| 31. |
- Hutzinger, O., et al.
(författare)
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From source to exposure : Some open questions
- 1993
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Ingår i: Chemosphere. - : Elsevier. - 0045-6535 .- 1879-1298. ; 27:1-3, s. 121-129
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Tidskriftsartikel (refereegranskat)abstract
- PCDD/PCDF are trace contaminants in industrial and thermal processes, whose formation often cannot be avoided. Although the most important sources seem to be recognized within the last years new sources have been discovered. Very often only limited data are available. For the understanding of human exposure it is necessary to understand the pathways from the source to target organs or organisms. Environmental concentrations of dioxins have to be analyzed under ectoxicological aspects. Transfer and transformation mechanisms to be considered are: evaporation, deposition, erosion, photochemical degradation
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| 32. |
- Lau, C., et al.
(författare)
-
Levels of selected organic compounds in materials for candle production and human exposure to candle emissions
- 1997
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Ingår i: Chemosphere. - : Elsevier. - 0045-6535 .- 1879-1298. ; 34:5-7, s. 1623-1630
-
Tidskriftsartikel (refereegranskat)abstract
- Polychlorinated dibenzo-p-dioxins (PCDD), dibenzofurans (PCDF) selected chlorinated pesticides, polycyclic aromatic hydrocarbons (PAH) and some volatile organic compounds (VOC) were analysed in the exhaust fumes of candles made from different waxes and finishing materials. To guarantee defined burning conditions a chamber was developed for the sampling of the exhaust fumes, Using a simple exposure model, the inhalative uptake of PCDD/PCDF by an adult person was calculated for different scenarios. It was shown that additional uptake of PCDD/PCDF caused by candle emissions does not contribute significantly to the total daily intake of these compounds. Emissions of PCDD/PCDF, benzo(a)pyrene and the VOC were then compared to limit value for working places. Even when many candles would be burnt at the same time in a small room, concentrations of the compounds investigated stay below 1 % of the tolerable limit values.
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| 33. |
- Rappe, Christoffer, et al.
(författare)
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PCDD and PCDF contamination in catfish feed from Arkansas, USA
- 1998
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Ingår i: Chemosphere. - : Elsevier. - 0045-6535 .- 1879-1298. ; 36:13, s. 2705-2720
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Tidskriftsartikel (refereegranskat)abstract
- One combined catfish feed sample from Arkansas, USA, and its eight ingredients were analyzed for PCDDs and PCDFs. One of the ingredients, soybean meal, was highly contaminated by PCDDs, especially the toxic 2,3,7,8-substituted congeners, e.g. 7.3 pg/g dry weight or 370 pg/g lipid for the 2,3,7,8-tetra CDD. The I-TEQ value for the soybean meal was 11.4 pg/g dry weight or 576 pg/g fat. The corresponding values for the combined catfish feed concentrations were approximately 3 times lower. The congener pattern, the congener profile and the ratio Sigma PCDDs/Sigma PCDFs for the soybean meal were quite unique. We are not aware of any environmental sample or technical product with similar characteristics. As a result, natural formation of the PCDDs found in the soybean meal cannot be ruled out.
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| 34. |
- Rappe, C., et al.
(författare)
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PCDDs and PCDFs in municipal sewage sludge and effluent from POTW in the State of Mississippi, USA
- 1998
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Ingår i: Chemosphere. - : Elsevier. - 0045-6535 .- 1879-1298. ; 36:2, s. 315-328
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Tidskriftsartikel (refereegranskat)abstract
- During the summer 1995, we collected sewage sludge and effluent samples from 17 publicly-owned treatment works (POTW) in the State of Mississippi, USA. Most PCDDs and PCDFs were detected in the sludge, and the hepta- and octaCDD congeners typically were dominant. One plant had an octaCDD value in sludge exceeding 400,000 pg/g d.m. The primary source probably is pentachlorophenol. An earlier US EPA finding of 116 pg/g d.m. 2,3,7,8-tetraCDD in sludge from the Corinth POTW was not confirmed in this study, where only 0.3 pg/g d.m. was measured. Most effluent samples were below the detection limit of approximately 10 pg/L for the tetra- through hexachlorinated congeners. The New Augusta POTW had the highest octaCDD value in effluent (2500 pg/L). This plant is a point source to the Leaf River.
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| 35. |
- Rappe, C., et al.
(författare)
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PCDDs and PCDFs in soil and river sediment samples from a rural area in the United States of America
- 1997
-
Ingår i: Chemosphere. - : Elsevier. - 0045-6535 .- 1879-1298. ; 34:5-7, s. 1297-1314
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Tidskriftsartikel (refereegranskat)abstract
- In 1994, we collected 36 soil samples and 61 sediment samples from southern Mississippi, USA. Each sample was analyzed for PCDDs and PCDFs by HRMS using either a polar or a non-polar HRGC column. Although most Cl-4 - Cl-8 PCDDs and PCDFs were detected in each sample, PCDD levels (particularly Cl-7 - Cl-8) were higher in sediment than soil samples. The PCDF pattern in two sediment samples indicated a possible PCB source. The concentrations of 2,3,7,8-tetra CDD and 2,3,7,8-tetra CDF were somewhat higher upstream of a pulp mill than downstream from the mill.
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| 36. |
- Schramm, K. W., et al.
(författare)
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Reduction of PXDD/F emissions. Low-temperature-separation of flyash in incinerators : Fugacity calculations
- 1990
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Ingår i: Staub, Reinhaltung der Luft. - : Springer. - 0039-0771. ; 50:7-8, s. 281-283
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Tidskriftsartikel (refereegranskat)abstract
- The emission of PXDD-F from incinerators depends on the partition between stackgas and flyash. Fugacity calculations show that the separation of the flyash at low temperatures lowers the total emission up to hundred fold.The emission of PXDD/F from incinerators depends on the partition between stack gas and fly ash. Fugacity calculations show that the separation of the flyash at low temperatures lowers the total emission up to hundredfold.
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| 37. |
- Fronaeus, Sture, et al.
(författare)
-
Iron-Manganese Redox Processes and Synergism in the Mechanism for Manganese-Catalyzed Autoxidation of Hydrogen Sulfiite
- 1998
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 37:19, s. 4939-4944
-
Tidskriftsartikel (refereegranskat)abstract
- SynopsisOn the basis of kinetic studies of the manganese-catalyzed autoxidation of sulfite and thermodynamic data for iron−manganese redox processes and manganese(II) and -(III) protolysis equilibria, the catalytically active species in the autoxidation is concluded to be a mixed-valence oxo-bridged manganese(II,III) complex. Iron−manganese synergism and triggering of the chain reaction by small concentrations of iron(III) can also be ascribed to formation of this bridged complex via rapid iron−manganese redox equilibria.AbstractThe mechanism for manganese-catalyzed aqueous autoxidation of hydrogen sulfite at pH 2.4 has been revised on the basis of previous comprehensive kinetic studies and thermodynamic data for iron-manganese redox processes and manganese(II) and -(III) protolysis equilibria. The catalytically active manganese species is concluded to be an oxo- (or hydroxo-) bridged mixed-valence complex of composition (OH)(MnOMnII)-O-III(aq) with a formation constant beta' of (3 +/- 1) x 10(4) M-1 from kinetics or ca. 7 x 10(4) M-1 from thermodynamics. It is formed via rapid reaction between Mn(H2O)(6)(2+) and hydrolyzed manganese(III) aqua hydroxo complexes, and it initiates the chain reaction via formation of a precursor complex with HSO3-, within which fast bridged electron transfer from S(IV) to Mn(III) takes place, resulting in formation of chain propagating sulfite radicals, SO3.-. The very high acidity of Mn3+(aq). indicating a strong bond Mn-III-OH2 in hydrolyzed manganese(III), makes an attack by HSO3- on substitution labile Mn(TI) in the bridged complex more favorable than one directly on manganese(III). The synergistic effect observed in systems containing iron as well as manganese and the chain initiation by trace concentrations of iron(III) of ca. 5 x 10(-8) M can also be rationalized in terms of formation of this bridged mixed-valence dimanganese(II,III) complex. The presence of iron(III) in a Mn(II)/HSO3- system results in rapid establishment of an iron-manganese redox equilibrium, increasing the concentration of manganese(III) and of the catalytically active bridged complex. The bridged complex oxidizes HSO3- several orders of magnitude faster than does iron(III) itself. Comparison with some previous studies shows that the different experimental rate laws reported do not necessarily indicate different reaction mechanisms. Instead, they can be rationalized in terms of different rate-determining steps within the same complex chain reaction mechanism, depending on the experimental conditions used.
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| 38. |
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| 39. |
- Löfgren, Lars, 1964, et al.
(författare)
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Exposure of commuters to volatile aromatic hydrocarbons from petrol exhaust
- 1991
-
Ingår i: The science of the total environment. ; 108, s. 225-233
-
Tidskriftsartikel (refereegranskat)abstract
- Twenty-two volatile aromatic hydrocarbons were determined in the air of an automobile during commuting. Sampling was made on Tenax cartridges and laboratory determinations were carried out using thermal desorption combined with temperature-programmed capillary gas chromatography. Selected hydrocarbons representative of petrol exhaust were determined in the automobile and in an electric commuter train during eight parallel commuter trips. In the automobile, the concentrations of benzene were 35-70 micrograms/m3 and those of total aromatic hydrocarbons 200-400 micrograms/m3. The petrol exhaust levels were 5-10 times higher in the automobile than in the compartment of the commuter train.
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| 40. |
- miettinen, heije, et al.
(författare)
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Laboratory study of N2O formation from burning char particles at FBC conditions
- 1995
-
Ingår i: Energy and Fuels. - 1520-5029. ; 9:1, s. 10-19
-
Tidskriftsartikel (refereegranskat)abstract
- Coal combustion in fluidized bed combuster is a cause of nitrous oxide emissions to the atmosphere. The formation of NzO seems to be related both to homogeneous and heterogeneous reactions taking place in the combustion process. The purpose of this investigation was to study the formation of NzO from burning char particles under different combustion conditions. The experiments were carried out in a fmed bed reactor containing quartz sand (SiOz) to support the coal particles. A monolayer of bituminous coal particles between two layers of quartz sand was devolatilized prior to the actual combustion in an argon flow. The coal particle sizes were varied between 0.090 and 2.80 mm. The inlet gas mixture contained NO, 0 2 , and Ar or just 0 2 and Ar. The oxygen concentration was varied between 0.5 and 20% 0 2 and the NO concentration was varied between 0 and 1000 ppm NO. The inlet gas flow was varied between 590 and 1581 mL/ min NTP (273 K, 1 atm) and the bed temperature was varied between 1023 and 1123 K. The off-gases were analyzed for NzO, NO, CO, and COZ. Addition of NO to the flue gas increased the NzO yield. A low combustion temperature also favors high yields of N20. A great influence of the oxygen concentration was found (high oxygen concentrations give low Nz0 yields), which indicates that the combustion conditions are very important for the NzO yield. A particle size of 1 mm gives the highest NzO yields.
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