As seen in other cases, the first initiative taken was the research activities by an academic
institution. Also national and local governments conducted fact-finding survey (however they
could not recognize the strong connection between the mercury pollution and Chisso’s
operation).
Under the pressure by social opinion, Chisso reluctantly introduced improved effluent
processing system by times. In 1968 it stopped producing acetaldehyde, whose production
process caused mercury discharge.
The amount of mercury discharged and sedimented in Minamata bay was estimated to be 70 -
150 tons. Since it was feared that mercury would continue to endanger marine environment
as well as human health, the Bottom Sludge Programme was launched in 1976. The bottom
sludge in Minamata bay seabed was scooped and fed into reclamation sited using a pump
specially designed to prevent turbidity in the dredging site. After this process, the
reclamation site was covered with non-contaminated mountain soil carefully.