In rivers, risk assessment requires taking into account both the complexity of contaminations (multiple substances at low concentrations), and the increasing demand for ecologically realistic biological endpoints used in toxicity testing. These issues can be tackled by coupling toxicity assessment using complex communities, such as periphyton, and complex contaminants like passive samplers extracts (PSE). Here we propose to review some recent progresses in ecotoxicology allowed by the joint use of PSE from POCIS (Polar Organic Chemical Integrative Samplers) and river periphyton. More specifically, we will present diverse experimental approaches, aiming at: -characterizing the 'toxic potential' of waters and applying the pollution community induced tolerance (PICT) approach to pesticide mixtures, -increasing the environmental realism in microcosm experiments by performing chronic low dose exposure to mixtures from PSE. We were able to detect PICT in periphyton collected in rivers showing a gradient of increasing pesticide concentrations or at sites with different contamination profiles using toxicity tests with PSE from the field. Then, we improved mixture toxicity assessment by implementing chronic exposure experiments with PSE as a complex contaminant, at low doses. The environmentally relevant concentrations tested drove community changes, in their structure (biomass, composition) as well as in their functions (enzymatic activities).