In the past two days, an environmental protection organization issued a report saying that a certain brand of tea contains highly toxic pesticides, which caused an uproar in an instant. Because right and wrong are often confused on some basic issues, the report of the organization will always become an excellent material for popular science people to vomit. Looking at this report carefully, it is the same again. For example, there is a passage in the report: "Only one sample of tea products sampled twice has one pesticide residue, and others can detect multiple pesticide residues, indicating that the amount of pesticides used in tea planting is large [1]." This description clearly confuses the two aspects of pesticide "variety quantity" and "use quantity"
The relevant detection amount did not exceed the national standard.
As can be seen from the table of this report, all kinds of standard pesticide residues in China have not exceeded the standard. The public will also notice that a considerable number of pesticides in the list have no domestic limit standards. I believe many people will ask at this time, where is the standard in China? It has to be admitted that the standards of these pesticides have not yet been determined due to the lack of toxicological research in China. So, in this case, can EU standards be used instead of China standards?
Data screenshot of this report.
I won't answer this question first, but please look at a set of data provided by FAS global agricultural product pesticide residue limit database [Note]: The limit of dicofol in cottonseed in the United States, Europe, Australia, Japan and South Africa is 0. 1mg/kg, while Brazil's requirements are more stringent, which is 0.0 1mg/kg, but it is moderate. The standard of methomyl in Japanese corn (0.02 mg/kg) is stricter than that in the United States and Australia (0. 1 mg/kg), but there is no standard in China, Europe, Canada, India and other countries. I believe that after reading these data, you should understand that due to the differences of race, economic and social development, environmental conditions and many other factors, the pesticide residue standards in different countries are different. Moreover, developed countries can have less stringent standards or even no standards, while developing countries can have harsh standards. In a word, the standard of pesticide residues is not as strict as possible, as long as it adapts to the actual situation of the country. Therefore, it is meaningless to mention that five pesticides exceed the standard in the report. By the way, the organization's report quoted a paper on pesticide toxicology, and these five pesticides that exceeded the standard were considered relatively harmless to human body in the literature [2].
Perhaps it is precisely because the concentration of "exceeding the standard" is not "amazing" and the harm is not great, so the organization has to use some pesticides with relatively high toxicity but far below the national standard to scare people. For example, dicofol and endosulfan, which have been banned, are highlighted. However, if you read the report carefully, you will find that the detection amount of these pesticides is not only within the national standards, but also very low. For example, in one sample, the concentration of endosulfan was found to be 0.0 1 mg/kg, while the standards in China and the European Union reached 20 and 30 mg/kg [1] respectively (note that the limit in the European Union is greater than that in China). How can this data with a difference of three orders of magnitude show that endosulfan is harmful to China people? Similarly, the toxic methomyl, dicofol and omethoate mentioned in the report are all below the environmental standards [1].
Why are banned pesticides detected?
Since dicofol and endosulfan mentioned in the report are banned pesticides, why are banned pesticides detected? Does this mean that they have been illegally used?
According to the organization's report, dicofol and endosulfan are prohibited pesticides used in tea trees. However, as "persistent organic pollutants", these two pesticides are inherently difficult to degrade. Half of the total amount of these two pesticides released into the environment will take at least a few years to degrade, and the total degradation may take decades or even hundreds of years, so the residue in the environment is inevitable. For example, the well-known DDT, although banned for 30 or 40 years, can still be detected in Antarctic penguins [3] and Inuit breast milk in the Arctic [4]. The research in Taihu Lake in 2002 showed that the relatively high concentration of dicofol and endosulfan in the atmosphere mainly came from the south of China (including South China and Fujian), indicating that these two pesticides were widely used in the south [5]; The national soil survey also found that the highest residue of endosulfan in China soil appeared in Zhejiang and Fujian (just the main tea producing areas), reaching 19 ng/g soil dry weight [6]. These pesticides are easy to volatilize into the atmosphere in the high temperature environment in the south, and there is a hydrophobic wax layer on the surface of plant leaves, which can directly adsorb pesticides in the atmosphere [9]. Therefore, even if these pesticides have stopped using, it is entirely possible to detect their presence in tea.
Some people say that tea leaves are generally new leaves, so in theory, tea leaves should be very clean, but I don't agree with this view. After the trees grow new leaves, because the wax contains no pollutants, the leaves at this time have the largest adsorption capacity and the fastest adsorption speed. Usually, within one or two weeks after germination, the adsorption capacity of new leaves to atmospheric organic pollutants can reach 40% of their maximum adsorption capacity [7]. So it is not surprising that there are pesticides in tea. As long as there are pesticides in the environment, there will be pesticides in tea. It is worth mentioning that the detection rate of these pesticides is very low, which just shows that pesticides in tea are not the result of direct application.
Although the use of pesticides in China has a long history, the environmental concentration of some pesticides is higher than that in other parts of the world, but it is still at the trace level, which is not enough to cause harm to human health in most parts of the country. I want to say one more thing here. Comparatively speaking, the heavy metal pollution incidents that broke out in China are more harmful, and the situation of heavy metals exceeding the standard in soil and crops in China is also frequently reported in newspapers. So I suggest you pay more attention to the problem of heavy metal residues, rather than obsessing about pesticide residues, which may be a more responsible approach to your health.
By the way:
Through the report released by the agency, I can't confirm whether they really detected dicofol. The main component of dicofol is O, p'-DDT [9]. Do the last three letters look particularly familiar? Yes, it is DDT that environmentalists often say in Silent Spring. However, DDT used as an insecticide when Silent Spring was published was technical DDT, and its main component was P, p'-DDT. Because P, p'-DDT is difficult to degrade, has the ability of long-distance transmission and can accumulate in animals [10], it was banned by major countries in the world in 1970s and 1980s (India banned it in 1990s). And its substitute is dicofol, because O, p'-DDT is easy to degrade. Dicofol did not officially enter the banned list of Stockholm Convention on Persistent Organic Pollutants until 2009. However, dicofol in the report is marked with "P, P", which indicates that the author of the report may not understand the difference between industrial DDT and dicofol, and its concentration value puzzles me.