Mercury and Minamata Bay
Q
What was mercury used for in the Minamata factory of Shin-Nippon Chisso Hiryo K.K.?
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A
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It was used as a substance for accelerating reactions (a catalyst) by which to produce acetaldehyde.
Mercury was used as a catalyst in the production of acetaldehyde.
Using mercury in the manufacturing process can boost acetaldehyde yields.
While a catalyst itself generally does not change in a chemical reaction, a reaction other than the targeted one (i.e., a side reaction) is assumed to have occurred in the Minamata factory of Shin-Nippon Chisso Hiryo K.K., resulting in methylmercury being produced, and the company let wastewater from the factory, which as a consequence contained methylmercury, flow out into the sea, untreated.
Q
What levels of mercury concentration do the fish now caught in Minamata Bay show?
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A
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Mercury concentration in fish has now dropped to safe levels.
In the period roughly between 1955 and 1975, very high levels of mercury, as much as several tens of ppm (ppm is a weight measure that stands for "parts per million"), used to be found in the fish from Minamata Bay; today, however, fish with mercury content in excess of the provisional criteria set by the national government (0.4 ppm for mercury and 0.3 ppm for methylmercury in total concentration) are no longer found to be present, according to the monitoring done by the Kumamoto Prefectural Government.
Therefore, the Governor of Kumamoto made a safety declaration in July 1997 and fishing was resumed.
Q
How much mercury had accumulated at the bottom of Minamata Bay before it was dredged and reclaimed?
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A
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It is said that nearly 150 tons of mercury had accumulated.
The total amount of mercury that was used at the Minamata factory of Shin-Nippon Chisso Hiryo K.K. is estimated to be between 380 and 455 tons, of which more than half is believed to have flowed away from the bay or have been released into the atmosphere. For reference, most of the mercury contained in the accumulation of sludge, which was present when the dredging and landfill operation began, is believed to have been an inert form of inorganic mercury (mercury sulfide).
Q
How big was the area of Minamata Bay that was reclaimed?
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A
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A tract of 58 hectares was reclaimed.
The Kumamoto Prefectural Government spent 14 years and 48.5 billion yen (of which 30.6 billion yen was covered by Chisso Corporation) to dredge up 1.51 million cubic meters of sludge in Minamata Bay, which was polluted with mercury-containing sludge, and to reclaim the Bay.
As a result, 58 hectares of reclaimed land was created.
This land, as wide as eight times the area of the Fukuoka Dome baseball stadium, now houses "Eco Park Minamata," which has sports fields and other facilities on the premises.