... Author(s), Wilkinson, Kevin J ; Lead, Jamie R. ... This site is also available in the followi... more ... Author(s), Wilkinson, Kevin J ; Lead, Jamie R. ... This site is also available in the following languages: Български Català Deutsch Ελληνικά English Español Français Hrvatski Italiano 日本語 ქართული Norsk/Bokmål Polski Português Русский Slovensky Svenska 中文(简) 中文(繁).
Measurements of the diffusion coefficients of five different humic substances (HS) have been perf... more Measurements of the diffusion coefficients of five different humic substances (HS) have been performed in water and in agarose hydrogels at several pH values (in the range of 3-10) and gel concentrations (in the range of 0.7-3% w/w). Fluorescence correlation spectroscopy (FCS) and classical diffusion cells were used in parallel to probe diffusion over both microscopic and mesoscopic distance scales. In general, agreement between the techniques was reasonable, which indicated that local nonhomogenities in the gel did not play an important role. Diffusion coefficients (D) in the gel were generally in the range of 0.9-2.5 x 10(-10) m2 s(-1) but were generally only 10-20% lower than in solution. At low pH values, one of the studied humic substances (a peat humic acid, PPHA) formed large aggregates that could not penetrate into the gel and therefore could not be defined by a single D value. The observed decreases of D in the gel for other HS were too large to be explained by the tortuousity and obstructive effects of the gel alone. D decreased slightly with increasing gel concentration and increased slightly with pH. Because modifications of D due to pH were similar in both the gel and the free solution, it is unlikely that complexation with the gel was greatly influenced by the pH. Rather, the main effect that appeared to decrease the diffusive flux in gels was likely small increases in the hydrodynamic radii of the humic macromolecules. An anomalous diffusion model was used to describe the FCS data in the gel. The characteristic exponent determined by fitting the autocorrelation functions with this model decreased only slightly (from 0.96 to 0.90) with increasing gel concentration providing support that HS complexation with the gel fibers was not very important. The results have important implications for our understanding of the fate and behavior of the HS and their associated pollutants and for interpreting metal speciation data obtained using gel-covered analytical sensors.
Cetylpyridinium chloride (CPC) is a surfactant that binds strongly to bacteria and bacterial biof... more Cetylpyridinium chloride (CPC) is a surfactant that binds strongly to bacteria and bacterial biofilms. In this study, fluorescence-based techniques were used to determine the penetration and adhesion of CPC when it was introduced in liposomes. In spite of a reduced adhesion as compared to pure CPC micelles, CPC-containing liposomes adhered significantly to the biofilms of Streptococcus mutans. In contrast, no binding was observed for liposomes that were composed of phosphatidylcholine-cholesterol. The influence of the charge of the liposome on its adhesion to biofilms was studied using cholesterol (Chol) and cholesterol sulfate (Schol). In spite of similar binding to the biofilms, positively charged CPC/Chol liposomes were located mainly in the core of the biofilm microcolonies, whereas the negatively charged CPC/Schol liposomes were mainly concentrated at their periphery. This effect may be attributed to the different availability of the CPC head group. In summary, this work demonstrates the high potential for tailoring drug nanovectors by modulating sterol selection in order to selectively target and bind biofilms.
Over the past decade, researchers have begun to use metals of the lanthanide family for numerous ... more Over the past decade, researchers have begun to use metals of the lanthanide family for numerous applications, including liquid crystal display (LCD) screens, optical fibers and laser technology. Unfortunately, little is presently known about their bioavailability or the mechanisms by which they might cause toxicity. This paper focuses on cerium, which is one of the most widely used lanthanides, and focuses on validating the biotic ligand model as a means to predict Ce bioaccumulation. Short term exposures to Ce were performed using the unicellular alga, Chlamydomonas reinhardtii, in order to better relate Ce bioavailability to its chemical speciation in solution. Maximum uptake fluxes (Jmax ) and affinity constants for the binding of cerium to the biological uptake sites (KS ) were established at pH 5.0 and pH 7.0. An apparent affinity constant of 1.8 × 10(7) M(-1) was observed at pH 5.0, with a larger value obtained at pH 7.0 (6 × 10(7) M(-1) ), albeit under conditions where equilibrium could not be confirmed. By evaluating cerium speciation using centrifugal ultrafiltration and single particle inductively coupled plasma spectrometry, it could be concluded that very little (∼30%) cerium was truly dissolved at pH 7.0, with the majority of the metal being present in colloidal species. Speciation was also monitored by fluorescence in order to evaluate Ce complexation by natural organic matter (NOM). The presence of NOM increased decreased Ce bioaccumulation in line with free Ce concentrations. Finally, competition with calcium for the metal uptake sites was shown to result in a decrease in cerium uptake by C. reinhardtii. This article is protected by copyright. All rights reserved.
ABSTRACT Years of experimentation in well-defined media has demonstrated that trace metal bioavai... more ABSTRACT Years of experimentation in well-defined media has demonstrated that trace metal bioavailability should be best predicted by the concentration (or activity) of the free cation (free ion activity model, FIAM). In the particular case of lead, uptake of Pb by Chlorella kessleri has been, however, shown to be higher in the presence of the Suwannee River fulvic acid and Suwannee River humic acid as compared to what was predicted by the free ion concentrations [Pb2+]. In order to estimate whether such exceptions of the FIAM can be extended to other freshwater phytoplankton, we measured the biouptake of Pb by C. reinhardtii another model phytoplankton, in solution containing these two model humic substances and for which free Pb2+ concentrations were evaluated using an ion-exchange technique. Our results showed that Pb internalization by C. reinhardtii can be directly related to the [Pb2+] but that the deviation from the FIAM when using C. kessleri was still observed under the present experimental conditions. Indeed, when using freshly isolated colloidal fraction (>3 kDa) of a marsh water and its photoaltered products, [Pb2+] measurements are shown to poorly predict Pb uptake by C. kessleri and surprisingly Pb uptake by C. reinhardtii.
The lecture will describe the physicochemical properties of the different groups of colloids and ... more The lecture will describe the physicochemical properties of the different groups of colloids and several possible interactions. Emphasis will be placed on the various types of organic components, including fulvic compounds. The role of each colloid class will be discussed with respect to homoaggregation (aggregation within a given colloid class) and heteroaggregation (aggregation among different colloid types). Based on a
Carbohydrates have been shown to attain 25% of the organic matter pool during periods of high pro... more Carbohydrates have been shown to attain 25% of the organic matter pool during periods of high productivity in a small eutrophic lake. The chemical nature of the organic matter in the wal.er column, as determined by its source, had an important influence on its role in the coagulation and aggregation of inorganic colloids. During periods of high productivity, inorganic colloids
In order to realize the vision of the Semantic Web, a semantic model for encoding content in the ... more In order to realize the vision of the Semantic Web, a semantic model for encoding content in the World Wide Web, efficient storage and retrieval of large RDF data sets is required. A common technique for storing RDF data (graphs) is to use a single relational database table, a triple store, for the graph. However, we believe a single triple
Comparative biochemistry and physiology. Toxicology & pharmacology : CBP
The purpose of this study was to determine the cumulative effects of exposure to either dissolved... more The purpose of this study was to determine the cumulative effects of exposure to either dissolved zinc or nanozinc oxide (nanoZnO) and air-time survival in freshwater mussels. Mussels were exposed to each forms of zinc for 96h then placed in air to determine survival time. A sub-group of mussels before and after 7days of exposure to air were kept aside for the determination of the following biomarkers: arachidonate-dependent cyclooxygenase (COX) and peroxidase (inflammation and oxidative stress), lipid metabolism (total lipids, esterases activity, HO-glycerol, acetyl CoA and phospholipase A2) and lipid damage (lipid peroxidation [LPO]). The results showed that air-time survival was decreased from a mean value of 18.5days to a mean value of 12days in mussels exposed to 2.5mg/L of nanoZnO although it was not lethal based on shell opening at concentrations below 50mg/L after 96h. In mussels exposed to zinc only, the median lethal concentration was estimated at 16mg/L (10-25 95% CI). Th...
The characterization of nanomaterials represents a complex analytical challenge due to their dyna... more The characterization of nanomaterials represents a complex analytical challenge due to their dynamic nature (small size, high reactivity, and instability) and the low concentrations in the environment, often below typical analytical detection limits. Analytical ultracentrifugation (AUC) is especially useful for the characterization of small nanoparticles (1-10 nm), which are often the most problematic for the commonly used techniques such as electron microscopy or dynamic light scattering. In this study, small polymeric nanomaterials (allospheres) that are used commercially to facilitate the distribution of pesticides in agricultural fields were characterized under a number of environmentally relevant conditions. Under most of the studied conditions, the allospheres were shown to have a constant hydrodynamic diameter (dH) of about 7.0 nm. Only small increases in diameter were observed, either at low pH or very high ionic strength or hardness, demonstrating their high physicochemical...
The increasing production of ZnO nanoparticles (nZnO) makes their analysis and characterization e... more The increasing production of ZnO nanoparticles (nZnO) makes their analysis and characterization extremely important from an ecological risk perspective, especially at the low concentrations at which they are expected to be found in natural waters. Single particle ICPMS (SP-ICPMS) is one of the few techniques available to detect and characterize nanoparticles at environmentally relevant concentrations. Unfortunately, at the very low particle concentrations where SP-ICPMS is performed, significant dissolution of the nZnO generally increases background levels of dissolved Zn to the point where measurements are not generally possible. By hyphenating SP-ICPMS with an ion-exchange resin, it was possible to characterize and quantify nZnO in order to gain insight into the nature of the nZnO in natural waters. Spiked and unspiked water samples were analyzed using a SP-ICPMS that was coupled to a column containing a strong metal binding resin (Chelex 100). In addition to the detection of ZnO nanoparticles and the determination of a size distribution in natural waters, it was possible to partition the dissolved Zn among free and/or labile and strongly bound Zn fractions. In two natural waters, a high proportion (ca. 93-100%) of dissolved Zn was measured, and the residual ZnO particles were mainly composed of small agglomerates (average sizes ranging from 133.6 to 172.4 nm in the surface water and from 167.6 to 216.4 nm in the wastewater effluent). Small numbers of small nanoparticles were also detected in nonspiked waters.
... Author(s), Wilkinson, Kevin J ; Lead, Jamie R. ... This site is also available in the followi... more ... Author(s), Wilkinson, Kevin J ; Lead, Jamie R. ... This site is also available in the following languages: Български Català Deutsch Ελληνικά English Español Français Hrvatski Italiano 日本語 ქართული Norsk/Bokmål Polski Português Русский Slovensky Svenska 中文(简) 中文(繁).
Measurements of the diffusion coefficients of five different humic substances (HS) have been perf... more Measurements of the diffusion coefficients of five different humic substances (HS) have been performed in water and in agarose hydrogels at several pH values (in the range of 3-10) and gel concentrations (in the range of 0.7-3% w/w). Fluorescence correlation spectroscopy (FCS) and classical diffusion cells were used in parallel to probe diffusion over both microscopic and mesoscopic distance scales. In general, agreement between the techniques was reasonable, which indicated that local nonhomogenities in the gel did not play an important role. Diffusion coefficients (D) in the gel were generally in the range of 0.9-2.5 x 10(-10) m2 s(-1) but were generally only 10-20% lower than in solution. At low pH values, one of the studied humic substances (a peat humic acid, PPHA) formed large aggregates that could not penetrate into the gel and therefore could not be defined by a single D value. The observed decreases of D in the gel for other HS were too large to be explained by the tortuousity and obstructive effects of the gel alone. D decreased slightly with increasing gel concentration and increased slightly with pH. Because modifications of D due to pH were similar in both the gel and the free solution, it is unlikely that complexation with the gel was greatly influenced by the pH. Rather, the main effect that appeared to decrease the diffusive flux in gels was likely small increases in the hydrodynamic radii of the humic macromolecules. An anomalous diffusion model was used to describe the FCS data in the gel. The characteristic exponent determined by fitting the autocorrelation functions with this model decreased only slightly (from 0.96 to 0.90) with increasing gel concentration providing support that HS complexation with the gel fibers was not very important. The results have important implications for our understanding of the fate and behavior of the HS and their associated pollutants and for interpreting metal speciation data obtained using gel-covered analytical sensors.
Cetylpyridinium chloride (CPC) is a surfactant that binds strongly to bacteria and bacterial biof... more Cetylpyridinium chloride (CPC) is a surfactant that binds strongly to bacteria and bacterial biofilms. In this study, fluorescence-based techniques were used to determine the penetration and adhesion of CPC when it was introduced in liposomes. In spite of a reduced adhesion as compared to pure CPC micelles, CPC-containing liposomes adhered significantly to the biofilms of Streptococcus mutans. In contrast, no binding was observed for liposomes that were composed of phosphatidylcholine-cholesterol. The influence of the charge of the liposome on its adhesion to biofilms was studied using cholesterol (Chol) and cholesterol sulfate (Schol). In spite of similar binding to the biofilms, positively charged CPC/Chol liposomes were located mainly in the core of the biofilm microcolonies, whereas the negatively charged CPC/Schol liposomes were mainly concentrated at their periphery. This effect may be attributed to the different availability of the CPC head group. In summary, this work demonstrates the high potential for tailoring drug nanovectors by modulating sterol selection in order to selectively target and bind biofilms.
Over the past decade, researchers have begun to use metals of the lanthanide family for numerous ... more Over the past decade, researchers have begun to use metals of the lanthanide family for numerous applications, including liquid crystal display (LCD) screens, optical fibers and laser technology. Unfortunately, little is presently known about their bioavailability or the mechanisms by which they might cause toxicity. This paper focuses on cerium, which is one of the most widely used lanthanides, and focuses on validating the biotic ligand model as a means to predict Ce bioaccumulation. Short term exposures to Ce were performed using the unicellular alga, Chlamydomonas reinhardtii, in order to better relate Ce bioavailability to its chemical speciation in solution. Maximum uptake fluxes (Jmax ) and affinity constants for the binding of cerium to the biological uptake sites (KS ) were established at pH 5.0 and pH 7.0. An apparent affinity constant of 1.8 × 10(7) M(-1) was observed at pH 5.0, with a larger value obtained at pH 7.0 (6 × 10(7) M(-1) ), albeit under conditions where equilibrium could not be confirmed. By evaluating cerium speciation using centrifugal ultrafiltration and single particle inductively coupled plasma spectrometry, it could be concluded that very little (∼30%) cerium was truly dissolved at pH 7.0, with the majority of the metal being present in colloidal species. Speciation was also monitored by fluorescence in order to evaluate Ce complexation by natural organic matter (NOM). The presence of NOM increased decreased Ce bioaccumulation in line with free Ce concentrations. Finally, competition with calcium for the metal uptake sites was shown to result in a decrease in cerium uptake by C. reinhardtii. This article is protected by copyright. All rights reserved.
ABSTRACT Years of experimentation in well-defined media has demonstrated that trace metal bioavai... more ABSTRACT Years of experimentation in well-defined media has demonstrated that trace metal bioavailability should be best predicted by the concentration (or activity) of the free cation (free ion activity model, FIAM). In the particular case of lead, uptake of Pb by Chlorella kessleri has been, however, shown to be higher in the presence of the Suwannee River fulvic acid and Suwannee River humic acid as compared to what was predicted by the free ion concentrations [Pb2+]. In order to estimate whether such exceptions of the FIAM can be extended to other freshwater phytoplankton, we measured the biouptake of Pb by C. reinhardtii another model phytoplankton, in solution containing these two model humic substances and for which free Pb2+ concentrations were evaluated using an ion-exchange technique. Our results showed that Pb internalization by C. reinhardtii can be directly related to the [Pb2+] but that the deviation from the FIAM when using C. kessleri was still observed under the present experimental conditions. Indeed, when using freshly isolated colloidal fraction (>3 kDa) of a marsh water and its photoaltered products, [Pb2+] measurements are shown to poorly predict Pb uptake by C. kessleri and surprisingly Pb uptake by C. reinhardtii.
The lecture will describe the physicochemical properties of the different groups of colloids and ... more The lecture will describe the physicochemical properties of the different groups of colloids and several possible interactions. Emphasis will be placed on the various types of organic components, including fulvic compounds. The role of each colloid class will be discussed with respect to homoaggregation (aggregation within a given colloid class) and heteroaggregation (aggregation among different colloid types). Based on a
Carbohydrates have been shown to attain 25% of the organic matter pool during periods of high pro... more Carbohydrates have been shown to attain 25% of the organic matter pool during periods of high productivity in a small eutrophic lake. The chemical nature of the organic matter in the wal.er column, as determined by its source, had an important influence on its role in the coagulation and aggregation of inorganic colloids. During periods of high productivity, inorganic colloids
In order to realize the vision of the Semantic Web, a semantic model for encoding content in the ... more In order to realize the vision of the Semantic Web, a semantic model for encoding content in the World Wide Web, efficient storage and retrieval of large RDF data sets is required. A common technique for storing RDF data (graphs) is to use a single relational database table, a triple store, for the graph. However, we believe a single triple
Comparative biochemistry and physiology. Toxicology & pharmacology : CBP
The purpose of this study was to determine the cumulative effects of exposure to either dissolved... more The purpose of this study was to determine the cumulative effects of exposure to either dissolved zinc or nanozinc oxide (nanoZnO) and air-time survival in freshwater mussels. Mussels were exposed to each forms of zinc for 96h then placed in air to determine survival time. A sub-group of mussels before and after 7days of exposure to air were kept aside for the determination of the following biomarkers: arachidonate-dependent cyclooxygenase (COX) and peroxidase (inflammation and oxidative stress), lipid metabolism (total lipids, esterases activity, HO-glycerol, acetyl CoA and phospholipase A2) and lipid damage (lipid peroxidation [LPO]). The results showed that air-time survival was decreased from a mean value of 18.5days to a mean value of 12days in mussels exposed to 2.5mg/L of nanoZnO although it was not lethal based on shell opening at concentrations below 50mg/L after 96h. In mussels exposed to zinc only, the median lethal concentration was estimated at 16mg/L (10-25 95% CI). Th...
The characterization of nanomaterials represents a complex analytical challenge due to their dyna... more The characterization of nanomaterials represents a complex analytical challenge due to their dynamic nature (small size, high reactivity, and instability) and the low concentrations in the environment, often below typical analytical detection limits. Analytical ultracentrifugation (AUC) is especially useful for the characterization of small nanoparticles (1-10 nm), which are often the most problematic for the commonly used techniques such as electron microscopy or dynamic light scattering. In this study, small polymeric nanomaterials (allospheres) that are used commercially to facilitate the distribution of pesticides in agricultural fields were characterized under a number of environmentally relevant conditions. Under most of the studied conditions, the allospheres were shown to have a constant hydrodynamic diameter (dH) of about 7.0 nm. Only small increases in diameter were observed, either at low pH or very high ionic strength or hardness, demonstrating their high physicochemical...
The increasing production of ZnO nanoparticles (nZnO) makes their analysis and characterization e... more The increasing production of ZnO nanoparticles (nZnO) makes their analysis and characterization extremely important from an ecological risk perspective, especially at the low concentrations at which they are expected to be found in natural waters. Single particle ICPMS (SP-ICPMS) is one of the few techniques available to detect and characterize nanoparticles at environmentally relevant concentrations. Unfortunately, at the very low particle concentrations where SP-ICPMS is performed, significant dissolution of the nZnO generally increases background levels of dissolved Zn to the point where measurements are not generally possible. By hyphenating SP-ICPMS with an ion-exchange resin, it was possible to characterize and quantify nZnO in order to gain insight into the nature of the nZnO in natural waters. Spiked and unspiked water samples were analyzed using a SP-ICPMS that was coupled to a column containing a strong metal binding resin (Chelex 100). In addition to the detection of ZnO nanoparticles and the determination of a size distribution in natural waters, it was possible to partition the dissolved Zn among free and/or labile and strongly bound Zn fractions. In two natural waters, a high proportion (ca. 93-100%) of dissolved Zn was measured, and the residual ZnO particles were mainly composed of small agglomerates (average sizes ranging from 133.6 to 172.4 nm in the surface water and from 167.6 to 216.4 nm in the wastewater effluent). Small numbers of small nanoparticles were also detected in nonspiked waters.
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