Formation of polychlorinated diphenyl ethers from condensation of chlorophenols with chlorobenzenes

BACKGROUND AND AIMS: Polychlorinated diphenyl ethers (PCDEs), which are among the members of persistent organic pollutants, and PCDEs have been determined in a number of environmental samples. The main possible sources are the technical production of chlorinated phenols and all processes of incomplete combustion. PCDEs were observed in the fly ash from a municipal waste incinerator (MWI). It was speculated that the condensation of chlorophenols with chlorobenzenes occurred via PCDEs to form polychlorinated dibenzofurans (PCDFs). Nevertheless, PCDEs formation from condensation of chlorophenols with chlorobenzenes has not been confirmed by experimental observation. The objective of this paper is to investigate the formation mechanism of PCDEs from the condensation of chlorophenols with chlorobenzenes. The results are expected to be helpful in understanding the formation of PCDEs and in controlling and abating PCDEs emissions from MWI. METHODS: The pyrolysis of pentachlorophenol (PCP) and/or polychlorobenzenes (PCBz) was carried out in a sealed glass tube. The reaction products were extracted and purified with K2CO3 solution. The samples were concentrated and then cleaned up on an alumina column. GC/MS was used for identification and quantification of reaction products. RESULTS AND DISCUSSION: The results showed that the pyrolysis of hexachlorobenzene (HCB) at 340 degrees C for 6 h led to the formation of decachlorodiphenyl ether (DCDE) (2.41 microg/mg) and octachlorodibenzo-p-dioxins (OCDD) (0.24 micropg/mg), while the pyrolysis of PCP yielded DCDE (13.08 microg/mg) and OCDD (180.13 microg/mg). In addition, the amount of DCDE formation from the pyrolysis of the mixture of PCP and HCB was 4.65 times higher than the total amount of DCDE formation from the pyrolysis of HCB and PCP, respectively. This indicated that PCP and HCB were prone to condensation and formation of DCDE. DCDE was the main congener of PCDEs from condensation of PCP with HCB at 340, 400 and 450 degrees C. A small amount of nonachlorodiphenyl ether (NCDE) was formed by dechlorination reaction at 450 degrees C. The condensation of PCP with 1,2,4,5-tetrachlorobenzene (Cl4Bz) formed 2,2',3,4,4',5,5',6-octachlorodiphenyl ether (OCDE). Small amounts of heptachlorodiphenyl ether (HpCDE) and hexachlorodiphenyl ether (HxCDE) were detected at 450 degrees C. Meanwhile, polychlorinated dibenzo-p-dioxins (PCDDs) and PCDFs were detected from the condensation of PCP and PCBz. CONCLUSIONS: Experimental studies clarified the behavior of the formation of PCDEs from condensation of polychlorophenols and PCBz. The condensation of polychlorophenols with PCBz formed PCDEs through elimination of HCl between polychlorophenols and PCBz molecules. Another pathway of PCDEs formation was elimination of H2O between two polychlorophenol molecules. In addition, dechlorination processes had caused the specific homologous pattern of PCDEs under higher temperatures.     

Formation of PCDD/Fs and PCBs in the process of production of 1,4-dichlorobenzene

The occurrence and distribution of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) in a typical process of production of 1,4-dichlorobenzene (p-DCB) were investigated systematically in this study. P5CDFs and H6CDFs were the main congeners of PCDD/Fs, while only low levels of other PCDD/Fs were detected in the samples. The concentrations of PCBs were up to 4614 ng/g in the semi-manufactured products, and 1797 ng/g in the product p-DCB. It was also found that high chlorinated PCB congeners increased with the further chlorination. The levels of PCDD/Fs decreased obviously in the purification process, while PCBs could not be removed effectively. Polychlorophenols and other important dioxin precursors (1,4-dichloro-2-phenoxybenzene and 2-phenyl-2',5,5'-trichlorophenol) were also analyzed. Polychlorophenols which ortho- and para-positions of the hydroxyl were substituted by chlorine were the main congeners. In addition, a possible pathway of the formation of PCDD/Fs and PCBs in the production of p-DCB was presented. The results of this article suggest that re-estimation on the risk of using p-DCB products, especially the products for daily use such as mothballs, is expected.     

用物元分析进行水质环境监测优化布点的研究

本文首次提出利用物元分析对水质环境监测优化布点的新方法。在确定了最佳和最次理想点基础上，建立了标准事物和节域事物的物元矩阵。该法具有计算简便、分析合理和容易推广的优点。     

Inhibition of PCDD/Fs formation from dioxin precursors by calcium oxide

Research aimed at understanding the inhibition effect of CaO on polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) formation form dioxins precursors, such as chlorophenols (CPs) and chlorobenzenes (CBs). The results indicated that a clear dioxin inhibition effect occurred both in open and sealed system when CaO was used. In the open system, PCDDs were the main congeners and the inhibition efficiency was all over 99% in the experiments. In the experiments with CaO, less than 0.1% of the initial PCP was detected in the absorption tube and only about 1% of the initial PCP was examined as calcium pentachlorophenate in the reaction tube. In the sealed system, the inhibition efficiency was over 90% at temperature range between 280 and 450 degrees C when PCP was used as model precursor. When HCB and 2,3,4,5-T4CP replaced PCP, significant inhibition effect was also observed. As CaO has the advantageous properties of non-toxicity and non-volatile nature, it is our hope that the result will contribute to the development of a new technique to cope with the problem of dioxin pollution in MWIs.     

Determination of hexabromocyclododecanes in sediments from the Haihe River in China by an optimized HPLC–MS–MS method

Hexabromocyclododecanes(HBCDs),a new type of persistent organic pollutants widely used as brominated flame retardants,have attracted wide attention due to their increasing level and toxicity. A method based on high-performance liquid chromatography mass spectrometry(HPLC–MS–MS)in electrospray ionization mode has been developed by optimization of various parameters,which effectively improved the separation degree and responsive intensity of α-,β-and γ-HBCD isomers. The concentrations and distribution profiles of three HBCD isomers were investigated in sediments from the Haihe River in China.It was observed that the concentrations of HBCDs varied in the range of 0.4–58.82 ng/g,showing a decreasing trend along the flow direction,possibly due to attenuation and biodegradation along the flow direction of the Haihe River. The distribution profile of α-,β-,γ-HBCD was 7.91%–88.6%,0–91.47%,and 0.62%–42.83%,respectively. Interestingly,α-HBCD dominated in most sample sites. This was different from the distribution profile in commercial industrial products,which might be attributed to the inter-transformation and different degradation rates of the three HBCD isomers. The potential ecological risk of HBCDs in sediment was characterized under the two-tiered procedure of the European Medicines Evaluation Agency for environmental risk assessment. Although the HBCDs in the selected section of the Haihe River presented "no risk" in the sediment compartment,its risk in sediment cannot be neglected since sediment is one of the important sinks and reservoirs of pollutants.     

Catalytic dechlorination of monochlorobenzene with a new type of nanoscale Ni(B)/Fe(B) bimetallic catalytic reductant

A unique type of nanoscale Ni(B)/Fe(B) bimetallic catalytic reductant was prepared and used for dechlorination of monochlorobenzene (MCB). The sample Ni(B)/Fe(B) was synthesized by an electroless plating method, in which nanoscale Ni(B) was deposited on the surface of nanoscale Fe(B) synthesized by chemical reduction. The results suggest that the nanoscale Ni(B)/Fe(B) bimetallic catalytic reductant has higher dechlorination efficiency than Ni/Fe(B) catalytic reductant prepared by replacing Fe(B) with Ni(2+) in aqueous solution. The Ni content was found to be an important factor in catalytic dechlorination, with the dechlorination rate increasing with Ni content. The electroless plating method improve the efficiency of the Ni(2+) in the solution. Dechlorination takes place with the existence of nanoscale Ni(B)/Fe(B) bimetallic catalytic reductant via a pseudo-first-order reaction.     

基于AHP的TOPSIS法在铁路工程环境影响评价的应用研究

利用AHP法赋权,运用TOPSIS法计算贴近度,建立铁路工程环境影响评价模型,进行多方案比选。结果表明,该方法既能够反映各指标的不同重要程度,也能够反映综合评价结果,计算简便、研究结果可靠,能够为铁路工程环境影响评价决策提供科学依据,具有一定借鉴意义。     

台湾城市生活垃圾焚烧处理现状

概述了台湾目前城市生活垃圾焚烧处理现状。以台湾最大的垃圾焚烧厂一台北市北投焚化厂为例,介绍了垃圾焚烧工艺及二次污染控制技术,并对台湾地区最新颁布的焚化炉空气污染排放标准进行了介绍。      

Polychlorinated dibenzo-p-dioxins and dibenzofurans in eggs of eight avian species from Dongting Lake, China

Concentrations of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) were determined in eggs of eight avian species collected from Dongting Lake of China to assess residue levels, accumulation patterns, and toxic potential in different avian species. Concentrations of total 2,3,7,8-substituted PCDD/Fs were in the range of 10.8-182pgg(-1) lipid weight. Eggs of great egret and lesser pied kingfisher contained higher levels of PCDD/Fs than eggs of other species, indicating the specific exposure and accumulation of PCDD/Fs relating to feeding habits and the life span. PCDD/Fs congener patterns varied among species. The patterns of PCDD/Fs in the eggs may be influenced by feeding habits, specific elimination, and metabolism. In general, concentrations of PCDDs were higher than those of PCDFs in avian eggs. On basis of lipid weight, total 2,3,7,8-TCDD toxic equivalents (TEQs) calculated based on the WHO TEFs for birds ranged from 2.04 to 42.0pgg(-1); and on basis of wet weight, total WHO-TEQs ranged from 0.19 to 1.59pgg(-1). 2,3,7,8-TCDF, 2,3,4,7,8-PeCDF, 2,3,7,8-TCDD, 1,2,3,7,8-PeCDD were the major contributors to TEQ concentration in most avian eggs, whereas 1,2,3,4,7,8-HxCDD also accounted for a major portion of TEQs in eggs of azure-winged magpie. Values of TEQs in avian eggs were lower than toxic threshold values, implying risk reduction and natural restoration of PCDD/Fs contamination in Dongting Lake region.     

太阳能级多晶硅生命周期环境影响评价

采用生命周期评价法对太阳能级多晶硅生产过程的环境影响进行评价. 基于Eco-Indicator99,建立了适用于我国的终点破坏类影响评价模型(Chinese endpoint damage model,CEDM). 对影响评价模型的资源属性参数进行了本地化研究,核算出以2010年为基准年、以我国为基准区域的资源属性本地化人均年度基准值(4.33×105 MJ). 采用现场和问卷调研的方式获得太阳能级多晶硅所有生命周期阶段的能量物质的输入、输出和环境外排数据,调研样本总产量达到2012年全国产量的80%. 结果表明:从环境影响的最终破坏受体来看,太阳能级多晶硅生命周期环境影响主要集中在对人体健康损害方面,占其整个环境影响的72.31%;其次是对资源衰竭方面的影响,占24.23%;对生态系统的损害最小,仅占3.46%. 在所有环境要素中,电的环境影响最高,占79.48%;其次是蒸汽消耗、工业硅原料,二者分别占13.18%、5.97%. 我国太阳能级多晶硅生命周期环境影响是欧洲平均水平的2倍多,主要是受电力结构所致,但在技术先进性和污染防治水平方面要优于欧洲平均水平.