The in situ caging of gammarids (Gammarus fossarum), developed by INRAE, has been used by French water agencies since 2018 to monitor chemical contamination. In 2022-2023, a study was carried out to optimise and extend the list of substances of interest to be analysed in caged gammarids. The methodology used was based on a bibliographic research and led to the construction of three datasets: (i) List of substances: This dataset contains identification details (name, CAS number, French SANDRE code and family) and monitoring information of the 1,751 candidates substances selected for the study; (ii) Substance characteristics: This dataset includes physico-chemical parameters (octanol/water partition coefficient, organic carbon/water partition coefficient, half-life of the substance through biodegradation, half-life of biotransformation in fish and bioconcentration factor) and Predicted No Effect Concentration (PNEC) values of the 1,751 candidate substances; (iii) Quantification frequencies (QF): This dataset contains 9,467 QF data for 1,633 candidate substances. These data come from French water agencies’ gammarus monitoring over the period 2020-2022 and from 132 studies on biota (crustaceans, molluscs, other invertebrates and fish) and sediment in fresh, transitional and marine waters over the period 2013-2022. For each QF data, the following information is provided: name of the substance, characteristics of the study (geographical scale, location, water type, number of sites, temporal scale, number of samples and matrix analysed), limit of quantification, method of analysis and study reference. The three data files are accompanied by 'dictionary' files describing the contents and sources of each field in the datasets.