Update:April 1, 2010

5) Water purification in the Jinzu River water system

4,COUNTERMEASURES AT POLLUTION-GENERATING SOURCE

Much metabolic activity occurs between the river bed and river water. And, dispite the countermeasures taken at the pollution-generation source, the river was contaminated with cadmium which has been deposited in the river bed over a long period of time. Judging from the relationship between the cadmium concentration found in river water and that found in the river bed of the Jinzu River water system, it was suggested that the cadmium concentration in the river bed and that at the foot of dams could be lowered to the point that concentration in river water would no longer be harmful, if proper countermeasures could be taken at the pollution-generating source. The fact is that cadmium concentration in the river bed at Jinzu River Dam No,1 was between 1.6 and 1.8 ppb in 1968. By 1975, the average concentration was 2.33 ppm, and eventually 1.39 ppm and 0.7 ppm by 1976 and 1992 respectively, showing the river to have been purified by the countermeasures taken at the pollution-generating source. Futhermore, the cadmium concentration in the Gyugakubi water supply that brought agricultural water to the contaminated area was also improved at the same time, to the upstream level of 0,1 ppb (Table 4-1,Fig.4-4 and 4-5).