. Multiple regression analysis between the total PAHs and physicochemical properties of the soils shows that total organic carbon (TOC) is the main factor controlling the migration of PAHs in the Hougou, Lanhuagou and Baishuwan spring catchments, while in the Shuifang spring catchment, there is no main factor impacting migration of PAHs.

Abstract:Batch experiment was performed to study effects of different aquatic factors (pH and iron intensity) on dispersibility of dissolved organic matter (DOM) extracted from Fulvic acid. It was found that the DOM extracted from fulvic acid (FDOM) remained high in dispersibility and did not precipate in solutions with pH between 2.0～7.0 and CaCl2 concentration between 0～1 500 mmol L-1 without precipitation. Column leaching experiments were conducted to investigate effect of FDOM on transport of polycyclic aromatic hydrocarbons (PAHs) in the soil. With continuous irrigation of FDOM, the concentrations of Phenanthrene (Phe), Pyrene (Pyr), and Benzo[a]pyrene (B[a]P) in leachate were significantly increased, and even a limited amount of Dibenzo (a, h) acenaphthene (DBA) was also detected in the leachate. After leaching, the leaching lost rate of Phe, Pyr, B[a]P and DBA in the surface soil was 92.06%, 92.07%, 84.52% and 23.27%, respectively. These findings indicated that FDOM could act as carrier facilitating PAHs transport in the soil, thus enhancing the possibility of PAHs moving deeper into the soil and ground water.

Abstract:Polycyclic aromatic hydrocarbons (PAHs) are a group of chemicals with potential carcinogenic, teratogenic and mutagenic effects, and are mainly produced out of incomplete combustion of biomass and fossil fuel. Excessive PAHs releasing into the atmosphere may accumulate in the soil through deposition, resulting in soil pollution. Currently the techniques available for bioremediation of PAHs-contaminated soils are mostly based on the degradation function of bacteria, while the potential of fungi in soil remediation is not yet fully understood. Fungi are important components of the soil ecosystem and extremely high in diversity. Quite a number of strains of fungi, mainly Basidiomycete and Ascomycete, are capable of degrading PAHs with their intracellular cytochrome P450 or extracellular ligninolytic enzymes. And some form Mycorrhizal symbiont with plant roots, which may degrade PAHs synergistically. Thanks to the feature of fungi degrading PAHs, they have their unique advantage in reducing the concentration and ecotoxicity of PAHs in soil. In this review, an overall introduction is presented to the diversity of PAHs-degrading fungi, and their PAHs-degrading mechanism, as well as the fungal remediation techniques currently available. In addition, the concerns and problems associated with fungal remediation are discussed and prospect of its development is predicted.

Abstract:Members of Sphingomonas genus played a key role in the biodegradation of polycyclic aromatic hydrocarbons (PAHs). However, little was available in the literature about diversity and population structure of genus Sphingomonas in petroleum-contaminated soils, and relationships between Sphingomonas and PAHs based on direct detection Sphingomonas strains with Sphingomonas genus-specific primers. In this paper, total soil DNA from the soil in Shenfu irrigation zone were amplified with newly designed Sphingomonas genus-specific primer set 732f-982r and then these amplified DNA fragments were separated by DGGE for analysis of genetic diversity of Sphingomonas in the soil of the irrigation zone. Results indicate that the newly developed primer set 732f-982r could be used for specific detection of strains belonging to the genus Sphingomonas. When PAHs contamination of the soil is at a low level, i.e. less than 5 mg kg-1, the diversity of Sphingomonas increased with rising PAHs concentration; but when the initial concentration of PAHs in lab incubation experiment is relatively high, the diversity of Sphingomonas decreased. Different concentrations of total petroleum hydrocarbons (TPH) lead to difference in Sphingomonas population, and soils the same in TPH contamination level are similar in Sphingomonas population.

Abstract:Fungal laccase can efficiently oxidize polycyclic aromatic hydrocarbons (PAHs), suggesting the potential of laccase-producing fungi for application to remediation of PAHs-contaminated soil. Based on its feature of being capable of oxidizing guaiacol into something red, a strain of laccase-producing fungus, F-1, was isolated from soil. According the BLAST alignment of near full-length 18S rRNA gene sequence, this strain is closely related to Myrothecium verrucaria. Both single factor and Plackett-Burman experiments were performed to assess F-1’s laccase-producing capacity. The laccase activity was found to be greatly increased by 2 orders of magnitude in specific culture medium, suggesting the significant effect of environment factors on laccase activity of F-1. Soil microcosms were set up with or without inoculation of F-1, and the PAHs contents were determined after 30-days of incubation. Results show that PhA, FluA, Pyr, BaA, Chr, BbF, BkF, BaP, DbA, BghiP and In[1,2,3-cd]P were degraded to varying extent in fungus inoculated microcosms, confirming the remedial potential of F-1 in PAHs-contaminated soil.

Abstract:A total of 420 farmland soil samples were collected, 96 from Suzhou area and 324 from Jiaxing area, for analysis of composition of PAHs and concentrations of the 15 types of PAHs under priority control with the aid of HPLC and for exploration of sources of the PAHs in the soil, using the ratioing technology and PCA. Results show that the total content of PAHs varied in the range from 45.4 μg kg-1 to 3 703 μg kg-1 and from 9.00 μg kg-1 to 2 421 μg kg-1 in Suzhou and Jiaxing, respectively. The mean concentration of B[a]P in the soils of Suzhou reached 21.4 μg kg-1, far beyond the maximum allowable value of 20.0 μg kg-1 set by the Former USSR. The content of PAHs in Suzhou displayed an increasing trend from south (Wujiang County) to north (Xiangcheng County), and much higher than in Jiaxing. And the content of PAHs in soils of Wujiang County and Jiashan County of Shanghai was rather higher. Phe, FluA, BbF, IP, and Pyr were the dominant PAHs in Suzhou, while Phe, FluA, Pyr, Chry, and BbF were in Jiaxing. The sources of the PAHs in the soils of the two regions were quite similar, mainly biomass, coal combustion and petroleum.