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521.
Slag arising in ferrochromium and stainless steel production is known to contain residual levels of trivalent chromium. As the chromium is normally bound in the slag matrix in various silicate or spinel phases, and hence not easily mobilised, utilisation or controlled disposal of such slag is generally considered unproblematic. Experimental test work with a number of slag materials indicates, however, that very gradual oxidation of trivalent to hexavalent chromium does occur when the slag is exposed to atmospheric oxygen, rendering a quantifiable but small portion of chromium in this much more mobile and toxic form. Mechanisms and rates of the oxidation reaction were investigated in a number of long-term studies using both original slag materials and artificial mixes of chromium and calcium oxides. Powders of these materials, some of them rolled into balls, were left to age under different conditions for periods of up to 12 months. In the slag samples, which contained between 1 and 3 wt.% chromium, 1000–10 000 μg Cr(VI) were found per gram of chromium within 6–9 months of exposure to an ambient atmosphere. The rate of the oxidation reaction decreased exponentially, and the reaction could generally be said to have ceased within 12 months. In mixtures of calcium and chromium oxides the oxidation reaction is presumed to occur at the boundaries between chromium oxide and calcium oxide phases through diffusion of oxygen along the grain boundaries and of Cr3+ across the boundaries, resulting in the formation of calcium chromate. In the slags, where calcium and chromium oxide can form a solid solution, the oxidation is likely to occur at the exposed surface of grains containing this solution. 相似文献
522.
Uwe Heiser Stefan Norra Doris Stüben Magnus von Wagner 《Environmental Sciences Europe》1999,11(1):15-19
For the application of sequential extraction of heavy metals from samples that can only be obtained in amounts of a few milligrams (micro samples, e.g. airborne dust fallout), the method afterZeien &Brümmer (1989) was progressed. A down scale to 1∶100 was carried out and the accuracy of this method with variable sample amounts of about 20 mg and an extraction volume of 500 μl was proofed with standard soil samples. The influence of variable extraction ratios (ratio of sample amount and volume of extraction solvent) and the influence of intensive treatment of dust sampled by the Bergerhoff-method (VDI 2119/2, 1972) prior sequential extraction, was within the precision of measurement of our method. Thus, we showed that sequential extraction can be applied for the investigation of heavy metal mobilization in micro samples with variable sample amounts. A first application of our method for microsamples was carried out to investigate airborne dust fallout and street sediments at two urban sites where different heavy metal immission rates due to traffic influence occur. These investigations will be presented in part 2 (“Sequential extraction of heavy metals from urban dust”). 相似文献
523.
Aalto P Hämeri K Paatero P Kulmala M Bellander T Berglind N Bouso L Castaño-Vinyals G Sunyer J Cattani G Marconi A Cyrys J von Klot S Peters A Zetzsche K Lanki T Pekkanen J Nyberg F Sjövall B Forastiere F 《Journal of the Air & Waste Management Association (1995)》2005,55(8):1064-1076
In this study, long-term aerosol particle total number concentration measurements in five metropolitan areas across Europe are presented. The measurements have been carried out in Augsburg, Barcelona, Helsinki, Rome, and Stockholm using the same instrument, a condensation particle counter (TSI model 3022). The results show that in all of the studied cities, the winter concentrations are higher than the summer concentrations. In Helsinki and in Stockholm, winter concentrations are higher by a factor of two and in Augsburg almost by a factor of three compared with summer months. The winter maximum of the monthly average concentrations in these cities is between 10,000 cm(-3) and 20,000 cm(-3), whereas the summer min is approximately 5000-6000 cm(-3). In Rome and in Barcelona, the winters are more polluted compared with summers by as much as a factor of 4-10. The winter maximum in both Rome and Barcelona is close to 100,000 cm(-3), whereas the summer minimum is > 10,000 cm(-3). During the weekdays the maximum of the hourly average concentrations in all of the cities is detected during the morning hours between 7 and 10 a.m. The evening maxima were present in Barcelona, Rome, and Augsburg, but these were not as pronounced as the morning ones. The daily maxima in Helsinki and Stockholm are close or even lower than the daily minima in the more polluted cities. The concentrations between these two groups of cities are different with a factor of about five during the whole day. The study pointed out the influence of the selection of the measurement site and the configuration of the sampling line on the observed concentrations. 相似文献
524.
Emil Kucera 《Environmental monitoring and assessment》1988,10(1):51-57
Lead (Pb) concentrations in 398 samples of dog whole blood were determined by atomic absorption method. All samples were within the normal range of values reported in literature, 95% of the samples had <8.0 g/100 ml lead. The correlation between blood lead level and the volume of traffic was highly significant. About 11% of the variability in concentration can be explained by the traffic flows near the animal's home. The findings confirm that traffic contributes a significant portion of the total inhaled lead. The use of dogs as environmental lead monitors is discussed. It is concluded that in non-occupational situations a survey of lead in blood of dogs may serve as a feasible, low-cost alternative to large-scale surveys of humans. 相似文献
525.
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528.
G. H. R. von Koenigswald 《Die Naturwissenschaften》1953,40(4):128-137
529.
Brian L. Beard L. Gordon Medaris-Jr Clark M. Johnson Emil Jelínek J. Tonika Lee R. Riciputi 《Geologische Rundschau》1995,84(3):552-567
The Mariánské Lázn complex (MLC) is located in the Bohemian Massif along the north-western margin of the Teplá-Barrandian microplate and consists of metagabbro, amphibolite and eclogite, with subordinate amounts of serpentinite, felsic gneiss and calcsilicate rocks. The MLC is interpreted as a metaophiolite complex that marks the suture zone between the Saxothuringian rocks to the north-west and the Teplá-Barrandian microplate to the south-east. Sm-Nd geochronology of garnet-omphacite pairs from two eclogite samples yields ages of 377±7, and 367±4 Ma. Samples of eclogite and amphibolite do not define a whole rock Sm-Nd isochron, even though there is a large range in Sm/Nd ratio, implying that the suite of samples may not be cogenetic. Eclogites do not have correlated
Nd values and initial 87Sr/86Sr ratios. Five of the eight eclogite samples have high
Nd values (+10.2 to +7.1) consistent with derivation from a MORB-like source, but variable 87Sr/86Sr ratios (0.7033 to 0.7059) which probably reflect hydrothermal seawater alteration. Three other eclogite samples have lower Nd values (+ 5.4 to –0.8) and widely variable 87Sr/86Sr ratios (0.7033 to 0.7096). Such low Nd values are inconsistent with derivation from a MORB, source and may reflect a subduction or oceanic island basalt component in their source. The MLC is an important petrotectonic element in the Bohemian Massif, providing evidence for Cambro-Ordovician formation of oceanic crust and interaction with seawater, Late Devonian (Frasnian-Famennian) high- and medium-pressure metamorphism related to closure of a Saxothuringian ocean basin, Early Carboniferous (Viséan) thrusting of the Teplá terrane over Saxothuringian rocks and Late Viséan extension. 相似文献
530.
Loikkanen Emil Oristo Satu Hämäläinen Natalia Jokelainen Pikka Kantala Tuija Sukura Antti Maunula Leena 《Food and environmental virology》2020,12(4):333-341
Food and Environmental Virology - The main animal reservoirs of zoonotic hepatitis E virus (HEV) are domestic pigs and wild boars, but HEV also infects cervids. In this study, we estimated the... 相似文献