What Happened? In 1907 the Chisso Corporation constructed a Chemical factory in the Japanese town of Minamata 1932 factory begins to manufacture acetaldehyde a by-product of which is mercury Mercury dumped into Minamata Bay and formed organic methyl mercury chloride which entered the food chain
What Happened Methyl mercury chloride saturated the sediment of Minamata Bay from here it entered shelf fish and other local fish Due to its high rate of Bio-magnification and extensive “ half life” there is a significant build up of Methyl mercury between trophic levels in the food chain The primary food source of the local residents came from fish in the bay causing a large build up of mercury levels build up: Over a period of 30 years between 70-150 tonnes of mercury were dumped into Minamata Bay Fish & Shellfish Humans Gray Mullet – 10.6 Kidney - 3.1-144.0 Crab - 35.7 Liver - 0.3-70.5
What Happened In the early 1950s symptoms of a strange disease began to be noticed, first in cats then in humans. Symptoms included : - Loss of motor control Loss of motor control Partial Paralysis Partial Paralysis Convulsions Convulsions Slurred speech Slurred speech Resulting in death Resulting in death In 1956 the cause of these symptoms was identified as heavy metal poisoning by medical researchers The Chisso Corporation deny responsibility but in 1959 install a “Cyclator” designed to control emissions from the factory but people continue to develop symptoms In 1968 the Chisso Corporation changed their production methods to nolonger include mercury
Minamata Bay Clean Up The clean up operation started in 1977 when the Minamata Bay Pollution Prevention Project was started. The Clean up operation was split up into two sections The deep, heavily contaminated areaThe deep, heavily contaminated area The shallow, less contaminated areaThe shallow, less contaminated area
Deep area of 580,000m 2 was completely enclosed with metal sheeting Shallow area of 1,510,000m 2 was dredged with a cutterless pump ship and poured into a reclaimed land area Covered in synthetic sheet and loam and then local mountain soil piled on to confine it.
Minamata Bay Clean Up Fears of secondary contamination concerns Strict surveillance installed around bay In 1987 the dredging was completed which reduced levels of Mercury to 0.06 -12ppm (average 4.65ppm) March 1990, Minamata Bay was declared safe after 48 million Yen had been spent on clean up
Cleaning Up Mercury Dredging into landfill Pump-and-Treat Place wells in the ground to extract out contaminated ground water Place wells in the ground to extract out contaminated ground water Leaching and extraction Used in conjuncture with Pump-and-Treat Used in conjuncture with Pump-and-Treat Form compounds HgS o or HgCl - Form compounds HgS o or HgCl - Thermal treatment Heating to 300 o for 1 hour can remove 99.5% of Mercury Heating to 300 o for 1 hour can remove 99.5% of Mercury Mercury can be recovered Mercury can be recovered High temperatures can be harmful to soil High temperatures can be harmful to soil
Cleaning Up Mercury Sediment Capping Electro-Kinetic Separation Mercury migrates towards electrodes placed in soil Mercury migrates towards electrodes placed in soil Phytoremediation Genetically Engineering using merA and merB Genetically Engineering using merA and merB Arabidopsis plant Arabidopsis plant Converts mercury to harmless vapour Converts mercury to harmless vapour 10 – 20 years away 10 – 20 years away
Conclusion Tragedy of Minamata is that it was a preventable problem Early action by the Chisso Corporation in treatment of waste effluent before entering sea. Or control of fishing and fish consumption By ignoring the problem it meant a lengthy and expensive geotechnical operation to undo damage The Minamata Bay Pollution Prevention Project did not get rid of the mercury, only contained. More effective and sustainable methods could have been employed
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