Understanding the occurrence and fate of current-use pesticides (CUPs) in coastal and open marine waters is essential for conducting exposure and risk assessments to ensure the protection of marine ecosystems from chemical pollution. While CUPs have been frequently studied in freshwater systems, knowledge of their behavior in marine environments remains fragmentary. This study investigated 28 CUPs across 50 sites along a transect from the Baltic outflow to pristine Arctic waters using ships of opportunity with installed FerryBox system. Overall, 14 CUPs were detected at least at one site at concentrations ranging from sub-ng/L to ng/L. CUP concentrations were higher in the Baltic outflow and decreased along the transect. Atrazine, simazine, tebuconazole, and propiconazole were detected in > 40 % of samples, including remote open sea regions, suggesting their potential for long-range marine transport. This Baltic Sea was identified as a major source of CUPs to connected marine systems. Additional CUPs were detected in the Baltic outflow, encompassing diuron, isoproturon, metazachlor, metolachlor, pyrazon, terbuthylazine, and chlortoluron. Ecotoxicological assessment indicated a moderate risk posed by metolachlor to algae. The use of the described infrastructure holds great promise for advancing our understanding of the occurrence and fate of CUPs in marine environments.

NIVA Norwegian Institute for Water Research Økernveien 94 0579 Oslo Norway

RECETOX Research Centre for Toxic Compounds in the Environment Masaryk University Kamenice 753 5 625 00 Brno Czech Republic

RECETOX Research Centre for Toxic Compounds in the Environment Masaryk University Kamenice 753 5 625 00 Brno Czech Republic; NIVA Norwegian Institute for Water Research Økernveien 94 0579 Oslo Norway

RECETOX Research Centre for Toxic Compounds in the Environment Masaryk University Kamenice 753 5 625 00 Brno Czech Republic; University of Natural Resources and Life Sciences Vienna Department of Forest and Soil Sciences Institute of Soil Research Peter Jordan Straße 82 1190 Vienna Austria

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