## 4 Conclusions  
This study successfully established and validated an analytical method utilizing liquid chromatography coupled with high-resolution mass spectrometry for the quantification of 18 pesticides in water bodies adjacent to agricultural and aquaculture regions in Greece and Albania. The efficient method showed method quantification limits ranging from 1.7 ng L\({}^{-1}\) to 90 ng L\({}^{-1}\); recovery rates ranged from 61 to 96% in the river water for medium spiking level, while for seawater, they were slightly higher (60-111%) due to increased ionic strength. In all cases, the repeatability and intra-laboratory reproducibility was less than 15%, while linearity was excellent in all cases. Matrix effect study in seawater revealed strong signal suppression (\(<\)\(-\)20%) only for dimethoate. Relatively low concentrations were measured in the real samples. The most frequently detected compounds at all sampling points were fenpyroximate (58%), myclobutanil (50%), and \(S\)-metolachlor (33%).  
By addressing a significant gap in existing literature, this study contributes novel data regarding the occurrence and concentration of these agrochemicals, thereby providing critical insights into the impact of agrochemical pollution on vulnerable aquatic ecosystems. Although the application of this method is exemplified through this specific case study, its broader applicability makes it a valuable model for pollutant monitoring in other regions that face comparable environmental challenges. These findings underscore the necessity for ongoing surveillance and assessment of pesticide residues to safeguard ecosystem health and to inform regulatory frameworks.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app142210329/s1](https://www.mdpi.com/article/10.3390/app142210329/s1)]([https://www.mdpi.com/article/10.3390/app142210329/s1](https://www.mdpi.com/article/10.3390/app142210329/s1)), Table S1. LC-ESI-HRMS data for the selected pesticides; Table S2. Extraction protocols tested for the optimization of the extraction method; Table S3. Recovery values (R%) for pesticide compounds after applying the three extraction protocols; Table S4. Physicochemical characteristics of the real water samples; Table S5. Pesticle compounds concentrations (ng L\({}^{-1}\)) detected in water including measurement uncertainty; Figure S1. (%) Percentage of compounds with recovery 70-120% in river and sea water; Figure S2. Position of the selected sampling points.  
Conceptualization, T.A.; methodology, V.B.; validation, C.N.; formal analysis, V.B. and D.G.; investigation, C.N.; resources, T.A.; data curation, C.N.; writing--original draft preparation, D.G.; writing--review and editing, C.N. and V.B.; visualization, C.N. and D.G.; supervision, V.B.; funding acquisition, T.A. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The data are contained within the article and the Supplementary Information file.  
The authors would like to thank the Unit of Environmental, Organic and Biochemical high-resolution analysis-Orbitrap-LC-MS of the University of Ioannina for providing access to the facilities.  
The authors declare no conflicts of interest.