Photochemical degradation of polycyclic aromatic hydrocarbons in oil films

Photochemical processes affect the fate of spilled oil in the environment, but the relative contribution and kinetics of these degradation pathways are not fully constrained. To address this problem, we followed the weathering of No. 6 fuel oil by periodically sampling rocks covered with a film of oil from Buzzards Bay, MA after the April 2003 Bouchard 120 oil spill. Two sets of polycyclic aromatic hydrocarbon (PAH) isomers, benzo[a]pyrene (BAP) and benzo[e]pyrene (BEP), and benz[a]anthracene (BAA) and chrysene (CHR), were found to have very different disappearance rates in spite of their close structural similarity (kBAA/kCHR approximately 2.0, kBAP/kBEP approximately 2.2). This well-documented phenomenon is suspected to arise from differing capacity for direct photoreaction in the oil film. To investigate the validity of this assumption, we developed a model to estimate the contribution of direct photolysis to the loss of these PAHs from the oil. Newly determined PAH quantum yields demonstrate that the efficiency of phototransformation in hydrophobic media are 2 orders of magnitude lower (Phi' approximately 10(-5)) than in aqueous systems, and the thickness and light-attenuating properties of the oil film reduce the potential for photoreaction by up to 2 orders of magnitude. Given these limiting factors, direct photolysis cannot account for the complete removal of these PAHs (except BAP). Additional results suggest that singlet oxygen photodegradation pathways are not favored in hydrophobic media, as they are in some mineral-associated and aqueous systems. Our results indicate that photomediated reactions with other compounds in the oil mixture were responsible for PAH photodegradation in the oil film.     

Production mechanism of hydroxylated PCBs by oxidative degradation of selected PCBs using TiO2 in water and estrogenic activity of their intermediates

The oxidative photodegradation behaviors of selected polychlorinated biphenyls (PCBs) [2,3,3',4'-tetraCB (BZ number: CB56), 2,3',4',5-tetraCB (CB70), and 3,4,4',5-tetraCB (CB81: coplanar PCB)] using titanium dioxide (TiO2) in water were investigated. The main purposes were to clarify the structural relation between the original PCBs and the intermediates derived by TiO2 oxidation and to evaluate the estrogenic activity in the treated PCBs during the oxidative reactions. Approximately 90% of the three tetraCBs decomposed within 120 min. Intermediates by decomposition of three tetraCBs, such as some OH-tetraCBs and OH-triCBs, carboxylic intermediates, phenolic intermediates, and other intermediates produced by the cleavage of a benzene ring were identified and quantified. In the degradation pathways, the produced amounts of OH-tetraCB and OH-triCB increased within 60 min of irradiation time. Estrogenic activities of the intermediates from the three tetraCBs in water were assessed by using a yeast two-hybrid assay system for human estrogen receptor alpha (hERalpha). The maximal estrogenic activities were induced by the solutions of decomposed CB81 with irradiation time at 60 min. We found that the solutions at an irradiation time of 60-120 min contained several 4-OH-tetraCBs and 4-OH-triCBs substituted with OH and Cl at para- and para'-positions. It is presumed that the chemical structures of the 4-OH-PCBs are similar to that of 17beta-estradiol (beta-E2); these intermediates present strong estrogenic activities. Moreover, we learned that there is a high possibility of conversion from some low toxic PCBs congeners to strong estrogenic OH-PCBs.     

Development of a Rhodococcus recombinant strain for degradation of products from anaerobic dechlorination of PCBs

The Gram-positive bacterium Rhodococcus sp. strain RHA1, naturally containing the biphenyl pathway, was electroporated with a broad host range plasmid containing the 4-chlorobenzoate (4-CBA) degradation operon (fcb) isolated from Arthrobacter globiformis strain KZT1. The recombinant strain grew in medium containing 4-CBA and 4-chlorobiphenyl (4-CB) as the only source of carbon, with stoichiometric release of chloride and a molar growth yield on 4-CB that suggested utilization of both biphenyl rings. In resting cell assays, similar rates of degradation were observed for wild-type and recombinant strains for the most common eight congeners from the anaerobic dechlorination of Aroclor 1242, but the recombinant strain accumulated lower amounts of chlorinated meta-cleavage products and no 4-CBA. Recombinant cells inoculated at 10(4) cells/g into nonsterile soil amended with 4-CB grew to 6-10(5) cells/g, a density consistent with the 4-CB consumed. 4-CB was removed only in the inoculated soil, and the recombinant strain did not grow in the same soil when it was not amended with 4-CB. The fcb operon remained stable in the recombinant strain reisolated from soil after 60 days. This work provides proof of concept that a Rhodococcus strain constructed to grow on a PCB would grow in nonsterile soil if the appropriate chlorobiphenyl is available.     

Calcium-promoted catalytic degradation of PCDDs, PCDFs, and coplanar PCBs under a mild wet process

The authors achieved highly efficient degradation of polychlorinated aromatic compounds, including polychlorinated dibenzo-p-dioxins, dibenzofurans, and dioxin-like compounds such as coplanar polychlorinated biphenyls (co-PCBs), which are known as persistent organic pollutants. Degradation was accomplished in 24 h through a simple stirring operation using safe and high workability metallic calcium, which acts as both a scavenger and a reducing agent, and Rh/C catalyst in an alcohol solution under mild conditions in a sealed tube at 25 degrees C without a temperature increase within 0.15 MPa of increasing internal pressure during the reaction. In this system, reductive dechlorination by metallic calcium and catalytic reduction by Rh/C and generated hydrogen gas, without any external addition of hydrogen, exert a synergistic effect on the degradation of chlorinated compounds. Alcohol was used as a proton source and hydrogen, which was generated by a side reaction, causes an increase in the activity of Rh/C catalyst. Through the degradation of 4-chloroanisole in ethyl alcohol, anisole and cyclohexyl methyl ether were obtained in good conversions. Using ethyl alcohol as a solvent, treatment of dioxins and co-PCBs in a solution was markedly effective for degradation to reduce 2806 pg TEQ/ml of initial concentration to 31.8 pg TEQ/ml; its yield was 98.5%. Moreover, degradation in methyl alcohol took place in a 99.3% yield. That concentration ultimately reached 20.3 pg TEQ/ml under a mild wet process. All congeners of dioxins and co-PCBs were degraded in high conversions. In this degradation, lower aliphatic alcohol, such as methyl alcohol, is effective for making a new calcium surface as compared to alcohol with more methylene chains. In addition, it seemed that a higher pressure of hydrogen was easily generated in methyl alcohol, and then catalytic degradation was effectivley influenced.     

Survey of dioxins, dioxin-like PCBs and marker PCBs in German feeds of plant origin

Within a representative survey the levels of dioxins (PCDD/PCDF), dioxin-like PCBs and marker PCBs in 206 German feed samples were analysed in the years 2004/2005. The sampling plan included compound feed (N = 115) and roughage and succulent feed (N = 91) and reflected the representative feeding situation in Germany. The median content of WHO-PCB-TEQ in analysed feed samples was 0.017 ng/kg [88% dry matter (d.m.)] and consequently more than a factor of 10 below the action level of 0.35 ng/kg (88% d.m.). A differentiation between compound feed and roughage and succulent feed showed that compound feed [median 0.007 ng/kg (88% d.m.)] were significantly lower contaminated with dioxin-like PCBs than roughage and succulent feed [median 0.058 ng/kg (88% d.m.)]. The median sum contents of the six marker PCBs were 0.16 μg/kg (88% d.m.) for compound feed and 0.56 μg/kg (88% d.m.) for roughage and succulent feed. The median of the WHO-PCDD/F-TEQ was 0.03 ng/kg (88% d.m.), the maximum level of 0.75 ng/kg (88% d.m.) was not exceeded. The median of the WHO-PCDD/F-PCB-TEQ was 0.05 ng/kg (88% d.m.) and consequently a factor of 25 below the maximum level of 1.25 ng/kg. Additionally the samples of roughage and succulent feed were analysed according to their contents of ash insoluble in HCl, representing a degree of the proportion of earthy components in feed. A slight correlation was found between ash insoluble in HCl and WHO-PCDD/F-TEQ (R ² = 0.59) whereas no correlation was found between ash insoluble in HCl and WHO-PCB-TEQ (R ² = 0.06).     

Survey of dioxins, dioxin-like PCBs and marker PCBs in German feeds of plant origin

Within a representative survey the levels of dioxins (PCDD/PCDF), dioxin-like PCBs and marker PCBs in 206 German feed samples were analysed in the years 2004/2005. The sampling plan included compound feed (N = 115) and roughage and succulent feed (N = 91) and reflected the representative feeding situation in Germany. The median content of WHO-PCB-TEQ in analysed feed samples was 0.017 ng/kg [88% dry matter (d.m.)] and consequently more than a factor of 10 below the action level of 0.35 ng/kg (88% d.m.). A differentiation between compound feed and roughage and succulent feed showed that compound feed [median 0.007 ng/kg (88% d.m.)] were significantly lower contaminated with dioxin-like PCBs than roughage and succulent feed [median 0.058 ng/kg (88% d.m.)]. The median sum contents of the six marker PCBs were 0.16 μg/kg (88% d.m.) for compound feed and 0.56 μg/kg (88% d.m.) for roughage and succulent feed. The median of the WHO-PCDD/F-TEQ was 0.03 ng/kg (88% d.m.), the maximum level of 0.75 ng/kg (88% d.m.) was not exceeded. The median of the WHO-PCDD/F-PCB-TEQ was 0.05 ng/kg (88% d.m.) and consequently a factor of 25 below the maximum level of 1.25 ng/kg. Additionally the samples of roughage and succulent feed were analysed according to their contents of ash insoluble in HCl, representing a degree of the proportion of earthy components in feed. A slight correlation was found between ash insoluble in HCl and WHO-PCDD/F-TEQ (R ² = 0.59) whereas no correlation was found between ash insoluble in HCl and WHO-PCB-TEQ (R ² = 0.06).     

Research Watch: PCBs in frogs

Contaminants.     

Research Watch: PCBs in sediments

Biodegradation.     

Research Watch: PCBs in soil

Soil.     

Research Watch: PCBs

Contaminants.     

突飞猛进的光化蚀刻工艺

介绍了光化蚀刻的由来和传统工艺流程中五种掩膜的制作方法及四种现代的光化蚀刻法流程及其应用范围。指出随着电子技术的不断发展,光化蚀刻这门技术已经拓展到了许多新的领域,形成了一定的生产规模,并且带动了相关企业的发展。     

Automated analysis for determination of PCBs in fish

An automated analytical method for determination of polychlorinated biphenyls (PCBs) in fish was developed using supercritical fluid extraction (SFE) in combination with an automated sample preparation instrument (Prep) and GC/MS. By incorporating basic alumina with the sample in the extraction process, and optimizing the amount of carbon dioxide used, fish lipid was selectively reduced. The extract was cleaned up on a Florisil cartridge with Prep. The method was evaluated using naturally contaminated tissues and by comparison of automated analytical method results with those obtained by the conventional method. Mean recovery of PCBs from 3 kinds of fish including hairtail, mackerel and yellowtail were 69.8%, 90.2% and 81.1%, respectively. This method is less laborious and requires far less organic solvent than the conventional method, but produced comparable results.     

Research Watch: PCBs in a lake

Contaminants.     

Photochemical behaviour of hydrolysed keratin

An investigation into the influence of UV irradiation on keratin hydrolysates was carried out using UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FTIR) and fluorescence spectroscopy. It was found that the absorption of keratin hydrolysates in solution increased during irradiation of the sample, most notably between 250-280 and 320-410 nm. The increase in absorbance in the region 320-410 was because of the new photoproducts formed during UV irradiation of keratin hydrolysates. The fluorescence of keratin hydrolysates was observed at 328 nm after excitation at 270 nm. UV irradiation caused fluorescence fading at 328 nm, and after 60 min of irradiation, a new broad weak band of fluorescence, attributable to new photoproducts, emerged in the UV wavelength region with emission maximum between 400 and 500 nm. FTIR spectroscopy results showed degradation of keratin under UV irradiation. A slight increase in oxidized sulphur species was also observed. The results obtained suggest that UV irradiation can be used as modifying agent for preparation of keratin hydrolysates for cosmetic applications.