Polycyclic aromatic compounds of environmental and occupational importance: Their occurrence, toxicity and the development of high purity certified reference materials, Part II

Synthesis and crystal structure of 4-acetylpyrene, C18H12O

C18H12O, triclinic, P 1 ‾ $P‾{1}$ (no. 2), a = 10.132(2) Å, b = 10.654(2) Å, c = 11.730(2) Å, α = 90.31(3)°, β = 102.38(3)°, γ = 104.81(3)°, V = 1193.2(4) Å3, Z = 4, R gt(F) = 0.0403, wR ref (F 2) = 0.1037, T = 293(2) K.

Host-guest interaction studies of polycyclic aromatic hydrocarbons (PAHs) in alkoxy bridged binuclear rhenium (I) complexes

The interaction of two neutral alkoxy bridged binuclear rhenium(I) complexes, 1 and 2 [{Re(CO)₃(1,4-NVP)}₂(μ₂-OR)₂] (1, R = C₄H₉; 2, R = C₁₀H₂₁; 1,4-NVP = 4-(1-naphthylvinyl)pyridine] with polycyclic aromatic hydrocarbons (PAH) is investigated. UV-vis absorption, emission, ¹H NMR spectral titrations, TCSPC lifetime studies and DFT theoretical calculations were carried out to examine the binding responses of complexes 1 and 2 with various PAHs such as pyrene, naphthalene, anthracene and phenanthrene. The UV-Vis absorption spectra showed an increase in absorbance of the metal-to ligand charge-transfer (MLCT) and ligand centered (LC) bands upon addition of various PAH molecules to 1 and 2, whereas the emission behavior was found to show emission quenching, which might occur through energy transfer pathway. The binding constants (K) of complexes 1 and 2 for various PAHs are found to be in the order of 10⁴ M^-1 with a 1:1 binding mode, as determined from UV-vis absorption and emission spectral titration studies. ¹H NMR spectral studies show that the chemical shifts of pyrene guest and the 1,4-NVP moiety of 2 are shifted up-field, whilst the alkoxy protons do not show any appreciable change in their chemical shifts. It is believed that the open cavities present in the Re(I) complexes may lead to the recognition of PAHs via CH···π interaction.

Enhanced Solubilization of Fluoranthene by Hydroxypropyl β-Cyclodextrin Oligomer for Bioremediation

Fluoranthene (FT) is a polycyclic aromatic hydrocarbon (PAH), consisting of naphthalene and benzene rings connected by a five-member ring. It is widespread in the environment. The hydrophobicity of FT limits its availability for biological uptake and degradation. In this study, hydroxypropyl β-cyclodextrin oligomers (HP-β-CD-ol) were synthesized with epichlorohydrin (EP), while the solubility enhancement of FT by HP-β-CD-ol was investigated in water. The synthesized HP-β-CD-ol was characterized by MALDI-TOF mass spectrometry (MS), ¹H NMR, and 13C NMR spectroscopy. The solubility of FT increased 178-fold due to the complex formation with HP-β-CD oligomers. The inclusion complexes of FT/HP-β-CD-ol were analyzed using Fourier-Transform Infrared (FT-IR), Differential Scanning Calorimetry (DSC), Scanning Electron Microscope (SEM), and Nuclear Overhauser Effect Spectroscopy Nuclear magnetic resonance (NOESY NMR) spectroscopy. On the basis of these results, HP-β-CD-ol is recommended as a potential solubilizer for the development of PAH removal systems.

Long-Term Monitoring of PAH Contamination in Sediment and Recovery After the Hebei Spirit Oil Spill

Approximately 10,900 t of crude oil was released 10 km off the west coast of Korea after the collision between the oil tanker Hebei Spirit and a barge carrying a crane in December 2007. To assess the areal extent and temporal trends of PAH contamination, 428 sediment samples were collected from December 2007 through May 2015 for PAH analysis. Sedimentary PAH concentrations measured immediately after the spill ranged from 3.2 to 71,200 ng g^-1, with a mean of 3800 ng g^-1. Increases in PAH concentrations were observed at stations 7-23, which were heavily oiled due to tidal currents and northwesterly wind that transported the spilled oil to these locations. Mean and maximum PAH concentrations decreased drastically from 3800 to 88.5 and 71,200 to 1700 ng g^-1, respectively, 4 months after the spill. PAH concentrations highly fluctuated until September 2008 and then decreased slowly to background levels. Reduction rate was much faster at the sandy beaches (k = 0.016) than in the muddy sites (k = 0.001). In muddy sediments, low attenuation due to low flushing rate in the mostly anaerobic sediment possibly contributed the persistence of PAHs. By May 2015 (~7.5 years after the spill), mean and maximum PAH concentrations decreased by 54 and 481 times, respectively, compared with the peak concentrations. The sedimentary PAH concentrations in the monitoring area have returned to regional background levels.

Characteristics of polycyclic aromatic hydrocarbons in food oils in Beijing catering services

The concentrations and characteristics of 16 polycyclic aromatic hydrocarbons (PAHs) in 48 oil samples randomly collected from 30 catering services that employ six cooking methods were quantified via high-performance liquid chromatography (HPLC). These 16 PAHs were detected in almost all of the samples. The levels of Σ16PAHs, Σ4PAHs, benzo[a]pyrene (BaP), and total BaP equivalents (ΣBaP_eq) for the six cooking methods exceeded the legal limit. The concentrations of Σ4PAHs were approximately 9.5 to 16.4 times the legal limit proposed by the European Commission (Off J Eur Union 215:4-8, 2011), and the level of BaP exceeded the national standard in China by 4.7- to 10.6-fold, particularly in oil from fried foods. Low molecular weight PAHs (LMW PAHs) were predominant in fried food oil from different catering services and accounted for 94.8 % of these oils, and the ΣBaP_eq of the high molecular weight PAHs (HMW PAHs) was 11.5-fold higher than that of the LMW PAHs. The concentrations of Σ16PAHs (3751.9-7585.8 μg/kg), Σ4PAHs (144.6-195.7 μg/kg), BaP (79.7-135.8 μg/kg), and ΣBaP_eq (231.0-265.4 μg/kg) were highest in the samples from fast food restaurants/buffets (FB), followed by those from fried food stalls (FS) and then cooking restaurants/cafeterias (RC). The results of this study suggest that the government should strengthen control and supervision of PAH contamination in food and edible oils.

Distribution and Photochemistry of Polycyclic Aromatic Hydrocarbons in the Baotou Section of the Yellow River During Winter

In this study, ice and water samples were collected from seven sites along the Baotou section of the Yellow River during winter 2013. Total polycyclic aromatic hydrocarbon (PAH) concentrations in the ice and in the water under the ice ranged from 21.3 to 59.4 ng L(-1), and from 38.3 to 222.4 ng L(-1), respectively. The average concentration in water under the ice was approximately 2.5 times greater than the average concentration in the ice phase. Four-ring PAHs dominated and accounted for 68.2 and 76.0 % of the total PAHs in ice and water, respectively. PAH concentrations were highest at sampling site S2 and were also relatively high at sites S4 and S5. PAH sources in ice and in water under the ice were similar. Three components were selected to represent the coal-combustion sources of PAHs. Because it was the main pollutant, and its concentrations were the highest, we examined the photodegradation behavior of fluoranthene and investigated the effects of light-sensitive materials (H2O2, acetone, and sediment) on fluoranthene photodegradation in the ice phase. Results showed that low H2O2 concentrations promoted photoconversion in the initial stage of the reaction and that degradation rates decreased later in the reaction. Likewise, high H2O2 concentrations promoted photoconversion. As acetone concentrations increased, the rates of fluoranthene-degradation decreased. Sediments may also have decreased the degradation rate of fluoranthene.

Polycyclic aromatic hydrocarbons and ecotoxicological characterization of sediments from the Huaihe River, China

The distribution, source, ecological risk and ecotoxicity of polycyclic aromatic hydrocarbons (PAHs) of sediments from 7 sampling sites, named as Xinyang (XY), Huainan (HN), Bengbu (BB), Xuyi (XuY), Fuyang (FY), Mengcheng (MC) and Zhengzhou (ZZ), in the Huaihe River basin, China, have been investigated. The total concentrations of 16 USEPA priority PAHs ranged from 62.9 to 2232.4 ng g⁻¹ dry weight (d.w.) with a mean concentration of 1056.8 ng g⁻¹ d.w. Through the assessment of ecological risk, we found that the levels of PAHs in the Huaihe River should not exert adverse biological effects. The total benzo[a]pyrene toxicity equivalent (TEQ) values calculated for samples varied from 0.01 to 194.1 ng g⁻¹ d.w., with an average of 65.9 ng g⁻¹. The toxicity data were accordant with the chemical analysis results in this study. HN, BB and ZZ showed the greatest pollution extent both in the chemical analysis and the study of ecotoxicological effects.

Measurement of short- and long-term toxicity of polycyclic aromatic hydrocarbons using luminescent bacteria

Growing concern over environmental contamination has stimulated rigorous efforts to establish reliable biological monitoring assays. Methodology was developed for measuring photoinduced short- and long-term toxicity of an important group of contaminants, polycyclic aromatic hydrocarbons (PAHs), using the luminescent bacterium Vibrio fischeri. The toxicity of most PAHs can be greatly enhanced on exposure of a living organism and/or the chemicals to ultraviolet (UV) radiation. There are two major mechanisms involved in photoinduced toxicity of PAHs: photosensitization and photomodification. In the former, production of singlet oxygen leads to cellular damage. In the latter, photooxidation of PAHs results in new compounds (usually oxygenated PAHs) that are often more toxic than their parent PAHs. Microbial toxicity assays were developed to measure short- and long-term photoinduced toxicity of PAHs. The bioassays were based on inhibition of luminescence and growth of V. fischeri. The short-term assay should detect toxicity of chemicals that are taken up rapidly and/or whose photosensitization activity is immediate. The long-term assay should identify chemicals where the rate of assimilation is slow and/or time is required for photoinduced effects to be realized. The assays were tested with 12 different PAHs. The short-term assay did not reveal photoinduced toxicity for any of the test chemicals. However, photoinduced toxicity was apparent in the long-term assay, indicating that short-term assays may be opaque to this key mechanism of PAH toxicity.

Poly(ethylene-co-acrylic acid) stationary phases for the separation of shape-constrained isomers

A new approach for the synthesis of long alkyl chain length stationary phases for use in reversed-phase liquid chromatography is described. Poly(ethylene-co-acrylic acid) copolymers (i.e., (-CH2CH2-)x[CH2CH(CO2H)-]y) with different levels of acrylic acid were covalently bonded to silica via glycidoxypropyl or aminopropyl linkages. 13C cross polarization magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy was used to characterize the new reversed-phase materials. Aspects of shape selectivity were evaluated for six different columns with Standard Reference Material (SRM) 869a, Column Selectivity Test Mixture for Liquid Chromatography. Selectivity for isomer separations was enhanced for stationary phases prepared with poly(ethylene-co-acrylic acid) containing a mass fraction of 5% acrylic acid. The relationship between alkyl conformation and chromatographic properties was studied by 13C magic angle spinning (MAS) NMR measurements, and correlations were made with the composition of the polymer. Finally, the effectiveness of this phase is demonstrated by the separation of several beta-carotene isomers.

Protein engineering of cytochrome p450(cam) (CYP101) for the oxidation of polycyclic aromatic hydrocarbons

Mutations of the active site residues F87 and Y96 greatly enhanced the activity of cytochrome P450(cam) (CYP101) from Pseudomonas putida for the oxidation of the polycyclic aromatic hydrocarbons phenanthrene, fluoranthene, pyrene and benzo[a]pyrene. Wild-type P450(cam) had low (<0.01 min(-1)) activity with these substrates. Phenanthrene was oxidized to 1-, 2-, 3- and 4-phenanthrol, while fluoranthene gave mainly 3-fluoranthol. Pyrene was oxidized to 1-pyrenol and then to 1,6- and 1,8-pyrenequinone, with small amounts of 2-pyrenol also formed with the Y96A mutant. Benzo[a]pyrene gave 3-hydroxybenzo[a]pyrene as the major product. The NADH oxidation rate of the mutants with phenanthrene was as high as 374 min(-1), which was 31% of the camphor oxidation rate by wild-type P450(cam), and with fluoranthene the fastest rate was 144 min(-1). The oxidation of phenanthrene and fluoranthene were highly uncoupled, with highest couplings of 1.3 and 3.1%, respectively. The highest coupling efficiency for pyrene oxidation was a reasonable 23%, but the NADH turnover rate was slow. The product distributions varied significantly between mutants, suggesting that substrate binding orientations can be manipulated by protein engineering, and that genetic variants of P450(cam) may be useful for studying the oxidation of polycyclic aromatic hydrocarbons by P450 enzymes.

Mutagenicity of C24H14 PAH in human cells expressing CYP1A1

Relatively little is known about the mutagenicity of C24H14 PAH, a diverse group of five- and six-ring PAH, some of which are present at trace levels in the environment. To better understand the mutagenicity of this class of compounds, 11 C24H14 PAH, including benzo[a]perylene, benzo[b]perylene, dibenzo[a,e]fluoranthene, dibenzo[a,f]fluoranthene, dibenzo[j,l]fluoranthene, dibenzo[a,h]pyrene, dibenzo[a,i]pyrene, dibenzo[e,l]pyrene, naphtho[1,2-b]fluoranthene, naphtho[2,3-a]pyrene, and naphtho[2,3-e]pyrene, were tested in a mutagenicity assay based on human h1A1v2 cells. h1A1v2 cells are a line of human B-lymphoblastoid cells that have been engineered to express cytochrome P4501A1 (CYP1A1), an enzyme capable of metabolizing promutagenic PAH. Mutagenicity was measured at the thymidine kinase (tk) locus following a 72-h exposure period. Our results show that nine of the compounds were mutagenic. Benzo[a]perylene, dibenzo[a,e]fluoranthene, dibenzo[a,i]pyrene, and naphtho[2,3-a]pyrene were the most potent mutagens, having minimum mutagenic concentrations (MMC) (i.e., the dose at which the induced response was twice that of the negative controls) in the 1-5 ng/ml range. Benzo[b]perylene, dibenzo[a,h]pyrene, dibenzo[a,f]fluoranthene, and naphtho[2,3-e]pyrene were somewhat less potent mutagens, having MMC in the 10-30 ng/ml range. Dibenzo[e,l]pyrene, which had an MMC of 280 ng/ml, was the least potent mutagen. Dibenzo[j,l]fluoranthene and naphtho[1,2-b]fluoranthene were not mutagenic at the doses tested (1-3000 ng/ml). The most mutagenic compounds were also quite toxic. At the highest doses tested, benzo[a]perylene, dibenzo[a,e]fluoranthene, dibenzo[a,i]pyrene, dibenzo[a,h]pyrene, and dibenzo[a,f]fluoranthene induced > 60% killing, and naphtho[2,3-a]pyrene and naphtho[2,3-e]pyrene induced > 50% killing. Benzo[b]perylene, dibenzo[e,l]pyrene, dibenzo[j,l]fluoranthene, and naphtho[1,2-b]fluoranthene induced < 50% killing at the highest doses tested. Comparing these results to a previous study in which nine other C24H14 PAH were tested for mutagenicity in this same assay, it was found that dibenzo[a]pyrene isomers were generally more mutagenic than the other groups of C24H14 PAH tested. These observations are discussed with emphasis given to identifying C24H14 PAH that may be important environmental mutagens.

The oxidation of naphthalene and pyrene by cytochrome P450cam

Mutants of the heme monooxygenase cytochrome P450cam in which Y96 had been replaced with hydrophobic residues, have been shown to oxidise naphthalene and pyrene with rates one to two orders of magnitude faster than the wild-type. Naphthalene was oxidised to 1- and 2-naphthol, probably via the 1,2-oxide intermediate. In the case of the Y96F mutant, naphthalene was oxidised at a rate comparable to camphor. Pyrene oxidation gave 1,6- and 1,8-pyrenequinone with no evidence for attack at the K-region, in contrast to mammalian enzymes. The results show that the Y96 residue plays a key role in controlling the substrate range of P450cam.

Bioavailability and biodegradation kinetics protocol for organic pollutant compounds to achieve environmentally acceptable endpoints during bioremediation

This paper is an extension of our previous studies on quantitating biodegradation kinetics in soil slurry and compacted soil systems. Previous studies had mainly used phenol as a test contaminant. Phenol represents hydrophilic compounds which exhibit high water solubility and low soil sorption characteristics. This paper extends the experimental protocol using polycyclic aromatic hydrocarbons (PAHs) as the test contaminants. PAHs are hydrophobic compounds with low water solubility and exhibit significant partitioning in soil organic carbon. Degradation rates of PAHs are much slower, thereby requiring acclimation of indigenous soil microbiota using microcosm reactors. The experimental protocol, elaborated in this paper, results in the measurement of biokinetic parameters which can be used to quantitate both ex situ and in situ bioremediation rates and assess the attainable endpoints. Biodegradation studies were conducted for naphthalene using soil slurry, soil wafer, and soil column reactors. Microcosm reactors were set-up to acclimate soil microbiota, and carbon dioxide evolution was used as a measure of acclimation. It was found that reasonable degree of PAH acclimation was achieved after 250 days of microcosm operation. Abiotic adsorption/desorption studies showed that equilibrium was achieved in about 20 hours and approximately 45% of the initial amount of naphthalene is adsorbed by the time equilibrium is attained. Further, desorption was much slower than adsorption with equilibrium being attained in 40 hours. Biokinetic parameters were derived from the cumulative oxygen uptake data of soil slurry, wafer, and column reactors using detailed mathematical models. The cumulative oxygen uptake in all three reactors were almost the same, since naphthalene primarily degraded in the soil phase and the extent of degradation in the aqueous phase was small.

Biodegradation of 1-nitropyrene

The metabolism of 14C-labeled 1-nitropyrene in microcosms containing nonsterile estuarine sediments, and in cultures of a Mycobacterium sp. previously isolated from oil-contaminated sediments was investigated. Although mineralization of 1-nitropyrene by pure cultures of the Mycobacterium sp. totaled only 12.3% after 10 days of incubation, over 80% of the ethyl acetate extractable 14C-labeled compounds consisted of 1-nitropyrene metabolites. High pressure liquid chromatographic analysis of 1-nitropyrene degradation products indicated that two major metabolites were formed. They were identified as 1-nitropyrene cis-9,10- and 4,5-dihydrodiols, based on their UV-visible, mass and NMR spectra. Time course studies in microcosms showed that 1-nitropyrene was degraded slowly under aerobic and anaerobic conditions in estuarine sediments. Less than 1% had been converted to 14CO2 after 8 weeks of aerobic incubation. The addition of 1-nitropyrene to anaerobic sediments resulted in no 14CO2 evolution; however, the nitro group of 1-nitropyrene was reduced to form 1-aminopyrene. Although the mineralization of 1-nitropyrene in sediments was slow, the Mycobacterium sp. metabolized 1-nitropyrene in pure culture. This bacterium appears promising for the bioremediation of this ubiquitous pollutant in contaminated waste.

Naphthalene biodegradation in environmental microcosms: estimates of degradation rates and characterization of metabolites

Naphthalene biodegradation was investigated in microcosms containing sediment and water collected from three ecosystems which varied in past exposure to anthropogenic and petrogenic chemicals. Mineralization half-lives for naphthalene in microcosms ranged from 2.4 weeks in sediment chronically exposed to petroleum hydrocarbons to 4.4 weeks in sediment from a pristine environment. Microbiological analysis of sediments indicated that hydrocarbon-utilizing microbial populations also varied among ecosystems and were 5 to 12 times greater in sediment after chronic petrogenic chemical exposure than in sediment from an uncontaminated ecosystem. Sediment from an ecosystem exposed to agricultural chemicals had a mineralization half-life of 3.2 weeks for naphthalene and showed about a 30-fold increase in heterotrophic bacterial populations in comparison to uncontaminated sediments, but only a 2- to 3-fold increase in hydrocarbon-degrading bacteria. Analysis of organic solvent-extractable residues from the microcosms by high-pressure liquid chromatography detected polar metabolites which accounted for 1 to 3% of the total radioactivity. Purification of these residues by thin-layer chromatography and further analysis by gas chromatography-mass spectrometry indicated that cis-1,2-dihydroxy-1,2-dihydronaphthalene, 1-naphthol, salicylic acid, and catechol were metabolites of naphthalene. These results provide useful estimates for the rates of naphthalene mineralization in different natural ecosystems and on the degradative pathway for microbial metabolism of naphthalene in freshwater and estuarine environments.