Home > Outline of Japan's Industrial Pollution Abatement > Approaches to Water Pollution Control (Case Study-2) Minamata City, Kumamoto Prefecture > (2) Effect of Methylmercury Compound on Human Health
Main content starts here.
Update:April 1, 2010
(2) Effect of Methylmercury Compound on Human Health
2.Mercury Poisoning and Control Responses
Methylmercury compound present in seawater is rapidly incorporated in the body of aquatic life such as fish, shellfish and planktons at a high density and is gradually accumulated as it is passed from one to another in the food chain, The total mercury concentration in the body of fish and shellfish had frequently reached to a considerable level especially at the early stages: 24ppm for a black porgy, 58ppm for a saury-pike, and 85ppm for a mussel.
In the greater part of Minamata Bay, a significant amount of mercury was present in the form of mercury sulfide in the bottom sludge. The mercury concentration nearby the effluent outlet in Hyakken has reached 2010ppm and gradually decreased as it goes outwards; where near the entrance of the bay the concentration is 12.2ppm. In the fishing village where Minamata Disease frequently occurred, people have habitually eaten less rice to be more dependent upon seafood in those days since the land was not fit for rice production, While the average fish consumption in Japan is currently 90-100g per day, they used to eat fish as much as 200-400g or even more than 1kg.
The onset of Minamata Disease does not start until methylmercury accumulation exceeds a certain level in the tissue, Methylmercury is absorbed 100% into the system through the intestines with oral intake, and 1% of the total accumulation is excreted everyday.
If it is consumed at a regular amount per week, methylmercury rapidly accumulates in the body at first. Then, the accumulation gradually declines in speed and finally becomes saturated in about a years time and would not make any further increase even if consumption continues. The accumulation limit of methylmercury is one hundred times the daily average consumption in this case (See Figure 3-6).
Previous cases of methylmercury poisoning and animal testing using monkeys have suggested accumulation under 0.5mg per kilogram of body weight does not develop toxic symptoms.
