Influence of iron and copper oxides on polychlorinated diphenyl ether formation in heterogeneous reactions

Polychlorinated Diphenyl Ethers in the Environment: A Review and Future Perspectives

Polychlorinated diphenyl ethers (PCDEs) are a class of synthetic halogenated aromatic compounds, which have gradually attracted widespread attention due to potential environmental risks to humans and ecosystems. This paper presents a literature review of research on PCDEs using PubMed, Web of Science and Google Scholar as search engines/databases with no constraints on publishing year or number. A total of 98 publications on the sources, environmental levels, environmental behavior and fate, synthesis and analysis and toxicology of PCDEs were retrieved. Existing studies have shown that PCDEs widely exist in the environment with the ability of long-range transport, bioaccumulation and biomagnification, which are almost comparable to polychlorinated biphenyls. They can elicit adverse effects including hepatic oxidative stress, immunosuppression, endocrine disorders, growth retardation, malformations, reduced fertility and increased mortality in organisms, among which some seem to be related to the activation of the aryl hydrocarbon receptor. PCDEs can be metabolized into other organic pollutants, such as hydroxylated and methoxylated PCDEs and even polychlorinated dibenzo-p-dioxins and furans through biotransformation, photolysis and pyrolysis reactions in the environment. Compared with reviews on PCDEs published previously, some new information and findings are summarized in this review, such as new sources, current environmental exposure levels, main metabolism pathways in aquatic organisms, acute toxicity data for more species and relationships between structural parameters and toxicity and bioaccumulation potentials of PCDE congeners. Finally, current research deficiencies and future research perspectives are proposed to facilitate the assessment of health and ecological risks of PCDEs.

Emissions of polychlorinated diphenyl ethers from a municipal solid waste incinerator during the start-up operation

This study examines the emissions of polychlorinated diphenyl ethers (PCDEs) during the start-up processes of a municipal solid waste incinerator (MSWI). Both normal and modified emission control start-ups were tested. Fifteen samples were taken from the flue gas with increasing furnace temperature. Peak PCDE concentrations of 1.48-10.3 ng/Nm(3) were observed at 8-11 h after the start of combustion, when the furnace temperature was in the range of 267-440 °C, that also needed for PCDD/F formation by de novo synthesis. The PCDE emissions could thus, be reduced by current control techniques. Furthermore, the modified control strategies inhibited PCDE formation at the beginning of combustion, and led to an 86% reduction in the maximum PCDE concentration. The overall start-up emissions were calculated as 1.01-3.08 mg, while the annual PCDE emissions with one start-up operation were found to be 7.48-9.64 mg. However, total PCDE emissions will increase by 12-69% if the number of start-up runs increases to between two and eight times per year. Consequently, the prevention of the unnecessary start-ups and advanced activation of the related emission control system are both efficient ways to reduce PCDE emissions.

Mechanisms of transformation of polychlorinated diphenyl ethers into polychlorinated dibenzo-p-dioxins and dibenzofurans

This study presents a detailed mechanistic account of the formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) from polychlorinated diphenyl ethers (PCDEs). It applies the recently developed meta hybrid M06-2X functional and deploys the 2,2'-dichlorodiphenylether (2,2'-DCDE) molecule as a representative model compound for all PCDEs congeners. We find that, exceedingly high activation enthalpies prevent the direct formation of PCDFs from PCDEs via unimolecular elimination of HCl or Cl2. Rather, loss of an ortho H/Cl atom initiates the transformation of PCDEs into PCDD/Fs. Subsequent formation of PCDFs takes place through ring-closure reactions with modest activation enthalpies, whereas the addition of a ground state oxygen molecule at an apparent ortho radical site of a PCDE congener commences a complex, yet very exothermic, mechanism leading to the formation of PCDDs. Splitting the ether linkage through H/Cl addition at the pivot carbon constitutes a major source for the formation of chlorophenoxy radicals and chlorobenzene molecules. Our kinetic and mechanistic analyses demonstrate that, the degree and pattern of chlorination of PCDEs display a negligible effect on the formation pathways of PCDD/Fs from PCDEs.

Reducing emissions of persistent organic pollutants from a diesel engine by fueling with water-containing butanol diesel blends

The manufacture of water-containing butanol diesel blends requires no excess dehydration and surfactant addition. Therefore, compared with the manufacture of conventional bio-alcohols, the energy consumption for the manufacture of water-containing butanol diesel blends is reduced, and the costs are lowered. In this study, we verified that using water-containing butanol diesel blends not only solves the tradeoff problem between nitrogen oxides (NOx) and particulate matter emissions from diesel engines, but it also reduces the emissions of persistent organic pollutants (POPs), including polycyclic aromatic hydrocarbons, polychlorinated dibenzo-p-dioxins and dibenzofurans, polychlorinated biphenyls, polychlorinated diphenyl ethers, polybrominated dibenzo-p-dioxins and dibenzofurans, polybrominated biphenyls and polybrominated diphenyl ethers. After using blends of B2 with 10% and 20% water-containing butanol, the POP emission factors were decreased by amounts in the range of 22.6%-42.3% and 38.0%-65.5% on a mass basis, as well as 18.7%-78.1% and 51.0%-84.9% on a toxicity basis. The addition of water-containing butanol introduced a lower content of aromatic compounds and most importantly, lead to more complete combustion, thus resulting in a great reduction in the POP emissions. Not only did the self-provided oxygen of butanol promote complete oxidation but also the water content in butanol diesel blends could cause a microexplosion mechanism, which provided a better turbulence and well-mixed environment for complete combustion.

Aquatic environments polluted with antibiotics and heavy metals: a human health hazard

Aquatic environments often receive wastewater containing pollutants such as antibiotics and heavy metals from hospital sewage, as well as contaminants from soil. The presence of these pollutants can increase the rate of exchange of resistant genes between environmental and pathogenic bacteria, which can make the treatment of various types of bacterial infections in humans and animals difficult, in addition to causing environmental problems such as ecological risk. In this study, two tetracycline-resistant Pseudomonas aeruginosa (EW32 and EW33), isolated from aquatic environments close to industries and a hospital in southeastern Brazil, were investigated regarding the possible association between tetracycline and heavy metal resistance. The isolate EW32 presented a conjugative plasmid with coresistance to tetracycline and copper, reinforcing the concern that antibiotic resistance by acquisition of plasmids can be induced by the selective pressure of heavy metals in the environment.