Minamata Disease and the Mercury Pollution of the Globe

Minamata Disease was discovered for the first time in the world at Minamata City, Kumamoto Prefecture, Japan, in 1956 (Minamata Disease Research Group; 1968, Harada M; 1995), and for the next time at Niigata City, Niigata Prefecture, Japan, in 1965 (Tsubaki T & Irukayama K; 1977). The both cases were attributed to the methyl mercury that was generated in the process for producing acetaldehyde using mercury as catalyst. Methyl mercury had accumulated in fishes and shellfishes and those who ate them had been poisoned with it. These cases of the poisoning with organic mercury poisoning were the first to take place in the world through the food chain transfer of its environmental pollution. The cases of organic mercury poisoning that had been known prior to Minamata Disease occurred as the result of the direct poisoning of those who were engaged in organic-mercury handling occupations or those who took it in accidentally (Hunter D et al; 1940, Lundgren KD et al; 1949). The Shiranui Sea that caused the first Minamata Disease i.e. that in Minamata has an area of 1,200 square kilometers and once enjoyed abundance of fishes, shellfishes and so forth and then a population of approximately 200,000 were engaged in fishery and other relative jobs. The residents living there were accustomed to eat fishes and shellfishes as main dishes throughout years. Some of them ate 500 grams of them a day. On the other hand, the residents living along the Agano River, Niigata, that caused the second Minamata disease also ate the fresh water fishes caught in great quantities there (Harada M; 1972, 1994). According to Prof. Tokuomi, sensory disturbance and constriction of the visual field were observed as an example of the typical symptoms of Minamata Disease among 100% of its patients, coordination disturbance among 93.5%, dysarthria among 88.2%, hearing disturbance among 85.3% and tremor among 75.8%. Besides, the patients’ serious symptoms were evidenced by the fact that 82.4% of them showed walking disturbance (Tokuomi H; 1960). They are typical symptoms of methyl mercury poisoning but, in fact, there are patients with various combinations of symptoms and with various degrees of symptoms that range from mild to serious cases. It can be said that the population of patients with non-typical symptoms is greater than that with typical symptoms. Particularly, glove and stocking type and perioral sensory disturbances were characteristically observed with Minamata Disease (Harada M; 1995). The Minamata Disease with such unique sensory disturbance alone has however been found out so far. The pattern of such sensory disturbance is similar to that of peripheral nervous disturbance. According to the study conducted lately, there are great possibilities that they may belong to the category of central nervous disturbance (Ninomiya T et al; 1995). Some chronic period or mild cases of coordination disturbance are difficult to identify. If this is the case, electroophthalmography (EOG) and optokinetic nystagmus pattern (OKP) can conveniently be used for obtaining referential data (Harada M; 1995). Particularly, in new-developing case of Minamata Disease, the possibilities of the occurrence of mild and non-typical symptoms are greater than those of typical serious symptoms. Table 1, Figure 1 shows the frequency of clinical symptoms and the pattern of sensory disturbance of those suspected of suffering from chronic Minamata Minamata Disease and the Mercury Pollution of the Globe http://www.einap.org/envdis/Minamata.html