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211.
The PCB and DDT contamination is described in the immediate vicinity of a transformer house (Odenwald, Germany). Samples were taken inside and outside the house and analyzed. For a toxicological assessment the measured values (according toBallschmiter PCB 77 and PCB 126) are converted into toxic equivalents. 相似文献
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214.
A model to estimate the entry length to a fully developed diffusive boundary layer above a sediment bed, such as those found in lakes, reservoirs, rivers, and estuaries, is presented. The model is used to determine how the length of a sediment bed in mass-transfer experiments influences the measured vertical diffusive flux at the sediment-water interface. A nondimensional local mass flux is introduced in the form of a Sherwood number (Sh) and expressed as a function of both the distance from the leading edge of the sediment bed (x) and the Schmidt number (Sc). Similarly, a mean Sherwood number (Sh(ave)) for a sediment bed of length (L) is introduced. The diffusive boundary layer grows with distance, and its thickness depends on the Schmidt number (i.e., the diffusive boundary layer gets thicker and develops more quickly as the Schmidt number decreases). For Schmidt numbers greater than or equal to 100, the diffusive boundary layer begins to develop slowly but is fully developed when the nondimensional horizontal coordinate (x+) is approximately 1000. The Sherwood number is largest (i.e., infinity) near the leading edge of the sediment bed (i.e., at x = 0), decreases as the distance from the bed increases, and, finally, approaches a constant value for a fully developed diffusive boundary layer (Sh(infinity)). In this paper, the distance to a fully developed diffusive boundary layer (L99) and the required length of a sediment bed are related explicitly to Sc, sheer velocity (U*), and the relative errors of local or average Sherwood numbers (Sh or Sh(ave), respectively) against the Sherwood number for the fully developed diffusive boundary layer (Sh(infinity)). The lengths L99 and L decrease as the Schmidt number increases and become independent of the Schmidt number when Sc is greater than 1000. A longer sediment bed is needed when the shear velocity or the Schmidt number is small (e.g., L99 and L approximately 1.0 m and 8.0 m, respectively, for Sc = 500, U* = 0.1 cm/s, and a 3% acceptable error). Experimental studies may not be able to meet these requirements and an adjustment of measured mass-transfer rates at a sediment-water interface may be necessary. The magnitude of that adjustment is up to 50%. Its dependence on the Schmidt number, shear velocity, and bed length is given in this paper. 相似文献
215.
216.
Gerecke AC Schärer M Singer HP Müller SR Schwarzenbach RP Sägesser M Ochsenbein U Popow G 《Chemosphere》2002,48(3):307-315
Concentrations of pesticides in Swiss rivers and lakes frequently exceed the Swiss quality goal of 0.1 microg/l for surface waters. In this study, concentrations of various pesticides (e.g., atrazine, diuron, mecoprop) were continuously measured in the effluents of waste water treatment plants and in two rivers during a period of four months. These measurements revealed that in the catchment of Lake Greifensee, farmers who did not perfectly comply with 'good agricultural practice' caused at least 14% of the measured agricultural herbicide load into surface waters. Pesticides, used for additional purposes in urban areas (i.e. protection of materials, conservation, etc.), entered surface waters up to 75% through waste water treatment plants. 相似文献
217.
Soils of the large sewage farm area south of Berlin are contaminated with heavy metals such as Cd, Cr, Cu, Hg, Ni, Pb, Zn. Based on earlier studies the total amount and the bioavailable proportions of heavy metals in soil samples were analysed. In some samples very high levels of total heavy metal concentrations were detected. For Pb, Cd, Cu and Hg the maximum values were 1360, 29.7, 817 and 40.8 mg/kg soil dry matter, respectively. The biovailable fractions of heavy metals which were found primarily in the acetate and EDTA fractions and to a lesser degree in the water extract account for about 50 % (Pb, Ni), 70 % (Cd) or 90% (Zn) of their total amount and may therefore pose a considerable environmental risk. 相似文献
218.
Heinz Gary H. Erdman Thomas C. Haseltine Susan D. Stafford Charles 《Environmental monitoring and assessment》1985,5(3):223-236
Residues of organochlorine pesticides, polychlorinated biphenyls (PCBs), polybrominated biphenyls (PBBs), polychlorinated styrenes (PCSs), and mercury were measured in the eggs of 10 species of colonial waterbirds nesting in areas around Green Bay or Lake Michigan from 1975 to 1980. Residues also were measured in the carcasses and brains of black-crowned night-herons (Nycticorax nycticorax). The highest residues were of PCBs, DDE, mercury, and dieldrin; for some species, levels of these chemicals possibly were high enough to have caused reproductive effects. Other organochlorine pesticides were found at low levels. Only trace amounts of PCSs and PBBs were found. Eggs of herring gulls (Larus argentatus) collected in 1977 from an island in Lake Michigan contained an average of 100 ppm PCBs and 33 ppm DDE; this was the most-contaminated species. Cattle egrets (Bubulcus ibis), the only bird that is not a fish eater, contained only small quantities of DDE and mercury. 相似文献
219.
A Gas Particle Partitioner (GPP) that allows highly efficient separation of gas and particles with no effect on the thermodynamic conditions and substantially no change of the gas composition has been developed. The GPP is a coaxial arrangement with inner and outer electrodes and utilizes a corona discharge to electrically charge the particles and a strong electric field to remove them from the sample flow. Several measures were taken to avoid an influence of the corona discharge on the gas composition. The GPP can be applied for various applications. This paper focuses on the use of the GPP as a pre-filter for gas analyzers, where zero pressure drop and a minimization of the influence of the corona discharge on the gas composition are the main objective. Due to its design, the GPP introduces no changes to the thermodynamic conditions. However, corona discharge is known to produce significant amounts of ozone and oxides of nitrogen. The effect of the corona on the gas composition of the sample flow was determined under various conditions. The gas concentrations strongly depended on several aspects, such as material and diameter of the corona wire and polarity of the corona voltage. Due to the measures taken to minimize an effect on the gas composition, the concentrations of these gases could effectively be reduced. Along with the maximum gas-particle separation efficiency of near 100%, the additional O3 concentration was 42 ppbV and the additional NO2 concentration 15 ppbV. If an efficiency of 95% is acceptable, the added concentrations can be as low as 2.5 ppbV (O3) and 0.5 ppbV (NO2), respectively. 相似文献
220.
Heinz Wilsdorf 《Die Naturwissenschaften》1951,38(11):250-258