Influence of hydrodynamics on the water pathway and spatial distribution of pesticide and metabolite concentrations in constructed wetlands.

Constructed wetlands (CWs) are likely to reduce pesticide levels reaching surface water. However, the distribution of the water flow path between the main channel and isolated areas may influence global pesticide mitigation. Little information is known about the influence of water pathways on pesticide mitigation. Thus, we performed tracer experiments at low and high flow rates (0.5 L/s and 4-7 L/s) in a pond CW and ditch CW to determine the localization of various hydraulic zones and to understand their implication on pesticide mitigation. The hydraulic performance reflecting the fraction of water transported from inlet to outlet passing through the whole of CW, was greater for the pond CW than for the ditch CW regardless of the flow rate, and greater at mean flow rates (MF) than at low flow rates (LF) due to a lower proportion of isolated areas at a MF (11%-68%) than at LF (38%-89%). Dispersion governed the water transport inside the isolated areas and the water convection inside the main channel. Consequently, dissolved pesticide concentrations are heterogeneously distributed in the CWs, i.e., in the main channel and isolated area, for both flow rates. However, one month after a no-flow period, this heterogeneity disappears, and dissolved pesticide concentrations become similar in the water of the whole CW due to dispersion. Furthermore, sedimentation and storage in sediments were greater in the isolated area than in the main channel, which is possibly due to a lower speed flow rate and a higher hydraulic residence time (HRT) in the isolated area than in the main channel. Thus, isolated areas act as effective's zones to mitigate pesticides from dissolved and particulate phases inside the CW during a complete drainage season (i.e., succession of high/low/no-flow periods).

Advantages of online SPE coupled with UPLC/MS/MS for determining the fate of pesticides and pharmaceutical compounds.

Laboratory experimentation is essential for our understanding of the fate and behaviour of pollutants. Many analytical techniques exist, but they all have disadvantages either in terms of sensitivity or of selectivity. The number of samples that can be analysed, the low volume of samples available during the experiment and the need to identify different degradates are all obstacles that new techniques are able to overcome. The work presented here summarizes progress in the field of metrology as concerns online solid phase extraction technology coupled with liquid chromatography followed by tandem mass spectrometry detection. Recently developed analytical techniques were validated for both 18 pesticides and their degradates and 17 pharmaceuticals and their degradates. Limits of quantification from 20 to 70 ng L(-1) for pharmaceuticals and from 15 to 25 ng L(-1) for pesticides and metabolites have been obtained, with linearity range up to 1 µg L(-1). The limits of quantification of a few nanograms per litre, the possibility of working on less than 1 mL of sample and the simultaneous quantification of the target products and their transformation products are all advantages that are demonstrated by two environmental applications. The first application concerns the evaluation of ecotoxicological effects of pesticides on aquatic organisms exposed in mesocosms. The second application aims to determine the adsorption constants of pharmaceutical molecules on soils and river sediments. For both applications, the robustness, range of linearity and limit of quantification of the developed analytical methods satisfy the requirements for laboratory experiments conducted under controlled conditions. Specific constraints generated by this type of experiment (adding CaCl2 for the adsorption study and filtration of the water coming from the mesocosms) were not found to limit the use of online SPE. These two preliminary studies show that new experimental fields are possible thanks to online solid phase extraction coupled with liquid chromatography.

Estimating 42 pesticide sampling rates by POCIS and POCIS-MIP samplers for groundwater monitoring: a pilot-scale calibration.

Pesticides occur in groundwater as a result of agricultural activity. Their monitoring under the Water Framework Directive is based on only a few spot-sampling measurements per year despite their temporal variability. Passive sampling, which was successfully tested in surface water to provide a more representative assessment of contamination, could be applied to groundwater for a better definition of its contamination. However, few reliable calibration data under low water flow are available. The objective of our study thus consisted in determining sampling rates by two types of passive samplers, a POCIS (polar organic chemical integrative sampler) for polar pesticides, and a POCIS-MIP sampler based on a receiving phase of molecular imprinted polymers, specific for AMPA and glyphosate under low flow conditions as exist in groundwater. To our knowledge, this is the first time that sampling rates (sampling rate represents the volume of water from which the analyte is quantitatively extracted by the sampler per unit time) are estimated for groundwater applications. Our calibrations took place in an experimental pilot filled with groundwater and with low water flow (a few metres per day). Pesticide uptake in POCIS showed good linearity, with up to 28 days before reaching equilibrium. Two types of accumulation in POCIS were noted (a linear pattern up to 28 days, and after a time lag of 7 to 14 days). Sampling rates for 38 compounds were calculated and compared with those available in the literature or obtained previously under laboratory conditions. The values obtained were lower by a factor 1 to 14 than those estimated under stirring conditions in the literature, whereas water flow velocity (m s-1) differed by a factor of 2000 to 10,000.

Environmental forensics in groundwater coupling passive sampling and high resolution mass spectrometry for screening.

One of the difficulties encountered when monitoring groundwater quality is low and fluctuating concentration levels and complex mixtures of micropollutants, including emerging substances or transformation products. Combining passive sampling techniques with analysis by high resolution mass spectrometry (HRMS) should improve environmental metrology. Passive samplers accumulate compounds during exposure, which improves the detection of organic compounds and integrates pollution fluctuations. The Polar Organic Chemical Integrative Sampler (POCIS) were used in this study to sequester polar to semi-polar compounds. The methodology described here improves our knowledge of environmental pollution by highlighting and identifying pertinent compounds to be monitored in groundwater. The advantage of combining these two approaches is demonstrated on two different sites impacted by agricultural and/or urban pollution sources where groundwater was sampled for several months. Grab and passive sampling were done and analyzed by liquid chromatography coupled to a hybrid quadrupole time-of-flight mass spectrometer (LC-QTOF). Various data processing approaches were used (target, suspect and non-target screening). Target screening was based on research from compounds listed in a homemade database and suspect screening used a database compiled using literature data. The non-target screening was done using statistical tools such as principal components analysis (PCA) with direct connections between original chromatograms and ion intensity. Trend plots were used to highlight relevant compounds for their identification. The advantage of using POCIS to improve screening of polar organic compounds was demonstrated. Compounds undetected in water samples were detected with these tools. The subsequent data processing identified sentinel molecules, molecular clusters as compounds never revealed in these sampling sites, and molecular fingerprints. Samples were compared and multidimensional visualization of chemical patterns such as molecular fingerprints and recurrent or specific markers of each site were given.

A sensitive analytical procedure for monitoring acrylamide in environmental water samples by offline SPE-UPLC/MS/MS.

The presence of acrylamide in natural systems is of concern from both environmental and health points of view. We developed an accurate and robust analytical procedure (offline solid phase extraction combined with UPLC/MS/MS) with a limit of quantification (20 ng L(-1)) compatible with toxicity threshold values. The optimized (considering the nature of extraction phases, sampling volumes, and solvent of elution) solid phase extraction (SPE) was validated according to ISO Standard ISO/IEC 17025 on groundwater, surface water, and industrial process water samples. Acrylamide is highly polar, which induces a high variability during the SPE step, therefore requiring the use of C(13)-labeled acrylamide as an internal standard to guarantee the accuracy and robustness of the method (uncertainty about 25 % (k = 2) at limit of quantification level). The specificity of the method and the stability of acrylamide were studied for these environmental media, and it was shown that the method is suitable for measuring acrylamide in environmental studies.

Applicability of polar organic compound integrative samplers for monitoring pesticides in groundwater.

Polar organic chemical integrative samplers (POCISs) for the monitoring of polar pesticides in groundwater were tested on two sites in order to evaluate their applicability by comparison with the spot-sampling approach. This preliminary study shows that, as in surface water, POCIS is a useful tool, especially for the screening of substances at low concentration levels that are not detected by laboratory analysis of spot samples. For quantitative results, a rough estimation is obtained. The challenge is now to define the required water-flow conditions for a relevant quantification of pesticides in groundwater and to establish more representative sampling rates for groundwater.