Acidic and non-acidic products from the photo-oxidation of the crude oil component dibenzothiophene dissolved in seawater

Prospective Approach to the Anaerobic Bioconversion of Benzo- and Dibenzothiophene Sulfones to Sulfide

Sulfur recovery from organic molecules such as toxic sulfones is an actual problem, and its solution through the use of environmentally friendly and nature-like processes looks attractive for research and application. For the first time, the possible bioconversion of organic sulfones (benzo-and dibenzothiophene sulfones) to inorganic sulfide under anaerobic conditions with simultaneous biogas production from glucose within a methanogenesis process is demonstrated. Biogas with a methane content of 50.7%-82.1% was obtained without H2S impurities. Methanogenesis with 99.7%-100% efficiency and 97.8%-100% conversion of benzo- and dibenzothiophene sulfones (up to 0.45 mM) to inorganic sulfide were obtained in eight days by using a combination of various anaerobic biocatalysts immobilized in a poly(vinyl alcohol) cryogel. Pure cell cultures of sulfate-reducing bacteria and/or H2-producing bacteria were tested as additives to the methanogenic activated sludge. The immobilized activated sludge "enhanced" by bacterial additives appeared to retain its properties and be usable multiple times for the conversion of sulfones under batch conditions.

Assessing the hydroxyl radical and volatilization roles in aquatic fate estimations of sulfur heterocycles: Dibenzothiophene derivatives

Polycyclic aromatic sulfur heterocycles (PASHs) and their alkyl derivatives can be released into aquatic systems via crude oil spills or runoff from petroleum-treated areas, such as asphalt. Dibenzothiophene (DBT) and its derivatives (C1-DBT, C2-DBT, and C4-DBT) were chosen as model compounds to investigate the relative impact of volatilization and hydroxyl radical degradation on estimates of their overall dissipation after entry into aquatic ecosystems as a function of depth using the exposure analysis modeling system (EXAMS). The hydroxyl radical rate constant (K _· OH ) and Henry's law constant of PASHs were determined in distilled water. The analogue C1-DBT reacted fastest with · OH relative to other PASHs. The C2-DBT and C4-DBT analogues had higher Henry's law constants compared with other derivatives. Steric hindrance by alkyl substituents on the sulfur moiety most strongly impacted measured rate and Henry's law constants between DBT and individual alkyl derivatives. These steric effects do not appear to be considered in the physical property estimation software EPI Suite. Simulated dissipation of PASHs using EXAMS suggests that volatilization is a dominant fate pathway for the higher molecular weight and less polar C2-DBT and C4-DBT at all depths and DBT and C1-DBT at 0.1-m. However, model scenarios suggest that hydroxyl radical degradation may significantly contribute to the degradation of more polar DBT and C1-DBT at 1-m and 2-m depths. Environ Toxicol Chem 2017;36:1998-2004. © 2017 SETAC.

Time to Say Goodbye to the 16 EPA PAHs? Toward an Up-to-Date Use of PACs for Environmental Purposes

The 16 EPA PAHs have played an exceptionally large role above all in environmental and analytical sciences in the last 40 years, but now there are good reasons to question their utility in many circumstances even though their use is so established and comfortable. Here we review the reasons why the list has been so successful and why sometimes it is seen as less relevant. Three groups of polycyclic aromatic compounds (PAC) are missing: larger and highly relevant PAHs, alkylated PACs, and compounds containing heteroatoms. Attempts to improve the situation for certain matrixes are known and here: (1) an updated list of PAHs (including the 16 EPA PAHs) for the evaluation of the toxicity in the environment (40 EnvPAHs); (2) a list of 23 NSO-heterocyclic compounds and 6 heterocyclic metabolites; and (3) lists of 10 oxy-PAHs and 10 nitro-PAHs are proposed for practical use in the future. A discussion in the scientific community about these lists is invited. Although the state of knowledge has improved dramatically since the introduction of the 16 EPA PAHs in the 1970s, this summary also shows that more research is needed about the toxicity, occurrence in the environment and chemical analysis, particularly of alkylated PAHs, higher molecular weight PAHs and substituted PACs such as amino-PAHs, cyano-PAHs, etc.. We also suggest that a long overdue discussion of an update of regulatory environmental PAH analysis is initiated.

Products of polycyclic aromatic sulfur heterocycles in oil spill photodegradation

Photo-oxidation is a potentially significant process in the degradation of crude oil spilled in the environment. The polycyclic aromatic sulfur heterocycles (PASHs) in an Egyptian crude oil (0.8 % sulfur) were photo-oxidized as a film on the surface of water in the presence of anthraquinone as photosensitizer under simulated solar irradiation. The polar photoproducts were characterized using negative ion electrospray ionization with time of flight mass spectrometry and, after trimethylsilylation, gas chromatography with mass spectrometry. The photoproducts identified revealed the presence of a large variety of sulfonic acids, aliphatic and aromatic acids, and alcohols. The data also give new information on the substituents of the aromatic compounds in the unexposed oil and indicate the presence of cyclohexyl substituted aromatic compounds.

Ultraviolet treatment and biodegradation of dibenzothiophene: Identification and toxicity of products

Biodegradation of pollutants often results in incomplete mineralization and formation of degradation products with unknown chemical and toxicological characteristics. Ultraviolet (UV) irradiation, a common technology used in water and wastewater treatment, may help reduce aqueous concentrations of degradation products produced during biological treatment and their associated hazards. Combined biological and UV transformations may be important in natural systems as well. We investigated the effects of UV irradiation (254 nm) on dibenzothiophene (DBT), a sulfur-containing polyaromatic hydrocarbon, in artificial seawater, and its effects on biodegradation products produced from mixed-community microbial transformations of DBT, including DBT sulfone, DBT sulfoxide, hydroxylated and carboxylated benzothiophenes, thiosalicylic acid, and others. Toxicity of solutions after UV exposure was monitored using bioluminescent bacteria (Vibrio fischeri) and by evaluating cardiac deformities in Fundulus heteroclitus embryos. The highest UV fluence reduced DBT concentration by 28% when DBT was present as the sole organic solute. In postbiodegradation solution, the same fluence reduced the initial concentration of DBT by 81%, and 11 DBT biodegradation products to trace levels. Regardless of UV fluence, DBT by itself produced minimal effects in Fundulus embryos but was moderately toxic to V. fischeri. Postbiodegradation solutions were highly toxic to both test organisms. The highest UV fluence slightly reduced toxicity of postbiodegradation solution to V. fischeri but exacerbated cardiac deformities in Fundulus embryos. Toxicity could not be attributed to specific products and was likely a result of mixture effects. These results emphasize that toxicity can increase during remediation and that multiple assays may be necessary for evaluation. The novel approach of combined biodegradation/UV treatment is promising, although further research is needed to reduce toxicity in the case of DBT.

Photooxidation products of polycyclic aromatic compounds containing sulfur

Photooxidation of crude oil components is an important process that removes pollutants from the environment. Polycyclic aromatic compounds (PACs) are known to be toxic to many life forms, but little is known about their photooxidation products in the aqueous phase. We here identify a large number of photoproducts from 11 benzothiophenes, a polycyclic aromatic sulfur heterocycle that is a major representative of PACs in crude oil. The investigated compounds contain two to four methyl groups and an ethyl or an n-octyl group. In water, the products arise through oxidation of alkyl side chains to aldehydes and carboxylic acids or through an opening in one of the aromatic rings. The product analysis was performed using gas chromatography with mass spectrometric or atomic emission detection. The main product is always a sulfobenzoic acid, which strongly lowers the pH of the solution. With long alkyl substituents, surfactants are formed, which may possess solubilizing properties in water. The larger the number of alkyl groups, the faster is the photooxidation. Several of the identified acidic compounds were also found when whole crude oil was photooxidized, showing that simulation with individual compounds reflects the situation in whole crude.

Laser photo-oxidative degradation of 4,6-dimethyldibenzothiophene

Degradation of 4,6-dimethyldibenzothiophene (DMDBT), persistent sulfur contaminant in fuel oils has been achieved in non-polar phase by laser-irradiating DMDBT alone and in the presence of hydrogen peroxide and molecular oxygen. The most efficient degradation in the presence of molecular oxygen is judged to be the first example of self-sensitized photo-oxygenation of thiophenes, in which DMDBT sequentially acts as 1O2 sensitizer and reactant.

Photolysis, oxidation and subsequent toxicity of a mixture of polycyclic aromatic hydrocarbons in natural waters

Photodegradation of a mixture of three polycyclic aromatic hydrocarbons fluorene (FLU), dibenzofuran (DBF), and dibenzothiophene (DBT) using UV and UV/H₂O₂ processes was studied. Treating a mixture of the PAHs stimulated a more realistic contamination composition present in polluted water. Effects of pH, PAH concentration, and water matrix composition on removal rates and efficiencies of these compounds are discussed. Batch experiments were conducted using both monochromatic low pressure (LP, 253.7 nm) and polychromatic medium pressure (MP, 200-400 nm) UV sources, in a quasi-collimated beam setup. A synergistic effect was observed during direct photolysis and LP-UV/H₂O₂ of the mixture as compared to photodegradation as a single component in an aqueous solution. Similar results were obtained for FLU using MP-UV/H₂O₂ whereas, degradation of DBF and DBT was inhibited in a mixture. Natural water enhanced the direct photolysis compared to laboratory buffered water, whereas, degradation of the PAHs in the natural water was inhibited using UV/H₂O₂ process. Toxicity testing using a luminescent inhibition bioassay was correlated to intermediates generated during UV-based oxidation reactions.

Polycyclic aromatic sulfur heterocycles as information carriers in environmental studies

Polycyclic aromatic hydrocarbons (PAHs) play a huge role in environmental analytical chemistry, both as pollutants and as markers for many processes. On the other hand, polycyclic aromatic sulfur heterocycles (PASHs; heterocyclic compounds related to PAHs) have been studied far less intensely, but such studies may lead to a great deal of information not available through the study of PAHs. Here we discuss analytical aspects of PASHs in environmental matrices and their use as information carriers. Since PASHs accompany PAHs in sampling and work-up, it is not necessary to expend much extra analytical effort in order to analyze them. This work reviews how they can provide information on diverse processes such as petroleum, industrial and vehicular pollution, and sources of air and marine pollution.

Photooxidation of dibenzothiophene on TiO2/hectorite thin films layered catalyst

A new titanium(IV) oxide-hectorite nanofilm photocatalyst was prepared on quartz slides. It was evaluated in the photooxidation of dibenzothiophene (DBT) in nonpolar organic solution (tetradecane), as a model for diesel fuel. A removal regimen was developed consisting of catalytic photooxidation followed by adsorption of products on silica gel. Photooxidation of DBT was performed with and without catalyst, at 254 and 300 nm. Comparison was made with a commercially available TiO(2) catalyst, Degussa P25. The catalyst was analyzed by nitrogen adsorption, XRD, SEM, and TGA-DTA. DBT concentrations were measured by HPLC and UV spectrophotometry. Preliminary qualititative analysis of products was performed by UV and HPLC. Results indicated that the outlined process was effective in reducing sulfur levels to below 10 ppm sulfur.

Sonochemical decomposition of dibenzothiophene in aqueous solution

Dibenzothiophene is decomposed rapidly by sonication in aqueous solution. Decomposition of dibenzothiophene follows a first-order reaction kinetics. The rate constant was found to increase with increasing ultrasonic energy intensity, temperature, and pH and decrease with increasing initial dibenzothiophene concentration. The activation energy was 12.6 kJ mol in the temperature range of 15-50 degrees C, suggesting a diffusion-controlled reaction. Hydroxydibenzothiophenes and dihydroxydibenzothiophenes were identified as reaction intermediates. It is proposed that dibenzothiophene is oxidized by OH radical to hydroxy-dibenzothiophenes and then to dihydroxy-dibenzothiophenes. Kinetic analysis suggests that approximately 72% of the dibcnzothiophene decomposition occurred via OH radical addition. A pathway and a kinetic model for the sonochemical decomposition of dibenzothiophene in aqueous solution are proposed.