2005 Volume 54 Issue 12 Pages 577-585
In the national and international guidelines for drinking water quality, it is recommended that arsenic (As) and selenium (Se) concentrations in drinking water do not exceed 0.01 mg L-1 (10 μg L-1) . Since As and Se concentrations are thought to be lower than 1/10 of the recommended values in>90% of surface river waters, it is difficult to describe nationwide As and Se concentration levels in Japan. The recently developed octapole reaction system for inductively coupled plasma mass spectrometry (ORS-ICP-MS) could achieve low detection limits for As and Se compared to atomic absorption spectrometry and ICP optical emission spectrometry. In this study, direct measurement of trace levels of As and Se in river water for 25 major rivers, 10 samplings per river, were carried out using ORS-ICP-MS. In order to determine As and Se, He gas and H2 gas, respectively, were introduced into the ORS as reaction gas.
The concentrations of As and Se were determined in more than 95% of the samples, and the cumulative probability distributions of these elements were on log-normal lines. Their respective geometric mean concentrations were calculated as 0.68μg L-1 and 0.062μg L-1, and the values were lower than the recommended ones. The concentration ranges of these elements in ten samples collected from the upper stream to the river mouth were usually narrow. Possibly, the observed concentrations originated from weathering of bedrock.