In 1909 Mitsui Corporation installed Potter's preferential flotation system to cope with
its ore-dressing process. As means to treat the poor zinc ore were developed, the amount of ore
increased, and the preferential system resulted in finer particles of tailing. The tailing slurry was
thrown into the Jinzu River and was then precipitated in the rice paddies of the Toyama district.
At the same time, the first cases of people suffering from Itai-Itai disease were reported.