Temporal scales of pesticide exposure and risks in German small streams Philipp Vormeier a,b , Verena C. Schreiner c , Liana Liebmann a,d , Moritz Link c , Ralf B. Schäfer c , Anke Schneeweiss c , Oliver Weisner a , Matthias Liess a,b, ⁎ a UFZ, Helmholtz Centre for Environmental Research, Department of System-Ecotoxicology, Permoserstrasse 15, 04318 Leipzig, Germany b RWTH Aachen University, Institute of Ecology & Computational Life Science, Templergraben 55, 52056 Aachen, Germany c RPTU Kaiserslautern-Landau, Institute for Environmental Sciences, 76829 Landau in der Pfalz, Germany d Goethe University Frankfurt, Institute of Ecology, Diversity and Evolution, Faculty of Biological Sciences, Department of Evolutionary Ecology & Environmental Toxicology (E3T), 60438 Frankfurt am Main, Germany HIGHLIGHTS GRAPHICAL ABSTRACT • Pesticides monitored with grab and event- driven sampling over several months • Highest event-related exposure of pesti- cides during May/June in Germany • Peak toxicity for invertebrates ten times higher than baseline • Peak toxicity for algae and aquatic plants six times higher than baseline • Pesticide exposure to be reduced by a fac- tor of 37 to meet National Action Plan goal ABSTRACT ARTICLE INFO Editor: Jay Gan Keywords: Agricultural pesticide pollution Pesticide application Surface water monitoring Event-driven sampling (EDS) Regulatory acceptable concentration (RAC) Water Framework Directive Following agricultural application, pesticides can enter streams through runoff during rain events. However, little information is available on the temporal dynamics of pesticide toxicity during the main application period. We inves- tigated pesticide application and large scale in-stream monitoring data from 101 agricultural catchments obtained from a Germany-wide monitoring from April to July in 2018 and 2019. We analysed temporal patterns of pesticide application, in-stream toxicity and exceedances of regulatory acceptable concentrations (RAC) for over 70 pesticides. On a monthly scale from April to July, toxicity to invertebrates and algae/aquatic plants (algae) obtained with event- driven samples (EDS) was highest in May/June. The peak of toxicity towards invertebrates and algae coincided with the peaks of insecticide and herbicide application. Future monitoring, i.e. related to the Water Framework Directive, could be limited to time periods of highest pesticide applications on a seasonal scale. On a daily scale, toxicity to inver- tebrates from EDS exceeded those of grab samples collected within one day after rainfall by a factor of 3.7. Within two to three days, toxicity in grab samples declined compared to EDS by a factor of ten for invertebrates, and a factor of 1.6 for algae. Thus, toxicity to invertebrates declined rapidly within 1 day after a rainfall event, whereas toxicity to algae remained elevated for up to 4 days. For six pesticides, RAC exceedances could only be detected in EDS. The exceedances of RACs coincided with the peaks in pesticide application. Based on EDS, we estimated that pesticide ex- posure would need a 37-fold reduction of all analysed pesticides, to meet the German environmental target to keep RAC exceedances below 1 % of EDS. Overall, our study shows a high temporal variability of exposure on a monthly but also daily scale to individual pesticides that can be linked to their period of application and related rain events. Science of the Total Environment 871 (2023) 162105 ⁎ Corresponding author at: UFZ, Helmholtz Centre for Environmental Research, Department of System-Ecotoxicology, Permoserstrasse 15, 04318 Leipzig, Germany. E-mail address: matthias.liess@ufz.de (M. Liess). http://dx.doi.org/10.1016/j.scitotenv.2023.162105 Received 10 November 2022; Received in revised form 3 February 2023; Accepted 4 February 2023 Available online 8 February 2023 0048-9697/© 2023 Published by Elsevier B.V. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv