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A. Kudo and R.R. Turner
the biosphere. This beneficial conversion of soluble mercury from the
industrial discharges was another form of natural decontamination or
immobilization.
4. Large-scale restoration of aquatic systems can be accomplished with sufficient
resources and great attention to minimizing adverse impacts of the restoration
activity itself. It seems likely that the Japanese learned not only what worked
well in the Minamata Bay project but also what failed to work or worked
poorly. Clearly, the project met the goal of removing all sediment in the bay
above 25 mg/kg, and seems also to have reduced the fish content of mercury
below the provisional regulatory standard of 0.4 mg/kg. Those contemplating
similar projects may also wonder how well some of the ameliorative strategies
worked, e.g., use of boundary nets and sonic fish-repelling device, use of
cutterless dredges and continuous turbidity monitoring. Were these simply
cosmetic strategies or were they effective (e.g., Nakayama et al. 1992) in
accomplishing their intended purpose? In addition, the authors of this review
chapter wondered how the restoration project was affected by the 200-year
rainfall that occurred in the midst of the dredging activity.
The accessible information on Minamata Bay prompts many questions which
may never be answered, or which can only be answered by scientists who have
been intimately involved with the site. Some questions have already been posed
above for future authors on this subject to contemplate answering. Key
additional questions follow:
1. What were the fate and effects of mercury released into Minamata Bay prior to
1950? Mercury began to be used at the Chisso plant in the early 1930S with an
early period of apparently substantial releases centered in the early 1940S (Fig.
2). While these releases were routed directly into the Yatsushiro Sea and not
Minamata Bay, it is surprising that no human victims who obtained food from
the affected area of the Yatsushiro Sea during that early period were ever
identified. Paradoxically, when plant discharges were temporarily rerouted to
the Yatsushiro Sea in 1958 as a mitigative strategy, new human victims were
identified and the discharge was returned to Minamata Bay.
2. Why was so little methylmercury ever found in bay sediments? Was this entirely
an artifact of the inferior analytical protocols available at the time or was some
biochemical decontamination process (e.g., Barkay et al. 1992) operating to
minimize the net production and accumulation of this form of mercury during
the period of highest releases of inorganic mercury from the plant?
3. Were direct discharges of methylmercury from the Chisso plant the chief
source of methylmercury in seafood until the processes which used mercury
were shut down? In spite of the research focused on this question in the 1960s
and later, controversy persists and handicaps attempts to synthesize generic
conceptual models ofroot causes of environmental disasters (e.g., Ellis 1989).
Acknowledgements. The authors are indebted to Dr. Junko Nakanishi of the Institute of
Environmental Science and Technology, Yokohama National University, for her assistance in
obtaining recent fish data from the Kumamoto Prefecture and for constructive comments on the
manuscript. George Southworth and Steve Lindberg of Oak Ridge National Laboratory in Oak Ridge,
TN USA also provided constructive comments on the manuscript. The author {A.K.} thanks Dr.
A. Kudo and R.R. Turner
the biosphere. This beneficial conversion of soluble mercury from the
industrial discharges was another form of natural decontamination or
immobilization.
4. Large-scale restoration of aquatic systems can be accomplished with sufficient
resources and great attention to minimizing adverse impacts of the restoration
activity itself. It seems likely that the Japanese learned not only what worked
well in the Minamata Bay project but also what failed to work or worked
poorly. Clearly, the project met the goal of removing all sediment in the bay
above 25 mg/kg, and seems also to have reduced the fish content of mercury
below the provisional regulatory standard of 0.4 mg/kg. Those contemplating
similar projects may also wonder how well some of the ameliorative strategies
worked, e.g., use of boundary nets and sonic fish-repelling device, use of
cutterless dredges and continuous turbidity monitoring. Were these simply
cosmetic strategies or were they effective (e.g., Nakayama et al. 1992) in
accomplishing their intended purpose? In addition, the authors of this review
chapter wondered how the restoration project was affected by the 200-year
rainfall that occurred in the midst of the dredging activity.
The accessible information on Minamata Bay prompts many questions which
may never be answered, or which can only be answered by scientists who have
been intimately involved with the site. Some questions have already been posed
above for future authors on this subject to contemplate answering. Key
additional questions follow:
1. What were the fate and effects of mercury released into Minamata Bay prior to
1950? Mercury began to be used at the Chisso plant in the early 1930S with an
early period of apparently substantial releases centered in the early 1940S (Fig.
2). While these releases were routed directly into the Yatsushiro Sea and not
Minamata Bay, it is surprising that no human victims who obtained food from
the affected area of the Yatsushiro Sea during that early period were ever
identified. Paradoxically, when plant discharges were temporarily rerouted to
the Yatsushiro Sea in 1958 as a mitigative strategy, new human victims were
identified and the discharge was returned to Minamata Bay.
2. Why was so little methylmercury ever found in bay sediments? Was this entirely
an artifact of the inferior analytical protocols available at the time or was some
biochemical decontamination process (e.g., Barkay et al. 1992) operating to
minimize the net production and accumulation of this form of mercury during
the period of highest releases of inorganic mercury from the plant?
3. Were direct discharges of methylmercury from the Chisso plant the chief
source of methylmercury in seafood until the processes which used mercury
were shut down? In spite of the research focused on this question in the 1960s
and later, controversy persists and handicaps attempts to synthesize generic
conceptual models ofroot causes of environmental disasters (e.g., Ellis 1989).
Acknowledgements. The authors are indebted to Dr. Junko Nakanishi of the Institute of
Environmental Science and Technology, Yokohama National University, for her assistance in
obtaining recent fish data from the Kumamoto Prefecture and for constructive comments on the
manuscript. George Southworth and Steve Lindberg of Oak Ridge National Laboratory in Oak Ridge,
TN USA also provided constructive comments on the manuscript. The author {A.K.} thanks Dr.