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1.
Aqueous 2-chloronapthalene was contacted with cast iron in batch systems, resulting in an initial rapid increase in the sorbed 2-chloronapthalene concentration (C s ) followed by a slow decline, and an initial rapid decline in the aqueous 2-chloronapthalene concentration (C a ) followed by a slower decline. The initial rapid partitioning of 2-chloronapthalene to the solid phase was due to its adsorption on elemental carbon present on the cast iron surface, while the residual aqueous phase 2-chloronapthalene underwent reductive dehalogenation at a slower rate through interaction with the metallic iron surface. The overall rate of change of total 2-chloronapthalene concentration (C T = C s +C a ) with time, i.e., (d/C T }{{d}t}) could be described by the expression,?k 1 ?M? (C a ) n , where M is the concentration of cast iron. The values of k 1 and n were determined to be 1.576 × 10?5 hr?1 g?1 iron L and 1.945 respectively. Equilibrium partitioning of 2-chloronapthalene between solid and aqueous phases could be described by a Freundlich isotherm, C s = K? [C a ] m , where m and K were determined to be 0.55 and 4.92 × 10?3 L g?1. Considering K to be the ratio of the adsorption (k 2) and desorption (k 3) rate constants, expressions were developed for describing the evolution of C s and C a with time. Putting k 3 = 1 hr?1 in these expressions resulted in adequate model fit to the experimental data. Napthalene was identified as the major dehalogenation by-product, with greater than 99 percent of the naphthalene produced partitioning to carbon present on the cast iron surface. No competition between 2-chloronapthalene and naphthalene for adsorption on the carbon surface was observed, suggesting non-specific adsorption of these compounds restricted only by the physical size of the molecules and the available carbon surface area.  相似文献   

2.
Irrigation with low-quality water may change soil hydraulic properties due to excessive electrical conductivity (ECw) and sodium adsorption ratio (SARw). Field experiments were conducted to determine the effects of water quality (ECw of 0.5–20 dS m?1 and SARw of 0.5–40 mol0.5 l?0.5) on the hydraulic properties of a sandy clay loam soil (containing ～421 g gravel kg?1 soil) at applied tensions of 0–0.2 m. The mean unsaturated hydraulic conductivity [K(ψ)], sorptive number (α) and sorptivity coefficient (S) varied with change in ECw and SARw as quadratic or power equations, whereas macroscopic capillary length, λ, varied as quadratic or logarithmic equations. The maximum value of K(ψ) was obtained with a ECw/SARw of 10 dS m?1/20 mol0.5 l?0.5 at tensions of 0.2 and 0.15 m, and with 10 dS m?1/10 mol0.5 l?0.5 at other tensions. Changes in K(ψ) due to the application of ECw and SARw decreased as applied tension increased. Analysis indicated that 13.7 and 86.3% of water flow corresponded to soil pore diameters <1.5 and >1.5 μm, respectively, confirming that macropores are dominant in the studied soil. The findings indicated that use of saline waters with an EC of <10 dS m?1 can improve soil hydraulic properties in such soils. Irrigation waters with SARw < 20 mol0.5 l?0.5 may not adversely affect hydraulic attributes at early time; although higher SARw may negatively affect them.  相似文献   

3.
The goals of the study were to determine the effectiveness of a laboratory-scale biofilter on the removal of methyl tert-butyl ether (MTBE) and investigate the operating parameter effects on biofilter performance. The experimental results show that average MTBE removals of 53.6–93.2% were observed at loads of 2.5–20.1 gm?3 h?1 and an empty-bed residence time of three minutes, after continuous operation for four months throughout the biofilter acclimation period. After a one-day recovery period operation, the biofilter system recovered from the introduction of a shock load. More than 99% removal efficiencies were achieved for the inlet MTBE concentration at 50 ppmv and with the highest residence time. MTBE removals at the bottom section of the biofilter were consistently lower than for the top section, which was attributed to insufficient microorganism growth in the bottom section. The parameters estimated by using the Michaelis-Menten equation were 1.116 ± 0.51 ppmv s?1 for the maximum removal rate (V m ), and 26.38 ± 17.21 ppmv for the half-saturation constant (Ks), evaluated at the biofilter exit.  相似文献   

4.
Air pollution can be a problem in industrial processes, but monitoring and controling the aerosols in the work place is not enough to estimate the occupational risk due to dust particle inhalation. The solubility in lung fluid is considered to estimate this risk. The aim of this study is to determine in vitro specific dissolution parameters for thorium (Th), uranium (U), and tantalum (Ta) associated to crystal lattice of a niobium mineral (pyrochlore). Th, U, and Ta dissolution factors in vitro were obtained using the Gamble solution (simulant lung fluid, SLF), particle induced X-ray emission, and alpha spectrometry as analytical techniques. Ta, Th, and U are present in the pyrochlore crystal lattice as oxide; however, they have shown different dissolution parameters. The rapid dissolution fraction (f r), rapid dissolution rate (λ r), slow dissolution rate (f s), and slow dissolution fraction (λ s) measured for tantalum oxide were equal to 0.1 and 0.45 and 0.00007 day?1, respectively. For uranium oxide, f r was equal to 0.05, λ r was equal to 1.1 day?1, and λ s was equal to 0.000068 day?1. For thorium oxide, f r was 0.025, λ r was 1.5 day?1, and λ s was 0.000065 day?1. These results show that chemical behavior of these three compounds in the SLF could not be represented by the same parameter. The ratio of uranium concentration in urine and feces samples from workers exposed to pyrochlore dust particle was determined. These values agree with the theoretical values of estimated uranium concentration using specific parameters for uranium oxide present in pyrochlore.  相似文献   

5.
Agrichemical spills and discharges to soil can cause point-source contamination of surface and ground waters. When high contaminant concentrations inhibit natural attenuation in soils, chemical treatments can be used to promote degradation and allow application of treated soils to agricultural lands. This approach was used to remediate soil containing >650 mg atrazine, >170 mg metolachlor and >18,000 mg nitrate kg?1. Results indicated a decrease in metolachlor concentration to <1 mg kg?1 within 95 days of chemical treatment with zerovalent iron (Fe0, 5% w/w) and aluminum sulfate (Al2(SO4)3, 2% w/w) but after one year >150 mg atrazine and >7000 mg nitrate kg?1 remained. Laboratory experiments confirmed that subsequent additions of sucrose (table sugar) to the chemically pretreated soil promoted further reductions in atrazine and nitrate concentrations. Field-scale results showed that adding 5% (w/w) sucrose to windrowed and pretreated soil significantly reduced atrazine (<38 mg kg?1) and nitrate (<2,100 mg kg?1) concentrations and allowed for land application of the treated soil. These results provide evidence that zerovalent iron in combination with Al2(SO4)3 and sucrose can be used for on-site, field-scale treatment of pesticide- and nitrate-contaminated soil.  相似文献   

6.
Using an improved titration technique, Lee and Brosset (1978) have established the presence in a number of lake waters of an acid withk a = 3 × 10?4. It is shown that higher concentrations of this acid, which seems to correspond to a functional group of humus, may under certain conditions drastically contribute to the lowering of pH of lake water.  相似文献   

7.
A higher-order closure model for canopy/surface exchange is presented and applied to an oak-hickory forest to model SO2 deposition for typical summertime conditions. The model is then used as a tool to investigate the sensitivity of modeled fluxes (the deposition velocity) and concentration profiles to the parameters used to compute the leaf boundary layer and stomatal resistances. Both the deposition velocity and concentration profiles show little sensitivity to variations in the leaf boundary-layer resistance (r b) since it generally comprises only a small fraction of the total resistance to diffusion from the air to the sub-stomatal cavity. The deposition velocity (V d ) is more sensitive to variations in the minimum stomatal resistance (r s ,min) and light response coefficient (β) than r b .It was found that 50% variations in β give a maximum difference of 0.2 cm s?1 in V d while 30% variations in r s , min produce a maximum difference of near 0.3 cm s?1.  相似文献   

8.

Purpose

This study was developed to improve understanding of the temporal variability of sediment delivery in a representative, intensively agricultural, headwater system of the U.S. Midwest by identifying the primary sediment source (i.e., uplands or channel banks) to the fine suspended sediment loads of three consecutive runoff events (with the third event being a flash flood) using naturally occurring radionuclides.

Materials and methods

Suspended sediment concentrations (C s) from discrete and continuous sampling techniques agreed well despite differences in operating principles. The total sediment flux (Q s) during each event was quantified over a 24-h period from the initiation of the rainfall using the following: (1) measured C s and flow discharges (Q w); (2) individual Q w?CQ s relationships for each event (herein called individual event relationships); and (3) a cumulative Q w?CQ s rating curve. The radionuclide tracers, beryllium-7 (7Be) and excess lead-210 (210Pbxs), were used with a simple two end-member mixing model to differentiate eroded upland surface soils and channel-derived sediments in the suspended loads of each event.

Results and discussion

Total load estimates from the measurement-based values and individual event relationships were similar, within 10?%, because they accounted for an observed non-linearity between C s and Q w (i.e., a clockwise hysteresis) during the events. The sediment rating curve assumed a linear relationship between C s and Q w and under-estimated the loads of the first two events while over-estimating the load of the flood event. The radionuclide partitioning quantified the proportion of eroded upland soils at 67?% for the first event, which was attributed to a ??first flush?? of readily available material from past events. For the subsequent and flood-event loads, 34?% and 21?% were respectively derived from the uplands, because less material was readily available for mobilization. Proportions are based on integrated samples for each event and are consistent with individual samples where available. During the flood event, stream bank mass failure was observed and bank erosion estimates from multiple methods compared favorably with the load results.

Conclusions

The radionuclide analysis showed decreasing proportions of eroded upland soils in the loads of the three successive events that was supported by observed clockwise hysteresis from source material exhaustion. Decreasing slopes observed in successive hysteresis plots for the events suggested that less material was readily available for mobilization following the first event flushing. The results of this study can assist watershed planners in identifying erosion-prone areas and determining optimal management strategies for sediment control.  相似文献   

9.
Reaeration coefficient (k), the rate of oxygen exchange between the atmosphere and water surface, is an important parameter for understanding water quality impairment and stream metabolism. We modified the propane injection method to measure gas exchange coefficients and evaluated its application for small streams. The tracer solution was prepared by solubilizing propane directly in a conservative solute solution, and it was injected as a constant-rate injection, a single slug, or an extended slug. Water samples were taken at four to five sampling stations along the study reach at the tracer concentration peak, and propane and conductivity were measured. The propane exchange rate (k propane) was calculated using the regression method with the propane/conductivity ratio against solute travel time (in hours). The mixed tracer injection method was conducted in four streams, and all k propane measurements (n?=?8) were statistically significant (p?<?0.05). The short-duration constant rate injection and extended slug injection provided k propane estimates with higher r 2 than the single slug injection. The k 20 measured with propane injection ranged from 5.4 to 40.0?day?1, and they were significantly correlated with empirically estimated k. The mixed tracer injection method with propane could potentially reduce field time, crew demands, and field equipment; thus, it would potentially lower the overall cost of gas exchange coefficient measurements and be an effective method in small, remote streams.  相似文献   

10.
The decomposition of rice and barley straw saccharides under field conditions was well represented by the first-order kinetics model of Yt=C1e?k1t+C2e?k2t, where Yt is the remaining amount at time t, k1 and k2 are the decomposition rate constants (time?1) for the labile fraction (C1) and the non-labile fraction (C2), respectively. About 82% of the total saccharide content of the rice straw was in the labile fraction with a rate constant 0.64–0.81, the values for the barley straw being 70–92% and 0.50–0.61, respectively. The non-labile fraction appeared to persist for a long time, with a half-value period of 9–59 months. Barley straw and its saccharides decomposed at a slower rate than rice straw. Much more favourable initial decomposition was observed in a paddy field than in an upland field. Mannose, fucose, rhamnose and ribose were synthesized in parallel with the flush of decomposition of straw saccharides.  相似文献   

11.
Searching for an effective and economical sand stabilization measure has an important significance in wind erosion control. Wind tunnel experiments were conducted to evaluate the sand-fixing effect of fly ash (FA) at three different application rates (10, 20, and 30?% (w/w) soil). The additional effect of polyacrylamide (PAM) was also studied under two different application rates (0.05 and 0.1?% (w/w) soil) on the basis of the optimum FA usage. The results indicated that the utilization of FA increased the threshold wind speed of the treated soil significantly, which was further increased by the addition of PAM. The soil treated with 20?% FA could most effectively withstand the pure wind with a wind speed of 8?m?s?1 for 10?min, while only the slightest wind erosion occurred after exposure to the sand-carrying wind with a wind speed of 8?m?s?1 for 10?min. However, moderate wind erosion occurred after exposure to both the pure wind and the sand-carrying wind with a wind speed of 14?m?s?1 for 10?min, respectively, and there was a decline in the wind erosion rate with the increase of FA application rate. The soil treated with 20?% FA and 0.05 or 0.1?% PAM could effectively withstand the pure wind with a wind speed of 14?m?s?1 for 30?min, while only the slightest wind erosion occurred after exposure to the sand-carrying wind with a wind speed of 14?m?s?1 for 30?min. The combination of a 20?% FA and 0.05?% PAM application rate is recommended to give effective and economical wind erosion protection.  相似文献   

12.
This paper describes the use of dry free hanging filters, as passive samplers to determine ozone in the ambient air. The filters, with a diameter of 25?mm, were impregnated with 5,5??-disodium indigo disulphonate (IDS), a reagent for ozone. From the amount of reacted indigo compound, found on the filter, and the ozone concentration in the ambient air, a pseudo rate constant k 1, of the reaction between ozone (O3) and IDS on the filter, is calculated. The range of measurement is between 9 and 205???g/m3 ambient ozone. The dry filter method is specific for ozone, while the Dutch standard method NEN2789, based on an aqueous solution of IDS, has to be corrected for the presence of NO x . From wind tunnel and field experiments, k 1 proved to vary between 0.7 and 1.5?×?10?6?m3?s?1 (??g O3)?1 at wind velocities between 1 and 3?m/s and at an exposure time of 60?min. Within these conditions, ozone concentrations have been determined with free hanging filters in four busy streets in Yogyakarta, Indonesia and at two background sites using an average value of k 1 of 1.2?×?10?6. Subsequently, the traffic NO emission was estimated from the difference of the O3 concentrations at both sides of a road. For an arbitrary situation, an NO emission of 255???g/s per metre road length was calculated. The filter method is inexpensive and practical, needs no electricity, is easily assembled and can be used to perform measurements in remote areas. It is shown here that this simple measurement technique may support air quality studies, e.g., in developing countries.  相似文献   

13.
The relationship between salinity (S), chlorinity (Cl) and density (d) for the ion polluted (S = 3 to 4.5‰) and stratified Onondaga Lake are presented. The data base includes 220 determinations of the major ionic components collected from ten equally spaced depths. The salinity (S) and ionic strength (I) in the lake can be estimated from S = 1.85 Cl ? 0.28, where Cl is in g kg?1 and I = 1.456 [Cl?] ? 0.039, where [Cl] is in mmol L?1. Due to the high concentration of Ca2+ in the lake, the seawater equation of state (Chen and Millero, 1977a) could not be used to estimate reliable densities for the lake (Δd ～ 100 × 10?6 g cm?3). A reliable equation of state for Onondaga Lake was derived from the composition data $$d = d_0 + A_v {\text{ }}CL + B_v {\text{ }}Cl^{3/2} $$ where d 0 is the density of water (g cm?3), A v is a temperature dependent parameter related to the infinite dilution apparent molal volumes and B v is related to the ion-ion interactions of the lake salts. The high ionic content of the lake depresses the temperature of maximum density to 3.18°C and alters the stratification of the lake. The salinity component of the stratification represents 40% of the total density stratification.  相似文献   

14.
The reaeration coefficient (K a) is an essential parameter to predict the dissolved-oxygen concentration in different aquatic ecosystems. The techniques applied to K a estimates require considerable efforts, since measuring this coefficient is a laborious and expensive task. Thus, the use of predictive equations wherein K a is found through hydraulic flow parameters is common. However, the available prediction equations lead to estimates often different from each other. A new predictive equation is addressed in the present study. The insertion of a dimensionless number resulting from the relation between the RMS (Root Mean Square) of the free-surface vertical velocity and the surface flow velocity is the great innovation of the study. The reaeration experiments and the surface vertical velocity mapping were performed in a circular hydraulic channel. The flow velocity varied from 0.25 to 0.64 m s?1, and depth varied from 0.09 to 0.15 m. The new equation led to more accurate results than the equations based on traditional hydraulic parameters such as the Reynolds and Froude numbers, mainly when it comes to K a values higher than 40 day?1. The sensitivity analysis has shown that the new dimensionless number is the most sensitive parameter of the herein proposed predictive equation and that the influence from the Reynolds and Froude numbers on K a weakens as turbulence gets more intense.  相似文献   

15.

Purpose

Nitrous oxide (N2O) production and reduction rates are dependent on the interactions with each other and it is therefore important to evaluate them within the context of simultaneously operating N2O emission and reduction. The objective of this study was to quantify the simultaneously occurring N2O emission and reduction across a range of subtropical soils in China, to gain a mechanistic understanding of potential N2O dynamics under the denitrification condition and their important drivers, and to evaluate the potential role of the subtropical soils as either sources or sinks of N2O through denitrification.

Materials and methods

Soils (45, from a range of different land uses and soil parent materials) were collected from the subtropical region of Jiangxi Province, China, and tested for their potential capacity for N2O emission and N2O reduction to N2 during denitrification. N2O emission and reduction were determined in a closed system under N2 headspace after the soils were treated with 200?mg?kg?1 NO 3 ? -N and incubation at 30?°C for 28?days. The soil physical and chemical properties, the temporal variations in headspace N2O concentration, and NO 3 ? -N and NH 4 + -N concentrations in the soil slurry were measured.

Results and discussion

Variations in N2O concentration (N) over incubation time (t) were consistent with an equation in which average R 2?=?0.84?±?0.11 (p?<?0.05): $ N = A \times \left( {1 - \exp \left( { - {k_1} \times t} \right)} \right) - B \times \exp \left( {{k_2} \times t} \right) $ , where A is the total N2O emission during the incubation, B is a constant, and k 1 and k 2 are the N2O emission constant and reduction constants, respectively. The results of the simulation showed that k 1 was greater than k 2. The reduced amount of NO 3 ? -N in the first 7?days of incubation and the N2O emission rate (the percentage of A value relative to the amount of NO 3 ? -N reduced during the 28-day incubation, R n) were able to explain 82.9?% (p?<?0.01) of the variation in total N2O emission (A) during the incubation for the soil samples studied, indicating that the total amount of N2O emitted was determined predominately by denitrification capacity. Soil organic carbon content and soil nitrogen mineralization are the key factors that determine differences in the amounts of reduced NO 3 ? -N among the soil samples. The R n value decreased with increasing k 2 (p?<?0.01), indicating that soils with higher N2O reduction capacity under these incubation conditions would emit less N2O per unit of denitrified NO 3 ? -N than the other soils. Results are valuable in the evaluation of net N2O emissions in the subtropical soils and the global N budget.

Conclusions

In a closed, anaerobic system, variations in N2O concentration in the headspace over the incubation time were found to be compatible with a nonlinear equation. Soil organic carbon and the amount of NH 4 + -N mineralized from the organic N during the first 7?days of incubation are the key factors that determine differences in the N2O emission constant (k 1), the N2O reduction constant (k 2), the total N2O emission during the incubation (A) and the N2O emission rate (R n).  相似文献   

16.
A Gram-negative bacterium strain LWD09, capable of growing aerobically on 3,4-dichloroaniline (DCA) as the sole carbon and energy source, was isolated from the farm field. This bacterium was identified as Myroides odoratimimus strain by morphological, physiological, and biochemical characteristics as well as 16S rDNA sequence. Analysis of culture pH, temperature, cells growth, and DCA concentration demonstrated that strain LWD09 could effectively degrade DCA without a lag phase. The kinetics of DCA degradation was well described using the Andrews equation, and the kinetic parameters were as follows: q max?=?1.74?h?1, K s?=?43.5?mg?L?1, and K i?=?230.3?mg?L?1. In addition, strain LWD09 was found to be moderately halophilic and showed the highest power of DCA degradation in 5% NaCl (w/w, %). With initial concentrations of 30, 100, and 200?mg?L?1, 100%, 80.4%, and 33.2% of DCA were transformed after 96?h in 5% NaCl, respectively. These results suggest that strain LWD09 has the potential to degrade DCA in saline wastewater. To date, this is the first report on the degradation of DCA by a M. odoratimimus strain with moderate salinity tolerance.  相似文献   

17.
Abstract

Heavy‐metal inhibition of nitrification in soils treated with reformulated nitrapyrin was investigated. Clarion and Okoboji soils were treated with ammonium sulfate [(NH4)2SO4] and a nitrification inhibitor. Copper(II) (Cu), Zinc(II) (Zn), Cadmium(II) (Cd), or Lead(II) (Pb) were added to each soil. A first‐order equation was used to calculate the maximum nitrification rate (K max), duration of lag period (t′), period of maximum nitrification (Δt), and the termination period of nitrification (t s). In the Clarion soil, the K max decreased from 12 mg kg?1 d?1 without the nitrification inhibitor to 4, 0.25, 0.86, and 0.27 mg kg?1 d?1, respectively, when the inhibitor and Cu, Zn, Pb, or Cd were applied. In the Okoboji soil, K max decreased from 22 mg kg?1 d?1 with no inhibitor to 6, 3, 4, and 2 mg kg?1 d?1, respectively, when an inhibitor and Cu, Zn, Pb, or Cd were added. The t′ varied from 8 to 25 d in the Clarion soil and from 5 to 25 d in the Okoboji soil, due to addition of Cu, Zn, Pb, or Cd and the inhibitor.  相似文献   

18.
Pedo-transfer functions (PTFs) have been widely used to estimate soil hydraulic properties in the simulation of catchment eco-hydrological processes. However, the accuracy of existing PTFs is usually inadequate for use. To develop PTFs for local use, soil columns were collected from a double rice-cropped agricultural catchment in subtropical central China. The PTFs for saturated soil hydraulic conductivity (Ks) and parameters (θs, α, and n) of the van Genuchten model for the soil water retention curve (SWRC) were obtained based on soil’s basic properties, and compared with models developed by Li et al. in 2007 and Wösten et al. in 1999, respectively. Our results indicated that Ks in the range of 0.04–1087 cm d?1 and θs in the range of 0.34–0.51 cm3 cm?3 were both well estimated with the R2adj of 0.72 and 0.87, respectively, but α (0.04–0.65 cm?1) and n (1.05–1.21) were relatively poorly predicted with the respective R2adj of 0.38 and 0.55, despite the use of more input parameters. Our local derived PTFs outperformed the other two existing models. However, if the local PTFs for paddy soils are not available, the Wösten et al. 1999 model can be proposed as a useful alternative. Therefore, this study can improve our understanding of the development and application of PTFs for predicting paddy soil hydraulic properties in China.  相似文献   

19.
Because soil hydraulic properties are indispensable for determining soil water retention and soil solute movement, their input for simulation models is essential. Many of these parameters cannot be estimated directly at the scale of interest, but can only be derived through inverse modeling. During this process, the parameters are generally adjusted using least-squares approach with Levenberg–Marquardt (LM) algorithms in which numerically simulated models are fitted to measured data. In this study we used a new inverse method to estimate the unsaturated soil hydro-dispersive properties from in-situ experiments. The method employs complex-variable-differentiation method (CVDM) to accurately predict of the hydraulic properties of the van Genuchten–Mualem models (θr, θs, α, ks, n). To the knowledge of the authors, it is first study use CVDM in soil physics. The optimization procedure was performed by using a continuous data set of daily in situ soil water content and bromide concentration measurements. Estimated parameters during the inversion showed high correlation (R2 = 0.88, RMSE = 0.013 and the model efficiency CE = 0.77) by using the CVDM-methods with the actual field measurements, compared with the traditional LM-algorithm (R2 = 0.81, RMSE = 0.021 and CE = 0.626). The results show that the new inverse analysis in the present work has the high accuracy, validity, uniqueness, and higher inversion efficiency. Meanwhile, the convergence and stability of the modified LM-algorithm are improved. Overall, it was concluded that the CVDM is promising method to estimate hydro-dispersive parameters in soil physics.  相似文献   

20.
The kinetics of cadmium uptake by Selenastrum capricornutum Printz was studied at 21 °C and 0 °C and at four different concentrations of free cadmium (10?9, 10?8, 10?7 and 10?3 M). The free cadmium concentrations in the medium were kept constant through buffering by a chelating agent (NTA). Initial uptake occurred within 10 min at both temperatures, indicating a fast process. At 21 °C, the cadmium uptake increased during the experimental sampling times from 0.12 to 50 h, whereas at 0 °C, the cadmium uptake remained constant after the first sampling time. Apparently, two different processes were involved in cadmium uptake, a first fast, probably passive process and a second slower, possibly physiological process. The cadmium uptake processes are described with a generalized metalligand complex formation model. The experimental dissociation constants for the fast (K R,F ) and the slow process (K R,S ) were reproducible for different experiments and they were both in the order of 5 10?6 mol L?1. For the slow process, the uptake- and release rate constants (k1 and k2) were quantified; for two experiments, the mean value for ki was 111±28 L mol?1 h?1 and the mean value for k 2 was (5.1±1.8) 10?4 h?1. These values were calculated using the fitted value of the cadmium uptake in the fast process.  相似文献   

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