Minamata disease, a debilitating illness of the nervous system caused by mercury poisoning, has reared its ugly head once more-not in Japan this time, but in fishing communities of the remote Amazon rainforest. The mercury, in a toxic organic form known as methyl mercury, is present in fish in the region. But there is confusion about whether it comes from gold mining or leaches from soils following deforestation.
This is the first time Minamata disease has been diagnosed outside the Japanese town of the same name. In the 1950s, some 1500 people from Minamata suffered terrible damage to their nervous systems, which resulted in uncontrollable shaking and muscle wasting, and produced appalling deformities in their children. They had eaten fish from a bay polluted by mercury from a metals plant.
Last week, Maszumi Harada of Kumamoto University and Junko Nakanishi from the Yokohama National University claimed that the same symptoms are showing up in the Amazon. Harada, an expert on the disease who works near Minamata, examined 50 people from 10 villages around San Luis do Tapaj's who had high levels of methyl mercury in their bodies. He found three with nervous symptoms peculiar to Minamata disease, including fits of trembling.
In the past, most cases of mercury poisoning in the Amazon have been among the million gold miners in Brazil, who use mercury to purify gold, and their families. Many had directly inhaled mercury fumes. The Minamata cases, however, involve methyl mercury, and the sufferers live hundreds of kilometres from the nearest mine.
Methyl mercury attacks the cerebellum, which coordinates voluntary movements, and destroys the personality, says Hiroshi Takahasi, an epidemiologist with the Japanese Ministry of Health and Welfare. "Survivors in Minamata are still suffering," he says. "It should not happen again."
But Harada says he expects to find many more victims in the Amazon. "The problem is much more widespread," agrees Donna Mergler of the University of Quebec at Montreal. She and her colleagues have also found neurological symptoms in the Amazonians, such as involuntary shaking, sensitivity to bright light, partial blindness and loss of muscle strength.
Harada and Mergler both say the victims consumed methyl mercury in fish. And they agree that the source is inorganic mercury converted into the more toxic methylated form by bacteria living in oxygen-starved conditions in river sediments-just as bacteria converted discharges in Minamata Bay.
But they disagree on the origin of the mercury. Harada, who has yet to publish his findings, believes the source is mercury used by gold miners. Miners release about 250 tonnes of mercury into the Amazon region each year, most ending up in rivers.
Mergler, however, thinks deforestation is the problem. "The widespread mercury contamination in fish is from leaching of natural mercury in soils and is released following slash-and-burn activities," she says. Her team estimates that only 3 per cent of the mercury comes from gold mining.
Takahasi warns that cleaning up the mercury could be near impossible: "The Japanese government spent millions of dollars to remove the polluted sediment from Minamata Bay. Can you imagine how difficult it would be in Brazil?"
Mergler's team offers a partial solution. It found that only fish that eat other fish contain dangerous levels of mercury, because concentrations are magnified with each step up the food chain. Herbivorous fish have lower levels, and mercury levels in fishing communities go down when they eat these. "We want to encourage villagers to rely more on these fish," she says.
Author: Fred Pearce
New Scientist magazine issue 6 Feb 99
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