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Pesticides are intensely used in the agricultural sector worldwide including smallholder farming. Poor pesticide use practices in this agronomic setting are well documented and may impair the quality of water resources. However, empirical data on pesticide occurrence in water bodies of tropical smallholder agriculture is scarce. Many available data are focusing on apolar organochlorine compounds which are globally banned. We address this gap by studying the occurrence of a broad range of more modern pesticides in an agricultural watershed in Uganda. During 2.5 months of the rainy season in 2017, three passive sampler systems were deployed at five locations in River Mayanja to collect 14 days of composite samples. Grab samples were taken from drinking water resources. In these samples, 27 compounds out of 265 organic pesticides including 60 transformation products were detected. In the drinking water resources, we detected eight pesticides and two insecticide transformation products in low concentrations between 1 and 50 ng/L. Also, in the small streams and open fetch ponds, detected concentrations were generally low with a few exceptions for the herbicide 2,4-D and the fungicide carbendazim exceeding 1 ug/L. The widespread occurrence of chlorpyrifos posed the largest risk for macroinvertebrates. The extensive detection of this compound and its transformation product 3,4,5-trichloro-2-pyridinol was unexpected and called for a better understanding of the use and fate of this pesticide., Environmental Science and Pollution Research, 30 (4), ISSN:0944-1344, ISSN:1614-7499

This codebook was developed and used to analyse evidence use in the public discourse on pesticides in Switzerland. This includes media articles, articles of trade magazines, and political documents (e.g., speeches, acts, consultations).

South Africa is the leading user of pesticides in Sub-Saharan Africa. Consequently, there is an urgent need to improve our understanding of which pesticides persist in the environment and how they are being transported to non-target environments. The presence of pesticides in non-target environments, such as surface water or groundwater, could be detrimental to aquatic ecosystems and human health.Our research focuses on monitoring for pesticides in the rivers of three agricultural catchments (Grabouw, Hex River Valley, and Piketberg) within the Western Cape, South Africa. Passive samplers are being deployed from March 2022 to March 2023, adding to a pre-existing dataset of analytical and pesticide application data from 2017 to 2019. Laboratory methods are being developed and validated at Stellenbosch University (SU) to analyze for pesticides using Liquid Chromatography-Mass Spectrometry. Duplicate samples were analyzed at the Swiss Federal Institute of Aquatic Research (Eawag), as a quality control step. Limits of Quantification were lower at Eawag and measured concentrations were typically higher compared to SU. These differences are likely due to variations in the instrument used and sample extraction procedure. Results from 2017-2019 indicate that 83% of samples contained five or more pesticides. In every year of sampling, total pesticide concentrations were typically attributable to a single/few compounds per catchment. Six pesticides exceeded Environmental Quality Standard (EQS) values in at least one of the sampling periods. Imidacloprid was highlighted as a pesticide of concern since it consistently exceeded EQS values over all sampling periods. Detection/exceedances of pesticides generally coincided with their application and rainfall events, except for imidacloprid and terbuthylazine. This suggests that alternate transport pathways, such as storage and input from groundwater, may be relevant. Recent results from 2022 sampling indicate that the concentrations of imidacloprid are decreasing; however, they are still exceeding EQS values. Lastly, expansion of the analytes in 2022 led to the detection of two new pesticides, dimethomorph and diphenylamine.Our results suggest that establishing a long-term data set regarding aquatic pesticide pollution in the Western Cape will lead to a better understanding of the trends and risks of pesticide use. This improved knowledge will lead to the development of targeted mitigation measures for more sustainable agricultural practices in South Africa and beyond.

Wicked problems exceed traditional sectoral and jurisdictional boundaries and involve multiple actors as stakeholders, victims, and culprits. Wicked problems inherently feature uncertainty and knowledge gaps. Science plays a crucial role in generating evidence for solving these problems and contributing to societal transformation. However, researchers may perceive and study problems detached from practitioners’ perceptions of the world. We use the example of smallholder pesticide management in Uganda and the three types of knowledge approach, a framework borrowed from transdisciplinary research, to disentangle knowledge gaps. To identify these gaps, we integrated and co-produce knowledge in a two-day participatory workshop applying design thinking. Our results show, that a transition towards safe pesticide management depends on changes in the system, such as a revision and implementation of exiting regulation or professionalization of agro-dealers. Furthermore, this transition is only possible if interventions address target groups beyond the individual farmers (e.g. agro-dealers or district government officials). Compared to existing academic knowledge, co-produced knowledge provides a broader systemic perspective and yields more fine grained insights about potential new pathways. This investigation confirms, that practitioners’ knowledge is more fine-grained and detailed, thus exemplifying how knowledge integration is essential to avoid a gap between what researchers investigate and what practitioners need.

Global change assessments have typically ignored synthetic chemical pollution, despite the rapid increase of pharmaceuticals, pesticides and industrial chemicals in the environment. Part of the problem reflects the multifarious origins of these micropollutants, which can derive from urban and agricultural sources. Understanding how micropollutants harm ecosystems is a major scientific challenge due to asymmetries of stress across trophic levels and ecological surprises generated by multiple drivers interacting in human-impacted landscapes. We used field assays above and below municipal wastewater treatment plants (WWTPs) in 60 sampling locations across 20 Swiss streams to test how micropollutants and nutrients originating from WWTPs affect two trophic levels (microbes and detritivores) and their role in leaf litter processing. Wastewater impacts were asymmetric across trophic levels, with the detritivore contribution declining relative to microbial-driven decomposition. The strength of negative impacts were context dependent, peaking at sites with the highest upstream abundances of detritivorous invertebrates. Diffuse pollution from intensive agriculture and wastewater-born micropollutants contributed to reduced litter processing rates, including indirect effects apparently mediated through negative influences of insecticides on detritivores. Asymmetries in stress responses across trophic levels can introduce quantitative changes in consumer-resource dynamics and leaf litter processing. This means functional redundancies at different trophic levels are insufficient to compensate for biodiversity losses, causing environmental stressors such as chemical pollutants to have pervasive ecosystem-level impacts., Oikos, 2023 (2), ISSN:0030-1299, ISSN:1600-0706

Phosphorus (P) is an essential element to all living beings but also a finite resource. P-related problems center around broken P cycles from local to global scales. This paper presents outcomes from the 9th International Phosphorus Workshop (IPW9) held 2019 on how to move towards a sustainable P management. It is based on two sequential discussion rounds with all participants. Important progress was reported regarding the awareness of P as finite mineable resource, technologies to recycle P, and legislation towards a circular P economy. Yet, critical deficits were identified such as how to handle legacy P, how climate change may affect ecosystem P cycling, or working business models to up-scale existing recycling models. Workshop participants argued for more transdisciplinary networks to narrow a perceived sciencepractice/policy gap. While this gap may be smaller in reality as illustrated with a Swiss example, we formulate recommendations how to bridge this gap more effectively., Ambio, 15, ISSN:0044-7447, ISSN:1654-7209

Tracking the occurrence of a broad variety of chemicals in the aquatic environment at a high temporal resolution over extended time periods is challenging. Here, we present a transportable platform...

Effluents of wastewater treatment plants can impact microbial communities in the receiving streams. However, little is known about the role of microorganisms in wastewater as opposed to other wastewater constituents, such as nutrients and micropollutants. We aimed therefore at determining the impact of wastewater microorganisms on the microbial diversity and function of periphyton, key microbial communities in streams. We used a flow-through channel system to grow periphyton upon exposure to a mixture of stream water and unfiltered or ultra-filtered wastewater. Impacts were assessed on periphyton biomass, activities and tolerance to micropollutants, as well as on microbial diversity. Our results showed that wastewater microorganisms colonized periphyton and modified its community composition, resulting for instance in an increased abundance of Chloroflexi and a decreased abundance of diatoms and green algae. This led to shifts towards heterotrophy, as suggested by the changes in nutrient stoichiometry and the increased mineralization potential of carbon substrates. An increased tolerance towards micropollutants was only found for periphyton exposed to unfiltered wastewater but not to ultra-filtered wastewater, suggesting that wastewater microorganisms were responsible for this increased tolerance. Overall, our results highlight the need to consider the role of wastewater microorganisms when studying potential impacts of wastewater on the receiving water body., Water Research, 225, ISSN:0043-1354, ISSN:1879-2448

Exposure assessment of pesticides has substantially improved over time, with methods that now include a combination of advanced analytical techniques and fate/transport models to evaluate their spatiotemporal distribution. However, the current regulatory environmental risk assessment considers thresholds from laboratory studies completed under standardized conditions that do not reflect environmental dynamics. Using the General Unified Threshold model for Survival (GUTS) model framework, we predicted the impact of time-varying pesticide exposures on the survival of gammarids in a small agricultural stream. The LP50 values were used as an additional metric for assessing risks (defined in GUTS as a multiplication factor applied to the concentration time series to induce 50% mortality by the end of exposure). Although real-case exposures to individual pesticides were predicted to produce little to no impact on survival, the LP50 values indicate acute (LP50 ≤ 100) and/or chronic (LP50 ≤ 10) toxicities for azoxystrobin, chlorpyrifos, diazinon, and imidacloprid, while risk to propiconazole exposure was considered very low (LP50 ≫ 100). Finally, the model was extended to reflect mixture toxicity via concentration addition. It predicted risks under acute and chronic exposures to organophosphates and neonicotinoids. Given that gammarids are simultaneously exposed to multiple chemicals and other stressors throughout their lifetime, a decline in survival probabilities due to chemical stress can likely influence their overall fitness. We recognize that some assumptions require validation, but our work included a level of realism that can assist risk managers when evaluating the cumulative consequences of chemical exposure. © 2020 American Chemical Society. ISSN:0013-936X ISSN:1520-5851

Monitoring freshwater biodiversity is essential to understand the impacts of human activities and for effective management of ecosystems. Thereby, biodiversity can be assessed through direct collection of targeted organisms, through indirect evidence of their presence (e.g. signs, environmental DNA, camera trap, etc.), or through extrapolations from species distribution models (SDM). Differences in approaches used in biodiversity assessment, however, may come with individual challenges and hinder cross-study comparability. In the context of rapidly developing techniques, we compared a triad of approaches in order to understand assessment of aquatic macroinvertebrate biodiversity. Specifically, we compared the community composition and species richness of three orders of aquatic macroinvertebrates (mayflies, stoneflies, and caddisflies, hereafter EPT) obtained via eDNA metabarcoding and via traditional in situ kicknet sampling to catchment-level based predictions of a species distribution model. We used kicknet data from 24 sites in Switzerland and compared taxonomic lists to those obtained using eDNA amplified with two different primer sets. Richness detected by these methods was compared to the independent predictions made by a statistical species distribution model using landscape-level features to estimate EPT diversity. Despite the ability of eDNA to consistently detect some EPT species found by traditional sampling, we found important discrepancies in community composition between the two approaches, particularly at local scale. Overall, the more specific set of primers, namely fwhF2/EPTDr2n, was most efficient for the detection of target species and for characterizing the diversity of EPT. Moreover, we found that the species richness measured by eDNA was poorly correlated to the richness measured by kicknet sampling and that the richness estimated by eDNA and kicknet were poorly correlated with the prediction of the statistical model. Overall, however, neither eDNA nor the traditional approach had strong links to the predictive models, indicating inherent limitations in upscaling species richness estimates. Future challenges include improving the accuracy and sensitivity of each approach individually yet also acknowledge their respective limitations, in order to best meet stakeholder demands addressing the biodiversity crisis we are facing.

Microbial life in natural biofilms is dominated by prokaryotes and microscopic eukaryotes living in dense association. In stream ecosystems, microbial biofilms influence primary production, elemental cycles, food web interactions as well as water quality. Understanding how biofilm communities respond to anthropogenic impacts, such as wastewater treatment plant (WWTP) effluent, is important given the key role of biofilms in stream ecosystem function. Here, we implemented 16S and 18S rRNA gene sequencing of stream biofilms upstream (US) and downstream (DS) of WWTP effluents in four Swiss streams to test how bacterial and eukaryotic communities respond to wastewater constituents. Stream biofilm composition was strongly affected by geographic location – particularly for bacteria. However, the abundance of certain microbial community members was related to micropollutants in the wastewater – among bacteria, micropollutant-associated members were found e.g. in Alphaproteobacteria, and among eukaryotes e.g. in Bacillariophyta (algal diatoms). This study corroborates several previously characterized responses (e.g. as seen in diatoms), but also reveals previously unknown community responses – such as seen in Alphaproteobacteria. This study advances our understanding of the ecological impact of the current wastewater treatment practices and provides information about potential new marker organisms to assess ecological change in stream biofilms., Science of The Total Environment, 807 (3), ISSN:0048-9697, ISSN:1879-1026

Over the past three decades, the Vietnamese Mekong Delta has experienced a significant increase in agricultural productivity, partly achieved through increased agrochemical use. To abate negative effects on human and environmental health, several national programs were launched to enhance safer pesticide use. This study aimed to assess the patterns and relationships of official sustainable agriculture educational programs, pesticide safety knowledge, and practices of smallholder farmers in the Mekong Delta. A cross-sectional survey was conducted with 400 smallholder farmers from three communes in Thoi Lai district (Can Tho province) from March to May 2020. Twenty-four questions on pesticide safety knowledge and practices were used to identify traits using latent class analysis. Adjusted generalized linear regression was used to assess determinants of pesticide safety knowledge and estimate associations of pesticide safety knowledge with pesticide practices. 96.2% of participants have used at least one WHO class II pesticide during the past year while the use of specific personal protective equipment was limited mainly due to unavailability (37.0%) or discomfort (83.0%). High education (Odds Ratio (OR), 95% Confidence Interval; 3.84, 1.70-9.45), exposure to official educational programs (1.87, 1.13-3.12), peer-to-peer knowledge exchange (3.58, 2.18-6.00), and learning from governmental extension services (2.31, 1.14-4.98) were positively associated with increased pesticide safety knowledge. Compared to poor practices, pesticide safety knowledge was increasingly positively associated with intermediate (1.65, 1.02-2.66) and good pesticide practices (8.96, 2.58-31.12). These findings highlight the importance of school education and educational programs, access to PPE, and addressing discomforts of PPE to improve the protection of farmers from pesticide exposures. Simultaneously, pesticide market authorization processes should be reconsidered to promote the authorization of less toxic products. Further in-depth studies on the nature of pesticides used, nonuse of personal protective equipment, and effectiveness of educational programs will further define leverage points for safer pesticide use.

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 runof and pesticides to surface waters. These model results have however not yet been validated with feld 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-specifc pesticide application data. Our results show that agricultural storm drainage inlets strongly infuence surface runof 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 felds with surface runof 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 felds and surface waters, and by their potential to deliver substantial pesticide loads to surface waters., Environmental Science and Pollution Research, 29 (29), ISSN:0944-1344, ISSN:1614-7499

Biotransformation is the most important process removing manmade chemicals from the environment, yet mechanisms governing this essential ecosystem function are underexplored. To understand these mechanisms, we conducted experiments in flow-through systems, by colonizing stream biofilms under different conditions of mixing river water with treated (and ultrafiltered) wastewater. We performed biotransformation experiments with those biofilms, using a set of 75 micropollutants, and could disentangle potential mechanisms determining the biotransformation potential of stream biofilms. We showed that the increased biotransformation potential downstream of wastewater treatment plants that we observed for specific micropollutants contained in household wastewaters (downstream effect) is caused by microorganisms released with the treated effluent, rather than by the in-stream exposure to those micropollutants. Complementary data from 16S rRNA amplicon-sequencing revealed 146 amplicon sequence variants (ASVs) that followed the observed biotransformation patterns. Our results align with findings for community tolerance, and provide clear experimental evidence that microorganisms released with treated wastewater integrate into downstream biofilms and impact crucial ecosystem functions., Water Research, 217, ISSN:0043-1354, ISSN:1879-2448

Small streams in catchments with agricultural land use are at high risk of diffuse pollution by herbicides. Fast transport processes can cause concentration peaks that exceed regulatory requirements. These processes have a high spatio-temporal variability and data characterizing their occurrence is often sparse. For this reason, such systems show a stochastic behavior at the resolution we observe them (same input and initial conditions lead to different output). Realistic model representations should acknowledge this pronounced apparent intrinsic stochasticity. However, a deterministic description of the physical and chemical processes at the catchment scale is state of the art in research and practice. We explore the potential of stochastic process formulations in combination with the Bayesian learning paradigm to (a) improve the quantification of the uncertainty of conceptual catchment-scale pesticide transport models and (b) gain new mechanistic insights about the system by interpreting the temporal evolution of the stochastic processes. This is done with the help of a framework for time-varying stochastic parameters. Thereby, we find that (a) the stochastic process formulation can lead to a more realistic characterization of the uncertainty of internal states and model output compared to the deterministic one, and that (b) the temporal dynamics of parameters resulting from the inference can highlight model deficits (and inspire improvements) such as a better sustained baseflow in dry periods. We also identify two key challenges: numerical difficulties in sampling the posterior and the question of where to introduce and how to constrain the additional degrees of freedom such that they are not misused. ISSN:0043-1397 ISSN:1944-7973

Spray drift is considered a major pesticide transport pathway to surface waters. Current research and legislation usually only considers direct spray drift. However, also spray drift on roads and subsequent wash-off to surface waters was identified as a possible transport pathway. Hydraulic shortcuts (storm drainage inlets, channel drains, ditches) have been shown to connect roads to surface waters, thus increasing the risk of drift wash-off to surface waters. However, the importance of this pathway has never been assessed on larger scales. To address this knowledge gap, we studied 26 agricultural catchments with a predominance of arable cropping (n = 17) and vineyards (n = 9). In these study sites, we assessed the occurrence of shortcuts by field mapping. Afterwards, we modelled the areas of roads drained to surface waters using a high-resolution digital elevation model (0.5 m resolution) and a multiple flow algorithm. Finally, we modelled drift deposition to drained roads and surface waters using a spatially explicit, georeferenced spray drift model. Our results show that for most sites, the drift to drained roads is much larger than the direct drift to surface waters. In arable land sites, drift to roads exceeds the direct drift by a factor of 4.5 to 18, and in vineyard sites by 35 to 140. In arable land sites, drift to drained roads is rather small (0.0015% to 0.0049% of applied amount) compared to typical total pesticide losses to surface waters. However, substantial drift to drained roads in vineyard sites was found (0.063% to 0.20% of applied amount). Current literature suggests that major fractions of the drift deposited on roads can be washed off during rain events, especially for pesticides with low soil adsorption coefficients. For such pesticides and particularly in vineyards, spray drift wash-off from drained roads is therefore expected to be a major transport pathway to surface waters., Science of The Total Environment, 809, ISSN:0048-9697, ISSN:1879-1026

River networks are one of the main routes by which the public could be exposed to environmental sources of antibiotic resistance, that may be introduced e.g. via treated wastewater. In this study, we applied a comprehensive integrated analysis encompassing mass-flow concepts, chemistry, bacterial plate counts, resistance gene quantification and shotgun metagenomics to track the fate of the resistome (collective antibiotic resistance genes (ARGs) in a microbial community) of treated wastewater in two Swiss rivers at the kilometer scale. The levels of certain ARGs and the class 1 integron integrase gene (intI1) commonly associated with anthropogenic sources of ARGs decreased quickly over short distances (2-2.5 km) downstream of wastewater discharge points. Mass-flow analysis based on conservative tracers suggested this decrease was attributable mainly to dilution but ARG loadings frequently also decreased (e.g., 55.0-98.5 % for ermB and tetW) over the longest studied distances (6.8 and 13.7 km downstream). Metagenomic analysis confirmed that ARG of wastewater-origin did not persist in rivers after 5 ~ 6.8 km downstream distance. sul1 and intI1 levels and loadings were more variable and even increased sharply at 5 ~ 6.8 km downstream distance on one occasion. While input from agriculture and in-situ positive selection pressure for organisms carrying ARGs cannot be excluded, in-system growth of biomass is a more probable explanation. The potential for direct human exposure to the resistome of wastewater-origin thus appeared to typically abate rapidly in the studied rivers. However, the riverine aquatic resistome was also dynamic, as evidenced by the increase of certain gene markers downstream, without obvious sources of anthropogenic contamination. This study provides new insight into drivers of riverine resistomes and pinpoints key monitoring targets indicative of where human sources and exposures are likely to be most acute., Water Research, 197, ISSN:0043-1354, ISSN:1879-2448

Agricultural intensification has led to a large increase in drained arable land and pastures worldwide over the last two centuries. The installation of land drains not only affects the water balance of a landscape, but also influences the susceptibility to erosion, nutrient cycling, transport of plant protection products (PPPs) and greenhouse gas emissions. Due to the complex nature of environmental systems, the direction in which the substance flows are affected remains unclear, as does the strength of the effects. In this literature review, the focus is on the most relevant site-specific factors that affect the soil moisture regime, erosion, nitrogen (N) and phosphorus (P) fluxes, and PPP fluxes under undrained and drained conditions. The considered factors are the topography, soil characteristics, drainage types, rainfall characteristics and land management. Case studies from temperate climate zones represent the basis of the discussion, with a focus on continental Europe and the USA. In most cases, drainage enhances the total annual water flows from arable fields, while the effects on peak flows were variable, with the local topography playing a crucial role. There exists a certain level of consensus in the literature that subsurface drainage methods reduce the risk of erosion, while surface drainage may increase erosion at the edge of drainage channels. Nitrogen fluxes are generally enhanced following drainage. This is especially true for organic soils with large stores of organically bound N and, therefore, a high loss potential. For P losses, the trend goes in the opposite direction, with generally reduced losses seen following drainage installation. Similar findings are expected in relation to PPP losses. However, these trends may reverse on flat terrain, where subsurface drainage may reduce the on-site retention of these compounds. Overall, the literature reveals the patterns by which drainage affects hydrology, nutrient and PPP fluxes, although it is also evident that the combination of site-specific factors is influential. This hence needs to be considered as part of any risk assessment or management decisions.

Surface runoff represents a major pathway for pesticide transport from agricultural areas to surface waters. The influence of artificial structures (e.g. roads, hedges, and ditches) on surface runoff connectivity has been shown in various studies. In Switzerland, so-called hydraulic shortcuts (e.g. inlet and maintenance shafts of road or field storm drainage systems) have been shown to influence surface runoff connectivity and related pesticide transport. Their occurrence and their influence on surface runoff and pesticide connectivity have, however, not been studied systematically. To address that deficit, we randomly selected 20 study areas (average size of 3.5 km2) throughout the Swiss plateau, representing arable cropping systems. We assessed shortcut occurrence in these study areas using three mapping methods, namely field mapping, drainage plans, and high-resolution aerial images. Surface runoff connectivity in the study areas was analysed using a 2×2 m digital elevation model and a multiple-flow algorithm. Parameter uncertainty affecting this analysis was addressed by a Monte Carlo simulation. With our approach, agricultural areas were divided into areas that are either directly, indirectly (i.e. via hydraulic shortcuts), or not at all connected to surface waters. Finally, the results of this connectivity analysis were scaled up to the national level, using a regression model based on topographic descriptors, and were then compared to an existing national connectivity model. Inlet shafts of the road storm drainage system were identified as the main shortcuts. On average, we found 0.84 inlet shafts and a total of 2.0 shafts per hectare of agricultural land. In the study catchments, between 43 % and 74 % of the agricultural area is connected to surface waters via hydraulic shortcuts. On the national level, this fraction is similar and lies between 47 % and 60 %. Considering our empirical observations led to shifts in estimated fractions of connected areas compared to the previous connectivity model. The differences were most pronounced in flat areas of river valleys. These numbers suggest that transport through hydraulic shortcuts is an important pesticide flow path in a landscape where many engineered structures exist to drain excess water from fields and roads. However, this transport process is currently not considered in Swiss pesticide legislation and authorization. Therefore, current regulations may fall short in addressing the full extent of the pesticide problem. However, independent measurements of water flow and pesticide transport to quantify the contribution of shortcuts and validating the model results are lacking. Overall, the findings highlight the relevance of better understanding the connectivity between fields and receiving waters and the underlying factors and physical structures in the landscape.

Agroecological schemes are implemented worldwide in order to reduce water quality impairment from agricultural pesticide use. However, evaluating the success or failure of these schemes is challenging because other influencing factors can confound their effects. For instance, aquatic pesticide pollution has been found to vary greatly due to the interannual variability in weather conditions (e.g., the timing, intensity, and duration of precipitation events) and changes in pesticide application practices (e.g., changing pest pressure, phasing-out and replacement of specific products, development of pesticide resistance).Our research investigates the necessary conditions to detect significant trends in pesticide concentrations in the context of the Swiss National Action Plan (NAP), which aims to halve aquatic pesticide pollution risk from agricultural pesticide use within Swiss river networks by 2027.We base our analyses for temporal trends on a calibrated model for pesticide transport at the catchment scale, which we use to separate the long-term effects of the NAP from interannual variability due to weather conditions. Our results indicate that the interannual variability due to weather conditions can override the effects of even a 50% reduction in pesticide application for rain-driven input. This implies that the concentration levels themselves may be insufficient to demonstrate the effectiveness of the NAP within a reasonable time horizon of a decade. This is because the lowering of in-stream pesticide concentrations can be due to the timing and intensity of precipitation relative to the application of pesticides and not from the effectiveness of pesticide mitigation measures. Therefore, we have further explored potential methods to account for the weather effects on the pesticide concentration levels. Accounting for the weather conditions by considering the dependence of concentration levels on discharge conditions during the application period improves the statistical power to detect trends.Furthermore, we assess the potential to extrapolate the trends observed at 23 monitoring sites from different catchments (varying in size 1 km2 to > 20,000 km2) across Switzerland to the entire Swiss river network. As a first step, we analyzed substances applied to corn because this crop is widespread in the country, is easy to follow as herbicides are applied only once a year, and only a few pesticides are applied. The analysis revealed that for some of these corn herbicides, the seasonal patterns were consistent across many catchments and in agreement with the crop specific expectations. However, for other herbicides we identified regional patterns with unexpected concentration peaks in the fall. This observation requires more detailed inquiries in regional use patterns and highlights the need to account for regionalized pesticide use when extrapolating monitoring data to larger scales.

Modern agriculture routinely uses Plant Protection Products (PPPs) to guarantee food security. However, PPPs can reach surface waters where they pose a threat to susceptible non-target organisms. Understanding the contamination sources and flowpaths is of utmost importance to design optimal pollution mitigation strategies. While highest concentration peaks typically occur during rainfalls following PPPs applications, a monitoring campaign in a small Swiss agricultural stream in 2019 detected several compounds in concentrations exceeding the precautionary limit of 100 ng/l by up to 14 times during a dry period. The further exploration of the time series revealed for the first time diel fluctuations of some PPPs. Such peculiar patterns excluded the occurrence of known contamination pathways including spray drift, wind erosion and dry deposition. Despite the availability of an unprecedented high-temporal resolution dataset, we were not able to disentangle the source-flowpath combination driving the observed peculiar dynamics.Here we present the results of the follow-up 1-day field campaign aiming to close this knowledge gap. The campaign was carried out on the dry day of August 12th 2020 and we collected water samples every 6 hours from the stream at 6 different locations and from 4 outlets of active tile drains.The results revealed widespread contamination by the fungicide fluopyram; its transformation product fluopyram-benzamide followed identical dynamics but its concentration was 10 times lower than the parent compound. This result is in line with the high DT50 of fluopyram and its broad use in the catchment. The data showed that diel fluctuations were a reoccurring phenomenon; concentrations were higher in the early morning and lower in the early evening at the most downstream location. However, the fluctuating PPPs showed a concentration peak in the upstream location at midday. We were able to narrow down the contamination sources of napropamide, clothianidin, and oxadixyl; the first is a current herbicide, the second is an insecticide not reapproved since 2020, while the third is an old fungicide banned in Switzerland in 2005, which we measured at approximately 200 ng/l. Finally, the investigated tile drains delivered PPPs at lower concentrations compared to the levels measured in the surface water, with the exception of the herbicide metamitron, which was measured at nearly 20 ng/l only at the outlet of 1 tile drain.The presented research suggested that contamination sources can be localized by means of grab samples collected along the stream. However, it was not conclusive on the flowpath delivering PPPs to the stream. We hypothesize that 2 processes may explain the reported patterns: (i) irrigation at the upstream locations in the early morning; (ii) intra-daily exchanges at the interface between surface water and contaminated shallow groundwater. We will complement the study with expert knowledge by local stakeholders, satellite-derived soil moisture indices, high-resolution land use data and regulatory information to establish a methodology to optimally identify critical source areas in dry periods, where mitigation strategies should be put in place.

We report a survey of the magnetic properties of metal-organic complexes coupled to ferromagnetic and antiferromagnetic surfaces. Using element-resolved X-ray magnetic circular dichroism, we investigate the magnetism of single, double, and triple-decker phthalocyanines focusing on MnPc, TbPc2, and Tb2Pc3 deposited on Ni, Mn, and CoO thin films. Depending on the number of Pc ligands, we find that the metal ions within the molecules couple either parallel or antiparallel to a ferromagnetic substrate. Whereas single-decker complexes such as MnPc form a unique magnetic entity with ferromagnetic films, the intrinsic single molecule magnet properties of TbPc2 and Tb2Pc3 remain largely unaltered. TbPc2 deposited on perpendicularly magnetized Ni films exhibits enhanced magnetic stability compared to TbPc2 in molecular crystals, opposite to TbPc2 deposited on in-plane magnetized Ni. Depending on the competition between uniaxial anisotropy, superexchange, and Zeeman interaction, the magnetic moment of TbPc2 can be aligned parallel or antiparallel to that of the substrate by modulating the intensity of an external magnetic field. This occurs also for Tb2Pc3, but the substrate-induced exchange coupling in triple-decker molecules is found to be short-ranged, that is, limited to the Tb ion closer to the ferromagnetic surface. Finally, we discuss the conditions required to establish exchange bias between molecules and antiferromagnetic substrates. We show that TbPc2 deposited on antiferromagnetic Mn thin films exhibits both exchange bias and enhanced coercivity when field cooled parallel to the out-of-plane easy axis. However, exchange bias does not extend to all molecules on the surface. On oxide antiferromagnets such as CoO we find no evidence of exchange bias for either TbPc2 or MnPc., We received financial support from the European Research Council (StG 203239 NOMAD), the Ministerio de Ciencia e Innovación (MAT2010-15659), the Agència de Gestió d'Ajuts Universitaris i de Recerca (2009 SGR 695), and the Swiss Competence Centre for Materials Science and Technology (CCMX).

Tracking the occurrence of a plethora of chemicals in the aquatic environment at high temporal resolution over extended periods is a huge challenge. Here, we present a transportable high-resolution mass spectrometry platform including a fully automated workflow for advanced data processing. It measured several thousand concentration data points at 20-min intervals over several weeks, providing unprecedented insights into pollution dynamics, e.g. acute pesticide toxicity peaks in a small creek, intra-day variation of illicit drugs in raw wastewater and identifying contamination clusters of unknowns. This enabling technology has potential for researching and managing chemicals in natural and technical environments beyond current possibilities, e.g. real-time control in process engineering and sewer operation (water management and environmental toxicology), industrial surveillance (law enforcement) and wastewater-based epidemiology (public health).

Aquatic pesticide pollution from both agricultural and urban pest control is a concern in many parts of the world. Making an accurate assessment of pesticide exposure is the starting point to protecting aquatic ecosystems. This in turn requires the design of an effective monitoring program. Monitoring is also essential to evaluate the efficacy of mitigation measures aimed to curb pesticide pollution. However, empirical evidence for their efficacy can be confounded by additional influencing factors, most prominently variable weather conditions. This review summarizes the experiences gained from long-term (>5 years) pesticide monitoring studies for detecting trends and provides recommendations for their improvement. We reviewed articles published in the scientific literature, with a few complements from selected grey literature, for a total of 20 studies which fulfill our search criteria. Overall, temporal trends of pesticide use and hydrological conditions were the two most common factors influencing aquatic pesticide pollution. Eighteen studies demonstrated observable effects to surface water concentrations from changes in pesticide application rates (e.g., use restriction) and sixteen studies from interannual variability in hydrological conditions during the application period. Accounting for seasonal- and streamflow-related variability in trend analysis is important because the two factors can obscure trends caused by changes in pesticide use or management practices. Other mitigation measures (e.g., buffer strips) were only detectable in four studies where concentrations or loads were reduced by > 45%. Collecting additional agricultural (e.g., pesticide use, mitigation measures) and environmental (e.g., precipitation, stream flow) data, as well as establishing a baseline before the implementation of mitigation measures have been consistently reported as prerequisites to interpret water quality trends from long-term monitoring studies, but have rarely been implemented in the past., Graphical abstract Image 1, Highlights • Aquatic pesticide pollution trends are mainly driven by pesticide use and hydrology. • Seasonal- and streamflow-related variability may obscure trends due to mitigation. • Baseline monitoring is required to interpret long-term water quality trends. • Agricultural and hydrological data collection should be included in monitoring.