SYNOPSIS Polycyclic Aromatic Hydrocarbons (PAHs) in Soil — a Review

PAHs are mainly produced by combustion processes and consist of a number of toxic compounds. While the concentrations of individual PAHs in soil produced by natural processes (e.g., vegetation fires, volcanic exhalations) are estimated to be around 1—10 μg kg⁻¹, recently measured lowest concentrations are frequently 10 times higher. Organic horizons of forest soils and urban soils may even reach individual PAH concentrations of several 100 μg kg⁻¹. The PAH mixture in temperate soils is often dominated by benzofluoranthenes, chrysene, and fluoranthene. The few existing studies on tropical soils indicate that the PAH concentrations are relatively lower than in temperate soils for most compounds except for naphthalene, phenanthrene, and perylene suggesting the presence of unidentified PAH sources. PAHs accumulate in C‐rich topsoils, in the stemfoot area, at aggregate surfaces, and in the fine‐textured particle fractions, particularly the silt fraction. PAHs are mainly associated with soil organic matter (SOM) and soot‐like C. Although the water‐solubility of PAHs is low, they are encountered in the subsoil suggesting that they are transported in association with dissolved organic matter (DOM). The uptake of PAHs by plants is small. Most PAHs detected in plant tissue are from atmospheric deposition. However, earthworms bioaccumulate considerable amounts of PAHs in short periods. The reviewed work illustrates that there is a paucity of data on the global distribution of PAHs, particularly with respect to tropical and southern hemispheric regions. Reliable methods to characterize bioavailable PAH pools in soil still need to be developed.     

上海市土壤中持久性毒害污染物和盐分含量特征研究

Some farmland soils in Shanghai had high salinity levels, suggesting secondary salinization of the soils. The soil problems in Shanghai were studied, including the salinity and nitrate nitrogen (NO₃^--N) concentrations, heavy metal pollution characteristics, and organochlorine pesticide (OCP) residual levels and polycyclic aromatic hydrocarbon (PAH) contents. Accumulation of NO₃^--N in vegetable soils was the most significant among different functional soils. Heavy metal pollution was significant in the samples collected from the sewage-irrigated land and roadside. The identification of the metal sources through multivariate statistical analysis indicated that Pb, Zn, Cu and Cr in urban soils were from the traffic pollutants; excessive application of fertilizer and irrigation were the main reasons for the metal pollution in agricultural soils; Ni in the observed soils was controlled by parent soils. OCPs could still be detected in farmland soils but degraded greatly in last 20 years after prohibition of their usage. PAHs with 2-3 rings were the main components in industrial soils. The concentrated PAHs in the investigated soils were likely from petroleum and coal combustion.     

城市土壤多环芳烃的特征和来源解析研究进展

Polycyclic aromatic hydrocarbons (PAHs) are mainly produced by combustion processes and consist of a number of toxic compounds.They are always emitted as a mixture and have become a major type of pollutants in urban areas.The degree of soil contamination by PAHs is of special concern in areas immediately in proximity to cities with heavy traffic,factories,older buildings,and infrastructure.The accumulation of soil PAHs is also affected by non-anthropogenic factors,such as climate,vegetation,and soil property.This paper reviews three typical source identification techniques,including diagnostic ratios,positive matrix factorization,and principle conrponents analysis.The advantages or disadvantages of these techniques are analyzed.It is recommended that multiple identification techniques be used to determine the sources in order to minimize the weaknesses inherent in each method and thereby to strengthen the conclusions for PAH source identification.     

中国南亚热带农业土壤中的多环芳烃

The contributions of persistent organic pollutants （POPs） from the subtropical regions of China to pollution of the global environment have been paid great attention; however, little is known about the state of POPs in agricultural ecosystems within these regions of China. This study primarily revealed the state of the contamination and distribution of polycyclic aromatic hydrocarbons （PAH） in agricultural soils in the subtropical regions. 115 surface soils （0-20 cm） were sampled in the breadbaskets of these regions. The concentrations and types of PAH were determined using gas chromatography linked to mass spectrometry （GC-MS）. The total PAH concentrations ranged from 22.1 to 1 256.9 ng g^-1 with a mean of 318.2 ± 148.2 ng g^-1. In general terms, the current PAH concentrations were lower than most PAH levels reported in a number of investigations from different countries and regions. PAH isomer ratios indicated that pyrolytic origins, such as fossil fuel combustion related to vehicle tail gas and industrial emissions, were the dominant sources of PAH in the southern subtropical areas of China. Although PAH concentrations decreased with decreasing pollution, population, and traffic density, to a great extent PAH compositions were similar throughout subtropical soils, with naphthalene, phenanthrene, fluoranthene, and benzo（b）fluoranthene being dominant.     

Pyrogenic polycyclic aromatic hydrocarbons in soils of reserved and anthropogenically modified areas: Factors and features of accumulation

The accumulation features of pyrogenic polycyclic aromatic hydrocarbons (PAHs) in soils were analyzed depending on the type of burning material and the combustion conditions (the temperature, oxygen access, and dispersion of the combustion products). The PAH accumulation features in the soils of three reserved areas of forest, steppe, and peat fires were revealed. The distribution features of the PAHs resulting from the anthropogenic pyrogenic processes (the household combustion of wood and the inflammation of coal dumps) in soils were established. The differences in the qualitative composition of the PAHs arriving to the soils from the different pyrogenic sources were shown.     

Water-Soluble Ions and Trace Metals in Airborne Particles Over Urban Areas of the State of São Paulo, Brazil: Influences of Local Sources and Long Range Transport

The atmosphere over Brazilian cities is influenced by a variety of emissions sources. In this study, aerosol collection and back-trajectory analysis were used to determine the influence of local and remote sources. Aerosols were collected at three locations within the state of São Paulo: one megacity and two cities in which sugar cane burning in the surroundings is observed. We quantified the major water-soluble inorganic ions and trace metals. As expected, vehicle emissions influenced the atmosphere of the megacity heavily, and sugar cane burning influenced that of the other locations. During the period of this experiment the back-trajectory analysis revealed that air masses are transported into the state from the northeast of Brazil, where biomass burning occurs. Multivariate statistical analysis revealed that the two principal components account for 48.5% of the total data variance. We conclude that local sources have a strong impact on the concentrations of particulate matter and pollutants. Remote sources also contribute to the concentrations of aerosol pollutants.     

Polycyclic aromatic hydrocarbons in green space soils in Shanghai: source,distribution, and risk assessment

Purpose

The purpose of this study is to study the major sources, concentrations, and distributions of polycyclic aromatic hydrocarbons (PAHs) in three different types of green space in Shanghai. In addition, we will quantitatively assess the burden of PAHs in the soil, as well as the potential carcinogenic risk of PAHs in humans. These results will provide valuable information for soil remediation and human health risk management.

Materials and methods

A total of 166 surface soil samples were collected in parks, greenbelts, and woodlands. Soils were extracted using accelerated solvent extraction (ASE). PAHs were analyzed by gas chromatography-mass spectrometry (GC-MS). The positive matrix factorization (PMF) model was used to identify major PAH emission sources and quantitatively assess their contributions to PAHs. The incremental lifetime cancer risk (ILCR) was used to quantify the potential health risk of PAHs.

Results and discussion

The average concentrations of ∑15 PAHs are 227?±?95 ng g^?1, 1632?±?251 ng g^?1, and 1888?±?552 ng g^?1 in the woodland, park, and greenbelt soils, respectively. The PMF results show that biomass (33%), coal (21%), vehicles (17%), natural gas (14%), oil (9%), and coke (7%) are the dominant sources of PAHs in the park soils. Diesel (40%), tire debris (30%), biomass (15%), gasoline (9%), and oil (5%) are the main sources in the greenbelt soils. Biomass (48%), vehicles (37%), and coal (15%) are the main sources in the woodland soils. The ILCRs of adults and children who are exposed to PAHs in soils range from 9.53?×?10^?8~1.42?×?10^?5.

Conclusion

In three types of green space in Shanghai, the dominant PAHs are high–molecular weight (HMW) compounds (≥?4 rings). This may be due to the proximity of the sampling site to emission sources. In addition, low–molecular weight (LMW) PAHs (with 2–3 rings) are relatively unstable, and these compounds are prone to volatilization and degradation. Source identification indicates that biomass combustion is the most dominant PAH source in the park and woodland soils, while vehicles are the dominant PAH source in the greenbelt soils. The ILCRs of adults and children indicate potential health risks, and children have a greater health risk than adults.

     

土壤中多环芳烃的分布特征及其来源分析

利用气相色谱法分析了南充市10个不同功能区表层土壤中美国环保署规定的16种优控多环芳烃（PAHs）的含量和组分特征,运用同分异构体比率揭示了其污染来源。研究表明,该区土壤中PAHs的含量在9.1～2269.1μg·kg-1之间,而且工业区的残留量大于农业区和居民区的残留量。按PAHs的环数来分,在工业污染区PAHs的含量总的趋势是四环〉二环〉三环〉五环〉六环;农业和居民区二环〉三环〉五环〉四环〉六环。该污染状况与国内外相关研究比较,处于中等污染水平。煤、木材和化石的燃烧是该地区土壤中PAHs污染的主要来源,苯并（a）蒽和菲是主要的超标化合物。     

Relationship Between Soil Concentrations of PAHs and Their Regional Emission Indices

Actual information on the level of accumulation of PAHs in soils, their inputs/outputs and fate is still unsatisfactory. The regional scale of data collection is important from practical point of view, since decisions regarding environment protection often require proper assessment of soil information aggregated on this level. The objective of the study was to define the regional levels of PAHs in soils and to examine the relationship with the parameters related to their inputs (emission factors) and to natural conditions (soil properties, geographical localisation). The territory of Poland, comprising 16 regions, was chosen as a model area representing the Central/East European countries. The concentrations of 16 PAH compounds were determined in 266 soil samples collected from 0 to 30-cm upper soil layer from agricultural lands. The data were supplemented with basic soil properties. The regional concentrations of Σ16PAHs were within the limits of 125–756 μg kg^?1 (geometric means) and did not exceed the limit values specified in Polish regulations. They complied also with European soil screening values for intermediate or negligible risk. The key variable affecting the accumulation of PAHs in soils was the regional emission of those contaminants, which described soil concentrations of PAHs in at least 50%; the results suggest time-dependent (delayed) reaction of soil environment to the emission changes. The effect was sensitive to PAH compositions in soils and was most pronounced in the case of higher molecular weight compounds (≥4 rings) transported predominantly with atmospheric particles. The regression models, comprising actual regional emission data, did not indicated on the increasing risk of PAHs accumulation in soils. The evaluations based on the regional content of benzo(a)pyrene in soils implied significant discrepancies between Polish and other internationally accepted criteria in soil contamination. The natural factors (soil characteristics and climate) affected the regional PAH concentrations in very small extent.     

Redistribution of organic pollutants in river sediments and alluvial soils related to major floods

Background, Aims, and Scope  More frequent occurrence of stronger floods in Europe as well as in other parts of the world in recent years raises major concern about the material damages, but also an important issue of contamination of the affected areas through flooding. The effects of major floods on levels and distribution of contamination with hydrophobic organic pollutants were examined from the continuous set of data for floodplain soils and sediments from a model industrial area in the Czech Republic where a 100-year flood occurred in 1997. The goal of this study was to evaluate the risk related to contamination associated with such extensive natural events and characterize the spatial and temporal distribution and dynamics of pollutants related to a major flooding shortly after the floods and also in the time period several years after floods. Methods  Sediments and alluvial soils from fourteen sites each were repeatedly sampled during the period from 1996 until 2005. The sampling sites represented five regions. Collected top-layer sediment and soil samples were characterized and analyzed for hydrophobic organic pollutants PCBs, OCPs and HCB using GC-ECD and PAHs using a GC-MS instrument. Spatial and temporal differences as well as the relative distribution of the pollutants were examined in detail by statistical analysis including multivariate methods with special emphases placed on the changes related to floods. Results  The organic pollutants levels in both alluvial soils and sediments exceeded the safe environmental limits at numerous sites. Pollutants concentrations and relative distribution as well as organic carbon content in both sediment and floodplain soils were significantly affected by the flooding, which resulted in a decrease of all studied contaminants in sediments and significant rise of the PAH pollution in the flooded soils. There was a unique and highly conserved PAH pattern in soils regardless of the floods and greater changes in PAH pattern in sediments related to floods. The relative distribution of individual PAHs reflected a combustion generated PAH profile. PAH levels in the river sediments rose again at the sites with continuous sources several years after floods. Discussion  The results showed different dynamics of PAHs and PCBs during the floods when PAHs were redistributed from the sediments to alluvial soils while PCBs have been washed out of the study regions. The data reveal longer contamination memory and consistent contamination pattern in soils, whereas sediments showed more dynamic changes responding strongly to the actual situation. The stable PAH pattern within the regions also indicates that a relative amount of all compounds is comparable across the samples and, thus, that the sources at different sites have similar character. Conclusions  Sediments have the potential to function as a secondary source of contamination for the aquatic ecosystem, but also for the floodplain soils and other flooded areas. The floods served as a vector of PAHs contamination from sediments to soils. The reloading of river sediments in time, namely with PAHs, due to present sources increases their risk as a potential source in the next bigger flood event both to the downstream river basin and affected alluvial soils. Recommendations and Perspectives  The results stress the importance of including the floodplain soil contamination in the risk assessment focused on flood effects. Floodplain soils have stable long-term environmental memory related to contamination levels, pattern and distribution, whereby they can provide relevant information on the overall contamination of the area. The sediments will continue to serve as a potential source of contaminants and alluvial soils as the catchment media reflecting the major flood events, especially until effective measures are taken to limit contamination sources. ESS-Submission Editor: Dr. Henner Hollert (Hollert@uni-heidelberg.de) This article is openly accessible!     

Polycyclic aromatic hydrocarbons (PAHs) in rural soils of Dongjiang River Basin: occurrence,source apportionment,and potential human health risk

Purpose

A comprehensive study was conducted to investigate the presence of polycyclic aromatic hydrocarbons (PAHs) in Dongjiang River Basin (DRB) soils and to evaluate their sources and ecological and health risk. In addition, factors affecting the distribution and fate of PAHs in the soils such as emission density, soil organic matter, degradation, etc. were studied.

Materials and methods

Surface soil (0–20 cm) samples from 30 sampling sites in the rural areas of DRB were collected and analyzed for 17 polycyclic aromatic hydrocarbons (16 EPA priority PAHs and perylene). Positive matrix factorization model was used to investigate the source apportionment of these PAHs, and an incremental lifetime cancer risk (ILCR) was used to estimate the integrated lifetime risks of exposure to soil-borne PAHs through direct ingestion, dermal contact, and inhalation collectively.

Results and discussion

The total PAH concentrations in the rural soils in DRB range from 23.5 to 231 μg/kg with a mean concentration of 116 μg/kg. The predominant PAHs in the rural soils were naphthalene, fluoranthene, phenanthrene, and benzo(b)fluoranthene. Cluster analysis was performed to classify the soil PAHs into three clusters, which could be indicative of the soil PAHs with different origins and different properties. Source apportionment results showed that coal, biomass, oil, commercial creosotes, and vehicle contributed 24 %, 24 %, 17 %, 17 %, and 18 % of the total soil PAH burden, respectively. The ILCR results indicated that exposure to these soil-borne PAHs through direct ingestion, dermal contact, and inhalation collectively produces some risk.

Conclusions

PAHs in the soils of the DRB will produce long-term influences on rivers and oceans via soil erosion and river transport. Therefore, PAHs in rural soils of DRB have potential impacts on the water supply and human health risk.     

Polycyclic Aromatic Hydrocarbons (PAHs) in Forest Floors of the Northern Czech Mountains

Forests of the Northern Czech mountains decline due to industrial emissions. To examine the state of soil contamination with PAHs we analyzed the concentrations of 20 PAHs in the O and A horizons of 4 lower and 4 upper slope sites under beech (Fagus sylvatica L.) in the Western (WE) and the Eastern Erzgebirge (EE, Kru?né Hory), the Isergebirge (IS, Jizerské Hory), and the Riesengebirge (RI, Krkono?e) at microsites affected and not affected by stem flow. Average PAH sum concentrations in the organic layers ranged between 2000 and 30000 μg kg^?1 increasing in the line WE <RI<EE<IS. PAH concentrations were significantly higher at upper than at lower slope sites indicating long-distance transport. Microsites affected by stem flow had significantly higher PAH concentrations but lower percentages of lower molecular PAHs than microsites not affected by stem flow. This was due to the water collecting effect of the beech bark. Lower molecular PAHs preferentially were sorbed to the bark or leached from the organic layers. PAH concentrations increased from Oi to Oa horizons but decreased in the mineral soil. This was the more pronounced the higher the molecular weight was. The slope of the regression line between the enrichment factors (concentration of a single PAH in the Oa divided by that in the Oi horizon) and the octanol-water partition coefficient decreased as the PAH concentration of the soils increased. This indicates that the microbial activity of organic layers may be reduced by soil contamination. Cluster analysis suggested that the sources of the PAH contamination in the WE were different from the other sites.     

Polycyclic aromatic hydrocarbons and polychlorinated biphenyls in urban and semi-urban soils of Havana,Cuba

Purpose

Polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in Havana were quantified and analyzed in relation to possible emission sources to assess metropolitan soil contaminations in a highly dynamic, urban environment. The results of this study will serve Cuban legislators as a basis to develop environmental quality standards for organic pollutants in soils.

Materials and methods

Possible emission sources as, e.g., the vicinity to roads or industrial plants and the influence of the land use were related to the organic contaminants concentrations. Therefore, 28 topsoils in the Havana urban and semi-urban area were sampled at agricultural (n?=?12), organoponic (urban gardens in the capital, n?=?8), public park (n?=?7), and remediation (on-site bioremediation of an oil refinery, n?=?1) sites. Their PAH and PCB concentrations were measured with gas chromatography mass spectroscopy and the total organic carbon (TOC) and black carbon (BC) concentrations with the chemo-thermal oxidation.

Results and discussion

The sum of the 16 PAH concentrations ranged from 0.04 mg/kg in agricultural and organoponic soils to up to 72 mg/kg in a public park at about 1.5 km distance from an oil refinery. The lowest sum of the seven PCB congener concentrations was also measured in organoponic soils (0.002 mg/kg) and the highest in an arable patch of land between the rail roads and a main road (0.1 mg/kg). Both, PAH as well as PCB soil concentrations in Havana were almost up to two orders of magnitudes higher compared to a soil monitoring in the neighboring province of Mayabeque, but overall in the typical range of urban soils reported by other studies. The pollutants showed no relationship between TOC and BC except for PAHs with BC. For PAHs, combustion was the main source.

Conclusions

A comparison of the pollutant concentrations with regulatory guidance values (RGV) of other countries revealed PCB concentrations in Havana soils far below these RGV. In contrast, some concentrations of benzo[a]pyrene, the most carcinogenic PAH, in agricultural and park soils in Havana exceeded some RGV. Thus, some public parks pose a risk according to the Canadian quality guidelines when people have direct contact with these soils but not if they were consuming products thereof.

     

Characteristics,sources, and in situ phytoremediation of polycyclic aromatic hydrocarbon in rural dumpsites

Purpose

Without precaution to deal with gas emissions and leachate generation, dumpsites have become a severe environmental problem in many developing countries. The objectives of this study were to investigate the pollution status of polycyclic aromatic hydrocarbons (PAHs) in dumpsite soil in rural areas of China and to verify phytoremediation effectiveness with Sedum alfredii Hance and alfalfa (Medicago sativa L.) under complex pollution conditions in PAH-contaminated soil.

Materials and methods

In this study, we collected soil cores from four dumpsites in rural areas of North China (Hebei Province) for analysis, and correspondingly conducted an in situ phytoremediation experiment using Sedum alfredii Hance and alfalfa (Medicago sativa L.) at one of these sites, monitoring the total PAH concentration in soil.

Results and discussion

Results showed generally moderate pollution by PAHs in soil samples from dumpsites with pockets of heavy pollution. PAH concentrations in dumpsite soil ranged from 827 to 1101 ng/g (dry weight). High-molecular-weight PAHs were present in higher proportions at oldest dumpsite in operation. Certain molecular ratios of PAHs can be used to diagnose the source of PAHs in soil, and it indicated that the main sources were combustion of domestic coal and biomass, as well as the automobile exhaust and kitchen exhaust. A 17-month in situ phytoremediation experiment resulted in the effective removal of PAHs in the Sedum alfredii and alfalfa plots, with total PAH concentrations decreasing by 82.4% and 81.3%, respectively. Furthermore, PAH concentrations in plants correlated to plant growth conditions.

Conclusions

This study indicated that the soils of the dumpsites were generally moderately polluted by PAHs, and some parts of the area were heavily polluted. Both Sedum alfredii and alfalfa absorbed PAHs from soil, and PAH concentrations in these two plants correlated to the growth conditions of the plants. Phytoremediation can effectively be used for PAH removal in open dumpsites.

     

天津表土中多环芳烃含量的空间分布特征与来源

采用聚类分析、方差分析和多重比较等统计方法,结合空间分异分析研究了天津表土中多环芳烃(PAHs)含量的多元和空间分布特征。结果表明,可根据样点PAHs含量和空间分布特征将天津地区划分为三个含量有显著差异且连续分布的区域,即南北低值区、市中心近郊次高值区和塘沽汉沽高值区。三区除PAHs含量有显著差别外,16种PAHs化合物的谱分布也有显著不同。根据不同化合物的含量关系及天津地区燃料消耗资料可以判定,南北低值区土壤中PAHs基本来自燃煤排放,而两个高值区污染来源复杂,除燃煤仍是主要来源外,其他重要来源还包括燃油和其他工业活动。     

Polycyclic Aromatic Hydrocarbons (PAHs) in the Aerosol of Higashi Hiroshima, Japan: Pollution Scenario and Source Identification

Polycyclic aromatic hydrocarbons (PAHs) are considered to be atmospheric pollutants and well-known human carcinogens. This study analyzes the pollution scenarios of PAHs in the aerosol of Higashi Hiroshima, Japan. We examined the characteristics, the influences of meteorological conditions, the distribution and seasonal variation of PAHs in aerosol samples collected from June 2000 to May 2001. The concentration of PAHs in the aerosol of Higashi Hiroshima was ranging from 11.8 to 157.5 μg/g with a mean concentration of 63.4 μg/g. Results showed that there is positive correlation between aerosol PAH concentrations and ambient temperature but a relatively little correlation with solar radiation. Seasonal variation was observed with a higher concentration during winter and lower concentration during summer. Apart from that, principal component analysis and molecular diagnostic ratios were also used to characterize and identify possible PAHs emission sources. Results obtained strongly suggested that vehicular emissions appeared to be the major source of aerosol PAHs in this study although other sources do have some degree of influence.     

Contamination of soils in the urbanized areas of Belarus with polycyclic aromatic hydrocarbons

The content of polycyclic aromatic hydrocarbons (PAHs) in the soils of urbanized areas, including the impact zones of Belarus, were studied. The concentrations of 16 PAHs in the soils were determined for individual and high-rise building zones, forests, and forest parks of Belarus. The levels of the PAH accumulation in the soils of different industrial enterprises and boiler stations were analyzed. Possible sources of soil contamination with PAHs were considered, and the structure of the PAHs in the soils was shown. The levels of the soil contamination were determined from the regulated parameters for individual compounds and the sum of 16 PAHs.     

Sediment–pore water partition of PAH source contributions to the Yellow River using two receptor models

Purpose

Understanding the fate and behavior of polycyclic aromatic hydrocarbon (PAH) sources in aquatic systems is important for the efficiency of control policies. In this work, a new approach??organic carbon-normalized sediment?Cpore water partition coefficients of PAH source contributions (logK??_Osource)??was developed to study the sediment?Cpore water partition of PAH source contributions. The focus of this study was the Yellow River, which is the second largest river in China and one of the largest rivers in the world.

Materials and methods

Sixteen priority US Environmental Protection Agency PAHs were analyzed in 14 surface sediments and 11 pore water samples. Principal component analysis?Cmultiple linear regression (PCA-MLR) and Unmix models were employed to estimate the source contributions of PAHs in sediments and pore water samples. Finally, logK??_Osource values were calculated according to the modeled source contributions of PAHs.

Results and discussion

??PAHs (sum of the 16 PAH concentrations) in 14 sediment samples and 11 pore water samples from the Yellow River were 1,415?±?726?ng?g^?1 dry weight (dw) and 123?±?57.4???g?l^?1, respectively. The source apportionment results indicate the following: (1) for sediment samples, the contributions to ??PAHs from vehicular emissions, coal combustion, and petrogenic sources were 41.07?C61.05, 38.83?C45.56, and 11.18?C14.92?%, respectively, and (2) for pore water samples, vehicular emissions were the most significant contributor (45.51?C69.39?%), followed by petrogenic sources (29.80?C34.22?%) and coal combustion (7.35?C21.59?%). Coal combustion had the highest logK??_Osource values (4.15?C4.26) among the three categories, followed by vehicular emissions (3.51?C3.57) and petrogenic sources (3.30?C3.43).

Conclusions

The possible categories of PAH sources identified by hierarchical cluster analysis, PCA-MLR, and Unmix models were consistent, indicating that vehicular emissions, coal combustion, and petrogenic sources were three important categories. The logK??_Osource values indicate that contributions from coal combustion had a higher partition for the sediment phase compared with the other two source categories.     

Comparison for plant uptake of phenanthrene and pyrene from soil and water

In this study, we evaluated (1) the plant uptake of polycyclic aromatic hydrocarbons (PAHs) from soil and water and (2) the applicability of the partition-limited model on the prediction of plant concentrations with respect to PAH contents in soils and other associated parameters. To accomplish these goals, the plant uptake of PAHs from culture solution and soils were extensively experimented. A steady state was shown for ryegrass kinetic uptake of phenanthrene and pyrene from water after about 48 h. As to the ryegrass uptake from soils, root and shoot concentrations of PAHs generally increased, while root concentration factors (RCFs) and shoot concentration factors (SCFs) tended to decrease with the increasing PAH concentrations in soils after 45 days. One note of interest is that root concentrations and RCFs of phenanthrene and pyrene for ryegrass uptake were larger than shoot concentrations and SCFs, irrespective of soil–plant and water–plant systems. However, root and shoot concentrations, or RCFs and SCFs, for ryegrass uptake from culture solution were always much higher than those for ryegrass uptake from soils at the same PAH concentrations in water or soil interstitial water, indicating that PAHs in culture solution would be more available and susceptible than those in soil interstitial water for uptake by plants. In addition, the partition-limited model showed a high level of model performance on prediction of plant uptake of phenanthrene and pyrene from soils, with the overall differences of the modeled and experimented concentrations in ryegrass roots or shoots less than 187%. This suggests that the partition-limited model might be a potentially useful instrument for vegetation-contamination assessment.     

Comparison of Fenton's Reagent and Ozone Oxidation of Polycyclic Aromatic Hydrocarbons in Aged Contaminated Soils (7 pp)

Background, Aim and Scope   Polycyclic aromatic hydrocarbons (PAHs) are formed as a result of incomplete combustion and are among the most frequently occurring contaminants in soils and sediments. PAHs are of great environmental concern due to their ubiquitous nature and toxicological properties. Consequently, extensive research has been conducted into the development of methods to remediate soils contaminated with PAHs. Fenton's reagent or ozone is the most commonly studied chemical oxidation methods. However, the majority of remediation studies use soils that have been artificially contaminated with either one or a limited number of PAH compounds in the laboratory. Hence, it is essential to extend such studies to soils contaminated with multiple PAHs under field conditions. Objectives   The objective of this study is to investigate the capacity of Fenton's reagent and ozone to degrade PAHs in soils. The soils have been collected from a number of different industrial sites and, therefore, will have been exposed to different PAH compounds in varying concentrations over a range of time periods. The capacity of Fenton's reagent and ozone to degrade PAHs in industrially contaminated soils is compared to results obtained in studies using soils artificially contaminated with PAHs in the laboratory. Materials and Methods: Nine soil samples, contaminated with PAHs, were collected from five different industrial sites in Sweden. For the Fenton's reagent procedure, the pH of the soil slurry samples was adjusted to pH 3 and they were kept at a constant temperature of 70oC whilst H2O2 was added. For the ozone procedure, soil samples were mixed with 50% water and 50% ethanol and kept at a constant temperature of 45 oC. Ozone was then continually introduced to each soil sample over a period of four hours. Following the Fenton's reagent and ozone oxidation procedures, the samples were filtered to isolate the solid phase, which was then extracted using pressurized liquid extraction (PLE). The sample extracts were cleaned up using open columns and then analysed by gas chromatography-mass spectrometry (GC-MS). Results: The relative abundance of the detected PAHs varied between soils, associated with different industries. For example, low molecular weight (LMW) PAHs were more abundant in soil samples collected from wood impregnation sites and high overall PAH degradation efficiencies were observed in soils originating from these sites. In the contaminated soils studied, PAHs were more effectively degraded using Fenton's reagent (PAH degradation efficiency of 40-86%) as opposed to ozone (PAH degradation efficiency of 10-70%). LMW PAHs were more efficiently degraded, using ozone as the oxidizing agent, whereas the use of Fenton's reagent resulted in a more even degradation pattern for PAHs with two through six fused aromatic rings. Discussion: The degradation efficiency for both methods was largely dependent on the initial PAH concentration in the soil sample, with higher degradation observed in highly polluted soils. LMW PAHs are more susceptible to degradation than high molecular weight (HMW) PAHs. As a result of this the relative abundance of large (often carcinogenic) PAHs increased after chemical oxidation treatment, particularly after ozone treatment. Repeated Fenton's reagent treatment did not result in any further degradation of soil PAHs, indicating that residual soil PAHs are strongly sorbed. The effectiveness of the two oxidation treatment approaches differed between industrial sites, thus highlighting the importance of further research into the influence of soil properties on the sorption capacity of PAHs. Conclusions: This study demonstrates that the degree to which chemical oxidation techniques can degrade soil bound PAHs chemical degradation is highly dependent on both the concentration of PAHs in the soils and the compounds present, i.e. the various PAH profiles. Therefore, similarities in the PAH degradation efficiencies in the nine soil samples studied were observed with the two chemical oxidation methods used. However, the degradation performance of Fenton's reagent and ozone differed between the two methods. Overall, Fenton's reagent achieved the highest total PAH degradation due to stronger oxidation conditions. LMW PAHs showed higher susceptibility to oxidation, whereas high molecular weight (HMW) PAHs appear to be strongly sorbed to the soils and therefore less chemically available for oxidation. This study highlights the importance of including soils collected from a range of contaminated sites in remediation studies. Such soil samples will contain PAH contaminants of varying concentrations, chemical and physical properties, and have been aged under field conditions. In addition to the chemical and physical properties of the soils, these factors will all influence the chemical availability of PAHs to oxidation. Recommendations and Perspectives: We recommend including aged contaminated soils in chemical degradation studies. In future chemical remediation work, we intend to investigate the potential influence of the chemical and physical properties of PAHs and soil parameters potential influence on the chemical oxidation efficiency in aged contaminated soils. Due to the vast number of contaminated sites there is a great need of efficient remediation methods throughout the world. This study shows the difficulties which may be experienced when applying remediation methods to a variation of contaminated sites.