Who is the culprit of this strange disease that prevailed 60 years ago?
If it is not Minamata disease, Japan's Minamata Bay may not be known to the world. More than 60 years ago, local fishermen had symptoms such as hand and foot paralysis, facial dementia, decreased vision, and neurological abnormalities. These people were diagnosed with a neurological disease. After investigation, it was found that Minamata disease is actually mercury poisoning, which is caused by local residents' long-term consumption of seafood containing methylmercury. Minamata disease has now become a proper term for a class of diseases and is a chronic mercury poisoning caused by organic mercury. disease.
Not long ago, the movie "Minamata Disease" starring Hollywood superstar Johnny Depp appeared at the Berlin International Film Festival, making the tragedy caused by environmental pollution more than 60 years ago once again presented to the world. At the same time, a team of scientists from the University of Saskatchewan, Canada recently announced the latest findings, saying that methylmercury, which has long been believed, was not the culprit that led to the tragedy.
In response, Hu Xiangang, a professor at the School of Environmental Science and Engineering of Nankai University, said that many years ago, it was widely believed that methylmercury was the culprit of Minamata disease. The culprit once again became confusing.
More than 60 years ago, the strange disease swept the Shuihu Bay
If it were not for a strange disease that was prevalent more than 60 years ago, Minamata Bay, known as the "Kyushu Mediterranean", would not have been known to the world. This small Japanese city is rich in seafood, and fishermen make a living from the sea. Since 1955, local fishermen have developed symptoms such as hand and foot paralysis, facial dementia, vision loss, and neurological abnormalities. These people have been diagnosed with a neurological disease. Later, more and more people suffered from this strange disease, and more and more people died as a result, and even infants and young children could not survive.
"This strange disease was the" Minamata disease "that shocked the world. After investigation, it was found that" Minamata disease "is actually mercury poisoning. It is caused by the local residents' long-term consumption of seafood containing methylmercury. The wastewater discharged by the company Zhisuo Company into the nearby waters. "Hu Xiangang introduced.
The vinyl chloride and vinyl acetate produced by the Chisso company use mercury-containing catalysts in the manufacturing process, which causes the discharged wastewater to contain a large amount of mercury. Mercury is then passed through the food chain: after being consumed by fish and shrimp in water, it is converted into methylmercury. Methylmercury enters the body through fish and shrimp, damaging the body. Methylmercury entering the brain shrinks the brain, damages nerve cells, and disrupts the cerebellum and sensory system that control the body's balance.
"Minamata disease has now become a proper term for a class of diseases, a chronic mercury poisoning disease caused by organic mercury." Hu Xiangang introduced.
Methylmercury is the most likely pollutant
"Actually, the evidence for the occurrence of Minamata disease was not sufficient." Hu Xiangang explained that due to the limitations of detection methods and scientific understanding at that time, the analysis of mercury forms in humans, animals, and even water was not sufficient. There is still much to be explored in the study of mercury morphology and transformation in China. At that time, it was mainly judged that the mercury-containing sewage discharged from the chemical plant was caused by the symptoms of the onset of the patient, the symptoms of methylmercury poisoning, and the discharge of wastewater from the chemical plant. By examining fish in contaminated water, scientists have found that fish contain a large amount of mercury, and then enter the body through the food chain to cause disease.
As people speculate, in 1959, when Minamata disease was raging, a doctor working at the Chisso factory went to ten cats to conduct experiments to mix industrial wastewater with cat food. Cats that have eaten the contaminated cat food begin to twitch and become paralyzed before death. The doctor dissected two of the cats, numbered 400 and 717, respectively. Their behavior and brain damage showed that they had the same disease as the leeches that were raging at the time.
"In the case of Minamata disease or similar mercury poisoning, the presence of organic mercury such as methylmercury can usually be detected in contaminated fish and diseased humans." According to Hu Xiangang, mercury can be divided into organic mercury and inorganic mercury In two forms of existence, inorganic mercury such as mercury chloride is difficult to enter the brain through the blood-brain barrier of the human, affecting the human nervous system. Organic mercury such as methylmercury can cross the blood-brain barrier and cause neurological diseases. Methylmercury is very toxic, as long as the amount of ear spoon and a half spoon can poison people.
The catalysts selected by the plant, mercury chloride and mercury sulfate, are also toxic, but they are both inorganic mercury. However, they can be turned into very toxic methylmercury in the bottom mud by a bacterial action called methylcobalamin. Methylmercury can be released at a rate of 1% per year, which causes secondary pollution to the upper seawater. Fish, shrimp and shellfish living here for a long time are most likely to be contaminated by methylmercury. It is determined that the mercury content of seafood in Minamata Bay has exceeded 50 times the edible amount.
Hu Xiangang explained that patients must contain a variety of organic mercury, which can be detected, but it is no longer possible to test the rigorous data of the human body at that time, and it is difficult to determine the value of statistical significance. But methylmercury is the most likely cause of neurological contamination, and it is by far the most recognized cause of Minamata disease.
Latest spectral results did not find methylmercury in the sample
Recently, x-ray spectrographers and colleagues at the University of Saskatchewan, Canada, reanalyzed the cerebellar sample of cat number 717 under a Stanford synchrotron radiation source in the United States. That is, they are blasted with x-rays, and the spectral results of specific molecular fingerprints are analyzed. After testing, the scientists found that the most spectrally compatible molecule did not contain methylmercury at all, and instead, 3/4 of the sample appeared to be another mercury organic compound (α-acetaldehyde mercury). The researchers speculated that this compound It may come directly from industrial wastewater.
The research report published by the research team in Environmental Science and Technology pointed out that this finding shows that the previous conclusion that methylmercury is a common form of mercury in Minamata disease should be re-examined. Play an important role. At the same time, they believe that because the previous research used insensitive detection technology, they missed the main form of mercury in leech samples.
"At present, the detection of methylmercury is mainly carried out by atomic fluorescence, chromatographic mass spectrometry and other technologies. Canadian scientists are using X-ray technology this time, which is mainly used to detect various forms of mercury. The molecular fingerprint of mercury usually refers to various types of mercury. Existing forms, such as various forms of organic mercury, inorganic mercury, and even particulate mercury, the accuracy of the detection results of this method is still very high. "Hu Xiangang introduced, although there is a good side to measuring the form of mercury by X-ray technology, But it also adds a lot of uncertainty. Because the organism is too complicated and the energy of X-rays is relatively high, the original components of the cat's cerebellar tissue may be destroyed during detection, and the properties of the original materials may be changed.
"The Canadian scientific team also confirmed that mercury was contained in samples of cat cerebellum that year, but the content of methylmercury was relatively small, mainly mercury sulfide. Then they calculated it through a computer and speculated that mercury sulfide may be derived from another organic mercury. Transformed. "Hu Xiangang said that their results are currently partly from computer speculation, and the proportion of this new mercury-containing organic matter needs to be further tested.
"In addition, there are also some uncertainties in the retesting test of the Canadian science team." Hu Xiangang analyzed, for example, the cerebellar sample of the cat number 717 was used for experimental speculation that year, and whether it can accurately reflect the human exposure. First a question mark was placed. And after more than 60 years of long storage, there may be some changes in the tissue of the sample, such as degradation, transformation into other forms of existence.
Many scientists around the world have also questioned this latest finding. Environmental scientists at Syracuse University in the United States say that this new mercury compound may be the product of cat metabolism or the product of long-term preservation of samples. Even though Minamata disease originates from wastewater sprayed directly from the factory, patients are directly exposed to mercury in edible seafood.
"Although there is controversy, the Canadian scientific team did use modern testing methods to clearly detect that the sample contained more mercury sulfide, and then inferred the exposure method of α-acetaldehyde mercury. Therefore, the scientific nature of this new discovery cannot be completely denied. Science encourages different viewpoints to collide with each other. "Hu Xiangang said that the Canadian research team has decided to expand the research sample and plans to test samples of Minamata disease victims stored in the National Minamata Disease Research Institute of Japan. The culprit of Minamata Disease found new evidence. (Chen Xi)