ZZ91 information: On November 2nd, a message from Weibo and WeChat was widely concerned: the salt contained in the salt contained plastic particles! This issue of Curiosity answers this question through experiments. Experimental site: Xi'an Jiaotong University Chemical Experiment Teaching Center (medical school district) Experimental sample: edible salt purchased by several supermarkets in Xi'an (seaweed iodized salt, low sodium and iodized salt) Laboratory staff: Li Jianjun, teacher of Chemistry Experiment Teaching Center, Xi'an Jiaotong University Experimental Consultant: Associate Dean of School of Science, Xi'an Jiaotong University, Director of Institute of Analytical Science of the School of Science, Professor Tang Yuhai, Vice President of the National Society of Medical Chemistry Weibo WeChat Forwarding News: Chinese salt contains plastic particles On November 2, Weibo and WeChat forwarded a message: The US Science American website reported on October 29 that researchers analyzed the common salt of 15 brands purchased from supermarkets across China and found them in salt granules. Polyethylene terephthalate for the production of ordinary plastic water bottles, as well as polyethylene, cellophane and many other plastics. Among them, sea salt is the most polluted by plastics. The researchers measured more than 1,200 plastic particles per pound (1 pound or 0.45 kg) of sea salt. The salt produced from salt lakes, salt wells and salt mines has a plastic particle content of about 15 to 800 capsules per pound. On November 3, more detailed information is reported. Originally, Dr. Shi Huahong, research team of East China Normal University, published an article on the pollution status of salt micro-plastics in China. After published online in the international environmental science journal Enviromental Science & Technology, the scientific American monthly website reported the results. According to a report on the Scientific American website, Sheri Mason, a researcher at the State University of New York at the University of Freedonia, said that producers generally extract sea salt from seawater by evaporation, a process other than water. Everything has been left behind, so it is very likely that sea salt is contaminated with plastic particles outside of China. There was no suspended particulate matter or sediment after the salt was dissolved for 20 hours. The reporter went to Xi'an Powder Lane China Resources Wanjia Supermarket, Ximen Wal-Mart Supermarket, and Songguang Supermarket in Guangbei Road to sample and purchase salt. It was found that the salt sold in these supermarkets is the same brand, with 350 grams of packaged seaweed iodized salt and 200g packaged low. Sodium plus iodized salt. Among them, the powder lane Huarun Wanjia, Ximen Woolma two kinds of packaging, and the pine forest supermarket on Guangbei Road only has 350 grams of seaweed iodized salt. The reporter sent the purchased samples to the Chemistry Experiment Teaching Center of Xi'an Jiaotong University. After the experimenter gave the salt sample number, put it into 5 beakers, then add distilled water to dissolve it, and prepare 5 parts of salt saturated solution. Professor Tang Yuhai introduced that plastic particles are insoluble in water, and if the salt is fully dissolved, if plastic particles are suspended in water or deposited on the bottom of the beaker. The five beakers that were fully dissolved and allowed to stand for about 20 hours were placed on the experimental console. Careful observation with the naked eye, except for some bubbles on the walls of individual beakers, the salt solution in the five beakers was clear and transparent, and no suspended particles or precipitates were found. Professor Tang Yuhai said that this means two situations: one is that there are no plastic particles in the five samples, and the other is the presence of plastic particles but the particle size is too small for the naked eye to observe. Subsequently, Teacher Li Jianjun sampled each sample separately with a straw and placed it under a microscope. In the case of the eyepiece 16 times and the objective lens 40 times, that is, the magnification of 640 times, the presence of foreign matter particles in the sample salt solution was not found. Is the microscope magnification too low, or does it require a more sophisticated method to test? According to the media reports, the article by East China Normal University has studied the salt of three different sources, sea salt, lake salt and well salt/rock salt. The experimental method is roughly “microscopically seeing the particle size, and the Fourier infrared spectrum is used to see the components. ". Professor Tang Yuhai said that although infrared spectrometers can be used for more detailed analysis, the premise is that there must be a certain amount. The sample salt solution did not see the presence of plastic particles under a 640-fold microscope, and such an amount could not be analyzed by an infrared spectrometer. If you want to make a more detailed observation, you may need to use a tunneling microscope. But plastic is a macromolecular structure. If it reaches such a small level, it is basically negligible. In addition, since plastics cannot be absorbed by the human body, even if a small amount of plastic particles enter the human body, most of them can be excreted. East China Normal University responded: foreign media reported that the salt micro-plastic data was seriously inaccurate As for the problems encountered in the experiment, the reporter contacted the Propaganda Department of the Party Committee of East China Normal University. The staff sent an article entitled "Marine micro-plastic pollution, the environmental problems that the world has to face together" as a reply. The article is written by Professor Li Daoji, the State Key Laboratory of Coastal Research at East China Normal University. Professor Li is also the earliest expert in the research of micro-plastics in the marine environment. Professor Li Daoji explained in the article that the foreign media reported that the news reports on micro-plastics in salt were inaccurate. The study focused on the approach of marine microplastics into the human food web, which was received by the international environmental science journal Environmental Science & Technology and published online August 20. On August 28th, Scientific American published a news report on Chinese salt containing microplastics based on online papers. The title and some of the texts highlight the "Chinese salt" and "Chinese consumers" do not rule out the purpose of attracting readers. The data on micro-plastics referenced in this report is seriously inaccurate. The maximum salt salt per kilogram in the original text is 681, but the report is about 1200 per pound (should be 308 per pound), which is inconsistent with the data and opinions in the paper. Professor Li Daoji believes that micro-plastics are ubiquitous in the environment. For example, researchers found that up to 400 micro-plastics per kilogram of honey, up to 13,000 per kilogram of soft tissue in Canadian cultured mussels. In contrast, the microplastics obtained from salt are minimal. Salt micro-plastics are just an example of the impact of living products on micro-plastics and are a warning to everyone. Microplastic According to Professor Li Daoji of East China Normal University in the article, in 2004, British researchers published a research paper on plastic debris in marine waters and sediments in the American journal Science, and proposed the concept of microplastics for the first time. Microplastics are more commonly defined as plastic fibers, granules or films that are less than 5 mm in size. Most of the microplastics found in the environment are on the micron level, which is often difficult to see with the naked eye. There are two main sources of marine micro-plastics: one is nascent micro-plastics, which refers to plastic industrial products with a particle size of less than 5 mm discharged into the marine environment through rivers, sewage treatment plants, etc.; the second is secondary plastics, which are made of large plastics. Garbage is caused by physical, chemical and biological processes that cause division and volume reduction. Studies have shown that the current amount of floating plastic waste in the world is estimated to be as high as 2.7 billion pieces and 250,000 tons. Marine organisms can not only directly ingest marine micro-plastics, but also indirectly ingest micro-plastics by feeding prey. 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No plastic particles in the salt were found under the microscope.
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