出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/01/25 07:47:49」(JST)
Itai-itai disease (イタイイタイ病, itai-itai byō?, lit. "it hurts-it hurts disease") was the name given to the mass cadmium poisoning of Toyama Prefecture, Japan, starting around 1912. The term "itai-itai disease" was coined by locals[1] for the severe pains (Japanese: 痛い itai) victims felt in the spine and joints. Cadmium poisoning can also cause softening of the bones and kidney failure. The cadmium was released into rivers by mining companies in the mountains, which were successfully sued for the damage. Itai-itai disease is known as one of the Four Big Pollution Diseases of Japan.[2]
Itai-itai disease was caused by cadmium poisoning due to mining in Toyama Prefecture. The earliest records of mining for gold in the area date back to 1710. Regular mining for silver started in 1589, and soon thereafter, mining for lead, copper, and zinc began. Increased demand for raw materials during the Russo-Japanese War and World War I, as well as new mining technologies from Europe, increased the output of the mines, putting the Kamioka Mines in Toyama among the world's top mines. Production increased even more before World War II. Starting in 1910 and continuing through 1945, cadmium was released in significant quantities by mining operations, and the disease first appeared around 1912.[1] Prior to World War II, the mining, controlled by the Mitsui Mining & Smelting Co., Ltd., increased to satisfy the wartime demand. This subsequently increased the pollution of the Jinzū River and its tributaries. The river was used mainly for irrigation of rice fields, but also for drinking water, washing, fishing, and other uses by downstream populations.[1]
Due to the cadmium poisoning, the fish in the river started to die, and the rice irrigated with river water did not grow well.[citation needed] The cadmium and other heavy metals accumulated at the bottom of the river and in the water of the river. This water was then used to irrigate the rice fields. The rice absorbed heavy metals, especially the cadmium. The cadmium accumulated in the people eating contaminated rice.
When the population complained to Mitsui Mining & Smelting Co. about this pollution, the company built a basin to store the mining waste water before leading it into the river. This proved ineffective, and many had already been sickened. The causes of the poisoning were not well understood and, up to 1946, it was thought to be simply a regional disease or a type of bacterial infection.[1]
Medical tests started in the 1940s and 1950s, searching for the cause of the disease. Initially, it was expected to be lead poisoning due to the lead mining upstream. Only in 1955 did Dr. Hagino and his colleagues suspect cadmium as the cause of the disease.[1] Toyama Prefecture also started an investigation in 1961, determining that the Mitsui Mining and Smelting's Kamioka Mining Station caused the cadmium pollution and that the worst-affected areas were 30 km downstream of the mine. In 1968, the Ministry of Health and Welfare issued a statement about the symptoms of itai-itai disease caused by the cadmium poisoning.[3]
The reduction of the levels of cadmium in the water supply reduced the number of new disease victims; no new victim has been recorded since 1946. While the victims with the worst symptoms came from Toyama prefecture, the government found victims in five other prefectures.
The mines are still in operation and cadmium pollution levels remain high, although improved nutrition and medical care has reduced the occurrence of itai-itai disease.[4]
One of the main effects of cadmium poisoning is weak and brittle bones. Spinal and leg pain is common, and a waddling gait often develops due to bone deformities caused by the cadmium. The pain eventually becomes debilitating, with fractures becoming more common as the bone weakens. Other complications include coughing, anemia, and kidney failure, leading to death.[4]
A marked prevalence in older, postmenopausal women has been observed. The cause of this phenomenon is not fully understood, and is currently under investigation. Current research has pointed to general malnourishment, as well as poor calcium metabolism relating to the women's age.[4]
Recent animal studies have shown that cadmium poisoning alone is not enough to elicit all of the symptoms of itai-itai disease.[4] These studies are pointing to damage of the mitochondria of kidney cells by cadmium as a key factor of the disease.
Twenty-nine plaintiffs, consisting of 9 victims and 20 family members of victims, sued the Mitsui Mining and Smelting Co. in 1968 in the Toyama Prefectural court. In June 1971, the court found the Mitsui Mining and Smelting Co. guilty. Subsequently, the company appealed to the Nagoya District Court in Kanazawa, but the appeal was rejected in August 1972. The Mitsui Mining and Smelting Co. agreed to pay for the medical care of the victims, finance the monitoring of the water quality performed by the residents, and pay reparations to the victims of the disease.[1]
People who consider themselves victims of itai-itai disease have to contact the Japanese Ministry of Health, Labor, and Welfare to have their claims assessed. Many victims were not satisfied with government actions and demanded a change in the official procedures. This caused the government to review the criteria for recognizing a victim legally; the government also reassessed the treatment of the disease.
A person is considered to have itai-itai disease if he or she lived in the contaminated areas, has kidney dysfunctions and softening of the bones, but not related heart problems. One hundred and eighty-four victims have been legally recognized since 1967, of whom 54 were recognized in the period from 1980 to 2000. An additional 388 people have been identified as potential victims, those who had not been officially examined yet.[1] Fifteen victims were still alive as of 1993[update].
The cadmium pollution had contaminated many agricultural areas. Heavy metal pollution affected many areas in Japan, and as a result the Prevention of Soil Contamination in Agricultural Land Law of 1970 was enacted. It ordered planting to be stopped so that restoration of the soil could be enacted to areas with 1ppm of cadmium or more contamination in the soil. Surveying in Toyama Prefecture began in 1971, and by 1977, 1500 hectacres along the Jinzū River were designated for soil restoration. These farmers were compensated for lost crops and for lost production in past years by the Mitsui Mining and Smelting, Toyama Prefecture, and the national government. As of 1992[update], only 400 hectares remained contaminated.[1]
In 1992, the average annual health expense compensation was ¥743 million. Agricultural damage was compensated with ¥1.75 billion per year, or a total of annually ¥2.518 billion. Another ¥620 million were invested annually to reduce further pollution of the river.[1]
On 17 March 2012, officials concluded the cleanup project of the cadmium-polluted areas in the Jinzū River basin. Eight-hundred and sixty-three hectares of topsoil had been replaced since the cleanup began in 1979 at a total cost of ¥40.7 billion. The project had been financed by the Japanese national government, Mitsui Mining, and the Gifu and Toyama prefectural governments.[5]
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