TOKYO: For Yasuko Tanaka, it started when the village cats turned into demons. One year, they were sleepy pets; the next, they were hyperactive monsters - screeching, scratching and jumping around as if possessed.

That was when she drew the connection between Japan’s worst case of industrial pollution in nearby Minamata and the splitting headaches, tunnel vision and shaking hands that she and several other villagers had been suffering.

On Monday more than 30 years later, researchers presented evidence that the mercury poisoning of Minamata bay in the 50s and 60s lasted longer, spread further and affected tens of thousands more people than previously believed.

The study by doctors at Kumamoto University could cost the Japanese government tens of millions of dollars as thousands of claimants seek recognition as having Minamata Disease - the nerve disorder caused by eating seafood from the polluted bay or nearby waters.

Symptoms of spasms, blurred vision and hearing loss were first recognized in the 50s when the ailment was called ‘itaiitabyo’ (ouch ouch disease), but it was not until 1968 that the government blamed the nearby Chisso chemical corporation for pumping mercury waste into the bay.

More than 900 victims died in agony. Many babies in the area were born with gnarled limbs. Thousands of victims were ostracized, first out of a mistaken fear that the disease might be contagious, and later, because their legal suits drew unwanted attention to the invisible pollution in this picturesque region.

In 1996, the government offered sufferers a modest settlement of about $2,200 in damages from Chisso and $180 a month in medical expenses from public funds. But since then it has only certified 2,264 victims, 1,435 of whom are already dead. Another 17,128 have applied for recognition.

According to the Kumamoto University research team, which is presenting its findings at a conference on mercury poisoning that started in Minamata on Monday, at least another 20,000 people are likely to be eligible.

The researchers found that harmful levels of pollution spread beyond Minamata Bay and lasted until 1970, 10 years longer than government estimates.

They also discovered that mercury damaged the central nervous system and impaired sight, hearing, smell, taste and touch when present at the level of just 10 parts per million in hair and umbilical cords. This is five times lower than the level recognised as harmful by the government.

The government, which has been accused of colluding with Chisso Corporation to cover up the environmental disaster, has never attempted to find out how many people were affected by Minamata disease. Instead, it has asked victims to come forward, which many are reluctant to do because they fear discrimination.—Dawn/The Guardian News Service.