We first selected metals of concern by comparing measurement data for as many metals as possible in rivers across Japan with toxicity test results performed under the same conditions. As the measurement dataset, we used results of dissolved metal concentrations surveyed at 450 sampling sites across 45 major rivers (i.e., 10 sites per river) in Japan during . For the toxicity test data, we used the IC10 (10% Inhibition Concentration) values for 50 metals, determined by chronic toxicity tests with Ceriodaphnia dubia . The toxicity tests were consistently conducted using filtered and sterilized tap water with a water hardness of approximately 70-80 mg/L. Although water quality parameters important for considering metal bioavailability (e.g., pH, water hardness, and dissolved organic matter; can vary among sampling sites and differ between the toxicity tests and sampling sites, the results of are considered ideal for the preliminary screening of metals of particular concern.