Biodegradation, bioaccessibility, and genotoxicity of diffuse polycyclic aromatic hydrocarbon (PAH) pollution at a motorway site

Diffuse pollution of surface soil with polycyclic aromatic hydrocarbons (PAHs) is problematic in terms of the large areas and volumes of polluted soil. The levels and effects of diffuse PAH pollution at a motorway site were investigated. Surface soil was sampled with increasing distance from the asphalt pavement and tested for total amounts of PAHs, amounts of bioaccessible PAHs, total bacterial populations, PAH degrader populations, the potential for mineralization of 14C-PAHs, and mutagenicity. Elevated PAH concentrations were found in the samples taken 1-8 m from the pavement. Soil sampled at greater distances (12-24 m) contained only background levels of PAHs. The total bacterial populations (CFU and numbers of 16S rDNA genes) were similar for all soil samples, whereas the microbial degrader populations (culturable PAH degraders and numbers of PAH dioxygenase genes) were most abundant in the most polluted samples close to the pavement. Hydroxypropyl-beta-cyclodextrin extraction of soil PAHs, as a direct estimate of the bioaccessibility, indicated that only 1-5% of the PAHs were accessible to soil bacteria. This low bioaccessibility is suggested to be due to sorption to traffic soot particles. The increased PAH level close to the pavement was reflected in slightly increased mutagenic activity (1 m, 0.32 +/- 0.08 revertants g(-1) soil; background/ 24 m: 0.08 +/- 0.04), determined by the Salmonella/ microsome assay of total extractable PAHs activated by liver enzymes. The potential for lighter molecular weight PAH degradation in combination with low bioaccessibility of heavier PAHs is proposed to lead to a likely increase in concentration of heavier PAHs over time. These residues are, however, likely to be of low biological significance.     

Desorption kinetics for field-aged polycyclic aromatic hydrocarbons from sediments

This study considers desorption kinetics for 12 field-aged polycyclic aromatic hydrocarbons (PAHs) desorbing from size- and density-fractionated sediments collected from two locations in the New York/New Jersey Harbor Estuary. Desorption kinetics for PAHs with a log octanol-water partition coefficient greater than 6 were well-described by a one-domain diffusion model that assumes that PAHs are initially uniformly distributed throughout spherical sediment aggregates. PAH hydrophobicity and sediment specific surface area were the parameters most strongly correlated with the magnitude of the observed diffusivity for the one-domain model. For less hydrophobic PAHs, a two-domain desorption model was used also, and the results suggest that a substantial fraction of these field-aged PAHs desorb via a relatively fast macro-mesopore diffusion mechanism. The model-predicted fraction of PAHs in the fast-diffusion regime by compound and sediment was highly correlated with the measured percent PAH desorption in 24 h. The fast-domain diffusivity was 100 times greater than the slow-domain diffusivity, was correlated with both PAH properties and sediment physical and chemical properties, and could be estimated by readily obtainable physical and chemical parameters. In contrast, the slow-domain diffusivity was not significantly correlated with PAH properties. Our results suggest that macro-mesopore diffusion may control mass transport of less-hydrophobic PAHs in estuarine sediments.     

Partitioning, extractability, and formation of nonextractable PAH residues in soil. 1. Compound differences in aging and sequestration

This study was carried out to assess the influence of physicochemical properties on PAH sequestration in sterile sewage sludge-amended arable soil. Radiolabeled phenanthrene (14C-9-Phe), pyrene (14C-4,5,9,10-Pyr), and benzo[a]pyrene (14C-7-B[a]P) were spiked and aged for up to 525 days in sterile soil microcosms. The degree of compound sequestration at various sampling times was determined by their extractability with organic solvents and release from soil residues by base saponification extraction. The amount of PAH extractable by butanol and dichloromethane decreased with compound aging in the soil. The decrease in PAH extractability with aging, and the formation of nonextractable bound residues, increased with compound molecular weight, KOW and KOC. The amount of total extractable PAH determined by sequential dichloromethane soxtec and methanolic saponification extraction decreased from 98%, 97%, and 94% at day 10 to 95%, 91%, and 77%, respectively for 14C-9-Phe, 14C-4,5,9,10-Pyr, and 14C-7-B[a]P after 525 days aging. During the same aging period there was an increase in the amount of PAH released from the soil by base saponification extraction, suggesting a progressive diffusion of PAHs into hydrolyzable and recalcitrant organic matter and mineral phases of soil. Calculated half-lives for the apparent loss of PAHs by sequestration in this experiment were dependent on the method used to extract them from soil. These half-lives ranged from 96 to 1,789 days depending on the compound, and are in agreement with values obtained from previous spiking experiments using nonsterile soils. These results suggest that a considerable fraction of PAHs assumed degraded in previous studies may have been sequestered within the organic carbon and, to a lesser extent, mineral phases of soil.     

Particle-scale investigation of PAH desorption kinetics and thermodynamics from sediment

Dredged sediment from Milwaukee Harbor showed two primary classes of particles in the <2 mm size range: a lighter-density coal- and wood-derived fraction with 62% of total PAHs and a heavier-density sand, silt, and clay fraction containing the remaining 38% of the PAHs. Room-temperature PAH desorption kinetic studies on separated sediment fractions revealed slow desorption rates for the coal-derived particles and fast desorption rates for the clay/silt particles. The effect of temperature on PAH release was measured by thermal program desorption mass spectrometry to investigate the desorption activation energies for PAHs on the different sediment particles. Three activated diffusion-based models and an activated first-order rate model were used to describe the thermal desorption of PAHs for four molecular weight classes. PAH binding with the coal-derived particles was associated with high activation energies, typically in the range of 115-139 kJ/mol. PAHs bound to the clay/silt material had much lower activation energy, i.e., in the range of 37-41 kJ/ mol for molecular weight 202. Among the desorption models tested, a spherical diffusion model with PAHs located like a rind on the outer 1-3 microm region best described the PAH thermal desorption response for coal-derived particles. This internal PAH distribution pattern on coalderived particles is based on prior direct measurement of PAH locations at the subparticle scale. These studies reveal that heterogeneous particle types in sediment exhibit much different amounts and binding of PAHs. PAHs associated with coal-derived particles aged over several decades in the field appear to be far from reaching an equilibrium sorption state due to the extremely slow diffusivities through the polymer-like coal matrix. These results provide an improved mechanistic perspective for the understanding of PAH mobility and bioavailability in sediments.     

Lowering of concentration of polycyclic aromatic hydrocarbons in liquid media by sorption into polyethylene terephtalate—a model study

Rapeseed oil and water were spiked with polycyclic aromatic hydrocarbon (PAH) solutions at the total levels of 955.1 and 711.4 g kg^–1, respectively, filled into polyethylene terephtalate (PET) cylindrical receptacles and the PAH concentrations in both liquid media followed for more than 90 h by HPLC. During this time, the PAH concentrations decreased by 315.1 in oil and 212.7 g kg^–1 in water due to an interaction of PAHs with PET. Using a modified kinetic equation, the diffusion coefficients for PAHs in both liquid media were determined. Values of the diffusion coefficients obtained indicate that the polarity of medium did not affect the rate of PAH removal. Calculation of the area occupied by a PAH molecule on the PET surface suggests that either the multilayer adsorption or the diffusion of PAHs into PET bulk came into account as the decisive factor bringing about the decrease of PAH concentrations in both media.     

Evolution of the concentrations of polycyclic aromatic hydrocarbons in burnt woodland soils

Little is known of the fate of polycyclic aromatic hydrocarbons (PAHs) in soils under burnt woodland. It is not clear what the behavior of the overlying wood ash layer will be along months. In this study, the levels of eight representative PAHs in the 1-5 cm layer of a periurban woodland soil that had undergone wildfire were compared with those measured in nearby and distant unburnt periurban woodland soils and in a distant unburnt rural woodland soil, and the levels at the burnt site were monitored during some 10 months. The analytical method optimized for the purpose afforded recoveries of 74-111% (depending on PAH) and repeatabilities (RSDs) better than 9%, with limits of detection ranging from 1 to 7 microg/kg. PAH levels in the 1-5 cm layer of the burnt periurban soil were very similar to those of distant unburnt periurban soil (188 vs 173 microg/kg), about seven times the 26 microg/kg measured in unburnt rural soil, which furthermore contained no detectable quantities of the highest molecular weight PAHs typical of traffic and other urban sources, as the periurban soils did. At the burnt site, PAH levels fell along the months (the total PAH level from 188 to 119 microg/kg), apparently as the result of rainfall and the prevention of further input from the atmosphere by the overlying layer of wood ash, which had a very high PAH adsorption capacity (1169 microg/kg) and did not itself appear to act as a source of PAHs. PAH transport may have been assisted by increased mobilization of PAHs associated with dissolvable organic matter due to an increase in soil pH due to alkaline ash components.     

PAHs and organic matter partitioning and mass transfer from coal tar particles to water

The coal tar found in contaminated soils of former manufactured gas plants and coking plants acts as a long-term source of PAHs. Organic carbon and PAH transfer from coal tar particles to water was investigated with closed-looped laboratory column experiments run at various particle sizes and temperatures. Two models were derived. The first one represented the extraction process at equilibrium and was based on a linear partitioning of TOC and PAHs between coal tar and water. The partition coefficient was derived as well as the mass of extractable organic matter in the particles. The second model dealt with mass transfer. Particle diffusion was the limiting step; organic matter diffusivity in the coal tar was then computed in the different conditions. A good consistency was obtained between experimental and computed results. Hence, the modeling of PAH migration in contaminated soils at the field scale requires taking into account coal tar as the source-term for PAH release.     

Rhizosphere gradients of polycyclic aromatic hydrocarbon (PAH) dissipation in two industrial soils and the impact of arbuscular mycorrhiza

Phytoremediation of organic pollutants depends on plant-microbe interactions in the rhizosphere, but the extent and intensity of such rhizosphere effects are likely to decrease with increasing distance from the root surface. We conducted a time-course pot experiment to measure dissipation of polycyclic aromatic hydrocarbons (PAHs) in the rhizosphere of clover and ryegrass grown together on two industrially polluted soils (containing 0.4 and 2 g kg(-1) of 12 PAHs). The impact of the fungal root symbiosis arbuscular mycorrhiza (AM) on PAH degradation was also assessed, as these fungi have previously improved plant establishment on PAH-polluted soils and enhanced PAH degradation in spiked soil. The two soils behaved differently with respect to the time-course of PAH dissipation. The less polluted and more highly organic soil showed low initial PAH dissipation rates, with small positive effects of plants after 13 weeks. At the final harvest (26 weeks), the amounts of PAHs extracted from nonplanted pots were higher than the initial concentrations. In parallel planted pots, PAH concentrations decreased as a function of proximity to roots. The most polluted soil showed higher initial PAH dissipation (25% during 13 weeks), but at the final harvest PAH concentrations had increased to values between the initial concentration and those at 13 weeks. An effect of root proximity was observed for the last harvest only. The presence of mycorrhiza generally enhanced plant growth and favored growth of clover at the expense of ryegrass. Mycorrhiza enhanced PAH dissipation when plant effects were observed.     

Removal of polycyclic aromatic hydrocarbons from contaminated soil by aqueous DNA solution

An aqueous DNA solution was applied for the extraction of polycyclic aromatic hydrocarbons (PAHs) from a spiked soil. Solubilities of 0.56, 11.78, and 11.24 mg L(-1) for anthracene, phenanthrene, and pyrene, respectively, were achieved after 1 day equilibration in 1% DNA. Using a spiked soil that contained 72 mg kg(-1) anthracene, 102 mg kg(-1) phenanthrene, and 99 mg kg(-1) pyrene, extractions of close to 88, 78, and 94%, respectively, were attained with 5% DNA at a 1:50 soil/extractant ratio. Maximum PAH dissolution occurred after 4-6 h. Comparative tests showed the main advantage of DNA over methyl-beta- and gamma-cyclodextrins and Tween 80 for pyrene removal. An ionic strength of 0.1 M NaCl was found necessary for maximum PAH dissolution and extraction. The performance of hexane regenerated DNA also remained stable after three stages of recycling. These results show the huge potential of DNA as an aqueous washing agent for PAH-contaminated soil.     

Polycyclic aromatic hydrocarbons in the atmosphere of the eastern Mediterranean

Atmospheric processes governing the fate of the polycyclic aromatic hydrocarbons (PAHs) in the atmosphere of the Eastern Mediterranean were studied for a two-year period (2000-2001). Atmospheric samples were collected off-shore over the Eastern Mediterranean Sea as well as at a background station in Northeastern Crete, Greece. PAH total concentration varied from 4.1 to 57.2 ng m(-3), with >90% in the gas phase. Gas-to-particle distribution of PAHs was correlated (R2 0.75-0.98, p < 0.001) with their subcooled vapor pressure. Seasonal changes in the total concentration of PAHs were not observed, while the origin of air mass was the dominant factor determining their atmospheric concentration levels. Air masses, originating from central and eastern Europe, were associated with the highest PAH concentrations. Gas-to-particle distribution of sigmaPAHs correlated well (R2 0.75-0.98, p < 0.001) with their subcooled vapor pressure. Tropospheric ozone concentration correlated with the vapor-phase PAH concentration (p < 0.001) but less (p < 0.01) with the particulate PAH concentration. Distribution of volatile PAHs over the Eastern Mediterranean basin was uniform. Conversely, particulate PAH concentrations were higher at sampling sites located close to urban centers. Calculated relative removal rates of PAHs associated with particles were significantly higher than those of volatile members.     

Removal of polycyclic aromatic hydrocarbons by low density polyethylene from liquid model and roasted meat

Low density polyethylene (LDPE) was used to remove polycyclic aromatic hydrocarbons (PAHs) from liquid media and roasted meat by sorption. Three liquid models and five carcinogenic PAHs were employed to monitor the sorption process, and amounts of chemicals were determined by GC-FID. More than 50% of the total adsorption occurred within 24 h for the selected PAHs in the three model systems. The water–oil system yielded the highest PAHs removal by LDPE; and the system containing phospholipid resisted the diffusion and resulted in the least adsorption among three models. Certain residual PAHs in the LDPE were significantly decreased to a range of 70.8–84.0% after 3 h of UV radiation, and benzo(a)pyrene was the most sensitive to UV among these PAHs. Removal of PAHs in roasted meat packaged under vacuum was achieved, and potent contamination by the PAHs in the LDPE may be avoided by subsequent UV irradiation.     

Quantitative high-resolution mapping of phenanthrene sorption to black carbon particles

Sorption of hydrophobic organic contaminants such as polycyclic aromatic hydrocarbons (PAHs) to black carbon (BC) particles has been the focus of numerous studies. Conclusions on sorption mechanisms of PAH on BC were mostly derived from studies of sorption isotherms and sorption kinetics, which are based on batch experiments. However, mechanistic modeling approaches consider processes at the subparticle scale, some including transport within the pore-space or different spatial pore-domains. Direct evidence based on analytical techniques operating at the submicrometer scale for the location of sorption sites and the adsorbed species is lacking. In this work, we identified, quantified, and mapped the sorption of PAHs on different BC particles (activated carbon, charcoal and diesel soot) on a 25-100 nm scale using scanning transmission X-ray microscopy (STXM). In addition, we visualized the pore structure of the particles by transmission electron microscopy (TEM) on the 1-10 nm-scale. The combination of the chemical information from STXM with the physical information from TEM revealed that phenanthrene accumulates in the interconnected pore-system along primary "cracks" in the particles, confirming an adsorption mechanism.     

Transformation of polycyclic aromatic hydrocarbons by laccase is strongly enhanced by phenolic compounds present in soil

Efficient transformation of several polycyclic aromatic hydrocarbons (PAHs) was obtained using a fungal laccase in the presence of phenolic compounds related to those formed in nature during the turnover of lignin and humus. The effect of these natural mediators, namely vanillin, acetovanillone, acetosyringone, syringaldehyde, 2,4,6-trimethylphenol, p-coumaric acid, ferulic acid, and sinapic acid, was compared with that of synthetic mediators such as 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS) and 1-hydroxybenzotriazole (HBT). Anthracene was significantly degraded by laccase in the absence of mediators, whereas benzo[a]pyrene and pyrene were weakly transformed (less than 15% after 24 h). Vanillin, acetovanillone, 2,4,6-trimethylphenol, and, above all, p-coumaric acid strongly promoted the removal of PAHs by laccase. 9,10-Anthraquinone was the main product detected from anthracene oxidation by all the laccase-mediator systems. The yield of anthraquinone formed was directly correlated with the amount of p-coumaric acid used. This compound resulted in a better laccase mediator than ABTS and close similarity to HBT, attaining 95% removal of anthracene and benzo[a]pyrene and around 50% of pyrene within 24 h. Benzo[a]pyrene 1,6-, 3,6-, and 6,12-quinones were produced during benzo[a]pyrene oxidation with laccase and p-coumaric acid, HBT, or ABTS as mediators, although use of the latter mediator gave further oxidation products that were not produced by the two other systems.     

Anaerobic,sulfate-dependent degradation of polycyclic aromatic hydrocarbons in petroleum-contaminated harbor sediment

It has previously been demonstrated that [14C]-labeled polycyclic aromatic hydrocarbons (PAHs) can be oxidized to 14CO2 in anoxic, PAH-contaminated, marine harbor sediments in which sulfate reduction is the terminal electron-accepting process. However, it has not previously been determined whether this degradation of [14C]-PAHs accurately reflects the degradation of the in situ pools of contaminant PAHs. In coal tar-contaminated sediments from Boston Harbor, [14C]-naphthalene was readily oxidized to 14CO2, but, after 95 d of incubation under anaerobic conditions, there was no significant decrease in the detectable pool of in situ naphthalene in these sediments. Therefore, to better evaluate the anaerobic biodegradation of the in situ PAH pools, the concentrations of these contaminants were monitored for ca. 1 year during which the sediments were incubated under conditions that mimicked those found in situ. There was loss of all of the PAHs that were monitored (2-5 ring congeners), including high molecular weight PAHs, such as benzo[a]pyrene, that have not previously been shown to be degraded under anaerobic conditions. There was no significant change in the PAH levels in the sediments amended with molybdate to inhibit sulfate-reducing bacteria or in sediments in which all microorganisms had been killed with glutaraldehyde. In some instances, over half of the detectable pools of in situ 2-3 ring PAHs were degraded. In general, the smaller PAHs were degraded more rapidly than the larger PAHs. A distinct exception in the Boston Harbor sediment was naphthalene which was degraded very slowly at a rate comparable to the larger PAHs. In a similar in situ-like study of fuel-contaminated sediments from Liepaja Harbor, Latvia, there was no decline in PAH levels in samples that were sulfate-depleted. However, when the Latvia sediments were supplemented with sufficient sodium sulfate or gypsum to elevate pore water levels of sulfate to approximately 14-25 mM there was a 90% decline in the naphthalene and a 60% decline in the 2-methylnaphthalene pool within 90 days. These studies demonstrate for the first time that degradation by anaerobic microorganisms can significantly impact the in situ pools of PAHs in petroleum-contaminated, anoxic, sulfate-reducing harbor sediments and suggest that the self-purification capacity of contaminated harbor sediments is greater than previously considered.     

Intra-aggregate mass transport-limited bioavailability of polycyclic aromatic hydrocarbons to Mycobacterium strain PC01

Biodegradation kinetics for three- and four-ring PAHs by Mycobacterium sp. strain PC01 were measured in whole and density-fractionated estuarine sediments and in a system without intra-aggregate mass transport limitations. The biokinetic data in the systems with and without intra-aggregate mass transport limitations were compared with abiotic PAH desorption kinetics. The results indicate that intra-aggregate mass transport limitations, and not the intrinsic bacterial PAH utilization capacity, were most important in controlling the rate of biodegradation of sediment-sorbed PAHs. Achievable extent of biodegradation could be predicted by the independently measured traction of desorbable PAHs in the fast-diffusion regime of a two-domain intra-aggregate mass transport model. A closed-form mathematical model was developed to describe sediment-pore water partitioning and rapid aqueous-phase diffusion of PAHs through the macropore and mesopore network of sediment aggregates, followed by first-order biodegradation of desorbed PAHs in the bulk aqueous domain. The model effectively predicted independent biodegradation kinetics of PAHs field-aged in two estuarine sediments. Despite low aqueous solubility of PAHs, macropore and mesopore diffusion may be an important mechanism controlling intra-aggregate mass transport and bioavailability of the most readily and extensively desorbed PAHs in sediments.     

PCB and PAH speciation among particle types in contaminated harbor sediments and effects on PAH bioavailability

This research provides particle-scale understanding of PCB and PAH distribution in sediments obtained from three urban locations in the United States: Hunters Point, CA; Milwaukee Harbor, WI; and Harbor Point, NY. The sediments comprised mineral grains (primarily sand, silt, and clays) and carbonaceous particles (primarily coal, coke, charcoal, pitch, cenospheres, and wood). The carbonaceous sediment fractions were separated from the mineral fractions based on their lower density and were identified by petrographic analysis. In all three sediments, carbonaceous particles contributed 5-7% of the total mass and 60-90% of the PCBs and PAHs. The production of carbonaceous particles is not known to be associated with PCB contamination, and it is very unlikely that these particles can be the source of PCBs in the environment Thus, it appears that carbonaceous particles preferentially accumulate PCBs acting as sorbents in the aqueous environment if PCBs are released directly to the sediment or if deposited as airborne soot particles. Aerobic bioslurry treatment resulted in negligible PAH loss from the carbonaceous coal-derived material in Milwaukee Harbor sediment but resulted in 80% of the PAHs being removed from carbonaceous particles in Harbor Point sediment. Microscale PAH extraction and analysis revealed that PAHs in Harbor Point sediment were associated mainly with coal tar pitch residue. PAHs present in semisolid coal tar pitch are more bioavailable than PAHs sorbed on carbonaceous particles such as coal, coke, charcoal, and cenosphere. Results of this study illustrate the importance of understanding particle-scale association of hydrophobic organic contaminants for explaining bioavailability differences among sediments.     

Effect of activated carbon amendment on bacterial community structure and functions in a PAH impacted urban soil

We collected urban soil samples impacted by polycyclic aromatic hydrocarbons (PAHs) from a sorbent-based remediation field trial to address concerns about unwanted side-effects of 2% powdered (PAC) or granular (GAC) activated carbon amendment on soil microbiology and pollutant biodegradation. After three years, total microbial cell counts and respiration rates were highest in the GAC amended soil. The predominant bacterial community structure derived from denaturing gradient gel electrophoresis (DGGE) shifted more strongly with time than in response to AC amendment. DGGE band sequencing revealed the presence of taxa with closest affiliations either to known PAH degraders, e.g. Rhodococcus jostii RHA-1, or taxa known to harbor PAH degraders, e.g. Rhodococcus erythropolis, in all soils. Quantification by real-time polymerase chain reaction yielded similar dioxygenases gene copy numbers in unamended, PAC-, or GAC-amended soil. PAH availability assessments in batch tests showed the greatest difference of 75% with and without biocide addition for unamended soil, while the lowest PAH availability overall was measured in PAC-amended, live soil. We conclude that AC had no detrimental effects on soil microbiology, AC-amended soils retained the potential to biodegrade PAHs, but the removal of available pollutants by biodegradation was most notable in unamended soil.     

Polycyclic aromatic hydrocarbons in the air in the St. Lawrence Basin (Québec)

High-volume air samples were collected from 1993 to 1996 in rural areas of Québec to investigate on the levels and the vapor-particle partitioning of polycyclic aromatic hydrocarbons (PAHs). Ranges for the mean concentrations of total PAHs (ng m(-3)) were as follows: Villeroy, 3.31-18.92; St. Anicet, 7.57-22.84; and Mingan, 0.50-0.53. Lower molecular weight PAHs predominated at all locations. Particle-gas partition coefficients (Kp) were in good correlation with their vapor pressures (r2 = 0.79-0.97) with slopes deviating from the expected value of -1. The curve of the fractions of PAHs on particles in St Anicet in 1995 fell on that of Lake Superior. In St. Anicet, fractions of phenanthrene, fluoranthene, pyrene, and chrysene on particles were close to those calculated from the soot-air partition coefficient (KSA). At all sites the mean ratios of particulate PAH of the same molecular weight but of very different reactivities were similar during the same sampling days, suggesting that particle-bearing PAHs in Villeroy and Mingan were of the same nature as those found in St. Anicet where adsorption onto soot particles was the major mechanism. Furthermore, the enthalpies of desorption for the predominant PAHs were close at all sites.     

Development of a passive sampler to measure personal exposure to gaseous PAHs in community settings

A sensitive, simple, and cost-effective passive sampling methodology was developed to quantify personal exposure to gaseous polycyclic aromatic hydrocarbons (PAHs). A Fan-Lioy passive PAH sampler (FL-PPS) is constructed from 320 sections of 1-cm long SPB-5 GC columns (0.75-mm i.d. and 7-microm film thickness), similar to a mini-honeycomb denuder. Given the unique feature of the GC column stationary phase, gaseous PAHs are collected on the inner surfaces of the columns by molecular diffusion and thermally desorbed to GC/MS for analysis. The sampling rates of FL-PPS were determined in the laboratory using a controlled test atmosphere containing eight PAHs for a range of face velocity, temperature, relative humidity, PAH concentration, and sampling duration. The sampling rate (mean, %RSD, cm3/min) was 26.7 (21%) for acenaphthylene, 37.6 (25%) for acenaphthene, 56.2 (13%) for fluorene, 49.1 (25%) for phenanthrene, 62.7 (22%) for anthracene, 65.4 (24%) for fluoranthene, and 64.4 (18%) for pyrene over a sampling duration of 8-48 h. The sampling rate for naphthalene was approximately 14.1 (12%) cm3/min over a sampling period of 8 h but decreased along with an increase of sampling time. The effects of temperature, humidity, face velocity, and PAH concentration on the sampling rate were not significant for all the compounds tested. A reasonable agreement (<30%) was obtained for most compounds measured by FL-PPS and a conventional active PAH sampling method colocated side-by-side in the field, but a sampling time of 24 h or longer was required for detection of less abundant PAHs in community settings.     

Sorptive behavior of nitro-PAHs in street runoff and their potential as indicators of diesel vehicle exhaust particles

This is the first report to reveal the particle-water distribution of nitropolycyclic aromatic hydrocarbons (NPAHs) and to discuss their potential risks and utility as indicators of diesel vehicle exhaust particles (DEP). Time-series samples of runoff were collected from a highway, and NPAHs and polycyclic aromatic hydrocarbons (PAHs) were determined by gas chromatography-mass spectrometry (GC-MS) to study their dynamic behavior. The concentrations of total NPAHs ranged from 11 to 73 ng/L in particulate phase (>0.7 mcirom) and from 2.3 to 4.9 ng/L in dissolved phase (<0.7 microm). Like their PAH analogs, most (81-97%) NPAHs were associated with particulate matter. The organic carbon-normalized in situ partition coefficients (Koc') of NPAHs observed in runoff events (10(5.8-6.3) for 2-nitrofluoranthene and 10(5.8-6.2) for 1-nitropyrene [1-NP]) were more than 1 order of magnitude higher than those expected from their Kow, indicating great affinity for particulate matter such as soot. Concentrations of PAHs and NPAHs adjusted by potency equivalency factors and induction equivalency factors showed that the potential risks of NPAHs were smaller than those of PAHs by a factor of more than a hundred for the particulate phase and morethan fourforthe dissolved phase. Comparison of concentrations and compositions of NPAHs and PAHs among runoff, DEP, gasoline vehicle exhaust particles, boiler exhaust particles, and aerosols suggested that the ratio of 1-NP to total PAHs (1-NP/PAH) is a useful indicator of DEP for source apportionment of PAHs among traffic-related sources. Source-apportionment of PAHs in the runoff by 1-NP/PAH and methylphenanthrene/phenanthrene ratios suggested that most PAHs in the runoff except the second flush peak were derived from DEP but that other pyrogenic sources contributed to the particles at the second flush and thus to the overall runoff particles.