Vectorization of agrochemicals: amino acid carriers are more efficient than sugar carriers to translocate phenylpyrrole conjugates in the <Emphasis Type="Italic">Ricinus</Emphasis> system

Producing quality food in sufficient quantity while using less agrochemical inputs will be one of the great challenges of the twenty-first century. One way of achieving this goal is to greatly reduce the doses of plant protection compounds by improving the targeting of pests to eradicate. Therefore, we developed a vectorization strategy to confer phloem mobility to fenpiclonil, a contact fungicide from the phenylpyrrole family used as a model molecule. It consists in coupling the antifungal compound to an amino acid or a sugar, so that the resulting conjugates are handled by active nutrient transport systems. The method of click chemistry was used to synthesize three conjugates combining fenpiclonil to glucose or glutamic acid with a spacer containing a triazole ring. Systemicity tests with the Ricinus model have shown that the amino acid promoiety was clearly more favorable to phloem mobility than that of glucose. In addition, the transport of the amino acid conjugate is carrier mediated since the derivative of the L series was about five times more concentrated in the phloem sap than its counterpart of the D series. The systemicity of the L-derivative is pH dependent and almost completely inhibited by the protonophore carbonyl cyanide 3-chlorophenylhydrazone (CCCP). These data suggest that the phloem transport of the L-derivative is governed by a stereospecific amino acid carrier system energized by the proton motive force.     

Transport of Sr2+ and SrEDTA2- in partially-saturated and heterogeneous sediments

Strontium-90 has migrated deep into the unsaturated subsurface beneath leaking storage tanks in the Waste Management Areas (WMA) at the U.S. Department of Energy's (DOE) Hanford Reservation. Faster than expected transport of contaminants in the vadose zone is typically attributed to either physical hydrologic processes such as development of preferential flow pathways, or to geochemical processes such as the formation of stable, anionic complexes with organic chelates, e.g., ethylenediaminetetraacetic acid (EDTA). The goal of this paper is to determine whether hydrological processes in the Hanford sediments can influence the geochemistry of the system and hence control transport of Sr(2+) and SrEDTA(2-). The study used batch isotherms, saturated packed column experiments, and an unsaturated transport experiment in an undisturbed core. Isotherms and repacked column experiments suggested that the SrEDTA(2-) complex was unstable in the presence of Hanford sediments, resulting in dissociation and transport of Sr(2+) as a divalent cation. A decrease in sorption with increasing solid:solution ratio for Sr(2+) and SrEDTA(2-) suggested mineral dissolution resulted in competition for sorption sites and the formation of stable aqueous complexes. This was confirmed by detection of MgEDTA(2-), MnEDTA(2-), PbEDTA(2-), and unidentified Sr and Ca complexes. Displacement of Sr(2+) through a partially-saturated undisturbed core resulted in less retardation and more irreversible sorption than was observed in the saturated repacked columns, and model results suggested a significant reservoir (49%) of immobile water was present during transport through the heterogeneous layered sediments. The undisturbed core was subsequently disassembled along distinct bedding planes and subjected to sequential extractions. Strontium was unequally distributed between carbonates (49%), ion exchange sites (37%), and the oxide (14%) fraction. An inverse relationship between mass wetness and Sr suggested that sandy sediments of low water content constituted the immobile flow regime. Our results suggested that the sequestration of Sr(2+) in partially-saturated, heterogeneous sediments was most likely due to the formation of immobile water in drier regions having low hydraulic conductivities.     

A comparison of concentration ratios for technetium and nutrient uptake by three plant species

Technetium (Tc) is a non-essential element for which accumulation mechanisms in plants have recently been discussed, but only from the viewpoint of existence of anion transport proteins in plant cells. In this study, using three kinds of plants (Cucumis sativus L., Raphanus sativus L., and Brassica chinensis L.), uptake of Tc and Re (a chemical analogue of Tc) were observed. The results showed that Tc and Re uptake occurred not only with water mass flow or active nutrient uptake, but also with uptake of nutrient cations such as K+. It is suggested here that most stable chemical form under aerobic conditions, TcO4-, is used in cation transport as a substitute ions, such as Cl-. After TcO4- passes through a root surface, it moves through the xylem together with cations. Due to these uptake mechanisms, Tc is highly accumulated in plants.     

Validation of photosynthetic-fluorescence parameters as biomarkers for isoproturon toxic effect on alga Scenedesmus obliquus

Photosynthetic-fluorescence parameters were investigated to be used as valid biomarkers of toxicity when alga Scenedesmus obliquus was exposed to isoproturon [3-(4-isopropylphenyl)-1,1-dimethylurea] effect. Chlorophyll fluorescence induction of algal cells treated with isoproturon showed inactivation of photosystem II (PSII) reaction centers and strong inhibition of PSII electron transport. A linear correlation was found (R2>or=0.861) between the change of cells density affected by isoproturon and the change of effective PSII quantum yield (PhiM'), photochemical quenching (qP) and relative photochemical quenching (qP(rel)) values. The cells density was also linearly dependent (R2=0.838) on the relative unquenched fluorescence parameter (UQF(rel)). Non-linear correlation was found (R2=0.937) only between cells density and the energy transfer efficiency from absorbed light to PSII reaction center (ABS/RC). The order of sensitivity determined by the EC-50% was: UQF(rel)>PhiM'>qP>qP(rel)>ABS/RC. Correlations between cells density and those photosynthetic-fluorescence parameters provide supporting evidence to use them as biomarkers of toxicity for environmental pollutants.     

Transepithelial transport and cellular accumulation of steroid hormones and polychlorobiphenyl in porcine kidney cells expressed with human P-glycoprotein

Endocrine disrupters such as sex hormone-like chemicals and the non-physiological ligands for aryl hydrocarbon receptor (AhR) exert many adverse biological effects. The ligands for AhR disturb gene expression downstream of the gene induced by estrogen receptor at a very low concentration. Thus, transepithelial transport and cellular accumulation of cortisol (COR) and estrogen as congeners of sex hormone-like chemicals, and 3,3^′,4,4^′-tetrachlorobiphenyl (TeCB) as one of the ligands for AhR were examined in a monolayer of porcine kidney cells transfected with human P-glycoprotein (LLC-COL). The net basal-to-apical transport of COR increased in LLC-COL compared to that in the wild type cells (LLC-PK1) the same as in vinblastine, whereas the net transport of estradiol (EST) was not detected in either cell group. Though the diffusion transports of EST for both directions, basal-to-apical and apical-to-basal, were higher than that of COR, cellular accumulation of EST was higher than that of COR. Transepithelial transport of TeCB was very low and the net basal-to-apical transport was not detected, while it was highly accumulated in the epithelial cells. The accumulation was slightly higher in LLC-COL than in LLC-PK1 at high dose.     

Cadmium effect on the structure of supra- and subpharyngeal ganglia and the neurosecretory processes in earthworm Dendrobaena veneta (Rosa)

Cadmium effects on the supra- and subpharyngeal ganglia, neurosecretion and RNA content in the neurosecretory cells were tested in earthworms Dendrobaena veneta exposed to 10 and 50 mg Cd kg(-1) in soil after 20 days of the experiment. Accumulation of cadmium in the ganglia of nervous system was also measured using AAS method. Cadmium was accumulated in the nervous system. The accumulated amount was proportional to Cd soil concentration and the exposure time. A considerable fall in neurosecretion and RNA content in the neurosecretory cells and neurosecretion in the neuropile (the axons) of both tested ganglia was induced by 50 mg Cd kg(-1). It seemed that neurosecretion synthesis and its axonal transport could be suppressed. Cadmium caused degenerative changes as vacuolization of the neurosecretory cells and neuropile in both tested ganglia.     

Dioxins,chlorophenols and other chlorinated organic pollutants in colloidal and water fractions of groundwater from a contaminated sawmill site

BACKGROUND, AIM, AND SCOPE: The distribution of chlorinated organic contaminants in groundwater and the importance of colloids were studied in groundwater from a sawmill site contaminated by chlorophenol preservatives. MATERIALS AND METHODS: The groundwater was fractionated into three different size ranges: (1) >0.7 mum, (2) 0.4-0.7 mum and (3) 0.2-0.4 mum and the filtered water phase. The concentrations of chlorophenols (CP), chlorinated phenoxy phenols (PCPP), chlorinated diphenyl ethers (PCDE), chlorinated dibenzofurans (PCDF) and chlorinated dibenzo-p-dioxins (PCDD) were determined in each fraction. The colloids were characterised regarding the chemical composition using X-ray photoelectron spectroscopy (XPS). RESULTS: Chlorophenols were mostly found in the water fraction and PCDD/Fs were found almost exclusively in the particulate fractions. For example, the filtered water phase contained 2,100 mug l(-1) and 0.72 ng l(-1) for CPs and PCDD/Fs, respectively, and the particulate fractions contained 27 mug l(-1) and 32 ng l(-1) for CPs and PCDD/Fs, respectively. XPS evaluation of the particulate phases showed no correlation between the surface chemistry of the particle properties and the distribution of chlorinated compounds. DISCUSSION: The results suggest that groundwater transport of CPs, PCPPs, PCDEs and PCDD/Fs may occur from contaminated sawmill sites and that the colloid-facilitated transport, especially of PCDD/Fs, is substantial. The results correlated well with previous studies of compounds sorbed to dissolved organic carbon, which indicate that dissolved and colloidal organic carbon facilitated the transport of PCDEs, PCDFs and PCDDs particularly. CONCLUSIONS: Several classes of chlorinated compounds were readily detected in the groundwater samples. Due to the differences in their physicochemical properties, CPs, PCPPs, PCDEs and PCDD/Fs vary in their partitioning between colloidal fractions and the filtered groundwater. The proportion of the bound fraction increased with an increasing hydrophobicity of the chlorinated compounds. The groundwater transport of colloid-associated pollutants from the site may be significant. RECOMMENDATIONS AND PERSPECTIVES: The results imply that colloidal particles <0.7 mum are freely mobile in groundwater from this site. The groundwater transport of colloid-associated pollutants may be significant. However, the extent of the problem is not yet known and, thus, further research is needed to evaluate the impact of colloidal transport of hydrophobic organic contaminants. In Sweden alone, 400 to 500 sawmill sites are estimated to be contaminated with PCDD/Fs as a result of the former use of CP-based wood preservatives. The widespread use of CP mixtures for a variety of applications, including wood preservation, indicates that potential colloidal transport will be an issue of concern in many countries.     

Identification of multixenobiotic defence mechanism (MXR) background activities in the freshwater bivalve Dreissena polymorpha as reference values for its use as biomarker in contaminated ecosystems

The biological defence mechanism called MXR or MXD for multixenobiotic resistance or defence protects cells against the entry and the accumulation of xenobiotics. As the defence is modulated by man made chemicals, MXR is used as a biomarker of organisms' exposure to environmental contamination. However, to reliably assess and evidence MXR induction, the use of a reference level is required. In this context, we focused on MXR background level in a freshwater bivalve, the zebra mussel Dreissena polymorpha, in order to propose its use as a reference during MXR evaluation. We monitored the MXR transport activity in mussels collected either in a natural population or in a caged population and then transplanted to clean water in the laboratory. The results showed that MXR activity was decreased to its baseline level after an eight to nine day depuration period (13.1+/-3.1; 7+/-2.6; 13.7+/-3.9 pmol RB min(-1)org(-1) after three experiments of laboratory depurations). Moreover, significant MXR induction was measured in depurated zebra mussels exposed to contaminated sites (39.6+/-3.7; 59.2+/-20.3 pmol RB min(-1)org(-1) after two experiments of field exposure), showing that the laboratory depuration did not affect the induction potential. The MXR responses (decrease as well as increase) occurred in few days and were highly significant, highlighting its reactivity in zebra mussels. Finally, this paper confirms the usefulness of MXR as a tool in biomonitoring studies and provides a protocol for field experiments that enables to establish and use the background level of MXR activity as a reference.     

Coupled effects of solution chemistry and hydrodynamics on the mobility and transport of quantum dot nanomaterials in the vadose zone

To investigate the coupled effects of solution chemistry and hydrodynamics on the mobility of quantum dot (QD) nanoparticles in the vadose zone, laboratory scale transport experiments involving single and/or sequential infiltrations of QDs in unsaturated and saturated porous media, and computations of total interaction and capillary potential energies were performed. As ionic strength increased, QD retention in the unsaturated porous media increased; however, this retention was significantly suppressed in the presence of a non-ionic surfactant in the infiltration suspensions as indicated by surfactant enhanced transport of QDs. In the vadose zone, the non-ionic surfactant limited the formation of QD aggregates, enhanced QD mobility and transport, and lowered the solution surface tension, which resulted in a decrease in capillary forces that not only led to a reduction in the removal of QDs, but also impacted the vadose zone flow processes. When chemical transport conditions were favorable (ionic strength of 5 × 10(-4)M and 5 × 10(-3)M, or ionic strengths of 5 × 10(-2)M and 0.5M with surfactant), the dominating phenomena controlling the mobility and transport of QDs in the vadose zone were meso-scale processes, where infiltration by preferential flow results in the rapid transport of QDs. When chemical transport conditions were unfavorable (ionic strength of 5 × 10(-2)M and 0.5M) the dominating phenomena controlling the mobility and transport of QDs in the vadose zone were pore-scale processes governed by gas-water interfaces (GWI) that impact the mobility of QDs. The addition of surfactant enhanced the transport of QDs both in favorable and unfavorable chemical transport conditions. The mobility and retention of QDs was controlled by interaction and capillary forces, with the latter being the most influential. GWI were found to be the dominant mechanism and site for QD removal compared with solid-water interfaces (SWI) and pore straining. Additionally, ripening phenomena were demonstrated to enhance QDs removal or retention in porous media and to be attenuated by the presence of surfactant.     

How Plants Cope with Foreign Compounds. Translocation of xenobiotic glutathione conjugates in roots of barley (Hordeum vulgare) (9 pp)

Background, Aim and Scope Numerous herbicides and xenobiotic organic pollutants are detoxified in plants to glutathione conjugates. Following this enzyme catalyzed reaction, xenobiotic GS-conjugates are thought to be compartmentalized in the vacuole of plant cells. In the present study, evidence is presented for long range transport of these conjugates in plants, rather than storage in the vacuole. To our knowledge this is the first report about the unidirectional long range transport of xenobiotic conjugates in plants and the exudation of a glutathione conjugate from the root tips. This could mean that plants possess an excretion system for unwanted compounds which give them similar advantages as animals. Materials and Methods: Barley plants (Hordeum vulgare L. cv. Cherie) were grown in Petri dishes soaked with tap water in the greenhouse. - Fluorescence Microscopy. Monobromo- and Monochlorobimane, two model xenobiotics that are conjugated rapidly in plant cells with glutathione, hereby forming fluorescent metabolites, were used as markers for our experiments. Their transport in the root could be followed sensitively with very good temporal and spatial resolution. Roots of barley seedlings were cut under water and the end at which xenobiotics were applied was fixed in an aperture with a thin latex foil and transferred into a drop of water on a cover slide. The cover slide was fixed in a measuring chamber on the stage of an inverse fluorescence microscope (Zeiss Axiovert 100). - Spectrometric enzyme assay. Glutathione S-transferase (GST) activity was determined in the protein extracts following established methods. Aliquots of the enzyme extract were incubated with 1-chloro-2,4-dinitrobenzene (CDNB), or monochlorobimane. Controls lacking enzyme or GSH were measured. - Pitman chamber experiments. Ten days old barley plants or detached roots were inserted into special incubation chambers, either complete with tips or decapitated, as well as 10 days old barley plants without root tips. Compartment A was filled with a transport medium and GSH conjugate or L-cysteine conjugate. Compartments B and C contained sugar free media. Samples were taken from the root tip containing compartment C and the amount of conjugate transported was determined spectro-photometrically. Results: The transport in roots is unidirectional towards the root tips and leads to exsudation of the conjugates at rates between 20 and 200 nmol min-1. The microscopic studies have been complemented by transport studies in small root chambers and spectroscopic quantification of dinitrobenzene-conjugates. The latter experiments confirm the microscopic studies. Furthermore it was shown that glutathione conjugates are transported at higher rates than cysteine conjugates, despite of their higher molecular weights. This observation points to the existence of glutathione specific carriers and a specific role of glutathione in the root. Discussion: It can be assumed that long distance transport of glutathione conjugates within the plant proceeds like GSH or amino acid transport in both, phloem and xylem. The high velocity of this translocation of the GS-X is indicative of an active transport. For free glutathione, a rapid transport-system is essential because an accumulation of GSH in the root tip inhibits further uptake of sulfur. Taking into account that all described MRP transporters and also the GSH plasmalemma ATPases have side activities for glutathione derivatives and conjugates, co-transport of these xenobiotic metabolites seems credible. - On the other hand, when GS-B was applied to the root tips from the outside, no significant uptake was observed. Thus it can be concluded that only those conjugates can be transported in the xylem which are formed inside the root apex. Having left the root once, there seems to be no return into the root vessels, probably because of a lack of inward directed transporters. Conclusions: Plants seem to possess the capability to store glutathione conjugates in the vacuole, but under certain conditions, these metabolites might also undergo long range transport, predominantly into the plant root. The transport seems dependent on specific carriers and is unidirectional, this means that xenobiotic conjugates from the rhizosphere are not taken up again. The exudation of xenobiotic metabolites offers an opportunity to avoid the accumulation of such compounds in the plant. Recommendations and Perspectives: The role of glutathione and glutathione related metabolites in the rhizosphere has not been studied in any detail, and only scattered data are available on interactions between the plant root and rhizosphere bacteria that encounter such conjugates. The final fate of these compounds in the root zone has also not been addressed so far. It will be interesting to study effects of the exuded metabolites on the biology of rhizosphere bacteria and fungi.     

Multi-process herbicide transport in structured soil columns: experiments and model analysis

Model predictions of pesticide transport in structured soils are complicated by multiple processes acting concurrently. In this study, the hydraulic, physical, and chemical nonequilibrium (HNE, PNE, and CNE, respectively) processes governing herbicide transport under variably saturated flow conditions were studied. Bromide (Br-), isoproturon (IPU, 3-(4-isoprpylphenyl)-1,1-dimethylurea) and terbuthylazine (TER, N2-tert-butyl-6-chloro-N4-ethyl-1,3,5-triazine-2,4-diamine) were applied to two soil columns. An aggregated Ap soil column and a macroporous, aggregated Ah soil column were irrigated at a rate of 1 cm h(-1) for 3 h. Two more irrigations at the same rate and duration followed in weekly intervals. Nonlinear (Freundlich) equilibrium and two-site kinetic sorption parameters were determined for IPU and TER using batch experiments. The observed water flow and Br- transport were inversely simulated using mobile-immobile (MIM), dual-permeability (DPM), and combined triple-porosity (DP-MIM) numerical models implemented in HYDRUS-1D, with improving correspondence between empirical data and model results. Using the estimated HNE and PNE parameters together with batch-test derived equilibrium sorption parameters, the preferential breakthrough of the weakly adsorbed IPU in the Ah soil could be reasonably well predicted with the DPM approach, whereas leaching of the strongly adsorbed TER was predicted less well. The transport of IPU and TER through the aggregated Ap soil could be described consistently only when HNE, PNE, and CNE were simultaneously accounted for using the DPM. Inverse parameter estimation suggested that two-site kinetic sorption in inter-aggregate flow paths was reduced as compared to within aggregates, and that large values for the first-order degradation rate were an artifact caused by irreversible sorption. Overall, our results should be helpful to enhance the understanding and modeling of multi-process pesticide transport through structured soils during variably saturated water flow.     

Source attribution for mercury deposition in the contiguous United States: regional difference and seasonal variation

Quantifying the contribution of emission sources responsible for mercury deposition in specific receptor regions helps develop emission control strategies that alleviate the impact on ecosystem and human health. In light of the maximum available control technology (MACT) rules proposed by U.S. Environmental Protection Agency (EPA) and the ongoing intergovernmental negotiation coordinated by United Nations Environmental Programme (UNEP) for mercury, the Community Multiscale Air Quality Modeling System (CMAQ-Hg) was applied to estimate the source contribution in six subregions of the contiguous United States (CONUS). The considered source categories include electric generating units (EGU), iron and steel industry (IRST), other industrial point sources excluding EGU and IRST (OIPM), the remaining anthropogenic sources (RA), natural processes (NAT), and out-of-boundary transport (BC). It is found that, on an annual basis, dry deposition accounts for two-thirds of total annual deposition in CONUS (474 Mg yr(-1)), mainly contributed by reactive gaseous mercury (about 60% of total deposition). The contribution from large point sources can be as high as 75% near the emission sources (< 100 km), indicating that emission reduction may result in direct deposition decrease near the source locations. Out-of-boundary transport contributes from 68% (Northeast) to 91% (West Central) of total deposition. Excluding the contribution from out-of boundary transport, EGU contributes to about 50% of deposition in the Northeast, Southeast, and East Central regions, whereas emissions from natural processes are more important in the Pacific and West Central regions (contributing up to 40% of deposition). This suggests that the implementation of the new EPA MACT standards will significantly benefit only these three regions. Emission speciation is a key factor for local deposition. The source contribution exhibits strong seasonal variation. Deposition is greater in warm seasons due to stronger Hg0 oxidation. However, the contribution from anthropogenic sources is smaller in warm seasons because of larger emissions from natural processes and stronger vertical mixing that facilitates transport.     

Chromium (III) removal by supported liquid membranes: a comparison among D2HEPA, DNNSA, and a novel extractant as carriers.

A facilitated transport study in supported liquid membranes (SLM) using the extraction reagents di-2-ethylexilfosphoric acid (D2HEPA), dinonylnaftalene sulfuric acid (DNNSA), and a novel complexing agent, trimethyl cis,cis-1,3,5-tripropyl-1,3,5 cyclohexenetricarboxilic acid (TTCHTCA) as carriers has been carried out. Organic solvents with different dielectric constants as diluents have been used to obtain the highest extraction and transport values. The results obtained have shown that, by using different organic phases (carrier and/or diluent), SLMs with different ion flux and transport ability can be obtained. The carrier concentration in the membrane and the chromium (III) [Cr(III)] ions concentration in aqueous phase have been varied to see the effect on transport of Cr(III) ions across the membrane. For the carriers D2HEPA and TTCHTCA, the transport of Cr(IlI), both in batch and in recirculation operation mode, has been studied. Very good results in terms of flux and transport have been obtained using TTCHTCA.     

Evaluation of chemical immobilization treatments for reducing heavy metal transport in a smelter-contaminated soil

Three chemical immobilization materials, agricultural limestone (AL), mineral rock phosphate (RP), and diammonium phosphate (DAP), were evaluated using solute transport experiments to determine their ability to reduce subsurface heavy metal transport in a smelter contaminated soil. Percent reductions in metals transported were based on comparison with cumulative totals of metal species eluted through 60 pore volumes from an untreated soil. Reductions of metal eluted from the AL treatment were 55% for Cd, 45.2% for Pb, and 21.9% for Zn. Rock phosphate mixed with soil at 60 and 180 g kg(-1) was generally ineffective for reducing Cd, Pb, and Zn elution with <27% reduction for Cd, Pb, and Zn. Rock phosphate placed under contaminated soil as a reactive barrier (i.e. layered RP) at 180 g kg(-1) reduced Cd 53% and Zn 24%, and was the most efficient treatment for reducing Pb (99.9%) transport. DAP treatments were superior to all other materials for reducing Cd and Zn elution with reduction >77% for Zn and >91% for Cd from the 90 g DAP kg(-1) treatment. Increasing DAP from 10 to 90 g kg(-1) increased total arsenic released from 0.13 to 29.5 mg kg(-1) and total P eluted from 2.31 to 335 mg. DAP at 10 g kg(-1) was the most effective treatment for immobilizing the combination of Cd, Pb, and Zn, with reductions of 94.6, 98.9, and 95.8%, respectively.     

Bacteria transport and deposition under unsaturated conditions: the role of the matrix grain size and the bacteria surface protein

Unsaturated (80% water saturated) packed column experiments were conducted to investigate the influence of grain size distribution and bacteria surface macromolecules on bacteria (Rhodococcus rhodochrous) transport and deposition mechanisms. Three sizes of silica sands were used in these transport experiments, and their median grain sizes were 607, 567, and 330 microm. The amount of retained bacteria increased with decreasing sand size, and most of the deposited bacteria were found adjacent to the column inlet. The deposition profiles were not consistent with predictions based on classical filtration theory. The experimental data could be accurately characterized using a mathematical model that accounted for first-order attachment, detachment, and time and depth-dependent straining processes. Visual observations of the bacteria deposition as well as mathematical modelling indicated that straining was the dominant mechanism of deposition in these sands (78-99.6% of the deposited bacteria), which may have been enhanced due to the tendency of this bacterium to form aggregates. An additional unsaturated experiment was conducted to better deduce the role of bacteria surface macromolecules on attachment and straining processes. In this case, the bacteria surface was treated using a proteolitic enzyme. This technique was assessed by examining the Fourier-transform infrared spectrum and hydrophobicity of untreated and enzyme treated cells. Both of these analytical procedures demonstrated that this enzymatic treatment removed the surface proteins and/or associated macromolecules. Transport and modelling studies conducted with the enzyme treated bacteria, revealed a decrease in attachment, but that straining was not significantly affected by this treatment.     

Modeling transport and deposition of contaminants to ecosystems of concern: a case study for the Laurentian Great Lakes

Transfer efficiency (TE) is introduced as a model output that can be used to characterize the relative ability of chemicals to be transported in the environment and deposited to specific target ecosystems. We illustrate this concept by applying the Berkeley-Trent North American contaminant fate model (BETR North America) to identify organic chemicals with properties that result in efficient atmospheric transport and deposition to the Laurentian Great Lakes. By systematically applying the model to hypothetical organic chemicals that span a wide range of environmental partitioning properties, we identify combinations of properties that favor efficient transport and deposition to the Lakes. Five classes of chemicals are identified based on dominant transport and deposition pathways, and specific examples of chemicals in each class are identified and discussed. The role of vegetation in scavenging chemicals from the atmosphere is assessed, and found to have a negligible influence on transfer efficiency to the Great Lakes. Results indicate chemicals with octanol-water (K(ow)) and air-water (K(aw)) partition coefficients in the range of 10(5)-10(7) and 10(-4)-10(-1) combine efficient transport and deposition to the Great Lakes with potential for biaccumulation in the aquatic food web once they are deposited. A method of estimating the time scale for atmospheric transport and deposition process is suggested, and the effects of degrading reactions in the atmosphere and meteorological conditions on transport efficiency of different classes of chemicals are discussed. In total, this approach provides a method of identifying chemicals that are subject to long-range transport and deposition to specific target ecosystems as a result of their partitioning and persistence characteristics. Supported by an appropriate contaminant fate model, the approach can be applied to any target ecosystem of concern.     

Modeling of electrodialytic and dialytic removal of Cr, Cu and As from CCA-treated wood chips

A one-dimensional model is developed for simulating the electrodialytic and dialytic treatment of a saturated bed of wood chips containing chromium, copper and arsenic. The movement of Cr, Cu and As is mathematically modeled taking into account the diffusion transport resulting from the concentration gradients of their compounds and the electromigration of their ionic, simple and complex species during the operation. The model also includes the electromigration of the non-contaminant principal ionic species in the system, H(+) and OH(-), proceeding from the electrolysis at the electrodes, Na(+) and NO(3)(-) used as electrolyte solutions in the electrode compartments, and oxalate ions and protons incorporated with the oxalic acid solution during wood chips incubation. The model simulation also takes into account that OH(-) generated on the cathode, during electrodialytic remediation, is periodically neutralized by addition of nitric acid in the cathode compartment. The anion and cation-exchange membranes are simply represented as ionic filters that preclude the transport of co-ions (the cations and anions respectively) with the exception of H(+), which is retarded but considered to pass through the anion-exchange membrane.     

Adsorption and transport of arsenate in carbonate-rich soils: coupled effects of nonlinear and rate-limited sorption

The transport and fate of arsenate in carbonate-rich soil under alkaline conditions was investigated with multiple approaches combining batch, sequential extraction and column experiments as well as transport modeling studies. Batch experiments indicated that sorption isotherm was nonlinear over a wide range of concentration (0.1-200 mg L(-1)) examined. As(V) adsorption to the calcareous soil was initially fast but then continued at a slower rate, indicating the potential effect of rate-limited sorption on transport. Column experiments illustrated that transport of As(V) was significantly retarded compared to a non-reactive tracer. The degree of retardation decreased with increasing As(V) concentration. As(V) breakthrough curves exhibited nonideal transport behavior due to the coupled effects of nonlinear and rate-limited sorption on arsenate transport, which is consistent with the results of modeling studies. The contribution of nonlinear sorption to the arsenate retardation was negligible at low concentration but increased with increasing As(V) concentration. Sequential extraction results showed that nonspecifically sorbed (easily exchangeable, outer sphere complexes) fraction of arsenate is dominant with respect to the inner-sphere surface bound complexes of arsenate in the carbonate soil fraction, indicating high bioavailability and transport for arsenate in the carbonate-rich soils of which Fe and Al oxyhydroxide fractions are limited.     

Transport of Escherichia coli in 25 m quartz sand columns

To help improve the prediction of bacteria travel distances in aquifers laboratory experiments were conducted to measure the distant dependent sticking efficiencies of two low attaching Escherichia coli strains (UCFL-94 and UCFL-131). The experimental set up consisted of a 25 m long helical column with a diameter of 3.2 cm packed with 99.1% pure-quartz sand saturated with a solution of magnesium sulfate and calcium chloride. Bacteria mass breakthrough at sampling distances ranging from 6 to 25.65 m were observed to quantify bacteria attachment over total transport distances (α(L)) and sticking efficiencies at large intra-column segments (α(i)) (>5m). Fractions of cells retained (F(i)) in a column segment as a function of α(i) were fitted with a power-law distribution from which the minimum sticking efficiency defined as the sticking efficiency of 0.001% bacteria fraction of the total input mass retained that results in a 5 log removal were extrapolated. Low values of α(L) in the order 10(-4) and 10(-3) were obtained for UCFL-94 and UCFL-131 respectively, while α(i)-values ranged between 10(-6) to 10(-3) for UCFL-94 and 10(-5) to 10(-4) for UCFL-131. In addition, both α(L) and α(i) reduced with increasing transport distance, and high coefficients of determination (0.99) were obtained for power-law distributions ofα(i) for the two strains. Minimum sticking efficiencies extrapolated were 10(-7) and 10(-8) for UCFL-94 and UCFL-131, respectively. Fractions of cells exiting the column were 0.19 and 0.87 for UCFL-94 and UCL-131, respectively. We concluded that environmentally realistic sticking efficiency values in the order of 10(-4) and 10(-3) and much lower sticking efficiencies in the order 10(-5) are measurable in the laboratory, Also power-law distributions in sticking efficiencies commonly observed for limited intra-column distances (<2m) are applicable at large transport distances(>6m) in columns packed with quartz grains. High fractions of bacteria populations may possess the so-called minimum sticking efficiency, thus expressing their ability to be transported over distances longer than what might be predicted using measured sticking efficiencies from experiments with both short (<1m) and long columns (>25 m). Also variable values of sticking efficiencies within and among the strains show heterogeneities possibly due to variations in cell surface characteristics of the strains. The low sticking efficiency values measured express the importance of the long columns used in the experiments and the lower values of extrapolated minimum sticking efficiencies makes the method a valuable tool in delineating protection areas in real-world scenarios.