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51.
Transport modeling of copper and cadmium with linear and nonlinear retardation factors 总被引:2,自引:0,他引:2
The predictive accuracy of using the one-dimensional advection–dispersion equation to evaluate the fate and transport of solute in a soil column is usually dependent on the proper determination of chemical retardation factors. Typically, the distribution coefficient (Kd) obtained by fitting the linear sorption isotherm has been extensively used to consider general geochemical reactions on solute transport in a low-concentration range. However, the linear distribution coefficient cannot be adequately utilized to describe the solute fate at a higher concentration level. This study employed the nonlinear equilibrium-controlled sorption parameters to determine the retardation factor used in column leaching experiments. Copper and cadmium transportation in a lateritic silty-clay soil column was examined. Through the explicit finite-difference calculations with a third-order total-variation-diminishing (TVD) numerical solution scheme, all results of the theoretical copper and cadmium breakthrough curves (BTCs) simulated by using the Freundlich nonlinear retardation factors revealed good agreement with the experimental observations. 相似文献
52.
Lian Ming Linhui Li YingXin Zhang Weiyun Lin Guanzhu Wang Sai Zhang 《Chemistry and Ecology》2014,30(1):76-86
Lab-scale experiments were conducted to investigate the effects of dissolved organic matter (DOM) on the desorption of Cd in freeze–thaw treated Cd-contaminated soils. The results indicated that DOM significantly facilitated the desorption of Cd from freeze–thaw treated soils when comparing with that of non-frozen soils. Effects of DOM on the Cd desorption were highly dependent on the soil type and contamination concentration. The maximum desorption ratios of Cd by DOM generated from straw and sludge were 15.6% and 13.65%, respectively, in brown soils, and the maximum desorption ratios reached 14.7% and 9.3%, respectively, when using black soils through the same treatment. The higher the Cd contamination concentration in soils, the higher the ratio of Cd desorption by DOM. This was because of the integrated effects of the soil properties changed by the freeze–thaw treatment and the species transformation of Cd. The characteristics of DOM, such as its concentration and properties, had shown obvious impacts on the Cd desorption by DOM. The desorption was promoted with the increased DOM concentration and the hydrophilic fraction, and lowered pH and the low-molecular-weight of DOM. 相似文献
53.
Cadmium biosorption properties of non-living, dried river green alga from a river source, and water hyacinth weed, Eichhornia crassipes from a lake in Zimbabwe have been investigated. The cadmium uptake was found to depend on initial pH, uptake being apparently minimal at low pH values and increasing with an increase in pH. Cadmium biosorption kinetics by both samples is fast, with 80% of total uptake occurring within 60?min. The effect of initial solution pH and initial cadmium concentration on cadmium biosorption from a cadmium solution has been studied. The data for algal biomass fitted the Langmuir monolayer adsorption isotherm, while the biosorption of the metal by water hyacinth weed fitted the Freundlich adsorption isotherm with 1/n values all less than 1. Maximum metal uptake capacities were recorded using 0.35?g of biomass and a 250?mg?L?1 cadmium solution at pH 6.5 and at 25°C and these were about 85 and 50?mg?L?1 for water hyacinth weed and green alga, respectively, showing that water hyacinth weed offered a greater potential for cadmium uptake. The absorption was described by pseudo-second order rate model and the rate constant and equilibrium sorption capacity are reported. 相似文献
54.
The effects of Cd at environmental concentrations (0–32 µg/L) on the green alga Parachlorella kessleri were investigated. At about 3 µg Cd/L, toxic effects of Cd are becoming evident, much lower than reported previously. At 8 µg/L and higher, pronounced adverse effects on growth, cell morphology, size, and physiological state are seen. Therefore, levels lower than 2 µg Cd/L should be employed to produce Cd-carrying algae for feeding experiments with organisms on the next trophic level, e.g. mussels, to avoid reduced food uptake. These findings also suggest that aquatic ecosystem conditions can be indirectly influenced via the impairment of the nutritional value of algae since they are the basic organisms of aquatic food chains. 相似文献
55.
AbstractInteraction of Se up to 8?mg?kg?1 soil and Cd at 5 and 15?mg?kg?1 soil in wheat at different salinities was evaluated. Se concentrations in wheat shoots were progressively increased in parallel to Se in soil but decreased by addition of Cd. With increasing salinity, Cd concentrations increased and Se decreased. At low salinity, low addition of Se to the soil reduced Cd accumulation. At moderate and high salinities, only high Se amendment led to decline in Cd uptake, at the expense of reduction in biomass yield. Se at 0.5?mg?kg?1 soil alleviated the negative effect of Cd on shoot yield. 相似文献
56.
Paul Jacquet 《毒物与环境化学》2013,95(4):269-285
Actually, embryos can be cultured from the one‐cell stage up to the blastocyst stage, and their development can be easily monitored at any time: severe effects caused by toxic compounds are traduced by rapid embryonic death, less pronounced effects can be expressed by a lowered cleavage activity or by an arrest of the development from a particular stage. The system can be improved by transferring the embryos at the blastocyst stage in another more complete medium where they can “implant”; and form an inner cell mass with differentiated ectoderm and endoderm. Since last years, it has also become possible to culture postimplantation rodent embryos for short periods involving a number of particularly critical stages of organogenesis, such as the formation and closure of the anterior neuropore. Embryo‐culture also represents a useful system to study cytogenetic effects of chemicals which are often linked to lethal or teratogenic effects. These different possibilities are illustrated by examples of studies already performed with metals, and dealing with their teratogenic and/or cytogenetic effects on pre‐ and postimplantation rodents. 相似文献
57.
Complex formation of Cd2+ and Zn2+ with thiol derivatives has been investigated by differential pulse polarography. The binding of Cd2+ and Zn2+ with cysteine (CySH), glutathione (GSH) and the model peptide N‐acetyl‐cysteine‐methylamide (ASH) reveals different stoichiometry. Thus, Cd2+ forms 1:1 and 1:2 complexes with CySH while 1:2 and 1:4 complexes have been observed with GSH and ASH, respectively. Overall formation constants of Cd2+ with CySH (Iogβ 2 15.3) and with GSH (Iogβ52 14.4) have been estimated using competitive complexation with nitrilotriacetic acid (NTA). Investigation of competition between Zn2+ and Cd2+ for the thiol complexation has underlined the role played by the amino group in CySH for the stabilization of Zn complexes in contrary to Cd complexes. 相似文献
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