Metal Speciation In Waters Research Articles

Evaluation of heavy metal speciation in waters of Hirakud reservoir: a Ramsar site in India.

The growing concern of aquatic heavy metal (HM) pollution is dependent on the toxic nature of its bio-available form. Thus, bio-availability is guided by the HM fractionation in water. This study was therefore conducted to evaluate the spatial impact on physicochemical fractionation of HM (Zn, Mn, Cu, and Fe) in the waters of the Hirakud reservoir in India. Speciation along different pores using a filtration technique was adopted to fractionate the HMs in water samples. The result suggests that the water of the study area is polluted with Cu (0.22-0.35mg/L), Mn (0.15-0.23mg/L), and Fe (1.90-3.10mg/L) that have crossed their permissible limits while Zn (0.17-0.97mg/L) was within the permissible standard. When studied for physical partitioning, the right dyke was comparatively more polluted than the left dyke. While the water samples were dominated by the dissolved fraction of heavy metals, it was construed that a large proportion of the HMs are in bio-available form. Further, a distinct impact of spatial variation on metal fractionation was also evident in the study with PCA revealing site-specific behaviour. Therefore, it can be concluded that multiple anthropogenic activities lead to the distribution and fractionation of HMs in water.

Heavy metal speciation in natural waters of water bodies of the Moscow chanal and the Volga-Baltic system

In this paper the thermodynamic calculation of heavy metal speciation in waters of water reservoirs of the Moscow Canal and the Volga-Baltic system (the Uglich, the Rybinsk, the Sheksninsky, the Vytegorsky and the Belousovsky reservoirs and Lake Onega) is presented. It has been shown that Sr, Ba, Fe, Mn, Zn, Ni, Co, Cd are mainly presented in free ions, the main forms for Cu are fulvate complexes and for Pb are fulvate and carbonate complexes.

Diffusive gradients in thin films for the measurement of labile metal species in water and soils: a review

The determination of the concentration of an environmental pollutant is not sufficient to assess the related health risk because this pollutant may not be bioavailable. Therefore, methods to determine pollutant bioavailability are more relevant to assess toxicity than measuring the total concentration. For instance, the diffusive gradient in thin films (DGT) is an in situ dynamic technique used to measure the concentration of labile compounds in the environment. Here we review the latest developments achieved in speciation and bioavailability of metals and metalloids using this technique. We detail the technique, common binding agents and diffusive gels. We give laboratory procedures to prepare the gels, and we explain calculations using the DGT-induced fluxes in soils (DIFS) modeling. DIFS models can predict the resupply capacities from soils to porewater, and the uptake of trace elements by plants. Procedures for in situ field deployments, including issues of biofilm growth, are also discussed.

Metal Speciation in Water of the Flooded Mine “Arsenic” (Karelia, Russia): Equilibrium-Kinetic Modeling with a Focus on the Influence of Humic Substances

Equilibrium-kinetic modeling allows investigating metal behavior in the water–rock-organic matter system with time to evaluate anthropogenic effects on the environment. In the article, the interactions of stagnant mine drainage water of the flooded mine “Arsenic” with ore and gangue minerals were simulated using different organic matter incorporation approaches. If the model is closed to humic substances (no additional organic matter input), most fulvic acids are bound in the Fe fulvate complex. While under the removal of Fe fulvate from the model, the Cu fulvate becomes prevalent, the contribution of the fulvate complexes with Zn, Mg, and Ca also increases. This scenario simulates the organo-mineral complexes behavior well and allows identifying the sequence of metal binding to organic ligands as follows Fe > Cu > Zn > Mg > Ca. The second scenario imitates the constant input of organic matter to the model (open system regarding humic substances). The dissolved metal concentrations in the model solution are extremely high in comparison to the mine drainage water. This scenario demonstrates that excessive input of organic matter leads to the accumulation of the metals in a dissolved form and blocks the secondary mineral formation despite the faster dissolution of the primary minerals under a more acidic pH than in the first scenario. However, despite the differences between the model solution and the mine drainage water, this scenario is useful to address specific issues associated with changes in natural and anthropogenic conditions. Both scenarios show the importance of organic matter incorporation to the equilibrium-kinetic models.

Trace Element’s Speciation in the Water and Bottom Sediments of the Pirogovo Reservoir

The composition and speciation of trace elements were studied in surface and interstitial waters along with solid phase of bottom sediments to characterize the abiotic segment of the Pirogovo Reservoir. It was found that the concentrations of metals in surface waters did not exceed the MACs for fishery basins, excluding Zn and Cu (2–9 and up to 2 MACs, respectively). According to thermodynamic calculations, the predominant metal speciation in water is free ions (Sr, Ba, Zn, Ni, Co, and Cd), as well as fulvate and carbonate complexes of Cu and Pb, respectively. Interstitial waters showed a regular increase of the fraction of the sulfate complexes of trace elements in loamy sediments. The solid phase of the latter as well was characterized by low anomalous concentrations of Zn, Cd, Co, and Ni. According to the data of extraction, the metals were either fixed in bottom sediments within crystal structure of silicates or bound to oxides and hydroxides of iron and manganese, excluding Cd and Mn, which are characterized by a considerable role of their exchangeable and bound to carbonates fraction in the particulate matter.

Trace element speciation in water and bottom sediments of the Pirogov water reservoir

The composition and speciation of trace elements (Cu, Pb, Zn, Cd, Ni, Co, Mn, Fe, Ba, and Sr) in surface water and bottom sediments of the Pirogov water reservoir have been studied. It was found that the metal content in surface water does not exceed the maximum permissible concentration (MPC) for fishery water reservoir excluded Zn (2–9 MPC) and Cu (up to 2 MPC). According to results of thermodynamic calculations, the predominant metal speciation in water is the free ion (Sr, Ba, Zn, Ni, Co, Cd), fulvate (Cu) and carbonate (Pb) complex. The interstitial water is characterized by an increase in the content of sulfate complex of trace elements in loams, the solid phase of which is also characterized by slightly anomalous contents of Zn, Cd, Co, and Ni. According to data of sequential selective procedure, metals are predominantly immobilized in solid phase of bottom sediments in the crystal structure of silicates or bounded to iron and manganese oxides. Only for Cd and Mn exchangeable and bound to carbonates fractions are characterized by considerable relative contents.

Quantification and Speciation of Trace Metals under Pollution Impact: Case Study of a Subarctic Lake

Monitoring the quantity and quality of metals in lake water is a major part of assessing water toxicity. A fundamental aspect of geochemical monitoring studies is the evaluation of the equilibrium distribution of metal speciation in water and the influence of environmental conditions on this process. It is important to understand the difference between the behavior of nanoparticles, dissolved particles, colloid particles, and suspended particles. This study involved environmental aquatic chemistry research and the assessment of the geochemical processes of metal speciation in an arctic lake in the metallurgical waste zone and other areas where natural processes prevail. Consecutive and parallel membrane filtration methods were used to compare the results of water analysis in Imandra Lake. The membrane pore sizes were 8, 1.2, 0.45, and 0.2 µm. The following filtrate characteristics were used: microfiltration-based mechanical suspension and oxidized contaminants (>8, 1.2, 0.45, 0.2, 0.1 μm), and ultrafiltration-based colloids, bacteria, viruses, etc. (less than 0.1 μm). Industrial effluents led to the formation of higher concentrations of elements (Ni, Cu, and Pb) in their labile forms. In the wastewater-mixing zone, the concentrations of most elements were evenly distributed in depth. In more distant areas, we found a significant increase in the concentration of elements in the near-bottom horizon in comparison with the surface water (Fe by more than three times). The obtained results showed that numerous elements had diverse distributions by speciation in the points located closer to the source of wastewater. This indicated the significant influence of the adsorption process on the system balance of elements such as Fe, Cu, and rare earth elements. The impact of the regional geochemical and anthropogenic speciation and the possible influence of climatic factors on the distribution of speciation were determined.

Dendritic Macrosurfactant Assembly for Physical Functionalization of HIPE-Templated Polymers.

High-internal-phase emulsion-templated macroporous polymers (polyHIPEs) have attracted much interest, but their surface functionalization remains a primary concern. Thus, competitive surface functionalization via physical self-assembly of macrosurfactants was reviewed. Dendritic and diblock-copolymer macrosurfactants were tested, and the former appeared to be more topologically competitive in terms of solubility, viscosity, and versatility. In particular, hyperbranched polyethyleneimine (PEI) was transformed into dendritic PEI macrosurfactants through click-like N-alkylation with epoxy compounds. Free-standing PEI macrosurfactants were used as molecular nanocapsules for charge-selective guest encapsulation and robustly dictated the surface of a macroporous polymer through the HIPE technique, in which the macroporous polymer could act as a well-recoverable adsorbent. Metal nanoparticle-loaded PEI macrosurfactants could similarly lead to polyHIPE, whose surface was dictated by its catalytic component. Unlike conventional Pickering stabilizer, PEI macrosurfactant-based metal nanocomposite resulted in open-cellular polyHIPE, rendering the catalytic sites well accessible. The active amino groups on the polyHIPE could also be transformed into functional groups of aminopolycarboxylic acids, which could efficiently eliminate trace and heavy metal species in water.

Trace metals pollution of waters and soils in Kardjali region, Bulgaria.

Trace metals pollution of surface waters and their nearby soils in the metallurgically polluted Kardjali region, Bulgaria, were studied. Thermodynamic modeling including the dissolved organic carbon (DOC) was carried out for evaluating the distribution of metal species in waters and soil solutions. Zn was found to be the most widespread pollutant in the water samples, followed by Cu, Mn, and Cd. Geoaccumulation indices of trace metals for the tested soils were calculated, indicating that regarding Al, Fe, Co, Ni, and Cu all soils are "uncontaminated". The most significant soil pollutant was found to be Cd, with all soils being either "extremely contaminated" by this metal or close to the limit, followed by Pb and Zn. The dynamics of trace metal chemical species distribution in surface waters and in the water-soluble soil fractions, as a result of possible spontaneous precipitations, was calculated by applying different thermodynamic models. Regarding Mn, Co, Ni, and Cd in waters and aqueous soil extracts and Zn in aqueous soil extracts, their free ion species prevailed, being more labile and hence toxic for the ecosystem. In the case of Al, Fe, Cu, Cd, and Pb in the waters and aqueous soil extracts and of Zn in waters, stable organic complexes with bidentate bonds, Me(OH)4- or Me(OH)02 prevailed.

Metal bioavailability and toxicity in freshwaters

Many factors influence metal speciation in freshwaters. Metal species that are more soluble are considered more bioavailable and toxic. However, evaluation of metal speciation in waters is a complex task. Moreover, the quantification of total and dissolved metals is not sufficient to determine toxic effects on the biota. Here, we review environmental parameters that influence metal bioavailability: mathematical models to predict toxicity, and the biological tools used to evaluate contamination in freshwaters ecosystems. The major points are the following: (1) we discuss many “exceptions” of chemical parameters that are deemed to increase metal bioavailability or to protect against metal uptake, such as pH and water hardness. We provide evidence of organisms and environmental conditions that break these rules and therefore should be considered when predicting impairment by metals. (2) We discuss the advances in mathematical modelling as a proxy to metal toxicity. (3) We discuss advantages and limitations of using multiple biological tools to assess toxicity, such as the use of biomarkers and microorganisms, zooplankton, benthic macroinvertebrates and fish communities. Biomarkers are efficient in detecting low concentrations of metals in a short-term exposition. Changes on biological community structure and composition are good tools to detect high metal concentration or chronic concentration in a long-term exposition. The use of multiple tools including chemical analyses and a set of biological indicators is recommended for a more accurate evaluation of metal impacts on freshwater systems.

Assessment of contamination, distribution and chemical speciation of trace metals in water column in the Dakar coast and the Saint Louis estuary from Senegal, West Africa

The water column from Dakar coast and Saint Louis estuary in Senegal, West Africa, was sampled in order to measure the contamination level by trace metals. The speciation of metals in water allowed performing a distribution between dissolved and particulate trace metals. For the dissolved metals, the metallic concentration and repartition between the organic fraction and the inorganic fraction were performed. The results show that the pollution of the estuary was more serious than in Dakar coast for Co, Cr, Ni, Pb and Zn; while, Cd and Cu were higher in Dakar coast. A strong affinity between metals and suspended particles has been revealed. Dissolved metals that have a tendency to form organic metal complexes are in decreasing order: Cd, Zn, Pb, Co=Cr=Mn, Cu and Ni. The results showed that the mobility of trace metals in estuary is controlled by dissolved organic carbon, while in coast it depends on chlorides.

Characterization of hydraulically reversible and irreversible fouling species in ultrafiltration drinking water treatment systems using fluorescence EEM and LC–OCD measurements

The application of the fluorescence excitation-emission matrix (EEM) approach and liquid chromatography–organic carbon detection (LC–OCD) analysis for the characterization of hydraulically reversible and irreversible fouling species, extracted from hollow fiber ultrafiltration (UF) membranes used in drinking water treatment, was demonstrated. Hydraulically reversible and irreversible fouling species were extracted from two pilot UF membrane systems operated in parallel with lake water as the feed. Two membrane cleaning protocols, hydraulic- and chemical-based (NaOCl and citric acid) cleaning, were considered. Colloidal/particulate matter together with protein-like and metal species in water appeared to contribute to the formation of a hydraulically removable fouling layer on the membranes. Hydraulically irreversible fouling, in contrast, was impacted considerably by humic substances (HS) and protein-like matter. The formation of an irreversible fouling layer was also likely influenced by interactions between the colloidal/particulate matter and metal species together with HS and protein-like matter. LC–OCD analysis revealed the presence of predominant levels of lower molecular weight HS-like matter – compared to the HS-like matter commonly present in lake water – in the citric acid extracted foulant fraction. The permeability loss due to hydraulically irreversible UF fouling was considerably greater than the permeability loss due to hydraulically reversible UF fouling. A permanent permeability loss (∼25–35% of the initial permeability) was present even after the application of considerably strong chemical cleaning protocols on both pilot systems. This study indicated that the fluorescence EEM approach can be applied for monitoring and characterization of membrane cleaning procedures and as a potential diagnostic tool for assessing the effectiveness of hydraulic- and chemical-based cleaning protocols employed in UF drinking water treatment operations using rapid off-line measurements. On the other hand, since the LC–OCD analysis technique is a comparatively time consuming method, it may be used for verification of the fluorescence EEM-based results of the foulant fractions.

Speciation of heavy metals in water and sediments of an urban lake system

The speciation pattern of heavy metals namely chromium, nickel, copper and lead in water and sediments of an urban lake system of high ecological significance was studied. The total available metal (dissolved) in water follows the sequence Ni>Cr>Pb>Cu. However, a different pattern Pb>Cu>Ni>Cr is observed for total available metal (metal in non-residual phases) in sediments. Significant spatial variations are observed in different geochemical forms of the metals as indicated by two-way ANOVA. This is attributed to localized anthropogenic activities. The anthropogenic parameters of water not only show statistically significant correlations among themselves but also positively correlate with the particulate forms of Cr, Cu and Pb. The total available forms of copper and lead correlate with the organic content of the sediments. Principal component analysis (PCA) separates the metals into three groups: I (Cr); II (Ni); III (Cu and Pb). The polluted sites were identified using hierarchical cluster analysis. Risk assessment code (RAC) analysis indicates low to medium risk due to Cr at most of the sites. However, Ni, Cu and Pb pose medium to high risk. But Pb at a few sites presents very high risk (RAC > 50%).

Metal speciation in natural waters and metal complexing with humic matter

The stability constants of metal and humic matter complexes extracted from different soils were calcu� lated. Speciation of metals in natural waters was deter� mined taking into account their chemical composition and content and properties of organic matter. We established metal speciation in water objects with account for competitive reactions resulting in forma� tion of hydroxide, hydrocarbonate, sulfate, and chlo� ride metal complexes and obtained a competitive series of metal activity in natural waters of the zones considered. An important specific feature of metals as contam� ination elements is the fact that when they occur in the environment, their potential toxicity and bioavailabil� ity depend significantly on their speciation. In recent years, lakes have been continuously enriched in haz� ardous elements such as Pb, Cd, Al, and Cr on a global (regional) basis [1]. Metals occur in natural waters as free ions, simple complexes with inorganic and organic ligands, and mineral and organic particles of molecules and ions sorbed on the surface. The occur� rence of soluble metal forms in natural waters depends on the presence of organic and inorganic anions. The most important organic ligands are humic matter (HM) washed out from soils; inorganic complexes formed include hydroxide groups, hydrocarbonates, sulfates, and chlorides. HM of natural waters com� posed of fulvic (FA) and humic (FA) acids contributes most significantly to metal inactivation. The concen� trations of these acids in surface waters attain 1– 100 mg/l [2, 3]. The concentrations of water biota exometabolites are much lower. Due to specific water formation in the whole humid territory of Russia, the colored waters are quite widespread. They are characterized by high concen� trations of humic matter, which is able to inactivate metals and to decrease their toxicity in natural waters. A characteristic feature of the water chemical compo� sition in these regions is elevated Fe, Al, and Mn con� centrations. Russian water quality standards concern� ing metals do not take into account regional and local specific features of the water chemical composition, which predefine speciation of metals and their ecotoxic properties. However, direct determinations are rather difficult. Our current task is to develop methods that would make it possible to forecast ele� ment speciation predefining toxic properties of water by the chemical composition of the water. The objective of this work was to investigate metal and humic matter complexing and to determine metal occurrence forms on the basis of experimentally obtained constants of metal and humic matter com� plexes extracted from typical soils of different natural climatic zones.

Assessing WHAM/Model VII against field measurements of free metal ion concentrations: model performance and the role of uncertainty in parameters and inputs

Environmental contextThe chemical speciation of metals in waters is of great importance in determining their transport, fate and effects in the environment. Modelling chemical speciation is valuable for making predictions about these effects. Here a model of metal speciation is tested against field data, and recommendations are made as to how both model and measurements might be improved in future. AbstractA key question in the evaluation of chemical speciation models is: how well do model predictions compare against speciation measurements? To address this issue, the performance of WHAM/Model VII in predicting free metal ion concentrations in field samples has been evaluated. A statistical sampling method considering uncertainties in input measurements, model parameters and the binding activity of dissolved organic matter was used to generate distributions of predicted free ion concentrations. Model performance varied with the metal considered and the analytical technique used to measure the free ion. Generally, the best agreement between observation and prediction was seen for aluminium, cobalt, nickel, zinc and cadmium. Important differences in agreement between model and observations were seen, depending upon the analytical technique. In particular, concentrations of free ion determined with voltammetric techniques were largely over-predicted by the model. Uncertainties in model predictions varied among metals. Only for aluminium could discrepancies between observation and model could be explained by uncertainties in input measurements and model parameters. For the other metals, the ranges of model predictions were mostly too small to explain the discrepancies between model and observation. Incorporating the effects of uncertainty into speciation model predictions allows for more rigorous assessment of model performance.

Speciation of heavy metals in water from the Uganda side of Lake Victoria

Different forms of copper Cu, zinc Zn, lead Pb and cadmium Cd in water from the Uganda side of Lake Victoria (25°C, pH 6.75–7.18), the second largest inland freshwater lake in the world, have been studied using ion‐exchange, dialysis and atomic absorption spectrophotometry. The results indicate that heavy metals Cu, Zn, Pb and Cd are present mainly in the cationic form (80–83%). Small quantities of anionic (13–22%), non‐ionic, dialyzable (4–8%), and non‐ionic, non‐dialyzable (< 1.3–4.4%) forms were also detected for all metals except Cd. The corresponding concentrations lay in the ranges: cationic, 0.06–0.99; anionic, < 0.001–0.25; non‐ionic, dialyzable, < 0.001–0.08; non‐ionic, non‐dialyzable, < 0.001–0.06 µg ml−1. The existence of the metals in non‐ionic and non‐dialyzable forms is attributable to metal associations with high relative molecular mass (RMM) organic matters.

In Situ Measurements of Labile Al and Mn in Acid Mine Drainage Using Diffusive Gradients in Thin Films

The technique of diffusive gradients in thin films (DGT) can be used for in situ measurements of labile metal species in water, but the application for this method on acid mine drainage (AMD) is complicated due to reduced sampler adsorption of metals at low pH. This study evaluates the use of DGT on labile Al and Mn in AMD (pH 3.1-4.2). DGT measurements were performed both in standard solutions in the laboratory and in situ in the field. Laboratory results show that DGT can be used in water with pH as low as 3.0 for Al and 4.0 for Mn without correcting for reduced adsorption. Below pH 4.0, the adsorption of Mn showed a linearly decrease with pH to approximately 55% at pH 3.0. Taking this correction into account revealed that 84-100% of the total dissolved Al and Mn measured in the field was DGT-labile. Measurements using DGT agreed well with predictions using the speciation program WHAM VI. This study shows that the use of DGT can be extended below the previously reported pH working range for Al, and for Mn using a simple linear correction with respect to pH, and demonstrates that the technique can be applied for monitoring time-integrated labile metal concentrations at AMD sites.

Speciation of metals in sediment and water in a river underlain by limestone: role of carbonate species for purification capacity of rivers

Rivers whose basins are underlain by limestone possess a high buffering capacity for discharged pollutants. During the discharge of metals in the aquatic environment, metals are partitioned between the sediment and the water column phases. Further partitioning of metals occurs within the sediment chemical fractions and metal speciation in water column, thus leading to the possible reduction of the toxic free hydrated metal ion. The present study focuses on one of Lebanon's rivers; the Nahr-Ibrahim whose basin is underlain by limestone and its river water is dominated by carbonate species due to the high pH and alkalinity values. The objectives of this study were: first, to determine the metal speciation (Fe, Zn, Pb and Cd) in the (operationally defined) sediment chemical fractions and metal speciation in river water; second, to evaluate the role of carbonate species in the self-purification process from metal pollutant inputs into the river. Bed sediments and water were collected from eight locations in one dry season (September, 1997), and a sequential chemical fractionation scheme was applied to the <75 μm sieved sediment fraction. The data show that the highest percentages of total metal content in sediment are for: Fe in the residual fraction followed by moderately reducible fraction, Zn and Pb in the carbonate and in the moderately reducible fractions and Cd primarily in the carbonate fraction. Aqueous metal speciation was predicted using AQUACHEM software interfaced to PHREEQC geochemical computer model. The water speciation data predicted that a high percentage of Pb and Zn were present as carbonate species, very low percentages as free hydrated ion species; whereas Cd exhibited high percentage occurrence as a free hydrated metal ion species. Iron was present in water mainly as ferric hydroxide ion pair species. This study has evaluated the role of carbonate species for self-purification process by the reported high percentage occurrence of metals in the carbonate sediment fraction and the interaction of metals with the carbonate water species.

Differential water quality in confined and free-flowing water bodies, Lebanon

Integrated management of water resources is a major critical issue to be addressed in combating water stress in developing countries, such as Lebanon. At present, surface water is not properly used in Lebanon. This emphasises the importance of assessing surface water quality as a projected means to increase water availability. This study involves two different water bodies, the freely flowing Nahr-Ibrahin River and the Qaraaoun Reservoir, an impoundment of the Litani River. Water samples were collected from 16 chosen sites of each water body at four different dates during the dry season. Measured water parameters were temperature, pH, conductivity, BOD, HCO3-, Ca2+, Mg2+, Cl-, SO42-, PO43-, NO3-, NH3, Fe, Mn, Zn, Pb, and Cd. Statistical analysis of the data revealed significant differences in water quality. The differences could be attributed to the fact that whereas the Qaraaoun reservoir is receiving domestic waste discharges that lead to an increase in the CO2 content and a pH decrease, the Nahr-Ibrahim River is influenced by agricultural runoffs and industrial discharges that increase the pH values. Consequently, the water metal speciation of the two water bodies was different. The study indicated that the differential quality of the two water bodies could be attributed to the nature of the water resources and exposure to contaminants. This is crucial in recommending intervention studies to protect quality and promote the role of surface water use, as an integrated component of water management in Lebanon.

Effect of solution composition, flow and deployment time on the measurement of trace metals by the diffusive gradient in thin films technique

Diffusive gradients in thin films (DGT) is a recently developed technique capable of in situ measurement of labile metal species in water. Tests of the performance of DGT were extended in this work to cover a wide range of environmentally relevant conditions. DGT accurately measured Cd concentrations in 0.01 M NaNO 3 solutions in the pH range 5–10 and Co, Mn and Zn concentrations, between pH 3.5 and 10. Cu was measured accurately between pH 2 and 10. Above pH 11 prolonged deployments were impractical due to swelling of the diffusive gel, but even at pH 12.9 significant fractions of the total Cd and Cu concentrations were measured by DGT units deployed for a day or less. Measurements of trace metals by DGT were unaffected by the presence of Ca at concentrations found in hard water. Errors due to changes in flow velocity were less than 10% above a flow of 0.02 m s −1, where the formation of a diffusive boundary layer becomes negligible for diffusive gels of ≥0.7 mm thickness. Therefore, DGT devices prepared with this diffusive gel thickness can confidently be used in most streams and rivers. However, in quiescent solutions the DGT measurement may only be 50% of the true concentration, confirming the need in quiet waters for parallel deployments of devices with different diffusive layer thickness. Quantitative DGT measurements of Cd over a 1 month period showed that neither the diffusive nor resin gel deteriorated with time. Collectively these results show that DGT behaves predictably over a wide range of solution conditions. For Cu it can be used in very acidic solutions. The upper pH limit for DGT measurement is governed by the stability of the gel. For this gel composition the realistic limit is pH 11.