2) Mechanism behind the outbreak

2.ITAI-ITAI DISEASE

It must k reiterated that the itai-itai disease occurred in a limited area 30 km downstream from Kamioka Mines. The underlying mechanism was as follows.

(1)The heavy metals discharged from the Kamioka Mines into the Jinzu River were deposited in the river bed, and accumulated especially at the bottom of Jinzu River Dams No. 1,2 and 3 downstream of the mines. A significant correlation was found between the cadmium concentration in river system water and that in the river bed. The cadmium in the river bed was dissolved in river water and polluted the agricultural water used in Osawano-cho and Fucyu-machi where the disease broke out (Fig.2-1).
(2)The cadmium dissolved in the agricultural water was absorbed by the soil in the rice patties, thereby contaminating it.
(3)Of the heavy metals that contaminated the soil, cadmium was absorbed by the rice some 3 times more than zinc, lead and copper, and concentrated inside unpolished rice. From surveys carried out from 1971 through 1976, the cadmium concentration in contaminated soil along the Jinzu River was found to be a maximum 4.85ppm(average 1.12ppm) compared to the 0.34ppm of uncontaminated soil, The maximum concentration of cadmium in unpolished rice produced in this region was 4.23ppm, while the average was 0.99ppm.
(4)The cadmium was introduced into the human body by eating rice of a high cadmium concentration. The cadmium impaired absorption in the urinary track of the kidney, The more the cells became exposed to cadmium, the more phosphate and calcium (bone forming constituents found in the blood) were discharged from the body with the urine, which lead to osteomalacia (Fig.2-2).

Fig. 2-1 Correlation between cadmium concentration in river water and the river bed of the Jinzu River water system

This is why the disease stood out more in women with fragile bones than in men with larger bones.

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