Polychlorinated biphenyls (PCBs) are a mixture of 209 individual chlorinated compounds commonly known as PCB congeners. These compounds are hydrophobic and are persistent in the environment. Their use was banned in the US a few decades ago because of harmful health effects. Therefore, detection of PCBs in environmental samples is increasingly important. To that end, we have developed a two-step simple and sensitive method for the detection of total PCBs. Specifically, our method involves dechlorination of PCBs to biphenyl followed by detection of biphenyl using a whole cell sensing system as the detection system. The whole cell sensing system consists of cells of the strain Pseudomonas pseudoalcaligenes KF707 harboring plasmid pSD7000. Plasmid pSD7000 contains the gene of lacZ, a reporter protein under the control of the bph operon. The detection is achieved through the emission of light afforded by the expression of reporter protein triggered by the presence of biphenyl. Due to the fact that this operon is activated only by few PCB congeners, a chemical dechlorination method was employed to convert all PCBs to biphenyl, and thus all the PCBs present in a given sample are able to be detected. The results showed that PCB congeners were rapidly (30?min) and efficiently (>98.5%) dechlorinated to biphenyl using a Mg/K2PdCl6 catalyst, and the biphenyl could be subsequently quantified using the whole cell sensing system. This hybrid analytical method that combines classical dechlorination with novel biosensing methods may find applications in the on-site monitoring of PCBs contamination levels. 相似文献
The combined synthesis and spectrometric characterization of 2,3,3'‐trichlorobiphenyl (PCB 20) and 3,3’,4‐trichlorobiphenyl (PCB 35) is described for the first time. By a combination of highly efficient column distillation and repeated recrystallizations it was possible to isolate the two products as reference materials with a purity exceeding 99%. X‐ray analysis of crystals of 2,3,3'‐trichlorobiphenyl positively identified the substitution pattern of the biphenyl moiety by chlorine atoms. The two phenyl rings are at an angle of 52°, while the relative disposition of the chlorine atoms on both rings is closer to anti than to syn. 相似文献
We studied the chemical dechlorination of the polychlorinated biphenyls (PCBs) in some dielectric oils via nucleophilic substitution
of the chloro atoms by polyethylene alkoxide. The influence of temperature, ultrasounds, polyethylene glycol (PEG) and base
type was investigated. Our findings show that dechlorination of PCBs by chemical treatment is effective at moderate temperature
(90–100°C) and is strongly dependent on the nature of matrix oil. Stirring affects the process yield by influencing the homogeneity
of the oil/glycol two-phase system. Ultrasounds can improve the process efficiency by making operating conditions less severe.
Selected article from the 6th European Meeting on Environmental Chemistry, University of Belgrade, Serbia and Montenegro organized
by Prof. Dr. Branimir Jovancicevic (). 相似文献
In this study, polychlorinated biphenyls (PCBs) were decomposed by low‐temperature heat treatment with metallic catalyst, and with metallic catalyst and a hydrogen source. Of the catalysts used, iron (Fe) was the most active catalyst for the decomposition of PCBs, and the decomposition was due to dechlorination. The addition of hydrogen sources accelerated the decomposition of PCBs in the presence of catalyst. Surface analysis of the catalyst using X‐ray photoelectron spectroscopy (XPS) suggested that the emitted chlorine was presumed to form metal chloride. The reactions of each homolog can be expressed by a successive first‐order reaction model. This means that a substituted chlorine is successively detached during this reaction. The overall decomposition rate in this reaction system was controlled by that of the lower chlorinated homologs. The decomposition rates with Fe and NaBH4 for the lower chlorinated homologs were about 10 times as fast as the rates with only Fe. 相似文献
The toxic and recalcitrant polychlorinated biphenyls (PCBs) adversely affect human and biota by bioaccumulation and biomagnification through food chain. In this study, an anaerobic microcosm was developed to extensively dechlorinate hexa- and hepta-CBs in Aroclor 1260. After 4 months of incubation in defined mineral salts medium amended PCBs (70 mmol·L–1) and lactate (10 mmol·L–1), the culture dechlorinated hexa-CBs from 40.2% to 8.7% and hepta-CBs 33.6% to 11.6%, with dechlorination efficiencies of 78.3% and 65.5%, respectively (all in moL ratio). This dechlorination process led to tetra-CBs (46.4%) as the predominant dechlorination products, followed by penta-(22.1%) and tri-CBs (5.4%). The number of meta chlorines per biphenyl decreased from 2.50 to 1.41. Results of quantitative real-time PCR show that Dehalococcoides cells increased from 2.39 ×105±0.5 × 105 to 4.99 × 107±0.32 × 107 copies mL–1 after 120 days of incubation, suggesting that Dehalococcoides play a major role in reductive dechlorination of PCBs. This study could prove the feasibility of anaerobic reductive culture enrichment for the dehalogenation of highly chlorinated PCBs, which is prior to be applied for in situ bioremediation of notorious halogenated compounds. 相似文献
Halogenated biphenyls are worldwide persistent pollutants of great environmental concern. In particular, polychlorinated biphenyls and polybrominated biphenyls have been globally used for industrial purposes until they were found highly toxic, mutagenic and carcinogenic to humans. Therefore, ecological strategies to remove halogenated biphenyls, such as enzyme-catalyzed degradation, are needed. Here, we studied the effect of substitution of F, Cl, Br or I at the 4,4′-positions of 2,3-dihydro-2,3-dihydroxybiphenyl-2,3-dehydrogenase (BphB) on the degradation of halogenated biphenyls by quantum and molecular mechanics. Results show that Boltzmann-weighted average degradation barriers of substituted BphB are all lower than the unsubstituted biphenyl, except for chlorinated biphenyl. The roles of residues nearby the active site, e.g., isoleucine89, asparagine115, serine142, asparagine143, proline184, methionine187 and threonine189, were also investigated.
The pollution of soil and aquatic environments by chlorinated aromatic pollutants (CAPs) such as polychlorobenzenes (PCBzs), polychlorophenols (PCPs), polychloro‐diphenyl ethers (PCDPEs), phenoxyacetic acids, etc., creates growing public anxiety. Phototransformation is an important process for pollutants in aquatic systems. This article extensively reviews the environmentally significant solution phase photochemistry of PCBzs as well as other CAPs derived therefrom. The paper includes photochemical fate of these CAPs at wavelengths >285 nm on the one hand and their photolysis in solution in aquatic systems on the other. In this article, photolytic reductive dechlorination and isomerization of PCBzs are reviewed together with the photoformation of several products including polychlorobiphenyls (PCBs) from PCBzs. Recently developed phenomena of photoincorporation of PCBzs into humic model monomers is also described. This review also describes the environmental photochemistry of chlorobenzene derivatives, namely, α‐substituted p‐chlorotoluenes of the general structure p‐ClC6H4CH2‐X (X = H, Cl, CN, COOH and OH), di‐through pentachlorophenols, PCDPEs (having Cl1–5 contents) with and without o‐OH substituents, and 2,4‐di‐ and 2,4,5‐trichlorophenoxyacetic acid (2,4‐D and 2,4,5‐T, respectively) as well as their esters and some formulations. 相似文献
The substitution of fossil fuels and fossil-based products with biofuels and biomass-based products is indispensable for a sustainable society and a green environment. The liquefaction of biomass to produce biofuels under sub- and/or super-critical water conditions is one of the most promising methods that might allow this substitution. Here, for the first time, we report the results of the liquefaction of woody biomass under sub-critical water conditions at 250, 300, and 350 °C using potassium tert-butoxide (t-BuOK) as a catalyst. To compare and evaluate the catalytic performance of t-BuOK, the experiments were also performed under identical conditions using KOH as the catalyst. The product distributions obtained using either KOH or t-BuOK as the catalyst were very similar. The total oil yields increased and the solid residue yields decreased when either KOH or t-BuOK were used at reaction temperatures of 300 and 350 °C. The total bio-oil yields obtained at 300 °C with t-BuOK and KOH were 41.9 weight (%) and 43.0 weight (%), respectively, whereas the total bio-oil yield from the thermal run at 300 °C was approximately 24.0 weight (%). Although the O/C ratio of the raw material is 0.70, the O/C ratios of the light and heavy bio-oils obtained from the KOH catalytic run are 0.38 and 0.25, respectively. In addition, the O/C ratios for the light and heavy oils obtained from the t-BuOK catalyst are 0.41 and 0.26, respectively. We estimate that the heating values of the light and heavy bio-oils obtained by either catalytic run (t-BuOK or KOH) are approximately 24 MJ kg?1 and 29 MJ kg?1, respectively 相似文献
We here report that by using electronegative gas of iodine and CO2 under negative corona discharge, tetraiodomethane could be synthesized at 70?°C and 1?atm without any catalyst, despite thermodynamically infeasible at ambience without electron discharge. The conversion of carbon dioxide reached 88.71?% at a gas flow rate of 0.06?L/min and a discharge frequency of 9.608?kHz. The anion-involved CO2 reduction process could be implemented efficiently under mild conditions, avoiding high temperature and high pressure. 相似文献
Spatial distribution, seasonal variation and potential inhalation risks of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) were investigated in the atmosphere of Beijing, using passive air samplers equipped with polyurethane foam disks. Concentrations of ΣPCDD/Fs, ΣPCBs and ΣPBDEs ranged from 8.4 to 179 fg WHO2005-TEQ/m3, 38.6–139 and 1.5–176 pg/m3, respectively. PCDFs showed higher air concentrations than those of PCDDs, indicating the influence of industrial activities and other combustion processes. The non-Aroclor congener, PCB-11, was detected in air (12.3–99.4 pg/m3) and dominated the PCB congener profiles (61.7–71.5% to ∑PCBs). The congener patterns of PBDEs showed signatures from both penta-BDE and octa-BDE products. Levels of PCDD/Fs, PCBs and PBDEs at the industrial and residential sites were higher than those at rural site, indicating human activities in urban area as potential sources. Higher air concentrations of PCDD/Fs, PCBs and PBDEs were observed in summer, which could be associated with atmospheric deposition process, re-volatilization from soil surface and volatilization from use of technical products, respectively. Results of inhalation exposure and cancer risk showed that atmospheric PCDD/Fs, dioxin-like PCBs and PBDEs did not cause high risks to the local residents of Beijing. This study provides further aid in evaluating emission sources, influencing factors and potential inhalation risks of the persistent organic pollutants to human health in mega-cities of China. 相似文献
The spatial and seasonal variation of polychlorinated biphenyls (PCBs) were investigated in water and sediment samples collected
from Songhua River, China, from 2007 to 2008. The total concentration of PCB congeners ranged from 1.1 to 14 ng/l in water
and 0.26–9.7 ng/g dry weight (dw) in sediment. The results of seasonal variation may suggest an impact to PCB concentration
in water from its atmospheric input, the dilution to PCBs concentrations of high stream in summer, and a general trend towards
increased volatilization in warmer conditions. From PCBs concentrations comparison between upstream and downstream of industrial
urban cities, it was obvious that industrial urban cities reflect an important pollutant source for PCBs in our study, also
with the evidences of high concentrations of PCBs occurring in high development industry and residential areas. Meanwhile,
the homologue profile of PCBs in Songhua was analyzed, whose comparison with published data indicates that the sources of
PCBs accumulated in the sediment may also came from the residue of PCBs production in China. Total five dioxin-like PCBs (CB-77,
81, 105, 114, and 126) and nine (CB-77, 81, 105, 114, 118, 123, 126, 156, and 167) were found in Songhua water and sediment. 相似文献
Contamination profiles of organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) were determined in six fish species from three selected regions along coastal waters off Savannah, GA, USA. Concentrations of PCBs were predominant (12–493 ng g?1 lw) followed by PBDEs (10–337 ng g?1 lw), OCPs such as DDTs (2.7–153 ng g?1 lw), chlordanes (3.8–34 ng g?1 lw), cyclodienes (<0.1–35 ng g?1 lw), mirex (<0.1–8.6 ng g?1 lw), γ-hexachlorocyclohexane (<0.1–1.4 ng g?1 lw), and hexachlorobenzene (<0.1–0.68 ng g?1 lw). The results indicated no region-specific difference in the contaminants however inter-species as well as intra-species differences were evident. Comparison of DDTs, PCBs, and PBDEs profiles in fish with those from other countries revealed that fish from coastal waters off Savannah contained relatively less concentrations of PCBs and chlorinated pesticides, while PBDE concentrations were comparable or even higher than fish samples from other regions. Polychlorinated biphenyl congeners and chlorinated pesticide tempoal trend data exhibited no increase of contamination levels. The levels of PCBs and chlorinated pesticides in fish from Savannah coastal waters were below the Food and Drug Administrations (FDA) established limits for human consumption. 相似文献
Two species of marine bivalve, Cerastoderma edule (Linnaeus) and Macoma balthica (Linnaeus), were exposed to particles contaminated with three commercial polychlorinated biphenyl (PCB) mixtures, Aroclors® 1242, 1254 and 1260. The accumulation of PCB in bivalve tissue was monitored for periods of up to 40 days. In addition to measuring total PCB concentrations, which reached 60 ppm of Aroclor 1242 in M. balthica, the fate of individual PCB homologues of different chlorine content, ranging from 2 to 8 chlorine atoms per biphenyl molecule, was also determined. Selective accumulation of PCBs with 5 chlorine atoms per biphenyl molecule occurred, whilst isomers of very low and very high molecular weights were accumulated at much slower rates. 相似文献
A method for the preparation of single crystals of PCB 35 suitable for single crystal X‐ray structure determination was developed. This method has already been proven suitable for 2,4'‐dichlorobiphenyl and may prove useful for other PCBs or related compounds. The crystals of PCB 35 are orthorhombic, spacegroup P21221 (a= 10.665(8), 6 = 3.825(3), c= 14.086(9) Å) and the structure was refined to R = 0.094 for 156 unique observed reflections and 43 parameters. Although the crystals were of poor quality, the structure determination unequivocally confirmed the substitution pattern of the biphenyl moiety by Cl atoms inferred previously from spectroscopic methods. The dihedral angle between the planes of the two phenyl rings is 33(2)°. 相似文献