Oxygenated polycyclic aromatic hydrocarbons and azaarenes in urban soils: a comparison of a tropical city (Bangkok) with two temperate cities (Bratislava and Gothenburg)

The effects of co-existing acridine on adsorption-desorption behavior of carbazole in soils: Co-sorption and mechanism insight

Carbazole (CBZ) and acridine (ACR) are polycyclic aromatic nitrogen heterocycles (PANHs) widely found in combined contaminated soils, while investigations on organic-organic interactions have been very limited. In this study, batch experiments were carried out on five soils with different properties, taking CBZ as a representative of PANHs and ACR as a co-existing contaminant. The adsorption isotherms of CBZ (50-1000 μg/L) were nonlinear. Soil organic matter (SOM) and cation exchange capacity (CEC) showed positive correlations with CBZ adsorption-desorption coefficients. The adsorption mechanisms of CBZ involved hydrogen bonding, π-π interaction, and cation-π bonding. Different concentrations of ACR had varying effects on CBZ. The adsorption of CBZ was inhibited with 250 μg/L ACR. The cooperative adsorption was observed on three soils with increasing ACR concentration (1000 μg/L) and led to more pronounced nonlinear isotherms. The S-shaped isotherms of ACR indicated that ACR was adsorbed to the soil surface in a perpendicular configuration. New adsorption sites were created allowing for increased CBZ adsorption through π-π interaction with ACR. Therefore, variations in soil properties and potential impacts of co-existing contaminants should be well considered when assessing the combined pollution of site soil. This will contribute to a more accurate estimation of environmental and health risks.

Air-soil cycling of oxygenated, nitrated and parent polycyclic aromatic hydrocarbons in source and receptor areas

Polycyclic aromatic hydrocarbons (PAHs) and their oxygenated and nitrated derivatives, OPAHs and NPAHs, are semivolatile air pollutants which are distributed and cycling regionally. Subsequent to atmospheric deposition to and accumulation in soils they may re-volatilise, a secondary source which is understudied. We studied the direction of air-soil mass exchange fluxes of 12 OPAHs, 17 NPAHs, 25 PAHs and one alkylated PAH in two rural environments being influenced by the pollutant concentrations in soil and air, by season, and by land cover. The OPAHs and NPAHs in samples of topsoil, of ambient air particulate and gas phases and in the gas-phase equilibrated with soil were analysed by GC-APCI-MS/MS. The pollutants soil burdens show a pronounced seasonality, a winter maximum for NPAHs and PAHs and a summer maximum for OPAHs. One order of magnitude more OPAH and parent PAH are found stored in forest soil than in nearby grassland soil. Among a number of 3-4 ring PAHs, the OPAHs benzanthrone and 6H-benzo(c,d)pyren-6-one, and the NPAHs 1- and 2-nitronaphthalene, 9-nitrophenanthrene and 7-nitrobenz(a)anthracene are found to re-volatilise from soils at a rural background site in central Europe in summer. At a receptor site in northern Europe, net deposition of polycyclic aromatic compounds (PACs) prevails and re-volatilisation occurs only sporadic. Re-volatilisation of a number of PACs, including strong mutagens, from soils in summer and even in winter indicates that long-range atmospheric transport of primary PAC emissions from central Europe to receptor areas might be enhanced by secondary emissions from soils.

A complex mixture of polycyclic aromatic compounds causes embryotoxic, behavioral, and molecular effects in zebrafish larvae (Danio rerio), and in vitro bioassays

Polycyclic aromatic compounds (PACs) are prevalent in the environment, typically found in complex mixtures and high concentrations. Our understanding of the effects of PACs, excluding the 16 priority polycyclic aromatic hydrocarbons (16 PAHs), remains limited. Zebrafish embryos and in vitro bioassays were utilized to investigate the embryotoxic, behavioral, and molecular effects of a soil sample from a former gasworks site in Sweden. Additionally, targeted chemical analysis was conducted to analyze 87 PACs in the soil, fish, water, and plate material. CALUX® assays were used to assess the activation of aryl hydrocarbon and estrogen receptors, as well as the inhibition of the androgen receptor. Larval behavior was measured by analyzing activity during light and darkness and in response to mechanical stimulation. Furthermore, qPCR analyses were performed on a subset of 36 genes associated with specific adverse outcomes, and the total lipid content in the larvae was measured. Exposure to the sample resulted in embryotoxic effects (LC50 = 0.480 mg dry matter soil/mL water). The mixture also induced hyperactivity in darkness and hypoactivity in light and in response to the mechanical stimulus. qPCR analysis revealed differential regulation of 15 genes, including downregulation of opn1sw1 (eye pigmentation) and upregulation of fpgs (heart failure). The sample caused significant responses in three bioassays (ERα-, DR-, and PAH-CALUX), and the exposed larvae exhibited elevated lipid levels. Chemical analysis identified benzo[a]pyrene as the predominant compound in the soil and approximately half of the total PAC concentration was attributed to the 16 PAHs. This study highlights the value of combining in vitro and in vivo methods with chemical analysis to assess toxic mechanisms at specific targets and to elucidate the possible interactions between various pathways in an organism. It also enhances our understanding of the risks associated with environmental mixtures of PACs and their distribution during toxicity testing.

Oxygenated and Nitrated Polycyclic Aromatic Hydrocarbons: Sources, Quantification, Incidence, Toxicity, and Fate in Soil—A Review Study

The genotoxicity, mutagenesis, and carcinogenic effects of polycyclic aromatic hydrocarbon (PAH) derivatives may exceed the parent PAHs. However, their influence on the soil environment has not been explored to a large extent. Oxygenated polycyclic aromatic hydrocarbons (OPAHs) and nitrated polycyclic aromatic hydrocarbons (NPAHs) are typical polar substituted compounds. We offer a review of the literature on the sources, quantification, incidence, toxicity, and transport of these compounds in soil. Although their environmental concentrations are lower than those of their parent compounds, they exert higher toxicity. Both types of substances are basically related to carcinogenesis. OPAHs are not enzymatically activated and can generate reactive oxygen species in biological cells, while NPAHs have been shown to be mutagenic, genotoxic, and cytotoxic. These compounds are largely derived from the transformation of PAHs, but they behave differently in soil because of their higher molecular weight and dissimilar adsorption mechanisms. Therefore, specialized knowledge of model derivatives is required. We also made recommendations for future directions based on existing research. It is expected that the review will trigger scientific discussions and provide a research basis for further study on PAH derivatives in the soil environment.

Sustainable remediation of dibenzofuran-contaminated soil by low-temperature thermal desorption: Robust decontamination and carbon neutralization

Thermal desorption (TD) is generally considered to be an effective but unsustainable technology. Decontamination performance, charring behaviors and physicochemical properties during TD of dibenzofuran-contaminated soil (DCS) are explored. After treatment at 300 °C for 20 min, the dibenzofuran concentration decreases from 3969.37 mg/kg to 17.29 mg/kg, lower than Chinese risk screening value. More than 99% of dibenzofuran in soil are removed at low temperature of 300 °C, meanwhile the organic carbon is partially retained in soil. Removal mechanism of DCS at 300 °C is proposed, including desorption, cracking, and charring. Char material of low H:C ratio is produced by the generation, polymerization and dehydrogenation of aromatic intermediates, and then increases carbon stocks and reduces the carbon footprint of contaminated soil. Meanwhile, due to the char generated, pH, cation exchange capacity and specific surface area of DCS heated at 300 °C are higher than those of raw DCS, promoting ecological restoration and enhancing carbon sink in soil ecosystems. The aforesaid saving energy, reducing carbon footprint and enhancing carbon sink are exactly the main innovative technologies for achieving carbon neutrality. Hence, it may be a contribution to climate change mitigation, in addition to a robust and sustainable remediation of organic contaminated soil.

Nitro- and oxy-PAHs in grassland soils from decade-long sampling in central Europe

Long-term exposure to polycyclic aromatic hydrocarbons (PAHs) and their nitrated (NPAHs) and oxygenated (OPAHs) derivatives can cause adverse health effects due to their carcinogenicity, mutagenicity and oxidative potential. The distribution of PAH derivatives in the terrestrial environment has hardly been studied, although several PAH derivatives are ubiquitous in air and long-lived in soil and water. We report the multi-annual variations in the concentrations of NPAHs, OPAHs and PAHs in soils sampled at a semi-urban (Mokrá, Czech Republic) and a regional background site (Košetice, Czech Republic) in central Europe. The concentrations of the Σ₁₈NPAHs and the Σ₁₁₊₂OPAHs and O-heterocycles were 0.31 ± 0.23 ng g^-1 and 4.03 ± 3.03 ng g^-1, respectively, in Košetice, while slightly higher concentrations of 0.54 ± 0.45 ng g^-1 and 5.91 ± 0.45 ng g^-1, respectively, were found in soil from Mokrá. Among the 5 NPAHs found in the soils, 1-nitropyrene and less so 6-nitrobenzo(a)pyrene were most abundant. The OPAHs were more evenly distributed. The ratios of the PAH derivatives to their parent PAHs in Košetice indicate that they were long-range transported to the background site. Our results show that several NPAHs and OPAHs are abundant in soil and that gas-particle partitioning is a major factor influencing the concentration of several semi-volatile NPAHs and OPAHs in the soils. Complete understanding of the long-term variations of NPAH and OPAH concentrations in soil is limited by the lack of kinetic data describing their formation and degradation.

Environmental contamination by heterocyclic Polynuclear aromatic hydrocarbons and their microbial degradation

Heterocyclic polynuclear aromatic hydrocarbons (PAHs) have been detected in all environmental matrices at few ppb to several ppm concentrations and they are characterized by high polarity. Some heterocyclic PAHs are mutagenic and carcinogenic to humans and various organisms. Despite being potent environmental pollutants, these compounds have received less attention. This paper focuses on the sources and occurrence of these compounds and their microbial degradation using diverse species of bacteria, fungi, and algae. Complete removal of 1.8 to 2614 mg/L of nitrogen heterocyclic PAH (PANH), 0.27 to 184 mg/L of sulfur heterocyclic PAH (PASH), and 0.6 to 120 mg/L of oxygen heterocyclic PAH (PAOH) compounds by various microbial species was observed between 3 h and 18 days, 8 h to 6 days, and 4 h to 250 h, respectively under aerobic condition. Strategies for enhancing the removal of heterocyclic PAHs from aquatic systems are also discussed along with the challenges.

Soil bacterial diversity and functionality are driven by plant species for enhancing polycyclic aromatic hydrocarbons dissipation in soils

Plant-microorganisms symbiosis has been widely used in developing strategies for the rhizoremediation of polycyclic aromatic hydrocarbon (PAHs) contaminated agricultural soils. However, understanding the potential mechanisms for using complex plant-microbe interactions to enhance rhizoremediation in contaminated soils is still limited. In this study, rhizosphere microbiomes were established by cultivating four types of cover crops for 15 months in a PAHs-contaminated field. The results showed that the PAHs removal rates were significantly higher in rhizosphere soils (55.2-82.3%) than the bare soils (20.5%). Of the four cover crops, the rhizosphere soils associated with the alfalfa and clover had higher removal rates for high molecular weight (HMW) PAHs (78.5-87.1%) than the grasses (39.0-46.2%). High-throughput sequencing analysis showed that bacterial community structure between the planted and bare soils, and among four cover crops rhizosphere soils were significantly different. The rhizosphere soils associated with the alfalfa and clover had more abundant degradation-related taxa. Correlation network analysis showed that bacterial communities with high removal rates have stronger interactions. Metagenome analysis indicated that the relative abundance of the key functional genes involved in PAHs degradation and nutrient metabolisms were significantly higher in rhizosphere soils, especially for alfalfa and clover. Overall, this study provides new insights for us to understand the mechanisms by different plants enhancing PAHs dissipation from the viewpoint of microbiology.

Insights into sources and occurrence of oxy- and nitro-PAHs in the alberta oil sands region using a network of passive air samplers

Mining-related activities in the Alberta Oil Sands Region (AOSR) are known to emit polycyclic aromatic hydrocarbons (PAHs) and related compounds to ambient air. This is a concern due to the toxicity of PAHs, including their transformation products such as nitrated (NPAHs) and oxygenated (OPAHs) PAHs. This is the first study that provided a more extensive outlook into the sources, occurrence in air, and spatial and seasonal patterns of NPAHs and OPAHs in the AOSR by using passive air sampling. A sampling campaign from 2013 to 2016 revealed concentrations of NPAHs that were much lower than those of OPAHs. The highest concentrations of NPAHs were concentrated in the region associated with extensive mining activities, with ∑NPAH concentrations ranging from 20 to 250 pg/m³. Within the oil sands (OS) mineable area, NPAHs associated with primary release appear more commonly, while NPAHs produced via oxidative transformation are predominant outside of this area. The concentrations of ∑OPAH ranged from 400 to 2400 pg/m³, with the highest air concentrations in the region located south of the main OS activity zone, with peak concentrations attributed to a 2016 forest fire event. Uptake of PAHs from ambient air and their subsequent conversion to generate OPAHs is believed to play an important role in wildfire emissions of OPAHs. The seasonal trend investigation was inconclusive, with NPAHs slightly higher during the winter, while OPAHs were slightly elevated during summer. A preliminary comparison of ambient concentrations of OPAHs and NPAHs in the AOSR to measurements in the Greater Toronto Area revealed a similar range of concentrations, but also a unique presence of certain NPAHs such as 4-nitrobiphenyl, 2-nitrodibenzothiophene, 2,8-dinitrodibenzothiophene and 6-nitrobenzo-(a)-pyrene. This indicates that AOSR might have its own NPAH profile - creating the need to better understand associated NPAH toxicity and propensity for long range transport.

Getting a better overview of a highly PAH contaminated soil: A non-targeted approach assessing the real environmental contamination

Over the last 40 years, soils contaminated with polycyclic aromatic hydrocarbons (PAH) were monitored according to a list of 16 PAH, established by the U.S. Environmental Protection Agency (EPA). This, however, is underestimating the danger to the environment and humanity because other high molecular weight PAHs, heterocycles (PAXH, X = N, O, S) and alkylated derivatives can also occur at the contaminated site. Here, a new non-targeted approach of highly contaminated soil (64.5 ± 9.5 g kg^-1 solvent extractable organics from the German Ruhrgebiet) is introduced, where ultrahigh resolution mass spectrometry is combined with multiple ionization methods to get a better overview of anthropogenic contamination at a former industrial site. In total, 21,958 elemental compositions were assigned for positive and negative mode measurements. The approach is strongly increasing the amount of data that can be obtained from a single contaminated soil, making an assessment of the real environmental risk possible. In addition to highly aromatized and (alkylated) high molecular weight PAH, other PAXH especially basic and neutral PANH with very high aromaticity were also detected. This shows that while regulations and routine analysis are still stuck in the 1960 s, modern analytical methods are present in the 21st century.

Global distribution of oxygenated polycyclic aromatic hydrocarbons in mineral topsoils

Hazardous oxygenated polycyclic aromatic hydrocarbons (OPAHs) originate from combustion (primary sources) or postemission conversion of polycyclic aromatic hydrocarbons (PAHs) (secondary sources). We evaluated the global distribution of up to 15 OPAHs in 195 mineral topsoils from 33 study sites (covering 52° N-47° S, 71° W-118 °E) to identify indications of primary or secondary sources of OPAHs. The sums of the (frequently measured 7 and 15) OPAH concentrations correlated with those of the Σ16EPA-PAHs. The relationship of the Σ16EPA-PAH concentrations with the Σ7OPAH/Σ16EPA-PAH concentration ratios (a measure of the variable OPAH sources) could be described by a power function with a negative exponent <1, leveling off at a Σ16EPA-PAH concentration of approximately 400 ng g^-1 . We suggest that below this value, secondary sources contributed more to the OPAH burden in soil than above this value, where primary sources dominated the OPAH mixture. This was supported by a negative correlation of the Σ16EPA-PAH concentrations with the contribution of the more readily biologically produced highly polar OPAHs (log octanol-water partition coefficient <3) to the Σ7OPAH concentrations. We identified mean annual precipitation (Spearman ρ = .33, p < .001, n = 143) and clay concentrations (ρ = .55, p < .001, n = 33) as important drivers of the Σ7OPAH/Σ16EPA-PAH concentration ratios. Our results indicate that at low PAH contamination levels, secondary sources contribute considerably and to a variable extent to total OPAH concentrations, whereas at Σ16EPA-PAH contamination levels >400 ng g^-1 , there was a nearly constant Σ7OPAH/Σ16EPA-PAH ratio (0.08 ± 0.005 [SE], n = 80) determined by their combustion sources.

Nitrated- and oxygenated-polycyclic aromatic hydrocarbon in urban soil from Nepal: Source assessment, air-soil exchange, and soil-air partitioning

In contrast to more frequently investigated priority pollutants, such as polycyclic aromatic hydrocarbons (PAHs), only little is known about the fate and distribution of nitrated- and oxygenated-PAHs (NPAHs and OPAHs) in urban soils, particularly in Indian sub-continent. Moreover, experimental data on air-soil exchange and soil-air partitioning are also lacking, which is critical in assessing the partitioning, fugacity coefficient, and secondary emission of PAH-derivatives. Hence, this article provides an insight into the fate, sources, air-soil exchange, and soil-air partitioning of PAH-derivatives on a molecular basis. Prospective health risk due to their exposure has also been discussed. The result showed that PAH-derivatives had significantly polluted all four Nepalese cities. Ʃ₁₅NPAHs and Ʃ₂OPAHs in soil were 4 and 20 times lower than their parent-PAHs, and ranged 396-2530 ng/g (median 458 ng/g) and 91.9-199 ng/g (median 94.9 ng/g), respectively. Ʃ₁₅NPAHs was higher than a few global studies, while Ʃ₂OPAHs was lower than some of the less urbanized/remote areas worldwide. The 6-Nitobenzo[a]pyrene (6-NBaP) was most abundant in soil, and accounted for 10-12% of Ʃ₁₅NPAHs, while Benzanthrone (BZONE) exceeded among OPAHs, and represented 71-76% of Ʃ₂OPAHs, respectively. Source identification study indicated that direct emissions from domestic/residential cooking and heating and secondary formations are the essential sources of derivative chemicals in soil. Fugacity fraction ratio (f_ratio) indicated volatilization from the soil. The soil-air partitioning study showed sorption by soil organic matter/black carbon has little role in soil-air partitioning of PAH-derivatives in Nepal's urban soil. The toxicity equivalency quotients (TEQs) of NPAHs (314 ± 102 ng/g) was estimated slightly higher than their parent-PAHs (294 ± 121 ng/g) suggesting a relatively higher risk of soil toxicity in Nepal.

Quantitative biomonitoring of polycyclic aromatic compounds (PACs) using the Sydney rock oyster (Saccostrea glomerata)

Increasing our understanding of the bioavailable fractions of polycyclic aromatic compounds (PACs) in an aquatic environment is important for the assessment of the environmental and human health risks posed by PACs. More importantly, the behaviour of polar polycyclic aromatic hydrocarbons (polar PAHs), which are metabolites of legacy PAHs, are yet to be understood. We, therefore, carried out a study involving Sydney rock oysters (Saccostrea glomerata) sourced from two locations, that had been exposed to PAH contamination, within an Australian south-east estuary. Biomonitoring of these oysters, following relocation from the estuary to a relatively isolated waterway, was done at 24 and 72 h after deployment and subsequently at 7, 14, 28, 52 and 86 days. Control samples from Camden Haven River were sampled for PAC analyses just before deployment, after 28 days and at the end of the study (day 86). Lipid-normalised concentrations in oyster tissues across the 86-day sampling duration, elimination rate constants (k₂), biological half-lives (t_1/2) and time required to reach 95% of steady-state (t₉₅) were reported for parent PAHs and the less-monitored polar PAHs including nitrated/oxygenated/heterocyclic PAHs (NPAHs, oxyPAHs and HPAHs) for the three differently sourced oyster types. Most of the depurating PAHs and NPAHs, as well as 9-FLO (oxyPAH), had k₂ values significantly different from zero (p < 0.05). All other oxyPAHs and HPAHs showed no clear depuration, with their concentrations remaining similar. The non-depuration of polar PAHs from oyster tissues could imply greater human health risk compared to their parent analogues.

Speciation and source apportionment of polycyclic aromatic compounds (PACs) in sediments of the largest salt water lake of Australia

Great ecological and human health risks may arise from the presence of polycyclic aromatic hydrocarbons (PAHs) in aquatic environments and particularly in sediments, where they often partition. In spite of the apparent risk, knowledge about PAHs and their polar derivatives in sediments is limited. We, therefore, carried out an assessment of the concentrations of parent PAHs and their derivatives (polar PAHs) in sediments of Lake Macquarie: the largest saltwater lake in the southern hemisphere. A total of 31 sediment samples along the pollution prone western shoreline of the estuary were analysed. Multiple source apportionment methods were used to investigate PAH sources contributing to parent and polar PAH concentrations in the estuarine sediments. Concentration levels were highest for high molecular weight (HMW) PAHs compared to low molecular weight (LMW) PAHs. The highest PAH concentrations were recorded for oxygenated PAHs (oxy-PAHs) compared to parent and other polar PAHs. Polycyclic aromatic hydrocarbon diagnostic ratios and compositional analysis showed that PAHs in Lake Macquarie were predominantly pyrogenic exhibiting strong positive correlation (R² = 0.972) with total PAH concentrations. Principal Component Analysis (PCA) identified three groupings of PAHs with oxy-PAHs and NPAHs dominating (40.2%). Carbazole, a heterocyclic PAH, was also a prominent contributor to sediment PAH concentrations. Atmospheric deposition, coal combustion and vehicular emissions were implicated as the major contributors to sediment pollution.

Isomer-selective biodegradation of high-molecular-weight azaarenes in PAH-contaminated environmental samples

Polycyclic aromatic nitrogen heterocycles, or azaarenes, normally co-occur with polycyclic aromatic hydrocarbons (PAHs) in contaminated soils. We recently reported that nontarget analysis using high resolution mass spectrometry of samples from four PAH-contaminated sites revealed a previously unrecognized diversity and abundance of azaarene isomers and their methylated derivatives. Here we evaluated their biodegradability by natural microbial communities from each site in aerobic microcosm incubations under biostimulated conditions. The removal of total quantifiable azaarenes ranged from 15 to 85%, and was related to the initial degree of weathering for each sample. While three-ring azaarenes were readily biodegradable, the five-ring congeners were the most recalcitrant. Microbial-mediated removal of four-ring congeners varied for different isomers, which might be attributed to the position of the nitrogen atom that also influences the physicochemical properties of azaarenes and possibly the susceptibility to transformation by relevant microbial enzymes. The presence of methyl groups also influenced azaarene biodegradability, which decreased with increasing degree of methylation. Several oxidation products of azaarenes were detected, including ketones and dioxygenated derivatives of three- and four-ring compounds. Our results indicate the susceptibility of some azaarenes to bioremediation, while suggesting the potential implications for risk from the persistence of less-biodegradable isomers and the formation of oxidized-azaarene derivatives.

Polycyclic aromatic compounds in urban soils of Stockholm City: Occurrence, sources and human health risk assessment

Polycyclic aromatic compounds (PACs) are ubiquitous pollutants that are found everywhere in our environment, including air, soil and water. The aim of this study was to determine concentrations, distribution, sources and potential health risk of 43 PACs in soils collected from 25 urban parks in Stockholm City, Sweden. These PACs included 21 PAHs, 11 oxygenated PAHs, 7 methylated PAHs, and 4 azaarenes whose concentrations ranged between 190 and 54 500, 30.5-5 300, 14.9-680, and 4.17-590 ng/g soil, respectively. Fluoranthene was found at the highest levels ranging between 17.7 and 9800 ng/g, benzo[a]pyrene between 9.64 and 4600 ng/g, and the highly potent carcinogen dibenzo[a,l]pyrene up to 740 ng/g. The most abundant oxy-PAH was 6H-benzo[cd]pyren-6-one (2.09-2300 ng/g). Primary sources of PAHs were identified by use of diagnostic ratios and Positive Matrix Factorization modelling and found to be pyrogenic including vehicle emissions and combustion of biomass. Estimating the incremental lifetime cancer risks (ILCRS) associated with exposure to PAHs in these soils indicated that the PAH levels in some parks constitute a considerable increased risk level for adults and children (total ILCR > 1 × 10^-4). Compared to worldwide urban parks contamination, we conclude that the PAC soil levels in parks of Stockholm City in general are low, but that some parks are more heavily contaminated and should be considered for clean-up actions to limit human health risks.

Polycyclic aromatic compounds (PAHs, oxygenated PAHs, nitrated PAHs and azaarenes) in soils from China and their relationship with geographic location, land use and soil carbon fractions

The assessment of risks arising from polycyclic aromatic compounds (PACs), particularly from the polar PACs [azaarenes (AZAs), oxygenated PAHs (OPAHs), nitrated PAHs (NPAHs)] requires us to understand the drivers of their spatial distribution. We determined the concentrations of 29 PAHs, 4 AZAs, 15 OPAHs and 11 NPAHs and their relationships with land use (urban vs. rural and forest vs. agriculture), climate (Qinghai-Tibetan plateau, temperate, sub tropical and tropical) and three C fractions (soil organic C, char, soot) in 36 mineral topsoils (0-5 cm) of China. The average concentrations±standard deviation of the Σ29PAHs, Σ16PAHs, Σ4AZAs, Σ15OPAHs and Σ11NPAHs were 352 ± 283, 206 ± 215, 5.7 ± 3.7, 108 ± 66.8 and 3.2 ± 3.4 ng g^-1, respectively. PAH, OPAH, NPAH and AZA concentrations were frequently not correlated within or across the regions reflecting different sources and turnover of PAHs and their derivatives. Temperate urban soils showed the highest and tropical rural soils the lowest concentrations of PACs. Forest soils had higher PACs concentrations than agricultural soils. Longitude correlated positively with the ∑29PAHs concentrations, because of increasing emissions of PAHs from East to West. The tropical and plateau regions with the lowest PAH concentrations, were dominated by low molecular weight PAHs (LMW-PAHs) with LMW/high molecular weight (HMW)-PAHs ratios >1, while the other two climatic regions with more industrial sites showed the opposite. Latitude correlated with NPAHs likely because of enhanced formation by photochemical reactions during transport in the atmosphere. The concentrations of the ∑29PAHs, ∑4AZAs, ∑15OPAHs, ∑11NPAHs and their individual components were only occasionally correlated with those of carbon fractions (soil organic C, soot and char) suggesting a small role of soil C pool properties in driving PACs concentrations. Our results demonstrate that the strongest drivers of PACs concentrations are land use and distance to PAC emission sources followed by climate and size and properties of the soil organic C pool.

Chemical (C, N, S, black carbon, soot and char) and stable carbon isotope composition of street dusts from a major West African metropolis: Implications for source apportionment and exposure

Street dust is a major source of pollution and exposure of residents of West Africa to toxic chemicals. There is however, limited knowledge about the chemical composition and sources of street dust in urban areas of sub-Saharan Africa. The total carbon (TC), nitrogen (TN), sulfur (TS) and the stable carbon isotope ratios (δ¹³C) contents of street dust sampled from 25 sites distributed across Kumasi (a metropolis in Ghana with a population of ca. 2 million) were determined. In addition, black carbon (BC) and their subunits (soot and char) in these samples were also determined. The concentrations of TC, TN and TS in the dusts were 5-71 mg g^-1, 0.3-4.3 mg g^-1 and 0.2-1.4 mg g^-1, respectively. The concentrations of TC, TN and TS were higher than at the background site of the metropolis by a factor of 5.1 (range: 1.7-12), 3.9 (1.1-13) and 2.8 (0.7-5), respectively. The BC, char and soot concentrations in these samples averaged 1.6 mg g^-1 (0.13-4.4), 1.2 mg g^-1 (0.08-3.7) and 0.36 mg g^-1 (0.05-1.5), respectively. The concentrations of BC, char and soot in the street dust were higher than in the background location by factors of 5 (range: 0.8-13), 6 (0.7-17) and 3 (0.5-12), respectively. The TC, TN, TS, BC, soot and char concentrations were positively correlated with each other and with polycyclic aromatic compounds (PAHs, oxygenated PAHs and azaarenes from a previous study), indicating their common origin and fate. The δ¹³C values ranged from -27 to -24 [‰], with more polluted sites being more depleted in ¹³C. Based on the chemical composition of the street dusts, the 25 sites could be clustered into four groups by hierarchical cluster analysis which reflect areas of varying anthropogenic influence and, accordingly, exposure to hazardous chemicals.

Sources and fate of polycyclic aromatic compounds (PAHs, oxygenated PAHs and azaarenes) in forest soil profiles opposite of an aluminium plant

Little is known about oxygenated polycyclic aromatic hydrocarbons (OPAHs) and azaarenes (AZAs) in forest soils. We sampled all horizons of forest soils from five locations at increasing distances from an Al plant in Slovakia, and determined their polycyclic aromatic compound (PACs) concentrations. The ∑29PAHs concentrations were highest in the Oa and lowest in the Oi horizon, while the ∑14OPAHs and ∑4AZAs concentrations did not show a consistent vertical distribution among the organic horizons. The concentration ratios of PAHs and OPAHs between deeper O horizons and their overlying horizon (enrichment factors) were positively correlated with the octanol-water partition coefficients (K_OW) at several locations. This is attributed to the slower degradation of the more hydrophobic PACs during organic matter decomposition. PACs concentrations decreased from the organic layer to the mineral horizons. The concentrations of ∑29PAHs (2400-17,000 ng g^-1), ∑14OPAHs (430-2900 ng g^-1) and ∑4AZAs (27-280 ng g^-1) in the mineral A horizon generally decreased with increasing distance from the Al plant. In the A horizons, the concentrations of ∑29PAHs were correlated with those of ∑14OPAHs (r = 0.95, p = 0.02) and ∑4AZAs (r = 0.93, p = 0.02) suggesting that bioturbation was the main transport process of PACs from the organic layer into the mineral soil. At each location, the concentrations of PACs generally decreased with increasing depth of the mineral soil. Enrichment factors of PAHs in the mineral horizons were not correlated with K_OW, pointing at colloid-assisted transport and bioturbation. The enrichment factors of OPAHs (in mineral horizons) at a site were negatively correlated with their K_OW values indicating that these compounds were leached in dissolved form. Compared to a study 13 years before, the concentrations of PAHs had decreased in the O horizons but increased in the A and B horizons because of soil-internal redistribution after emissions had been reduced.

Occurrence and leachability of polycyclic aromatic compounds in contaminated soils: Chemical and bioanalytical characterization

An important concern regarding sites contaminated with polycyclic aromatic compounds (PACs) is the risk of groundwater contamination by release of the compounds from soils. The goal of this study was to investigate the occurrence and leachability of 77 PACs including polycyclic aromatic hydrocarbons (PAHs) and heterocyclic aromatic compounds (NSO-PACs) among total aryl hydrocarbon receptor (AhR) agonists in soils from historical contaminated sites. A novel approach combining chemical and bioanalytical methods in combination with characterization of leachability by use of a column leaching test was used. Similar profiles of relative concentrations of PACs were observed in all soils, with parent PAHs accounting for 71 to 90% of total concentrations in soils. Contribution of oxy-PAHs, alkyl-PAHs and N-PACs ranged from 2 to 9%, 3 to 9% and 1 to 14%, respectively. Although the contributions of groups of PACs were small, some compounds were found in similar or greater concentrations than parent PAHs. Leachable fractions of 77 PACs from soils were small and ranged from 0.002 to 0.54%. Polar PACs were shown to be more leachable than parent PAHs. The contribution of analyzed PACS to overall AhR-mediated activities in soils and leachates suggests presence of other AhR agonists in soils, and a potential risk. Only a small fraction of AhR agonists was available in soils, indicating an overestimation of the risk if only total initial concentrations in soils would be considered in risk assessment. The results of the study strongly support that focus on 16US EPA PAHs may result in inadequate assessment of risk and hazard of PACs in complex environmental samples.

A 150-year record of polycyclic aromatic compound (PAC) deposition from high Andean Cajas National Park, southern Ecuador

The temporal profiles of polycyclic aromatic compounds (PACs) in lake sediments reflect past changes in emissions, transport and deposition of these pollutants and, thus, record natural and anthropogenic processes. We document fluxes of PACs [(polycyclic aromatic hydrocarbons (PAHs), oxygenated PAHs (OPAHs) and azaarenes (AZAs)] deposited in two tropical high-altitude lakes in the Cajas National Park (Ecuadorian Andes, 2°50'S, 79°10'W). In remote and high elevation Laguna Fondococha (4130m a.s.l.), the temporal fluxes of OPAHs and AZAs were similar to those of PAHs suggesting similar sources. A significant increase of PAC deposition after the 1950s reflects Ecuador's economic development. PAH fluxes were relatively low (∑27PAHs (without retene and perylene): 0.86-11.21ngcm^-2yr^-1) with a composition pattern typical for long-range atmospheric transport (high 9-fluorenone/fluorene ratios) and biomass burning (30% low molecular weight PAHs). PAHs diagnostic of high temperature combustion (industry, traffic) make up 20-25% of total PAHs. Perylene concentrations increase linearly with increasing sediment depth suggesting diagenetic in-situ production. At lower elevations (Laguna Llaviucu, 3140m a.s.l.) and closer to urban areas, PAC fluxes in the past decades were 4-5 times higher than in the remote high-elevation lake. Laguna Llaviucu also showed higher concentrations of high molecular weight pyrogenic PAHs and a greater diversity of AZAs. Individual OPAHs and AZAs reflect mainly combustion activities. In Laguna Llaviucu, which is at a lower elevation (3140m a.s.l.) and closer to the city, molecular ratios suggest short-range atmospheric transport and deposition of PACs. A very foggy climate (170 rainy days per year) with the precipitation maximum at 3500m removes PACs very efficiently (by wet deposition) from the atmosphere at very short distances from emission sources. This partly explains why L. Llaviucu shows higher fluxes of PACs than the higher elevation L. Fondococha. This study presents the first historical record of organic pollutants from environmental archives in Ecuador.

Occurrence of carbazoles in dust and air samples from different locations in Germany

9H-carbazole is generated from incomplete combustion of diverse fossil fuels and biomass, in tobacco smoke and from industrial processes, while halogenated carbazoles have natural and anthropogenic sources. We analyzed 9H-carbazole and 14 halogenated carbazoles in dust samples from 14 schools, 13 daycare centers, and 13 residences, as well as 5 indoor air samples from residences in Munich, Germany. Overall, we present first data of various carbazoles in different indoor environments without visible combustion sources. The median (95th percentile) values of the halogenated analytes mainly detected in the entire study group were 10.3ng/g (308ng/g) for 9H-carbazole, 13.3ng/g (735ng/g) for 3,6-dichloro-9H-carbazole, 6.2ng/g (159ng/g) for 1,3,6-tribromo-9H-carbazole, and 1.2ng/g (21.1ng/g) for 2,7-dibromo-9H-carbazole. For most of the target analytes, the highest concentrations were observed in dust samples from schools, and the lowest were found in residences. In the air samples, all analytes were found only at low levels, with median values of 7.7pg/m³ for 9H-carbazole and 6.1pg/m³ for 2,3,6,7-tetrachloro-9H-carbazole. For 9H-carbazole, "typical" and "high" non-dietary intake of children through dust ingestion using median and 95th percentile values were calculated to be 0.03ng/kg b.w. and 1.1ng/kg b.w. daily, respectively. Due to limited toxicological information and exposure data for other relevant pathways (e.g., dietary intake), the risk assessment is inconclusive. Nevertheless, there are indications that 9H-carbazole has carcinogenic properties and that halogenated carbazoles have dioxin-like toxicities. Therefore, further research is essential.

Diversity and Abundance of High-Molecular-Weight Azaarenes in PAH-Contaminated Environmental Samples

Azaarenes are N-heterocyclic polyaromatic pollutants that co-occur with polycyclic aromatic hydrocarbons (PAHs) in contaminated soils. Despite the known toxicity of some high-molecular-weight azaarenes, their diversity, abundance, and fate in contaminated soils remain to be elucidated. We applied high-resolution mass spectrometry and mass-defect filtering to four PAH-contaminated samples from geographically distant sites and detected 232 azaarene congeners distributed in eight homologous series, including alkylated derivatives and two hitherto unknown series. Four- and five-ring azaarenes were detected among these series, and the most abundant nonalkylated congeners groups (C₁₃H₉N, C₁₅H₉N, C₁₇H₁₁N, C₁₉H₁₁N, and C₂₁H₁₃N) were quantified. The profiles of congener groups varied among different sites. Three-ring azaarenes presented higher concentrations in unweathered sites, while four- and five-ring azaarenes predominated in weathered sites. Known toxic and carcinogenic azaarenes, such as benzo[c]acridine and dibenzo[a,h]acridine, were detected along with their multiple isomers. Our results highlight a previously unrecognized diversity and abundance of azaarenes in PAH-contaminated sites, with corresponding implications for environmental monitoring and risk assessment.

Cancer risk from polycyclic aromatic compounds in fine particulate matter generated from household coal combustion in Xuanwei, China

Polycyclic aromatic hydrocarbons (PAHs) and their polar derivatives (oxygenated PAHs: OPAHs and azaarenes: AZAs) were characterized in fine particulates (PM_2.5) emitted from indoor coal combustion. Samples were collected in Xuanwei (Yunnan Province), a region in China with a high rate of lung cancer. A sample from the community with the highest mortality contained the highest total concentration of PAHs, OPAHs and AZAs and posed the highest excess cancer risk from a lifetime of inhaling fine particulates. Positive correlations between total carbonyl-OPAHs, total AZAs and total PAHs implied that the emissions were dependent on similar factors, regardless of sample location and type. The calculated cancer risk ranged from 5.23-10.7 × 10^-3, which is higher than the national average. The risk in each sample was ∼1-2 orders of magnitude higher than that deemed high risk, suggesting that the safety of these households is in jeopardy. The lack of potency equivalency factors for the PAH derivatives could possibly have underestimated the overall cancer risk.

Azaarenes in fine particulate matter from the atmosphere of a Chinese megacity

Azaarenes (AZAs) are toxicologically relevant organic compounds with physicochemical properties that are significantly different from the well-studied polycyclic aromatic hydrocarbons (PAHs). However, little is known about their concentrations, seasonal variations, fate, and relationship with PAHs in air. This paper reports the temporal variations in the concentrations and composition patterns of AZAs in PM2.5 that was sampled once per 6 days from outdoor air of Xi'an, China from July 2008 to August 2009. The concentrations of the ∑AZAs, quinoline (QUI), benzo[h]quinoline (BQI), and acridine (ACR) in PM2.5 were 213-6441, 185-520, 69-2483, and 10-3544 pg m(-3), respectively. These concentrations were higher than those measured in urban areas of Western Europe. AZA compositional patterns were dominated by BQI and ACR. The high concentration of AZAs, high AZA/related PAH ratio, and the dominance of three-ring AZAs (BQI and ACR) in PM2.5 of Xi'an are all in contrast to observations from Western European and North American cities. This contrast likely reflects differences in coal type and the more intense use of coal in China. The PM2.5-bound concentration of AZA in winter season (W) was higher than during the summer season (S) with W/S ratios of 5.7, 1.4, 4.1, and 13, for ∑AZAs, QUI, BQI, and ACR, respectively. Despite their significantly different physicochemical properties, AZAs were significantly (p < 0.05) positively correlated with their related PAHs and pyrogenic elemental carbon. The changes in AZA concentrations were positively correlated with ambient pressure but negatively correlated with ambient temperature, wind speed, and relative humidity. This trend is similar to that observed for the related PAHs. We conclude that Xi'an and possibly other Chinese cities have higher emission of AZAs into their atmosphere because of the more pronounced use of coal. We also conclude that in spite of differences in physicochemical properties between AZAs and related PAHs, the atmospheric dynamics and relationships with meteorological factors of both compound groups are similar.

Characterization of chemical components and bioreactivity of fine particulate matter (PM2.5) during incense burning

The chemical and bioreactivity properties of fine particulate matter (PM2.5) emitted during controlled burning of different brands of incense were characterized. Incenses marketed as being environmentally friendly emitted lower mass of PM2.5 particulates than did traditional incenses. However, the environmentally friendly incenses produced higher total concentrations of non-volatile polycyclic aromatic hydrocarbons (PAHs) and some oxygenated polycyclic aromatic hydrocarbons (OPAHs). Human alveolar epithelial A549 cells were exposed to the collected PM2.5, followed by determining oxidative stress and inflammation. There was moderate to strong positive correlation (R > 0.60, p < 0.05) between selected PAHs and OPAHs against oxidative-inflammatory responses. Strong positive correlation was observed between interleukin 6 (IL-6) and summation of total Group B2 PAHs/OPAHs (∑7PAHs/ΣOPAHs). The experimental data indicate that emissions from the environmentally friendly incenses contained higher concentrations of several PAH and OPAH compounds than did traditional incense. Moreover, these PAHs and OPAHs were strongly correlated with inflammatory responses. The findings suggest a need to revise existing regulation of such products.

Occurrence, distribution and health risk from polycyclic aromatic compounds (PAHs, oxygenated-PAHs and azaarenes) in street dust from a major West African Metropolis

Scientific evidence suggests that the burden of disease on urban residents of sub-Saharan African Countries is increasing, partly as a result of exposure to elevated concentrations of toxic environmental chemicals. However, characterization of the levels, composition pattern and sources of polycyclic aromatic compounds (PACs) in environmental samples from African cities is still lacking. This study measured the PAHs, oxygenated-PAHs (OPAHs) and azaarene (AZAs) content of street dusts collected from Kumasi, Ghana (a major metropolis located in the tropical forest zone of West Africa). The ∑Alkyl+parent-PAHs, ∑OPAHs and ∑AZAs concentration in street dust averaged 2570 ng g(-1) (range: 181-7600 ng g(-1)), 833 ng g(-1) (57-4200 ng g(-1)) and 73 ng g(-1) (3.3-240 ng g(-1)), respectively. The concentrations of ∑Alkyl+parent-PAHs were strongly correlated (n=25) with ∑OPAHs (r=0.96, p<0.01) and ∑AZAs (r=0.94, p<0.01). The ∑OPAHs concentrations were also strongly correlated with ∑AZAs (r=0.91, p<0.01). Concentrations of individual PAHs in these street dusts were enriched at between 12 and 836 compared to their average concentrations in background soils from same city, demonstrating the high influence of traffic emissions. Several individual OPAHs and AZAs had higher concentrations than their related and often monitored parent-PAHs. The estimated incremental lifetime cancer risks due to the parent-PAHs in street dusts was >10(-6) indicating high risk of contracting cancer from exposure to street dust from Kumasi. The contribution of OPAHs, AZAs, and alkyl-PAHs in street dust to cancer risk could not be quantified because of lack of toxicity equivalency factors for these compounds; however this could be significant because of their high concentration and known higher toxicity of some polar PACs and alkyl-PAHs than their related parent-PAHs.

Characterizing the parent and oxygenated polycyclic aromatic hydrocarbons in mangrove sediments of Hong Kong

Parent and oxygenated polycyclic aromatic hydrocarbons (PAHs) were investigated in mangrove sediments of Hong Kong. Most of the analytes were detected, and the dominant carbonylic and hydroxylated PAHs in mangrove sediments were 9-fluorenone and 2-hydroxy fluorene, respectively. The concentration of 9-fluorenone and 9,10-anthraquinone was higher than their parent PAHs. Moreover, the concentration of total organic matter (TOM) related with those of the parent PAHs and carbonylic PAHs, except for hydroxylated PAHs, which indicated that TOM was not the only factor regulating the distribution of oxygenated PAHs. Nevertheless, the parent PAHs in mangrove sediments was correlated positively with carbonylic PAHs which demostrated not only the similar source but also the fate of these two compound class. However, hydroxylated PAHs had different source by comparing with parent PAHs and carbonylic PAHs, they were probably originated from biodegradation and accumulated in mangrove sediments.

Accumulation of polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs (OPAHs) in organic and mineral soil horizons from four U.S. remote forests

We characterized distributions of 23 polycyclic aromatic hydrocarbons (Σ23PAH) and nine oxygenated PAHs (Σ9OPAH) in four remote forests. We observed highest Σ23PAH and Σ9OPAH concentrations in a coniferous forest in Florida, particularly in organic layers which we attributed to frequent prescribed burning. Across sites, Σ23PAH and Σ9OPAH concentrations strongly increased from surface to humidified organic layers (+1626%) where concentrations reached up to 584 ng g(-1). Concentrations in mineral soils were lower (average 37 ± 8 ng g(-1)); but when standardized per unit organic carbon (OC), PAH/OC and OPAH/OC ratios were at or above levels observed in organic layers. Accumulation in litter and soils (i.e., enrichment factors with depth) negatively correlated with octanol-water partition coefficients (Kow) and therefore was linked to water solubility of compounds. Concentrations of Σ9OPAHs ranged from 6 ± 6 ng g(-1) to 39 ± 25 ng g(-1) in organic layers, and from 3 ± 1 ng g(-1) to 11 ± 3 ng g(-1) in mineral soils, and were significantly and positively correlated to Σ23PAHs concentrations (r(2) of 0.90) across sites and horizons. While OPAH concentrations generally decreased from organic layers to mineral soil horizons, OPAH/OC ratios increased more strongly with depth compared to PAHs, in particular for anthrone, anthraquinone, fluorenone, and acenaphthenequinone. The strong vertical accumulation of OPAH relative to OC was exponentially and negatively correlated to C/N ratios (r(2)=0.67), a measure that often is used for tissue age. In fact, C/N ratios alone explained two-thirds of the variability in OPAH/OC ratios suggesting particularly high retention, sorption, and persistency of OPAHs in old, decomposed carbon fractions.

Polycyclic aromatic hydrocarbons (PAHs) and their derivatives (alkyl-PAHs, oxygenated-PAHs, nitrated-PAHs and azaarenes) in urban road dusts from Xi'an, Central China

Urban road dusts are carriers of polycyclic aromatic compounds (PACs) and are therefore considered to be a major source of contamination of other environmental compartments and a source of exposure to PACs for urban populations. We determined the occurrence, composition pattern and sources of several PACs (29 alkyl- and parent-PAHs, 15 oxygenated-PAHs (OPAHs), 4 azaarenes (AZAs), and 11 nitrated-PAHs (NPAHs)) in twenty urban road dusts and six suburban surface soils (0-5cm) from Xi'an, central China. The average concentrations of ∑29PAHs, ∑4AZAs, ∑15OPAHs, and ∑11NPAHs were 15767, 673, 4754, and 885 n gg(-1) in road dusts and 2067, 784, 854, and 118 ng g(-1) in surface soils, respectively. The concentrations of most individual PACs were higher in street dusts than suburban soils, particularly for PACs with molecular weight>192 g mol(-1). The enrichment factors of individual PACs were significantly positively correlated with log KOA and log KOW, indicating an increasing deposition and co-sorption of the PACs in urban dusts with decreasing volatility and increasing hydrophobicity. Significant correlations between the concentrations of individual and sum of PACs, carbon fractions (soot and char), and source-characteristic PACs (combustion-derived PAHs and retene, etc.), indicated that PAHs, OPAHs and AZAs were mostly directly emitted from combustion activities and had similar post-emission fates, but NPAHs were possibly more intensely photolyzed after deposition as well as being emitted from vehicle exhaust sources. The incremental lifetime cancer risk (ILCR) resulting from exposure to urban dust bound-PACs was higher than 10(-6), indicating a non-negligible cancer risk to residents of Xi'an.