Restoration of the environment
Because methylmercury remained a considerable concentration in bottom sediment of the related water areas even after the discharge of the methylmercury compound was stopped, in order to remove this bottom sediment, from 1974 to 1990, Kumamoto Prefecture carried out the project for dealing with about 1,500,000 cubic meters of bottom sediment of Minamata Bay that contained mercury more than the removal standard (25ppm of total mercury) by means of dredging and landfill, and for making 58ha. landfill, at a total cost 48 billion yen (of this total, the responsible company bore 30.5 billion yen). In 1976, Niigata Prefecture carried out dredging river bottom sediment that contained mercury more than the removal standard around the drainage outlets of Showa Denko plant by the burden of the responsible company.