Generally, karst aquifers and springs are highly susceptible to contamination due to the high permeability and, therefore, groundwater flow velocities. The often thin soil cover, accompanied by dolines, can lead to fast infiltration of precipitation water loaded with mobilized contaminants such as pesticides and their transformation products. To date, continuous, temporally highly resolved in-situ monitoring to decipher concentration dynamics for a broad range of pesticides is missing. Therefore, a transportable HPLC-HRMS/MS system (MS2field) was positioned at two karst study sites in the Swiss Jura. Water samples were collected and analyzed for pesticides and their transformation products in-situ every 20 min for 6 weeks in 2021 and 8 weeks in 2022. During the spraying season in 2021, six rain events at site 1 and three at site 2 in 2022 were captured. Concurrently, the water quality parameters electrical conductivity, pH, nitrate, turbidity, and water level, were monitored continuously at high temporal resolution. Further, bacterial cell counts were monitored via online flow cytometry. In 2021, several pesticides and pesticide transformation products were detected in peak concentrations after rain events, of which metamitron showed the highest concentration of up to 1000 ng/L. In one rain event, the Swiss federal and EU drinking water limit of 100 ng/L was exceeded for up to 38 h. Compared with highly frequent MS2field samples collected every 20 min, 42-hours composite samples severely underestimated peak concentrations for all compounds, especially for labile ones. Therefore, it was demonstrated that exceedences of the regulatory limit would have been missed if just composite sampling would have been conducted. Peak concentrations of pesticides coincided with peaks in nitrate concentration and bacterial cell counts following rain events. The correlation analysis showed strong correlations between the three analyzed contaminants (pesticides, nitrate and bacteria), and the proxy parameters electrical conductivity, and pH. The investigation of a second spring revealed similar dynamics indicating that these can be expected in other karst aquifers as well.

Agricultural pesticides transported to surface waters pose a major risk for aquatic ecosystems. Modelling studies indicate that the inlets of agricultural storm drainage systems can considerably increase the connectivity of surface runoff and pesticides to surface waters. These model results have however not yet been validated with field measurements. In this study, we measured discharge and concentrations of 51 pesticides in four out of 158 storm drainage inlets of a small Swiss agricultural catchment (2.8 km2) and in the receiving stream. For this, we performed an event-triggered sampling during 19 rain events and collected plot-specific pesticide application data. Our results show that agricultural storm drainage inlets strongly influence surface runoff and pesticide transport in the study catchment. The concentrations of single pesticides in inlets amounted up to 62 µg/L. During some rain events, transport through single inlets caused more than 10% of the stream load of certain pesticides. An extrapolation to the entire catchment suggests that during selected events on average 30 to 70% of the load in the stream was transported through inlets. Pesticide applications on fields with surface runoff or spray drift potential to inlets led to increased concentrations in the corresponding inlets. Overall, this study corroborates the relevance of such inlets for pesticide transport by establishing a connectivity between fields and surface waters, and by their potential to deliver substantial pesticide loads to surface waters.

Karst aquifers are an important water resource for a large part of the world’s population. Because of their natural susceptibility towards contamination, they have to be managed carefully. Human activities such as agriculture, roads or settlements in karst aquifer catchments often lead to the contamination of karstic springs. Due to their special geology, they are at risk of both, long- and short-term contamination. Long-term contamination is due to adsorption of anthropogenic substances in the overlaying soil, the epikarst or rock matrix whereas short-term contamination can be due to spills or precipitation events. Such precipitation events can lead to the mobilization of substances. These are then readily transported to karstic springs where pollutant peaks might be observed. However, current monitoring strategies are not suitable (infrequent, regular sampling intervals) to reveal such peaks. The goal of this study was in a first step, to investigate the contamination level of ten karstic springs (part of NAQUA Swiss National Groundwater Monitoring) in the Swiss Jura, screening for plant protection products (PPP) and transformation products (TP). This was achieved by a monitoring campaign that was conducted from March 2020 until October 2020. Two-week composite samples were collected in addition to the continuous acquisition of electrical conductivity and water level, i.e. spring discharge. Samples were then analyzed by large volume direct injection into a HPLC-HRMS/MS setup using a target list of 130 compounds (105 PPP’s, 25 TP’s). Analysis of a first batch of samples of three springs did not reveal many compounds with elevated concentrations (33 detections in 15 samples above 100 ng/L of 3 compounds: chloridazone desphenyl, chloridazone methyl desphenyl, chlorothalonil TP R471811). No PPP’s were observed to be continuously leaching from the catchment and the aquifer in concentrations above 100 ng/L. The detected compounds above 100 ng/L were TP’s which indicates that their parent compounds might be adsorbed to the aquifer matrix or the soil cover, therefore leaching TP’s continuously or pulse like during rain events. In total, 19 compounds were detected above their quantification limits. Of those, 10 PPP’s and 9 TP’s were found. We further evaluated spring responses during rain events based on electrical conductivity and determined response times between 3 and 5.5 hours. Since two-week composite samples cannot reveal short-term concentration dynamics given the fast response times and dilution (both leading to low concentrations in composite samples), we will conduct a sampling campaign with a different strategy in 2021. Therein, in a second step, the goal is to study the pollutant dynamics induced by precipitation events with temporally highly resolved measurements. To achieve this we will install a transportable, liquid chromatography, high resolution mass spectrometer at three selected springs and conduct an automatic sampling and analysis with a high temporal resolution.

Agricultural pesticides can enter surface waters through various pathways and impair the water quality. In the past, numerous studies have been conducted for certain entry paths such as surface runoff, direct drift into water bodies or preferential flow to drainage systems. Man-made hydraulic shortcuts (e.g. road storm drains or manholes of tile drainage systems) might potentially also play a major role for pesticide inputs into surface waters. However, they have been largely overlooked in the past. This study is the first one to measure pesticide concentrations in hydraulic shortcuts in agricultural catchments. For our analysis, we selected a small catchment (2.8km2) with predominant arable land use in the Swiss Plateau. We installed a rain event-based sampling system at six locations in the catchment: water level proportional samplers at four road storm drainage inlets, one auto sampler in a manhole collecting water from the tile and road drainage system, and another auto sampler in the stream at the outlet of the catchment. In addition, we measured rainfall in the catchment as well as discharge or water level at each of the six sampling locations. During spring and summer of 2019, samples were collected during 19 rain events. In a first step, the samples from the drainage inlets were analyzed. Liquid chromatography coupled to high-resolution mass spectrometry was used to quantify concentrations of 40 pesticides known to be applied in the catchment. The obtained results support the hypothesis that hydraulic shortcuts can be relevant for pesticide transport. First, a wide variety of compounds was detected: 33 substances were found in the samples, 7 were not detected. Per rain event, 4 to 15 pesticides were measured on average. Second, some of the compounds were found in very high concentrations: some exceeded concentrations of 5 µg/L and reached up to 60 µg/L. Ecological quality criteria are known for 15 of the analyzed substances. Based on the sum of the respective risk quotients, nearly a third of the samples posed an acute ecological risk. In most cases, the elevated risk could almost exclusively be attributed to the two herbicides Dimethenamide and Terbuthylazine, as well as to the fungicide Epoxiconazole. Azoxystrobin, Cyproconazole, Mesulfuron-methyl, Metamitron and Metribuzin added to the overall risk to a lesser extent. In a next step, samples taken by the auto sampler will be analyzed to obtain time series of the rain events and to link the findings from storm drain inlets to the concentration dynamics observed in the receiving drainage system and the river itself.

Pesticide contamination of agricultural streams has widely been analysed in regions of high intensity agriculture such as in Western Europe or North America. The situation of streams subject to low intensity agriculture relying on human and animal labour, as in parts of Romania, remains unknown. To close this gap, we determined concentrations of 244 pesticides and metabolites at 19 low-order streams, covering sites from low to high intensity agriculture in a region of Romania. Pesticides were sampled with two passive sampling methods (styrene-divinylbenzene (SDB) disks and polydimethylsiloxane (PDMS) sheets) during three rainfall events and at base flow. Using the toxic unit approach, we assessed the toxicity towards algae and invertebrates. Up to 50 pesticides were detected simultaneously, resulting in sum concentrations between 0.02 and 37 mu g L-1. Both, the sum concentration as well as the toxicities were in a similar range as in high intensity agricultural streams of Western Europe. Different proxies of agricultural intensity did not relate to in-stream pesticide toxicity, contradicting the assumption of previous studies. The toxicity towards invertebrates was positively related to large scale variables such as the catchment size and the agricultural land use in the upstream catchment and small scale variables including riparian plant height, whereas the toxicity to algae showed no relationship to any of the variables. Our results suggest that streams in low intensity agriculture, despite a minor reported use of agrochemicals, exhibit similar levels of pesticide pollution as in regions of high intensity agriculture. (C) 2020 Elsevier Ltd. All rights reserved.

Insecticides such as pyrethroids and organophosphates are extensively used globally. Once released into surface water bodies, they can pose a major threat to aquatic ecosystems already at trace concentrations. Therefore, selected pyrethroids and organophosphates are listed as priority substances within the European Water Framework Directive with chronic quality criteria in the picogram per liter range. Previously applied analytical methods were unable to detect pyrethroids and organophosphates at ecotoxicological relevant concentrations, thereby hindering the assessment of surface water quality. In this work, we developed an ultra-sensitive method for the analysis of 12 pyrethroid and two organophosphate insecticides in surface waters. This method is based on the liquid–liquid extraction of surface water samples with n-hexane to achieve large enrichment factors (4000×) and subsequent chemical analysis by gas chromatography coupled to tandem mass spectrometry using atmospheric pressure chemical ionization, a soft ionization technique. Quality control parameters including the method limits of quantification (12.5–125 pg L−1), intra-day precision (1–22%), intra-day accuracy (84–133%), and absolute recoveries covering liquid–liquid extraction (67–114%) showed that the method is sensitive and robust and therefore suitable for the analysis of pyrethroids and organophosphates in surface waters. The developed method was applied to Swiss surface water samples and detected pyrethroids and organophosphates below the ecotoxicological relevant concentrations, exemplifying the suitability of the proposed method for aquatic monitoring.

To protect the ecosystem and drinking water resources in Switzerland and in the countries of the downstream catchments, a new Swiss water protection act entered into force in 2016 aiming to reduce the discharge of micropollutants from wastewater treatment plants (WWTPs). As a consequence, selected WWTPs must be upgraded by an advanced treatment for micropollutant abatement with suitable and economic options such as (powdered) activated carbon treatment or ozonation. WWTP Neugut (105'000 people equivalent) was the first WWTP in Switzerland to implement a long-term full-scale ozonation. Differing specific ozone doses in the range of 0.35-0.97 g O3/g DOC were applied to determine the adequate ozone dose to fulfill the requirements of the Swiss water protection act. Based on this assessment, a specific ozone dose of 0.55 g O3/g DOC is recommended at this plant to ensure an average abatement of the twelve selected indicator substances by ≥80% over the whole treatment. A monitoring of 550 substances confirmed that this dose was very efficient to abate a broad range of micropollutants by >79% on average. After ozonation, an additional biological post-treatment is required to eliminate possible negative ecotoxicological effects generated during ozonation caused by biodegradable ozonation transformation products (OTPs) and oxidation by-products (OBPs). Three biological treatments (sand filtration, moving bed, fixed bed) and granular activated carbon (GAC, fresh and pre-loaded) filtration were evaluated as post-treatments after ozonation. In parallel, a fresh GAC filter directly connected to the effluent of the secondary clarifier was assessed. Among the three purely biological post-treatments, the sand filtration performed best in terms of removal of dissolved organic carbon (DOC), assimilable organic carbon (AOC) and total suspended solids (TSS). The fresh activated carbon filtration ensured a significant additional micropollutants abatement after ozonation due to sorption. The relative abatement of the indicator substances ranged between 20 and 89% after 27'000 bed volumes (BV) and was still substantial at 50'000 BV. In an identical GAC filter running in parallel and being fed with the effluent of the secondary clarifier, the elimination was less efficient. Seven primary OTPs (chlorothiazide and six N-oxides) formed during ozonation could be quantified thanks to available reference standards. Their concentration decreased with increasing specific ozone doses with the concomitant formation of other OTPs. The seven OTPs were found to be stable compounds and were not abated in the biological post-treatments. They were sorbed in the fresh GAC filter, but less efficiently than the corresponding parent compounds. Two OBPs, bromate (BrO3-) and N-nitrosodimethylamine (NDMA), were formed during ozonation but did not exceeded 5 μg/L for bromate and 30 ng/L for NDMA at the recommended specific ozone dose of 0.55 g O3/g DOC. NDMA was well abated in all post-treatments (minimum 41% during fixed bed filtration, maximum 83% during fresh GAC filtration), while bromate was very stable as expected.

This study aimed at gaining knowledge on the degradation pathway during biological treatment of wastewater of diclofenac and 4'-hydroxydiclofenac, its main human metabolite. For that purpose, an aerobic MBR was acclimatised to diclofenac, and the MBR biomass subsequently incubated with C-14-diclofenac or C-14-4'hydroxydiclofenac over 25 days. It was demonstrated that diclofenac degradation was much slower and limited than that of 4'-hydroxydiclofenac. Indeed, after 18 days of batch incubation, diclofenac was removed up to 40%, this rate remained stable till the end of the experiment, while 4'-hydroxydiclofenac was completely degraded within nine days. The analyses of supernatant samples have shown that diclofenac degradation led to four transformation products, more polar than the parent compound, one of them being 4'-hydroxydiclofenac. The degradation of 4'-hydroxydiclofenac led to the formation of the same metabolites than those detected during diclofenac degradation. With these results, the hydroxylation of diclofenac to 4'-hydroxydiclofenac was identified as one major bottleneck in diclofenac degradation during biological treatment of wastewater. (C) 2015 Published by Elsevier B.V.