No abstract

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.

<p>Plant protection products (PPPs) are used routinely in modern agriculture and they can reach surface waters from treated fields or equipment handling areas. Assessing water contamination for a broad set of PPPs is challenging due to the episodic occurrence of concentration peaks. The traditional workflow of taking samples in the field, transferring to the lab, possible storing, and sample preparation and analysis strongly limits sampling frequency and duration of sampling campaign, in particular for labile PPPs.</p><p>Here we present for the first time results from the on-site platform MS<sup>2</sup>field quantifying hundreds of PPPs with 20 minutes temporal resolution continuously yielding concentrations in real-time. MS<sup>2</sup>field is a fully automated mobile unit to be deployed in the field, where it collects water samples and performs target and non-target high-resolution mass spectrometry with limits of quantification in the low range of ng/l. For the presented application, MS<sup>2</sup>field was deployed in a small agricultural catchments in 2019 (May – July, 41 days of observation) in the Swiss Plateau close to Lake Constance. This application resulted in 3000 samples, which can be analyzed for up to 600 compounds yielding 1.8 million measured concentrations.</p><p>The high temporal resolution allows first for a proper quantification of peak concentration. Overall, the time-series encompassed nine rain events, during which extreme concentration peaks occurred. The fungicides fluopyram achieved 30 µg/l and cyprodinil exceeded 5 µg/l, while the herbicide napropamide reached 5 µg/l. Also during dry periods, high concentrations were observed: fungicides peaked to 2 µg/l, herbicides to 0.9 µg/l, and insecticides to 0.1 µg/l.</p><p>Yet, the temporal resolution makes it possible to investigate in great detail the PPPs dynamics during rainfall events of different characteristics yielding insights about potential PPPs sources and pathways. To that end, we compared the measured concentrations of tens of selected PPPs with meteorological observations and water level data available at 10 minutes resolution for the different events.</p><p>The high-time resolution relationships between measured concentrations and water levels of these compounds revealed interesting patterns. For the same PPP, the patterns generally differed widely across different rainfall events. For some groups of different PPPs we observed very similar patterns during the same event. However, this similarity did not always hold across different events. This suggests that the patterns were controlled by event-specific combinations of PPPs availability and hydrological response in different parts of the catchment.</p><p>The measured concentrations-water level relationships were often hysteretic in nature. Supply limitation and transport limitation might control hysteresis. Supply limitation may refer to the lack of PPP residues in the environment; otherwise, strong adsorption can decrease PPPs availability. Transport limitation may predominate during hydrological conditions not suitable for a substantial mobilization and movement of PPPs. Comparison of different hysteresis patterns shall provide insights into the interplay between site- and event-specific mobilization of PPPs and their chemical properties leading to the understanding of how to minimize water contamination in the future.</p>

Plant Protection Products (PPPs) pose a threat to surface water quality worldwide. While small streams compose the majority of the stream lengths and are crucial for biodiversity, their exposure patterns to PPPs and transformation products (TPs) are largely understudied in dry periods. This knowledge gap can lead to ineffective monitoring strategies for addressing water quality issues. Here, we focus on two extended dry periods the in-depth analysis of a unique continuous high-frequency (20 min) concentrations dataset for 60 PPPs and TPs. The dataset refers to the monitoring of a small tile-drained agricultural stream over 41 days from May to July in 2019. The overall 2560 concentration data per compound obtained with the on-site mass spectrometer MS2Field platform revealed: (i) surprisingly high maximum concentrations (hundreds to thousands ng/l for some compounds) over extended periods of time, (ii) novel diel fluctuations of concentrations in the order of hundreds of ng/l for some PPPs and TPs, (iii) unexpected high concentrations (up to 220 ng/l) of a legacy compound (the fungicide oxadixyl withdrawn from the Swiss market in 2005). We hypothesized the cause of our findings was rooted in high PPPs levels in the shallow groundwater. To investigate this, we complemented our measurements with the long-term Swiss national monitoring program integrating samples over 14 days at the same location. The continuous long-term measurements found a few PPPs all year-round, thus indicating the presence of persistent contamination sources in the catchment. Next, we collected spatially distributed grab samples in tile drain outlets and stream water on a dry summer day in 2020. The dry-day campaign not only confirmed our hypothesis given the measured high concentrations of PPPs and TPs in tile drain outlets but also highlighted large spatial variability in measured concentrations along the stream. Hereafter, we highlight the questions that different monitoring schemes can answer in dry conditions. This information was relevant to observe for the first time, and thus foresee, the dynamic patterns of PPPs and TPs in the aquatic ecosystem in dry summer conditions, with the latter generally becoming more frequent due to climate change.

<p>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.</p><p>For our analysis, we selected a small catchment (2.8km<sup>2</sup>) 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.</p><p>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.</p><p>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.</p><p>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.</p><p>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.</p>