Despite many efforts for improving the monitoring of an increasing number of chemicals (and their potential by-products), for a more comprehensive and exhaustive estimate of aquatic organism exposure, there is still some questions in relation with both temporal and spatial representativeness of the spot sampling, and also with chemical targeted analysis. As highlighted by Ort et al. (2010), discrete and low frequency sampling can be problematic due to the heterogeneity of aquatic environments and the dynamic of pollution levels. An alternative to spot sampling lies in the use of passive samplers. In this context, passive sampling techniques play a key role since they allow the integration of various events, occurring in natural aquatic environments (i.e. floods and peaks of contamination) while being able to decrease drastically the limits of quantification. However, some limitations are already well known for passive samplers, especially the accuracy of the measurement in relation with environmental conditions. Parameters such as temperature and flow velocity have substantial influence on the reliability of the measured concentrations; this is mainly due to the difference between controlled laboratory conditions, stable and used for the calibration, and those encountered in the field, inevitably more variable. There are various approaches to overcome these issues such as field calibrations, the use of Performance Reference Compounds (PRCs), etc. Besides these metrological aspects, there are also some scientific questions about the representativeness of the fraction of analytes isolated by the devices, especially in terms of bioavailability. At a more operational level, it must be checked if these fractions are in compliance with Environmental Quality Standards (EQS) established by the Water Framework Directive (WFD). Finally, the use of passive sampler extracts in combination with bioassays opens many opportunities to study mixture effects. However, such approaches can be qualified as "black box" since they require further developments to characterize more precisely the compounds responsible of the observed effects, and their possible interactions within the mixture.