Oxidation Of Polycyclic Aromatic Hydrocarbons Research Articles

Advanced oxidation of polycyclic aromatic hydrocarbons in tropical soil: Self-catalytic utilization of natural iron contents in an oxygenation reactor supported with persulfate

The catalysts derived from natural iron minerals in the advanced oxidation process offer several advantages. However, their utilization in soil remediation is restricted due to the presence of soil impurities, which can inhibit the catalytic activity of these minerals. The soils in tropical regions exhibit lower organic matter content, limited cation exchange capacity, and are non-saline, this enhances the efficiency of utilizing natural iron minerals from tropical soil as a catalyst. In this regard, the catalytic potential of naturally iron-bearing tropical soil was investigated to eliminate phenanthrene (PHE), pyrene (PYR), and benzo[α]pyrene (B[α]P) using an oxygenated reactor supported with persulfate (PS). The system showed an efficient performance, and the removal efficiencies under the optimum conditions were 81 %, 73 %, and 86 % for PHE, PYR, and B[α]P, respectively. This indicated that the catalytic activity of iron was working efficiently. However, there were changes in the soil characteristics after the remediation process such as a significant reduction in iron and aluminum contents. The scavenging experiments demonstrated that HO•had a minor role in the oxidation process, SO4•− and O2•− emerged as the primary reactive species responsible for the effective degradation of the PAHs. Moreover, the by-products were monitored after soil remediation to evaluate their toxicity and to propose degradation pathways. The Mutagenicity test showed that two by-products from each PHE and B[α]P had positive results, while only one by-product of PYR showed positive. The toxicity tests of oral rat LD50 and developmental toxicity tests revealed that certain PAHs by-products could be more toxic from the parent pollutant itself. This study represents a notable progression in soil remediation by providing a step forward in the application of the advanced oxidation process (AOP) without requiring additional catalysts to activate oxidants and degrade pollutant PAHs from the soil.

Cardiolipin Membranes Promote Cytochrome c Transformation of Polycyclic Aromatic Hydrocarbons and Their In Vivo Metabolites.

The catalytic properties of cytochrome c (Cc) have captured great interest in respect to mitochondrial physiology and apoptosis, and hold potential for novel enzymatic bioremediation systems. Nevertheless, its contribution to the metabolism of environmental toxicants remains unstudied. Human exposure to polycyclic aromatic hydrocarbons (PAHs) has been associated with impactful diseases, and animal models have unveiled concerning signs of PAHs' toxicity to mitochondria. In this work, a series of eight PAHs with ionization potentials between 7.2 and 8.1 eV were used to challenge the catalytic ability of Cc and to evaluate the effect of vesicles containing cardiolipin mimicking mitochondrial membranes activating the peroxidase activity of Cc. With moderate levels of H2O2 and at pH 7.0, Cc catalyzed the oxidation of toxic PAHs, such as benzo[a]pyrene, anthracene, and benzo[a]anthracene, and the cardiolipin-containing membranes clearly increased the PAH conversions. Our results also demonstrate for the first time that Cc and Cc-cardiolipin complexes efficiently transformed the PAH metabolites 2-hydroxynaphthalene and 1-hydroxypyrene. In comparison to horseradish peroxidase, Cc was shown to reach more potent oxidizing states and react with PAHs with ionization potentials up to 7.70 eV, including pyrene and acenaphthene. Spectral assays indicated that anthracene binds to Cc, and docking simulations proposed possible binding sites positioning anthracene for oxidation. The results give support to the participation of Cc in the metabolism of PAHs, especially in mitochondria, and encourage further investigation of the molecular interaction between PAHs and Cc.

Formation of Polystyrene Coated Persulfate Slow-Release Candles for Polycyclic Aromatic Hydrocarbon Oxidation in Water

Formation of Polystyrene Coated Persulfate Slow-Release Candles for Polycyclic Aromatic Hydrocarbon Oxidation in Water

Insights into secondary organic aerosol formation from the day- and nighttime oxidation of polycyclic aromatic hydrocarbons and furans in an oxidation flow reactor

Abstract. Secondary organic aerosols (SOAs) formed by oxidation of typical precursors largely emitted by biomass burning, such as polycyclic aromatic hydrocarbons (PAHs) and furans, are still poorly characterized. We evaluated and compared the formation yields, effective density (ρeff), absorption Ångström exponent (α), and mass absorption coefficient (MAC) of laboratory-generated SOAs from three furan compounds and four PAHs. SOAs were generated in an oxidation flow reactor under day- (OH radicals) or nighttime (NO3 radicals) conditions. The ρeff, formation yields, α, and MAC of the generated SOAs varied depending on the precursor and oxidant considered. The ρeff of SOAs formed with OH and NO3 tended to increase with particle size before reaching a “plateau”, highlighting potential differences in SOA chemical composition and/or morphology, according to the particle size. Three times lower SOA formation yields were obtained with NO3 compared with OH. The yields of PAH SOAs (18 %–76 %) were five to six times higher than those obtained for furans (3 %–12 %). While furan SOAs showed low or negligible light absorption properties, PAH SOAs had a significant impact in the UV–visible region, implying a significant contribution to atmospheric brown carbon. No increase in the MAC values was observed from OH to NO3 oxidation processes, probably due to a low formation of nitrogen-containing chromophores with NO3 only (without NOx). The results obtained demonstrated that PAHs are significant SOA precursors emitted by biomass burning, through both, day- and nighttime processes, and have a substantial impact on the aerosol light absorption properties.

Degradation of polycyclic aromatic hydrocarbons in oil deodorizer distillates: Kinetics, degradation product identification and toxicity

Polycyclic aromatic hydrocarbons (PAHs) with strong carcinogenicity can cause great threat to human health. However, limited research has focused on the degradation of PAHs in oil deodorizer distillates (ODDs). In this study, E. coli expressing plasmid PodAB were applied in ODD samples to degrade PAHs and compared with white rot fungi (WRF). Prediction model for reactive sites of PAHs and the toxicity of degradation products were developed using density functional theory (DFT) calculations and quantitative structure–activity relationship (QSAR), respectively. The results indicated that the degradation rate of PAHs in ODD reached up to 59.28% using E. coli with the co-expression of pBRCD, which provided the electron carrier. The prediction results using nucleophilic index was consistent with the identification results of GC-MS, which may be more suitable for predicting the PAH oxidation products. Moreover, the R2 of developed QSAR reached 0.8976 for the correlation coefficient between predicted and observed toxicity value, which can be applied to predict the toxicity of degradation products. This work proposes a potential tool for PAH removal in ODD as well as a simple method for predicting PAH oxidation products as well as their toxicity.

Low levels of flavonoids in Arabidopsis thaliana during phenanthrene exposure suggest new roles for a flavanone 3-hydroxylase

Polycyclic aromatic hydrocarbons (PAHs) contamination impacts the well-being of fauna, flora, and the environment. PAHs are a group of compounds consisting of two or more benzene rings. Due to their structure, PAHs are very stable, generally non-reactive and resistant to biodegradation; yet these compounds are cytotoxic in biological systems. In plants, PAHs induce oxidative stress and cell death, and inhibit growth. Previous PAH exposure studies from our laboratory showed an up-regulation of the Arabidopsis thaliana gene At3g51240. At3g51240 encodes a flavanone 3-hydroxylase (F3H), an enzyme catalyzing the hydroxylation of flavanones, key intermediates in the flavonoid biosynthesis pathway. Considering that flavonoids may act as antioxidants and protect cells against oxidative stress, we hypothesized that F3H was important in alleviating PAH-induced stress symptoms. Analysis of flavonoid content by high performance liquid chromatography showed low levels of flavonoids in phenanthrene-treated plants. Analysis of At3g51240 loss-of-function mutant plant lines growing on phenanthrene-containing growth media showed reduced phenotypic stress responses. Interestingly, low levels of H2O2 were observed in the mutant plants, suggesting that this putative flavanone 3-hydroxylase may be involved in PAH oxidation, with the consequent H2O2 generation. Furthermore, in vitro assays with purified recombinant 6xHis tagged AT3G51240 showed enzyme activity on the PAH when phenanthrene was used as a substrate. Together, these data suggest that F3H is involved in PAH detoxification in planta with the subsequent accumulation of toxic metabolites. This research also indicates the potentiality of using specialized metabolism enzymes such as oxidoreductase in the genetic engineering of plants to remediate PAH-contaminated soils.

Occurrence and Sources of Polycyclic Aromatic Hydrocarbons and Factors Influencing Their Accumulation in Surface Sediment of a Deep-Sea Depression, Namely, the Tatar Trough (Tatar Strait, the Sea of Japan)

The concentrations of 14 polycyclic aromatic hydrocarbons (PAHs) in the sediment of the Tatar Trough were studied. Despite the increase in PAH concentrations over recent decades, which is likely the result of the handling and transportation of fossil fuels, PAH levels and ecological risk were found to be low. The spatial pattern revealed that higher PAH concentrations were mainly in the deeper water sites, suggesting that trough slope failure transported the PAHs to the deeper part of the basin. There was no correlation between the PAHs and grain size or the PAHs and organic carbon that is related to the PAH input from a variety of sources and the heterogeneity of organic matter. The PAH composition, isomer ratio, and PCA identified two areas with different PAH sources. The most northern part of the Tatar Trough received petrogenic PAHs that are probably transported downslope from the northern Tatar Strait where fossil fuels are handled in some ports. Another trough part was polluted by the PAHs from the combustion of coal and biomass and the exhaust of marine vehicles. The minor presence of genes responsible for aerobic PAH destruction can be explained by the anaerobic degradation of PAHs or the spontaneous creation of favorable conditions that promote bacterial PAH oxidation.

Oxidation of Polycyclic Aromatic Hydrocarbons with Mono-Oxygen Donors Catalysed by Triaryl-Manganese(III) Corroles

Abstract: The oxidation of polycyclic aromatic hydrocarbons (PAH) with mono-oxygen donors such as iodosylbenzene, hydrogen peroxide and tert-butyl hydroperoxide in the presence of selected 5,10,15-triarylmanganese( III) corroles as catalysts were examined under different reaction conditions. The effect of reaction conditions on triaryl-manganese(III) corroles catalysts and oxidants is discussed. It was observed that in a solvent system consisting of a mixture of dichloromethane and acetonitrile, the oxidation of anthracene with tertbutyl hydroperoxide catalysed by tri(aryl)manganese(III)corroles worked better than with hydrogen peroxide or iodosylbenzene as the oxidants. The oxidation of anthracene with hydroxo-manganese(IV)corroles was also examined in organic solvents under mild conditions. UV-Vis and other spectroscopic data were used to determine the oxidative mechanism for the oxidation of anthracene and other polycyclic aromatic hydrocarbons with mono-oxygen donors catalysed by triaryl-manganese(III)corroles.

Oxidation of Polycyclic Aromatic Hydrocarbons: Evidence of Similarities in Thermochemical Properties and Reaction Paths

ABSTRACT This work elaborates similarities of thermochemical properties and oxidation kinetics among several polycyclic aromatic hydrocarbons. The systems considered are benzene (A1), naphthalene (A2), phenanthrene (A3), pyrene (A4), and the larger ones, benzo[ghi]perylene (A6) and coronene (A7). For each system, thermochemical properties, bond energies and oxidation kinetics are calculated and compared. Interpretation of the results revealed strong similarities and redundancies in behavior among these systems. The results imply that reactions are not dependent on the size of the molecules and, therefore, reaction paths and kinetic barriers determined with high-level calculations for small molecules can be used as estimates in the investigation of larger aromatic hydrocarbons to avoid expensive calculation efforts.

Roles of Natural Phenolic Compounds in Polycyclic Aromatic Hydrocarbons Abiotic Attenuation at Soil-Air Interfaces through Oxidative Coupling Reactions.

Little information is available on the roles of natural phenolic compounds in polycyclic aromatic hydrocarbons (PAHs) attenuation at dry soil-air interfaces. The purpose of this study was to determine the roles of model phenolic constituents of soil organic matter (SOM) on the abiotic attenuation of PAHs. The phenolic compounds can significantly change the attenuation rates of PAHs, among which hydroquinone was the most effective in promoting anthracene and benzo[a]anthracene attenuation. Product identification and sequential extraction experiments revealed hydroquinone enhanced the formation of oxidative coupling products and promoted the incorporation of PAHs into humic analogues, thereby reducing potential risks to humans and ecosystems. Electron paramagnetic resonance spectroscopy analyses showed both PAHs and phenolic compounds could donate electrons to Lewis acid sites of soil minerals, resulting in the generation of persistent free radicals (PFRs). PFRs could promote the generation of ·OH to enhance PAH oxidation and could cross-couple with PAHs, resulting in high-molecular-weight oxidative coupling products. This study revealed for the first time the reaction mechanism between PAHs and phenolic components of SOM under relatively dry conditions and provided new insights into promoting PAHs detoxification in soils but also a potential strategy to increase the organic carbon sequestration.

Kill two birds with one stone: Solubilizing PAHs and activating PMS by photoresponsive surfactants for the cycle remediation of contaminated groundwater

Polycyclic aromatic hydrocarbons (PAHs) represent a dangerous threat to the groundwater environment. PAHs are difficult to be effectively removed from groundwater because of their hydrophobicity. In this study, a combination of a Gemini photosensitive surfactant (N1, N2-bis[4-[4-[(4-butylphenyl) azo] phenoxy] butyl]-N1, N2-tetramethylethane-1,2-diammonium bromide, AzoPBT) with peroxymonosulfate (PMS) is developed to treat PAHs-contaminated groundwater. To investigate the reaction mechanism of the PMS/AzoPBT process, we chose naphthalene (Nap) and phenanthrene (Phe) as target pollutants. The quenching experiments, electron paramagnetic resonance (EPR) spectroscopy and the identified degradation products indicated that singlet oxygen could contribute to the degradation of PAHs. A tentative solution for Phe degradation was proposed based on the degradation products. The role of surfactant micelles in the PMS/AzoPBT process is further explored. The positively charged micelles in the PMS/AzoPBT process escalate the removal of PAHs by electrostatically polymerizing Br- and HSO5- in the solution. Although increasing the number of micelles can enhance the solubilization of PAHs by surfactant solutions, the encapsulation of PAHs by micelles can “protect” PAHs, which hinders the removal of PAHs. The PMS/AzoPBT process can be applied in a broad range of pH values. In the process of recycling AzoPBT to activate PMS to remediate groundwater, PAHs can be completely removed in the first cycle, and 51.4 % of them can be removed after four times of surfactant use. The combination of photoresponsive surfactants and PMS achieves efficient oxidation of PAHs without additional activators while increasing the solubility of PAHs in groundwater. This novel technology of PAHs-contaminated groundwater treatment may provide insights into the degradation mechanism of the PMS/AzoPBT process.

Electrochemistry-enhanced peroxymonosulfate activation by CoAl-LDH@biochar for simultaneous treatment of heavy metals and PAHs

An EC/CoAl-LDH@biochar/PMS system is proposed in this study for activation of PMS and removal of heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs). In this system, over 90% of HMs and PAHs could be effectively removed after 40 min. Compared to other systems, the synergy between CoAl-LDH@biocahr and electrochemistry (EC)-peroxymonosulfate (PMS) had an excellent ability to eliminate the combined pollutants. The precise effect of the experimental parameters, including pH, CoAl-LDH@biochar dose, current density, and PMS concentration, on HMs-PAHs removal was determined, and the system was found to have a broad working pH range. The presence of EC can overcome the inhibition of anions in the degradation of PAHs due to the direct oxidation of PMS and PAHs on the cathode. The scavenging tests confirmed that the free radical and non-radical processes contributed to the degradation of PAHs. It is also revealed that EC can promote the continuous circulation of transition metals, which enhances the activation of PMS. The adsorption on the surface of CoAl-LDH@biochar and electrochemical deposition were the two main mechanisms for HMs removal. Furthermore, the electrode and CoAl-LDH@biochar possessed favorable recyclability in five consecutive cycles. This study has provided a promising and cost-effective approach for treatment of HM-PAH co-contaminated wastewater.

Secondary Organic Aerosol Formation from Semi-Volatile and Intermediate Volatility Organic Compounds in the Fall in Beijing

Intermediate volatility organic compounds (IVOCs) and semi-volatile organic compounds (SVOCs) have recently been proposed as important precursors of secondary organic aerosol (SOA). In the present work, 97 volatile organic compounds (VOCs) and 80 intermediate volatility and semi-volatile organic compounds (IVOCs and SVOCs) were measured by online gas chromatography-mass spectrometer/flame ionization detection (GC-MS/FID), and offline thermal desorption gas chromatography-mass spectrometer (TD-GC-MS), respectively. The average concentration of speciated VOCs, IVOCs, and SVOCs were 22.36 ± 9.02 μg m−3, 1.01 ± 0.32 μg m−3, and 0.10 ± 0.17 μg m−3. Alkanes and polycyclic aromatic hydrocarbons (PAHs) are the main compounds of total S/IVOCs. With the increase in molecular weight, the concentrations decreased in the gas phase, while increasing in the particle phase. Vehicular emission is the most significant source according to the carbon preference index (CPI) and the carbon of the most abundant alkane (Cmax). The yield method was used to estimate SOA from the oxidation of VOCs and S/IVOCs. The estimated SOA mass from IVOCs and SVOCs (0.70 ± 0.57 μg m−3) was comparable to that of VOCs (0.62 ± 0.61 μg m−3), and the oxidation of PAHs and alkanes took up 28.70 ± 8.26% and 51.97 ± 20.77% of the total SOA estimation, respectively. Compared to previous work, our study provided detailed molecular information of ambient S/IVOC species and elucidated their importance on SOA formation. Despite their low concentration, S/IVOCs species are important SOA precursors which shared comparable contribution compared with VOCs.

A ReaxFF molecular dynamics study of polycyclic aromatic hydrocarbon oxidation assisted by nitrogen oxides

Fossil fuel-derived soot poses a persistent problem. A joint reduction is conducted via the reaction between NOx and soot. The underlying reaction mechanisms of large polycyclic aromatic hydrocarbons (PAHs), as well as the interactions between O2, NO and NO2, have been extensively investigated by ReaxFF molecular dynamics simulations for the first time. The pyrolysis and oxidation of coronene are conducted at 2500 K and 50 atm. Coronene in the pyrolysis system first experiences dehydrogenation reactions and subsequently undergoes recombination reactions, leading to the formation of large PAHs. Among the three oxidizers, NO2 is the strongest in coronene oxidation, followed by NO and O2. Meanwhile, the O radical is identified as the key species for PAH oxidation. In the presence of O2, the formation of O radicals requires the assistance of H radicals that are formed by the dehydrogenation of PAHs, which retards the oxidation process. In the presence of NO, O radicals can be directly formed via reactions of NO → N+O and N + NO ⇌ N2 + O. NO2 first undergoes a decomposition reaction: NO2 → NO + O, followed by NO decomposition. O-addition and N-addition, as well as subsequent fragmentation reactions including the generation of COx and (H)CN are important routes in PAH oxidation. Furthermore, compared to NO, NO2 provides more O radicals that significantly accelerate PAH oxidation. This study provides fundamental insight into PAH oxidation that may help to design strategies to inhibit soot and NOx emissions at the source.

Polycyclic aromatic hydrocarbons and their oxygenated derivatives in urban aerosol: levels, chemical profiles, and contribution to PM2.5 oxidative potential

The concentrations of polycyclic aromatic hydrocarbons (PAHs) and quinones, a subgroup of oxygenated PAHs (oxy-PAHs), were measured in PM2.5 samples collected during warm (May–June 2019) and cold (February–March 2020) seasons in the city of Bologna, Italy. Total PAHs concentration was nearly double in winter (6.58 ± 1.03 ng m−3) compared with spring (3.16 ± 0.53 ng m−3), following the trend of the PM2.5 mass concentration. Molecular diagnostic ratios suggested that, together with traffic, biomass burning was the dominant emission source contributing to the peaks of concentration of PM2.5 registered in the cold season. Quinone level was constant in both seasons, being 1.44 ± 0.24 ng m−3, that may be related to the increased secondary formation during warm season, as confirmed by the higher Σoxy-PAHs/ΣPAHs ratio in spring than in winter. The oxidative potential (OP) of the PM2.5 samples was assessed using acellular dithiothreitol (DTT) and ascorbic acid (AA) assays. The obtained responses showed a strong seasonality, with higher volume-normalized (OPV) values in winter than in spring, i.e., OPVDTT: 0.32 ± 0.15 nmol min−1 m−3 vs. 0.08 ± 0.03 nmol min−1 m−3 and OPVAA: 0.72 ± 0.36 nmol min−1 m−3 vs. 0.28 ± 0.21 nmol min−1 m−3. Both OPVDTT and OPVAA responses were significantly associated with total PAHs, as a general descriptor of redox-active PAH derivatives, associated with co-emission from burning sources or secondary atmospheric oxidation of parent PAHs. Otherwise, only winter OPVDTT responses showed a significant correlation with total Ʃoxy-PAHs concentration.

Contrasting resistance of polycyclic aromatic hydrocarbons to atmospheric oxidation influenced by burning conditions

The oxidation of polycyclic aromatic hydrocarbons (PAHs) determines their lifetime, toxicity and consequent environmental and climate impacts. The residential solid fuel burning composes of a substantial fraction of PAH emissions; however, their oxidation rate is yet to be explicitly understood, which is complicated by the contrasting emission factors under different combustion conditions and their subsequent evolution in the atmosphere. Here we used a plume evolution chamber using ambient oxidants to simulate the evolution of residential solid fuel burning emissions under real-world solar radiation, and then to investigate the oxidation process of the emitted PAHs. Contrasting oxidation rate of PAHs was found to be influenced by particles with or without presence of substantial amount of black carbon (BC). In the flaming burning phase, which contained 46% of BC mass fraction and 8% of organic aerosol (OA) internally mixed with BC, the larger PAHs (with 4–7 rings) was rapidly oxidized 12% for every hour of evolution under solar radiation; however, the larger PAHs from smoldering phase tended to maintain unmodified during the evolution, when 95% of OA was externally mixed with only minor fraction of BC (<5%). This may be ascribed to the complex morphology of BC, allowing more exposure for the internally-mixed OA to the oxidants; in contrast with those externally-mixed OA which was prone to be coated by condensed secondary substances. This raises an important consideration about the particle mixing state in influencing the oxidation of PAHs, particularly the coating on PAHs which may extend their lifetime and environmental impacts.

The laccase mediator system at carbon nanotubes for anthracene oxidation and femtomolar electrochemical biosensing.

We investigated the use of POXA1b laccase from Pleurotus ostreatus for the oxidation of anthracene into anthraquinone. We show that different pathways can occur depending on the nature of the redox mediator combined to laccase, leading to different structural isomers. The laccase combined with 2,2'-azine-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) leads to the formation of 1,4-anthraquinone and/or 1,2-anthraquinone. The unprecedented role of carbon nanotubes (CNTs) as redox mediators for oxidation of anthracene into 9,10-anthraquinone is shown and corroborated by density-functional theory (DFT) calculations. Owing to the efficient adsorption of anthraquinones at CNT electrodes, anthracene can be detected with low limit-of-detection using either laccase in solution, CNT-supported laccase or laccase immobilized at magnetic beads exploiting the adhesive property of a chimeric hydrophobin-laccase.

Effect of magnetite on the catalytic oxidation of polycyclic aromatic hydrocarbons in fly ash from MSW incineration: A comparative study of one-step and two-step hydrothermal processes

Polycyclic aromatic hydrocarbons (PAHs), many of which are carcinogenic, teratogenic, and mutagenic, exist in fly ash (FA) produced from municipal solid waste incineration (MSWI). Hydrothermal treatment (HT) is an efficient approach to remove PAHs from MSWI FA. Here, magnetite (Fe3O4) was used as the catalyst and hydrogen peroxide (H2O2) as the oxidant for one-step and two-step catalytic hydrothermal methods. When the magnetite dosage increased to 15 wt%, the maximum degradation rates of PAHs were 84.36% and 92.51%, respectively; however, the toxicity equivalent quantity (TEQ) degradation rates of the PAHs both increased upon increasing the magnetite dose. At 20 wt% Fe3O4, the maximum TEQ degradation rates of the PAHs were 93.29% and 97.76%, respectively. The reaction between OH and PAHs is non-selective, which means that LMW, MMW, and HMW PAHs were all degraded. The decrease in TEQ was mainly due to the degradation of HMW PAHs, i.e., those with five rings. Under the same Fe3O4 dose, oxidant dose, and reaction time, the detoxification of PAHs by the two-step method was significantly better than that of the one-step method, possibly because the two-step method more effectively produced OH. The first step degraded more than 90% of PAHs, and the residual PAHs in the HT products of the first step limited the utilization of the oxidant during the second step. The minerals in the HT products implied that the two-step hydrothermal method not only produced more OH, which reacted with PAHs, but also generated metal-magnetite substitution, which affected its surface reactivity during heavy metal adsorption and catalysis. These results revealed that both magnetite and the two-step hydrothermal treatment degraded PAHs. 20 wt% magnetite was the optimal amount during the two-step hydrothermal catalytic oxidation of MSWI FA.

Remediation of polycyclic aromatic hydrocarbons by sulfate radical advanced oxidation: Evaluation of efficiency and ecological impact

Remediation of polycyclic aromatic hydrocarbon (PAH) contamination in soil remains expensive and difficult. Sulfate radical advanced oxidation processes (SR-AOPs) can be used for in situ PAH oxidation but their efficiency and ecological impacts require evaluation. Here, we tested the remediation efficiency and ecological impacts of an SR-AOP combining sodium persulfate and ferrous sulfate (FS), the FS SR-AOP with the chelating agent citric acid (FS+CA), and the FS SR-AOP with chelating agent and the surfactant IGEPALCA-720 (FS+CA+IG) compared with natural attenuation (control, CK). We measured PAH, soil physicochemical properties (pH, soil organic matter [SOM]), and soil biological properties (polyphenol oxidase [PPO] activity, peroxidase [POD] activity, soil microbes) in contaminated soil samples after incubation with FS, FS+CA, FA+CA+IG, or CK for 1, 15, and 30 d. Compared with CK, all SR-AOPs significantly decreased PAH after 1 d, with FS+CA+IG showing the highest efficiency (80.8%) and PAH removal peaking at 15 d. FS+CA+IG treatment reduced SOM the least and soil pH the most; after 30 d, SOM recovered to ~80% of the level observed in CK, but soil pH decreased further. PPO and POD activities were highest after 15 and 30 d of FS+CA+IG treatment. Real-time quantitative PCR demonstrated that SR-AOPs significantly decreased quantities of PAH-degrading bacteria, soil bacteria, fungi, and actinobacteria at 1 d, but after 30 d, the microbes recovered to levels similar to those observed in CK, with no significant differences among SR-AOPs. SR-AOPs reduced bacterial diversity and changed the dominant phylum from Acidobacteria to Firmicutes. In summary, SR-AOP treatment with both the chelating agent and the surfactant produced the best PAH removal and least SOM destruction but the largest pH decrease, although some factors recovered with longer incubation. This study provides key information for improving PAH remediation and evaluating its ecological impact

Effects of polycyclic aromatic hydrocarbon structure on PAH mineralization and toxicity to soil microorganisms after oxidative bioremediation by laccase

While bioremediation using soil microorganisms is considered an energy-efficient and eco-friendly approach to treat polycyclic aromatic hydrocarbon (PAH)-contaminated soils, a variety of polar PAH metabolites, particularly oxygenated ones, could increase the toxicity of the soil after biodegradation. In this study, a typical bio-oxidative transformation of PAH into quinones was investigated in soil amended with laccase using three PAHs with different structures (anthracene, benzo[a]anthracene, and benzo[a]pyrene) to assess the toxicity after oxidative bioremediation. The results show that during a 2-month incubation period the oxidation process promoted the formation of non-extractable residues (NERs) of PAHs, and different effects on mineralization were observed among the three PAHs. Oxidation enhanced the mineralization of the high-molecular-weight (HMW) PAHs (benzo[a]anthracene and benzo[a]pyrene) but inhibited the mineralization of the low-molecular-weight (LMW) PAH (anthracene). The inhibition of anthracene suggests increased toxicity after oxidative bioremediation, which coincided with a decrease in soil nitrification activity, bacterial diversity and PAH-ring hydroxylating dioxygenase gene copies. The analysis of PAH metabolites in soil extract indicated that oxidation by laccase was competitive with the natural transformation processes of PAHs and revealed that intermediates other than quinone metabolites increased the toxicity of soil during subsequent degradation. The different metabolic profiles of the three PAHs indicated that the toxicity of soil after PAH oxidation by laccase was strongly affected by the PAH structure. Despite the potential increase in toxicity, the results suggest that oxidative bioremediation is still an eco-friendly method for the treatment of HMW PAHs since the intermediates from HMW PAHs are more easily detoxified via NER formation than LMW PAHs.