Should I drink the first glass of water in a disposable paper cup?
　　
　　 The truth: This is a "small suggestion" about disposable paper cups circulated on Weibo recently. This suggestion has the following main points:
　　
　　1) There is usually wax on the inner wall of paper cups. 2) These waxes will melt above 40°C. 3) According to 1) and 2) the paper cup cannot be filled with hot drinks. 4) The paper cup contains harmful substances. 5) Soak the paper cup with water for four or five minutes to fully remove harmful substances. 6) According to 4) and 5) the first glass of water in the paper cup cannot be drunk.
　　
　　 These points are not entirely nonsense, some of which involve facts, but more of them are misunderstandings. To analyze the right or wrong of this suggestion, you first need to have a basic understanding of disposable paper cups.

　　All paper cups have wax? Speaking from the types of paper cups
　　
　　 "The inner wall of disposable paper cups is usually coated with a thin layer of wax." This sentence can only be counted as one-third correct.
　　
　　 At present, domestic disposable paper cups can be divided into three types according to their purpose: cold drink cups, hot drink cups and ice cream cups[1]. According to the coating of paper cups, it can also be divided into three types: wax-coated cups, polyethylene-coated cups and straight-walled double-layer cups [2].
　　
Wax-coated cups are similar to the kind of paper cups described in rumors. The surface is coated with a layer of wax to prevent water; the polyethylene-coated cups are covered with a thin layer of polyethylene on the cup walls; the straight-walled double-layer cups have two cup walls. Layers of paper, air between the papers, good heat insulation performance.
　　
　　Because the wax will melt when heated, the wax-coated cup can only be used as a cold drink cup. If you want to hold hot drinks, you need to add a layer of emulsion. The straight wall double-layer cup uses this kind of coating, and because the double-layer cup has good heat insulation, it is often used as a hot drink cup and an ice cream cup. Polyethylene coated cup is a new technology, the advantage is that cold and hot drinks can be handled freely, and the surface is smoother, and the outside of the cup can be easily printed with exquisite patterns, so it is very popular in the fast food industry.
　　
　　It can be said that polyethylene coated cups are now the mainstream paper cup products. However, the industry standards for paper cups still include waxed paper cups [3], and the research work on such paper cups is still being done [4], so consumers still have the opportunity to come into contact with waxed paper cups.
　　
　　 Paper cup wax melts when it exceeds 40℃? That must be a substandard product
　　
　　 According to the paper cup industry standard "QB2294-2006 Paper Cup", the paper cup performance requirements, waxed paper cups use food-grade paraffin. The national standard "GB7189-2010 Food Grade Paraffins" classifies this type of paraffins according to their melting points. There are 8 types of paraffins from No. 52, No. 54 to No. 66. No. 52 paraffin requires a melting point not lower than 52°C and not higher than 54°C. The melting point of No. 54 paraffin is not lower than 54°C, not higher than 56°C, and so on.
　　
　　 That is to say, if you hold hot drinks, the wax layer of the waxed cup will indeed melt, but for a qualified waxed paper cup, the temperature should at least exceed 50°C.
　　
　　 What about hot drinks in waxed paper cups? Because wax-coated paper cups rely on the wax layer to isolate water, if the wax layer melts, water will penetrate into the cup body, making the paper cup soft and even leaking.
　　
　　 And the qualified paper cups use food-grade paraffin. Even if you accidentally drink it into your stomach, you don’t have to worry, the paraffin will not cause harm to your body. The real danger of using a cold drink cup to hold hot water is that the paper cup will lose water resistance after the paraffin is melted, and it will be easily penetrated by the hot water and burn the user.

　　Harmful substances in paper cups
　　
　　Paper cups may be mixed with a lot of harmful substances during the production process. For example, illegal manufacturers use fluorescent agents, and the paints and additives used in the outer wall of the paper cups to spray patterns bring lead, arsenic and organic solvents[5][6]. The process may also be contaminated by microorganisms.
　　
　　 Regarding hazardous substances in paper cups, the industry standards stipulate as follows:
　　
　　 If it is a qualified paper cup that meets the standards, it contains very few harmful substances, which is not enough to cause harm to the human body. It is also impossible to require paper cups to be completely free of these substances, such as lead and arsenic, which exist in nature, and their content can only be reduced during the production process. Although it is technically feasible, the cost will be very high and it has no practical significance. . It is more appropriate to limit their content within a safe range.
　　
　　 Is 5 minutes enough to remove harmful substances?
　　
A more detailed description than the saying "Don't drink the first cup of water" is, "Scalding with boiling water for four or five minutes before using a disposable paper cup can fully remove harmful substances." This argument has a wide range of influences, some formal Newspapers are recommending this "tip".
　　
　　With boiling water, is only 5 minutes enough to get rid of harmful substances in the cup?
　　
　　 If there are really pathogenic bacteria in the cup, soaking in water at 100°C for 5 minutes can basically kill the propagules of ordinary bacteria. However, this refers to heating at 100°C for 5 minutes, which is impossible in daily use.
　　
　　As for lead, arsenic and fluorescent substances, soaking in hot water for five minutes has little effect. Regarding this problem, we can think in reverse. If soaking in 100℃ water for 5 minutes can remove all the remaining harmful substances, this method has long been used in industrial production to produce safer paper cups. Have consumers do it themselves?
　　
As for the unqualified paper cups, the number of pathogenic bacteria and the amount of other harmful substances cannot be estimated. Even if the method of boiling water for 5 minutes has a certain effect, there is no guarantee that these harmful substances can be completely removed or reduced to a safe level. standard. Choosing qualified paper cups is the best policy. For qualified paper cups, it is not necessary to pour the first cup of water.
　　
　　 However, the actual situation is always diverse, and what I said above is more about buying new paper cups. Even if it is a qualified paper cup, if it is useless for a long time after opening, it is likely that the microorganisms have exceeded the standard. In this case, the safest way is to treat these paper cups as substandard products-throw them away and buy new ones. .
　　
　　How to choose a safe paper cup
　　
　　 In fact, choosing paper cups is the same as buying food. You need to see if there is a clear QS mark, manufacturer information, and production date on the paper cup packaging. Don't buy unlicensed paper cups for cheap. In addition, you must also look at the scope of application indicated on the package. A regular disposable paper cup will indicate the applicable temperature of the paper cup. If you buy a cold drink cup, don't use it to hold hot water, so as to avoid water leakage and scalding.
　　
　　If you are dining out, the paper cups of some large fast food chains can still be used with confidence. It is difficult to guarantee the paper cups used by restaurants with poor environment and no sanitation license. What's more, food safety is not guaranteed in such a place. Even if the "5-minute disinfection method" is really effective, it is useless. It is better not to eat in such a place.
　　
　　 Conclusion: The most common polyethylene coated cups on the market do not have melting wax, and hot or cold drinks are not a problem. Waxed paper cups are cold drink cups, and indeed the wax layer will melt because of the hot water, but the result is that the paper cups will seep water. Scalding with boiling water for four or five minutes will not remove the harmful substances. If it is a qualified paper cup, it is okay to drink the first cup of water. If it is a substandard paper cup, do not drink the first few cups of water.