Photodegradation and biodegradation study of benzo(a)pyrene in different liquid media

Environmental significance of PAH photoproduct formation: TiO2 nanoparticle influence, altered bioavailability, and potential photochemical mechanisms

Interactions between polycyclic aromatic hydrocarbons (PAHs) and titanium dioxide (TiO2) nanoparticles (NPs) can produce unforeseen photoproducts in the aqueous phase. Both PAHs and TiO2-NPs are well-studied and highly persistent environmental pollutants, but the consequences of PAH-TiO2-NP interactions are rarely explored. We investigated PAH photoproduct formation over time for benzo[a]pyrene (BaP), fluoranthene (FLT), and pyrene (PYR) in the presence of ultraviolet A (UVA) using a combination of analytical and computational methods including, identification of PAH photoproducts, assessment of expression profiles for gene indicators of PAH metabolism, and computational evaluation of the reaction mechanisms through which certain photoproducts might be formed. Chemical analyses identified diverse photoproducts, but all PAHs shared a primary photoproduct, 9,10-phenanthraquinone (9,10-PQ), regardless of TiO2-NP presence. The computed reaction mechanisms revealed the roles photodissociation and singlet oxygen chemistry likely play in PAH mediated photochemical processes that result in the congruent production of 9,10-PQ within this study. Our investigation of PAH photoproduct formation has provided substantial evidence of the many, diverse and congruent, photoproducts formed from physicochemically distinct PAHs and how TiO2-NPs influence bioavailability and time-related formation of PAH photoproducts.

The unique biodegradation pathway of benzo[a]pyrene in moderately halophilic Pontibacillus chungwhensis HN14

Benzo[a]pyrene (BaP), as the typical representative of polycyclic aromatic hydrocarbons (PAHs), is a serious hazard to human health and natural environments. Though the study of microbial degradation of PAHs has persisted for decades, the degradation pathway of BaP is still unclear. Previously, Pontibacillus chungwhensis HN14 was isolated from high salinity environment exhibiting a high BaP degradation ability. Here, based on the intermediates identified, BaP was found to be transformed to 4,5-epoxide-BaP, BaP-trans-4,5-dihydrodiol, 1,2-dihydroxy-phenanthrene, 2-carboxy-1-naphthol, and 4,5-dimethoxybenzo[a]pyrene by the strain HN14. Furthermore, functional genes involved in degradation of BaP were identified using genome and transcriptome data. Heterogeneous co-expression of monooxygenase CYP102(HN14) and epoxide hydrolase EH(HN14) suggested that CYP102(HN14) could transform BaP to 4,5-epoxide-BaP, which was further transformed to BaP-trans-4,5-dihydrodiol by EH(HN14). Moreover, gene cyp102(HN14) knockout was performed using CRISPR/Cas9 gene-editing system which confirmed that CYP102(HN14) play a key role in the initial conversion of BaP. Finally, a novel BaP degradation pathway was constructed in bacteria, which showed BaP could be converted into chrysene, phenanthrene, naphthalene pathways for the first time. These findings enhanced our understanding of microbial degradation process for BaP and suggested the potential of using P. chungwhensis HN14 for bioremediation in PAH-contaminated environments.

Efficient benzo(a)pyrene degradation by coal gangue-based catalytic material for peroxymonosulfate activation

A low cost and green peroxymonosulfate (PMS) activation catalyst (CG-Ca-N) was successfully prepared with coal gangue (CG), calcium chloride, and melamine as activator. Under the optimal conditions, the CG-Ca-N can remove 100 % for benzo(a)pyrene (Bap) in an aqueous solution after 20 min and 72.06 % in soil slurry medium within 60 min, which also display excellent reuse ability toward Bap after three times. The removal of Bap is significantly decreased when the initial pH value was greater than 9 and obviously inhibited in the presence of HCO3- or SO42-. The characterization results indicated that the addition of calcium chloride could stabilize and increase the content of pyridinic N during thermal annealing, resulting in the production of •OH, SO4•- and 1O2. Based on electron paramagnetic resonance (EPR) and active radical scavenging experiments, 1O2 could be identified to be the dominant role in Bap degradation. Overall, this work opened a new perspective for the low cost and green PMS catalysts and offered great promise in the practical remediation of organic pollution of groundwater and soil.

Excited State Kinetics of Benzo[a]pyrene Is Affected by Oxygen and DNA

Benzo[a]pyrene is a widespread environmental pollutant and a strong carcinogen. It is important to understand its bio-toxicity and degradation mechanism. Herein, we studied the excited state dynamics of benzo[a]pyrene by using time-resolved fluorescence and transient absorption spectroscopic techniques. For the first time, it is identified that benzo[a]pyrene in its singlet excited state could react with oxygen, resulting in fluorescence quenching. Additionally, effective intersystem crossing can occur from its singlet state to the triplet state. Furthermore, the interaction between the excited benzo[a]pyrene and ct-DNA can be observed directly and charge transfer between benzo[a]pyrene and ct-DNA may be the reason. These results lay a foundation for further understanding of the carcinogenic mechanism of benzo[a]pyrene and provide insight into the photo-degradation mechanism of this molecule.

Enhanced transformation capability towards benzo(a)pyrene by Fe(III)-modified manganese oxides

Manganese oxides (Mn oxides) are ubiquitous and may coexist with Fe(III) ions in soil environments. In this study, acid birnessite, alkaline birnessite, cryptomelane, pyrolusite, manganite, and their Fe(III)-modified analogues were synthesized and used for benzo(a)pyrene transformation. Fe-modified Mn oxides show a markedly enhanced transformation capability towards benzo(a)pyrene. Specifically, the benzo(a)pyrene transformation rate constants k for Bir-H, Bir-OH, Cry, Pyr, and Man were 0.49, 0.080, 0.0071, 0.0055, and 0.0022 h^-1, respectively. After Fe(III) modification, the transformation rate constants were increased to 22, 2.7, 0.25, 0.0072 and 0.0098 h^-1, respectively. Fe(III)-modified layered birnessites exhibited better activity than Fe(III)-modified tunnel Mn oxides, which was attributed to their high Fe(III) contents and abundant active free radicals. Fe(III) was found to accept electrons from benzo(a)pyrene, thereby accelerating the benzo(a)pyrene transformation. Moreover, modification with Fe(III) increased the surface adsorbed water and oxygen, and promoted the generation of active free radicals. Finally, the physicochemical and biochemical properties of transformation products showed the environmental benefits of this process. Overall, the results indicate that the occurrence of Fe(III) ions could promote the removal of PAHs in Mn oxides-rich soils, and this study provides a credible understanding of PAH fates in natural soils.

Dynamics and Mass Balance of Polycyclic Aromatic Hydrocarbons in and Around the Seto Inland Sea, Japan

Polycyclic aromatic hydrocarbons (PAHs) were analyzed to elucidate the distribution, ecological risk, pathways, and fluxes of these pollutants in and around the Seto Inland Sea, an industrialized coastal region of Japan. High molecular weight PAHs (5-6 rings) were primarily found in regions close to the bay estuaries, and their proportions decreased at distances further from the estuaries (offshore areas), where low molecular weight PAHs (2-4 rings) were more ubiquitous. Screening-level risk assessments revealed that the PAHs found in the sediments should have no adverse effects on benthic communities. A mass balance for PAHs in the Seto Inland Sea, calculated based on data collected in the field and published literature findings, showed the PAH flux into the Seto Inland Sea from atmospheric deposition were ca. 6 times higher than that from riverine inflows. Comparison of the amount of the PAH mass flux between the Seto Inland Sea and the sea of the Europe and Asian countries indicated that the Seto Inland Sea is less polluted than the Gulf of Lion, the Mediterranean Sea, and the Bohai Sea, China and more polluted than the Yellow Sea. This paper is the first to determine the fluxes of PAHs in the coastal region of Japan.

The joint adverse effects of aged nanoscale plastic debris and their co-occurring benzo[α]pyrene in freshwater mussel (Anodonta anatina)

Although the presence of small-scale plastics, including nanoscale plastic debris (NPD, size <1 μm), is expected in the environment, our understanding of their potential uptake and biodistribution in organisms is still limited. This mostly is because of the limitations in analytical techniques to characterize NPD in organisms' bodies. Moreover, it is still debatable whether aged NPD can sorb and transfer chemicals into organisms. Here, we apply iron oxide-doped polystyrene nanoparticles (Fe-PS NPs) of 270 nm size to quantify the uptake and biodistribution of NPD in freshwater mussels (Anodonta anatina). The Fe-PS NPs were, first, oxidized using heat-activated potassium persulfate treatments to produce NPD (aged particles). Then, the sorption of benzo[a]pyrene (B[α]P), as a model of organic chemicals, into the aged NPD was studied. Chemical oxidation (i.e. aging) significantly decreased the sorption of B[α]P into the particles over 5 days when compared to pristine particles. After 72-h of exposure, A. anatina accumulated NPD in the gills and digestive gland. When exposed to the mixture of NPD and B[α]P, the number of particles in the gills and digestive gland increased significantly compared to the mussels exposed to NPD alone. Moreover, the mixture of NPD and B[α]P increased the activity of Superoxide dismutase and Catalase enzymes in the exposed mussels when compared to the control and to the NPD alone. The present study provides evidence that aged NPD not only could accumulate and alter the toxicity profile of organic chemicals in aquatic organisms, but the chemicals also could facilitate the uptake of NPD (combined effects).

Self-sensitized photochlorination of benzo[a]pyrene in saline water under simulated solar light irradiation

Chlorinated organic compounds are ubiquitously detected in saline waters. The photochlorination of organic compounds is one possible source, and chlorine radicals originating from other photosensitive substances have been reported to be responsible for organic compounds chlorination in previous reports. In this study, benzo[a]pyrene (BaP) chlorination in 10% acetonitrile/NaCl aqueous solution was initiated by self-sensitization of BaP, while chlorine radicals were not involved in the reaction. After 45 min of photoreaction in four seawater samples, chlorinated product (6-ClBaP) accounted for 10-17% of the fraction of transformed BaP, which was higher than that previously reported. The influences of Cl^-, pH, humic acid, electron donors, and particulate matter on the formation of chlorobenzo[a]pyrene were systematically investigated. A self-sensitized photochlorination reaction mechanism was proposed as follow: photoexited BaP was activated to singlet state and then transformed to triplet state through inter-system crossing. Then the excited triplet state and oxygen formed [³BaP*-³O₂] or [BaP-¹O₂] complex, which further reacted with Cl^- to produce 6-ClBaP.

Tailored photocatalysts and revealed reaction pathways for photodegradation of polycyclic aromatic hydrocarbons (PAHs) in water, soil and other sources

Polycyclic aromatic hydrocarbons (PAHs), which are in the class of persistent organic pollutants, are considered as hazardous pollutants. To date, these compounds were detected globally in soil, sludge, water, and other contamination sources. A variety of treatment methods have been used in recent years to degrade PAHs in the environment. Photocatalysis, among advanced techniques, is proposed as the most effective method for the treatment of PAHs. In this context, we introduce the classification of PAHs, summarize, and highlight the recent studies on photodegradation of various types of PAHs. A series of efficient photocatalysts, including TiO₂-, Ag₃PO₄-, ZnO-, MHCFs-based, and others, have been reported with the potential result for photodegradation of PAHs. Focus is also placed on revealing several possible reaction pathways for different types of PAHs that have been proposed in the literature. Particular attention to current status, challenges, and prospects in the future for enhanced photodegradation of PAHs are also discussed.

Fabrication of dual catalytic microcapsules by mesoporous graphitic carbon nitride (mpg-C3N4) nanoparticle–enzyme conjugate stabilized emulsions

Dual catalytic microcapsules (MCs) were fabricated by simultaneous self-assembly and cross-linking of mpg-C₃N₄ nanoparticles (NPs) and lipase conjugates at oil–water interface.

Source, spatial distribution, and toxicity potential of Polycyclic Aromatic Hydrocarbons in sediments from Iran's environmentally hot zones, the Persian Gulf

Surface sediments, sampled from Iranian coast of the Persian Gulf (n = 134), were analyzed in order to track spatial distribution of PAHs and their related eco-hazards. The levels of PAHs were in the range of 1.98-814 ng g^-1 dw and the region was lowly to moderately polluted. The profile of PAHs was mainly composed of 2,3-ring chemicals and suggested a local source of PAHs and relatively fresh inputs. Statistical analysis and molecular fingerprints proposed that the basin receives PAHs from multiple origins including petrogenic and pyrogenic (traffic and auto emission) ones. Spatial distribution of organic matter and fine fraction of the sediments had a horizontally increasing trend in the studied basin. ∑₁₆PAHs showed significant positive correlation with TOC and fine fraction (p < 0.05) and the spatial deposition of ∑₁₆PAHs followed the spatial trends of TOC and fine fraction. Spatial mapping techniques confirmed that Pars Special Economic Energy Zone (PSEEZ) is the hot zone of PAH pollution. A combination of source availability, finer sediments, and great organic matter levels were the main effective factors that highlighted the deposition of PAHs in the PSEEZ. The Nayband Bay, as the Iran's first national marine Park, possibly received PAHs from its adjacent zone, the PSEEZ. On the other hand, low organic matter and sandy nature of the Nayband Bay was not suitable for effective sequestration of PAHs. Thus, the biota of Nayband Park was encountering with relatively severe multiple eco-hazards due to both ecological and economic factors.

A systematic study of the effects of solvents on phenanthrene photooxidation

A systematic study of the photooxidation of phenanthrene under simulated environmental conditions was conducted in vitro using polar (methanol, acetonitrile) and non-polar (isooctane, hexane) solvents as media. In all solvents, phenanthrene concentration decreased exponentially as exposure time increased. Fourier-transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS) analysis were used to investigate the structural changes induced by photooxidation. After 24 h of photooxidation, FTIR showed the formation of characteristic bands of carboxylic acid in all solvents. In non-polar solvents, characteristic phenanthrene peaks were completely depleted after 48 h. In polar solvents, phenanthrene peaks disappeared at a slower rate, with peaks in acetonitrile disappearing at 72 h and methanol persisting at trace levels at 96 h. The reaction rate was higher in non-polar solvents. The obtained half-lives were observed in the following order: isooctane (13.2 h) > hexane (13.5 h) > methanol (18.0 h) > acetonitrile (22.8 h). FTIR and GC-MS results were in good agreement and showed the formation of carboxylic acids, aldehydes, and ketones in polar solvents and carboxylic acids, alkanes, and alkanoic acids in non-polar solvents. Products such as primary amides induced by solvent effects were observed in acetonitrile. Based on the results, the solvents were rated and a solvent selection guide for photooxidation of PAHs was provided.

Distribution of coal and coal combustion related organic pollutants in the environment of the Upper Silesian Industrial Region

In this study, a large sample set (276) was separated into up to 15 groups, including coal, fly ash, total particulate matter, coal wastes, river sediments, and different water types. Grouping the sample set into these categories helped to identify the typical features of combustion or water-washing and compare them using newly developed polycyclic aromatic hydrocarbon diagnostic ratios. A wide range of organic pollutants were identified in samples, including aromatic and polycyclic hydrocarbons, nitrogen-heterocycles, sulphur-heterocycles + trithiolane, and polycyclic aromatic hydrocarbons substituted with oxygen functional groups. The distribution of compounds was significantly influenced by water washing or combustion. During the self-heating of coal wastes, secondary compounds such as chlorinated aromatics (chlorobenzene, chloroanthracene, etc.) or light sulphur compounds (e.g. benzenethiol and benzo[b]thiophene) were formed (synthesised). Since these compounds are generally absent in sedimentary organic matter, their origin may be connected with high-temperature formation in burning coal dumps. These compounds should be identified as persistent organic pollutants (POPs) in the environment. The newly defined diagnostic ratios have worked well in separating samples (petrogenic and pyrogenic) and have pointed out the effect of incomplete combustion on self-heated coal waste, ash from domestic furnaces, or water washing and biodegradation of the studied compounds.

Electrochemically modified dissolved organic matter accelerates the combining photodegradation and biodegradation of 17α-ethinylestradiol in natural aquatic environment

The photochemical conversion and microbial transformation of pollutants mediated by dissolved organic matter (DOM), including 17α-ethinylestradiol (EE2), are often accompanied in natural water. However, there are few studies to explore the connection and mechanism between the two processes. This research aims to investigate the mechanism of DOM after electrochemically modification mediated EE2 combining photodegradation and biodegradation in the environment and it want to explain the natural phenomena of DOM after electrochemical advanced treatment entering the water environment mediated EE2 natural degradation. The results showed that combining photodegradation with biodegradation rates of EE2 mediated by DOM and electrochemically modified DOM (E-DOM) were promoted obviously. The efficiency of EE2 biodegradation was shown to be strongly correlated with electron accepting capacity (EAC) of DOM. Electrochemical modification can increase the EAC of DOM leading to EE2 biodegradation accelerated, and it also can form more triplet-state DOM moieties to promote the EE2 photodegradation in irradiation conditions, due to the increasing of quinone-type structures in DOM. Moreover, cell polymeric secretion (CPS) secreted from the microorganism could be stimulated to an excited state by irradiation, and that also accelerated EE2 degradation. Photolysis combined with biochemical degradation yielded less toxic degradation products. This study shows that the emission of DOM in wastewater after electrochemical treatment could accelerate estrogen degradation and play a positive role on the pollutant transformation in the environment.

Solubility Enhancement of Polycyclic Aromatic Hydrocarbons by an Eco-Friendly Ester-Linked Gemini Surfactant and its Mixtures with Conventional Surfactants

The present study deals with the solubility enhancement of the two polycyclic aromatic hydrocarbons (PAHs) anthracene and pyrene in the aqueous micellar system of the cationic ester-containing cleavable gemini surfactant ethane-1,2-diyl-bis(N,N-dimethyl-N-tetradecylammoniumacetoxy) dichloride (14-E2-14 = C14H29(CH3)2N+(CH2COOCH2)2N+(CH3)2C14H29 · 2Cl−)), and its equimolar binary mixtures with some typical conventional cationic, anionic and non-ionic surfactants. The surface tension and conductivity measurements were used to evaluate the physicochemical parameters such as the critical micelle concentration (CMC), the interaction parameter (βm) and Gibbs excess free energy of micellization (ΔGexm) of the systems. The extent of solubilization of the micellar systems towards PAHs has been quantified in terms of molar solublization ratio (MSR), micellar/water partition coefficient (ln Km) and the standard Gibbs free energy of solubilization (ΔGs0). Above the CMC, all studied single as well as binary gemini-conventional surfactant systems show an increase in solubilization of the PAHs. For pure systems, the MSR value of Brij 58 was found to be significantly higher than that of the other amphiphiles. Amongst the mixed surfactant systems, the solubility enhancement of anthracene is found to be maximum in the 14-E2-14 + SDS/SDBS system whereas the system14-E2-14 + Brij 58 shows a higher solubility for pyrene.

Natural Porphyrins Accelerating the Phototransformation of Benzo[a]pyrene in Water

Phototransformation is one of the most important transformation pathways of organic contaminants in the water environment. However, how active compounds enable and accelerate the phototransformation of organic pollutants remains to be elucidated. In this study, the phototransformation of benzo[a]pyrene (BaP, the first class "human carcinogens") by various natural porphyrins under solar irradiation was investigated, including chlorophyll a, sodium copper chlorophyllin, hematin, cobalamin, and pheophorbide a. Transformation efficiency of BaP varied considerably with chemical stabilities of the porphyrins. Porphyrins with a lower stability displayed higher BaP transformation efficiencies. BaP transformation had a significant positive correlation with the production of singlet oxygen. Identical phototransformation products of BaP were observed for all investigated porphyrins, and the main products were identified as BaP-quinones, including BaP-1,6-dione, BaP-3,6-dione, and BaP-6,12-dione. The mechanism of natural porphyrins accelerating the BaP phototransformation in water was proposed to proceed via the photocatalytic generation of singlet oxygen resulting in the transformation of BaP to quinones.

Photolysis of polycyclic aromatic hydrocarbons (PAHs) on Fe3+-montmorillonite surface under visible light: Degradation kinetics, mechanism, and toxicity assessments

Photochemical behavior of various polycyclic aromatic hydrocarbons (PAHs) on Fe³⁺-modified montmorillonite was explored to determine their potential kinetics, pathways, and mechanism under visible light. Depending on the type of PAH molecules, the transformation rate follows the order of benzo[a]pyrene ≈ anthracene > benzo[a]anthracene > phenanthrene. Quantum simulation results confirm the crucial role of "cation-π" interaction between Fe³⁺ and PAHs on their transformation kinetics. Primary intermediates, including quinones, ring-opening products and benzene derivatives, were identified by gas chromatography-mass spectrometer (GC-MS), and the possible photodegradation pathway of benzo[a]pyrene was proposed. Meanwhile, radical intermediates, such as reactive oxygen species (ROS) and free organic radicals, were detected by electron paramagnetic resonance (EPR) technique. The photolysis of selected PAHs, such as anthracene and benzo[a]pyrene, on clay surface firstly occurs by electron transfer from PAHs to Fe³⁺-montmorillonite, followed by degradation involving photo-induced ROS such as ·OH and ·O₂^-. To investigate the acute toxicity of photolysis products, the Microtox^® toxicity test was performed during the photodegradation processes of various PAHs. As a result, the photo-irradiation initially induces increased toxicity by generating reactive intermediates, such as free organic radicals, and then the toxicity gradually decreases with increasing of reaction time. Overall, the present study provides useful information to understand the fate and photo-transformation of PAHs in contaminated soils.

Watershed-scale modeling on the fate and transport of polycyclic aromatic hydrocarbons (PAHs)

PAHs are potentially carcinogenic substances that are persistent in the environment. Increasing concentrations of PAHs were observed due to rapid urbanization, thus; monitoring PAHs concentrations is necessary. However, it is expensive to conduct intensive monitoring activities of a large number of PAHs. This study addressed this issue by developing a multimedia model coupled with a hydrological model (i.e., Soil and Water Assessment Tool (SWAT)) for Taehwa River (TR) watershed in Ulsan, the industrial capital of South Korea. The hydrologic module of the SWAT was calibrated, and further used to simulate the fate and transport of PAHs in soil and waterbody. The model demonstrated that the temporal or seasonal variation of PAHs in soil and waterbody can be well reproduced. Meanwhile, the spatial distribution of PAHs showed that urban areas in TR watershed have the highest PAH loadings compared to rural areas. Sensitivity analyses of the PAH soil and PAH water parameters were also able to determine the critical processes in TR watershed: degradation, deposition, volatilization, and wash off mechanism. We hope that this model will be able to aid the stakeholders in: regulating PAH concentrations emitted by various sources; and also apply the model to other Persistent Organic Pollutants (POPs).

Uptake and translocation of benzo[a]pyrene (B[a]P) in two ornamental plants and dissipation in soil

Pot experiments were conducted to evaluate the phytoremediation of B[a]P contaminated soil using two ornamental plants (Tagetes patula and Mirabilis jalapa). The results showed that the dry biomass of two plants was increased at low B[a]P contaminated soil and then inhibited with increasing B[a]P concentrations. It exhibited a significantly positive linear relationship between B[a]P absorption in roots, stems, leaves and shoots of the tested plants and the concentration of B[a]P in soils (P<0.01). Meanwhile, the contents of B[a]P in different tissues of the plants increased with growing time. After planting T. patula and M. jalapa, plant-promoted biodegradation of B[a]P was account for 79.5-99.8% and 71.1-99.9%, respectively, whereas the amount of B[a]P dissipation enhancement was only 0.2-20.5% and 0.1-28.9%, respectively. Moreover, low bioaccumulation factor (BF) and translocation factor (TF) values indicated that T. patula and M. jalapa took up B[a]P from contaminated soil and transferred them to the aerial parts with low efficiency. The B[a]P removal rates in rhizosphere soils at different growing stages of T. patula and M. jalapa were 2.7-26.8% and 0.4%-33.9%, respectively, higher than those of non-rhizopshere soils. Therefore, the presence of T. patula and M. jalapa roots was effective in promoting the phytoremediation of B[a]P contaminated soils.

Removal of polycyclic aromatic hydrocarbons (PAHs) from inorganic clay mineral: Bentonite

There has been limited study of the removal of polycyclic aromatic hydrocarbons (PAHs) from inorganic clay minerals. Determining the amount of PAH removal is important in predicting their environmental fate. This study was carried out to the degradation and evaporation of PAHs from bentonite, which is an inorganic clay mineral. UV apparatus was designed specifically for the experiments. The impacts of temperature, UV, titanium dioxide (TiO2), and diethylamine (DEA) on PAH removal were determined. After 24 h, 75 and 44 % of ∑12 PAH in the bentonite were removed with and without UV rays, respectively. DEA was more effective as a photocatalyst than TiO2 during UV application. The ∑12 PAH removal ratio reached 88 % with the addition of DEA to the bentonite. It was concluded that PAHs were photodegraded at high ratios when the bentonite samples were exposed to UV radiation in the presence of a photocatalyst. At the end of all the PAH removal applications, higher evaporation ratios were obtained for 3-ring compounds than for heavier ones. More than 60 % of the amount of ∑12 PAH evaporated consisted of 3-ring compounds.

Photocatalytic degradation of polycyclic aromatic hydrocarbon benzo[a]pyrene by iron oxides and identification of degradation products

Photocatalytic decay profiles of polycyclic aromatic hydrocarbon (PAH) benzo[a]pyrene (B[a]P) have been investigated on various synthesized iron oxides and on soil surfaces under a set of diverse conditions. Samples were analysed using the developed HPLC procedure. Results of the present study demonstrate fastest photodisintegration of B[a]P on goethite followed by haematite, magnetite, akaganeite and maghemite, respectively. The effect of soil pH, irradiation wavelength and iron oxide and oxalic acid dose on the degradation of B[a]P was evaluated. The studies revealed enhancement in photodegradation in the presence of oxalic acid due to the occurrence of fenton like reaction. The results showed faster B[a]P degradation under short wavelength UV radiation. Rate constants in acidic, neutral and alkaline soils under optimum dissipation conditions were 1.11×10(-2), 7.69×10(-3) and 9.97×10(-3) h(-1), respectively. The study indicates that iron oxides along with oxalic acid are effective photocatalyst for the remediation of benzo[a]pyrene contaminated soil surfaces. The degradation products of B[a]P in the soils of different pH in presence of goethite were identified and degradation pathways proposed. Peaks due to toxic metabolites such as diones, diols and epoxides disappear after 120 h in all the three soils.

Photochemical degradation of PAHs in estuarine surface water: effects of DOM, salinity, and suspended particulate matter

The photodegradation of several polycyclic aromatic hydrocarbons (PAHs) including phenanthrene, benzo(a)pyrene, and benzo(e)pyrene was studied under different estuarine conditions to elucidate the effects of dissolved organic matter (DOM), salinity, and suspended particles on PAH photodegradation in the estuarine surface water. Besides the competitive light absorption effect, DOM can accelerate the photodegradation of small PAHs such as phenanthrene by enhancing the formation of reactive intermediates and inhibit the photodegradation of large PAHs such as benzo[a]pyrene (BaP) and benzo[e]pyrene (BeP) by binding the PAH molecules. High salinity would accelerate the photodegradation of PAHs; however, the magnitude and direction of the salt effect are complicated in the presence of DOM due to the "salting-out" effect on the binding of PAHs with DOM. Suspended particulate matter in the estuary provides an alternative solid-phase photodegradation pathway for PAHs, which proceeds faster than the aqueous phase. Particulates apparently exert different effects on the photodegradation of phenanthrene (Phe) and BaP as a result of the combined effects of light absorption, particulate organic matter, PAH surface sorption, and concentration dilution in the presence of suspended particulate matter.

Photolysis degradation of polyaromatic hydrocarbons (PAHs) on surface sandy soil

Polycyclic aromatic hydrocarbons (PAHs) are potent environmental pollutants, and some of them have been identified as carcinogenic and mutagenic. To advance the knowledge of the environmental fate of PAHs, we systematically investigated the influence of different UV wavelengths irradiation on photolysis of PAHs on sandy soil under tow wavelengths (254 and 306 nm) UV irradiation for six PAHs. In addition, kinetic model and influence of several parameters on PAHs photolysis have been studied. The results obtained indicated that UV radiation with a wavelength of 306 nm was more efficient in the photolysis of the polycyclic aromatic hydrocarbons. Our results showed that fluoranthene (Flt) was the fastest in decomposition, has the greatest value for the coefficient of photolysis (7.4 × 10(-3) h(-1)), and has less half-life, reaching 94 h when using a wavelength of 254 nm. The results indicated that the pyrene (Pyr) was more resistant to photolysis in comparison with indeno(1,2,3-cd) pyrene (IP) and fluoranthene (Flt). The results indicate that photolysis is a successful way to remediate the six studied PAHs compounds.

Migration of PAHs in food industry sludge to the air during removal by UV and TiO2

This study was conducted to investigate the evaporation ratios of polycyclic aromatic hydrocarbons (PAHs) from the food industry treatment sludge. Five PAH compounds having different ring numbers were targeted. The effects of temperature, UV and TiO2 on PAH evaporation were also studied. All applications were performed in a specially designed apparatus. The air in the apparatus was vacuumed to collect the evaporated PAHs on the PUF cartridges. Then, these PUF cartridges were extracted for determination of PAHs. The PAH concentrations were measured by a gas-chromatography mass-spectrometer (GC-MS). 91% of the initial ∑5 PAHs in the sludge was evaporated into the air at the end of the UV application. However, this value decreased to 21% when UV was not employed. Initial and final PAH levels in the sludge were measured to determine the removed PAHs which refer to the addition of degraded and evaporated PAHs. The results indicated that the UV-TiO2 application at high temperatures was considered an appropriate PAH removal method because it restricted the evaporation of PAHs while it removed high levels of PAHs. PAHs were mainly removed from the sludge by degradation rather than evaporation with this application.

Migration of polycyclic aromatic hydrocarbons (PAHs) in urban treatment sludge to the air during PAH removal applications

In the present study, the amounts of polycylic aromatic hydrocarbons (PAHs) penetrating into air during PAH removal applications from the urban treatment sludge were investigated. The effects of the temperature, photocatalyst type, and dose on the PAH removal efficiencies and PAH evaporation were explained. The sludge samples were taken from an urban wastewater treatment plant located in the city of Bursa, with 585,000 equivalent population. The ultraviolet C (UV-C) light of 254 nm wavelength was used within the UV applications performed on a specially designed setup. Internal air of the setup was vacuumed through polyurethane foam (PUF) columns in order to collect the evaporated PAHs from the sludge during the PAH removal applications. All experiments were performed with three repetitions. The PAH concentrations were measured by gas chromatography-mass spectrometry (GC-MS). It was observed that the amounts of PAHs penetrating into the air were increased with increase of temperature, and more than 80% of PAHs migrated to the air consisted of 3-ring compounds during the UV and UV-diethylamine (DEA) experiments at 38 and 53 degrees C. It was determined that 40% decrease was ensured in sigma12 (total of 12) PAH amounts with UV application and 13% of PAHs in sludge penetrated into the air. In the UV-TiO2 applications, a maximum 80% of sigma12 PAH removal was obtained by adding 0.5% TiO2 of dry weight of sludge. The quantity of PAH penetrating into air did not exceed 15%. UV-TiO2 applications ensured high levels of PAH removal in the sludge and also reduced the quantity of PAH penetrating into the air. Within the scope of the samples added with DEA, there was no increase in PAH removal efficiencies and the penetration of PAHs into air was not decreased. In light of these data, it was concluded that UV-TiO2 application is the most suitable PAH removal alternative that restricts the convection of PAH pollution.

Naphthalene degradation in seawater by UV irradiation: the effects of fluence rate, salinity, temperature and initial concentration

A large amount of oil pollution at sea is produced by the operational discharge of oily wastewater. The removal of polycyclic aromatic hydrocarbons (PAHs) from such sources using UV irradiation has become attractive, yet the photolysis mechanism in seawater has remained unclear. This study examines the photodegradation kinetics of naphthalene in natural seawater through a full factorial design of experiments (DOE). The effects of fluence rate, salinity, temperature and initial concentration are investigated. Results show that fluence rate, temperature and the interaction between temperature and initial concentration are the most influential factors. An increase in fluence rate can linearly promote the photodegradation process. Salinity increasingly impedes the removal of naphthalene because of the existence of free-radical scavengers and photon competitors. The results will help understand the photolysis mechanism of PAHs and develop more effective methods for treating oily seawater generated from offshore industries.

Removal of polycyclic aromatic hydrocarbons in aqueous environment by chemical treatments: a review

Due to their carcinogenic, mutagenic and teratogenic potential, the removal of polycyclic aromatic hydrocarbons (PAHs) from aqueous environment using physical, biological and chemical processes has been studied by several researchers. This paper reviews the current state of knowledge concerning PAHs including their physico-chemical properties, input sources, occurrence, adverse effects and conventional and alternative chemical processes applied for their removal from water. The mechanisms and reactions involved in each treatment method are reported, and the effects of various variables on the PAH degradation rate as well as the extent of degradation are also discussed. Extensive literature analysis has shown that an effective way to perform the conversion and mineralization of this type of substances is the application of advanced oxidation processes (AOPs). Furthermore, combined processes, particularly AOPs coupled with biological treatments, seem to be one of the best solutions for the treatment of effluents containing PAHs.

The potential of gibberellic acid 3 (GA3) and Tween-80 induced phytoremediation of co-contamination of Cd and Benzo[a]pyrene (B[a]P) using Tagetes patula

The present study was conducted to investigate the effectiveness of GA(3) and Tween-80 on enhancing the phytoremediation of Cd-B[a]P co-contaminated soils. Results showed that the addition of GA(3) and GA(3)-Tween-80 enhanced Tagetes patula growth by 14%-32% and 23%-55%, respectively, relative to the control group. However, under independent GA(3)-treated soils, Cd and B[a]P concentrations in the shoots of the plants decreased by 15%-33% and 15%-53%, respectively, compared with CK. By contrast, the shoot concentration and accumulation of Cd under GA(3)-Tween-80 treatment increased by 0.01-0.46 and 1.33-1.55 times, respectively, whereas those of B[a]P increased from 0.57 to 0.82, and 1.33 to 1.55 times, respectively, compared with those of the control. Optimal result for Cd phytoextraction was obtained under combined 5 mmol Tween-80 kg(-1) and 1 mmol GA(3) kg(-1) treatment, and the maximum removal rate of B[a]P was obtained after the application of 5 mmol Tween-80 kg(-1) and 5 mmol GA(3) kg(-1).

Evidence for in situ production of chlorinated polycyclic aromatic hydrocarbons on tidal flats: environmental monitoring and laboratory scale experiment

This study investigated environmental distributions and production mechanisms of chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs) in the sediments from some tidal flats located in Asia. Cl-PAHs were found in sediments taken from Arao tidal flat, Kikuchigawa River and Shirakawa River. The range of ∑Cl-PAHs was from 25.5 to 483 pg g(-1) for Kikuchigawa River and Arao tidal flat, respectively. Concentrations of PAHs and Cl-PAHs showed no significant correlations (r=0.134). This result suggests that the origins of these compounds differ. In the identified Cl-PAH isomers, the most abundant Cl-PAH isomer was 9,10-dichloroanthracene (9,10-di-Cl-ANT) in the three sites. In general, concentrations of Cl-ANTs in the coastal environment are about 3-5 orders of magnitude lower than those of anthracene (ANT). However, concentration ratios between Cl-ANTs and ANT (Cl-ANTs/ANT) in the sediments ranged from 4.1% to 24.6%. This result indicated that Cl-PAHs were not generated under industrial processes but the high concentration ratios have resulted from the contribution of photochemical production of Cl-ANTs in the sediments because ANT is known to have high photochemical reactivity. For examining this phenomenon, ANT adsorbed onto glass beads was irradiated with UV under the mimicked field conditions of tidal flats. As a result, it was noticed that, while chlorinated derivatives were negligible in a light-controlled group, production of 2-Cl-ANT, 9-Cl-ANT and 9,10-diCl-ANT on the irradiated surface were found in this study. These results suggest that photochemical reaction of PAHs can be a potential source of the occurrence of Cl-PAHs in the coastal environment.

Superior photodecomposition of pyrene by metal ion-loaded TiO₂ catalyst under UV light irradiation

BACKGROUND

The photocatalytic degradation of pyrene under UV (125 W Hg-Arc, 10.4 mW/cm2) irradiation of TiO2 aqueous suspension has been found to be highly improved with the dissolved transition metal ions like Cu2+, Fe3+, Ag+, and Au3+, etc. As the reduction potential of these metals lies below the conduction band (CB) position (−0.1 eV) of TiO2, the photoexcited electron transfer occurs more readily and reduces electron–hole recombination rate. Therefore, it has a beneficial influence on the photocatalytic ability of TiO2 because of rapid Fermi energy equilibrium between the CB of TiO2 and its surface adsorbed metal ions.

RESULTS AND DISCUSSION

The Fermi level is referred to as the electrochemical potential and plays an important role in the band theory of solids. When metal and semiconductor are in contact, electron migration from photoirradiated semiconductor to the deposited metal occurs at the interface until two Fermi levels equilibrate and enhanced the photocatalytic activity of semiconductor photocatalyst. Ni2+ having more negative reduction potential (−0.25 eV) than the CB of TiO2 imparts negligible co-catalytic activity to TiO2 photoreaction. It also revealed that loading of Au3+ ions displayed higher degradation rate of pyrene than Au photodeposition. Furthermore, when the amount of dissolved Fe+3 and Au3+ ions gradually increases from 0.1 to 2 wt.%, the pyrene photodecomposition rate also become faster.

Multiphoton spectral analysis of benzo[a]pyrene uptake and metabolism in a rat liver cell line

Dynamic analysis of the uptake and metabolism of polycyclic aromatic hydrocarbons (PAHs) and their metabolites within live cells in real time has the potential to provide novel insights into genotoxic and non-genotoxic mechanisms of cellular injury caused by PAHs. The present work, combining the use of metabolite spectra generated from metabolite standards using multiphoton spectral analysis and an "advanced unmixing process", identifies and quantifies the uptake, partitioning, and metabolite formation of one of the most important PAHs (benzo[a]pyrene, BaP) in viable cultured rat liver cells over a period of 24 h. The application of the advanced unmixing process resulted in the simultaneous identification of 8 metabolites in live cells at any single time. The accuracy of this unmixing process was verified using specific microsomal epoxide hydrolase inhibitors, glucuronidation and sulfation inhibitors as well as several mixtures of metabolite standards. Our findings prove that the two-photon microscopy imaging surpasses the conventional fluorescence imaging techniques and the unmixing process is a mathematical technique that seems applicable to the analysis of BaP metabolites in living cells especially for analysis of changes of the ultimate carcinogen benzo[a]pyrene-r-7,t-8-dihydrodiol-t-9,10-epoxide. Therefore, the combination of the two-photon acquisition with the unmixing process should provide important insights into the cellular and molecular mechanisms by which BaP and other PAHs alter cellular homeostasis.

Phytoremediation for co-contaminated soils of benzo[a]pyrene (B[a]P) and heavy metals using ornamental plant Tagetes patula

Pot-culture experiments were conducted to investigate the single effect of benzo[a]pyrene (B[a]P) and the joint effect of metal-B[a]P on the growth of Tagetes patula and its uptake, accumulation and dissipation of heavy metals and B[a]P. Results showed that the low concentration of B[a]P (≤10 mg kg(-1)) could facilitate plant growth and resulted in an increase in biomass at the rate of 10.0-49.7% relative to the control. There were significantly positive correlations between the concentrations of B[a]P accumulated in tissues of the plants and soil B[a]P (P<0.001). However, the occurrence of Cd, Cu and Pb had inhibitive effects on plant growth and B[a]P uptake and accumulation on the whole. T. patula still exhibited a steady feature of Cd-hyperaccumulator under combined contaminated soils. By contrast, the effectiveness of Cu and Pb absorption in the plants was very weak. Plant-promoted biodegradation of B[a]P was the dominant contribution, 79.2-92.4% and 78.2-92.9% of dissipation of B[a]P came from plant-biodegradation under single B[a]P and metal-B[a]P contaminated soils, respectively. Therefore, T. patula might be useful for phytoremediation of B[a]P and B[a]P-Cd contaminated sites.

Electron-accepting potential of solvents determines photolysis rates of polycyclic aromatic hydrocarbons: experimental and density functional theory study

Photochemical behaviour of polycyclic aromatic hydrocarbons (PAHs) is strongly dependent on the physical and chemical nature of the media in/on which they exist. To understand the media effects, the photolysis of phenanthrene (PHE) and benzo[a]pyrene (BaP) in several solvents was investigated. Distinct photolysis rate constants for PHE and BaP in the different solvents were observed. Some theoretical parameters reflecting the solvent properties were computed and employed to explain the solvent effects. Acetone competitively absorbed light with PHE and BaP, and the excited acetone molecules played different roles for the photodegradation of PHE and BaP. The photolysis rate constants of PHE and BaP in hexane, isopropanol, ethanol, methanol, acetonitrile and dichloromethane were observed to correlate with the electron-accepting potential of the solvent molecules. Absolute electronegativity of the solvents linearly correlated with the photolytic activity (log k) of the PAHs significantly. The results are important for better understanding the photodegradation mechanism of PAHs in different media.

Polycylic aromatic hydrocarbons in rape seeds with relation to their growing site and thermal treatment

A significant source of polycyclic aromatic hydrocarbons (PAH) in human diet is vegetable oils, especially those produced from plants grown in regions where the soil and the atmosphere are contaminated with these chemicals. Contamination with PAH of vegetable oils may also occur in the process of plant material drying with smoke or exhaust fumes, or in the course of extraction of that material with solvents containing trace amounts of PAH. The objective of this study was to determine the relationship between the levels of PAH present in rape seeds and the occurrence of these compounds in cultivation region and the relationship of the levels of PAH in rape seeds to thermal treatment after harvest. Rape seeds and pods from experimental fields and rape seeds subjected to thermal treatment in dryers obtained from suppliers of the raw material were examined and compared. Cleanup of extracts was performed with high-resolution size exclusion chromatography (SEC) and final determinations were by Trace Ultra/PolarisQ gas chromatography-mass spectroscopy (GC-MS). The results obtained indicated that during thermal treatment of rape seeds the concentration of PAH increased, but the levels of benzo[a]pyrene did not exceed threshold permissible levels. Data demonstrate that rapeseed cultivation in the presence of PAH results in higher levels of contaminants; however, the PAH levels still did not exceed the maximal allowable levels in Poland.

Simultaneous analysis of the photocatalytic degradation of polycyclic aromatic hydrocarbons using three-dimensional excitation–emission matrix fluorescence and parallel factor analysis

Polycyclic aromatic hydrocarbons (PAHs) may be photochemically degraded. Monitoring of degradation process of PAHs is carried out by traditional methods, which normally imply time-consuming procedures that do not allow the chemical process to be analyzed in real time. In the present study, photodegradation kinetics of dibenz[a,h]anthracene, benz[a]anthracene, benz[a]pyrene and benz[k]fluorantene were investigated in aqueous solutions under different conditions. A 2(3) factorial design was used for optimizing the degradation process. Fluorescence spectroscopy is a fast, cheap and sensitive analytical method, attractive for use in conjunction with chemometric methods; in this case three-way analytical methodology based on fluorescence excitation-emission matrix (EEM) and parallel factor analysis (PARAFAC) was employed. A four-factor PARAFAC model made it possible to resolve the species presents in the degradation mixture and quantify the relative concentration of the analytes throughout the degradation. Several different parameters, such as core consistency, percentage of fit and correlation coefficients between recovered and reference spectra were employed to determine the suitable number of factors for the PARAFAC model. This new methodology allows us to determine satisfactorily the PAHs concentration during the photodegradation in mixtures of arbitrary composition, representing an interesting alternative to the conventional techniques normally used for the monitoring of degradation reactions.

Effects of riboflavin on the phototransformation of benzo[a]pyrene

Riboflavin (Vitamin B2) is a natural dye-sensitizer habitually present in natural waters. Effects of riboflavin as photosensitizer on the transformation of benzo[a]pyrene (BaP) (10 microM) in the aqueous-organic solvent (water/acetonitrile/methanol 50/40/10) were investigated in this study. The photolysis half life of BaP in solution containing 50 microM riboflavin was 5 min, compared to 98 min in the absence of riboflavin. The rate of phototransformation of BaP increased as the concentration of riboflavin was raised from 10 microM to 100 microM under both natural sunlight and UVA irradiation. The half life of BaP in the presence of 50 microM riboflavin was 10.6 min and 43.1 min when exposed to visible range of natural sunlight and UVA irradiation respectively. Riboflavin decomposes under natural sunlight. Lumichrome, a principal photoproduct of riboflavin, was shown to photosensitize BaP under natural sunlight after photolysis of riboflavin. Our study indicated that other photoproducts from riboflavin, such as lumiflavin, were also involved in the phototransformation of BaP under sunlight when riboflavin diminished. The major photoproducts in the photolysis of BaP were identified as 1,6-benzo[a]pyrene-dione, 3,6-benzo[a]pyrene-dione, 6,12-benzo[a]pyrene-dione by using high performance liquid chromatography (HPLC). All these products were detected in the samples which were irradiated under different light sources and in the presence or absence of riboflavin. The possible phototransformation mechanism was discussed.

Biodegradation kinetics of linear alkylbenzene sulphonates in sea water

This article reports the primary biodegradation kinetics of linear alkylbenzene sulphonates (LAS) in sea water from the Bay of Cadiz (South West of the Iberian Peninsula). The authors used the biodegradation test guideline proposed by the Office of Prevention, Pesticides, and Toxic Substances of the United States Environmental Protection Agency; 835.3160 "Biodegradability in sea water" in its shake flask variant. High performance liquid chromatography (HPLC) has been employed for the analysis of the surfactant material. The surfactant shows a primary biodegradation kinetic in accordance with a logistic model, the kinetic parameters t (50) and lag time were calculated by means of a easy quantitative procedure introduced. Mean values of 6.15 +/- 0.45 and 6.67 +/- 0.6 days were obtained for t (50) and lag time, respectively. These results indicate that although LAS has a high primary biodegradation rate in sea water, it biodegrades slower than in similar tests conducted in river water.

Photochemical behavior of benzo[a]pyrene on soil surfaces under UV light irradiation

The rates of photodegradation and photocatalysis of benzo[a]pyrene (BaP) on soil surfaces under UV light have been studied. Different parameters such as temperature, soil particle sizes, and soil depth responsible for photodegradation, catalyst loads and wavelength of UV irradiation blamed for photocatalysis have been monitored. The results obtained indicated that BaP photodegradation follows pseudo-first-order kinetics. BaP photodegradation was the fastest at 30 degrees C . The rates of BaP photodegradation at different soil particle size followed the order: less than 1 mm>less than 0.45 mm>less than 0.25 mm. When the soil depth increased from 1 mm to 4 mm, the half-life increased from 13.23 d to 17.73 d. The additions of TiO2 or Fe2O3 accelerated the photodegradation of BaP, and the photocatalysis of BaP follows pseudo-first-order kinetics. Changes in catalyst loads of TiO2 (0.5%, 1%, 2%, and 3% (wt)) or Fe2O3 (2%, 5%, 7%, and 10% (wt)) did not significantly affect the degradation rates. Both BaP photocatalysis in the presence of TiO2 and Fe2O3 were the fastest at 254 nm UV irradiation.