Aquatic organisms modulate the bioreactivity of engineered nanoparticles: focus on biomolecular corona.

The increased use of nanoparticle (NP)-enabled materials in everyday-life products have raised concerns about their environmental implications and safety. This motivated the extensive research in nanoecotoxicology showing the possibility that NPs could cause harm to the aquatic organisms if present at high concentrations. By contrast, studies dealing with influence that organisms could exert on the fate and thus effects of NPs are still very rare. Drawing on the existing up-to-date knowledge we critically discuss the formation of biomolecular corona as one of the mechanisms by which organisms exerted control on the NPs fate in the aquatic and biotic environments. We focused the formation of corona by exogeneous and endogenous biomolecules and illustrated the discussion with the specific example of phytoplankton and aquatic invertebrate species. We highlighted the necessity to incorporate the concept of biomolecular corona within more general framework considering the feedback of aquatic organisms and the control they exert in shaping the fate and impact of NPs in the aquatic and biological environment. In our view such broader perspective will contribute to get novel insights into the drivers of environmental transformations of NPs and their mechanisms, which are important in environmental risk assessment.

Asymmetrical Flow Field-Flow Fractionation Methods for Quantitative Determination and Size Characterization of Thiols and for Mercury Size Speciation Analysis in Organic Matter-Rich Natural Waters.

Asymmetrical flow field-flow fractionation (AF4) efficiently separates various macromolecules and nano-components of natural waters according to their hydrodynamic sizes. The online coupling of AF4 with fluorescence (Fluo) and UV absorbance (UV) detectors (FluoD and UVD, respectively) and inductively coupled plasma-mass spectrometry (ICP-MS) provides multidimensional information. This makes it a powerful tool to characterize and quantify the size distributions of organic and inorganic nano-sized components and their interaction with trace metals. In this study, we developed a method combining thiol labeling by monobromo(trimethylammonio)bimane bromide (qBBr) with AF4-FluoD to determine the size distribution and the quantities of thiols in the macromolecular dissolved organic matter (DOM) present in highly colored DOM-rich water sampled from Shuya River and Lake Onego, Russia. We found that the qBBr-labeled components of DOM (qB-DOM) were of humic type, characterized by a low hydrodynamic size (d h < 2 nm), and have concentrations <0.3 µM. After enrichment with mercury, the complexes formed between the nano-sized components and Hg were analyzed using AF4-ICP-MS. The elution profile of Hg followed the distribution of the UV-absorbing components of DOM, characterized by slightly higher sizes than qB-DOM. Only a small proportion of Hg was associated with the larger-sized components containing Fe and Mn, probably inorganic oxides that were identified in most of the samples from river to lake. The size distribution of the Hg-DOM complexes was enlarged when the concentration of added Hg increased (from 10 to 100 nM). This was explained by the presence of small iron oxides, overlapping the size distribution of Hg-DOM, on which Hg bound to a small proportion. In addition, to provide information on the dispersion of macromolecular thiols in colored DOM-rich natural water, our study also illustrated the potential of AF4-FluoD-UVD-ICP-MS to trace or quantify dynamic changes while Hg binds to the natural nano-colloidal components of surface water.

Asymmetrical Flow Field-Flow Fractionation Coupled to ICP-MS for Characterization of Trace Metal Species in the Environment from Macromolecular to Nano-Assemblage Forms: Current Challenges for Quantification.

Asymmetrical flow field-flow fractionation (AF4) is a powerful technique employed for the separation of macromolecules, nanoparticles, and their assemblages according to their hydrodynamic behavior. It is well known that at this size range, complex interactions can occur between components (e.g. surface adsorption, aggregation) controlling the fate of trace metals (TMs) bound to them. AF4 coupling to inductively coupled plasma mass spectrometry (ICP-MS) allows the quantification of metal-containing species at trace levels present in environmental and biological systems on a size-composition basis. The combination of AF4-ICP-MS with other online detectors provides additional information that allows the assessment of the origin of analytes present in mixtures and complex matrixes with minimal sample preparation, which is crucial for understanding the behavior of trace metal contaminants. Despite the increasing use of AF4-ICP-MS in environmental contexts, we acknowledge that the quantification of inorganic species using such combined techniques requires further development of standardized procedures and need certified reference materials. In this review, we also discuss critical endpoints within the ICP-MS instrument coupled to AF4 that need to be controlled before quantitative measurements can be validated. Then, we illustrate how the combination of different online detectors in addition to ICP-MS offers an integrated picture of natural components states, thus providing key information on the changes in behavior of trace metal species and metallic nanoparticles (MNPs) as observed in both environmental samples and biofluids.

Species-specific isotope tracking of mercury uptake and transformations by pico-nanoplankton in an eutrophic lake.

The present study aims to explore the bioaccumulation and biotic transformations of inorganic (iHg) and monomethyl mercury (MMHg) by natural pico-nanoplankton community from eutrophic lake Soppen, Switzerland. Pico-nanoplankton encompass mainly bacterioplankton, mycoplankton and phytoplankton groups with size between 0.2 and 20 µm. Species-specific enriched isotope mixture of 199iHg and 201MMHg was used to explore the accumulation, the subcellular distribution and transformations occurring in natural pico-nanoplankton sampled at 2 different depths (6.6 m and 8.3 m). Cyanobacteria, diatoms, cryptophyta, green algae and heterotrophic microorganisms were identified as the major groups of pico-nanoplankton with diatoms prevailing at deeper samples. Results showed that pico-nanoplankton accumulated both iHg and MMHg preferentially in the cell membrane/organelles, despite observed losses. The ratios between the iHg and MMHg concentrations measured in the membrane/organelles and cytosol were comparable for iHg and MMHg. Pico-nanoplankton demethylate added 201MMHg (~4 and 12% per day depending on cellular compartment), although the involved pathways are to further explore. Comparison of the concentrations of 201iHg formed from 201MMHg demethylation in whole system, medium and whole cells showed that 82% of the demethylation was biologically mediated by pico-nanoplankton. No significant methylation of iHg by pico-nanoplankton was observed. The accumulation of iHg and MMHg and the percentage of demethylated MMHg correlated positively with the relative abundance of diatoms and heterotrophic microorganisms in the pico-nanoplankton, the concentrations of TN, Mg2+, NO3-, NO2-, NH4+ and negatively with the concentrations of DOC, K+, Na+, Ca2+, SO42-. Taken together the results of the present field study confirm the role of pico-nanoplankton in Hg bioaccumulation and demethylation, however further research is needed to better understand the underlying mechanisms and interconnection between heterotrophic and autotrophic microorganisms.

Microbial community diversity and composition in river sediments contaminated with tetrabromobisphenol A and copper.

The microbial community composition in aquatic ecosystems have received increased attention. However, the knowledge gap relative to the responses of bacterial, archaeal and fungal communities in co-contaminated river sediments remain poorly studied. Here, we investigated the changes of tetrabromobisphenol A (TBBPA) and copper (Cu) concentrations and the responses of microbial communities in co-contaminated sediments during long-term incubation. TBBPA concentrations significantly decreased over time, whereas Cu concentrations remained relatively stable over the 60-day incubation. Abundances of the bacterial 16S rRNA, archaeal 16S rRNA and fungal ITS genes ranged from 6.53 × 106 to 1.26 × 109 copies g-1, 1.12 × 106 to 5.47 × 106 copies g-1 and 5.33 × 103 to 7.51 × 104 copies g-1 in the samples, respectively. A total of 11, 6 and 5 bacterial, archaeal and fungal phyla were identified across all samples. Bacterial, archaeal and fungal communities mainly consisted of members from the phyla Proteobacteria and Acidobacteria, Methanomicrobia and Woesearchaeia as well as Agaricales and Helotiales, respectively. Fungal communities showed a stronger response to pollutant addition after a long incubation compared with bacterial and archaeal communities. The variance analysis results revealed that the bacterial, archaeal and fungal microbial communities of all treatments were distinctly distributed into two separated clusters according to incubation time. However, the three microbial communities did not significantly change in response to pollutant types, which was consistent with variation in relative abundances of the three microbial communities. These findings improve our understanding of the ecotoxicological effects of co-exposure on sediment microbial communities.

When Environmental Chemistry Meets Ecotoxicology: Bioavailability of Inorganic Nanoparticles to Phytoplankton.

The present review critically examines the state-of-the-art of the research concerning the likely environmental implications of engineered nanoparticles (ENPs) with specific emphasis on their interactions with phytoplankton in the aquatic environment. Phytoplankton plays a key role in the global carbon cycle and contributes to the half of the global primary production, thus representing some of the Earth ' s most critical organisms making the life on our planet possible. With examples from our own research and the literature, we illustrate what happens when aquatic organisms are unintentionally exposed to metal-containing ENPs, which are increasingly released into the environment from nano-enabled materials. We highlight the complexity of the ENPs behavior in the aquatic environment and focus on the three key steps of the bioavailability process: exposure availability, uptake availability and toxico-availability. The influence of the phytoplankton on the ENPs fate in the aquatic environment is discussed, too.

Safer-by-design biocides made of tri-thiol bridged silver nanoparticle assemblies.

Silver nanoparticles (AgNPs) are efficient biocides increasingly used in consumer products and medical devices. Their activity is due to their capacity to release bioavailable Ag(i) ions making them long-lasting biocides but AgNPs themselves are usually easily released from the product. Besides, AgNPs are highly sensitive to various chemical environments that triggers their transformation, decreasing their activity. Altogether, widespread use of AgNPs leads to bacterial resistance and safety concerns for humans and the environment. There is thus a crucial need for improvement. Herein, a proof of concept for a novel biocide based on AgNP assemblies bridged together by a tri-thiol bioinspired ligand is presented. The final nanomaterial is stable and less sensitive to chemical environments with AgNPs completely covered by organic molecules tightly bound via their thiol functions. Therefore, these AgNP assemblies can be considered as safer-by-design and innovative biocides, since they deliver a sufficient amount of Ag(i) for biocidal activity with no release of AgNPs, which are insensitive to transformations in the nanomaterial.

Dissolved Organic Matter and Associated Trace Metal Dynamics from River to Lake, Under Ice-Covered and Ice-Free Conditions.

The present study investigates the changes in dissolved organic matter (DOM) composition and its influences on trace metal dispersion from the Shuya River (SR) in the Petrozavodsk Bay of Lake Onega during ice-covered and ice-free periods. Humic substances (HS) found in the SR dominated the composition of DOM through the river-bay-lake continuum in both periods. When the bay was ice-covered, both the aromaticity and the size of HS varied in the water column according to a horizontal stratification and decreased in the bay, while under ice-free conditions, they decreased along the river-lake gradient, suggesting in both cases a decrease in the proportion of HS with high aromatic character. These findings were associated with an overall decrease in the proportion of HS components that have the highest molecular masses. The quantification of metal bound to HS revealed that these characteristics were associated with a decrease in the binding capacity of the HS for Fe and Al but not Cu while dispersing in the bay to the lake. Pb was found to bind on HS, but its behavior in the bay could not be related to the HS dispersion nor to the changes in HS properties.

Colloidal Size and Redox State of Uranium Species in the Porewater of a Pristine Mountain Wetland.

Uranium (U) speciation was investigated in anoxically preserved porewater samples of a natural mountain wetland in Gola di Lago, Ticino, Switzerland. U porewater concentrations ranged from less than 1 µg/L to tens of µg/L, challenging the available analytical approaches for U speciation in natural samples. Asymmetrical flow field-flow fractionation coupled with inductively coupled plasma mass spectrometry allowed the characterization of colloid populations and the determination of the size distribution of U species in the porewater. Most of the U was associated with three fractions: <0.3 kDa, likely including dissolved U and very small U colloids; a 1-3 kDa fraction containing humic-like organic compounds, dispersed Fe, and, to a small extent, Fe nanoparticles; and a third fraction (5-50 nm), containing a higher amount of Fe and a lower amount of organic matter and U relative to the 1-3 kDa fraction. The proportion of U associated with the 1-3 kDa colloids varied spatially and seasonally. Using anion exchange resins, we also found that a significant proportion of U occurs in its reduced form, U(IV). Tetravalent U was interpreted as occurring within the colloidal pool of U. This study suggests that U(IV) can occur as small (1-3 kDa), organic-rich, and thus potentially mobile colloidal species in naturally reducing wetland environments.

Interaction of silver nanoparticles with metallothionein and ceruloplasmin: impact on metal substitution by Ag(i), corona formation and enzymatic activity.

The release of Ag(i) from silver nanoparticles (AgNPs) unintentionally spread in the environment is suspected to impair some key biological functions. In comparison with AgNO3, in-depth investigations were carried out into the interactions between citrate-coated AgNPs (20 nm) and two metalloproteins, intracellular metallothionein 1 (MT1) and plasmatic ceruloplasmin (Cp), both involved in metal homeostasis. These were chosen for their physiological relevance and the diversity of their various native metals bound because of thiol groups and/or their structural differences. Transmission electron microscopy (TEM), and dynamic light scattering (DLS), UV-vis and circular dichroism (CD) spectroscopies were used to study the effects of such intricate interactions on AgNP dissolution and proteins in terms of metal exchanges and structural modifications. The isolation of the different populations formed together with on-line quantifications of their metal content were performed by asymmetrical flow field-flow fractionation (AF4) linked to inductively coupled plasma mass spectrometry (ICP-MS). For the 2 proteins, Ag(i) dissolved from the AgNPs, substituted for the native metal, to different extents and with different types of dynamics for the corona formed: the MT1 rapidly surrounded the AgNPs with the transient reticulate corona thus promoting their dissolution associated with the metal substitution, whereas the Cp established a more stable layer around the AgNPs, with a limited substitution of Cu and a decrease in its ferroxidase activity. The accessibility and lability of the metal binding sites inside these proteins and their relative affinities for Ag(i) are discussed, taking into account the structural characteristics of the proteins.

Transcriptomic approach for assessment of the impact on microalga and macrophyte of in-situ exposure in river sites contaminated by chlor-alkali plant effluents.

Water quality degradation is a worldwide problem, but risk evaluation of chronic pollution in-situ is still a challenge. The present study aimed to evaluate the potential of transcriptomic analyses in representative aquatic primary producers to assess the impact of environmental pollution in-situ: the microalga Chlamydomonas reinhardtii and the macrophyte Elodea nuttallii were exposed 2 h in the Babeni Reservoir of the Olt River impacted by chlor-alkali plant effluent release resulting in increased concentrations of Hg and NaCl in receiving water. The response at the transcriptomic level was strong, resulting in up to 5485, and 8700 dysregulated genes (DG) for the microalga and for the macrophyte exposed in the most contaminated site, respectively. Transcriptomic response was congruent with the concentrations of Hg and NaCl in the water of the impacted reservoir. Genes involved in development, energy metabolism, lipid metabolism, nutrition, and RedOx homeostasis were dysregulated during in-situ exposure of both organisms. In addition, genes involved in the cell motility of C. reinhardtii and development of the cell wall of E. nuttallii were affected. DG were in line with adverse outcome pathways and transcriptomic studies reported after exposure to high concentrations of Hg and NaCl under controlled conditions in the laboratory. Transcriptomic response provided a sensitive measurement of the exposure as well as hints on the tolerance mechanisms of environmental pollution, and is thus promising as an early-warning tool to assess water quality degradation.

Photo-transformation of pedogenic humic acid and consequences for Cd(II), Cu(II) and Pb(II) speciation and bioavailability to green microalga.

Humic substances (HS) play key role in toxic metal binding and protecting aquatic microorganisms from metal-induced stress. Any environmental changes that could alter HS concentration and reactivity can be expected to modify metal complexation and thus affect metal speciation and bioavailability to microalgae. The present study explores the influence of increased solar irradiance on the chemical structures and molecular weight of Elliott soil humic acid (EHA) and the associated consequences for Cd(II), Cu(II) and Pb(II) complexation and intracellular metal content in microalga. The results demonstrate that high radiance doses induce an oxidation of EHA with a formation of low molecular weight acids, an increase of -OH and -COOH group abundance, and a drop in EHA hydrodynamic size and molecular weight. The photo-induced structural changes are accompanied with a release of metal from M-EHA complexes and narrowing their size distribution, which in turn results in an increase of the intracellular Cd, Cu and Pb contents in microalga Chlamydomonas reinhardtii in agreement with the measured free metal ions concentrations.

Impaired liver function in Xenopus tropicalis exposed to benzo[a]pyrene: transcriptomic and metabolic evidence.

BACKGROUND: Despite numerous studies suggesting that amphibians are highly sensitive to cumulative anthropogenic stresses, the role pollutants play in the decline of amphibian populations remains unclear. Amongst the most common aquatic contaminants, polycyclic aromatic hydrocarbons (PAHs) have been shown to induce several adverse effects on amphibian species in the larval stages. Conversely, adults exposed to high concentrations of the ubiquitous PAH, benzo[a]pyrene (BaP), tolerate the compound thanks to their highly efficient hepatic detoxification mechanisms. Due to this apparent lack of toxic effect on adults, no studies have examined in depth the potential toxicological impact of PAH on the physiology of adult amphibian livers. This study sheds light on the hepatic responses of Xenopus tropicalis when exposed to high environmentally relevant concentrations of BaP, by combining a high throughput transcriptomic approach (mRNA deep sequencing) and a characterization of cellular and physiological modifications to the amphibian liver. RESULTS: Transcriptomic changes observed in BaP-exposed Xenopus were further characterized using a time-dependent enrichment analysis, which revealed the pollutant-dependent gene regulation of important biochemical pathways, such as cholesterol biosynthesis, insulin signaling, adipocytokines signaling, glycolysis/gluconeogenesis and MAPK signaling. These results were substantiated at the physiological level with the detection of a pronounced metabolic disorder resulting in a possible insulin resistance-like syndrome phenotype. Hepatotoxicity induced by lipid and cholesterol metabolism impairments was clearly identified in BaP-exposed individuals. CONCLUSIONS: Our data suggested that BaP may disrupt overall liver physiology, and carbohydrate and cholesterol metabolism in particular, even after short-term exposure. These results are further discussed in terms of how this deregulation of liver physiology can lead to general metabolic impairment in amphibians chronically exposed to contaminants, thereby illustrating the role xenobiotics might play in the global decline in amphibian populations.

Cell-wall-dependent effect of carboxyl-CdSe/ZnS quantum dots on lead and copper availability to green microalgae.

The present study examines the effect of carboxyl-CdSe/ZnS quantum dots (QDs) on Cu and Pb availability to microalgae with different cell wall characteristics: Chlorella kesslerii possessing a cellulosic cell wall and two strains of Chlamydomonas reinhardtii, a wall-less and a walled strain containing glycoproteins as the main cell wall component. Results demonstrated that QDs decreased Pb and Cu intracellular contents ({Cu}(int) and {Pb}(int)) in walled strains by a factor of 2.5 and 2, respectively, as expected by the decrease of about 70% and 40% in the dissolved Cu and Pb concentrations. QDs increased {Cu}(int) and {Pb}(int) in wall-less strain by a factor of 4 and 3.5. These observations were consistent with the observed association of QDs to the wall-less C. reinhardtii, and lack of association to walled algal strains. Suwannee River humic acid did not influence metal association to QDs, but decreased {Cu}(int) and {Pb}(int) in all microalgae.

Toxicokinetic of benzo[a]pyrene and fipronil in female green frogs (Pelophylax kl. esculentus).

A general consensus that an increased logK(ow) led to an increase in xenobiotic uptake and bioaccumulation is accepted. In this study we compared the toxicokinetics of two chemically different xenobiotics, i.e. benzo[a]pyrene and fipronil in female green frogs. Surprisingly, the uptake rates and the bioconcentration factors (BCF) of the two contaminants were not predicted by their logK(ow). The uptake rates obtained were of the same order of magnitude for the two contaminants and the BCFs measured for fipronil were about 3-fold higher than those obtained for benzo[a]pyrene. Fipronil appeared to be more recalcitrant than benzo[a]pyrene to detoxification processes leading to the accumulation of sulfone-fipronil especially in the ovaries. This phenomenon may explain reproductive influence of this contaminant described in other studies. Detoxification processes, including metabolism and the excretion of pollutants, are of importance when considering their persistence in aquatic organisms and trying to quantify their risks.

Effect of humic substance photoalteration on lead bioavailability to freshwater microalgae.

The present study provides results on the influence of humic substance (HS) photoalteration on lead availability to the freshwater microalga Chlorella kesslerii . The evolution of the free lead-ion concentrations measured by the ion exchange technique [Pb](IET) and intracellular lead contents was explored in the presence of Suwannee River humic (SRHA) and fulvic (SRFA) acids, as well as Aldrich humic acid (AHA) exposed at increasing radiance doses under a solar simulator. Modifications of HS characteristics highly relevant to Pb complexation and accumulation of HS to algal surfaces, including Fourier transform infrared spectroscopy, were followed. It was demonstrated that simulated sunlight exposure of HS increased [Pb](IET) in the medium for SRFA and SRHA, but had no effect for AHA. No clear relationship was observed between the changes in free lead-ion concentrations and intracellular content in alga for all studied HS, suggesting that HS photodegradation products also exhibit Pb complexation properties, and that direct interactions between HS and alga are affected. Indeed, photoalteration of humic substances reduced the adsorption of HS to the algal surface; the effect was more pronounced for SRFA and AHA and less significant for SRHA. The bioavailability results were consistent with the characterization of the phototransformation of humic substances: Pb speciation changes followed the modification of the relative abundance of the carboxylic groups and their molecular environment, while the reduced HS adsorption to the alga correlated with losses of the double bond abundance and aromaticity.

Uptake of Cd(II) and Pb(II) by microalgae in presence of colloidal organic matter from wastewater treatment plant effluents.

The present study addresses the key issue of linking the chemical speciation to the uptake of priority pollutants Cd(II) and Pb(II) in the wastewater treatment plant effluents, with emphasis on the role of the colloidal organic matter (EfOM). Binding of Cd(II) and Pb(II) by EfOM was examined by an ion exchange technique and flow field-flow fractionation coupled to inductively coupled plasma mass spectrometry in parallel to bioassays with green microalga Chlorella kesslerii in ultrafiltrate (<1 kDa) and colloidal isolates (1 kDa to 0.45 mum). The uptake of Cd by C. kesslerii was consistent with the speciation analysis and measured free metal ion concentrations, while Pb uptake was much greater than that expected from the speciation measurement. Better understanding of the differences in the effects of the EfOM on Cd(II) and Pb(II) uptake required to take into account the size dependence of metal binding by EfOM.

Colloidal organic matter from wastewater treatment plant effluents: Characterization and role in metal distribution.

Colloidal organic matter from wastewater treatment plants was characterized and examined with respect to its role in metal distribution by using tangential flow ultrafiltration, liquid chromatography coupled with organic carbon and UV detectors, and an asymmetrical flow field-flow fractionation (AFlFFF) multidetection platform. Results revealed that a humic-like fraction of low aromaticity with an average molar mass ranging from 1600 to 2600Da was the main colloidal component. High molar mass fractions (HMM), with molar mass ranges between 20 and 200kDa, were present in lower proportions. Ag, Cd, Cu, Cr, Mn and Zn were found mainly in the dissolved phase (<0.45microm) and their distribution between colloidal and truly dissolved fractions was strongly influenced by the distribution of dissolved organic carbon. AFlFFF coupled to ICP-MS showed that Ag, Cd, Cu, Cr, Mn and Zn associate to the low molar mass fraction of the colloidal pool, whereas Al, Fe and Pb were equally bound to low and high molar mass fractions.

Influence of inorganic complexes on the transport of trace metals through permeation liquid membrane.

Under specific conditions (pH, concentrations), trace metals may form, with environmental inorganic ligands, neutral complexes which, in principle, might diffuse passively through biological membranes or influence the response of (bio)analytical sensors for trace metals based on permeation liquid membrane (PLM). In this study, metal (Cu, Cd, Pb) transport through the planar PLM device was evaluated in the presence of major environmental inorganic ligands such as sulfate, carbonate and chloride under conditions where neutral complexes may be formed (up to 73% of neutral metal complex in the solution). In the presence of sulfate, comparison of predicted and experimental PLM fluxes of Cu, Pb and Cd, suggests that passive transport of neutral sulfate-metal complexes does not occur. This was confirmed by comparing fluxes in the presence and absence of carrier. In the presence of carbonate (for Cd, Cu and Pb) and chloride (for Pb and Cd), however, experimental PLM fluxes were greater than predicted (up to 4 and 25 times in the presence of carbonate and chloride, respectively), but experiments in the absence of carrier in the membrane revealed that no passive transport of neutral complexes (MCl(2) or MCO(3)) occurs through PLM. A possible mechanism is discussed. In parallel to the experiments with PLM, the influence of carbonate on the internalization fluxes of Cu(II) and Pb(II) by the freshwater algae, Chlamydomonas reinhardtii, was assessed. Similarly to the results of PLM, the fluxes of these two metals were larger than expected (based on the free metal ion activity model). Thus, even though PLM and bioaccumulation mechanisms are certainly different, similar unexpected behaviours occur for the metal transport through the PLM and biological membrane of C. reinhardtii, in the presence of carbonate.

Determination of Ni2+ using an equilibrium ion exchange technique: Important chemical factors and applicability to environmental samples.

In natural waters, the determination of free metal concentrations is a key parameter for studying bioavailability. Unfortunately, few analytical tools are available for determining Ni speciation at the low concentrations found in natural waters. In this paper, an ion exchange technique (IET) that employs a Dowex resin is evaluated for its applicability to measure [Ni(2+)] in freshwaters. The presence of major cations (e.g. Na, Ca and Mg) reduced both the times that were required for equilibration and the partition coefficient to the resin (lambdaNi). IET measurements of [Ni(2+)] in the presence of known ligands (citrate, diglycolate, sulfoxine, oxine and diethyldithiocarbamate) were verified by thermodynamic speciation models (MINEQL(+) and VisualMINTEQ). Results indicated that the presence of hydrophobic complexes (e.g. Ni(DDC)(2)(0)) lead to an overestimation of the Ni(2+) fraction. On the other hand, [Ni(2+)] measurements that were made in the presence of amphiphilic complexes formed with humic substances (standard aquatic humic acid (SRHA) and standard aquatic fulvic acid (SRFA)) were well correlated to free ion concentrations that were calculated using a NICA-DONNAN model. An analytical method is also presented here to reduce the complexity of the calibration (due to the presence of many other cations) for the use of Dowex equilibrium ion exchange technique in natural waters.