The Lez is a coastal river located in the department of Herault, under the influence of a Mediterranean climate. The watershed of the Lez covers a total area of 536 km2. The source of the Lez is the main resurgence of a karst drainage system. Lez receives in summer a low-flow support provided by the Canal Bas Languedoc (BRL) coming from Rhône River. On the studied area, the Lirou is one of the major tributary characterized by a low anthropic pressure. For this study, the main goal is to assess the vulnerability of water resources to agronomics activities (pesticides impact) using passive samplers (POCIS and Chemcatcher). The objective is to demonstrate the applicability of passive samplers both as quantitative tool for monitoring the quality of drinking water resource as well as screening tool for the diagnosis of water bodies potentially affected by pesticides. During 20 days exposure, the POCIS and Chemcatcher were deployed on four sites: P1 at the Lez source, P2 located at 8 km downstream from the spring, P3 corresponding to the outlet water Canal BRL, P4 located on the Lez at 300 m from the outlet Canal BRL. Estimated concentrations by the passive samplers were calculated using sampling rates determined at laboratory scale together with in-situ sampling rates (in-situ Rs). Integrate concentration from POCIS and Chemcatcher have been compared to data obtained through the analysis of water samples. For the 4 investigated sites, the average concentrations of pesticides measured do not exceed 30 ng/L. Furthermore, the results show the impact of exposure conditions (temperature and velocity of water) on POCIS and Chemcatcher efficiency. Whether for screening or for quantitative approach, passive samplers (POCIS and Chemcatcher) have shown their efficiency on identifying pesticides compared to conventional sampling method, and have allowed to obtain an accurate and representative picture of the actual level of water contamination by pesticides.
