Comparison of microbial pyrene and benzo[a]pyrene mineralization in liquid medium, soil slurry, and soil

The microbial degradation of 14C-pyrene and 14C-benzo[a]pyrene by a bacterial mixed culture was studied within a mixture of the PAHs phenanthrene, anthracene, pyrene, fluoranthene, and benzo[a]pyrene as sole carbon source in the different culture systems: (i) liquid medium, (ii) soil slurry (surface and grinding influence), and (iii) soil. The fate of these two labeled compounds was followed in these systems with an emphasis on mineralization to carbon dioxide, extractability, and adsorption to humic materials and formation of unextractable residual. Mineralization showed the most obvious differences: soil slurries achieved the best results both concerning the extent of mineralization and the time required. The highest extent of pyrene mineralization (54% within 21 days) was observed in soil slurries; in liquid media, pyrene mineralization was slower, but reached approximately the same extent (54% in 150 days); in soils, mineralization reached only 36% of added pyrene after 160 days. Benzo[a]pyrene was mineralized in a mixture of PAHs in soil slurries to an extent of 34% within 70 days, whereas mineralization in liquid medium and soil occurred in the range of 5% (70 days). Mineralization of benzo[a]pyrene in sand slurries was lower compared to soil slurries (19% in sand slurries vs. 32% in soil slurries within 50 days).     

一株多环芳烃降解菌的筛选及其降解特性

微生物修复是治理土壤多环芳烃(polycyclic aromatic hydrocarbons, PAHs)污染的主要方法,而高效降解菌筛选是微生物修复技术的重要基础。从北京焦化厂土壤中筛选分离得到一株PAHs降解菌Q3,通过生理生化和16S rDNA等分析手段鉴定其为Rhodococcus rhodochrous。结果表明：该菌株对芘的耐受能力较强,可降解初始浓度为200 mg·L⁻¹的芘;该菌株具有降解广谱性,可利用苯并[a]芘、苯并[b]荧蒽、二苯并[a,h]蒽、苯并[g,h,i]苝等9种PAHs为唯一碳源进行代谢,特别是对苯并[a]芘等高环PAHs具有较好的降解效果;此外,该菌株可有效降解模拟液中的混合PAHs,并且对野外被PAHs长期污染的土壤具有较好的强化修复效果。投加菌株处理后的处理组与对照组相比,土壤PAHs总去除率提高了24%。以上结果表明该菌株对环境中被PAHs污染的土壤具有较好的强化修复潜力,可为PAHs污染土壤的微生物修复技术提供技术参考。     

Soil mobility of surface applied polyaromatic hydrocarbons in response to simulated rainfall

Polyaromatic hydrocarbons (PAHs) are emitted from a variety of sources and can accumulate on and within surface soil layers. To investigate the level of potential risk posed by surface contaminated soils, vertical soil column experiments were conducted to assess the mobility, when leached with simulated rainwater, of six selected PAHs (naphthalene, phenanthrene, fluoranthene, pyrene, benzo(e)pyrene and benzo(ghi)perylene) with contrasting hydrophobic characteristics and molecular weights/sizes. The only PAH found in the leachate within the experimental period of 26 days was naphthalene. The lack of migration of the other applied PAHs was consistent with their low mobilities within the soil columns which generally paralleled their log K _oc values. Thus, only 2.3 % of fluoranthene, 1.8 % of pyrene, 0.2 % of benzo(e)pyrene and 0.4 % of benzo(ghi)perylene were translocated below the surface layer. The PAH distributions in the soil columns followed decreasing power relationships with 90 % reductions in the starting levels being shown to occur within a maximum average depth of 0.94 cm compared to an average starting depth of 0.5 cm. A simple predictive model identifies the extensive time periods, in excess of 10 years, required to mobilise 50 % of the benzo(e)pyrene and benzo(ghi)perylene from the surface soil layer. Although this reduces to between 2 and 7 years for fluoranthene and pyrene, it is concluded that the possibility of surface-applied PAHs reaching and contaminating a groundwater aquifer is unlikely.     

Treatment of PAHs in contaminated soil by extraction with aqueous DNA followed by biodegradation with a pure culture of Sphingomonas sp

The biodegradation of polycyclic aromatic hydrocarbons (PAHs) in aqueous deoxyribonucleic acid (DNA) solution from contaminated soil washing was investigated. Initial data with a model effluent consisting of anthracene, phenanthrene, pyrene and benzo[a]pyrene that were individually dissolved in 1% aqueous DNA solution confirmed their positive degradation by Sphingomonas sp. at around 10(8)CFU mL(-1) initial cell loading. For anthracene and phenanthrene, complete removal was achieved within 1h treatment. Degradation of pyrene and benzo[a]pyrene took a relatively longer time of a few days and weeks, respectively. DNA-dissolved PAHs were also degraded relatively faster than PAH crystals in aqueous medium to suggest that the binding of the PAHs in the polymer does not pose serious constraint to bacterial uptake. The DNA was stable against the PAH-degrading bacteria. Parallel experiments with actual DNA solutions obtained during pyrene extraction from an artificially spiked soil also showed similar results. Close to 100% pyrene degradation was achieved after 1d treatment. With its chemical stability, the cell-treated DNA was re-used up to four cycles without a considerable decline in extraction performance.     

A two-stage process using electrokinetic remediation and electrochemical degradation for treating benzo[a]pyrene spiked kaolin

An innovative process that combines soil electrokinetic remediation and liquid electrochemical oxidation for the degradation of organic compounds present in a polluted soil was developed and evaluated by using benzo[a]pyrene spiked kaolin. In order to increase benzo[a]pyrene solubility during electrokinetic treatment, the addition of a co-solvent or surfactant, such as ethanol or Brij 35, as flushing solution was tested. The research carried out demonstrated the influence of the desorption agent employed on benzo[a]pyrene remediation from the kaolin matrix. Thus, if the flushing solution was ethanol at 40%, there was no presence of contaminant in either chamber. On the contrary, when a solution of surfactant Brij 35 was used, benzo[a]pyrene was transported towards the cathode chamber, where it was collected. Moreover, the extent of this recovery depends on the pH profile on the soil. When no pH control was used, around 17% of initial contaminant was detected in the cathode chamber; however, when pH control was applied, the recovery of benzo[a]pyrene could be higher than 76%, when the pH control in the anode chamber was set at 7.0.In order to obtain the total degradation of mobilised benzo[a]pyrene from the contaminated soil, the liquid collected by electrokinetic remediation was oxidised by electrochemical treatment. This oxidation was accomplished via an electrochemical cell with a working volume of 0.4 L, and graphite as electrode material. The benzo[a]pyrene was almost totally degraded in 1 d, reaching a degradation of about 73% in 16 h.     

Occurrence and assessment of polycyclic aromatic hydrocarbons in soils from vegetable fields of the Pearl River Delta, South China

Surface soil (0-20 cm) samples from nine representative vegetable fields located in Guangzhou, Shenzhen, Zengcheng and Huadu within the Pearl River Delta, South China were collected and analyzed for 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs) using gas chromatography coupled to mass spectrometry (GC-MS). Total concentrations of 16 PAHs (Sigma(PAHs)) ranged from 160 to 3700 microg kg(-1). Large variations were observed also between concentrations of individual PAHs from different vegetable fields and within the site as well. Acenapthylene, benzo[b]fluoranthene, fluoranthene, benzo[a]pyrene and benzo[k]fluoranthene were consistently the most prevalent individual PAHs. The values of PAH isomer ratios [anthracene/(anthracene+phenanthrene) and fluoranthene/(fluoranthene+pyrene)] indicate that combustion processes are the major sources of PAHs. Concentrations of PAHs were poorly correlated with organic carbon concentrations of soils, suggesting different sources and also indicating that the PAH pollution of this area is recent. The same outcome is confirmed by the predominance of PAHs with fewer rings (相似文献   

Rapid quantification of polycyclic aromatic hydrocarbons in hydroxypropyl-beta-cyclodextrin (HPCD) soil extracts by synchronous fluorescence spectroscopy (SFS)

Synchronous fluorescence spectroscopy (SFS) was directly applied to rapidly quantify selected polycyclic aromatic hydrocarbons (PAHs: benzo[a]pyrene and pyrene) in aqueous hydroxypropyl-beta-cyclodextrin (HPCD) soil extract solutions from a variety of aged contaminated soils containing four different PAHs. The method was optimized and validated. The results show that SFS can be used to analyse benzo[a]pyrene and pyrene in HPCD based soil extracts with high sensitivity and selectivity. The linear calibration ranges were 4.0x10(-6)-1.0x10(-3)mM for benzo[a]pyrene and 6.0x10(-6)-1.2x10(-3)mM for pyrene in 10mM HPCD aqueous solution alone. The detection limits according to the error propagation theory for benzo[a]pyrene and pyrene were 3.9x10(-6) and 5.4x10(-6)mM, respectively. A good agreement between SFS and HPLC was reached for both determinations of PAHs in HPCD alone and in soil HPCD extracts. Hence, SFS is a potential means to simplify the present non-exhaustive hydroxypropyl-beta-cyclodextrin (HPCD)-based extraction technique for the evaluation of PAH bioavailability in soil.     

采油废水中多环芳烃的生态风险评价

先利用C-18固相萃取小柱富集大港油田港东联合处理站污水处理站的采油废水中16种多环芳烃(PAHs,即萘、苊烯、苊、芴、菲、蒽、荧蒽、芘、、苯并[a]蒽、苯并[b]荧蒽、苯并[k]荧蒽、苯并[a]芘、茚并[1,2,3-cd]芘、二苯并[a,h]蒽和苯并[g,h,i]苝),再用气相色谱/质谱(GC/MS)分析测定其浓度,以评价PAHs的去除率和生态风险。结果表明:(1)采油废水经处理后,COD、石油类去除率分别达到82.27%、91.06%;外排水COD、石油类达到《污水综合排放标准》(GB 8978—1996)一级标准要求,优于中国采油废水处理的一般水平。(2)采油废水主要以2、3环的PAHs为主,约占总量的93%以上。(3)苯并[a]芘超过《地表水环境质量标准》(GB 3838—2002)中限值。(4)处理前的采油废水中蒽、菲和苯并[a]芘具有一定的生态风险;处理后的外排水中萘、蒽、菲、荧蒽、苯并[a]芘的暴露浓度(PEC)/预测无效应浓度(PNEC)均小于1,目前尚未对环境造成威胁。但是8种PAHs(苊烯和苯并类PAHs除外)总和表现出较大的毒性,需要引起重视。     

Eisenia fetida increased removal of polycyclic aromatic hydrocarbons from soil

The removal of phenanthrene, anthracene and benzo(a)pyrene added at three different concentrations was investigated with or without earthworms (Eisenia fetida) within 11 weeks. Average anthracene removal by the autochthonous micro-organisms was 23%, 77% for phenanthrene and 13% for benzo(a)pyrene, while it was 51% for anthracene, 47% for benzo(a)pyrene and 100% for phenanthrene in soil with earthworms. At 50 and 100mg phenanthrene kg(-1)E. fetida survival was 91% and 83%, but at 150 mg kg(-1) all died within 15 days. Survival of E. fetida in soil amended with anthracene < or = 1000 mg kg(-1) and benzo(a)pyrene < or = 150 mg kg(-1) was higher than 80% and without weight loss compared to the untreated soil. Only small amounts of PAHs were detected in the earthworms. It was concluded that E. fetida has the potential to remove large amounts of PAHs from soil, but more work is necessary to elucidate the mechanisms involved.     

Bioaccumulation of cyclopenta[cd]pyrene and benzo[ghi]fluoranthene by mussels transplanted in a coastal lagoon

The bioaccumulation of two isomeric non-alternant non-priority polycyclic aromatic hydrocarbons (PAHs), namely cyclopenta[cd]pyrene and benzo[ghi]fluoranthene, was investigated in caged mussels (Mytilus galloprovincialis) exposed for 30 days in three sites of a coastal lagoon (Pialassa Baiona, Ravenna, Italy) contaminated by pyrogenic PAHs. The concentration of cyclopenta[cd]pyrene and benzo[ghi]fluoranthene increased from undetectable levels in reference mussels withdrawn from the Adriatic sea to 10-30 ng g(-1) dry weight in transplanted mussels. Other contaminants bioaccumulated by caged mussels included pyrene, fluoranthene and mercury. Whilst the isomer concentration ratio pyrene/fluoranthene in biota was comparable to that observed in sediments, the cyclopenta[cd]pyrene/benzo[ghi]fluoranthene ratio was much lower in mussels than in sediments. The lower sediment biota accumulation factor of cyclopenta[cd]pyrene with respect to that of benzo[ghi]fluoranthene was tentatively attributed to the greater biological activity of the former compound, which contains a reactive olefinic bond in the cyclopenta fused ring moiety. Given the higher mutagenic activity of cyclopenta[cd]pyrene with respect to other priority PAHs, its bioaccumulation from contaminated sediments may rise considerably the overall toxicity of PAH residues in exposed biota.     

Studies on polycyclic aromatic hydrocarbons in two sediment cores from the huaxi reservoir,china: Assessment of levels,sources, and ecological risk

This study investigated the levels, sources and ecological risks of 16 polycyclic aromatic hydrocarbons (PAHs) in two sediment cores that were collected along the Huaxi Reservoir. The spatial distributions and residue levels of the 16 priority PAHs in the sediments from the Huaxi Reservoir were analyzed for their potential ecological risk, source apportionment and contribution to the total PAH residue. The concentration level of the total PAHs (TPAHs) was in the range 1805 ng·g^?1 to 20023 ng·g^?1 based on dry weight, and the content of PAHs in the Huaxi Reservoir exhibited a gradual upward trend. The PAH congener ratios fluoranthene/(fluoranthene + pyrene) and indeno[1, 2, 3-cd]pyrene/(indeno[1, 2, 3-cd]pyrene + benzo[g, h, i]perylene) were used to identify the source. The main source of the low molecular weight PAHs was wood and coal combustion, whereas the high molecular weight PAHs were primarily from petroleum combustion sources. The results of an ecological risk assessment demonstrated that ACE poses a potential ecological risk, while FLU, NAP, ANT, BaP, DBA, PHEN and PYR can have serious ecological risks.     

The temporal variability of the profile of carcinogenic polycyclic aromatic hydrocarbons in urban air: a study in a medium traffic area in Rome, 1993–1998

The constancy, both temporal and spatial, of the profile of polycyclic aromatic hydrocarbons (PAHs) relative to benzo[a]pyrene (BaP) is a prerequisite to using the BaP-indicator approach in the carcinogenic risk assessment for PAHs. The principal aim of this study was to provide a contribution to validate this approach, by studying the variability of the profile at a typical urban site through a multi-year data set and by comparing the profiles available for different cities. Seven carcinogenic PAHs (benz[a]anthracene, benzo[b+j+k]fluoranthenes, BaP, indeno[1,2,3-cd]pyrene, dibenz[a,h]anthracene) were determined in PM₁₀ 24-h samples collected every third day at a road site; moreover, benzo[e]pyrene was determined as a reference PAH due to its stability. The profile was found stable from year to year. Besides, it was similar to those recently found in other European cities (observed differences within a factor of four) and to those elaborated from earlier (1970s–1980s) investigations. The substantial similarity of profiles, both temporal (on an annual basis) and spatial, supports the validity of the BaP-indicator approach. Large PAH-to-PAH differences were, however, found in the seasonal pattern of profile: they were explained by the different atmospheric degradability of PAHs, whose effect is enhanced under the meteoclimatic conditions typical of the European Mediterranean countries. PAH annual means showed a slight declining trend since 1994. In the last sampling year, mean concentration of BaP was 1.2 ng m⁻³. Within-year differences among monthly averaged PAH concentrations were observed, as large as up to 44-fold for BaP, underlining the need for whole-year monitoring.     

Leaves of Quercus ilex L. as biomonitors of PAHs in the air of Naples (Italy)

Polycyclic aromatic hydrocarbons (PAHs) were determined by the GC-MS chromatography in the leaves of Quercus ilex L., an evergreen Mediterranean oak, to monitor the degree of pollution in the urban area of Naples compared to remote areas. Leaf samples were collected in July 1998 from four urban parks, six roadsides and two sites in remote areas. The total PAH contents in Q. ilex leaves ranged from 106.6 in a control site to 4607.5 ng/g d.w. along a road with a high traffic flow. The mean concentration factors (urban/control) were 3.8 for the parks and 15 for the roads. The contribution of carcinogenic PAHs (benz[a]anthracene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenz[a,h]anthracene, indeno[1,2,3-c,d]pyrene) was higher in urban area and differed according to the site, ranging from 6.7% to 21.3%. The total PAH burden in control sites was dominated by the low molecular weight PAHs, whilst along the urban roads fluoranthene, pyrene and benz[a]anthracene among the measured PAHs showed the highest values. PAHs were positively correlated (P<0.01) to trace metals measured in a previous study.     

Contamination of polycyclic aromatic hydrocarbons (PAHs) in microlayer and subsurface waters along Alexandria coast,Egypt

The residues of seven polycyclic aromatic hydrocarbons (PAHs) pollutants in microlayer and subsurface seawater samples collected from Alexandria coast, Egypt, were analyzed by gas chromatography–electron-impact mass spectrometry-selected ion monitoring mode (GC–MS-SIM). The pollutants studied were, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, chrysene and benzo[a]pyrene. Total PAH levels in microlayer ranged from 103 to 523 ng/l, while it ranged in subsurface samples from 13 to 120 ng/l. The Western Harbor location recorded the highest level of PAHs pollutant over all the other location for both subsurface and microlayer waters. The two major PAHs in microlayer water at the Western Harbor were fluorene and phenanthrene, making up 27% and 20% of the total PAHs, while the two major PAHs in subsurface water at the Eastern Harbor were phenanthrene and fluoranthene recording up 21% each of the total PAHs. The total PAH levels were generally in the nano-gram per liter for microlayer and subsurface seawater samples. The dominant PAHs in both subsurface and microlayer samples were fluoranthene, pyrene and benzo[a]pyrene. The microlayer enrichment factor at Alexandria’s Mediterranean coast was ranged from 29 for fluorene to 3 for phenanthrene and benzo[a]pyrene which showed PAHs concentration in the microlayer with an average of five times more than the total PAH in the subsurface samples.     

Distribution characteristics of polycyclic aromatic hydrocarbons with particle size in urban aerosols at the roadside in Ho Chi Minh City,Vietnam

The purpose of this study was to characterize size distributions of atmospheric polycyclic aromatic hydrocarbons (PAHs) with 4–6 rings at the roadside in Ho Chi Minh City, Vietnam. Ten PAHs (fluoranthene, pyrene, triphenylene, benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, benzo[ghi]perylene and indeno[1,2,3-cd]pyrene) in atmospheric particulate matters (PM) at the roadside were measured in the dry and rainy seasons in 2005 at Ho Chi Minh City, using a low-pressure cascade impactor. The PM were separated into nine fractions by their aerodynamic diameter, i.e. >9.0, 9.0–5.8, 5.8–4.7, 4.7–3.3, 3.3–2.1, 2.1–1.1, 1.1–0.7, 0.7–0.4 and <0.4 μm (a final filter). PAHs were analyzed by high-performance liquid chromatography with fluorescence detection. Total PAHs measured were higher in the rainy season than in the dry season. The mass of coarse particles occupied a higher fraction than that of fine particles in both seasons. Total PAHs were mainly concentrated in particles with aerodynamic diameter smaller than 0.4 μm. The particle size distributions of PAHs investigated were bi-modal with a peak in fine particle mode (<2.1 μm) and another peak in coarse particle mode (>2.1 μm). Generally, 5,6-ring PAHs associated mainly with fine particles and 4-ring PAHs spread out in both fine and coarse particles.     

Benzo[a]pyrene degradation by Sphingomonas yanoikuyae JAR02

Batch experiments were conducted to characterize the degradation of benzo[a]pyrene, a representative high molecular weight (HMW) polycyclic aromatic hydrocarbon (PAH), by Sphingomonas yanoikuyae JAR02. Concentrations up to the solubility limit (1.2 microg l(-1)) of benzo[a]pyrene were completely removed from solution within 20 h when the bacterium was grown on salicylate. Additional experiments with [(14)C]7-benzo[a]pyrene demonstrated 3.8% mineralization over 7 days when salicylate was present is solution, and one major radio-labeled metabolite was observed that accounted for approximately 10% of the initial radio-label. Further characterization of the radio-labeled metabolite using HPLC/MS and HPLC/MS/MS identified radio-labeled pyrene-8-hydroxy-7-carboxylic acid and unlabeled pyrene-7-hydroxy-8-carboxylic acid as novel ring-cleavage metabolites, and a benzo[a]pyrene degradation pathway was proposed. Results indicate that biostimulation of HMW PAH degradation by salicylate, a water-soluble, non-toxic substrate, has significant potential for in situ bioremediation.     

Characterization and concentrations of polycyclic aromatic hydrocarbons in emissions from different heating systems in Damascus,Syria

Traffic has long been recognized as the major contributor to polycyclic aromatic hydrocarbon (PAH) emissions to the urban atmosphere. Stationary combustion sources, including residential space heating systems, are also a major contributor to PAH emissions. The aim of this study was to determine the profile and concentration of PAHs in stack flue gas emissions from different kinds of space heaters in order to increase the understanding of the scale of the PAH pollution problem caused by this source. This study set out to first assess the characteristics of PAHs and their corresponding benzo[a]pyrene equivalent emissions from a few types of domestic heaters and central heating systems to the urban atmosphere. The study, enabled for the first time, the characterization of PAHs in stationary combustion sources in the city of Damascus, Syria. Nine different types of heating systems were selected with respect to age, design, and type of fuel burned. The concentrations of 15 individual PAH compounds in the stack flue gas were determined in the extracts of the collected samples using high-performance liquid chromatography system (HPLC) equipped with ultraviolet–visible and fluorescence detectors. In general, older domestic wood stoves caused considerably higher PAH emissions than modern domestic heaters burning diesel oil. The average concentration of ΣPAH (sum of 15 compounds) in emissions from all types of studied heating systems ranged between 43?±?0.4 and 316?±?1.4 μg/m³. Values of total benzo[a]pyrene equivalent ranged between 0.61 and 15.41 μg/m³.     

The effect of ryegrass (Lolium perenne) on decrease of PAH content in long term contaminated soil

The biodegradation of polycyclic aromatic hydrocarbons in microecosystems containing long-term contaminated soil was investigated. Soil was contaminated by different chemicals, including PAHs since World War II. Aging of the soil was expected to act as a principal factor limiting biodegradation. Half of the microecosystems contained ryegrass (Lolium perenne) and long-term selected natural soil microflora originally present in contaminated soil. The others contained contaminated soil with natural microflora only. Half of the microecosystems in each parallel experiment was fertilised with N-P-K fertiliser. Cultivation was carried out at 12 and 18 months in a greenhouse with a natural photoperiod and the ability to degrade 15 chosen PAH was investigated. For analysis, the soil from each pot was divided into three horizontal layers for mutual comparison among layers and each layer was further divided into four equal samples. Soil extracts were analysed using HPLC. After a one-year-cultivation period the content of the monitored PAHs declined to 50%. Mostly, there were no significant differences between the microecosystems. Best degraded were fluoranthene and pyrene, which were the major contaminants present in original soil. Also, other compounds were successfully degraded, even benzo[a]pyrene and benzo[ghi]perylene. Dibenz[a,h]anthracene and indeno[1,2,3-cd]pyrene were the only PAHs, examined that showed no significant degradation. Although some differences between the soil layers were detected, no conclusive trends could be found. However, significantly lower concentrations of PAHs were determined mostly in the bottom layer of the analysed profiles. In vegetated microecosystems the decline of PAHs concentrations was more remarkable after 18 months cultivation.     

Contents and sources of polycyclic aromatic hydrocarbons and organochlorine pesticides in vegetable soils of Guangzhou, China

We investigated contents, distribution and possible sources of PAHs and organochlorine pesticides (Ops) in 43 surface and subsurface soils around the urban Guangzhou where variable kinds of vegetables are grown. The results indicate that the contents of PAHs (16 US EPA priority PAHs) range from 42 to 3077 microg/kg and the pollution extent is classified as a moderate level in comparison with other investigations and soil quality standards. The ratios of methylphenanthrenes to phenanthrene(MP/P), anthracene to anthracene plus phenanthrene (An/178), benz[a]anthracene to benz[a]anthracene plus chrysene (BaA/228), indeno[1,2,3-cd]pyrene to indeno[1,2,3-cd]pyrene plus benzo[ghi]perylene (In/In+BP) suggest that the sources of PAHs in the soil samples are mixed with a dominant contribution from petroleum and combustion of fossil fuel. The correlation analysis shows that the PAHs contents are significantly related to total organic carbon contents (TOC) (R2=0.75) and black carbon contents (BC) (R2=0.62) in the soil samples. Dichlorodiphenyltrichloroethane and metabolites (DDTs) and hexachlorocyclohexanes and metabolites (HCHs) account largely for the contaminants of OPs. The concentrations of DDTs range from 3.58 to 831 microg/kg and the ratios for DDT/(DDD+DDE) are higher than 2 in some soil samples, suggesting that DDT contamination still exists and may be caused by its persistence in soils and/or impurity in the pesticide dicofol. The concentrations of HCHs are 0.19-42.3 microg/kg.     

Dynamics of PAH deposition, cycling and storage in a mixed-deciduous (Quercus-Fraxinus) woodland ecosystem

Estimates of standing biomass and fluxes of biomass in a mixed-deciduous woodland were derived, and used with results for concentrations of seven polycyclic aromatic hydrocarbons (PAHs) in different compartments of the woodland system to quantitatively assess some of the key fluxes and burdens of PAHs in this complex system. We quantified PAH burdens in air, in leaves of three deciduous tree species, in leaf litter and in soil, and uptake of PAHs by the tree leaves; PAH fluxes in litterfall, and deposition to the litter layer on the woodland floor during winter were calculated from these data. Air burdens exhibited marked seasonal variations for all compounds, with lowest values in summer when combustion-related emissions were low. Leaves did not accumulate large burdens of PAHs while on the trees and consequently, litterfall-associated fluxes of PAHs were small, representing only a fraction of the burdens in the litter layer to which they were deposited. Higher PAH burdens in air in winter, combined with the organic-matter-rich nature of the litter layer, are thought to be responsible for fluxes of PAHs to the litter layer in winter being 20-170 times the peak litterfall fluxes. The soil compartment was calculated to contain 25 years' worth of deposition of benzo[ghi]perylene, the most recalcitrant PAH in this study. Storage quotients for fluoranthene, pyrene, benzo[k]fluoranthene and benzo[a]pyrene burdens in soil represented 7-10 years' worth of deposition, while fluorene and phenanthrene storage in soil approached unity with inputs (1 and 3 years' worth of deposition, respectively). The relative importance of storage and loss processes was therefore closely related to the physico-chemical properties of the PAH, and is discussed in relation to the cycling of carbon in the woodland.