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Researchers have hypothesized that there is a second agent. Many of the victims showed high levels of barium, a heavy metal in the soil that seeps into mushrooms.

“There is a lot of work left to do,” Fontaine said. “We really need additional lab investigations.”

Problems with poisonous mushrooms are common throughout Asia, said Diderik De Vleeschauwer, a spokesman for the U.N. Food and Agriculture Organization regional office in Thailand.

“Normally we expect people to have knowledge of what they can and can’t eat. One would think there is indigenous knowledge available about what they can forage,” he said. “But these are accidents that can happen.”