Intestinal absorption of the acetamiprid neonicotinoid by Caco-2 cells: Transepithelial transport,cellular uptake and efflux

The human intestinal absorption of acetamiprid (AAP) using the Caco-2 cell line reveals that AAP flux was active in a bidirectional mode with an apparent permeability coefficient of 26^.10^?6 cm·s^?1 at 37°C. Apical uptake was concentration-dependent and unsaturated for AAP concentrations up to 200 μ M. AAP cell preloading demonstrated the involvement of active transport mechanisms. Arrhenius plot analysis revealed an unusual profile with two apparent activation energies suggesting two transport processes. Uptake Vi studies indicated the involvement of a sodium-dependent transporter, the presence of a common transporter of AAP and nicotine and the involvement of Ti-sensitive ATP-dependent efflux transporters. Apical efflux investigations showed the involvement of inward active transporter(s). Whereas vincristine had no effect on intracellular accumulation, taxol and daunorubicin treatments unexpectedly led to 10% and 23% reductions respectively, suggesting that the latter shared a common inward transporter with AAP. All these results suggest full and express AAP absorption in vivo with transport involving both inward and outward, passive and active mechanisms. Thus, AAP or its metabolites could be representative of a risk for human health after its ingestion in food.     

On the uptake and release of zinc (65Zn) in the growing alga Selenastrum capricornutum Printz

A Zn- and pH-buffered medium was used to study the accumulation of Zn in batch-cultured algae (Selenastrum capricornutum Printz.). All experiments were carried out using (65)Zn radiotracers, which were measured by gamma-ray spectrometry. Zinc was applied in the presence of nitrilotriacetic acid (NTA), leading to free Zn(2+) concentrations ranging from 4.2 x 10(-11) to 1.6 x 10(-7) mol litre(-1). During the 75-h experiments, the rates of Zn influx and efflux were determined, the latter with full consideration for algal growth rates. Algal growth stopped completely at a free Zn(2+) concentration of 1.6 x 10(-8) mol litre(-1). Initial Zn binding was determined and, based on free Zn(2+) concentrations, presented by the apparent dissociation constant K(diss) and capacity C as 4.6 x 10(-9) mol litre(-1) and 19.8 x 10(6) mol gDW(-1), respectively. The rate constant of Zn efflux could be calculated as a constant 0.021 +/- 0.003 h(-1), irrespective of the Zn concentrations applied. The rates of Zn influx were expressed by the V(max) and K(M) values as 3.3 x 10(-10) mol gDW(-1) s(-1) and 6.3 x 10(-9) mol litre(-1), respectively. These values, which are based on applied free Zn(2+) concentrations, are compatible with the operation of a high-affinity low-concentration carrier mechanism. The results suggest that, under the conditions applied, free Zn(2+) may be the most relevant Zn species for Zn uptake; furthermore, relative growth rate may be regarded as a relatively sensitive signal for Zn stress circumstances.     

Biotreatment of hydrogen sulfide- and ammonia-containing waste gases by fluidized bed bioreactor

Gas mixtures of H2S and NH3 are the focus of this study of research concerning gases generated from animal husbandry and treatments of anaerobic wastewater lagoons. A heterotrophic microflora (a mixture of Pseudomonas putida for H2S and Arthrobacter oxydans for NH3) was immobilized with Ca-alginate and packed into a fluidized bed reactor to simultaneously decompose H2S and NH3. This bioreactor was continuously supplied with H2S and NH3 separately or together at various ratios. The removal efficiency, removal rate, and metabolic product of the bioreactor were studied. The results showed that the efficiency remained above 95% when the inlet H2S concentration was below 30 ppm at 36 L/hr. Furthermore, the apparent maximum removal and the apparent half-saturation constant were 7.0 x 10(-8) g-S/cell/day and 76.2 ppm, respectively, in this study. The element sulfur as a main product prevented acidification of the biofilter, which maintained the stability of the operation. As for NH3, the greater than 90% removal rate was achieved as long as the inlet concentration was controlled below 100 ppm at a flow rate of 27 L/hr. In the NH3 inlet, the apparent maximum removal and the apparent half-saturation constant were 1.88 x 10(-6) g-N/cell/day and 30.5 ppm, respectively. Kinetic analysis showed that 60 ppm of NH3 significantly suppressed the H2S removal by Pseudomonas putida, but H2S in the range of 5-60 ppm did not affect NH3 removal by Arthrobacter oxydans. Results from bioaerosol analysis in the bioreactor suggest that the co-immobilized cell technique applied for gas removal creates less environmental impact.     

Photoinductive efficiency of soil extracted humic and fulvic acids

Humic and fulvic acids extracted from soils of different genesis were investigated for their ability to photoinduce the transformation of fenuron (2 x 10(-4) mol(-1)) at 365 nm. The ratio of the initial rate of fenuron consumption over the rate of light absorption by humic substances was found to be higher for fulvic acids (range 2.0 x 10(-3) to 9.0 x 10(-5)) than for humic acids (range 1.7 x 10(-4) to - 3.6 x 10(-5)). Within the FAs population, this ratio decreased as the specific absorption coefficient at 365 nm increased. It seems therefore that most of 365-nm absorbing components have no photoinductive activity and even reduce that of photoinductive chromophores.     

Laboratory migration experiments with radionuclides and natural colloids in a granite fracture

Natural colloids in groundwater could facilitate radionuclide transport, provided the colloids are mobile, are present in sufficient concentrations and can adsorb radionuclides. This paper describes the results of a laboratory migration study carried out with combinations of radionuclides and natural colloids within a fracture in a large granite block to experimentally determine the impact of colloids on radionuclide transport. The 85Sr used in this study is an example of a moderately sorbing radionuclide, while the 241Am is typical of a strongly sorbed radionuclide with very low solubility. The natural colloids used in this study were isolated from granite groundwater from Atomic Energy of Canada (AECL) Underground Research Laboratory (URL), and consisted of mostly 1-10 nm organic colloids, along with lesser amounts of 10-450 nm colloids (organics and aluminosilicates). The measured coefficients for radionuclide sorption onto these colloids were between 3 x 10(2) and 1 x 10(3) ml/g for 85Sr, and between 7 x 10(4) and 7 x 10(5) mg/l for 241Am. The 85Sr sorption on the natural colloids appeared to be reversible. Migration experiments in the granite block were carried out by establishing a flow field between two boreholes (out of a total of nine) intersecting a main horizontal fracture. These experiments showed that dissolved 85Sr behaved as a moderately sorbing tracer, while dissolved 241Am was completely adsorbed by the fracture surfaces and showed no evidence of transport. However, when natural colloids were injected together with dissolved 241Am, a small amount of 241Am transport was observed, demonstrating the ability of natural colloids to facilitate the transport of radionuclides with low solubility. Natural colloids had only a minor effect on the transport of 85Sr. In a separate experiment to test the effect of higher colloid concentrations on 85Sr migration, synthetic colloids were produced from Avonlea bentonite. The introduction of a relatively high concentration of bentonite colloids actually reduced 85Sr transport because, compared to natural colloids, the bentonite colloids were less mobile and they sorbed 85Sr more strongly.     

Numerical modeling of oxygen exclusion experiments of anaerobic bioventing

A numerical and experimental study of transport phenomena underlying anaerobic bioventing (ABV) is presented. Understanding oxygen exclusion patterns in vadose zone environments is important in designing an ABV process for bioremediation of soil contaminated with chlorinated solvents. In particular, the establishment of an anaerobic zone of influence by nitrogen injection in the vadose zone is investigated. Oxygen exclusion experiments are performed in a pilot scale flow cell (2 x 1.1 x 0.1 m) using different venting flows and two different outflow boundary conditions (open and partially covered). Injection gas velocities are varied from 0.25 x 10(-3) to 1.0 x 10(-3) cm/s and are correlated with the ABV radius of influence. Numerical simulations are used to predict the collected experimental data. In general, reasonable agreement is found between observed and predicted oxygen concentrations. Use of impervious covers can significantly reduce the volume of forcing gas used, where an increase in oxygen exclusion efficiency is consistent with a decrease in the outflow area above the injection well.     

Arsenic accumulation and speciation in the submerged macrophyte Ceratophyllum demersum L.

Introduction

Ceratophyllum demersum L. is a widespread submerged macrophyte in aquatic environments.

Methods

Simulation experiments were conducted in the laboratory to investigate arsenic (As) accumulation, speciation, and efflux of C. demersum exposed to arsenate and arsenite solutions.

Results

Plant shoots showed a significant accumulation of As with a maximum of 862 and 963???g?As?g^?1 dry weight after 4?days of exposure to 10???M arsenate and arsenite, respectively. Regardless of whether arsenate or arsenite was supplied to the plants, arsenite was the predominant species in plant shoots. Furthermore, a dramatically higher influx rate of arsenate compared with arsenite was observed in C. demersum exposed to As solutions without the addition of phosphate (P). Arsenate uptake was considerably inhibited by P in this study, suggesting that arsenate is taken up by C. demersum via the phosphate transporters. However, arsenite uptake was unaffected by P and markedly reduced in the presence of glycerol and antimonite (Sb), indicating arsenite shares the aquaporin transport pathway. In addition, C. demersum rapidly reduces arsenate to arsenite in the shoot of the plant and extrudes most of them (>60?%) to the external solutions. The efflux of arsenite was much higher than that of arsenate; the former is supposed to be both active and passive processes, and the latter through passive leakage.

Conclusion

C. demersum is a strong As accumulator and an interesting model plant to study As uptake and metabolism due to the lack of a root-to-shoot translocation barrier.     

Change in the antimicrobial resistance profile of Pseudomonas aeruginosa from soil after exposure to herbicides

The extensive use of pesticides represents a risk to human health and to the environment. This study aimed to investigate if the exposure to atrazine and diuron, two herbicides widely used in Brazil, could induce changes in the susceptibility profile to aztreonam, colistin and polymyxin B antimicrobials in isolates of P. aeruginosa obtained from soil samples by using the determination of minimum inhibitory concentration (MIC) test. Three isolates had an increase of MIC to aztreonam after exposure to both herbicides and one isolate did not show any MIC change. The MexAB-OprM efflux pump has already been upregulated in these isolates and the herbicides atrazine and diuron did not increase MexAB-OprM overexpression. Therefore, the decrease in aztreonam susceptibility was not directly related to this pump, suggesting that probably other mechanisms should be involved.     

Biokinetics of cadmium, selenium, and zinc in freshwater alga Scenedesmus obliquus under different phosphorus and nitrogen conditions and metal transfer to Daphnia magna

The uptake of Cd, Se(IV) and Zn by the freshwater alga Scenedesmus obliquus and the subsequent transfer and release budget in Daphnia magna were investigated under different nutrient additions and cell incubation conditions. An increase in ambient phosphate concentrations from 0.5 micromol l(-1) to 50 micromol l(-1) significantly increased the intracellular accumulation of Cd (by 18x) and Zn (by 5x), but decreased the accumulation of Se (by 126x) in the alga. The percentage of these metals distributing in the intracellular pool of algae also increased substantially with increasing ambient P concentrations. Nitrate addition from 5.0 to 200 micromol l(-1) did not influence the uptake of any of the three metals, although a significant decrease in the intracellular Se distribution was observed. Radiolabeled algae under different nutrient manipulations (semi-continuous culture, starvation, and P-pulse treatments) were used to measure trophic transfer assimilation efficiency (AE) in Daphnia. When the algal cells were grown in a semi-continuous culture, starved for N and P, or were treated with P-pulse, the AEs of Cd and Zn were generally independent of the nutritional conditions, but the Se AE was significantly affected by different P levels. The efflux rate constants, determined during 10 d depuration following 7 days of dietary uptake, decreased significantly for Cd and Zn, but were relatively constant for Se with increasing P concentration. N-addition caused no effect on the metal efflux rate constants. P- or N-additions did not influence the release budget (including molting, neonates, excretion and feces) for all three elements in Daphnia. Our study indicated that phosphate enrichment may substantially increase metal uptake in green alga S. obliquus. Responses of trophic transfer in Daphnia to nutrient enrichment were metal specific. P-enrichment can possibly lead to considerable decrease on Se transfer from algae to zooplankton.     

In situ anion diffusion experiments using radiotracers

Diffusion experiments in compacted bentonite have been carried out in situ using the borehole laboratory CHEMLAB. The "ordinary" anion iodide and the redox-sensitive pertechnetate ion have been investigated. In spite of strongly reducing groundwater conditions, technetium was found to diffuse mostly unreduced as TcO4-, although in some spots in the compacted clay, the activity was significantly higher, which may be explained by reduction of some TcO4- by iron-containing minerals in the bentonite. The measured concentration profiles in the clay cannot be accommodated by assuming one single diffusion process. The experimental data are modeled assuming two diffusion paths, intralamellar diffusion and diffusion in external water. The apparent diffusivity for the intralamellar diffusion was found to be 8.6 x 10(-11) m2 s(-1) for iodide with a capacity factor of 0.1, while the apparent diffusivity for the diffusion in external water was found to be 5 x 10(-14) m2 s(-1) with alpha=2.26. The corresponding values for Tc were found to be Da= 6 x 10(-11) m2 s(-1), alpha=0.1 and Da= 1 x 10(-13) m2 s(-1), alpha=0.46, respectively. The diffusion constants and capacity factors obtained in this study are in accordance with data from laboratory experiments.     

Photochemistry in the mixed aqueous solution of nitrobenzene and nitrous acid as initiated by the 355 nm UV light

The 355 nm photon-initiated microscopic reaction mechanisms of the mixed aqueous solution of nitrobenzene and nitrous acid in the presence or absence of O(2) were studied by the laser flash photolysis technique. The main transient absorption peaks in the recorded spectra were assigned and the growth/decay trends of several transient species were investigated. It was found that the OH radical formed from the photolysis of nitrous acid triggered most of the subsequent radical reactions. The rate constant of the reaction between OH radical and nitrobenzene was measured to be (3.4 +/- 0.1) x 10(9) l mol(-1) s(-1). The product from this reaction, namely C(6)H(5)NO(2)-OH adduct, was found to react with O(2) to yield C(6)H(5)NO(2)-OHO(2) adduct with a rate constant of (1.6 +/- 0.2) x 10(9) l mol(-1) s(-1). Final steady-state products were identified by GC/MS analysis and were in accordance with the transient spectroscopic results. The possible reaction pathways were proposed.     

A Note on Comparison of Statistical and Analytical Results for Calculating Oxides of Nitrogen Concentrations

A question often asked about analytical diffusion models is “How do the analytical results for calculating pollution concentrations compare with those obtained by statistical techniques?” Miller and Holzworth (1967) have developed a simple analytical diffusion model that yields relative pollution concentrations, x/Q, as a function of afternoon mixing depth, mean transport wind speed, and city size. This analytical model may also be used in reverse to determine apparent afternoon source strengths from observed afternoon pollution concentrations. The apparent source strengths may then be used with the model on independent data to estimate pollution concentrations. It is the purpose of this note to compare results of calculating average afternoon concentrations of oxides of nitrogen (NO_x) by use of the Miller-Holzworth model with those obtained from statistical regression equations.     

The impact of methanogenesis on flow and transport in coarse sand

The effects of biofilm growth and methane gas generation on water flow in porous media were investigated in an anaerobic two-dimensional sand-filled cell. Inoculation of the lower portion of the cell with a methanogenic culture and addition of methanol to the bottom of the cell led to biomass growth and formation of a gas phase. Biomass distributions in the water and on the sand in the cell were measured by protein analysis. The biofilm distribution on sand was observed by confocal laser scanning microscopy. The formation, migration, distribution and saturation of gases in the cell were visualized by the charge-coupled device (CCD) camera. The effects of biofilm and gas generation on water flow were separated by performing one tracer test in the presence of both biofilm and a gas phase and a second tracer test after removal of the gas phase through water flushing. The results of tracer tests demonstrated that flow and transport in the two-dimensional cell were significantly affected by both gas generation and biofilm growth. Gas generated at the bottom of the cell in the biologically active zone moved upwards in discrete fingers, so that gas phase saturations (gas-filled fraction of void space) in the biologically active zone at the bottom of the cell did not exceed 40-50%, while gas accumulation at the top of the cell produced gas phase saturations as high as 80%. The greatest reductions in water phase permeability, based on measurements of reductions in water phase saturations, occurred near the top of the box as a result of the gas accumulation. In contrast the greatest reductions in permeability due to biofilm growth, based on measurements of biofilm thickness, occurred in the most biologically active zone at the bottom of the cell, where gas phase saturations were approximately 40-50%, but permeability reductions due to biofilm growth were estimated to be 80-95%.     

Arsenic(V) removal with a Ce(IV)-doped iron oxide adsorbent

The removal of arsenic(V) by a new Ce-Fe adsorbent was evaluated under various conditions. Under an initial As(V) of 1.0 mg l(-1), the adsorption capacity of the Ce-Fe absorbent was constant around a value of 16 mgg(-1) over a wide pH range (3-7), while a maximum adsorption capacity of 8.3 mgg(-1) was obtained over a narrow pH range around 5.5 for activated alumina, a conventional adsorbent. Kinetics of adsorption obeys a pseudo-first-order rate equation with the rate constant K(ad) as 1.84 x 10(-3) min(-1). The pattern of adsorption of As(V) by the adsorbent fitted well both the Langmuir and Freundlich models. A Langmuir Q(0) of 70.4 mgg(-1) was obtained at an initial pH of 5.0 and temperature of 20 degrees C, significantly higher than those of other adsorbents reported. Phosphate seriously inhibited the removal of As(V) while fluoride did not compete with As(V) even at an F/As molar ratio as high as 30, suggesting that the adsorption sites for As(V) and fluoride were different. Salinity, hardness, and other inorganic anions such as Cl(-), NO(3)(-), and SO(4)(2-) had no apparent effect on As(V) adsorption. Fourier transform infrared spectra of Ce-Fe adsorbent before and after As(V) adsorption demonstrated that M-OH groups plays an important role for As(V) ions removal in the adsorption mechanisms of Ce-Fe adsorbent.     

Nitrogen Dioxide Absorption and Sulfide Oxidation in Aqueous Sulfide

ABSTRACT

Rates of nitrogen dioxide (NO₂) absorption and sulfide oxidation were measured in a highly characterized stirred cell contactor at 55 °C, with O₂ present in the gas phase. The rate constant of the reaction between NO₂ and sul-fide at 55 °C was determined to be 26.4 x10⁵ M^-1sec^-1. A reaction mechanism was proposed that is consistent with the kinetic data. NO₂ absorption initiates sulfide oxidation in the presence of oxygen. The rate of sulfide oxidation increased with sulfide and oxygen concentration and with the rate of NO₂ absorption. Furthermore, thiosulfate was an effective inhibitor of sulfide oxidation.     

Pentachlorophenol association with fulvic acids from recycled wastes

The apparent water solubility of pentachlorophenol was measured at pH=6 and at 25 degrees C in pure water, aqueous solutions of three salts (NaCl, KNO(3) and CaCl(2) at 0.010, 0.10 and 1.0M) and in aqueous solutions of three fulvic acids samples extracted from a natural soil (sFA), composted sewage sludge (csFA) and composted livestock's material (lsFA). A solubility enhancement method was developed for the measurement of partition coefficients (K(oc), L/kg organic carbon). Pentachlorophenol associates strongly with the fulvic acid samples and the calculated K(oc) were the following (averages and standard deviations): (sFA) (211+/-22) x 10(2), (csFA) (253+/-26) x 10(2), (lsFA) (235+/-10) x 10(2). For comparison purposes the K(oc) for pyrene were also calculated for the three FA samples and were the following: (sFA) (119+/-10) x 10(2), (csFA) (239+/-21) x 10(2), (lsFA) (92+/-10) x 10(2). The analysis of variance (one-way ANOVA) of the effect of the type of FA sample on the solubilization of pentachlorophenol and pyrene shows that this factor causes significant differences on the aqueous solubilization of these two organic substances.     

Effects of cold-dark storage on growth of Cylindrotheca closterium and its sensitivity to copper

Cylindrotheca closterium cells were maintained at low temperature (4+/-1 degrees C) and dark conditions up to 21 weeks to assess the effect on survival and physiological status. From a control culture under standard conditions, three densities were prepared: (A) 2 x 10(4), (B) 10 x 10(4), and (C) 25 x 10(4) cells ml(-1). Weekly, inoculums of each stored density were exposed to continuous light and at 20+/-1 degrees C. Sensitivity to copper for microalgal cultures was evaluated in order to assess possible changes in cells sensitivity due to storage. Concurrently, assays with a control culture were carried out in order to assess the sensitivity of C. closterium to copper and to be able to generate a standard sensitivity control chart with a mean value of EC50-72 h+/-2SD (standard deviation). Density-C presented higher cell yield values, between 40% and 80% relative to control culture. Cell density showed to be important feature that may be taken into account in cell storage experiments. There was an increase in sensitivity of cells submitted to storage; however results always kept in the range established as standard sensitivity with no statistically significant difference with regards to control culture. EC50-72 h mean value for the control culture was 29+/-10 mug Cul(-1), while for densities-A, B and C were 22+/-7; 23+/-9 and 23+/-8 microg Cul(-1), respectively. In spite of drastic changes in the environmental conditions due to storage, it is concluded that C. closterium cells stored during 5 months remained metabolically active and with no significant change in its sensitivity.     

Modelling of silica diffusion experiments with 32Si in Boom Clay

A mathematical model describing the dissolution of nuclear glass directly disposed in clay combines a first-order dissolution rate law with the diffusion of dissolved silica in clay. According to this model, the main parameters describing the long-term dissolution of the glass are etaR, the product of the diffusion accessible porosity eta and the retardation factor R, and the apparent diffusion coefficient D(app) of dissolved silica in clay. For determining the migration parameters needed for long-term predictions, four Through-Diffusion (T-D) experiments and one percolation test have been performed on undisturbed clay cores. In the Through-Diffusion experiments, the concentration decrease after injection of 32Si (radioactive labelled silica) was measured in the inlet compartment. At the end of the T-D experiments, the clay cores were cut in thin slices and the activity of labelled silica in each slice was determined. The measured activity profiles for these four clay cores are well reproducible. Since no labelled silica could be detected in the outlet compartments, the Through-Diffusion experiments are fitted by two In-Diffusion models: one model assuming linear and reversible sorption equilibrium and a second model taking into account sorption kinetics. Although the kinetic model provides better fits, due to the sufficiently long duration of the experiments, both models give approximately similar values for the fit parameters. The single percolation test leads to an apparent diffusion coefficient value about two to three times lower than those of the Through-Diffusion tests. Therefore, dissolved silica appears to be strongly retarded in Boom Clay. A retardation factor R between 100 and 300 was determined. The corresponding in situ distribution coefficient K(d) is in the range 25-75 cm(3) g(-1). The apparent diffusion coefficient of dissolved silica in Boom Clay is estimated between 2 x 10(-13) and 7 x 10(-13) m(2) s(-1). The pore diffusion coefficient is in the range from 6 x 10(-11) to 1 x 10(-10) m(2) s(-1).     

Characterization on the toxic mechanism of two fluoroquinolones to trypsin by spectroscopic and computational methods

Abstract

Ciprofloxacin (CPFX) and enrofloxacin (ENFX), two of the most widely used fluoroquinolones (FQs), pose a great threat to humans and the ecosystem. In this study, the toxic mechanisms between the two FQs and trypsin were evaluated by means of multiple spectroscopic methods, as well as molecular docking. During the fluorescence investigations, both FQs quenched the intrinsic fluorescence of trypsin effectively, which was due to the formation of moderately strong complexes (mainly through van der Waals forces and hydrogen bonds). The binding of two FQs not only caused the conformational and micro-environmental changes of trypsin, but also changed its molecular activity; shown by the UV–Visible absorption spectroscopy, synchronous fluorescence spectroscopy, and functional tests. The established methods in this work can help to comprehensively understand the transport of FQs in the human body.