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 (composed of microalgae, bacteria, fungi, protozoa, etc.), 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, at identifying the compounds responsible for toxicity in the mixture (effect-directed analyses –EDA), and at 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. From a pesticide mixture that proved to be toxic, we performed successive fractionation steps to identify, through an EDA approach, the substance(s) responsible for toxicity. In the mixture we used, however, no individual fraction was found to explain the impacts of the cocktails, whereas combinations of fractions did. This highlights the need to consider the “mixture issue” in environmental risk assessment. One way to improve mixture toxicity assessment is to implement chronic exposure experiments with PSE. We successfully performed artificial channel experiments using of 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). Altogether, these encouraging results open wide perspectives for a more realistic risk assessment, from both biological and chemical points of view.