The pesticide monitoring in the Orgeval catchment (France) was initiated in 2008 in order to understand the long-term fate of pesticides and to validate the transfer model developed within the framework of PIREN-Seine. Thus, 12 years of contamination data are now available for a list of molecules that is still evolving according to new uses. At the same time, past phytosanitary practices were determined in the basin. The assessments of current uses are extracted from the BNV-D for the Seine-et-Marne department. A focus is made on the emblematic substances for which the evolution trend can be directly related to the seasonal dynamics of phytosanitary uses, such as chlortoluron and metolachlor. Atrazine, which was banned in 2003, and terbuthylazine, which was re-used in 2018, are interesting to compare because these triazines have similar properties but are not homologated at the same time. The metabolite / active ingredient ratios are used to show the dynamics of contamination in the river and in the groundwater, and to highlight groundwater-river exchanges. However, when studying these data, some inconsistencies appear, suggesting a new origin for atrazine and simazine. Key points ✓ The use of commercial terbuthylazine-based specialities brings atrazine and simazine residues into the catchment. ✓ The metabolite/active ingredient ratios make it possible to trace groundwater-river exchanges. ✓ Weed control practices in maize pose a high risk of river contamination.