EPA water quality criteria because water quality standards for aquatic life are available in Japan for only total Zn (30 μg/L). Any concentration below the quantification or detection limit was operationally replaced with half the corresponding limit for operational purposes (see Table for specific values). We then selected 194 sites where the sum of TUs ≥ 1 as metal-contaminated sites (Figure ). In this study, a sum of TUs >1 was used as the conservative criterion for selection, not to accurately assess risk, but rather to select sites where ecological risks could be of concern. Together with a line of empirical evidence that the exceedance of the sum of TUs beyond 1 does not necessarily lead to population or community-level effects on aquatic organisms, such as fish and macroinvertebrates , it is important to note that such impacts may not always be observed at the selected metal-contaminated sites.