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391.
In this paper, Loofa egyptiaca (LE), an agricultural plant cultivated in Egypt, was used to prepare low-cost activated carbon (LEC1 and LEC2) adsorbents. The adsorbents (LE, LEC1 and LEC2) were evaluated for their ability to remove direct blue 106 dye from aqueous solutions. Batch mode experiments were conducted using various parameters such as pH, contact time, dye concentration and adsorbent concentration. The surface chemistry of LE, LEC1 and LEC2 was analyzed by scanning electron microscopy (SEM). The experimental data were examined using Langmuir, Freundlich, Temkin and Harkins–Jura isotherms. The results showed that the adsorption of direct blue 106 was maximal at the lowest value of pH (pH = 2). Removal efficiency was increased with an increase in dye concentration and a decrease in amount of adsorbent. Maximum adsorption capacity was found to be 57.14, 63.3 and 73.53 mg/g for LE, LEC1 and LEC2 respectively. Kinetics were also investigated using pseudo-first-order, pseudo-second-order and intra-particle diffusion models. The experimental data fitted very well with the pseudo-first-order and pseudo-second-order kinetic models. The results indicate that LE, LEC1 and LEC2 could be employed as adsorbents for the removal of direct blue dye from aqueous solutions. 相似文献
392.
393.
Daniel Q. Tong Nicholas Z. Muller Haidong Kan Robert O. Mendelsohn 《Environment international》2009,35(8):1109-1117
Human exposure to ambient ozone (O3) has been linked to a variety of adverse health effects. The ozone level at a location is contributed by local production, regional transport, and background ozone. This study combines detailed emission inventory, air quality modeling, and census data to investigate the source–receptor relationships between nitrogen oxides (NOx) emissions and population exposure to ambient O3 in 48 states over the continental United States. By removing NOx emissions from each state one at a time, we calculate the change in O3 exposures by examining the difference between the base and the sensitivity simulations. Based on the 49 simulations, we construct state-level and census region-level source–receptor matrices describing the relationships among these states/regions. We find that, for 43 receptor states, cumulative NOx emissions from upwind states contribute more to O3 exposures than the state's own emissions. In-state emissions are responsible for less than 15% of O3 exposures in 90% of U.S. states. A state's NOx emissions can influence 2 to 40 downwind states by at least a 0.1 ppbv change in population-averaged O3 exposure. The results suggest that the U.S. generally needs a regional strategy to effectively reduce O3 exposures. But the current regional emission control program in the U.S. is a cap-and-trade program that assumes the marginal damage of every ton of NOx is equal. In this study, the average O3 exposures caused by one ton of NOx emissions ranges from ? 2.0 to 2.3 ppm-people-hours depending on the state. The actual damage caused by one ton of NOx emissions varies considerably over space. 相似文献
394.
L. León Vintró P.I. Mitchell A. Omarova M. Burkitbayev H. Jiménez Nápoles N.D. Priest 《Journal of environmental radioactivity》2009
New data are reported on the concentrations, isotopic composition and speciation of americium, plutonium and uranium in surface and ground waters in the Sarzhal region of the Semipalatinsk Test Site, and an adjacent area including the settlement of Sarzhal. The data relate to filtered water and suspended particulate from (a) streams originating in the Degelen Mountains, (b) the Tel′kem 1 and Tel′kem 2 atomic craters, and (c) wells on farms located within the study area and at Sarzhal. The measurements show that 241Am, 239,240Pu and 238U concentrations in well waters within the study area are in the range 0.04–87 mBq dm−3, 0.7–99 mBq dm−3, and 74–213 mBq dm−3, respectively, and for 241Am and 239,240Pu are elevated above the levels expected solely on the basis of global fallout. Concentrations in streams sourced in the Degelen Mountains are similar, while concentrations in the two water-filled atomic craters are somewhat higher. Suspended particulate concentrations in well waters vary considerably, though median values are very low, at 0.01 mBq dm−3, 0.08 mBq dm−3 and 0.32 mBq dm−3 for 241Am, 239,240Pu and 238U, respectively. The 235U/238U isotopic ratio in almost all well and stream waters is slightly elevated above the ‘best estimate’ value for natural uranium worldwide, suggesting that some of the uranium in these waters is of test-site provenance. Redox analysis shows that on average most of the plutonium present in the microfiltered fraction of these waters is in a chemically reduced form (mean 69%; 95% confidence interval 53–85%). In the case of the atomic craters, the proportion is even higher. As expected, all of the americium present appears to be in a reduced form. Calculations suggest that annual committed effective doses to individual adults arising from the daily ingestion of these well waters are in the range 11–42 μSv (mean 21 μSv). Presently, the ground water feeding these wells would not appear to be contaminated with radioactivity from past underground testing in the Degelen Mountains or from the Tel′kem explosions. 相似文献
395.
Fertilization with 2.5 t/ha limestone: (83% CaCO3, 8% MgO, 6% K2O, 3% P2O5) reduces the 137Cs transfer from spruce forest soil into plants like fern (Dryopteris carthusiana) and blackberry (Rubus fruticosus) by a factor of 2–5 during at least 11 years as measured by the aggregated transfer factor Tag. In 1997 and 2006 these results were confirmed by additional measurements of the 137Cs transfer factor TF, related to the root zone (Oh horizon), which were explained by the selective sorption of 137Cs in the root zone by measurements of the Radiocaesium Interception Potential (RIP) in fertilized (RIP > 179 meq/kg) and non-fertilized soils (RIP < 74 meq/kg). 相似文献
396.
J.T. Smith N.V. Sasina A.I. Kryshev N.V. Belova A.V. Kudelsky 《Journal of environmental radioactivity》2009
Empirical relations between the 90Sr concentration factor (CF) and the calcium concentration in freshwater aquatic systems have previously been determined in studies based on data obtained prior to the Chernobyl accident. The purpose of the present research is to review and compare these models, and to test them against a database of post-Chernobyl measurements from rivers and lakes in Ukraine, Russia, Belarus and Finland. It was found that two independently developed models, based on pre-Chernobyl empirical data, are in close agreement with each other, and with empirical data. Testing of both models against new data obtained after the Chernobyl accident confirms the models’ predictive ability. An investigation of the influence of fish size on 90Sr accumulation showed no significant relationship, though the data set was somewhat limited. 相似文献
397.
Typologically identical (dwarf birch-herb-dwarf shrub-moss) open and closed larch forests growing on the same altitudinal transect have proved to differ in the structural-functional organization of lower vegetation layers. Coverage, general species composition, and species richness of the herb-dwarf shrub layer are higher in the open forest than in the closed forest. Correlations between individual species of vascular plants weaken upon transition from the open to the closed forest. Conversely, the coverage of the lichen-moss layer increases in the closed forest, which contributes to its role as a factor of selection of vascular plant species against the background of the prevailing influence of the tree layer. 相似文献
398.
399.
The results of studies on postfire succession in larch forests of the permafrost zone are discussed. The main directions of successional processes in burned-out areas of different ages are described. It has been shown that secondary pyrogenic successions in larch forests follow the scheme of rapid regeneration without tree species replacement and the model of succession tolerance. Groups of plant species with different life strategies and indicator species characterizing different stages of the overgrowing of burned-out areas have been identified. 相似文献
400.
The remote effect of the nuclear polyhedrosis virus on the gypsy moth was studied for the first time under natural conditions.
In the generation that developed from infected eggs, the weight of pupae was reduced, sex ratio was altered, and female fecundity
and egg fertility were lower than in control individuals. The F1 progeny of these moths were characterized by an increased rate of latent virus carriage and high mortality caused by the
combined effect of polyhedrosis and insect parasites. 相似文献