Passive samplers to quantify micropollutants in sewer overflows: accumulation behaviour and field validation for short pollution events

Breaking barriers in passive sampling: The potential of PTFE membranes in the monitoring of hydrophilic micropollutants

Passive samplers are key tools to sample hydrophilic micropollutants in water. Two main approaches address the influence of hydrodynamics: (1) determining site-specific sampling rate (RS) by characterizing kw, the mass transfer coefficient of the water-boundary layer (WBL), and (2) reducing WBL impact using a diffusive material to control the uptake. The first requires calibration data and the second has only been achieved using fragile diffusive material. This study assesses the transfer of hydrophilic contaminants through polytetrafluoroethylene (PTFE; 30 µm thick), a new membrane material with lower sorption than commonly used polyethersulfone (PES). Combined for the first time in a Chemcatcher-like configuration, we calibrated the modified samplers for 44 micropollutants to provide RS - kw relationships for in-situ RS determination (approach 1). Micropollutants accumulated over 2000 times more on the sorbent than on PTFE. PTFE-based RS (0.027 to 0.300 L day-1) were 2.5 higher than previously reported with PES. Membrane property measurements (porosity, tortuosity) indicated that accumulation is primarily controlled by the membrane. Extrapolation indicated that using thicker PTFE membranes (≥ 100 µm) would shift uptake control entirely to the membrane in river conditions (approach 2). This finding could enable RS prediction based on contaminants properties, thus representing a significant advancement in passive sampling.

A ng/L Level LC-MS Method Using Membrane SPE as Sampling Technology: Determination of Nine Halobenzoquinones in Potable Water

A promising method was established for the determination of nine halobenzoquinones (HBQs) in potable water by membrane solid-phase extraction (MSPE) pretreatment and the liquid chromatography-mass spectrometry (LC-MS) method. A 500 mL water sample was taken for enrichment by the SDB-RPS membrane, which was previously activated by methanol and ultrapure water. The sample was eluted with methanol and re-dissolved with the initial mobile phase after nitrogen blowing. Then, it was detected in negative ion mode using the working curve, and HBQs were quantified by the external standard method. The linearity was satisfactory in the concentration range of 4-1000 ng/L, with correlation coefficients of 0.9963~0.9994. The recoveries were 73.5~126.6% at three spiked levels, with relative standard deviations (RSDs) of 6.8~15.5%. The limits of detection (LOD, S/N = 3) values were 0.1~0.7 ng/L. The results demonstrate that the MSPE-LC-MS method is reliable, rapid, and sensitive for the simultaneous analysis of nine HBPs in potable water.

Efficient and practical in-jar silicone rubber based passive sampling for simultaneous monitoring of emerging fungicides in water and soils

The occurrence and ecological impacts of emerging fungicides in the environment has gained increasing attention. This study applied an in-jar passive sampling device based on silicone rubber (SR) film to measuring the freely dissolved concentration (Cfree) of 6 current-use fungicides as a critical index of bioavailability in water and soils. The kinetics parameters including SR-water, soil-water, and organic carbon-water partition coefficients and sampling rates of the target fungicides were first attained and characterized well with their physicochemical properties. The in situ and ex situ field deployment in Hefei City provided the assessment of contaminated levels for these fungicides in rivers and soils. The Cfree of triadimefon and azoxystrobin was estimated at 0.54 ± 0.07-17.4 ± 2.5 ng L-1 in Nanfei River and Chao Lake, while triadimefon was only found in Dongpu Reservoir water with Cfree below 0.66 ± 0.04 ng L-1. The results exhibited that the equilibrium duration of 7 d was suitable for water application but a longer interval of 14 d was recommended for soil sampling. This work demonstrated the advantages of the proposed strategy in terms of fast monitoring within 2 weeks and high sensitivity down to detection limits in 0.5-5 ng L-1. The in-jar passive sampling device can be extrapolated to the evaluation for a wide coverage of organic pollutants in water and soils.

Performance comparison of three passive samplers for monitoring of polar organic contaminants in treated municipal wastewater

Over the past decades, several types of passive samplers have been developed and used to monitor polar organic compounds in aquatic environments. These samplers use different sorbents and barriers to control the uptake into the sampler, but their performance comparison is usually not well investigated. This study aimed to directly compare the performance of three samplers, i.e., the Polar Organic Chemical Integrative Sampler (POCIS), the Hydrogel-based Passive Sampler (HPS, an upscaled version of o-DGT), and the Speedisk, on a diverse suite of pharmaceuticals, per- and polyfluoroalkylated substances (PFAS), and pesticides and their metabolites. The samplers were deployed side-by-side in the treated effluent of a municipal wastewater treatment plant for different exposure times. All samplers accumulated a comparable number of compounds, and integrative uptake was observed for most compounds detected up to 28 days for POCIS, up to 14 days for HPS, and up to 42 days for Speedisk. In the integrative uptake phase, consistent surface-specific uptake was observed with a significant correlation between samplers (r ≥ 0.76) despite differences in sampler construction, diffusion barrier, and sorbent material used. The low sampling rates compared to the literature and the low estimated overall mass transfer coefficient suggests that the water boundary layer was the main barrier controlling the uptake for all samplers. Although all devices provided comparable performance, Speedisk overcomes POCIS and HPS in several criteria, including time-integrative sampling over a long period and physical durability.

An improved Chemcatcher-based method for the integrative passive sampling of 44 hydrophilic micropollutants in surface water - Part A: Calibration under four controlled hydrodynamic conditions

When monitoring water quality with hydrophilic integrative passive sampling devices, it is crucial to use accurate sampling rates (R_S) that account for exposure conditions such as hydrodynamics. This study aims at calibrating Chemcatcher-like passive samplers - styrene-divinylbenzene reverse phase sulfonate (SDB-RPS) extraction disk covered by a polyethersulfone (PES) membrane - at four water flow velocities (5 to 40 cm s^-1) in a channel system. First, the four hydrodynamic conditions were characterized by measuring the mass transfer coefficients of the water boundary layer (k_w) at the surface of the samplers using the alabaster dissolution method. Then, fifty-six samplers were deployed in the channels and exposed for 7 different intervals varying from 1 to 21 days. Thus, R_S were determined at four different k_w for 44 hydrophilic compounds, ranging from 0.015 to 0.115 L day^-1. Relationships were established between k_w and R_S using models for mixed rate control by the membrane and the water boundary layer. The estimated parameters of those relationships are suitable for the determination of accurate R_S when k_w is measured in situ, for example by co-deploying silicone disks spiked with performance and reference compounds (PRC) as implemented in Part B.

An improved Chemcatcher-based method for the integrative passive sampling of 44 hydrophilic micropollutants in surface water - Part B: Field implementation and comparison with automated active sampling

Integrative passive sampling is particularly useful in the monitoring of hydrophilic contaminants in surface water, but the impact of hydrodynamics on contaminant uptake still needs to be better considered. In part A (Glanzmann et al., 2023), Chemcatcher-like hydrophilic samplers (i.e., SDB-RPS extraction disks covered by PES microporous membranes) were calibrated to determine the sampling rates R_S of 44 hydrophilic contaminants (pesticides, pharmaceuticals, industrial products) taking into account the hydrodynamic conditions. In this study, Chemcatcher-like passive sampling devices that allowed co-deploying hydrophilic samplers and performance reference compounds (PRC)-spiked silicone disks were tested in a Swiss river with intermediate water velocities (5-50 cm s^-1, 23 cm s^-1 on average) during 11 consecutive 14-day periods. The PRC dissipation from silicone disks - combined with the calibration data from part A - allowed to determine in-situ R_S that took into account hydrodynamic conditions. The obtained aqueous time-weighted average (TWA) concentrations were found to be robust with good concordance between duplicates (mean quotient of 1.16 between the duplicates). For most measurements (76 %), TWA concentrations showed no major difference (<factor 2) from concentrations obtained with automated sampling (14-day composite samples). This observation was also valid for TWA concentrations calculated with extrapolated R_S at infinite water velocity (R_S,MAX), revealing that the added value of using in-situ R_S compared to R_S,MAX is limited above intermediate water velocities (>20 cm s^-1). R_S from the literature (R_S,LIT) - obtained at water velocities between 8 and 37 cm s^-1 - were also shown to provide comparable TWA concentrations in the studied hydrodynamic conditions (average water velocity of 24 cm s^-1). The estimated errors due to the use of R_S,MAX or R_S,LIT rather than in-situ R_S are given as a function of the water velocity to determine in which conditions the developed method is required (or not) in monitoring programs.

In situ calibration of passive sampling methods for urban micropollutants using targeted multiresidue GC and LC screening systems

In this study, Chemcatcher^TM (CC) and Polar Organic Chemical Integrative Samplers (POCIS) passive samplers were chosen to investigate trace organic chemical residues in urban streams of the megacity of Sydney, Australia. In situ calibration with these passive samplers investigated 1392 organic chemicals. Six sets of CC passive samplers fitted with SDB-XC or SDB-RPS disks and six POCIS containing Oasis HLB sorbent were deployed at three sites. Every week for six weeks across three deployments, composite water samples were retrieved from autosamplers, along with one set of CC/POCIS passive samplers. Samples were analysed by Automated Identification and Quantification System (AIQS) GC/MS or LC/QTOF-MS database methods with 254 chemicals detected. The most frequently detected compounds under GC/MS analysis were aliphatic, pesticides, phenols, PAHs, sterols and fatty acid methyl esters while from LC/QTOF-MS analysis these were pesticides, pharmaceuticals, and personal care products. Sampling rates (R_s) ranged between <0.001 - 0.132 L day^-1 (CC SDB-XC, 18 chemicals), <0.001 - 0.291 L day^-1 (CC SDB-RPS, 28 chemicals), and <0.001 - 0.576 L day^-1 (POCIS Oasis HLB, 30 chemicals). Assessment of deployment duration indicated that about half of the chemicals that were continuously detected across all deployment weeks had maximal simple linear regression R² values at four weeks for CC SDB-RPS (seven of 13 chemicals) and at three weeks for POCIS Oasis HLB (seven of 14 chemicals). Where ranges of R_s recorded from the estuarine site were able to be compared to ranges of R_s from one or both freshwater sites, only tributyl phosphate had a higher range of R_s out of 21 possible chemical comparisons, and suggested salinity was an unlikely influence on R_s. Whereas relatively higher rainfall of the third round of deployment aligned with higher R_s across the estuarine and freshwater sites for CC SDB-RPS and POCIS for nearly all possible comparisons.

A Review on Polyethersulfone Membranes in Polar Organic Chemical Integrative Samplers: Preparation, Characterization and Innovation

The membranes in polar organic chemical integrative samplers (POCIS) enclose the receiving sorbent and protect it from coming into direct contact with the environmental matrix. They have a crucial role in extending the kinetic regime of contaminant uptake, by slowing down their diffusion between the water phase and the receiving phase. The drive to improve passive sampling requires membranes with better design and enhanced performances. In this review, the preparation of standard polyethersulfone (PES) membranes for POCIS is presented, as well as methods to evaluate their composition, morphology, structure, and performance. Generally, only supplier-related morphological and structural data are provided, such as membrane type, thickness, surface area, and pore diameter. The issues related to the use of PES membranes in POCIS applications are exposed. Finally, alternative membranes to PES in POCIS are also discussed, although no better membrane has yet been developed. This review highlights the urge for more membrane characterization details and a better comprehension of the mechanisms which underlay their behavior and performance, to improve membrane selection and optimize passive sampler development.

A decade of monitoring micropollutants in urban wet-weather flows: What did we learn?

Urban wet-weather discharges from combined sewer overflows (CSO) and stormwater outlets (SWO) are a potential pathway for micropollutants (trace contaminants) to surface waters, posing a threat to the environment and possible water reuse applications. Despite large efforts to monitor micropollutants in the last decade, the gained information is still limited and scattered. In a metastudy we performed a data-driven analysis of measurements collected at 77 sites (683 events, 297 detected micropollutants) over the last decade to investigate which micropollutants are most relevant in terms of 1) occurrence and 2) potential risk for the aquatic environment, 3) estimate the minimum number of data to be collected in monitoring studies to reliably obtain concentration estimates, and 4) provide recommendations for future monitoring campaigns. We highlight micropollutants to be prioritized due to their high occurrence and critical concentration levels compared to environmental quality standards. These top-listed micropollutants include contaminants from all chemical classes (pesticides, heavy metals, polycyclic aromatic hydrocarbons, personal care products, pharmaceuticals, and industrial and household chemicals). Analysis of over 30,000 event mean concentrations shows a large fraction of measurements (> 50%) were below the limit of quantification, stressing the need for reliable, standard monitoring procedures. High variability was observed among events and sites, with differences between micropollutant classes. The number of events required for a reliable estimate of site mean concentrations (error bandwidth of 1 around the "true" value) depends on the individual micropollutant. The median minimum number of events is 7 for CSO (2 to 31, 80%-interquantile) and 6 for SWO (1 to 25 events, 80%-interquantile). Our analysis indicates the minimum number of sites needed to assess global pollution levels and our data collection and analysis can be used to estimate the required number of sites for an urban catchment. Our data-driven analysis demonstrates how future wet-weather monitoring programs will be more effective if the consequences of high variability inherent in urban wet-weather discharges are considered.

Determining the Mass Transfer Coefficient of the Water Boundary Layer at the Surface of Aquatic Integrative Passive Samplers

Passive sampling devices (PSDs) offer key benefits for monitoring chemical water quality, but the uptake process of PSDs for hydrophilic compounds still needs to be better understood. Determining mass transfer coefficients of the water boundary layer (k_w) during calibration experiments and in situ monitoring would contribute toward achieving this; it allows for combining calibration data obtained at different temperature and hydrodynamic conditions and facilitate the translation of laboratory-derived calibration data to field exposure. This study compared two k_w measurement methods applied to extraction disk housings (Chemcatcher), namely, alabaster dissolution and dissipation of performance reference compounds (PRCs) from silicone. Alabaster- and PRC-based k_w were measured at four flow velocities (5-40 cm s^-1) and two temperatures (11 and 20 °C) in a channel system. Data were compared using a relationship based on Sherwood, Reynolds, and Schmidt numbers. Good agreement was observed between data obtained at both temperatures, and for the two methods. Data were well explained by a model for mass transfer to a flat plate under laminar flow. It was slightly adapted to provide a semi-empirical model accounting for the effects of housing design on hydrodynamics. The use of PRC-spiked silicone to obtain in situ integrative k_w for Chemcatcher-type PSDs is also discussed.

Effect of rainfall characteristics on the sewer sediment, hydrograph, and pollutant discharge of combined sewer overflow

Significant management needs raised in urban sewer system to facilitate urban resilience to rainstorm. The work investigated the effects of temporal evolution of rainfall on hydrograph and pollutant discharge of CSO over an intensive observation period of 12 months, with special attention to differences in temporal scale for supporting management decision making. The characteristics of rainfall in different temporal scales helped overflow-risk identification and assessment. Prolonged dry seasons over 112 days in the CSO monitored year 2018 increased the sediment buildup in the pipes. The built sediment was mostly flushed out to overflow (and the treatment facility) by initial rainfall during 47 h. Following CSO hydraulics and pollutant discharge follows initial peak patterns which responded to rainfall patterns. Results of Redundancy analysis and network analysis showed that the combined effects of rainfall, urbanization, and sediments as "CSO troika" are the driving forces for CSO pollutants in the long-term. The improved characterization of CSO events and the associated pollutants has refined our understanding of how overflow hydrograph and pollutant discharge responds to rainfall temporally, which methodology supported decision making in the combining source/process control with terminal management for facilizing urban resilience.

Passive Sampler Exchange Kinetics in Large and Small Water Volumes Under Mixed Rate Control by Sorbent and Water Boundary Layer

Exchange kinetics of organic compounds between passive samplers and water can be partly or completely controlled by transport in the sorbent. In such cases diffusion models are needed. A model is discussed that is based on a series of cosines (space) and exponentials (time). The model applies to mixed rate control by sorbent and water boundary layer under conditions of fixed aqueous concentrations (open systems, infinite water volumes, in situ sampling) and fixed amounts (closed systems, finite water volumes, ex situ sampling). Details on the implementation of the model in computational software and spreadsheet programs are discussed, including numerical accuracy. Key parameters are Biot number (ratio of internal/external transfer resistance) and sorbent/water phase ratio. Small Biot numbers are always indicative of rate control by the water boundary layer, but for large Biot numbers this may still be the case over short time scales. Application to environmental monitoring of nonpolar compounds showed that diffusion models are rarely needed for sampling with commonly used single-phase polymers. For determining sorption coefficients in batch incubations, the model demonstrated a profound effect of sorbent/water phase ratio on time to equilibrium. Application of the model to sampling of polar organic compounds by extraction disks with or without a membrane showed that moderate to major sorbent-controlled kinetics is likely to occur. This implies that the use of sampling rate models for such samplers needs to be reconsidered. Environ Toxicol Chem 2021;40:1241-1254. © 2021 SETAC.

A review of combined sewer overflows as a source of wastewater-derived emerging contaminants in the environment and their management

Emerging contaminants such as pharmaceuticals, illicit drugs and personal care products can be released to the environment in untreated wastewater/stormwater mixtures following storm events. The frequency and intensity of combined sewer overflows (CSOs) has increased in some areas due to increasing urbanisation and climate change. Therefore, this review provides an up-to-date overview on CSOs as an environmental source of emerging contaminants. Other than compounds with high removal, those chiral species subject to enantioselective changes (i.e. degradation or inversion) during wastewater treatment can be effective markers of CSO discharge in the environment. A proposed framework for the selection of emerging contaminants as markers of CSOs is outlined. Studies have demonstrated that CSOs can be the main source of emerging contaminants with high removal efficiency during wastewater treatment (e.g. > 90%). However, the impact of CSOs on the environment is location specific and requires decision-making on their appropriate management at catchment level. This process would be aided by further studies on CSOs which incorporate the monitoring of emerging contaminants and their effects in the environment with those more routinely monitored pollutants (e.g. pathogens and priority substances). Mitigation and treatment strategies for emerging contaminants in CSOs are also discussed.

Limitations of Integrative Passive Samplers as a Tool for the Quantification of Pharmaceuticals in the Environment - A Critical Review with the Latest Innovations

This review starts with a presentation of the theory of kinetic uptake by passive sampling (PS), which is traditionally used to distinguish between integrative and equilibrium samplers. Demonstrated limitations of this model for the passive sampling of pharmaceuticals from water were presented. Most notably, the contribution of the protective membrane in the resistance to mass transfer of lipophilic analytes and the well documented effect of external parameters on sampling rates contributed to the greatest uncertainty in PS application. The diffusion gradient in thin layer (DGT) technique seems to reduce the effect of external parameters (e.g., flow rate) to some degree. The laboratory-determined integrative uptake periods over defined sampler deployments was compared, and the discrepancy found suggests that the most popular Polar Organic Chemical Integrative Sampler (POCIS) could in some cases utilized as an equilibrium sampler. This assertion is supported by own calculations for three pharmaceuticals with extremely different lipophilic characters. Finally, the reasons performance reference compounds (PRCs) are not recommended for the reduction in uncertainty of the TWAC found by adsorptive samplers were presented. It was concluded that techniques of passive sampling of pharmaceuticals need a new uptake model to fit the current situation.

Passive sampler phases for pesticides: evaluation of AttractSPE™ SDB-RPS and HLB versus Empore™ SDB-RPS

In this study, three different passive sampling receiving phases were evaluated, with a main focus on the comparability of established styrene-divinylbenzene reversed phase sulfonated (SDB-RPS) sampling phase from Empore™ (E-RPS) and novel AttractSPE™ (A-RPS). Furthermore, AttractSPE™ hydrophilic-lipophilic balance (HLB) disks were tested. To support sampling phase selection for ongoing monitoring needs, it is important to have information on the characteristics of alternative phases. Three sets of passive samplers (days 1-7, days 8-14, and days 1-14) were exposed to a continuously exchanged mixture of creek and rainwater in a stream channel system under controlled conditions. The system was spiked with nine pesticides in two peak scenarios, with log K_OW values ranging from approx. - 1 to 5. Three analytes were continuously spiked at a low concentration. All three sampling phases turned out to be suitable for the chosen analytes, and, in general, uptake rates were similar for all three materials, particularly for SDB-RPS phases. Exceptions concerned bentazon, where E-RPS sampled less than 20% compared with the other phases, and nicosulfuron, where HLB sampled noticeably more than both SDB-RPS phases. All three phases will work for environmental monitoring. They are very similar, but differences indicate one cannot just use literature calibration data and transfer these from one SDB phase to another, though for most compounds, it may work fine.

Sampling rates for passive samplers exposed to a field-relevant peak of 42 organic pesticides

Pesticide concentrations in agricultural streams are often characterised by a low level of baseline exposure and episodic peak concentrations associated with heavy rainfall events. Traditional sampling methods such as grab sampling, which are still largely used in governmental monitoring, typically miss peak concentrations. Passive sampling represents a cost-efficient alternative but requires the additional determination of sampling rates to calculate time-weighted average (TWA) water concentrations from the accumulated pesticide mass in the sampler. To date, sampling rates have largely been determined in experiments with constant exposure, which does not necessarily reflect field situations. Using Empore styrene-divinylbenzene (SDB) passive sampler disks mounted in metal holders, we determined sampling rates for 42 organic pesticides, of which 27 sampling rates were lacking before. The SDB disks were in an artificial channel system exposed to a field-relevant pesticide peak. We used an open-source algorithm to estimate coefficients of equations for the accumulated pesticide mass in disks and to determine exposure time-dependent sampling rates. These sampling rates ranged from 0.02 to 0.98 L d^-1 and corresponded to those from previous studies determined with constant exposure. The prediction of sampling rates using compound properties was unreliable. Hence, experiments are required to determine reliable sampling rates. We discuss the use of passive sampling to estimate peak concentrations. Overall, our study provides sampling rates and computer code to determine these under peak exposure designs and suggests that passive sampling is suitable to estimate peak pesticide concentrations in field studies.

POCIS Calibration for Organic Compound Sampling in Small Headwater Streams

Field-based atrazine sampling rates (R_s ) obtained by the polar organic chemical integrative sampler (POCIS) method were measured in 9 headwater streams over 3 yr covering 5 to 6 exposure periods of 2 to 3 wk/site/yr. Rates were best in line with the model R_s  = 148 mL/d, with a standard deviation of 0.17 log units (factor 1.5). The POCIS canisters reduced mass transfer coefficients of the water boundary layer by a factor of 2 as measured by alabaster dissolution rates. A mechanistic model that accounts for flow and temperature effects yielded a fair estimate of the effective exchange surface area (12.5 ± 0.8 cm² ). This model could only be tested for higher flow velocities because of uncertainties associated with the measurement of flow velocities <1 cm/s. Pictures of sorbent distributions in POCIS devices showed that the effective exchange surface area varied with time during the exposures. Error analysis indicated that sorbent distributions and chemical analysis were minor error sources. Our main conclusion is that an atrazine sampling rate of 148 mL/d yielded consistent results for all 3 yr across 9 headwater streams. Environ Toxicol Chem 2020;39:1334-1342. © 2020 SETAC.

Spatial Differences among Micropollutants in Sewer Overflows: A Multisite Analysis Using Passive Samplers

Untreated sewer overflows can contaminate receiving waters with micropollutants. Although concentrations of discharged micropollutants can be ecotoxicologically relevant, only limited data is available to assess occurrence and spatial differences among sewer overflow catchments. Therefore, we present an innovative type of data obtained with passive samplers at 20 combined sewer overflow sites (2-7 events per site; 95 events in total). The data sheds light on concentration ranges for 13 representative polar organic micropollutants and shows that micropollutants in both municipal wastewater and stormwater can be relevant sources of contaminants. We identify indicator micropollutants for further studies: benzotriazole (80% interquantile of time-weighted average concentration: 250-4800 ng/L), carbamazepine (33-910 ng/L), diclofenac (78-1000 ng/L), carbendazim (21-900 ng/L), diazinon (2.1-53 ng/L), diuron (22-1100 ng/L), mecoprop (98-5300 ng/L), metolachlor (6-230 ng/L), and terbutryn (29-810 ng/L). These concentration estimates are assumed to be on the safe side for comparison with environmental quality standards (EQS). A majority of sewer overflow sites (13 of 20) show discharge concentrations above acute EQS for at least one micropollutant and thus would have to rely on dilution by receiving waters to not exceed any EQS. The intersite variability among sewer overflows exceed the within-site variability. Hence, future monitoring studies should cover more sewer overflow sites. No correlation could be found with event durations, specific storage volume or land use data, thus showing the complexity of micropollutant occurrence and indicating that other factors led to the observed high spatial variability. In conclusion, our results clearly show the potential relevance of micropollutants in sewer overflows and the need to assess site-specific measures.

Impact of Combined Sewer Systems on the Quality of Urban Streams: Frequency and Duration of Elevated Micropollutant Concentrations

Water quality in urban streams is highly influenced by emissions from WWTP and from sewer systems particularly by overflows from combined systems. During storm events, this causes random fluctuations in discharge and pollutant concentrations over a wide range. The aim of this study is an appraisal of the environmental impact of micropollutant loads emitted from combined sewer systems. For this purpose, high-resolution time series of river concentrations were generated by combining a detailed calibrated model of a sewer system with measured discharge of a small natural river to a virtual urban catchment. This river base flow represents the remains of the natural hydrological system in the urban catchment. River concentrations downstream of the outlets are simulated based on mixing ratios of base flow, WWTP effluent, and CSO discharge. The results show that the standard method of time proportional sampling of rivers does not capture the risk of critical stress on aquatic organisms. The ratio between average and peak concentrations and the duration of elevated concentrations strongly depends on the source and the properties of the particular substance. The design of sampling campaigns and evaluation of data should consider these characteristics and account for their effects.

Quantitative use of passive sampling data to derive a complete seasonal sequence of flood event loads: a case study for maize herbicides in Luxembourg

Pesticides are the class of compounds with the most dynamic behaviour in their surface water occurrence: their episodic release to surface waters is closely related to the date of application and the following weather conditions and poses substantial challenges to monitoring in order to yield accurate mass transfer figures. Moreover, pesticide use, dose and time of application are largely unknown catchment wide and pose an essential problem as to the realism and reliability of pesticide fate modelling as well as accurate farmer counselling. Spatially and temporally highly resolved monitoring establishing pesticide sources was logistically unthinkable until the advent of passive samplers which combine ease of deployment and continuous sampling. However, because research on passive sampler performance has been mainly driven by analytical precision issues, doubts were high as to whether passive samplers could yield accurate time weighted averages in the field, all the more so that the number of field validations is to this day very limited. Here we present a study that used a combination of spatially distributed passive- and autosamplers to capture the runoff dynamics of pesticides used for maize crops in a 82 km2 catchment in Luxembourg. We demonstrate that passive samplers are capable of accurately monitoring episodic emissions of pesticides through a longitudinal profile in a catchment, thus allowing the identification of pesticide source areas. Thanks to the time-proportional nature of the passive sampling it was furthermore possible to calculate event mean concentrations and loads which were behaving temporally according to the physico-chemical properties of the compounds and to the timing and extent of mobilising discharge.

Detection and Quantification of Photosystem II Inhibitors Using the Freshwater Alga Desmodesmus subspicatus in Combination with High-Performance Thin-Layer Chromatography

We present a novel tool for detecting and monitoring photosystem II (PSII) inhibitors, using the freshwater alga Desmodesmus subspicatus, in environmental samples fractionated by high-performance thin-layer chromatography (HPTLC). After chromatographic separation of a sample on a HPTLC plate, the algal suspension is sprayed homogeneously on the plate, and PSII-inhibition by specific sample components is detected based on changes in fluorescence yield, viewed by a maxi Imaging-Pulse-Amplitude-Modulation fluorometer. Dose-dependent responses to the PSII-inhibitor herbicides atrazine and diuron, frequently detected in water bodies, are demonstrated without and with chromatographic separation. The limits of quantification for atrazine and diuron with chromatographic separation were 1.94 ng and 99 pg, respectively, allowing the detection of environmentally relevant concentrations of these herbicides. The developed method was also employed to analyze sample extracts collected during a passive sampling campaign in surface waters. The obtained data correlated well with results from LC-MS/MS chemical analysis but also revealed unknown PSII-inhibiting activities. The proposed methodology represents a rapid and sensitive screening tool for the simultaneous effect-based detection of PSII-inhibitors in environmental samples.