Are Mushrooms Rich in Heavy Metals? Analysis of a WeChat Moments Rumor
Rumor: Mushrooms should not be eaten in large quantities. You can eat at most 200g per month. Although mushrooms are good, they have a very important characteristic: an extremely strong ability to accumulate heavy metals, up to more than 100 times. Mushrooms will accumulate almost all heavy metals, such as lead, mercury, and nickel. However, our bodies have no mechanism to excrete heavy metals. Over time, these heavy metals will accumulate in the renal tubules, and in severe cases may even cause necrosis of the renal tubules.
Truth: Mushrooms are our common name for edible macrofungi, including many varieties such as button mushrooms, shiitake mushrooms, enoki mushrooms, shaggy mane mushrooms, and so on. Compared with green plants, mushrooms do have a stronger ability to accumulate heavy metals. Some foreign researchers have conducted surveys on the heavy metal content of wild mushrooms. In recent years, many research institutions in China have also investigated cultivated edible mushrooms. For example, in 2007 a study investigated the heavy metal content of edible fungi in the Beibei area of Chongqing. This area is both an important industrial base and a production base for edible fungi. The researchers analyzed heavy metals such as lead, cadmium, mercury, and arsenic in oyster mushrooms, shaggy mane mushrooms, enoki mushrooms, Hypsizygus marmoreus, and straw mushrooms produced in the area, and found that straw mushrooms had the strongest heavy metal accumulation ability. All straw mushroom samples were found to exceed the standard for mercury, and one third of straw mushroom samples exceeded the standard for lead; 14% of shaggy mane mushroom samples exceeded the standard for mercury; 4% of shiitake mushroom samples exceeded the standard for lead; 29% of Hypsizygus marmoreus samples exceeded the standards for both mercury and lead.[1]
The phenomenon of excessive heavy metals in mushroom foods is not limited to Chongqing. Golden mushrooms from the Qinghai-Tibet Plateau have likewise been found to exceed the standards for cadmium and mercury, and their levels of lead and arsenic were also far higher than those in shiitake mushrooms and button mushrooms. Research on another macrofungus——lingzhi——also reached similar results. Although some people regard it as a miraculous medicine, some researchers have found that some samples are rich in lead. Researchers in Taiwan, China also investigated Brazil mushrooms (that is, Hypsizygus marmoreus, also called Agaricus blazei), and likewise found that nearly half of the samples exceeded the standard for cadmium. However, in 2009, researchers from Zhejiang Forestry University and other institutions conducted spot checks on mushroom samples on the Zhejiang market and did not find excessive heavy metals, only that compared with ordinary vegetables their content was indeed relatively high and exceeded the heavy metal limit standards for vegetables.[2]
However, heavy metals are actually not essential elements for mushrooms, and they bring no benefit to mushroom growth. So why is the heavy metal content in mushrooms high? Where do these heavy metals come from? In fact, the reason for the high heavy metal content is that mushrooms produce some proteins that can chelate with heavy metals, generating nontoxic chelates through chelation with heavy metals to detoxify, thereby making mushrooms "not afraid" of heavy metals; and in the environment, especially in polluted environments, there are often large amounts of heavy metals, so mushrooms "accidentally" take these heavy metals into their own bodies, accumulating more and more.
The heavy metals in mushrooms, unlike the toxins synthesized by some poisonous mushrooms themselves, come from the environment and are not something the mushrooms want. If the growing medium is not contaminated, the mushrooms we love are still a very good food. Some farmers do not understand the environmental conditions and use sludge to cultivate mushrooms. Although sludge contains many nutrient elements, if rivers and other natural water bodies have excessively high heavy metal content due to pollution discharge, using it to grow mushrooms may cause serious excessive heavy metals in the mushrooms.
So, will these heavy metals affect the human body? Think about it: mushrooms can handle absorbed heavy metals by synthesizing chelating proteins, so saying humans "have no mechanism to excrete heavy metals" is somewhat belittling ourselves. In fact, metallothioneins with similar functions also exist in the human body, and if the amount of heavy metals in the body increases, more metallothioneins will be induced, improving detoxification capacity. In addition, glutathione in the liver can also bind with heavy metal ions and further excrete them through the digestive tract, playing a detoxifying role. For some specific heavy metals, there are also specific metabolic pathways to achieve detoxification and excretion. For example, arsenic in the human body can be converted into the less toxic monomethylarsenic and dimethylarsenic, which are more easily excreted from the body. Organs such as the kidneys, liver, and even lungs all have the function of excreting heavy metals. Generally speaking, unless toxic heavy metals are ingested in a large amount at one time or continuously over the long term beyond the dose, the human body's own ability to metabolize heavy metals can protect us from their toxic harm.
Judging from the investigation results of some research institutions that do not have food regulatory functions, mushroom foods on the Chinese market do indeed have excessive heavy metals. So what should we do if we like eating mushrooms? Generally speaking, wild mushrooms have higher heavy metal content than cultivated ones, and mushrooms that require soil-covered cultivation, such as button mushrooms, shaggy mane mushrooms, and Hypsizygus marmoreus, are easily contaminated by heavy metals in the soil. Relatively speaking, mushrooms cultivated with straw have lower heavy metal content.
As ordinary people, it is difficult for us to accurately judge heavy metal contamination in food. I hope our environmental monitoring departments and food safety management departments can be more effective, for ourselves and even more for our descendants, leaving behind an agricultural economy with a greater sense of safety.
Conclusion: Partly confirmed. Edible macrofungi such as mushrooms may indeed have excessive heavy metals, which is related to whether the cultivation medium contains large amounts of heavy metals. The human body itself has the ability to metabolize heavy metals, but long-term continuous intake of toxic heavy metals beyond the dose may indeed bring harm.
References:
[1] Li Yong, Zhang Xiaoyan, Yuan Lin, Investigation and Analysis of Heavy Metal Content in Edible Fungi in the Beibei Area of Chongqing, Journal of Chongqing Normal University (Natural Science Edition), 2007, Issue 01, 1-5
[2] Wei Hailong, Chai Zhenlin, Wu Xueqian, Lu Aihua, Shang Suwei, Zhu Jieli, Background Values of Heavy Metals in Mushrooms in Zhejiang Province and Quality Safety Evaluation, Zhejiang Forestry Science and Technology, 2009, Vol. 29, No. 3, 39-42
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Yesterday, a netizen consulted this newspaper, saying that she saw an article on WeChat claiming that you cannot eat more than 200 grams of mushrooms per month, otherwise heavy metals will exceed the standard. For this reason, the reporter interviewed Xie Baogui, an appointed expert of the National Edible Fungi Industry Technology System and a professor at Fujian Agriculture and Forestry University. He told the reporter that this claim is a rumor and that as long as there is no human-added factor, edible fungi products are very safe.
After reading the WeChat article, the netizen did not dare eat mushrooms
This netizen surnamed Ye said that her family all love eating mushrooms, shiitake mushrooms, enoki mushrooms, tea tree mushrooms, wood ear mushrooms, and so on, and they must buy these edible fungi when going to the vegetable market or supermarket. She had always believed that edible fungi are rich in amino acids, multiple vitamins, and minerals. But recently she saw an article in WeChat Moments saying that mushrooms should not be eaten in large quantities and that you can eat at most only 200 grams per month, because mushrooms have an extremely strong ability to accumulate heavy metals. Over time, these heavy metals will accumulate in the renal tubules, and in severe cases will cause renal tubular necrosis.
She said that after seeing this article, she did not dare eat them, and also told her mother not to buy them, but her family loves eating them, so what should she do?
The reporter found that this article circulating online was written by a doctor who claimed to have "once studied at the Pathology Institute of the University Hospital of Zurich" and who came into contact with a doctoral student in the biochemistry department named Guhl who studied fungi. He revealed that mushrooms should not be eaten in large quantities and that you can eat at most 200 grams per month. Because although mushrooms are good, their ability to accumulate heavy metals is extremely strong, up to 100 times. The author of the article also said, "I saw a report in the Neue Zurcher Zeitung saying that in radiation-contaminated areas of Ukraine and Germany from the Chernobyl nuclear accident, the prescription given by experts was to vigorously plant mushrooms to accumulate the heavy metals and harmful metals in these radiation-contaminated areas, so as to restore these areas to pre-contamination levels as quickly as possible." A sampling by the Ministry of Agriculture: heavy metal content in edible fungi is far below the national standard
"Absurd and completely groundless." In response, yesterday the reporter interviewed Xie Baogui, an appointed expert of the National Edible Fungi Industry Technology System and a professor at Fujian Agriculture and Forestry University. When the reporter told Professor Xie the content of this WeChat article, he flatly denied it: "This is a rumor. A while ago a friend also asked me whether mushrooms accumulate heavy metals. I was very surprised, because the healthy dietary concepts that the Food and Agriculture Organization of the United Nations and the World Health Organization have always promoted include eating mushrooms. Edible fungi have always been regarded as healthy food."
Professor Xie said that regarding the safety of edible fungi, in 2010 the Ministry of Agriculture randomly sampled 2,000 fresh mushroom products from across the country to test pesticide residues and heavy metals. As for the content of the heavy metal lead, the test results showed that the average content per kilogram of fresh edible fungi was 0.065 milligrams, far below the content stipulated by the national standard (1 milligram), and also below the standard of the International Food and Agriculture Organization/World Health Organization (FAO/WHO) (weekly intake per kilogram of body weight not exceeding 0.025 milligrams).
"If according to the FAO/WHO standard, a 60-kilogram adult would have to eat more than 92 kilograms of fresh edible fungi in a month to have a problem of excessive lead intake." Xie Baogui said that citizens cannot possibly eat edible fungi as their staple food, so there is no such thing as excessive heavy metals, unless they are artificially added.
Edible fungi produced under simulated contaminated conditions are still very safe
He said that the year before last, his team had just completed the major special project of the Provincial Department of Science and Technology, "Research on Breeding of New Edible Fungi Varieties and Safe Production Technology." This research project gathered more than 30 experts from across the province and conducted a 3-year study on pesticide residues and heavy metal content in ten major edible fungi. They tested and analyzed 10 major edible fungi products on the market, including shiitake mushrooms, button mushrooms, enoki mushrooms, tea tree mushrooms, king oyster mushrooms, Xiuzhen mushrooms, shaggy mane mushrooms, lion's mane mushrooms, Agaricus blazei, and Auricularia cornea, and found that they not only met the requirements of China's pollution-free food standards, but also met Japan's Positive List System and the EU's food standards.
This research project also simulated the production of edible fungi when cultivation materials were contaminated to varying degrees, tested the pesticide and heavy metal content they contained, and established regression equations between cultivation materials and pesticide and heavy metal content in the fruiting bodies, thereby predicting the safety of edible fungi products. "The research results show that although the sources of raw materials differ, as long as there is no human-added factor, edible fungi products are all very safe, and the problem mentioned in the article was not found." Professor Xie said.
Source of the WeChat article: idle chat by an obstetrician-gynecologist
Xie Baogui said that out of curiosity, he also went online to trace the origins of this article. This article existed as early as 2008 and came from an obstetrician-gynecologist with the online name "White Coat Salted Rice." In July 2010, "White Coat Salted Rice" published the article again on a Sina blog. This blog post, according to "White Coat Salted Rice," came from idle chatting when inviting a doctoral student at the University of Zurich named "Old Gu" to a meal. It was not quoted from a research report, nor did it come from the investigation results of an authoritative testing institution. It was more of a joke, with subjective ideas.