Polycyclic aromatic hydrocarbons in mountain soils of the subtropical Atlantic

Surface soil samples from various altitudes on Tenerife Island, ranging from sea level up to 3400 m above mean sea level, were analyzed to study the distribution of 26 polycyclic aromatic hydrocarbons (PAHs) in a remote subtropical area. The stable atmospheric conditions in this island define three vertically stratified layers: marine boundary, trade-wind inversion, and free troposphere. Total PAH concentrations, 1.9 to 6000 microg/kg dry wt., were high when compared with those in tropical areas and in a similar range to those in temperate areas. In the marine boundary layer, fluoranthene (Fla), pyrene (Pyr), benz [a]anthracene (BaA), and chrysene (C + T) were largely dominant. The predominance of Fla over Pyr may reflect photo-oxidative processes during atmospheric transport, although coal combustion inputs cannot be excluded. The PAHs found in higher concentration in the soils from the inversion layer were benzo[b + j]fluoranthene (BbjF) + benzo[k]fluoranthene (BkF) > benzo[e]pyrene (BeP) approximately indeno[1,2, 3-cd]pyrene (Ind) > benzo[a]pyrene (BaP) approximately benzo[ghi]perylene (Bghi) > coronene (Cor) approximately dibenz[a,h]anthracene (Dib), reflecting that high temperatures and insolation prevent the accumulation of PAHs more volatile than BbjF in significant amounts. These climatic conditions involve a process of standardization that prevents the identification of specific PAH sources such as traffic, forest fires, or industrial inputs. Only soils with high total organic carbon (TOC) (e.g., 10-30%) preserve the more volatile compounds such as phenanthrene (Phe), methylphenanthrenes (MPhe), dimethylphenanthrenes (DMPhe), and retene (Ret). However, no relation between PAHs and soil TOC and black carbon (BC) was found. The specific PAH distributions of the free tropospheric region suggest a direct input from pyrolytic processes related to the volcanic emission of gases in Teide.     

Integrating biodegradation and electroosmosis for the enhanced removal of polycyclic aromatic hydrocarbons from creosote-polluted soils

This paper presents a hybrid technology of soil remediation based on the integration of biodegradation and electroosmosis. We employed soils with different texture (clay soil and loamy sand) containing a mixture of polycyclic aromatic hydrocarbons (PAH) present in creosote, and inoculation with a representative soil bacterium able to degrade fluorene, phenanthrene, fluoranthene, pyrene, anthracene, and benzo[a]pyrene. Two different modes of treatment were prospected: (i) inducing in soil the simultaneous occurrence of biodegradation and electroosmosis in the presence of a biodegradable surfactant, and (ii) treating the soils sequentially with electrokinetics and bioremediation. Losses of PAH due to simultaneous biodegradation and electroosmosis (induced by a continuous electric field) were significantly higher than in control cells that contained the surfactant but no biological activity or no current. The method was especially successful with loamy sand. For example, benzo[a]pyrene decreased its concentration by 50% after 7 d, whereas 22 and 17% of the compound had disappeared as a result of electrokinetic flushing and bioremediation alone, respectively. The use of periodical changes in polarity and current pulses increased by 16% in the removal of total PAH and in up to 30% of specific compounds, including benzo[a]pyrene. With the aim of reaching lower residual levels through bioremediation, an electrokinetic pretreatment was also evaluated as a way to mobilize the less bioaccessible fraction of PAH. Residual concentrations of total biodegradable PAH, remaining after bioremediation in soil slurries, were twofold lower in electrokinetically pretreated soils than in untreated soils. The results indicate that biodegradation and electroosmosis can be successfully integrated to promote the removal of PAH from soil.     

Polycyclic aromatic hydrocarbon storage in a typical Cerrado of the Brazilian savanna

There may be important biological sources of polycyclic aromatic hydrocarbons (PAHs) to the global environment, particularly of naphthalene, phenanthrene, and perylene, that originate in the tropics. We (i) studied the distribution of PAHs among different compartments of a typical Cerrado to locate their sources and (ii) quantified the PAH storage of this ecosystem. The sum of 20 PAH (sigma20PAHs) concentrations ranged from 25 to 666 microg kg(-1) in plant tissue, 7.4 to 32 microg kg(-1) in litterfall, 206 to 287 microg kg(-1) in organic soil, and 10 to 79 microg kg(-1) in mineral soil. Among the living biomass compartments, the bark had the highest mean PAH concentrations and coarse roots the lowest, indicating that PAHs in the plants originated mainly from aboveground sources. Naphthalene and phenanthrene were the most abundant individual PAHs, together contributing 33 to 96% to the sigma20PAHs concentrations. The total storage of the X20PAHs in Cerrado was 7.5 mg m(-2) to a 0.15-m soil depth and 49 mg m(-2) to a 2-m soil depth. If extrapolated to the entire Brazilian Cerrado region, roughly estimated storages of naphthalene and phenanthrene correspond to 7300 and 400 yr of the published annual emissions in the United Kingdom, respectively. The storage of benzo[a]pyrene, a typical marker for fossil fuel combustion, in the Cerrado only corresponds to 0.19 yr of UK emissions. These results indicate that the Brazilian savanna comprises a huge reservoir of naphthalene and phenanthrene originating most likely from the aboveground parts of the vegetation or associated organisms. Thus, the Cerrado might be a globally important source of these PAHs.     

Differential responses of eubacterial, Mycobacterium, and Sphingomonas communities in polycyclic aromatic hydrocarbon (PAH)-contaminated soil to artificially induced changes in PAH profile

Recent reports suggest that Mycobacterium is better adapted to soils containing poorly bioavailable polycyclic aromatic hydrocarbons (PAHs) compared to Sphingomonas. To study this hypothesis, artificial conditions regarding PAH profile and PAH bioavailability were induced in two PAH-contaminated soils and the response of the eubacterial, Mycobacterium, and Sphingomonas communities to these changed conditions was monitored during laboratory incubation. Soil K3663 with a relatively high proportion of high molecular weight PAHs was amended with phenanthrene or pyrene to artificially change the soil into a soil with a relatively increased bioavailable PAH contamination. Soil AndE with a relatively high proportion of bioavailable low molecular weight PAHs was treated by a single-step Tenax extraction to remove the largest part of the easily bioavailable PAH contamination. In soil K3663, the added phenanthrene or pyrene compounds were rapidly degraded, concomitant with a significant increase in the number of phenanthrene and pyrene degraders, and minor and no changes in the Mycobacterium community and Sphingomonas community, respectively. However, a transient change in the eubacterial community related to the proliferation of several gamma-proteobacteria was noted in the phenanthrene-amended soil. In the extracted AndE soil, the Sphingomonas community initially developed into a more diverse community but finally decreased in size below the detection limit. Mycobacterium in that soil never increased to a detectable size, while the eubacterial community became dominated by a gamma-proteobacterial population. The results suggest that the relative bioavailability of PAH contamination in soil affects bacterial community structure but that the behavior of Mycobacterium and Sphingomonas in soil is more complex than prospected from studies on their ecology and physiology.     

搅拌棒吸附萃取气相色谱法测定地表水中多环芳烃

建立了新型的搅拌棒吸附萃取（SBSE）和热脱附系统（TDU）结合的气相色谱（GC）测定地表水中多环芳烃的方法。考察了萃取时间、搅拌条件及萃取温度对实验的影响,对7种多环芳烃（萘、荧蒽、苯并[b]荧蒽、苯并[k]荧蒽、苯并[ghi]苝、茚并[1,2,3-cd]芘和苯并[a]芘）的加标回收率为89.17%～99.38%,相对标准偏差（RSD）为1.6%～5.6%（n=3）。通过实际样品中PAHs的分析表明,该法快速、灵敏、简单,能满足痕量分析的需求。     

Comparison of plant families in a greenhouse phytoremediation study on an aged polycyclic aromatic hydrocarbon-contaminated soil

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous, recalcitrant, and potentially carcinogenic pollutants. Plants and their associated rhizosphere microbes can promote PAH dissipation, offering an economic and ecologically attractive remediation technique. This study focused on the effects of different types of vegetation on PAH removal and on the interaction between the plants and their associated microorganisms. Aged PAH-polluted soil with a total PAH level of 753 mg kg(-1) soil dry weight was planted with 18 plant species representing eight families. The levels of 17 soil PAHs were monitored over 14 mo. The size of soil microbial populations of PAH degraders was also monitored. Planting significantly enhanced the dissipation rates of all PAHs within the first 7 mo, but this effect was not significant after 14 mo. Although the extent of removal of lower-molecular-weight PAHs was similar for planted and unplanted control soils after 14 mo, the total mass of five- and six-ring PAHs removed was significantly greater in planted soils at the 7- and 14-mo sampling points. Poaceae (grasses) were the most effective of the families tested, and perennial ryegrass was the most effective species; after 14 mo, soils planted with perennial ryegrass contained 30% of the initial total PAH concentration (compared with 51% of the initial concentrations in unplanted control soil). Although the presence of some plant species led to higher populations of PAH degraders, there was no correlation across plant species between PAH dissipation and the size of the PAH-degrading population. Research is needed to understand differences among plant families for stimulating PAH dissipation.     

Sequential supercritical fluid extraction (SSFE) for estimating the availability of high molecular weight polycyclic aromatic hydrocarbons in historically polluted soils

Sequential supercritical fluid (CO2) extraction (SSFE) was applied to eight historically contaminated soils from diverse sources with the aim to elucidate the sorption-desorption behavior of high molecular weight polycyclic aromatic hydrocarbons (PAHs). The method involved five extraction phases applying successively harsher conditions by increasing fluid temperature and density mobilizing target compounds from different soil particle sites. Two groups of soils were identified based on readily desorbing (available) PAH fractions obtained under mildest extraction conditions (e.g., readily desorbing fractions of fluoranthene and pyrene significantly varied between the soils ranging from <10 to >90%). Moreover, extraction behavior strongly correlated with molecular weight revealing decreasing available PAH fractions with increasing weight. Physicochemical soil parameters such as particle size distribution and organic dry mass were found to have no distinct effect on the sorption-desorption behavior of PAHs in the different soils. However, PAH profiles significantly correlated with readily available pollutant fractions; soils with relatively less mobile PAHs had higher proportions of five- and six-ring PAHs and vice versa. Eventually, biodegradability corresponded well with PAH recoveries under the two mildest extraction phases. However, a quantitative relationship was only established for soils with biodegradable PAHs. Out of eight soils, five showed no biodegradation including the four soils with the lowest fraction of readily desorbing PAHs. Only one soil (which was found to be highly toxic to Vibrio fischeri) did not match the overall pattern showing no PAH biodegradability but large fractions of highly mobile PAHs, concluding that mass transfer limitations may only be one of many factors governing biodegradability of PAHs.     

Phytoremediation of polycyclic aromatic hydrocarbons in manufactured gas plant-impacted soil

Contamination of soil by hazardous substances poses a significant threat to human, environmental, and ecological health. Cleanup of the contaminants using destructive, invasive technologies has proven to be expensive and more importantly, often damaging to the natural resource properties of the soil, sediment, or aquifer. Phytoremediation is defined as the cleanup of contaminated sites using plants. There has been evidence of enhanced polycyclic aromatic hydrocarbons (PAHs) degradation in rhizosphere soils for a limited number of plants. However, research focusing on the degradation of PAHs in the rhizosphere of trees is lacking. The objective of this study was to assess the potential use of trees to enhance degradation of PAHs located in manufactured gas plant-impacted soils. In greenhouse studies with intact soil cores, acenaphthene, anthracene, fluoranthene, naphthalene, and phenanthrene decreased significantly (p < 0.05) in green ash (Fraxinus pennsylvanica Marshall) and hybrid poplar (Populus deltoides x P. nigra DN 34) phytoremediation treatments when compared to the unplanted soil control. Increases in PAH microbial degraders in rhizosphere soil were observed when compared to unvegetated soil controls. In addition, the rate of degradation or biotransformation of PAHs was greatest for soils with black willow (Salix nigra Marshall), followed by poplar, ash, and the unvegetated controls. These results support the hypothesis that a variety of plants can enhance the degradation of target PAHs in soil.     

Sequential accelerated solvent extraction of polycyclic aromatic hydrocarbons with different solvents: performance and implication

Sixteen USEPA priority polycyclic aromatic hydrocarbons (PAHs) extracted by Soxhlet extraction (S-PAHs) with dichloromethane and routine accelerated solvent extraction (A-PAHs) with 1:1 toluene/methanol, respectively, were investigated in 24 soil samples from two cities in the center of the Pearl River Delta, South China. Polycyclic aromatic hydrocarbons, methylphenanthrene and perylene, in two soils, two sediments, and an immature oil shale were also sequentially extracted by accelerated solvent extraction (ASE) with each of four different organic solvents for three times. The A-PAHs' concentrations are 2.41 times the S-PAHs' concentrations. For sequential three ASEs, PAHs in the first extract account for 56 to 67% of their total concentrations in the sequential three extractions and toluene displays the best extraction performance among the four solvents. Diagnostic ratios of PAHs in Soxhlet extraction, routine ASE, and sequential ASE with each solvent for a given sample are very similar, suggesting their identical petrogenic and pyrogenic sources in the soils and sediments. But the PAH ratios for the shale have an obvious petrogenic origin. The perylene/5-ring PAH ratios indicate a diagenetic source, especially in the shale and sediments. The correlation analysis shows that A-PAHs/S-PAHs is better associated with the contents of total organic carbon (TOC) than those of black carbon (BC). The above results indicate the significant petrogenic origin of PAHs and the important effect of organic matter on their extraction and distribution in the investigated field soils/sediments.     

Polycyclic aromatic hydrocarbon release from a soil matrix in the in vitro gastrointestinal tract

Soil ingestion is an important exposure route by which immobile soil contaminants enter the human body. We assessed polycyclic aromatic hydrocarbon (PAH) release from a contaminated soil, containing 49 mg PAH kg(-1), using a SHIME (Simulator of the Human Intestinal Microbial Ecosystem) reactor comprising the stomach, duodenal, and colon compartments. Polycyclic aromatic hydrocarbon release was defined as that fraction remaining in the digest supernatant after centrifugation for 5 min at 1500 x g. The PAH release in the stomach digest was only 0.44% of the total PAH present in soil, resulting in PAH concentrations of 23 micrograms PAH L(-1) chyme. The lower PAH releases in duodenum (0.13%) and colon (0.30%) digests, compared with the stomach digest, were thought to be attributed to combined complexation and precipitation with bile salts, dissolved organic matter, or colon microbiota. We studied these complexation processes in an intestinal suspension more in depth by preparing mixtures of 9-anthracenepropionic acid, a Bacillus subtilis culture, and cholin as model compounds for PAHs, organic matter, and bile salts, respectively. Bile salts or organic matter in the aqueous phase initially enhance PAH desorption from soil. However, desorbed PAHs may form large aggregates with bile and organic matter, lowering the freely dissolved PAH fraction in the supernatant. Using the model compounds, mathematical equations were developed and validated to predict PAH complexation processes in the gastrointestinal tract. Contaminant release and subsequent complexation in the gut is an important prerequisite to intestinal absorption and thus bioavailability of that contaminant. The data from this research may help in understanding the processes to which PAHs are subjected in the gastrointestinal tract, before intestinal absorption.     

Effect of electrokinetics on the bioaccessibility of polycyclic aromatic hydrocarbons in polluted soils

Bioaccessibility is one of the most relevant aspects to be considered in the restoration of soils using biological technologies. Polycyclic aromatic hydrocarbons (PAH) usually have residual fractions that are resistant to biodegradation at the end of the biological treatment. In some situations, these residual concentrations could still be above legal standards. Here, we propose that the available knowledge about electroremediation technologies could be applied to enhance bioremediation of soils polluted with PAH. The main objective of this study was to show that a previous electrokinetic treatment could reduce the PAH residual fractions when the soil is subsequently treated by means of a bioremediation process. The approach involved the electrokinetic treatment of PAH-polluted soils at a potential drop of 0.9 to 1.1 V/cm and the subsequent estimations of bioaccessibility of residual PAHs after slurry-phase biodegradation. Bioaccessibility of PAH in two creosote-polluted soils (clay and loamy sand, total PAH content averaging 300 mg/kg) previously treated with an electric field in the presence of nonionic surfactant Brij 35 was often higher than in untreated controls. For example, total PAH content remaining in clay soil after bioremediation was only 62.65 +/- 4.26 mg/kg, whereas a 7-d electrokinetic pretreatment had, under the same conditions, a residual concentration of 29.24 +/- 1.88 mg/kg after bioremediation. Control treatments without surfactant indicated that the electrokinetic treatment increased bioaccessibility of PAHs. A different manner of electric field implementation (continuous current vs. current reversals) did not induce changes in PAH bioaccessibility. We suggest that this hybrid technology may be useful in certain bioremediation scenarios, such as soils rich in clay and black carbon, which show limited success due to bioavailability restrictions, as well as in highly heterogeneous soils.     

Degradation of polycyclic aromatic hydrocarbons by combined chemical pre-oxidation and bioremediation in creosote contaminated soil

The ability of pre-oxidation to overcome polycyclic aromatic hydrocarbons (PAH) recalcitrance to biodegradation was investigated in creosote contaminated soil. Sand and peat artificially spiked with creosote (quality WEI C) were used as model systems. Ozonation and Fenton-like treatment were proved to be feasible technologies for PAH degradation in soil. The efficiency of ozonation was strongly dependent on the water content of treated soil samples. The removal of PAH by Fenton-like treatment depended on the applied H2O2/soil weight ratio and ferrous ions addition. It was determined that the application of chemical oxidation in sand resulted in a higher PAH removal and required lower oxidant (ozone, hydrogen peroxide) doses. The enhancement of PAH biodegradability by different pre-treatment technologies also depended on the soil matrix. It was ascertained that combined chemical and biological treatment was more efficient in PAH elimination in creosote contaminated soil than either one alone. Thus, the combination of Fenton-like and the subsequent biological treatment resulted in the highest removal of PAH in creosote contaminated sand, and biodegradation with pre-ozonation was found to be the most effective technology for PAH elimination in peat.     

Removal of polycyclic aromatic hydrocarbons from aqueous solution on soybean stalk-based carbon

Soybean [ (L.) Merr.] stalk-based carbons were prepared by phosphoric acid activation at different carbonization temperatures. Characteristics of the prepared carbon, including specific surface area, iodine number, and amount of methylene blue sorption, were determined. Experiments on phenanthrene, naphthalene, and acenaphthene, as representatives of polycyclic aromatic hydrocarbons (PAHs), removal from aqueous solution by the prepared carbon were conducted at different levels of carbon addition. The results indicated that the specific surface area, iodine number, and amount of methylene blue sorption increased with an increase of carbonization temperature. The maximum values were observed at 700°C and were 287.63 m g, 508.99 mg g, and 90.14 mg g, respectively. The removal efficiencies of phenanthrene, naphthalene, and acenaphthene tended to increase with increasing carbon amounts and carbonization temperature. The optimal removal performance was obtained under the experimental conditions of carbon concentrations of 0.04 g 32 mL and carbonization temperature of 700°C, and the removal efficiencies of phenanthrene, naphthalene, and acenaphthene were 99.89, 100, and 95.64%, respectively. The performance of the prepared carbon was superior to that of commercial activated carbon. Additionally, for the same carbon concentrations, the removal efficiency of PAHs on prepared carbons followed the order: phenanthrene > naphthalene > acenaphthene. Results obtained from this work provide some insight into the reuse of an agricultural residue, and also provide a new application for the treatment of PAHs in contaminated water utilizing activated carbon prepared from agricultural residues.     

Effects of agronomic practices on phytoremediation of an aged PAH-contaminated soil

Phytoremediation offers an ecologically and economically attractive remediation technique for soils contaminated with polycyclic aromatic hydrocarbons (PAHs). In addition to the choice of plant species, agronomic practices may affect the efficiency of PAH phytoremediation. Inorganic nutrient amendments may stimulate plant and microbial growth, and clipping aboveground biomass might stimulate root turnover, which has been associated with increases in soil microbial populations. To assess the influence of fertilization and clipping on PAH dissipation in a nutrient-poor, aged PAH-contaminated soil, a 14-mo phytoremediation study was conducted using perennial ryegrass (Lolium perenne) as a model species. Six soil treatments were performed in replicate: unplanted; unplanted and fertilized; planted; planted and fertilized; planted and clipped; and planted, clipped, and fertilized. Plant growth, soil PAH concentrations, and the concentrations of total and PAH-degrading microorganisms were measured after 7 and 14 mo. Overall, planting (with nearly 80% reduction in total PAHs) and planting + clipping (76% reduction in total PAHs) were the most effective treatments for increased PAH dissipation after 14 mo. Fertilization greatly stimulated plant and total microbial growth, but negatively affected PAH dissipation (29% reduction in total PAHs). Furthermore, unplanted and fertilized soils revealed a similar negative impact (25% reduction) on PAH dissipation after 14 mo. Clipping did not directly affect PAH dissipation, but when combined with fertilization (61% reduction in total PAHs), appeared to mitigate the negative impact of fertilization on PAH dissipation. Therefore, fertilization and clipping may be included in phytoremediation design strategies, as their combined effect stimulates plant growth while not affecting PAH dissipation.     

小麦秸秆生物炭对石油烃污染土壤的修复作用

以小麦秸秆为原材料,在300℃下缺氧裂解3、6、8 h制备生物炭,比较了3种生物炭的产率、pH值、灰分以及C、H、N元素含量,表征了300℃、6 h生物炭的表面形态,并用其作为修复材料,对大港油田的石油污染土壤进行修复。结果表明,随裂解时间的延长,生物炭产率下降,pH值升高,灰分含量增加,H/C值下降,但产率、pH值、灰分和H/C值都是从3h到6h差异显著,6h到8h差异不显著。C元素含量先升高后下降。石油污染土壤经生物炭修复14 d和28 d后,总石油烃降解率分别为45.48％和46.88％,均显著高于对照组。修复14 d后土壤中的萘、苊、苯并[a]蒽、屈、苯并[b]荧蒽、苯并[k]荧蒽、苯并[a]芘、茚并[1,2,3-cd]芘也都有不同程度的下降,其中苯并[a]芘含量下降幅度达98.18％,其他几种PAH的降解率也都高于对照组,28 d后这些PAH的含量又有上升趋势。这说明小麦秸秆裂解时间对生物炭的性质有影响;300℃、6 h生物炭可以用来修复石油污染的土壤。     

Modeling the fate of benzo[a]pyrene in the wastewater-irrigated areas of Tianjin with a fugacity model

A Level III fugacity model was applied to characterize the transfer processes and environmental fate of benzo[a]pyrene in wastewater-irrigated areas of Tianjin, China. The physical-chemical properties and transfer parameters of benzo[a]pyrene were used in the model and the concentration distribution of benzo[a]pyrene in sediment, soil, water, air, fish, and crop compartments, as well as transfer fluxes across the compartments, were then derived under steady-state assumptions. The calculated results were compared with monitoring data for air, soil, water, and sediment collected from the literature. The results indicate that there was generally good agreement and the differences were within an order of magnitude for air, soil, and sediment. The concentration of benzo[a]pyrene in the ambient air in the area was very low with a majority present sorbed to aerosol. In the water compartment, approximately 70% of benzo[a]pyrene dissolved in water phase. Relatively high concentrations of the compound were found in the soil and sediment, with the soil serving as the dominant sink in the area. Benzo[a]pyrene, with a slow metabolic rate, was found to accumulate in fish in the area.     

Solubilization of mixed polycyclic aromatic hydrocarbons through a rhamnolipid biosurfactant

The solubilization of phenanthrene (PHE) and pyrene (PYR) by rhamnolipid biosurfactant was systematically investigated. The solubilities of both polycyclic aromatic hydrocarbons (PAHs) were increased linearly with the biosurfactant concentration at above critical micelle concentration. A competitive effect was observed between PHE and PYR. The solubility of PHE in a mixed system was lower than that in a single PAH system, whereas the solubility of PYR in a mixed system was enhanced. This is because the hydrophobicity of PYR is higher than that of PHE, so PYR is favored in the competitive solubilization. The combined effect of biosurfactant and dissolved organic matter (DOM) on PAH solubilization was also examined. Two kinds of DOM (derived from soil and from compost) were used. There was an obvious enhancement of solubility for PHE and PYR in systems with concurrence of DOM and biosurfacrant compared with systems with only DOM or biosurfactant; however, the enhancement in the mixed system was less than their additive. This could be explained as the formation of a DOM-biosurfactant complex. In addition, the solubility enhancement of PAHs in a compost-DOM system was higher than that in a soil-DOM system. This could be explained as functional group differences of two DOM types.     

Polycyclic aromatic hydrocarbons (PAHs) in soils of the Moscow Region--concentrations, temporal trends, and small-scale distribution

The knowledge of the environmental fate of polycyclic aromatic hydrocarbons (PAHs) is restricted to few climatic regions of the world almost excluding the Taiga. Our objectives were to (i) separate anthropogenic from background contributions to PAH concentrations and (ii) determine temporal trends in PAH concentrations during the last century including the change in distribution of PAHs in interior and exterior portions of aggregates in soils of the Moscow region. Along a southeast-bound transect from Moscow (windward in winter) and at a background location northeast of Moscow (leeward in winter), seven topsoil samples were collected in 1910-1954 and 35 in 1998-2003. We fractionated the soils in interior and exterior portions of aggregates > 10 mm and remaining soil without aggregates. The sum of 21 PAHs (sigma21PAHs) concentrations in recent bulk soil ranged from 59 to 1350 ng g(-1). The concentrations of all PAHs were lower outside than in Moscow. The range of the concentrations of the sigma21PAHs in archived soil samples (159-1280 ng g(-1)) was similar as in recent soils. In most recent and archived samples, naphthalene and phenanthrene, were most abundant. The concentrations of low-molecular-weight PAHs decreased during the last century at most sites; those of high-molecular-weight compounds increased. The sigma21PAHs concentrations were accumulated in the exterior of aggregates (109%) and depleted in the interior (95%) relative to the concentration in bulk soil (defined as 100%), which was similar to that in the soil without aggregates (99%). The differences between aggregate interior and exterior did not change during the last century. The dominance of naphthalene and phenanthrene is typical of remote regions. The urban influence on PAH concentrations in the last century was small.     

Soil-to-root transfer and translocation of polycyclic aromatic hydrocarbons by vegetables grown on industrial contaminated soils

Polycyclic aromatic hydrocarbons (PAHs) are possible contaminants in some former industrial sites, representing a potential risk to human health if these sites are converted to residential areas. This work was conducted to determine whether PAHs present in contaminated soils are transferred to edible parts of selected vegetables. Soils were sampled from a former gasworks and a private garden, exhibiting a range of PAH concentrations (4 to 53 to 172 to 1263 and 2526 mg PAHs kg-1 of dry soil), and pot experiments were conducted in a greenhouse with lettuce (Lactuca sativa L. var. Reine de Mai), potato (Solanum tuberosum L. var. Belle de Fontenay), and carrot (Daucus carota L. var. Nantaise). At harvest, above- and below ground biomass were determined and the PAH concentrations in soil were measured. In parallel, plates were placed in the greenhouse to estimate the average PAH-dust deposition. Results showed that the presence of PAHs in soils had no detrimental effect on plant growth. Polycyclic aromatic hydrocarbons were detected in all plants grown in contaminated soils. However, their concentration was low compared with the initial soil concentration, and the bioconcentration factors were low (i.e., ranging from 13.4 x 10(-4) in potato and carrot pulp to 2 x 10(-2) in potato and carrot leaves). Except in peeled potatoes, the PAH concentration in vegetables increased with the PAH concentration in soils. The PAH distribution profiles in plant tissues and in soils suggested that root uptake was the main pathway for high molecular weight PAHs. On the opposite, lower molecular weight PAHs were probably taken up from the atmosphere through the leaves as well as by roots.     

Pyrene degradation in forest humus microcosms with or without pine and its mycorrhizal fungus

The mineralization potential of forest humus and the self-cleaning potential of a boreal coniferous forest environment for polycyclic aromatic hydrocarbon (PAH) compounds was studied using a model ecosystem of acid forest humus (pH = 3.6) and pyrene as the model compound. The matrix was natural humus or humus mixed with oil-polluted soil in the presence and absence of Scots pine (Pinus sylvestris L.) and its mycorrhizal fungus (Paxillus involutus). The rates of pyrene mineralization in the microcosms with humus implants (without pine) were initially insignificant but increased from Day 64 onward to 47 microg kg(-1) d(-1) and further to 144 microg kg(-1) d(-1) after Day 105. In the pine-planted humus microcosms the rate of mineralization also increased, reaching 28 microg kg(-1) d(-1) after Day 105. The 14CO2 emission was already considerable in nonplanted microcosms containing oily soil at Day 21 and the pyrene mineralization continued throughout the study. The pyrene was converted to CO2 at rates of 0.07 and 0.6 microg kg(-1) d(-1) in the oily-soil implanted microcosms with and without pine, respectively. When the probable assimilation of 14CO2 by the pine and ground vegetation was taken into account the most efficient microcosm mineralized 20% of the 91.2 mg kg(-1) pyrene in 180 d. The presence of pine and its mycorrhizal fungus had no statistically significant effect on mineralization yields. The rates of pyrene mineralization observed in this study for forest humus exceeded the total annual deposition rate of PAHs in southern Finland. This indicates that accumulation in forest soil is not to be expected.