NATURAL AND ARTIFICIAL MERCURY DECONTAMINATION - OTTAWA RIVER AND MINAMATA BAY (YATSUSHIRO SEA)

Every day, man creates new processes and materials whose properties are not fully known and are sometimes toxic to him and the environment. One of the worst cases was in Minamata Bay, Japan where a fatal accident occurred due to mercury pollution. The accident was unique in many aspects thus forcing the establishment of a new decontamination process for polluted areas. Two mercury polluted sites, the Ottawa River, Canada and Minamata Bay (Yatsushiro Sea), Japan, have been investigated to establish a fundamental approach for decontamination with special emphasis on natural and artificial processes and their problems. Artificial decontamination on bottom sediments has primarily cleaned-up Minamata Bay and the near-by Yatsushiro Sea considerably, an acceleration of the natural processes by 31.5 years. The surrounding area will be fully cleaned-up by natural forces, following the artificial work, by 2011 AD (or 20 years from now). This means that the natural decontamination has a half-life of 9.5 years in Yatsushiro Sea. For the Ottawa River, only natural processes were applied to clean-up the river system. It took 5 years for physical components to be decontaminated (a half-life of 1.20 years) while it took a longer period for biological components. This last finding was also true for Minamata Bay. This delay may be due to the longer life span of the biota and their efficient processes of bioaccumulation from diluted surrounding water. Based on the findings herein, a combination of both artificial and natural decontamination methods is recommended in consideration with the given environmental conditions.