Measurement of fluoride ion in the river-water flowing into Lake Biwa

To study the effect of biotite granite on the concentration of fluoride ion in the river-water around it, the concentration of the ion in several river-water samples flowing into Lake Biwa, in Shiga Prefecture, Japan, was measured by using ion chromatography. Several biotite granite plutons around Lake Biwa were contributed to relatively high concentration of fluoride ion in river-water around the plutons. By this study and previously reported result on the river-water flowing in the Rokko Granite, in Hyogo Prefecture, Japan, it was supposed that the degree of the distribution depends on the age of each pluton and the extent of its weathering.