SciCombinator

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Concept: Anthracene

255

Emissions of organic substances with potential toxicity to humans and the environment are a major concern surrounding the rapid industrial development in the Athabasca oil sands region (AOSR). Although concentrations of polycyclic aromatic hydrocarbons (PAHs) in some environmental samples have been reported, a comprehensive picture of organic contaminant sources, pathways, and sinks within the AOSR has yet to be elucidated. We sought to use a dynamic multimedia environmental fate model to reconcile the emissions and residue levels reported for three representative PAHs in the AOSR. Data describing emissions to air compiled from two official sources result in simulated concentrations in air, soil, water, and foliage that tend to fall close to or below the minimum measured concentrations of phenanthrene, pyrene, and benzo(a)pyrene in the environment. Accounting for evaporative emissions (e.g., from tailings pond disposal) provides a more realistic representation of PAH distribution in the AOSR. Such indirect emissions to air were found to be a greater contributor of PAHs to the AOSR atmosphere relative to reported direct emissions to air. The indirect pathway transporting uncontrolled releases of PAHs to aquatic systems via the atmosphere may be as significant a contributor of PAHs to aquatic systems as other supply pathways. Emission density estimates for the three PAHs that account for tailings pond disposal are much closer to estimated global averages than estimates based on the available emissions datasets, which fall close to the global minima. Our results highlight the need for improved accounting of PAH emissions from oil sands operations, especially in light of continued expansion of these operations.

Concepts: Phenanthrene, Organic chemistry, Anthracene, Aromaticity, Naphthalene, Petroleum, Hydrocarbon, Polycyclic aromatic hydrocarbon

29

Polycyclic aromatic hydrocarbons (PAHs) are regarded as key molecules in the astrochemical evolution of the interstellar medium, but the formation mechanism of even their simplest prototype-naphthalene (C(10)H(8))-has remained an open question. Here, we show in a combined crossed beam and theoretical study that naphthalene can be formed in the gas phase via a barrierless and exoergic reaction between the phenyl radical (C(6)H(5)) and vinylacetylene (CH(2) = CH-C ≡ CH) involving a van-der-Waals complex and submerged barrier in the entrance channel. Our finding challenges conventional wisdom that PAH-formation only occurs at high temperatures such as in combustion systems and implies that low temperature chemistry can initiate the synthesis of the very first PAH in the interstellar medium. In cold molecular clouds, barrierless phenyl-type radical reactions could propagate the vinylacetylene-mediated formation of PAHs leading to more complex structures like phenanthrene and anthracene at temperatures down to 10 K.

Concepts: Aromaticity, Hydrogen, Anthracene, Benzene, Naphthalene, Atom, Chemical reaction, Polycyclic aromatic hydrocarbon

26

Trichoderma asperellum H15, a previously isolated strain characterized by its high tolerance to low (LMW) and high molecular weight (HMW) PAHs, was tested for its ability to degrade 3-5 ring PAHs (phenanthrene, pyrene, and benzo[a]pyrene) in soil microcosms along with a biostimulation treatment with sugarcane bagasse. T. asperellum H15 rapidly adapted to PAH-contaminated soils, producing more CO2 than uncontaminated microcosms and achieving up to 78 % of phenanthrene degradation in soils contaminated with 1,000 mg Kg(-1) after 14 days. In soils contaminated with 1,000 mg Kg(-1) of a three-PAH mixture, strain H15 was shown to degrade 74 % phenanthrene, 63 % pyrene, and 81 % of benzo[a]pyrene. Fungal catechol 1,2 dioxygenase, laccase, and peroxidase enzyme activities were found to be involved in the degradation of PAHs by T. asperellum. The results demonstrated the potential of T. asperellum H15 to be used in a bioremediation process. This is the first report describing the involvement of T. asperellum in LMW and HMW-PAH degradation in soils. These findings, along with the ability to remove large amounts of PAHs in soil found in the present work provide enough evidence to consider T. asperellum as a promising and efficient PAH-degrading microorganism.

Concepts: Anthracene, Pyrene, Aromaticity, Phenanthrene, Archaea, Trichoderma, Bioremediation, Polycyclic aromatic hydrocarbon

25

Polycyclic Aromatic Hydrocarbons (PAHs) are diverse organic contaminants released into the environment by both natural and anthropogenic activities. These compounds have negative impacts on plants growth and development. Although there are many reports on their existence in different parts of plant, their uptake and translocation pathways and mechanisms are not well understood yet. This paper highlights the uptake, translocation and accumulation of PAHs by wheat, sunflower and alfalfa through an experimental study under controlled conditions. Seeds were cultivated in a soil containing 50 mg/kg of phenanthrene and fluorene and their concentrations in plants roots and shoots were determined using a gas chromatograph after 7 and 14 days. The results showed that phenanthrene and fluorene concentrations in the treated plants were increased over the time. PAHs bioavailability was time and species dependent and generally, phenanthrene uptake and translocation was faster than that of fluorene, probably due to their higher Kow. Fluorene tended to accumulate in roots, but phenanthrene was transported to aerial parts of plants.

Concepts: Seed, Aromaticity, Phenanthrene, Root, Naphthalene, Anthracene, Polycyclic aromatic hydrocarbons, Polycyclic aromatic hydrocarbon

25

Rhamnolipid was applied to degrade anthracene and pyrene in reversed micelles. The parameters in degradation were optimized for the purpose of improving degradation rates. The proper amount of rhamnolipid (RL) used for degrading anthracene was 0.065 mM, while 0.075 mM for pyrene. However, reaction time for degrading both anthracene and pyrene was 48 h. The optimum water content, pH, laccase concentration, polycyclic aromatic hydrocarbon (PAH) initial concentration, and volume ratio of n-hexanol to isooctane for both were found out. The highest degradation rates of anthracene and pyrene were 37.52 and 25.58 %, respectively. Although the degradation rates were not higher than the results previous literatures reported, this method was of novelty and provided guidance in application in degrading PAHs by reversed micellar system, especially for biosurfactant-based reversed micelles.

Concepts: Anthracene, Aromaticity, Pyrene, Hydrocarbon, Aromatic hydrocarbon, Naphthalene, Benzene, Polycyclic aromatic hydrocarbon

7

A hard cap espresso machine has been used in combination with liquid chromatography with molecular fluorescence detection for the determination of polycyclic aromatic hydrocarbons (PAHs) from contaminated soils and sediments providing appropriate extraction efficiencies and quantitative results. Naphthalene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benz[a]anthracene, chrysene, benz[b]fluoranthene, benz[k]fluoranthene, benz[a]pyrene, dibenz[a,h]anthracene, benz[ghi]perylene, and indeno[1,2,3-cd]pyrene were used as target compounds. It should be mentioned that the pairs benz[a]anthracene-chrysene and dibenz[a,h]anthracene-benz[ghi]perylene peaks coelute under the employed chromatographic conditions; thus, those compounds were determined together. PAHs were extracted from 5.0 g of soil, previously homogenized, freeze-dried, and sieved to 250 μm, with 50 mL of 40 % (v/v) acetonitrile in water at a temperature of 72 ± 3 ⁰C. The proposed procedure is really fast, with an extraction time of 11 seconds, and it reduces the required amount of organic solvent to do the sample preparation. The obtained limit of detection for the evaluated PAHs was from 1 to 38 µg kg-1. Recoveries were calculated using clean soils spiked with 100, 500, 1000, and 2000 µg kg-1 PAHs with values ranging from 81 to 121%, and good precision with relative standard deviation values lower than 30%. The method was validated using soil and sediment certified reference materials, and also using real samples by comparison with ultrasound-assisted extraction, as reference methodology, obtaining statistically comparable results. Thus, the use of hard cap espresso machines in the analytical laboratories offers tremendous possibilities as low cost extraction units for the extraction of solid samples.

Concepts: Standard deviation, Polycyclic aromatic hydrocarbons, Anthracene, Pyrene, Benzene, Chromatography, Analytical chemistry, Polycyclic aromatic hydrocarbon

2

Endophytes have been isolated from a large diversity of plants and have shown to enhance the remediation efficiency of plants, but little information is available on the influence of endophytic bacteria on phytoremediation of widespread environmental contaminants such as polyaromatic hydrocarbons (PAHs). In this study we selected a naturally occurring endophyte for its combined ability to colonize plant roots and degrade phenanthrene in vitro. Inoculation of two different willow clones and a grass with Pseudomonas putida PD1 was found to promote root and shoot growth and protect the plants against the phytotoxic effects of phenanthrene. In addition there was 25-40% removal of phenanthrene from soil by the willow and grasses inoculated with PD1 when compared to the uninoculated controls. Epifluorescent microscopy using fluorescent protein tagging of PD1 confirmed the presence of bacteria inside the root tissue. Inoculation of willows with PD1 consistently improved the growth and health when grown in hydroponic systems with high concentrations of phenanthrene. To our knowledge this is the first time that the inoculation of willow plants has been shown to improve the degradation of PAHs and improve the health of the host plants, demonstrating the potential wide benefit to the field of natural endophyte-assisted phytoremediation.

Concepts: Symbiosis, Anthracene, Soil, Polycyclic aromatic hydrocarbon, Fungus, Root, Endophyte, Plant

0

Direct inlet probe (DIP) was used as an introduction and a pre-separation step for atmospheric pressure photoionization time-of-flight ion mobility spectrometry (APPI-TOF-IMS) for the first time. IMS is an analytical technique used to separate and identify ionized molecules in the gas phase and under atmospheric pressure based on their mobility. The utilization of DIP prior to IMS gives the possibility to introduce the analytes into the gas phase and provides an additional separation based on their vapor pressure. The proof-of-principle study was done on example of eight polycyclic aromatic hydrocarbons (PAHs) with the ring number from 2 to 5, namely naphthalene, fluorene, anthracene, phenanthrene, pyrene, fluoranthene, benzo[a]pyrene, and benzo[k]fluoranthene. All these compounds are included in EPA priority pollutant list. Moreover, benzo[a]pyrene and benzo[k]fluoranthene are marked by EPA as probably carcinogen compounds and also included into SCF and EU lists. To increase the sensitivity of DIP-APPI-IMS the analysis was performed using a dopant assisted ionization method (benzene, 74mgL-1in N2). It was found that the heating rate of the interface plays a crucial role for the whole analytical procedure. To prove the ability of this method to analyze PAHs in the mixture, the mixtures containing up to five PAHs were analyzed. The LODs for the analyzed compounds obtained with DIP-APPI-IMS were found to be in the tens- or hundreds-of-microgram-per-liter range. The obtained results are promising enough to ensure the potential of DIP as an introduction and a pre-separation step for ion mobility based methods.

Concepts: Pressure, Aromaticity, Anthracene, Pyrene, Naphthalene, Benzene, Mass spectrometry, Polycyclic aromatic hydrocarbon

0

Biochar has high potential for organic pollutant immobilization due to its powerful sorption capacity. Nevertheless, potential risks may exist when biochar-sorbed organic pollutants are bioavailable. A direct plant exposure assay in combination with an organic solvent extraction experiment was carried out in this study to investigate the bioavailability of polycyclic aromatic hydrocarbons (PAHs) with the application of pine needle biochars pyrolyzed under different temperatures (100, 300, 400, and 700 °C; referred as P100-P700 accordingly). Biochar reduced solvent extractability and plant uptake of PAHs including naphthalene (Naph), acenaphthene (Acen), phenanthrene (Phen), and pyrene (Pyr), especially for three- and four-ring PAHs (Phen and Pyr) with high-temperature biochar. Plant uptake assay validates with organic solvent extraction for bioavailability assessment. Sorption of PAHs to biochars reduced plant uptake of PAHs in roots and shoots by lowering freely dissolved PAHs. Aging process reduced the bioavailability of PAHs that were bound to biochar. High pyrolysis temperature can be recommended for biochar preparation for purpose of effectively immobilizing PAHs, whereas application of moderate-temperature biochar for PAH immobilization should concern the potential risks of desorption and bioavailability of PAHs.

Concepts: Aromaticity, Solubility, Anthracene, Carbon, Phenanthrene, Naphthalene, Benzene, Polycyclic aromatic hydrocarbon

0

We describe a novel, short, and flexible approach to diverse N-doped polycyclic aromatic hydrocarbons (PAHs) by a gold-catalyzed π-extension reaction of anthranils employing o-ethynylbiaryls as reagents. This strategy uses easily accessible starting materials, is simple due to high step and atom economy and shows good functional-group compatibility as well as scaling-up potential. Mechanistically, the tandem reaction is proposed to involve a nucleophilic addition/ring opening/regiospecific C-H annulation/protodeauration terminated by a Friedel-Crafts-type cyclization. Photophysical studies of the products indicated violet-blue fluorescence emission with quantum yields up to 0.45.

Concepts: Photon, Anthracene, Benzene, Aromatic hydrocarbon, Aromaticity, Naphthalene, Organic chemistry, Polycyclic aromatic hydrocarbon