TAIJI, Wakayama Pref. — Researchers have found extremely high methyl mercury concentrations in the hair of some residents of Taiji, Wakayama Prefecture, where people have a tradition of eating whale and dolphin, but none have developed any related illnesses.

The researchers said Sunday that of 1,137 residents tested, the methyl mercury density in 43 exceeded the level recognized by the World Health Organization as capable of causing neurological damage. The tests covered roughly a third of the town’s residents.

Experts were at a loss to explain why none of Taiji’s residents have mercury-related health problems.

The National Institute for Minamata Disease, which conducted the testing at the request of the Taiji Municipal Government, “will continue to research” why no symptoms were observed, institute Director General Koji Okamoto said.

The town of some 3,500 people took hair from 1,137 residents who underwent regular health checkups and agreed to submit the samples for tests from last June to August and this February. It was the first time the town had tested hair samples.

The average amount of methyl mercury found in the hair of Taiji residents was 11.0 parts per million for men and 6.63 ppm for women, compared with an average of 2.47 ppm for men and 1.64 ppm for women in tests conducted in 14 other locations in Japan, according to the institute, which is based in Minamata, Kumamoto Prefecture.

Of those with extremely high mercury levels, 182 underwent further tests to check their vision and other senses and the ability to exercise. None was found to have symptoms typically observed in mercury poisoning patients, the institute said in material distributed at the news conference.

“At this point, (eating whale and dolphin) has had no impact on residents’ health, but we will continue to ask the National Institute for Minamata Disease to research further,” Taiji Mayor Kazutaka Sangen said in a press release.

Okamoto couldn’t explain why some of the residents had high mercury levels but no symptoms.

“It may be because Taiji people accumulate methyl mercury by eating natural food, while other cases (in Minamata, Niigata and Iraq) were caused by chemical substances containing methyl mercury that were leaked into nature by human error,” he said. “That is my speculation without scientific evidence. We will continue to research that.”

The WHO recognizes 50 ppm as the minimum level at which mercury poisoning can occur, as was the case with the Minamata disease outbreak in Niigata in the 1960s.

The Taiji tests found that 43 people had levels in excess of 50 ppm, with the highest having 139 ppm.

Okamoto hinted that the 50 ppm number may not be reliable because 250 ppm was the lowest level at which people in Iraq developed symptoms in the 1970s, meaning the minimum level probably varies.

He said he will try to submit a scientific paper on the Taiji results in hopes of getting international scientists to weigh in.

The institute didn’t give the 43 residents any dietary advice, Okamoto said, noting that, “It’s important that they decide what they should eat.”

Methyl mercury exists naturally in the sea but is toxic if condensed. It has been found to accumulate in dolphins, whales and large fish near the top of food chain.

Taiji, featured in the Oscar-winning film “The Cove,” which details its annual dolphin slaughters, conducted the hair tests amid international criticism from animal rights activists that the town is allegedly poisoning its residents by allowing them to eat the marine mammals.

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