Ozone Oxidation of Surface-Adsorbed Polycyclic Aromatic Hydrocarbons: Role of PAH−Surface Interaction

The key characteristics of cardiotoxicity for the pervasive pollutant phenanthrene

The key characteristic (KCs) framework has been used previously to assess the carcinogenicity and cardiotoxicity of various chemical and pharmacological agents. Here, the 12 KCs of cardiotoxicity are used to evaluate the previously reported cardiotoxicity of phenanthrene (Phe), a tricyclic polycyclic aromatic hydrocarbon (PAH), and major component of fossil fuel-derived air pollution. Phe is a semi-volatile pollutant existing in both the gas phase and particle phase through adsorption onto or into particulate matter (PM). Phe can translocate across the airways and gastrointestinal tract into the systemic circulation, enabling body-wide effects. Our evaluation based on a comprehensive literature review, indicates Phe exhibits 11 of the 12 KCs for cardiotoxicity. These include adverse effects on cardiac electromechanical performance, the vasculature and endothelium, immunomodulation and oxidative stress, and neuronal and endocrine control. Environmental agents that have similarly damaging effects on the cardiovascular system are heavily regulated and monitored, yet globally there is no air quality regulation specific for PAHs like Phe. Environmental monitoring of Phe is not the international standard with benzo[a]pyrene being frequently used as a proxy despite the two PAH species exhibiting significant differences in sources, concentration variations and toxic effects. The evidence summarised in this evaluation highlights the need to move away from proxied PAH measurements and develop a monitoring network capable of measuring Phe concentration. It also stresses the need to raise awareness amongst the medical community of the potential cardiovascular impact of PAH exposure. This will allow the production of mitigation strategies and possibly the development of new policies for the protection of the societal groups most vulnerable to cardiovascular disease.

Molecular signatures of organic particulates as tracers of emission sources

Chemical signature of airborne particulates and deposition dusts is subject of study since decades. Usually, three complementary composition markers are investigated, namely, (i) specific organic compounds; (ii) concentration ratios between congeners, and (iii) percent distributions of homologs. Due to its intrinsic limits (e.g., variability depending on decomposition and gas/particle equilibrium), the identification of pollution sources based on molecular signatures results overall restricted to qualitative purposes. Nevertheless, chemical fingerprints allow drawing preliminary information, suitable for successfully approaching multivariate analysis and valuing the relative importance of sources. Here, the state-of-the-art is presented about the molecular fingerprints of non-polar aliphatic, polyaromatic (PAHs, nitro-PAHs), and polar (fatty acids, organic halides, polysaccharides) compounds in emissions. Special concern was addressed to alkenes and alkanes with carbon numbers ranging from 12 to 23 and ≥ 24, which displayed distinct relative abundances in petrol-derived spills and exhausts, emissions from microorganisms, high vegetation, and sediments. Long-chain alkanes associated with tobacco smoke were characterized by a peculiar iso/anteiso/normal homolog fingerprint and by n-hentriacontane percentages higher than elsewhere. Several concentration ratios of PAHs were identified as diagnostic of the type of emission, and the sources of uncertainty were elucidated. Despite extensive investigations conducted so far, the origin of uncommon molecular fingerprints, e.g., alkane/alkene relationships in deposition dusts and airborne particles, remains quite unclear. Polar organics resulted scarcely investigated for pollution apportioning purposes, though they looked as indicative of the nature of sources. Finally, the role of humans and living organisms as actual emitters of chemicals seems to need concern in the future.

Evaluation of OH Radical Reaction Positions in 3-Ring PAHs Using Transition State Energy and Atomic Charge Calculations

In this study, transition state energy and atomic charge were calculated using the Gaussian 09 program with focus on three-ring PAHs, such as acenaphthylene and anthracene, which are most likely found in contaminated sites. The calculation results were then compared with the radical reaction positions reported in the existing literature. Because the energy difference between the reactant and the transition state according to the reaction position was very small, no distinct correlation was obtained when results were compared with those of the OH radical test findings reported in the literature. It was also found that the charge calculation makes it possible to accurately predict the radical reaction position of the target material. In addition, MK and HLY charges were found to be more accurate than CHelpG charges in predicting the radical reaction positions. The charge calculation can also be applied in predicting radical reaction positions for hazardous materials with different molecular structures.

A review of potentially harmful chemicals in crumb rubber used in synthetic football pitches

Recycling end-of-life tires (ELTs) reduces waste and provides a low-cost source of energy and materials such as crumb rubber, used as infill in artificial turf football pitches. However, some concerns were raised and remain about its safety. The potentially toxic human exposure to chemicals such as polycyclic aromatic hydrocarbons (PAHs), metals and others (volatile organic compounds (VOCs), plasticizers, antioxidants and additives) existing in ELTs (and in the resulting crumb rubber) is being studied, with no definitive conclusions. The literature existing so far suggests the possibility of their release from synthetic turf infill into the environment as water leachates and to the air surrounding the pitches, but there is the need of further research, also to assess the contribution of other materials present in synthetic turf. The database available comprised crumb rubber infill studies from pitches in 6 countries (USA, Norway, Netherlands, Portugal, Italy, Spain) and revealed a myriad of hazardous chemicals, with benzo[a]pyrene (n.d.-4.31 ± 3.95 mg/kg) and zinc (n.d.-14150 ± 1344 mg/kg) often exceeding the established limits. A dependence on indoor/outdoor conditions and the age of the source material was evaluated, often showing significative differences. From this standpoint, this review is intended to add knowledge about the presence of contaminants in this recycled material, aiming to ensure the safety of end-users and the environment.

Redox toxicology of environmental chemicals causing oxidative stress

Living organisms are surrounded with heavy metals such as methylmercury, manganese, cobalt, cadmium, arsenic, as well as pesticides such as deltamethrin and paraquat, or atmospheric pollutants such as quinone. Extensive studies have demonstrated a strong link between environmental pollutants and human health. Redox toxicity is proposed as one of the main mechanisms of chemical-induced pathology in humans. Acting as both a sensor of oxidative stress and a positive regulator of antioxidants, the nuclear factor erythroid 2-related factor 2 (NRF2) has attracted recent attention. However, the role NRF2 plays in environmental pollutant-induced toxicity has not been systematically addressed. Here, we characterize NRF2 function in response to various pollutants, such as metals, pesticides and atmospheric quinones. NRF2 related signaling pathways and epigenetic regulations are also reviewed.

Intense electrochemiluminescence from an organic microcrystal accelerated H2O2-free luminol system for microRNA detection

The 9,10-diphenylanthracene microcrystals (DPA MCs) was developed as a novel coreactant accelerator for H₂O₂-free luminol system, which was attributed to the efficiently catalysis towards dissolved O₂ for more reactive oxygen species generation.

Real-time analysis of the homogeneous and heterogeneous reactions of pyrene with ozone by SPAMS and CRD-EAS

Single particle aerosol mass spectrometry (SPAMS) and Cavity ring-down aerosol extinction albedo spectroscopy (CRD-EAS) were applied in this work to real-time investigate the chemical and physical characteristics of the homogeneous and heterogeneous reactions of O₃ with pyrene in a Teflon reaction chamber. Suspended pyrene coated polystyrene latex spheres (PSLs) were generated by vaporization-condensation. Ozonation products and particle size distribution during the reactions were detected in real-time using a SPAMS instrument. Among these products, the peaks at m/z of 262 and 278, assigned to 4,5,9,10-dipyrenequinone and 1-hydroxy-4,5,9,10-dipyrenequinone, respectively, were first detected to our knowledge. The mechanism for the formation of reaction product was also proposed based on the real time monitoring. With increasing the ozone concentration, the size growth of the original pyrene-coated particles and the formation of new fine particles and size growth were observed continuously. The optical characteristics were also investigated using a laboratory-developed CRD-EAS instrument. The extinction and scattering coefficients were observed to increase approximately five and four times, respectively. The absorption coefficient also increased because more polar oxidation products coated on the particles exhibiting higher light absorption ability than pyrene, and meanwhile, the single scattering albedo reduced from 0.88 to 0.77 which indicated the reactions could cause positive climate forcing. Using the on-line mass spectrometry and optic spectroscopy instruments, a systematic analysis method was developed to characterize the chemical and physical properties of homogeneous and heterogeneous reactions in real-time, which will help to investigate and understand the formation of new particles and particle growth in the atmosphere.

Formation and Evolution of Solvent-Extracted and Nonextractable Environmentally Persistent Free Radicals in Fly Ash of Municipal Solid Waste Incinerators

Environmentally persistent free radicals (EPFRs) are emerging contaminants occurring in combustion-borne particulates and atmospheric particulate matter, but information on their formation and behavior on fly ash from municipal solid waste (MSW) incinerators is scarce. Here, we have found that MSW-associated fly ash samples contain an EPFR concentration of 3-10 × 10¹⁵ spins g^-1, a line width (ΔH_p-p) of ∼8.6 G, and a g-factor of 2.0032-2.0038. These EPFRs are proposed to be mixtures of carbon-centered and oxygen-centered free radicals. Fractionation of the fly ash-associated EPFRs into solvent-extracted and nonextractable radicals suggests that the solvent-extracted part accounts for ∼45-73% of the total amount of EPFRs. Spin densities of solvent-extracted EPFRs correlate positively with the concentrations of Fe, Cu, Mn, Ti, and Zn, whereas similar correlations are comparatively insignificant for nonextractable EPFRs. Under natural conditions, these two types of EPFRs exhibit different stabilization that solvent-extracted EPFRs are relatively unstable, whereas the nonextractable fraction possesses a long life span. Significant correlations between concentrations of solvent-extracted EPFRs and generation of hydroxyl and superoxide radicals are found. Overall, our results suggest that the fractionated solvent-extracted and nonextractable EPFRs may experience different formation and stabilization processes and health effects.

Formation of Polycyclic Aromatic Hydrocarbon Oxidation Products in α-Pinene Secondary Organic Aerosol Particles Formed through Ozonolysis

Accurate long-range atmospheric transport (LRAT) modeling of polycyclic aromatic hydrocarbons (PAHs) and PAH oxidation products (PAH-OPs) in secondary organic aerosol (SOA) particles relies on the known chemical composition of the particles. Four PAHs, phenanthrene (PHE), dibenzothiophene (DBT), pyrene (PYR), and benz(a)anthracene (BaA), were studied individually to identify and quantify PAH-OPs produced and incorporated into SOA particles formed by ozonolysis of α-pinene in the presence of PAH vapor. SOA particles were characterized using real-time in situ instrumentation, and collected on quartz fiber filters for offline analysis of PAHs and PAH-OPs. PAH-OPs were measured in all PAH experiments at equal or greater concentrations than the individual PAHs they were produced from. The total mass of PAH and PAH-OPs, relative to the total SOA mass, varied for different experiments on individual parent PAHs: PHE and 6 quantified PHE-OPs (3.0%), DBT and dibenzothiophene sulfone (4.9%), PYR and 3 quantified PYR-OPs (3.1%), and BaA and benz(a)anthracene-7,12-dione (0.26%). Further exposure of PAH-SOA to ozone generally increased the concentration ratio of PAH-OPs to PAH, suggesting longer atmospheric lifetimes for PAH-OPs, relative to PAHs. These data indicate that PAH-OPs are formed during SOA particle formation and growth.

Effects of air/fuel ratio and ozone aging on physicochemical properties and oxidative potential of soot particles

Fuel combustion conditions and atmospheric aging processes can affect the physicochemical properties of soot particles, which further change the oxidative potential (OP) of soot. In this study, we generated two soot samples under higher and lower air/fuel ratio (A/F) conditions, and further treated them with ozone (O₃) at a level similar to that in the polluted atmosphere. The physicochemical properties and OP values (measured by dithiothreitol (DTT) assay, OP^DTT) of fresh and ozonised soot samples were compared to investigate the influences of A/F and O₃ aging. Both A/F and O₃ aging significantly affected soot physicochemical properties and OP^DTT values. Lower A/F was favourable for generating soot particles containing more polycyclic aromatic hydrocarbon (PAH), water-soluble organic carbon (WSOC), and light-absorbing organics, but fewer oxygen-containing groups. After O₃ aging, a decline in PAHs and increase in oxygen-containing groups and WSOC were observed in both aged soot samples. In addition, both lower A/F and O₃ aging enhanced soot OP^DTT values. Soot generated under lower A/F was more sensitive to O₃ aging, after which there was a significantly greater change in physicochemical characteristics, in turn contributing substantially to the greater OP increase observed in low-A/F soot.

Co-metabolic degradation of naphthalene and pyrene by acclimated strain and competitive inhibition kinetics

A dominant strain named Ochrobactrum sp. was isolated from soils contaminated with coal tar. The batch experiments were carried out to study the co-metabolic degradation of pyrene by Ochrobactrum MB-2 with naphthalene as the main substrate and the effects of several significant parameters such as naphthalene concentration, pH and temperature on removal efficiency were explored. The results showed that Ochrobactrum MB-2 effectively degraded naphthalene and that the addition of naphthalene favored the degradation of pyrene. The maximum elimination efficiency of naphthalene (10 mg L^-1) and pyrene (1 mg L^-1) was achieved at pH 7 and 25 °C, and the corresponding values were 99 and 41%, respectively. A competitive inhibition model based on the Michaelis-Menten equation was used to characterize the inhibitory effect of pyrene on naphthalene degradation. The values of the half-saturation coefficient for naphthalene (K_S) and dissociation constant of enzyme-inhibitor complex (K_C) were determined to be 4.93 and 1.38 mg L^-1, respectively.

Impacts of photochemical ageing on the half-lives and diagnostic ratio of polycyclic aromatic hydrocarbons intrinsic to PM2.5 collected from 'real-world' like combustion events of wood and rice straw burning

The present experimental study describes the characteristics of polycyclic aromatic hydrocarbons (PAHs) emitted with PM_2.5 particles during wood and rice straw burning as well as impacts of photochemical ageing on the half lives of particulate PAHs and their diagnostic ratio values. The photochemical degradation kinetics experiments were carried out by exposing the PM_2.5 to light and synthetic air flow. Pseudo first order rate constants were calculated based on PAH loss as a function of exposure time. Relatively quick degradation of lighter PAHs (3-rings) [(0.2-0.5)h^-1] than heavier PAHs (4-6 rings) [(0.0005-0.03)h^-1] indicates substantial impact of PAH-substrate interaction through π-π stacking with the carbonaceous substrates. Moreover, our results showed distinct PAH diagnostic ratios (DR) for wood and rice straw burnings which, however, change with time due to photochemical degradation. The later may add uncertainties in the applications of DR values for source apportionment. Furthermore, considerably large half lives (100-3000 h) of the carcinogenic PAHs as estimated under ambient solar radiation may cause poor and adverse air quality in long range and therefore demands immediate regulations against uncontrolled biomass burning.

Evaluating Computational and Structural Approaches to Predict Transformation Products of Polycyclic Aromatic Hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) undergo transformation reactions with atmospheric photochemical oxidants, such as hydroxyl radicals (OH•), nitrogen oxides (NOx), and ozone (O3). The most common PAH-transformation products (PAH-TPs) are nitrated, oxygenated, and hydroxylated PAHs (NPAHs, OPAHs, and OHPAHs, respectively), some of which are known to pose potential human health concerns. We sampled four theoretical approaches for predicting the location of reactive sites on PAHs (i.e., the carbon where atmospheric oxidants attack), and hence the chemoselectivity of the PAHs. All computed results are based on density functional theory (B3LYP/6-31G(d) optimized structures and energies). The four approaches are (1) Clar's prediction of aromatic resonance structures, (2) thermodynamic stability of all OHPAH adduct intermediates, (3) computed atomic charges (Natural Bond order, ChelpG, and Mulliken) at each carbon on the PAH, and (4) average local ionization energy (ALIE) at atom or bond sites. To evaluate the accuracy of these approaches, the predicted PAH-TPs were compared to published laboratory observations of major NPAH, OPAH, and OHPAH products in both gas and particle phases. We found that the Clar's resonance structures were able to predict the least stable rings on the PAHs but did not offer insights in terms of which individual carbon is most reactive. The OHPAH adduct thermodynamics and the ALIE approaches were the most accurate when compared to laboratory data, showing great potential for predicting the formation of previously unstudied PAH-TPs that are likely to form in the atmosphere.

Volatilization and oxidative artifacts of PM bound PAHs collected at low volume sampling (1): Laboratory and field evaluation

Laboratory and field studies were carried out to assess the effects of oxidative degradation and volatilization on PM₁₀ bound polycyclic aromatic hydrocarbons (PAHs), collected at low volume condition according to the EU sampling reference method EN12341:2014 (flow rate 2.3 m³ h^-1), on 47 mm quartz filters. For the laboratory experiments, pairs of twin samples were collected in field and, after treatments favoring decomposition or/and volatilization of PAHs on one sample, the PAH amount was compared with that of the corresponding untreated sample. Ozone exposure caused a general PAHs decay with more marked effects on benzo [a]pyrene, perylene and benz [a]anthracene; these compounds showed, similarly to benzo [ghi]perylene, correlations between ozone dose and losses. Treatments with zero air exhibited losses due to volatilization even for 5-ring PAHs up to benzo [a]pyrene, whereas a linear dependence was observed between filter PAH load and losses for benzo [a]anthracene, chrysene and benzofluoranthenes. Concentrations on samples collected simultaneously over 48, 24, 12 and 6 h were compared. Results confirmed a lack of temporal auto-consistency in the PAHs sampling methodology here adopted. In particular higher atmospheric PAH concentrations were ascertained on samples constituted by cumulative filters exposed over shorter sampling times. When 24-h and 2 × 12-h samples were compared, comparable losses were evaluated in the hot and cold seasons. This finding shows that, although in summer meteorology conditions favor sampling artifacts, the effectiveness of these phenomena continue in the winter, probably due to the larger amount of PAH available on the sampling filter (total PAHs ∼ 10 vs 0.5 ng m^-3).

Ultrafine Particulate Matter Combined With Ozone Exacerbates Lung Injury in Mature Adult Rats With Cardiovascular Disease

Particulate matter (PM) and ozone (O3) are dominant air pollutants that contribute to development and exacerbation of multiple cardiopulmonary diseases. Mature adults with cardiovascular disease (CVD) are particularly susceptible to air pollution-related cardiopulmonary morbidities and mortalities. The aim was to investigate the biologic potency of ultrafine particulate matter (UFPM) combined with O3 in the lungs of mature adult normotensive and spontaneously hypertensive (SH) Wistar-Kyoto rats. Conscious, mature adult male normal Wistar-Kyoto (NW) and SH rats were exposed to one of the following atmospheres: filtered air (FA); UFPM (∼ 250 μg/m3); O3 (1.0 ppm); or UFPM + O3 (∼ 250 μg/m3 + 1.0 ppm) combined for 6 h, followed by an 8 h FA recovery period. Lung sections were evaluated for lesions in the large airways, terminal bronchiolar/alveolar duct regions, alveolar parenchyma, and vasculature. NW and SH rats were similarly affected by the combined-pollutant exposure, displaying severe injury in both large and small airways. SH rats were particularly susceptible to O3 exposure, exhibiting increased injury scores in terminal bronchioles and epithelial degeneration in large airways. UFPM-exposure groups had minimal histologic changes. The chemical composition of UFPM was altered by the addition of O3, indicating that ozonolysis promoted compound degradation. O3 increased the biologic potency of UFPM, resulting in greater lung injury following exposure. Pathologic manifestations of CVD may confer susceptibility to air pollution by impairing normal lung defenses and responses to exposure.

The effect of gas-phase polycyclic aromatic hydrocarbons on the formation and properties of biogenic secondary organic aerosol particles

When secondary organic aerosol (SOA) particles are formed by ozonolysis in the presence of gas-phase polycyclic aromatic hydrocarbons (PAHs), their formation and properties are significantly different from SOA particles formed without PAHs. For all SOA precursors and all PAHs, discussed in this study, the presence of the gas-phase PAHs during SOA formation significantly affects particle mass loadings, composition, growth, evaporation kinetics, and viscosity. SOA particles formed in the presence of PAHs have, as part of their compositions, trapped unreacted PAHs and products of heterogeneous reactions between PAHs and ozone. Compared to 'pure' SOA particles, these particles exhibit slower evaporation kinetics, have higher fractions of non-volatile components, like oligomers, and higher viscosities, assuring their longer atmospheric lifetimes. In turn, the increased viscosity and decreased volatility provide a shield that protects PAHs from chemical degradation and evaporation, allowing for the long-range transport of these toxic pollutants. The magnitude of the effect of PAHs on SOA formation is surprisingly large. The presence of PAHs during SOA formation increases mass loadings by factors of two to five, and particle number concentrations, in some cases, by more than a factor of 100. Increases in SOA mass, particle number concentrations, and lifetime have important implications to many atmospheric processes related to climate, weather, visibility, and human health, all of which relate to the interactions between biogenic SOA and anthropogenic PAHs. The synergistic relationship between SOA and PAHs presented here are clearly complex and call for future research to elucidate further the underlying processes and their exact atmospheric implications.

Chemical toxicology of reactive species in the atmosphere: two decades of progress in an electron acceptor and an electrophile

Air pollutants such as diesel exhaust particles (DEP) are thought to cause pulmonary diseases such as asthma as a result of oxidative stress. While DEP contain a large number of polycyclic aromatic hydrocarbons, we have focused on 9,10-phenanthrenequinone (9,10-PQ) and 1,2-naphthoquinone (1,2-NQ) because of their chemical properties based on their oxidative and chemical modification capabilities. We have found that 9,10-PQ interacts with electron donors such as NADPH (in the presence of enzymes) and dithiols, resulting in generation of excess reactive oxygen species (ROS) through redox cycling. We have also shown that 1,2-NQ is able to modify protein thiols, leading to protein adducts associated with activation of redox signal transduction pathways at lower concentrations and toxicity at higher concentrations. In this review, we briefly introduce our findings from the last two decades.

The degradation mechanism of sulfamethoxazole under ozonation: a DFT study

Sulfamethoxazole (SMX), a kind of antibiotic, remains in the environment and threatens public health. Ozone as a strong and green oxidant was widely used for selective oxidation degradation of residual SMX. However, it is hard to elucidate the detailed oxidation mechanism through current experimental approaches. A theoretical study has been carried out herein for exploring possible ozonation pathways of SMX. Two reaction mechanisms, viz., direct addition (DA) and H atom transfer (HAT), are considered. The results show that the primary oxidation of aromatic rings (benzene or isoxazole rings) of SMX follows the DA mechanism, featuring an electrophilic addition. Whereas, the oxidation of amino and methyl groups of SMX follows the HAT mechanism. Following the proposed mechanisms, the primary oxidation products detected in previous experiments could reasonably be obtained according to the current calculations. More importantly, O₃ molecules as an electrophilic agent feasibly attack the moiety having a large orbital contribution to the highest occupied molecular orbital (HOMO) of sulfonamides. This result suggests that the primary ozonation site of sulfonamides could be theoretically predictable through the information of their frontier molecular orbitals. Meanwhile, a positive correlation between the O₃-mediated HAT energy barriers and bond dissociation energies has been found for N-H and C-H bond oxidations.

Variations of polycyclic aromatic hydrocarbons in ambient air during haze and non-haze episodes in warm seasons in Hangzhou, China

To investigate the characteristics of polycyclic aromatic hydrocarbons (PAHs) during haze episodes in warm seasons, daily PM_2.5 and gaseous samples were collected from March to September 2015 in Hangzhou, China. Daily samples were further divided into four groups by the definition of haze according to visibility and relative humidity (RH), including non-haze (visibility, >10 km), light haze (visibility, 8-10 km, RH <90 %), medium haze (visibility, 5-8 km, RH <90 %), and heavy haze (visibility, <5 km, RH <90 %). Significantly higher concentrations of PM_2.5-bound PAHs were found in haze days, but the mean PM_2.5-bound PAH concentrations obviously decreased with the aggravation of haze pollution from light to heavy. The gas/particle partitioning coefficients of PAHs decreased from light-haze to heavy-haze episodes, which indicated that PM_2.5-bound PAHs were restricted to adhere to the particulate phase with the aggravation of haze pollution. Absorption was considered the main mechanism of gas/particle partitioning of PAHs from gaseous to particulate phase. Analysis of air mass transport indicated that the PM_2.5-bound PAH pollution in haze days was largely from regional sources but also significantly affected by long-range air mass transport. The inhalation cancer risk associated with PAHs exceeded the acceptable risk level markedly in both haze and non-haze days.

Heterogeneous chemistry and reaction dynamics of the atmospheric oxidants, O3, NO3, and OH, on organic surfaces

Heterogeneous chemistry of the most important atmospheric oxidants, O₃, NO₃, and OH, plays a central role in regulating atmospheric gas concentrations, processing aerosols, and aging materials.

Formation of environmentally persistent free radicals from the heterogeneous reaction of ozone and polycyclic aromatic compounds

In the 1980s long-lived radical species were identified in cigarette tar. Since then, environmentally persistent free radicals (EPFRs) have been observed in ambient particulate matter, and have been generated in particulate matter generated from internal combustion engines. For the first time, we measure in situ the formation and decay of EPFRs through the heterogeneous reaction of ozone and several polycyclic aromatic compounds (PAC). Solid anthracene (ANT), pyrene (PY), benzo[a]pyrene (BAP), benzo[ghi]perylene (BGHIP), 1,4-naphthoquinone (1,4NQ), and 9,10-anthraquinone (AQ) were reacted with gas-phase ozone in a flow system placed in the active cavity of an electron paramagnetic resonance (EPR) spectrometer, and the formation of radicals was measured on the timescale of tens of minutes at ambient levels of ozone down to 30 ppb. For most substrates the net radical production is initially rapid, slows at intermediate times, and is followed by a slow decay. For oxidized solid BAP, radical signal persists for many days in the absence of ozone. To evaluate the effect of substrate phase, the solid PAHs were also dissolved in squalane, an organic oil inert to ozone, which yielded a much higher maximum radical concentration and faster radical decay when exposed to ozone. With higher mobility, reactants were apparently able to more easily diffuse and react with each other, yielding the higher radical concentrations. The EPR spectra exhibit three radicals types, two of which have been assigned to semiquinone species and one to a PAH-derived, carbon-centered radical. Although our system uses levels of PAC not typically found in the environment it is worth noting that the amounts of radical formed, on the order of 10(18) radicals per g, are comparable to those observed in ambient particulate matter.

A theoretical study of the ozonolysis of C60: primary ozonide formation, dissociation, and multiple ozone additions

We present an investigation of the reaction of ozone with C60 fullerene using electronic structure methods. Motivated by recent experiments of ozone exposure to a C60 film, we have characterized stationary points in the potential energy surface for the reactions of O3 with C60 that include both the formation of primary ozonide and subsequent dissociation reactions of this intermediate that lead to C-C bond cleavage. We have also investigated the addition of multiple O3 molecules to the C60 cage to explore potential reaction pathways under the high ozone flux conditions used in recent experiments. The lowest-energy product of the reaction of a single ozone molecule with C60 that results in C-C bond breakage corresponds to an open-cage C60O3 structure that contains ester and ketone moieties at the seam. This open-cage product is of much lower energy than the C60O + O2 products identified in prior work, and it is consistent with IR experimental spectra. Subsequent reaction of the open-cage C60O3 product with a second ozone molecule opens a low-energy reaction pathway that results in cage degradation via the loss of a CO2 molecule. Our calculations also reveal that, while full ozonation of all bonds between hexagons in C60 is unlikely even under high ozone concentration, the addition of a few ozone molecules to the C60 cage is favorable at room temperature.

Chemical and toxicological evolution of carbon nanotubes during atmospherically relevant aging processes

The toxicity of carbon nanotubes (CNTs) has received significant attention due to their usage in a wide range of commercial applications. While numerous studies exist on their impacts in water and soil ecosystems, there is a lack of information on the exposure to CNTs from the atmosphere. The transformation of CNTs in the atmosphere, resulting in their functionalization, may significantly alter their toxicity. In the current study, the chemical modification of single wall carbon nanotubes (SWCNTs) via ozone and OH radical oxidation is investigated through studies that simulate a range of expected tropospheric particulate matter (PM) lifetimes, in order to link their chemical evolution to toxicological changes. The results indicate that the oxidation favors carboxylic acid functionalization, but significantly less than other studies performed under nonatmospheric conditions. Despite evidence of functionalization, neither O3 nor OH radical oxidation resulted in a change in redox activity (potentially giving rise to oxidative stress) or in cytotoxic end points. Conversely, both the redox activity and cytotoxicity of SWCNTs significantly decreased when exposed to ambient urban air, likely due to the adsorption of organic carbon vapors. These results suggest that the effect of gas-particle partitioning of organics in the atmosphere on the toxicity of SWCNTs should be investigated further.

Degradation of polycyclic aromatic hydrocarbons in crumb tyre rubber catalysed by rutile TiO2 under UV irradiation

The polycyclic aromatic hydrocarbons (PAHs) in crumb tyre rubber were firstly degraded under UV irradiation in the presence of rutile TiO2 and hydrogen peroxide. The effects of light intensity, catalyst amount, oxidant amount, initial pH value, co-solvent content, and reaction time on degradation efficiency of typical PAHs in crumb tyre rubber were studied. The results indicated that UV irradiation, rutile TiO2, and hydrogen peroxide were beneficial to the degradation of PAHs and co-solvent could accelerate the desorption of PAHs from crumb tyre rubber. Up to 90% degradation efficiency of total 16 PAHs could be obtained in the presence of rutile TiO2 (1 wt%) and hydrogen peroxide (1.0 mL) under 1800 µW cm(-2) UV irradiation for 48 h. The high molecular weight PAHs (such as benz(a)pyrene) were more difficult to be degraded than low molecular weight PAHs (such as phenanthrene, chrysene). Moreover, through the characterization of reaction solution and degradation products via GC-MS, it was proved that the PAHs in crumb tyre rubber were successfully degraded.

The removal of fluoranthene by Agaricus bisporus immobilized in Ca-alginate modified by Lentinus edodes nanoparticles

Fruiting bodies of Agaricus bisporus (A. bisporus) were entrapped in Ca-alginate modified by Lentinus edodes nanoparticles (CA-LENP) to adsorb and biodegrade fluoranthene (FLU) efficiently from an aqueous solution in a fluidized bed bioreactor.

Degradation of polycyclic aromatic hydrocarbons (PAHs) in textile dyeing sludge by O3/H2O2 treatment

The main advantage of O₃/H₂O₂ treatment lies in the acceleration of the O₃ transformation process by the addition of H₂O₂. The removal rate (within 30 min) increased by 27% for Ph and 21% for An through the addition of H₂O₂ to the O₃ process.

Degradation of polycyclic aromatic hydrocarbons in a coking wastewater treatment plant residual by an O3/ultraviolet fluidized bed reactor

Coking wastewater treatment plant (CWWTP) represents a typical point source of polycyclic aromatic hydrocarbons (PAHs) to the water environment and threatens the safety of drinking water in downstream regions. To enhance the removal of residual PAHs from bio-treated coking wastewater, a pilot-scale O3/ultraviolet (UV) fluidized bed reactor (O3/UV FBR) was designed and different operating factors including UV irradiation intensity, pH, initial concentration, contact time, and hydraulic retention time (HRT) were investigated at an ozone level of 240 g h(-1) and 25 ± 3 °C. A health risk evaluation and cost analysis were also carried out under the continuous-flow mode. As far as we know, this is the first time an O3/UV FBR has been explored for PAHs treatment. The results indicated that between 41 and 75 % of 18 target PAHs were removed in O3/UV FBR due to synergistic effects of UV irradiation. Both increased reaction time and increased pH were beneficial for the removal of PAHs. The degradation of the target PAHs within 8 h can be well fitted by the pseudo-first-order kinetics (R (2) > 0.920). The reaction rate was also positively correlated with the initial concentrations of PAHs. The health risk assessment showed that the total amount of carcinogenic substance exposure to surface water was reduced by 0.432 g day(-1). The economic analysis showed that the O3/UV FBR was able to remove 18 target PAHs at a cost of US$0.34 m(-3). These results suggest that O3/UV FBR is efficient in removing residuals from CWWTP, thus reducing the accumulation of persistent pollutant released to surface water.

The effect of structural compositions on the biosorption of phenanthrene and pyrene by tea leaf residue fractions as model biosorbents

To enhance the removal efficiency of polycyclic aromatic hydrocarbons (PAHs) by natural biosorbent, sorption of phenanthrene and pyrene onto raw and modified tea leaves as a model biomass were investigated. Tea leaves were treated using Soxhlet extraction, saponification, and acid hydrolysis to yield six fractions. The structures of tea leaf fractions were characterized by elemental analysis, Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). The amorphous cellulose components regulated the sorption kinetics, capacity, and mechanism of biomass fractions. The adsorption kinetics fit well to pseudo-second-order model and isotherms followed the Freundlich equation. By the consumption of the amorphous cellulose under acid hydrolysis, both the aliphatic moieties and aromatic domains contributed to total sorption, thus sorption capacities of the de-sugared fractions were dramatically increased (5–20-fold for phenanthrene and 8–36-fold for pyrene). All de-sugared fractions exhibited non-linear sorption due to strong specific interaction between PAHs and exposed aromatic domains of biosorbent, while presenting a relative slow rate because of the condensed domain in de-sugared samples. The availability of strong sorption phases (aromatic domains) in the biomass fractions were controlled by polar polysaccharide components, which were supported by the FTIR, CHN, and SEM data.

Oxidation of c60 aerosols by atmospherically relevant levels of o3

Atmospheric processing of carbonaceous nanoparticles (CNPs) may play an important role in determining their fate and environmental impacts. This work investigates the reaction between aerosolized C60 and atmospherically relevant mixing ratios of O3 at differing levels of humidity. Results indicate that C60 is oxidized by O3 and forms a variety of oxygen-containing functional groups on the aerosol surface, including C60O, C60O2, and C60O3. The pseudo-first-order reaction rate between C60 and O3 ranges from 9 × 10(-6) to 2 × 10(-5) s(-1). The reaction is likely to be limited to the aerosol surface. Exposure to O3 increases the oxidative stress exerted by the C60 aerosols as measured by the dichlorofluorescein acellular assay but not by the uric acid, ascorbic acid, glutathione, or dithiothreitol assays. The initial prevalence of C60O and C60O2 as intermediate products is enhanced at higher humidity, as is the surface oxygen content of the aerosols. These results show that C60 can be oxidized when exposed to O3 under ambient conditions, such as those found in environmental, laboratory, and industrial settings.

Electrochemical conversion of unreactive pyrene to highly redox-active 1,2-quinone derivatives on a carbon nanotube-modified gold electrode surface and its selective hydrogen peroxide sensing

Pyrene (PYR) is a rigid, carcinogenic, unreactive, and nonelectrooxidizable compound. A multiwalled carbon nanotube (MWCNT)-modified gold electrode surface-bound electrochemical oxidation of PYR to a highly redox-active surface-confined quinone derivative (PYRO) at an applied potential of 1 V versus Ag/AgCl in pH 7 phosphate buffer solution has been demonstrated in this work. Among various carbon nanomaterials examined, the pristine MWCNT-modified gold electrode showed effective electrochemical oxidation of the PYR. The MWCNT's graphite impurity promotes the electrochemical oxidation reaction. Physicochemical and electrochemical characterizations of MWCNT@PYRO by Raman spectroscopy, FT-IR, X-ray photoelectron spectroscopy, and GC-MS reveal the presence of PYRO as pyrene-tetrone within the modified electrode. The quinone position of PYRO was identified as ortho-directing by an elegantly designed ortho-isomer-selective complexation reaction with copper ion as an MWCNT@PYRO-Cu(2+/1+)-modified electrode. Finally, a cytochrome c enzyme-modified Au/MWCNT@PYRO (i.e., Au/MWCNT@PYRO-Cyt c) was also developed and further demonstrated for the selective biosensing of hydrogen peroxide.

Rate acceleration of the heterogeneous reaction of ozone with a model alkene at the air-ice interface at low temperatures

The kinetics of the ozonation reaction of 1,1-diphenylethylene (DPE) on the surface of ice grains (also called "artificial snow"), produced by shock-freezing of DPE aqueous solutions or DPE vapor-deposition on pure ice grains, was studied in the temperature range of 268 to 188 K. A remarkable and unexpected increase in the apparent ozonation rates with decreasing temperature was evaluated using the Langmuir-Hinshelwood and Eley-Rideal kinetic models, and by estimating the apparent specific surface area of the ice grains. We suggest that an increase of the number of surface reactive sites, and possibly higher ozone uptake coefficients are responsible for the apparent rate acceleration of DPE ozonation at the air-ice interface at lower temperatures. The increasing number of reactive sites is probably related to the fact that organic molecules are displaced more to the top of a disordered interface (or quasi-liquid) layer on the ice surface, which makes them more accessible to the gas-phase reactants. The effect of NaCl as a cocontaminant on ozonation rates was also investigated. The environmental implications of this phenomenon for natural ice/snow are discussed. DPE was selected as an example of environmentally relevant species which can react with ozone. For typical atmospheric ozone concentrations in polar areas (20 ppbv), we estimated that its half-life on the ice surface would decrease from ∼5 days at 258 K to ∼13 h at 188 K at submonolayer DPE loadings.

Adsorption and transformation of PAHs from water by a laccase-loading spider-type reactor

The remediation of polycyclic aromatic hydrocarbons (PAHs) polluted waters has become a concern as a result of the widespread use of PAHs and their adverse impacts on water ecosystems and human health. To remove PAHs rapidly and efficiently in situ, an active fibrous membrane, laccase-loading spider-type reactor (LSTR) was fabricated by electrospinning a poly(D,L-lactide-co-glycolide) (PDLGA)/laccase emulsion. The LSTR is composed of beads-in-string structural core-shell fibers, with active laccase encapsulated inside the beads and nanoscale pores on the surface of the beads. This structure can load more laccase and retains higher activity than do linear structural core-shell fibers. The LSTR achieves the efficient removal/degradation of PAHs in water, which is attributed to not only the protection of the laccase activity by the core-shell structure but also the pre-concentration (adsorption) of PAHs on the surface of the LSTR and the concentration of laccase in the beads. Moreover, the effects of pH, temperature and dissolved organic matter (DOM) concentration on the removal of PAHs by the LSTR, in comparison with that by free laccase, have been taken into account. A synergetic mechanism including adsorption, directional migration and degradation for PAH removal is proposed.

Assessment of the effect of degradation by atmospheric gaseous oxidants on measured annual average benzo[a]pyrene mass concentrations

A novel method for assessing the effect of degradation by atmospheric species on measured annual average benzo[a]pyrene (BaP) concentrations is presented. The method is based on assessing the difference in measured BaP mass concentrations using different sampling periods and extrapolation using assumed pseudo-first order reaction rate kinetics to produce the expected BaP mass concentration when theoretical sampling periods of zero duration are used - during which no degradation would be observed. The results suggest that the use of a one day sampling period as specified by the required reference method for BaP assessment in the UK may result in an underestimation of the annual average BaP mass concentration by approximately 6%. This is relatively small compared to the overall uncertainty of the measurement.

Influence of organic coatings on pyrene ozonolysis at the air-aqueous interface

Glancing angle laser-induced fluorescence was used to investigate the effects of organic monolayer coatings on the ozonation kinetics of pyrene at the air-aqueous interface. Fluorescence spectra show that both 1-octanol and octanoic acid coatings give rise to similar decreased polarity at the interface relative to the uncoated surface and show a similar propensity of pyrene to partition to the interface. Ozonation kinetics follow a Langmuir-Hinshelwood mechanism, indicating a surface reaction. At high ozone concentrations, a monolayer coating of 1-octanol enhances the rate relative to the uncoated surface and a coating of octanoic acid decreases the rate. Pyrene fluorescence is most efficiently quenched by ozone in the presence of a 1-octanol coating, followed by the uncoated surface, and least efficiently quenched by ozone in the presence of octanoic acid. In agreement with earlier work, a significant photoenhancement of the ozonation is observed at the uncoated surface; however, no enhancement is observed with monolayer coatings of either organic. Quantum chemical calculations indicate a reasonable binding of ozone by the carboxylic acid group (in both its dissociated and undissociated forms). We suggest that the inhibition of the water surface reaction by a monolayer of octanoic acid is due to the sequestration of ozone by the carboxylic acid group.

Sorption of polycyclic aromatic hydrocarbons on electrospun nanofibrous membranes: sorption kinetics and mechanism

Five types of nanofibrous membranes were prepared by electrospinning poly(ε-caprolactone) (PCL), poly(D,L-lactide) (PDLLA), poly(lactide-co-caprolactone) (P(LA/CL)), poly(D,L-lactide-co-glycolide) (PDLGA) and methoxy polyethylene glycol-poly(lactide-co-glycolide) (MPEG-PLGA), respectively. These electrospun nanofibrous membranes (ENFMs) were used to adsorb anthracene (ANT), benz[a]anthracene (BaA) and benzo[a]pyrene (BaP) from aqueous solution, and the sorption kinetics and isotherms of these PAHs on the five ENFMs were investigated. The pseudo-second-order model (PSOM) can well describe the sorption kinetics of the three PAHs on five ENFMs, and the partition-adsorption model (PAM) can interpret the sorption processes of PAHs on the ENFMs. PCL ENFMs, which had the largest surface areas (8.57 m(2)g(-1)), exhibited excellent sorption capacity for ANT at over 4112.3 ± 35.5 μg g(-1). Moreover, the hydrophobicity and pore volume of ENFMs significantly affected the sorption kinetics and sorption capacity of the PAHs. The main sorption mechanisms of three PAHs on the PDLLA ENFMs included hydrophobic interactions and pore-filling, while those of PCL, P(LA/CL) and PDLGA ENFMs were dominated by the hydrophobic interactions. The sorption mechanisms of MPEG-PLGA ENFMs primarily included pore-filling, hydrogen bonding interactions and hydrophobic interactions. Additionally, π-π bonding interaction was also deduced to be involved in all of ENFMs sorption systems.

The chemical biology of naphthoquinones and its environmental implications

Quinones are a group of highly reactive organic chemical species that interact with biological systems to promote inflammatory, anti-inflammatory, and anticancer actions and to induce toxicities. This review describes the chemistry, biochemistry, and cellular effects of 1,2- and 1,4-naphthoquinones and their derivatives. The naphthoquinones are of particular interest because of their prevalence as natural products and as environmental chemicals, present in the atmosphere as products of fuel and tobacco combustion. 1,2- and 1,4-naphthoquinones are also toxic metabolites of naphthalene, the major polynuclear aromatic hydrocarbon present in ambient air. Quinones exert their actions through two reactions: as prooxidants, reducing oxygen to reactive oxygen species; and as electrophiles, forming covalent bonds with tissue nucleophiles. The targets for these reactions include regulatory proteins such as protein tyrosine phosphatases; Kelch-like ECH-associated protein 1, the regulatory protein for NF-E2-related factor 2; and the glycolysis enzyme glyceraldehyde-3-phosphate dehydrogenase. Through their actions on regulatory proteins, quinones affect various cell signaling pathways that promote and protect against inflammatory responses and cell damage. These actions vary with the specific quinone and its concentration. Effects of exposure to naphthoquinones as environmental chemicals can vary with the physical state, i.e., whether the quinone is particle bound or is in the vapor state. The exacerbation of pulmonary diseases by air pollutants can, in part, be attributed to quinone action.