Mercury Contamination of Minamata Bay
155
mercury content (Hosokawa 1993). Fish monitoring has also been continued after
all dredging and reclamation work was completed (e.g., see Fig. 5).
5
Lessons Learned and Implications for Other Sites
It is to be hoped that the most important lesson from Minamata Bay, concerning
the great human costs of unregulated releases of a toxicant into the environment,
has been learned by the global community. However, the current extraction of
gold by garimpos in South America using the primitive amalgamation
technology (Lacerda and Salomons 1991), and some recent examples of
imprudent discharges of mercury in less environmentally conscious countries
as cited by D'Itri (1991), may give some doubt to this hope. There are a number of
other lessons, including some still known almost exclusively to the Japanese
people who planned, executed and/or observed the restoration of the bay. Some
of the latter lessons and other experiences for this site will hopefully be shared in
the future via more English and Japanese language publications. The authors of
this chapter gleaned the following lessons from the available literature:
1. Cleaning up contaminated aquatic systems can be extremely expensive and
take a long time. Hosokawa (1993) placed the total cost for the Minamata Bay
project at 48500 million yen (500000000 US dollars). More than a decade
was required to plan and execute the restoration.
2. Direct and early involvement of all stakeholders in such restoration projects,
including especially the public, is a critical requirement if proposed
engineering remedies are to be accepted, and those implementing the
remedies trusted. Well before the present "Superfund" process in the United
States was formulated to include such stakeholders in selecting remedies, the
Japanese government was facing a distrusting and litigative citizenry from the
very community they sought to assist.
3. The benefits of natural decontamination should not be discounted or
undervalued. Kudo (1992) placed a considerable monetary value on the
dilution and burial of Hg-contaminated sediment in the Yatsushiro Sea that
attended the occurrence of a major natural hydrologic event (200-year
rainfall). However, burial of all sediments with mercury levels greater than
25 mg/kg was unlikely ever to occur in Minamata Bay without intervention
because much of the most highly contaminated sediment was exposed at low
tide and thus subjected to continuous resuspension and transport into deeper
water. It can only be speculated at this point that the use of a criterion for
sediment dredging based on water depth might have reduced cost and been as
effective as the use of the provisional standard to guide dredging. It seems
likely that the Japanese considered such an option, perhaps enhanced by
artificial burial under a sand layer, and simply rejected it in favor of a more
secure remedy. As proven by a number of studies, the mercury in bay
sediments was bound largely in insoluble sulfides and effectively isolated from
155
mercury content (Hosokawa 1993). Fish monitoring has also been continued after
all dredging and reclamation work was completed (e.g., see Fig. 5).
5
Lessons Learned and Implications for Other Sites
It is to be hoped that the most important lesson from Minamata Bay, concerning
the great human costs of unregulated releases of a toxicant into the environment,
has been learned by the global community. However, the current extraction of
gold by garimpos in South America using the primitive amalgamation
technology (Lacerda and Salomons 1991), and some recent examples of
imprudent discharges of mercury in less environmentally conscious countries
as cited by D'Itri (1991), may give some doubt to this hope. There are a number of
other lessons, including some still known almost exclusively to the Japanese
people who planned, executed and/or observed the restoration of the bay. Some
of the latter lessons and other experiences for this site will hopefully be shared in
the future via more English and Japanese language publications. The authors of
this chapter gleaned the following lessons from the available literature:
1. Cleaning up contaminated aquatic systems can be extremely expensive and
take a long time. Hosokawa (1993) placed the total cost for the Minamata Bay
project at 48500 million yen (500000000 US dollars). More than a decade
was required to plan and execute the restoration.
2. Direct and early involvement of all stakeholders in such restoration projects,
including especially the public, is a critical requirement if proposed
engineering remedies are to be accepted, and those implementing the
remedies trusted. Well before the present "Superfund" process in the United
States was formulated to include such stakeholders in selecting remedies, the
Japanese government was facing a distrusting and litigative citizenry from the
very community they sought to assist.
3. The benefits of natural decontamination should not be discounted or
undervalued. Kudo (1992) placed a considerable monetary value on the
dilution and burial of Hg-contaminated sediment in the Yatsushiro Sea that
attended the occurrence of a major natural hydrologic event (200-year
rainfall). However, burial of all sediments with mercury levels greater than
25 mg/kg was unlikely ever to occur in Minamata Bay without intervention
because much of the most highly contaminated sediment was exposed at low
tide and thus subjected to continuous resuspension and transport into deeper
water. It can only be speculated at this point that the use of a criterion for
sediment dredging based on water depth might have reduced cost and been as
effective as the use of the provisional standard to guide dredging. It seems
likely that the Japanese considered such an option, perhaps enhanced by
artificial burial under a sand layer, and simply rejected it in favor of a more
secure remedy. As proven by a number of studies, the mercury in bay
sediments was bound largely in insoluble sulfides and effectively isolated from