Prediction of the bioavailability of potentially toxic elements in freshwaters. Comparison between speciation models and passive samplers

Self-flocculating Chlorella vulgaris: A high-efficiency purification mechanism of radioactive Th4+ in an aquatic environment

This study aimed to investigate the purification of radioactive thorium (Th4+) by Chlorella vulgaris in aquatic environments. Single-factor experiments and response surface optimization tests identified optimal purification conditions. The purification and metabolic response mechanisms of Chlorella to Th4+ were elucidated using physiological and biochemical analyses, three-dimensional excitation-emission matrix (3D-EEM) analysis, and metabolomic profiling. Increases in the Th4+ concentration caused Chlorella to self-flocculate, significantly improving the Th4+ purification efficiency. Under optimal conditions, the Th4+ purification efficiency for Th4+ in wastewater by Chlorella stabilized between 94.3 % and 98.2 %. Morphological analysis revealed that the purified Th4+ existed mainly in a stable residual state. Chlorella efficiently purified wastewater during treatment by regulating environmental pH, performing redox reactions, and utilizing extracellular polymeric substances (EPS) to interact with Th4+. Metabolomic analysis indicated that Chlorella adapted to the Th4+-contaminated environment and enhanced its purification function by adjusting the synthesis of metabolites, such as carbohydrates, nucleotides, and amino acids. Chlorella demonstrated a remarkable self-flocculation phenomenon and a high-efficiency purification capability for Th4+, offering new possibilities for environmental remediation. Its purification mechanism involves environmental regulation, redox reactions, and complex metabolic adjustments. The results presented here provide theoretical support for environmental remediation using Chlorella.

Remobilization characteristics and diffusion kinetic processes of sediment zinc (Zn) in a tidal reach of the Pearl River Estuary, South China

Exploration of the remobilization mechanism of trace metals in estuarine sediments remain challenging because of dynamic hydrochemical conditions. This study integrated a chemical sequential extraction procedure (BCR), the diffusive gradient in thin films (DGT) and high-resolution dialysis techniques, and Visual MINTEQ ver.3.1 to identify the seasonal mobilization characteristics of sediment Zn within a tidal reach, South China. The mobility of sediment Zn based on the BCR procedure contradicted the results of DGT analysis. In summer, reductive dissolution of Fe/Mn oxides was the key driver of sediment Zn remobilization; during winter, cation exchange reactions facilitated the mobilization of Zn in the brackish water zone. The time-dependence ratios of DGT-labile Zn and dissolved Zn concentrations (mean: 0.34-0.81) indicated the sediment solid phase had partially sustained capacity to resupply Zn to the porewater in both seasons. Sediments generally functioned as a source of Zn in the freshwater zone with organically complexed Zn being diffusively released into the water column at rates of 0.3-15.5 μg·m^-2·d^-1. In the brackish water zone, the dominant Zn species were transformed into free Zn ions and Zn-inorganic complexes and migrated into sediment, with respective influxes of 18.9-70.7 μg·m^-2·d^-1 and 18.9-68.3 μg·m^-2·d^-1, which shifted to a sink of Zn.

Appraisal on the role of passive sampling for more integrative frameworks on the environmental risk assessment of contaminants

Over time multiple lines of research have been integrated as important components of evidence for assessing the ecological quality status of water bodies within the framework of Environmental Risk Assessment (ERA) approaches. One of the most used integrative approaches is the triad which combines, based on the weight-of-evidence, three lines of research, the chemical (to identify what is causing the effect), the ecological (to identify the effects at the ecosystem level) and the ecotoxicological (to ascertain the causes of ecological damage), with the agreement between the different lines of risk evidence increasing the confidence in the management decisions. Although the triad approach has proven greatly strategic in ERA processes, new assessment (and monitoring) integrative and effective tools are most welcome. In this regard, the present study is an appraisal on the boost that passive sampling, by allowing to increase information reliability, can give within each of the triad lines of evidence, for more integrative ERA frameworks. In parallel to this appraisal, examples of works that used passive samplers within the triad are presented providing support for the use of these devices in a complementary form to generate holistic information for ERA and ease the process of decision-making.

Impacts of wastewater effluents and seasonal trends on levels of antipsychotic pharmaceuticals in water and sediments from two cold-region rivers

Most pharmaceuticals are found at trace concentrations in aquatic systems, but their continuous release and potential accumulation can lead to adverse health effects in exposed organisms. Concentrations can vary temporally, driven by variations in discharges of receiving waters, sorption to sediments, and other biotic and abiotic exchange processes. The principal aim of this research was to better understand the occurrence, trends, and dynamics of pharmaceuticals in a cold-climate, riverine environment. To this end, a suite of seven representative antipsychotic pharmaceuticals was measured upstream and downstream of two wastewater treatment plants (WWTPs) in Saskatchewan, Canada, located in the South Saskatchewan River and Wascana Creek, respectively, across three seasons. Concentrations of analytes were in the ng/L range and generally greater downstream of both WWTPs compared to upstream. Some compounds, including the tricyclic antidepressant amitriptyline, which was the most abundant analyte in water and sediment from both sites and across seasons, reached low μg/L concentrations. Data collected from this research effort indicate contamination with antipsychotic pharmaceuticals, with the potential to adversely impact exposed organisms.

Bioaccumulation of 35 metal(loid)s in organs of a freshwater mussel (Hyriopsis cumingii) and environmental implications in Poyang Lake, China

Benthic bioaccumulation of hazardous materials has been a great challenge to the health of lake ecosystems. As representative benthic macroinvertebrates, freshwater mussels and their accumulation characteristics have been regarded as effective indicators for assessing potential risks induced by sedimentary metal(loid)s in lakes. Here we profile organ-specific accumulation of 35 metal(loid)s in a freshwater mussel (Hyriopsis cumingii) and their correlations to metal speciation in sediments of Poyang Lake, the largest lake of China. Significant organ-specific characteristics of metal accumulation were found in gills, though higher thallium (Tl) and selenium (Se) were found in the hepatopancreas, and greater arsenic (As) mostly accumulated in gonads. Pearson correlation analysis revealed that the bioaccumulation of silver (Ag), cobalt (Co), and rare earth elements (ΣREE) in gills and As in gonads were closely associated with those in bioavailable fraction of sediments. Based on the biochemical analysis in the major organs, gills exhibited the highest enzymatic activity compared with hepatopancreas and gonads. Sedimentary metals, particularly for available Ag, Co, and ΣREE, play key roles in causing lipid peroxidation in gills and significantly promote the activities of superoxide dismutase (SOD)/glutathione reductase (GR), while many metals (e.g., cadmium, manganese, Se) inhibit the glutathione (GSH) content in gonads and hepatopancreas. Our study indicates a high physiological sensitivity of mussels to these target metals, which highlights the significance of organ-specific accumulation of metal(loid)s in understanding the potential ecological risks of sedimentary metal(loid)s in lake ecosystems.

Assessment of dissolved mercury by diffusive gradients in thin films devices in abandoned ponds impacted by small scale gold mining

In order to fulfil the Minamata Convention on Mercury, it is necessary to monitor the Hg contamination in freshwater ecosystems nearby artisanal and small scale gold mining (ASGM) areas. Since most of these ASGM communities are located in remote areas, a convenient method for sampling, preserving and transporting samples is needed. In this study we evaluated the feasibility of the diffusive gradient in thin-films (DGT) technique to detect and quantify the labile fraction of Hg and other metals (Pb, Cu, Zn, Cd, Ni, Mn and Cr) in a hard-to-reach gold mining district in the state of Chocó, Colombia. We deployed DGT at sampling sites along the Atrato river and abandoned mining ponds (AMPs) which were deserted in different periods since 1997 to 2019 (6-15 years). In average, the labile THg concentrations in AMPs (148.9 ± 43.2 ng L^-1) were a 50% higher than in the river water (99.9 ± 37.4 ng L^-1). In the ponds, no significant differences were found in labile Hg with respect abandonment period. Labile Ni (0.9-493.1), Mn (1.33-11.48), Cu (0.030-2.233), and Zn (0.67-10.29) (in μg L^-1) were found in higher amounts than for the rest of metals. Labile concentrations of metals are related with their downstream proximity to gold mining activities, being higher in devices deployed close to ASGM sites. Moreover, this study demonstrates the feasibility of the DGT technique to sample, transport, storage, and preserve labile Hg from hard-to-reach ASGM areas.

The Effect of Supramolecular Humic Acids on the Diffusivity of Metal Ions in Agarose Hydrogel

Humic acids are known as natural substances of a supramolecular nature. Their self-assembly ability can affect the migration of heavy metals and other pollutants in nature. The formation of metal-humic complexes can decrease their mobility and bioavailability. This study focuses on metal ions diffusion and immobilization in humic hydrogels. Humic acids were purchased from International Humic Substances Society (isolated from different matrices—peat, soil, leonardite, water) and extracted from lignite mined in Czech Republic. Copper(II) ions were chosen as a model example of reactive metals for the diffusion experiments. The model of instantaneous planar source was used for experimental data obtained from monitoring the time development of copper(II) ions distribution in hydrogel. The effective diffusion coefficients of copper(II) ions showed the significant dependence on reaction ability of humic hydrogels. Lower amounts of the acidic functional groups caused an increase in the effective diffusion coefficient. In general, diffusion experiments seem to act as a valuable method for reactivity mapping studies on humic substances.

Effective concentration signature of Zn in a natural water derived from various speciation techniques

The uptake of nutrients or toxicants by different organisms in aquatic systems is known to correlate with different fractions of the nutrient's or toxicant's total concentration. These fractions can be provided by different analytical techniques, from which the better correlation is expected to be found for those with a characteristic length comparable to that in the considered organism uptake. An effective concentration signature can be built up with the concentration values associated to the availability (i.e. fluxes in dynamic techniques) of the nutrient or toxicant measured by various analytical techniques with different characteristic lengths. Here, this new representation was obtained for the pool of Zn complexes in the Mediterranean stream Riera d'Osor (Girona, Catalonia, Spain) with a suite of four analytical techniques. Absence of Gradients and Nernstian Equilibrium Stripping (AGNES) and Polymer Inclusion Membrane (PIM) devices provided the free Zn concentration. Linear Anodic Stripping Voltammetry provided a labile fraction (defined here as c_LASV, higher than the free concentration), related to the diffusion layer scale. Diffusion Gradients in Thin-films provided higher labile fractions (known as DGT concentrations, c_DGT) connected to the different characteristic lengths of different configurations (e.g. one or two resin discs) longer, in any case, than that corresponding to LASV. The combination of the information retrieved by the techniques allowed to quantify lability degrees of the pool of Zn complexes and to build up the effective concentration signature for this water.

Geochemical distribution and speciation of Tl and other trace metals in upper Beijiang River in South China: Approach of in-situ DGT monitoring

Mining activities frequently result in severe contamination of river water. This study aimed to better understand the spatial distribution characteristics of Tl and other metals (e.g., Al, Cd, Co, Mn, Ni, Zn, Pb, V, As, Mo, and Sb), and to assess their risks to human health. Surface water samples were collected from the upper Beijiang River (South China) via grab sampling and the diffusive gradients in thin-films (DGT) technique. The concentrations of Tl measured by grab sampling and δ-MnO₂-DGT ranged from 0.045 μg L^-1 to 0.231 μg L^-1 and from 0.056 μg L^-1 to 0.131 μg L^-1, respectively. Most of the metals monitored were below the threshold levels allowed by the drinking water standard in China, except for As, Sb, and Mn at specific sampling sites. The concentrations of other metals measured by grab sampling were higher than those measured using the DGT technique because of the differences in speciation during these measurements. The hazard quotient (5.43 × 10^-4-8.0 × 10^-1 for grab sampling and 2.23 × 10^-4-2.8 × 10^-1 for DGT technique) for the monitored trace metals demonstrated minimal health risk to human beings. The pollution status of these toxic metals in the study area was generally acceptable. As was found to be potentially the most harmful metal in the studied area, with hazard quotients at some sampling sites calculated by grab sampling of >1. It has previously been suggested that As is the most important non-carcinogenic contaminant. The combination of grab sampling and the DGT technique provides a comprehensive understanding of trace metals, especially Tl, in terms of potential bioavailability and ecological assessment.

Seasonal variations of cadmium (Cd) speciation and mobility in sediments from the Xizhi River basin, South China, based on passive sampling techniques and a thermodynamic chemical equilibrium model

Understanding the speciation and mobilization mechanisms of potentially toxic metals in sediments is critical to aquatic ecosystem health and contamination remediation in urban rivers. In this study, chemical sequential extraction, a thermodynamic chemical equilibrium model (Visual MINTEQ ver. 3.1), diffusive gradient in thin films (DGT), and high-resolution dialysis (HR-Peeper) techniques were integrated to identify seasonal variations in cadmium (Cd) mobility in sulfidized sediments. Acid-soluble Cd was the dominant geochemical fraction in sediments, followed by residual, oxidizable, and reducible Cd. The DGT-labile Cd concentration was associated with various geochemical processes and was independent of the total concentration and geochemical fractionation of Cd in sediments. Sulfate reduction facilitated the formation of insoluble CdS and induced low Cd concentrations in sediment porewater. Sulfide oxidation was principally responsible for lowered porewater pH and elevated Cd concentrations in summer. Strongly acidic conditions promoted release of sediment Cd but might reduce the binding efficiency of Chelex resin gel for dissolved Cd, leading to underestimation of the mobility of sediment Cd. Sediments generally functioned as a sink for Cd in winter and shifted to acting as a source in summer, releasing Cd into the overlying water mainly as Cd-S complexes with high potential to migrate downstream.

Geochemical fractionation study in combination with equilibrium based chemical speciation modelling of Cd in finer sediments provide a better description of Cd bioavailability in tropical estuarine systems

Geochemical fractionation study of cadmium (Cd) in combination with equilibrium based chemical speciation modelling (visual MINTEQ) in finer sediment samples (silt and clay portion), provided a better description of Cd bioavailability for sessile organisms (like oysters) in the Zuari estuary, west coast of India. A substantial fraction of total Cd in the finer sediment samples was present as water soluble, exchangeable and carbonate/bicarbonate forms and showed a strong positive relationship with Cd-bioaccumulation in oysters (Magallana sp.) from the study area. Cadmium bioaccumulation (ranged from 2.4-7.9 mg·kg^-1) in soft tissues of the edible oyster was high (higher than the maximum permissible limit for human consumption) throughout the study period of one year. Equilibrium based speciation modelling suggest that sedimentary CdCl₂, CdCl⁺ and Cd²⁺ were responsible for Cd bioaccumulation in the oysters. This study describes that combination of geochemical fractionation study of metals in finer sediments and equilibrium based speciation modelling can be very useful in comprehending link between sedimentary metal speciation and its bioaccumulation in sessile organisms.

Investigation on trace metal speciation and distribution in the Scheldt estuary

The biogeochemical behavior of Cd, Co, Cr, Cu, Ni and Pb along the historically polluted Scheldt estuary (Belgium - The Netherlands) was investigated in this study. As never studied before in this area, labile trace metals were measured using the passive sampling technique of Diffusive Gradients in Thin-films (DGT), while total dissolved and particulate trace metal concentrations were assessed using classic active sampling techniques. This dual approach allowed us to highlight the variations of trace metal speciation and distribution in the estuarine surface waters, considering environmental and physicochemical gradients along the transect. The large data set obtained was then compared with literature data of historical measurements along the Scheldt (from 1980 until now), but also from other estuaries. As emphasized by our results, trace metal mobility and partitioning along the Scheldt estuary was mainly driven by biogeochemical reactions which were strongly influenced by gradients of specific estuarine physico-chemical parameters, such as salinity, turbidity, temperature and so on. Hence, all species of trace metals displayed a non-conservative behavior. More precisely, dissolved labile fractions of trace metals showed higher levels in the middle estuary, where many solubilization and remobilization processes occurred due to turbulent mixing mechanisms and an increasing salinity. Our study confirmed the decreasing trend historically observed for particulate metals along the Scheldt, as well as the rising concentrations recorded for dissolved trace metals which might also lead to an increase of their labile fraction measured by the DGT. Finally, these preliminary results suggested that a more regular monitoring of labile metal along the Scheldt estuary is essential to have an in-depth understanding of trace metal speciation and to review bioavailability of trace metals within estuarine ecosystems.

Enhanced removal of Co(II) and Ni(II) from high-salinity aqueous solution using reductive self-assembly of three-dimensional magnetic fungal hyphal/graphene oxide nanofibers

Layer-structured graphene oxide excellent carrier for modifications; however, its poor recoverability and stability preclude its application in wastewater treatment fields. Herein, three-dimensional magnetic fungal hyphal/graphene oxide nanofibers (MFHGs) were assembled by a reductive self-assembly (RSA) strategy for the efficient capture of Co(II) and Ni(II) from high-salinity aqueous solution. The RSA strategy is inexpensive, eco-friendly and easy to scale up. The obtained MFHGs enhanced the dispersity and stability of graphene oxide and exhibited excellent magnetization and large coercivity, leading to satisfactory solid-liquid separation performance and denser sediment. The results of batch removal experiments showed that the maximum removal capacity of MFHGs for Ni(II) and Co(II) was 97.44 and 104.34 mg/g, respectively, in 2 g/L Na₂SO₄ aqueous solution with a pH of 6.0 at 323 K, and the effects of initial pH and ionic strength on Co(II) and Ni(II) removal were explored. Yield residue analysis indicated that the high porosity and oxygen-containing functional groups of MFHGs remarkably improved their Co(II)- and Ni(II)-removal capacities. According to the analysis, hydroxyl groups and amine groups participated in the chemical reaction of Co(II) and Ni(II) removal, and cation-exchange chemical adsorption was dominant during the Co(II)- and Ni(II)-removal process. Based on the attributes of MFHGs, a continuous-flow recycle reactor (CFRR) was proposed for emergency aqueous solution treatment and exhibited satisfactory removal efficiency and regeneration performance. The combination of MFHGs and the proposed CFRR is a promising water treatment strategy for rapid treatment applications.

Using silicone rubber and polyvinylchloride as equilibrium passive samplers for rapid and sensitive monitoring of pyrethroid insecticides in aquatic environments

Passive sampling to regularly identify the occurrence of pyrethroid insecticides in urban streams is a crucial work of risk management with respect to intrinsic toxicity of pyrethroids to aquatic organisms. Polymeric films, based on an equilibrium sampling principle, have found increasing use as passive samplers for hydrophobic contaminants. Herein, we investigated two thin-film samplers, namely silicone rubber (SR) and polyvinylchloride (PVC), compatible with a suite of 8 pyrethroids, for measuring freely dissolved concentrations (C_free) in water. The characteristics of SR and PVC samplers were estimated in terms of equilibrium partitioning coefficients (K_f) with log units of 3.90-4.67 and sampling rates (R_s) of 0.011-0.016 L/h. The parameters were correlated positively with octanol-water partition coefficients of the compounds, whereas independent on water solubility. A strong agreement between C_free obtained from the two samplers was observed in a range of 0.1-10 μg/L for pyrethroids under laboratory simulated conditions. Both of SR and PVC were confirmed as equilibrium samplers with faster sampling rates of pyrethroids that equilibrated on films within only one week, and higher accumulation at factors of 5.3-12.5 and 1.5-2.4 compared to a performance reference compound (PRC)-preload sampler. Additionally, the comparable results of the two passive sampling methods in multiple field applications indicated that the direct deployment of the two samplers without PRCs calibration can provide reliable assessment of trace concentrations. This study demonstrated the routine utilization of SR and PVC as promising tools for rapid and sensitive in-situ monitoring of pyrethroids, and indicators for the bioavailability against total chemical concentrations in variable aquatic environments.

Evaluation of diffusive gradients in thin films (DGT) technique for speciation of trace metals in estuarine waters - A multimethodological approach

Understanding the potential bioavailability of trace metals (TM) in marine systems is of prime importance to implement adapted regulations and efficiently protect our coastal and estuarine waters. In this study Diffusive Gradients in Thin films (DGT) technique with two different pore size was used to evaluate the potentially bioavailable fractions (DGT-labile) of Cd, Co, Cu, Ni, Pb and Zn at various depths of a highly stratified estuary (the Krka River estuary, Croatia) both in winter and summer. DGT-labile concentrations were compared to (1) total dissolved concentrations, (2) concentrations of labile species measured by anodic stripping voltammetry (ASV-labile) for Cu and (3) concentrations derived by chemical speciation modelling. High correlation between dissolved and DGT-labile concentrations was found for all metals, except for Zn where contamination problems prevented reliable conclusions. Percentages of DGT-labile fractions over total dissolved concentrations were (AVG ± SD): 92 ± 3%, 64 ± 2%, 23 ± 5%, 61 ± 3% and 57 ± 6% for Cd, Pb, Cu, Ni and Co, respectively. No significant difference was found between trace metal concentrations measured with an open pore and restricted pore devices, implying the predominance of kinetically labile metal complexes smaller than 1 nm. For Cu, ASV-labile and DGT labile concentrations were highly correlated (0.97) with ASV-labile concentration being around 35% lower than that of the DGT-labile. Modelling of chemical speciation reliably predicted dynamic (free, inorganic and part of organic complexes) concentration of Cd, whereas dynamic concentrations of Cu and Pb were underestimated by 32% and 65%, respectively. In view of the relative simplicity of DGT devices, they are well suited for the monitoring effort of coastal waters, informing on potentially bioavailable concentrations of TM and thereby, helping to achieve good environmental status of coastal waters, as stipulated within the EU Water Framework Directive.

Agarose Hydrogels Enriched by Humic Acids as the Complexation Agent

The transport properties of agarose hydrogels enriched by humic acids were studied. Methylene blue, rhodamine 6G and Cu(II) ions were incorporated into hydrogel as diffusion probes, and then their release into water was monitored. Cu(II) ions as well as both the dyes studied in this work have high affinity to humic substances and their interactions strongly affected their diffusion in hydrogels. It was confirmed that humic acids retarded the transport of diffusion probes. Humic acids' enrichment caused the decrease in the values of effective diffusion coefficients due to their complexation with diffusion probes. In general, the diffusion of dyes was more affected by the complexation with humic acids in comparison with Cu(II) ions. The effect of complexation was selective for the particular diffusion probe. The strongest effect was obtained for the diffusion of methylene blue. It was assumed that metal ions interacted preferentially with acidic functional groups. In contrast to Cu(II) ions, dyes can interact with acidic functional groups, and the condensed cyclic structures of the dye probes supported their interactions with the hydrophobic domains of humic substances.

Trace metal speciation in North Sea coastal waters

Most trace metals exhibit a dual role in marine waters, acting as nutrients at low concentration and being toxic at high concentration. But besides concentration range, speciation is also an important factor. They both show both seasonal and spatial variations. A thorough comparison between total dissolved and particulate concentrations estimated from manual sampling and an assessment of the bioavailability using Diffusive Gradients in Thin Films (DGT) has been performed in this work for Cd, Co, Cu, Ni and Pb, at several sampling points of the Belgian Coastal Zone (BCZ). Additional information to trace back the origin and identify the anthropogenic fingerprint of Suspended Particulate Matter (SPM) was measured using stable carbon isotope measurements in particulate organic matter. Our results show that: (i) particulate and total dissolved metal concentrations are higher at two stations, one in the harbor of Oostende and one offshore; (ii) dissolved and particulate trace metal concentrations do not correlate with the dissolved labile fractions; and (iii) SPM in the harbor zone is likely from allochthonous sources, while in the offshore station marine origin has been evidenced. Our results indicate that, even though contamination is higher in the harbor zones, the trace metal toxicity, which is linked to the metal bioavailability, is most likely not higher than in the open sea. However, with increasing acidification of the ocean, a shift from particulate to dissolved phase might lead to increasing adverse effects on the coastal environment.

Rigorous Physicochemical Framework for Metal Ion Binding by Aqueous Nanoparticulate Humic Substances: Implications for Speciation Modeling by the NICA-Donnan and WHAM Codes

Latest knowledge on the reactivity of charged nanoparticulate complexants toward aqueous metal ions is discussed in mechanistic detail. We present a rigorous generic description of electrostatic and chemical contributions to metal ion binding by nanoparticulate complexants, and their dependence on particle size, particle type (i.e., reactive sites distributed within the particle body or confined to the surface), ionic strength of the aqueous medium, and the nature of the metal ion. For the example case of soft environmental particles such as fulvic and humic acids, practical strategies are delineated for determining intraparticulate metal ion speciation, and for evaluating intrinsic chemical binding affinities and heterogeneity. The results are compared with those obtained by popular codes for equilibrium speciation modeling (namely NICA-Donnan and WHAM). Physicochemical analysis of the discrepancies generated by these codes reveals the a priori hypotheses adopted therein and the inappropriateness of some of their key parameters. The significance of the characteristic time scales governing the formation and dissociation rates of metal-nanoparticle complexes in defining the relaxation properties and the complete equilibration of the metal-nanoparticulate complex dispersion is described. The dynamic features of nanoparticulate complexes are also discussed in the context of predictions of the labilities and bioavailabilities of the metal species.

Phosphorus mobility in dam reservoir affected by redox oscillations: An experimental study

The internal sedimentary phosphorus (P) load of aquatic systems is able to support eutrophication, especially in dam-reservoir systems where sedimentary P stock is high and where temporary anaerobic conditions occur. The aim of this study therefore is to examine the response of sedimentary P exposed to redox oscillations. Surface sediments collected in the Champsanglard dam-reservoir (on the Creuse River, France) were subjected to two aerobic phases (10 and 12 days) alternated with two anaerobic periods (21 and 27 days) through batch incubations. The studied sediment contained 77 ± 3 μmol/g DW of P, mainly associated with the ascorbate fraction (amorphous Fe/Mn oxyhydroxides). The used sediment was rich in organic matter (OM) (21% ± 1%) with primarily allochthone signature. Our results showed that redox oscillations enhance dissolved inorganic phosphorus release at sediment/water interface. During the first anaerobic stage, the P release was mainly controlled by the dissolution/precipitation of iron minerals. The more pronounced increase of P release during the second anaerobic stage (44%) was due to various mechanisms related to the change in quality of dissolved organic matter (DOM), namely a higher SUVA₂₅₄ and humification indices. The release of more refractory DOM (rDOM) served to lower the microbial metabolism activity, possibly favored iron oxyhydroxide aggregation and thus limiting iron reduction. In addition, rDOM is able to compete for mineral P sorption sites, leading to a greater P release. In reservoir with predominant allochthone OM input, the release of more aromatic DOM therefore plays an important role in P mobility.

Polymer inclusion membrane to access Zn speciation: Comparison with root uptake

Metal speciation studies can be performed with a new technique based on a functionalized membrane. The estimation of not only the total amount of metal, but also the metal available to living organisms is very important. In this context, we have investigated the use of a polymer inclusion membrane (PIM) in a new tool for the determination of free metal ion concentration. In order to check the usefulness of PIM devices in metal speciation studies and metal availability to potato plants (Solanum tuberosum), Zn has been chosen as a case study. The PIM designed for Zn transport uses polyvinyl chloride (PVC) as polymer and di-(2-ethylhexyl) phosphoric acid (D2EHPA) as carrier, with 0.01M nitric acid in the receiving solution. The stability of the PIM has been demonstrated and good linearity of PIM-device fluxes (J_PIM) with free metal concentration was observed for total metal concentrations ranging from 3μM up to 70μM. The presence of different ligands, such as ethylenediaminetetraacetic acid (EDTA), humic acid (HA) and citrate, greatly influences the measured J_PIM because the formation of metal complexes in the donor phase decreases the free Zn concentration in the sample. Good correlation has been found when comparing PIM fluxes and metal accumulation in potato plants roots in the presence of EDTA. But, the root uptake did not change when adding citrate and HA to the hydroponic medium, so the uptake does not always follows the Free Ion Activity Model (FIAM). These ligands might induce physiological changes in the roots and enhance metal uptake.