Hydrophobic Polycyclic Aromatic Hydrocarbons Research Articles

Preparation of dicationic ionic liquid modified silica stationary phase for mixed-mode liquid chromatography and its application for food additive detection

BackgroundFood safety has become an essential aspect of public concern and there are lots of detection means. Liquid chromatography plays a dominating role in food safety inspection because of its high separation efficiency and reproducibility. However, with the increasing complexity of real samples and monitoring requirements, conventional single-mode chromatography would require frequent column replacement and cannot separate different kinds of analytes on a single column simultaneously, which is costly and time-consuming. There is a great need for fabricating mixed-mode stationary phases and validating the feasibility of employing mixed-mode stationary phases for food safety inspection. ResultsThis work fabricated multifunctional stationary phases for liquid chromatography to determine diverse food additives under the mixed mode of RPLC/HILIC/IEC. Two dicationic ionic liquid silanes were synthesized and bonded onto the silica gel surface. The functionalized silica was characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and elemental analysis. Both columns provide satisfactory separation performance towards 6 hydrophilic nucleosides, 4 hydrophobic polycyclic aromatic hydrocarbons, and 5 anions. Great repeatability of retention (RSD <0.1 %) and column efficiency (100330 plate/m) were obtained. Thermomechanical analysis and linear solvation energy relationship investigated the retention mechanism. Finally, the better in two prepared columns was employed to separate and determine the contents of NO2− and NO3− in vegetables(highest 4906 mg kg−1 NO3− in spinach), preservatives in bottled beverages (180.8 mg kg−1 sodium benzoate in soft drink), and melamine in milk with satisfactory performance and recovery rates ranging from 96.4 % to 105.6 %. SignificanceThis work developed a novel scheme for preparing mixed-mode stationary phases by dicationic ionic liquid which provides great separation selectivity. Most importantly, this work proved the superiority of employing mixed-mode stationary phases for food safety inspection, which might avoid high-cost and frequent changes of columns and chromatography systems in the near future.

Mechanistic Implications of the Varying Susceptibility of PAHs to Pyro-Catalytic Treatment as a Function of Their Ionization Potential and Hydrophobicity.

Transition metal catalysts in soil constituents (e.g., clays) can significantly decrease the pyrolytic treatment temperature and energy requirements for efficient removal of polycyclic aromatic hydrocarbons (PAHs) and, thus, lead to more sustainable remediation of contaminated soils. However, the catalytic mechanism and its rate-limiting steps are not fully understood. Here, we show that PAHs with lower ionization potential (IP) are more easily removed by pyro-catalytic treatment when deposited onto Fe-enriched bentonite (1.8% wt. ion-exchanged content). We used four PAHs with decreasing IP: naphthalene > pyrene > benz(a)anthracene > benzo(g,h,i)perylene. Density functional theory (DFT) calculations showed that lower IP results in stronger PAH adsorption to Fe(III) sites and easier transfer of π-bond electrons from the aromatic ring to Fe(III) at the onset of pyrolysis. We postulate that the formation of aromatic radicals via this direct electron transfer (DET) mechanism is the initiation step of a cascade of aromatic polymerization reactions that eventually convert PAHs to a non-toxic and fertility-preserving char, as we demonstrated earlier. However, IP is inversely correlated with PAH hydrophobicity (log Kow), which may limit access to the Fe(III) catalytic sites (and thus DET) if it increases PAH sorption to soil OM. Thus, ensuring adequate contact between sorbed PAHs and the catalytic reaction centers represents an engineering challenge to achieve faster remediation with a lower carbon footprint via pyro-catalytic treatment.

An ultra-stable and sensitive Ag-HP-β-CD/GO/NCF SERS substrate combine with the coffee-ring effect strategy for trace PAHs detection

This study proposes an ultra-stable and highly sensitive SERS substrate based on Ag nanoparticles/graphene oxide nanosheets hybrids decorated nanocellulose fiber (Ag/GO/NCF), which was further functionalized with hydroxypropyl-β-cyclodextrin (Ag-HP-β-CD/GO/NCF) for the trace detection of polycyclic aromatic hydrocarbons (PAHs). The Ag/GO hybrid structure enables the substrate to exhibit high SERS activity through the synergistic effect of electromagnetic and chemical enhancement. Simultaneously, the three-dimensional skeleton structure of NCF serves as a support matrix, ensuring the exceptional stability of the substrate. Furthermore, this study introduces a SERS measurement strategy utilizing the coffee-ring effect and explores parameters optimization to further enhance the detection sensitivity while maintaining the homogeneity and reproducibility. With the affinity effect of HP-β-CD and the enrichment effect of the delocalized π-electron system in GO, the hydrophobic PAHs could easily approach the SERS hotspots and achieve their trace detection. The limit of detection (LOD) for four representative PAHs, including pyrene, fluoranthene, phenanthrene and fluorene, are found to be 3.32 ug/L, 3.65 ug/L, 40.97 ug/L and 56.24 ug/L, respectively. These results highlight the potential application of this highly efficient SERS platform in environmental monitoring.

Nanoleaf-derived carbon materials as a sensitivity coating for solid‑phase microextraction of polycyclic aromatic hydrocarbons.

Metal-organic framework-derived carbon materials have shown extensive application in the sensitive extraction of polycyclic aromatic hydrocarbons (PAHs), but more active sites for its adsorption were still a tireless pursuit. In this study, ZIF-nanoleaf-derived carbon (NLCs) was synthesized and developed as a solid-phase microextraction (SPME) fiber (NLCs-F). The extraction performance was compared with ZIF-dodecahedron-derived carbon (DHCs) coated fiber (DHCs-F), which was prepared by only changing the ratio of the reactants. The unique morphology of NLCs provided abundant adsorption active sites for the selected PAHs, while the large average aperture facilitated selective extraction of high molecular weight analytes. Additionally, the high carbon content enhanced the strong enrichment capability for hydrophobic PAHs. Hence, the prepared NLCs-F coupled with GC-MS showed a good correlation coefficient (0.9975) in a wide linear range, low limits of detection (0.3-1.8ng L-1), satisfactory repeatability, and reproducibility, which made it apply in the enrichment of PAHs in actual tea and coffee samples.

Metatranscriptomic responses and microbial degradation of background polycyclic aromatic hydrocarbons in the coastal Mediterranean and Antarctica

Although microbial degradation is a key sink of polycyclic aromatic hydrocarbons (PAH) in surface seawaters, there is a dearth of field-based evidences of regional divergences in biodegradation and the effects of PAHs on site-specific microbial communities. We compared the magnitude of PAH degradation and its impacts in short-term incubations of coastal Mediterranean and the Maritime Antarctica microbiomes with environmentally relevant concentrations of PAHs. Mediterranean bacteria readily degraded the less hydrophobic PAHs, with rates averaging 4.72 ± 0.5 ng L h−1. Metatranscriptomic responses showed significant enrichments of genes associated to horizontal gene transfer, stress response, and PAH degradation, mainly harbored by Alphaproteobacteria. Community composition changed and increased relative abundances of Bacteroidota and Flavobacteriales. In Antarctic waters, there was no degradation of PAH, and minimal metatranscriptome responses were observed. These results provide evidence for factors such as geographic region, community composition, and pre-exposure history to predict PAH biodegradation in seawater.

Chitosan/polyacrylic acid/octadecene double-crosslinked network hydrogel functionalized porous silica microspheres for multimode liquid chromatographic separation

In this study, chitosan (CS) and polyacrylic acid (PAA) were used to construct a double-crosslinked network hydrogel, which was employed as the functional material for silica microspheres to prepare a CS/PAA hydrogel modified liquid chromatographic stationary phase. During preparation, octadecene (ODE) was introduced into the CS/PAA hydrogel to improve its hydrophobicity and separation ability. The electrostatic interaction between the amino group of CS and the carboxyl group of PAA effectively prevented the swelling of the CS/PAA hydrogel, which ensured the successful application of the obtained CS/PAA hydrogel@SiO2 in chromatographic analysis. Polar nucleosides/bases and B-vitamins were selectively separated using hydrophilic interaction liquid chromatography. Hydrophobic polycyclic aromatic hydrocarbons and alkylphenols were effectively separated through reversed-phase liquid chromatography. Moreover, the effective separation of aromatic positional isomers and chiral enantiomers was achieved. This study confirms the potential application of the CS/PAA hydrogel in chromatographic separation. What is noteworthy is that the method developed in this study also provides a feasible strategy to solve the swelling issue associated with the hydrogel-based liquid chromatographic stationary phase.

Treatment of Hydrophobic Polycyclic Aromatic Hydrocarbons and Toxicity Using GO-TiO2-Sr(OH)2/SrCO3 Nanocomposite via Photocatalytic Degradation

In this study, the effects of increasing sun light irradiation time (30 min, 120 min, 240 min and 360 min), increasing photocatalytic power (10 W, 50 W and 100 W), increasing graphene oxide (GO) nanoparticle concentrations (2 mg/l, 4 mg/l and 8 mg/l), increasing titanium dioxide (TiO2) nanoparticle concentrations (1 mg/l, 3 mg/l, 6 mg/l and 9 mg/l), increasing GO-TiO2-Sr(OH)2/SrCO3 nanocomposite concentrations (1 mg/l, 2 mg/l and 4 mg/l) on the destructions of four hydrophobic polycyclic aromatic hydrocarbons (PAHs) in a real petrochemical industry wastewater in Izmir (Turkey) were investigated. The yields in more hydrophobic PAHs with high benzene rings [benzo[a]pyrene (BaP) and benzo[k]fluoranthene (BkF)] were as high as the less hydrophobic PAHs with lower benzene rings [acenaphthylene (ACL) and carbazole (CRB)]; at pH=7.0, at 22oC after 360 min sun light irradiation time, respectively. Maximum 97%ACL, 98%CRB, 98%BaP and 99%BkF PAHs removals was detected at 4 mg/l GO-TiO2-Sr(OH)2/SrCO3 nanocomposite concentration, under 100 mW/cm2 sun light intensity, at 100 W photocatalytic power, at 360 min sun light irradiation time, at pH=7.0 and at 22oC, respectively. The effective PAHs concentrations caused 50% mortality in Daphnia magna cells increased from initial EC50=342.56 mg/l to EC50=631.05 mg/l, at pH=7.0 and at 22oC after 360 min photocatalytic degradation time resulting in a maximum acute toxicity removal of 99.99%, at 4 mg/l GO-TiO2- Sr(OH)2/SrCO3 nanocomposite concentration. The Daphnia magna acute toxicity was significantly reduced.

Pickering emulsion-enhanced Vibrio fischeri assay for ecotoxicity assessment of highly hydrophobic polycyclic aromatic hydrocarbons

Accurate ecotoxicity assessment of contaminated soil is critical to public health, and the luminescent bacteria (Vibrio fischeri) method is the most commonly used. Hydrophobic compounds such as polycyclic aromatic hydrocarbons (PAHs) in soil cannot be in contact with luminescent bacteria due to their low water solubility so that the luminescence inhibitory effect cannot be observed. The underestimated biological toxicity makes the test unreliable and en-dangers public health and safety. The commonly adopted improved method of adding cosolvents has limited effect, it was only effective for low-hydrophobicity chemicals and could not be used for ecotoxicity evaluation of high-hydrophobicity chemicals. Therefore, we constructed Pickering emulsions using luminescent bacteria modified with n-dodecanol in which PAHs were dissolved in the oil phase, n-tetradecane. Then the luminescent bacteria could tightly adhere to the oil-water interface and contact PAHs. As a result, their bioluminescence was suppressed to varying degrees depending on the chemical species and concentrations. With no solubility limitation, highly hydrophobic PAHs could even completely inhibit bacterial bioluminescence, hence the toxicity information was accurately displayed and the median effect concentration (EC50) values could be calculated. This Pickering emulsion-based method was successfully applied for the accurate ecotoxicity evaluation of highly hydrophobic PAHs and soil samples contaminated with them, which all previous methods could not achieve. This method overcomes the problem of ecotoxicity evaluation of hydrophobic compounds, and has great potential for practical application, whether it is pure chemicals or various real samples from the ecological environment.

Preparation and application of graphene oxide functionalized melamine-formaldehyde aerogel coated solid-phase microextraction tube

因具有良好的萃取性能,有机气凝胶已被应用于样品前处理领域,为了进一步改善其对多环芳烃类污染物的萃取能力,利用氧化石墨烯对三聚氰胺-甲醛气凝胶进行改性,制备了一种氧化石墨烯功能化三聚氰胺-甲醛气凝胶,将其作为萃取涂层涂覆到不锈钢丝表面,通过扫描电镜和X射线光电子能谱对萃取涂层进行表征,结果表明氧化石墨烯并未破坏气凝胶的三维网络多孔结构。将4根气凝胶涂覆的不锈钢丝装进一根长度30 cm、内径0.75 mm的聚醚醚酮管内,制备了一种新型的纤维填充型固相微萃取管。将萃取管与高效液相色谱联用,构建管内固相微萃取-液相色谱在线富集分析系统。以8种多环芳烃(萘(Nap)、苊烯(Acy)、苊(Ace)、芴(Flu)、菲(Phe)、蒽(Ant)、荧蒽(Fla)和芘(Pyr))作为模型分析物,评价了萃取管的萃取性能,考察了氧化石墨烯对气凝胶萃取性能的改善,结果表明萃取效率被提升至最高2.5倍。详细考察了样品体积、样品流速、样品中有机溶剂浓度以及脱附时间对于萃取效率的影响,并建立了管内固相微萃取-液相色谱在线分析方法。该法对8种多环芳烃分析物的检出限为0.001~0.005 μg/L,萘、苊烯、苊、芴的线性范围为0.017~20.0 μg/L,菲、蒽的线性范围为0.010~20.0 μg/L,荧蒽和芘的线性范围为0.003~15.0 μg/L,精密度良好(日内重复性RSD≤4.8%,日间重复性RSD≤8.6%)。研究所发展的分析方法比已报道的某些分析方法具有更好的灵敏度、更宽的线性范围和更短的分析时间,并具有在线富集和在线分析的独特优点。将该分析方法应用于常见饮用水(包括瓶装矿泉水和饮水机的直饮水)中多环芳烃的分析检测,加标回收率试验结果(76.3%~132.8%)表明该分析方法能够高灵敏、快速、准确地检测饮用水中痕量多环芳烃污染物。经过稳定性考察,发现研究所制备的固相微萃取管在实验过程中表现出良好的使用寿命和化学稳定性。

Fine particles and pyrogenic carbon fractions regulate PAH partitioning and burial in a eutrophic shallow lake

Aquatic particles and organic carbon (OC) regulate the occurrence and transport of hydrophobic organic contaminants such as polycyclic aromatic hydrocarbons (PAHs) in water-suspended particle-sediment interfaces. Conventional studies on the mechanisms regulating the relationships between PAHs and total particles/OC have ignored micro-scale regulatory factors such as particle size and OC composition. Field research in the eutrophic shallow Lake Taihu, China, revealed that the fine particle fractions 2.7–10 μm in diameter had stronger PAH adsorption capacity and significantly regulated PAH particle size distribution and water-particle partitioning. Selective PAH biodegradation by planktonic microorganisms probably significantly weakened the capacity of the coarse fractions to regulate PAHs. OC fragments at different temperature gradients had markedly different influences on the particle size distribution of PAHs. High-temperature pyrogenic OC fractions (part of black carbon) were the principal OC regulatory factors for medium-to high-molecular-weight PAHs. However, the OC fragments did not directly affect the particle distribution of low-molecular-weight PAHs. During particle deposition and burial, microbial PAH utilization and efficiency probably regulated the burial potential of various hydrophobic PAH species. Biodegradation of relatively less hydrophobic PAHs with octanol-water partition coefficients (log Kow) < 5.8 showed an increasing trend with decreasing PAH hydrophobicity. Biological pump action of the relatively higher hydrophobic PAH species (log Kow > 5.8) showed a decreasing trend with increasing PAH hydrophobicity. The discoveries of the present work further clarified the mechanisms of PAH partitioning and burial in a eutrophic shallow lake and collectively provides a valuable reference for modeling the transport and dispersal mechanisms of hydrophobic, particle-bound organic contaminants in other aquatic ecosystems.

Roles of oxidant, activator, and surfactant on enhanced electrokinetic remediation of PAHs historically contaminated soil.

Electrokinetic (EK) remediation technology can enhance the migration of reagents to soil and is especially suitable for in situ remediation of low permeability contaminated soil. Due to the long aging time and strong hydrophobicity of polycyclic aromatic hydrocarbons (PAHs) from historically polluted soil, some enhanced reagents (oxidant, activator, and surfactant) were used to increase the mobility of PAHs, and remove and degrade PAHs in soil. However, under the electrical field, there are few reports on the roles and combined effect of oxidant, activator, and surfactant for remediation of PAHs historically contaminated soil. In the present study, sodium persulfate (PS, oxidant, 100 g L-1) or/and Tween 80 (TW80, surfactant, 50 g L-1) were added to the anolyte, and citric acid chelated iron(II) (CA-Fe(II), activator, 0.10 mol L-1) was added to catholyte to explore the roles and contribution of enhanced reagents and combined effect on PAHs removal in soil. A constant voltage of 20 V was applied and the total experiment duration was 10 days. The results showed that the removal rate of PAHs in each treatment was PS + CA-Fe(II) (21.3%) > PS + TW80 + CA-Fe(II) (19.9%) > PS (17.4%) > PS + TW80 (11.4%) > TW80 (8.1%) > CK (7.5%). The combination of PS and CA-Fe(II) had the highest removal efficiency of PAHs, and CA-Fe(II) in the catholyte could be transported toward anode via electromigration. The addition of TW80 reduced the electroosmotic flow and inhibited the transport of PS from anolyte to the soil, which decreased the removal of PAHs (from 17.4 to 11.4% with PS, from 21.3 to 19.9% with PS+CA-Fe(II)). The calculation of contribution rates showed that PS was the strongest enhancer (3.3~9.9%), followed by CA-Fe(II) (3.9~8.5%) (with PS), and the contribution of TW80 was small and even negative (-1.4~0.6%). The above results indicated that the combined application of oxidant and activator was conducive to the removal of PAHs, while the addition of surfactant reduced the EOF and the migration of oxidant and further reduced the PAHs removal efficiency. The present study will help to further understand the role of enhanced reagents (especially surfactant) during enhanced EK remediation of PAHs historically contaminated soil.

Interlaboratory Study of Polyethylene and Polydimethylsiloxane Polymeric Samplers for Ex Situ Measurement of Freely Dissolved Hydrophobic Organic Compounds in Sediment Porewater.

We evaluated the precision and accuracy of multilaboratory measurements for determining freely dissolved concentrations (C free) of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in sediment porewater using polydimethylsiloxane (PDMS) and low‐density polyethylene (LDPE) polymeric samplers. Four laboratories exposed performance reference compound (PRC) preloaded polymers to actively mixed and static ex situ sediment for approximately 1 month; two laboratories had longer exposures (2 and 3 months). For C free results, intralaboratory precision was high for single compounds (coefficient of variation 50% or less), and for most PAHs and PCBs interlaboratory variability was low (magnitude of difference was a factor of 2 or less) across polymers and exposure methods. Variability was higher for the most hydrophobic PAHs and PCBs, which were present at low concentrations and required larger PRC‐based corrections, and also for naphthalene, likely due to differential volatilization losses between laboratories. Overall, intra‐ and interlaboratory variability between methods (PDMS vs. LDPE, actively mixed vs. static exposures) was low. The results that showed C free polymer equilibrium was achieved in approximately 1 month during active exposures, suggesting that the use of PRCs may be avoided for ex situ analysis using comparable active exposure; however, such ex situ testing may not reflect field conditions. Polymer‐derived C free concentrations for most PCBs and PAHs were on average within a factor of 2 compared with concentrations in isolated porewater, which were directly measured by one laboratory; difference factors of up to 6 were observed for naphthalene and the most hydrophobic PAHs and PCBs. The C free results were similar for academic and private sector laboratories. The accuracy and precision that we demonstrate for determination of C free using polymer sampling are anticipated to increase regulatory acceptance and confidence in use of the method. Environ Toxicol Chem 2022;41:1885–1902. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Evaluation of the adsorption efficiency of carcinogenic PAHs on microplastic (polyester) fibers—preliminary results

Paper presents the results of investigations on sorption capacity of selected carcinogenic polycyclic aromatic hydrocarbons (PAHs) on microplastics fibers. Accumulation of organic micropollutants such as PAHs is indicated as one of the important problems in the case of microplastics present in surface water, including sea water. Concentrations of the micropollutants can reach even several mg/kg of microplastics. An unrecognized problem are sorption capacities of microfibers towards PAHs. Recent research works indicate that microfibers are commonly present in sewage sludge. Content of the fibers in this waste material can reach over 23000 particles per 1 kg of sludge dry matter. The fibers mainly come from cloth washing. It is obvious that the adsorption capacity of the fibers can affect the concentration of PAHs in sewage sludge. The aim of the study was to evaluate sorption capacities of polyester fibers towards PAHs. Adsorption of PAHs were provided under static conditions. After 24 h of adsorption 1255 μg/g of carcinogenic PAHs was adsorbed onto the polyster fibers. Amount of 6-ring PAHs was equal to 154 μg/g, whereas 5- i 4- ring ones, 562 and 539 μg/g, respectively. The results have confirmed that hydrophobic PAHs can be adsorbed onto polystyrene fibers and as a result cumulate in sewage sludge.

Microplastics contributed much less than organic matter to the burial of polycyclic aromatic hydrocarbons by sediments in the past decades: a case study from an urban lake.

The role of microplastics in burying hydrophobic organic compounds remains largely unknown. Sediment cores collected from the center of a typical urban lake (Lake Qianhu) in China were chosen to explore the contribution of microplastics to the burial of polycyclic aromatic hydrocarbons (PAHs) by sediments, and to elucidate how this contribution changed with microplastic composition and the hydrophobicity of PAHs on a decade scale. Our results showed that the concentration of individual PAHs adsorbed by microplastics varied from detection limit (LOD) to 7.2 mg g-1 MP, which was much higher than the LOD to 31.0 μg g-1 TOC buried by total organic carbon. However, the amount of individual PAHs adsorbed by microplastics only contributed to 0-34.2% of that in sediments. Changes in the composition of microplastics, including the increased proportion of polyethylene and polypropylene : polyethylene polymer in sediments, resulted in the average microplastic sediment burial ratios (MSBRs) of most PAHs increasing by 0.13% to 2.7% in the period from 1997 to 2018 compared with those in the period from 1975 to 1996. The average MSBRs varied with the hydrophobicity of PAHs, which increased with log Kow value if it varied from 3.45 to 5.20, but decreased with log Kow if it was in the range of 5.30 to 6.50. Our study provides novel knowledge on the contribution of microplastics to the burial of PAHs by sediments.

Assessing method performance for polycyclic aromatic hydrocarbons analysis in sediment using GC-MS: method validation and principal component analysis for quality control

ABSTRACT Polycyclic aromatic hydrocarbons (PAHs) belong to the persistent organic pollutant class and are ubiquitously present in the environment. As a consequence of their high hydrophobicity, PAHs in aquatic environments tend to rapidly sink down to the bottom sediments which are the most important reservoirs of PAHs in the aquatic environment. This paper presents the validation and further performance evaluation of a method modified in-house for PAHs’ sample preparation and analysis in sediment using gas chromatography-mass spectrometry (GC-MS). The method validation covers determining the calibration linear range, method detection and quantitation limits, method recovery and precision, method uncertainty and further internal and external quality control steps. Principal component analysis was used to identify the influence of different variables on method performance and indicated main clustering by PAH molecule size. The results of a two-year quality control programme show that the variations in method performance were not statistically significant in comparison to the parameters set during the validation experiments. Trueness expressed as recovery was very similar for spiked sediment samples and the analysed certified reference material (CRM) (70.6–113%). Expanded uncertainty ranged from 40.4% to 50.9% with higher values noted for the highly hydrophobic PAHs benzo(a)pyrene and benzo(g,h,i)perylene.

Advances in bacterial Rieske non-heme iron ring-hydroxylating dioxygenases that initiate polycyclic aromatic hydrocarbons degradation

Polycyclic aromatic hydrocarbons (PAHs) are a class of persistent organic pollutants, which have received widespread attentions due to their carcinogenic and mutagenic toxicity. The microbial degradation of PAHs are usually started from the hydroxylation, followed by dehydrogenation, ring cleavage and step-by-step removal of branched chains, and finally mineralized by the tricarboxylic acid cycle. Rieske type non-heme iron aromatic ring-hydroxylating dioxygenases (RHOs) or cytochrome P450 oxidases are responsible for the conversion of hydrophobic PAHs into hydrophilic derivatives by the ring hydroxylation. The ring hydroxylation is the first step of PAHs degradation and also one of the rate-limiting steps. Here, we review the distribution, substrate specificity, and substrate recognition mechanisms of RHOs, along with some techniques and methods used for the research of RHOs and PAHs.

Water-induced release of recalcitrant polycyclic aromatic hydrocarbons from soil organic matter during microwave-assisted solvent extraction

Polycyclic aromatic hydrocarbons (PAHs) in soil can be recalcitrant to solvent extraction after aging. We showed in this study that mixing a small amount of water in the extracting solvent during microwave-assisted extraction (MAE) can release recalcitrant PAHs, resulting in significant improvement in the analyzed concentrations. The improvement factor (F) for the total of 16 priority PAHs (∑PAH16) listed by the United States Environmental Protection Agency was 1.44–1.55 for field soils. By comparing the F values for different soil organic components, we demonstrated that the recalcitrant PAHs were primarily associated with biochar, humic acid (HA), and humin (HM), with the F values for ∑PAH16 of 1.94, 6.62, and 4.59, respectively. The results showed that the recalcitrant PAHs comprised a sequestered fraction and a desorption-limited fraction. NMR spectra showed that water worked alone at elevated temperature to promote hydrolysis of biochar and destroy the macromolecular structure, thus causing the release of the otherwise sequestered PAHs during MAE. The substantial reduction in F values for HA and HM after demineralization indicated sequestration of PAHs in organic-mineral complexes, which can be destroyed by hot water treatment. The release of the sequestered fraction was nonselective and independent of compound hydrophobicity. In comparison, the release of the desorption-limited fraction was positively affected by the hydrophobicity of PAHs and was facilitated by the presence of water in the extracting solvent. The results of this study provide important insights into the sequestration and release of recalcitrant PAHs in soil.

Hydrophobic polymer tethered magnetic zirconium-based metal-organic framework as advance and recyclable adsorbent for microwave-assisted extraction of polycyclic aromatic hydrocarbons from environmental water samples

Hydrophobic poly (glycidyl methacrylate) tethered magnetic amino-functional zirconium metal-organic framework (UiO-66-NH2) was fabricated for the first time for rapid microwave-assisted magnetic solid-phase extraction of trace polycyclic aromatic hydrocarbons from environmental water samples. UiO-66-NH2 endowed the nanocomposite with remarkable specific surface area (175.2 m2/g) and short diffusion route, while poly (glycidyl methacrylate) provided hydrophobic interaction towards hydrophobic polycyclic aromatic hydrocarbons, both of which contributed to the satisfactory extraction performance. The successful preparation of the nanocomposite was confirmed by transmission electronic microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, N2 adsorption-desorption experiment, powder X-ray diffraction patterns, contact angle measurement and vibrating sample magnetometry. In addition, an optimized protocol for microwave-assisted magnetic solid-phase extraction was carried out, including adsorbent amount (20–160 mg), adsorption time (30–150 s), desorption time (10–80 s) and desorption solvents (methanol, acetonitrile, acetone and ethyl acetate). Under the most favorable conditions, the microwave-assisted method afforded magnetic solid-phase extraction with short extraction time (1 min), a wide linear response (1.56–200 μg/L), good linearity (R2 ≥ 97.83%), low limits of detection (0.04–4.68 μg/L) and good precision (RSD ≤ 6.39%) for six polycyclic aromatic hydrocarbons. The proposed method was successfully applied in analysis of real water samples with mean recoveries in the range of 82.6–118.4% at three spiked levels and the relative standard deviations less than 10.7%. The results indicated that our developed method had great potential in enrichment and detection of trace polycyclic aromatic hydrocarbons in real aqueous samples.

A coagulation-flocculation process combined with continuous adsorption using eggshell waste materials for phenols and PAHs removal from landfill leachate

A sequential treatment consisting of coagulation/flocculation followed by transport column experiment was adopted and used in this work for the treatment of landfill leachate containing phenols and polycyclic aromatic hydrocarbons (PAHs). Coagulation experiment was performed in a standard jar test apparatus using alum as coagulant material. In column experiments, natural eggshell material was used as filter media after calcinations at 750oC either separately or combined with granular activated carbon (GAC). Alum addition at a predetermined optimum dose (3.5 g/L) caused a reduction in total suspended solids (TSS), chemical oxygen demand (COD), total phenols, and total (PAHs) by 82%, 32%, 24%, and 34% respectively. Specific PAHs analysis revealed higher binding affinity of more hydrophobic PAHs toward particles with 50% reduction than those of less hydrophobic PAHs with only 6% reduction. The results obtained from the transport column experiments indicate that calcined eggshell (ESC) particularly when applied as a mixture with GAC can be used as promising adsorbent for both phenols and PAHs. 95% of phenols and PAHs were removed during the first 1,500 pore volumes (PV) of column operation while &gt; 80% were obtained at the end of the experiment (3,500 PV).

Possibilities of poly(methyl methacrylate) as a passive sampler for determination of bioavailable concentrations in seawater.

Solvent-treated poly(methyl methacrylate) (PMMA) was recently introduced as a passive sampler for determining bioavailable concentrations, i.e., freely dissolved concentrations. However, the much knowledge required to obtain accurate bioavailable concentrations using the thus treated PMMA, applied in a marine environment, is still lacking. In this study, uptake experiments with PMMA after solvent treatment were conducted to investigate its uptake capacity and the effects of water temperature and salinity on the PMMA-water partition coefficient (KPMMA-W) for polycyclic aromatic hydrocarbons (PAHs). Thus, PMMA passive samplers preloaded with performance reference compounds were exposed to seawater to first estimate the deployment time and then to confirm if the PMMA could give the residual concentrations of PAH in mussel. The less hydrophobic PAHs (log octanol-water partition coefficient<5.5) had higher uptake capacity of PMMA-uptake was increased by a factor of up to 10. Whereas for these PAHs the KPMMA-W values and seawater temperature showed a parabolic relationship, the effect of salinity on KPMMA-W was not observed. The less hydrophobic PAH concentrations in seawater can be measured using the PMMA passive sampler over a period of about three weeks. For the PAHs detected in both PMMA and mussel, the PAH concentrations in mussel predicted from PMMA were found to be within one order of magnitude of the measured concentrations. This, therefore, suggests that solvent-treated PMMA could be used as a passive sampler to provide information on bioavailable concentrations for less hydrophobic PAHs.