| The isotope-dilution method to determine the polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans(PCDFs) was established in the study using high-resolution Gas Chromatography/high-resolution mass spectrometry(HRGC/HRMS) on the basis of US EPA1613 as well as the other labs' analysis method in the world, and reach the internationally advanced level。The detection and concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/PCDFs) in 58 soils and 3 sediments collected from a rapidly industrialized area of China, Pearl River Delta was reported. And primarily identify the possible sources had been done through comparing difference of the character of homologue and isomer percentage profile between the soil/sediment and known sources.The results showed that the total concentrations of PCDDs/PCDFs were 85.5 to 14525 pg/g (dry weight), and the concentrations of 2,3,7,8-tetrachlorinated dibenzo-p-dioxin (TCDD) toxicity equivalent concentration (I-TEQ) were 0.09 to 19.7 pg/g (dry weight). According to the Germany and the USA guidelines for I-TEQ (International Toxity equal quotient)concentrations, the TEQ concentrations for 44 of the 58 (68.7%) soil samples examined, with I-TEQ < 5 pg/g (dry wt), represented no human health hazards. The remaining 14 (or 31.3%) soil samples contained TEQs between 5 and 40 pg/g (dry wt), and should be used with precaution. The TEQs of PCDDs/DFs for three sediment samples represent no risk to aquatic life. The relative higher total concentrations and I-TEQ of PCDDs/DFs in a few samples, which were collected from the suburban area (11, 21, 27, 28, 40, 41, 43, 44, 51, 52 and 53), residential and commercial area (50) and industrial area (5, 7 and 31) indicated the presence of potential point sourced pollution.The homologue and isomer profiles of PCDDs/DFs and the spatial distribution suggest that the sources of PCDDs/PCDFs are mixed in soils, but the impurities of technical pentachlorophenol (PCP) were possibly the main sources in the samples that contain high concentration of PCDDs/DFs. The bad correlation between the concentration of dioxins and EC in the soil/sediment was detected, which furthermore showed that the combustion process was not the main source of dioxins in the Pearl River Delta. PCDDs/DFs were also detected in soils from the three tops of mountains, suggesting wide dispersal behavior of PCDDs/DFs existing in this region via dry and wet deposition.Moreover, primary identification of dioxins' sources has been done with the domestic burning of coals and charcoal for barbecue. The result showed that dioxins had been detected in the particles and gas from the stack of burning the charcoal and coals which were formed of the marine facies and marine-terrestrial alternative facies in the Carboniferous and Permian Period. In this study, the total concentration and I-TEQ of PCDDs/DFs of all particle samples in the stack were 742.2-20731 and 4.0-413.9 pg/kg converted coal or charcoal, respectively.The I—TEQ of dioxins per gram ash from the stack was 0.6-88.4pg. In general, with the increasing of content of chlorine in the sample, the concentration of 2378-PCDDs/DFs and total concentration increasd as well as the I-TEQ/kg coal and the I-TEQ/g soot. As regard for coal, the I-TEQ in the stack of the honeycomb-coal-briquette collected from Hancheng coalfield was the highest, the I-TEQ/kg coal was 383.3pg and the I-TEQ/g soot was 77.4pg. The I-TEQ/g soot from the stack of the honeycomb-coal-briquette Taiyuan Formation, Shanxi Formation coleeted from Xi mountain of Shanxi Province and Yanzhou of Shandong was also high, was 36.4, 26.5 and 8.9 pg/g respectively. Base on the Germany' guideline of risk assessment of soil, some measures need to take when contacting it, for example to clean the stack. On the whole, the domestic-coal-burning process genenrated more PCDFs than PCDDs, even in the case PCDFs lower than PCDDs, the concentration of PCDFs was comparable with that of PCDDs. The homologue characterized that the concentration of TCDFs and OCDD was higher than others, the percentage profile of congener characterized that 2,3,7,8—TCDF and 2,3,4,7,8-PeCDF contributed the major of the I-TEQ.The concentration and I-TEQ from the charcoal for barbecue was very high, the total concentration was 13053pg and 1850pg per kg charcoal for retail and pack charcoal, the I-TEQ was 413.9pg and 141.0pg/kg charcoal, and the I-TEQ/g soot was 88.4 pg and 69.6 pg respectively. So it is evidently necessary to study in detail in order to acquire the exactly dioxin concentration from the process of burning of charcoal for barbecue. |
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