Biologist treks across Southwestern China to answer the 'killer mushroom' question

His findings, published online in Applied and Environmental Biology, shattered a myth started by a 2010 article in the journal Science, claiming the Trogia venenata mushroom contained high concentrations of the metal barium, causing high blood pressure, cardiac arrests and sudden deaths in southwestern China over the past 30 years. The deaths mainly occurred in small villages, some of which saw nearly one-third of their population perish quickly.

"Although there was no published evidence supporting the theory that barium in the T. venenata mushroom was the leading culprit of what was called Sudden Unexplained Death (SUD), it was picked up as a fact by almost all of the major news media," said Xu, associate professor of biology and a member of the Michael G. DeGroote Institute for Infectious Disease Research at McMaster University. "These reports caused significant concern among the public about potentially high levels of barium in wild edible mushrooms in southwest China."

Every summer since 2009, Xu and his team have travelled across the Yunnan province, collecting fruiting bodies of T. venenata as well as other mushrooms from villages severely impacted by these deaths.

Researchers tested the mushrooms and found the barium concentration was so low it would require a person weighing 150 pounds to consume at least 35 kg of dried T. venenata for it to be lethal. In fact, the barium concentration in these mushrooms is the same as in common foods, such as fresh meat and poultry.

The majority of SUDs, since 1978 in Yunnan Province, occurred in apparently healthy people, mostly young females, during the rainy season from June to August.

While previous studies suggested certain mushrooms could accumulate heavy metals, there was no information about high levels of barium in wild edible mushrooms. The speculation and subsequent media reports generated significant concern among health officials, the general public and all levels of government and severely impacted the economy by affecting trade of many wild, edible Chinese mushrooms, such as Matsutake, truffles, morels and Chanterelles.

Although Xu's results show these mushrooms contain low levels of barium, he says barium can't be ruled out as a contributor to the deaths, given that high levels of barium were found in the blood, urine and hair samples of some of the victims. Yet, his study does suggest that barium in mushrooms was unlikely the leading cause. "Though there are a couple of leads," he said, "further investigation is needed to discover what the true cause was for these mysterious deaths."