Improving elution strategies for Chelex®-DGT passive samplers.

Elution of Chelex® binding layers, commonly used for the diffusive gradients in thin films technique (DGT), is recognized as the most important contributor to the uncertainty of DGT measurements. Limiting uncertainty requires the use of optimized procedures and suitable elution recoveries (f e ). This work therefore investigated elution robustness to propose improved strategies. A wide range of conditions were investigated for the main elution parameters (Chelex® particle size, elution time, Chelex® loading, and eluent concentration and volume) on Al(III), Cd(II), Co(II), Cr(III), Cu(II), Ni(II), Pb(II), and Zn(II). Results showed that the choice of elution conditions should be a compromise driven by study constrains in terms of accuracy, repeatability, sensitivity, and targeted elements. Using experimentally determined recoveries should improve accuracy by approximately 5 to 10% compared to the use of recoveries from the literature. Fast elution of 1 h can be achieved without significant loss of recovery and repeatability except for Cr(III) (8 h minimum). Elution recovery depended on Chelex® loading for Zn and Cr and introducing recoveries adapted to the loading could improve accuracy up to, respectively, 11 and 27%. When standard recoveries are used, a 0.85 f e value would be more appropriate than the common value of 0.8 to minimize inaccuracy (except for Cr). Some flexibility can be applied to elution conditions without a significant change in recovery for most elements: HNO3 concentration of 1-15 M, volume of 1-2 mL, duration of 8-48 h. Cr(III) was unique in its sensitivity to elution condition variations; thus, choice is more restricted for this element. Graphical abstract Decisional tree for choosing elution procedure and recoveries for Chelex®-DGT.

Polycyclic aromatic hydrocarbons and n-alkanes in sediments of the Upper Scheldt River Basin: contamination levels and source apportionment.

The Scheldt River system is located in northern France, Belgium and the Netherlands and includes a dense network of rivers, which contributed to the urban and industrial development in this area. Three sediment cores, collected in the Upper Scheldt River (Helkijn) and two of its tributaries (the Lys River at Wervik and the Espierre Canal), were analysed for n-alkanes and polycyclic aromatic hydrocarbons (PAHs). Total n-alkane and PAH concentrations in all the sampled cores ranged from 2.8 to 29 mg kg(-1) and from 4.9 to 96 mg kg(-1), respectively. The contributions of biogenic, petrogenic and pyrolytic sources were investigated using n-alkane indexes and PAH diagnostic ratios. n-alkane chromatograms were characterized by the predominance of odd over even long chain n-alkanes (produced by terrestrial plants) and by the occurrence of a broad unresolved complex mixture (UCM) which evidenced biodegraded petroleum residues. For the three studied cores, correlations between the concentrations of UCM and n-alkanes (both expressed on an organic carbon basis) indicated a common origin or similar pathways of these allochtonous compounds to the aquatic environment. Wervik sediments were distinguished by higher n-alkane concentrations and by a major aquatic biogenic source for low molecular weight n-alkanes. The prevalence of combustion-derived PAHs was indicated by the high contribution of four, five and six rings compounds and was confirmed by isomer ratios. Higher levels of low molecular weight PAHs in Helkijn surface sediments suggested modest petrogenic inputs in this navigable canal. High PAH concentrations in Espierre sediments could be explained by a major historical contamination from urban and industrial emissions.

Two sampling strategies for an overview of pesticide contamination in an agriculture-extensive headwater stream.

Two headwaters located in southwest France were monitored for 3 and 2 years (Auvézère and Aixette watershed, respectively) with two sampling strategies: grab and passive sampling with polar organic chemical integrative sampler (POCIS). These watersheds are rural and characterized by agricultural areas with similar breeding practices, except that the Auvézère watershed contains apple production for agricultural diversification and the downstream portion of the Aixette watershed is in a peri-urban area. The agricultural activities of both are extensive, i.e., with limited supply of fertilizer and pesticides. The sampling strategies used here give specific information: grab samples for higher pesticide content and POCIS for contamination background noise and number of compounds found. Agricultural catchments in small headwater streams are characterized by a background noise of pesticide contamination in the range of 20-70 ng/L, but there may also be transient and high-peak pesticide contamination (2000-3000 ng/L) caused by rain events, poor use of pesticides, and/or the small size of the water body. This study demonstrates that between two specific runoff events, contamination was low; hence the importance of passive sampler use. While the peak pesticide concentrations seen here are a toxicity risk for aquatic life, the pesticide background noise of single compounds do not pose obvious acute nor chronic risks; however, this study did not consider the risk from synergistic "cocktail" effects. Proper tools and sampling strategies may link watershed activities (agricultural, non-agricultural) to pesticides detected in the water, and data from both grab and passive samples can contribute to discussions on environmental effects in headwaters, an area of great importance for biodiversity.

Passive sampling of anionic pesticides using the Diffusive Gradients in Thin films technique (DGT).

DGT passive samplers using Oasis® HLB or Oasis® MAX sorbent were developed for anionic pesticides sampling. They were tested using four model compounds (i.e. bentazon, chlorsulfuron, ioxynil and mecoprop). Polyacrylamide diffusive gel was found to be more suitable than agarose gel for most anionic pesticides sampling. An elution procedure was optimized and diffusion coefficients were determined for quantitative use of the samplers. Depending on the DGT configuration used (HLB or MAX), accuracies better than 30% were demonstrated in laboratory for pH from 3 to 8 and ionic strengths from 10-2 to 1 M. Combined with the effective binding capacities of samplers (≥9 µg for each pesticide) and limits of quantification of the method (≤13 ng.L-1 using Q-TOF detector) monitoring of numerous aquatic systems can be expected. Except for ioxynil, accurate quantifications were demonstrated in laboratory using a spiked natural water for HLB-DGT whereas MAX-DGT did not give satisfactory results. A further in situ validation was performed in two rivers and showed identical detection frequency between HLB-DGT and POCIS of anionic pesticides (bentazon and mesotrione) whereas calculated concentrations, although within the same order of magnitude, could differ (<70%). HLB-DGT could therefore constitute an interesting alternative to other passive samplers for the monitoring of several anionic pesticides in aquatic systems but more work is required for quantification of molecules from hydroxybenzonitrile chemical group (ioxynil).

Key role of the sorption process in alteration of metal and metalloid quantification by fouling development on DGT passive samplers.

The DGT technique (diffusive gradients in thin films) is widely used for passive sampling of labile trace metals and metalloids in natural waters. Although development of fouling on the protective membranes is frequently observed, its effect on DGT sampling has been barely investigated. This study evaluates the influence of fouling on sampling of trace cationic metals Cd(II), Cu(II), Ni(II) and Pb(II) and oxyanions As(V), Cr(VI), Sb(V) and Se(VI). Fouling was developed in situ on polycarbonate membranes in four diverse natural freshwater environments and sampling alteration was assessed in controlled laboratory experiments. Accumulation of oxyanions and Ni was unaltered in the presence of fouling whereas significant alteration occurred in sampling of Cd, Cu and Pb (at pH ∼5.4). Characterization of the fouled membranes highlighted the intervention of sorption phenomenon as sampling alteration was systematically observed alongside element sorption onto fouled membrane. A preliminary flowchart for identifying potentially biased quantifications linked to fouling development during in situ DGT deployment in natural waters is proposed.

Simultaneous measurement of Cr(III) and Cr(VI) in freshwaters with a single Diffusive Gradients in Thin Films device.

Few attempts have been made to sample labile chromium with the DGT passive sampler (Diffusive Gradients in Thin Films) and, currently, no single device allows the simultaneous determination of both Cr(III) and Cr(VI). In this work, a procedure based on only one device combined with innovative selective elution is evaluated to assess chromium speciation. A zirconium binding gel is used to accumulate both Cr(III) and Cr(VI). Cr(VI) is quantitatively and selectively eluted by NaOH, allowing the subsequent determination of Cr(III). Accurate quantification of both species is demonstrated in synthetic solutions for pH ranging from 4 to 6 and ionic strength ranging from 10(-3) to 5×10(-2)M. Cr(VI) quantification is altered only for [SO4(2-)]≥5×10(-3)M. The method allows successful quantification of labile Cr(III) and Cr(VI) in spiked natural water. The limit of quantification of the procedure is suitable for trace level monitoring (0.03µgL(-1) for Cr(VI) and 1µgL(-1) for Cr(III), for a one-week deployment at 20°C) and the effective capacity of the sampler (∼25µg for each Cr oxidation state) should allow long term deployments. These results highlight the potential of this new procedure for a simple and effective chromium speciation analysis in natural waters.

Overview of the Chemcatcher® for the passive sampling of various pollutants in aquatic environments Part B: Field handling and environmental applications for the monitoring of pollutants and their biological effects.

The Chemcatcher(®) has been used for a wide range of environmental applications in various media (river water, seawater, sewage water, and treated wastewater). The aim of part B of this review is to compile and discuss the results obtained during these applications, from a screening or quantitative monitoring of water contamination, to a comparison with biomonitoring and bioassays. Special attention will also be paid to, firstly, the influence of environmental factors on analyte uptake and, secondly, the use of Performance and Reference Compounds for the in situ correction of sampling rates.

Overview of the Chemcatcher® for the passive sampling of various pollutants in aquatic environments Part A: Principles, calibration, preparation and analysis of the sampler.

The passive sampler Chemcatcher(®), which was developed in 2000, can be adapted for various types of water contaminants (e.g., trace metals, polycyclic aromatic hydrocarbons, pesticides and pharmaceutical residues) depending on the materials chosen for the receiving phase and the membrane. The Chemcatcher(®) has been used in numerous research articles in both laboratory experiments and field exposures, and here we review the state-of-the-art in applying this passive sampler. Part A of this review covers (1) the theory upon which the sampler is based (i.e., brief theory, calculation of water concentration, Performance and Reference Compounds), (2) the preparation of the device (i.e., sampler design, choice of the membrane and disk, mounting of the tool), and (3) calibration procedures (i.e., design of the calibration tank, tested parameters, sampling rates).

Improvement of POCIS ability to quantify pesticides in natural water by reducing polyethylene glycol matrix effects from polyethersulfone membranes.

The presence of polyethylene glycol compounds (PEG) in extracts from polar organic chemical integrative samplers (POCIS) was shown by high resolution time-of-flight mass spectrometry. PEG compounds, which are released by polyethersulfone (PES) membranes used to build POCIS, can induce matrix effects during quantification of performance reference compounds (PRC, DIA-d5) and target pesticides by mass detection, even after chromatographic separation. Dilution of POCIS extracts can reduce this matrix effect, but dilution may induce a decrease in POCIS performance, primarily for quantification limits. To reduce PEG interference during chromatographic analysis, a simple non-damaging washing protocol for PES membranes is proposed. The method consists of 2 successive baths of washing solution (140 mL per membrane) of ultrapure water (UPW) and methanol (50/50), stirred at 300 rotations per minute (rpm), followed by a final membrane rinse with UPW (140 mL). The signal from PEG compounds was significantly decreased for washed membranes (between 4 and 6 fold lower). After field deployment, total ion current chromatograms of extracts from POCIS built with washed PES membranes did not display a significant PEG fingerprint. This led to improved quantification accuracy for compounds co-eluting with PEG, i.e. PRC (performance and reference compound, DIA-d5) and some pesticides and metabolites. With washed membranes, an accurate quantification of PRC and pesticides sampled by POCIS was indeed possible without a large extract dilution; 10 times instead of the 25 times needed in unwashed conditions. Assuming that the PRC approach corrects for environmental conditions and sampling rates (Rs), a proper PRC (DIA-d5) quantification significantly improved pesticide time weighted average concentration (TWAC) determination in natural water after field deployment.

Coupling passive sampling and time of flight mass spectrometry for a better estimation of polar pesticide freshwater contamination: Simultaneous target quantification and screening analysis.

The aim of this study was first to develop and validate an analytical method for the quantification of 35 polar pesticides and 9 metabolites by ultra-high-performance-liquid chromatography combined with a high resolution time-of-flight mass spectrometer detector (UHPLC-(Q)-TOF). Various analytical conditions were investigated (eluent composition and mass parameters) to optimize analyte responses. Analytical performance (linearity, limit of quantification, and accuracy) was then evaluated and interference in the extract of a passive sampler exposed in freshwater (POCIS: Polar Organic Chemical Integrative Sampler) was studied. The proposed quantification method was validated for 43 compounds with variation of calibration slopes below 10% in environmental matrix. For the unvalidated compound DIA (atrazine-desisopropyl: an atrazine metabolite), interference increased the error of concentration determination (50%). The limits of quantification obtained by combining POCIS and UHPLC-(Q)-TOF for 43 target compounds were between 0.1 (terbuthylazine) and 10.7 ng/L (acetochlor). Secondly, the method was successfully applied during a 14-day POCIS river exposure, and gave concentration values similar to a more commonly used triple quadrupole detector regarding concentration, but allowed for the detection of more compounds. Additionally with the targeted compound quantification, the (Q)-TOF mass spectrometer was also used for screening non-target compounds (other pesticides and pharmaceuticals) in POCIS extracts. Moreover, the acquisition of full scan MS data allowed the identification of the polyethylene glycol (PEG) compounds which gave unresolvable interference to DIA, and thus questions the ability of DIA to be used as performance reference compound (PRC) to determine sampling rates in situ. This study therefore illustrates the potential, and proposes a pathway, of UHPLC-(Q)-TOF combined with POCIS in situ pre-concentration for both quantitative and screening analyses of organic contaminants in water.

Estimates of pesticide concentrations and fluxes in two rivers of an extensive French multi-agricultural watershed: application of the passive sampling strategy.

In this study, the passive sampling strategy was evaluated for its ability to improve water quality monitoring in terms of concentrations and frequencies of quantification of pesticides, with a focus on flux calculation. Polar Organic Chemical Integrative Samplers (POCIS) were successively exposed and renewed at three sampling sites of an extensive French multi-agricultural watershed from January to September 2012. Grab water samples were recovered every 14 days during the same period and an automated sampler collected composite water samples from April to July 2012. Thirty-nine compounds (pesticides and metabolites) were analysed. DEA, diuron and atrazine (banned in France for many years) likely arrived via groundwater whereas dimethanamid, imidacloprid and acetochlor (all still in use) were probably transported via leaching. The comparison of the three sampling strategies showed that the POCIS offers lower detection limits, resulting in the quantification of trace levels of compounds (acetochlor, diuron and desethylatrazine (DEA)) that could not be measured in grab and composite water samples. As a consequence, the frequencies of occurrence were dramatically enhanced with the POCIS compared to spot sample data. Moreover, the integration of flood events led to a better temporal representation of the fluxes when calculated with the POCIS compared to the bimonthly grab sampling strategy. We conclude that the POCIS could be an advantageous alternative to spot sampling, offering better performance in terms of quantification limits and more representative data.

Can POCIS be used in Water Framework Directive (2000/60/EC) monitoring networks? A study focusing on pesticides in a French agricultural watershed.

In this study, the main current limitations in the application of the Polar Organic Chemical Integrative Sampler (POCIS) in regulatory monitoring programmes were evaluated. POCIS were exposed from March to December by successive periods of 14 days in the River Trec (Lot et Garonne, France) and analysed for 34 pesticides. The study of the uncertainty related to the POCIS data was performed and we concluded that it might be up to 138%, which is higher than European Union requirements but this issue was adequately counterbalanced by the gain of temporal representativeness. Comparison with data from the official monitoring programme from the French Water Agency showed that the POCIS is already suitable for both operational and investigative monitoring. The sampled fraction issue, and then compliance with Environmental Quality Standards, was also addressed. It was confirmed that POCIS samples only the dissolved fraction of dimethenamid and showed that for compounds like atrazine, desethylatrazine and metolachlor, the POCIS concentration is equivalent to the whole water concentration. For dimethenamid, which exhibited a tendency to adsorb on suspended matter, a method was suggested to assess the raw water concentration from the POCIS measure. Finally, an innovative procedure for using passive sampler data for compliance checks in the framework of surveillance monitoring is proposed.

DGT-labile As, Cd, Cu and Ni monitoring in freshwater: toward a framework for interpretation of in situ deployment.

The use of the Diffusive Gradient in Thin Film sampler (DGT) as a monitoring tool for regulatory programs is currently evaluated. In this context, the impact of commonly followed procedures on the accuracy of DGT-labile As, Cd, Cu, and Ni quantification was studied. Initial sampler contamination yields to define quantification limits instead of using blank subtraction, thus avoiding artifact concentrations. Not considering the alteration of element diffusion by the filter membrane leads to significant underestimation. However, diffusion coefficients determined on a non-fouled membrane were found to be suitable for the studied site, making it possible to use data from the literature. When diffusive boundary layer formation is neglected, no loss of accuracy is recorded provided the layer is thinner than 0.5 mm. Finally, exploration of potential biases allowed initiating a framework that might help limit inaccuracies in DGT-labile concentration estimation and interpretation, especially in a low contamination context.

Potential risks of metal toxicity in contaminated sediments of Deûle river in northern France.

The aim of this paper was to evaluate the potential sediment cumulative damage and toxicity due to metal contamination in a polluted zone of Deûle river (in northern France) from nearby two smelters. Metal-enrichment factors and geoaccumulation indices measured with sediment depth revealed that--compared to background levels either in local reference soils or in world rivers sediments/suspended particulate matter--Cd contributed to the highest pollution levels, followed by Zn, Pb and to a much lesser extent Cu and Ni. A comparison of the vertical distribution of AVS (acid volatile sulfides), SEM (simultaneously extracted metals), TMC (total metal concentrations), TOC (total organic carbon) and interstitial water-metal concentrations in the sediment allowed us to highlight the extent of toxicity caused by Cd, Pb, Zn, Ni and Cu and to raise the possibility of their association with certain geochemical phases. To assess the actual environmental impacts of these metals in Deûle river, numerical sediment quality guidelines were further used in the present work. Sedimentary Pb, Zn, and Cd contents largely exceeded PEC (probable effect concentration) values reported as consensus-based sediment quality guidelines for freshwater ecosystems. As for risks of toxicity from pore waters, metal concentrations reached their maxima at the surficial layers of the sediment (1-3 cm) and IWCTU (Interstitial Water Criteria Toxicity Unit) observed for Pb and to a lesser extent Cd, violated the corresponding water quality data recommended by USEPA.

Sources of PCDD/Fs, non-ortho PCBs and PAHs in sediments of high and low impacted transboundary rivers (Belgium-France).

PAHs, PCDD/Fs and non-ortho PCBs have been assessed in Yser and Upper-Scheldt river sediments. Higher contamination levels were observed in the Upper-Scheldt sediments: maximum concentrations for the 16 US-EPA PAHs, PCDD/Fs and non-ortho PCBs respectively amount to 8.9 mg kg(-1), 12 ng TEQ kg(-1) and 5.1 ng TEQ kg(-1). Diagnostic PAH ratios in sediments and atmospheric samples suggest that the PAH compounds are from pyrolytic origin, more specifically combustion processes. The huge consumption of coal in cokes-ovens and smelters and its use for house-heating in Northern France, although decreasing during the last decades, are in support of that suggestion. PCDD/F fingerprints in sediments and deposition material indicate that OCDD is the dominant congener. In addition use of pentachlorophenol (PCP) in the past led to a minor contribution of PCDD/Fs in our sediment samples. Non-ortho PCBs form a substantial fraction of the total TEQ concentrations observed in the sediments. Since the 1980s and 1990s a substantial reduction of the PCDD/F sediment concentrations is observed, but this is not the case for the PAHs.