I. Safety of genetically modified foods
Transgenic means that one or more plants or animals or even human genes are implanted into a certain organism, so as to show the new characteristics that the transferred genes can't have naturally, so as to improve the quality of its products, increase its nutritional components, increase its resistance to diseases, pests and diseases, increase its yield, resist reversal and extend its shelf life. Gene food is a product made from genetically modified organisms and processed for human consumption. Genetically modified food is a new technology.
1, the main deficiency of transgenic technology itself.
(1), loose technology: Gene technology transfers a heterologous gene from one organism to another. Although its DNA can be accurately cut, it cannot accurately implant new genes into another organism, thus affecting the basic functions of other genes in this organism. Scientists can't predict the new unknown protein after plant genotyping, and they can't predict the immature effect on the receptor completely and accurately.
(2) Side effects: Gene technology is just like a surgeon performing heart surgery. Scientists can't fully know in advance that DNA surgery on living things may lead to mutation and harm to the environment and people. Although the experiment is very mature, we can't grasp all the information that may affect human beings in the face of the strong pressure of nature.
(3) Large-scale crop yield reduction: Gene technology gains profits by constantly selling seeds, which means that when farmers plant transgenic seeds, all the plants planted have the same genes. When fungi, viruses and pests attack these special plants, serious yield reduction will occur.
(4) Seriously affect the whole food supply: insects, birds and wild animals will carry transgenic seeds to nearby fields. When transgenic plants produce pollen, they will cross-pollinate transgenic crops and wild animals, and all crops, organic matter or inorganic matter are easily polluted by cross-pollination.
2. Health hazards
(1), the safety test has not been conducted for a long time: genetically modified food has changed the natural properties of the food we eat, and the biological substances it uses are not the part provided by human food safety. No one knows whether this food is safe without long-term safety test.
(2) Toxin production: Genetically modified food will produce unpredictable biological mutation, which will produce higher levels and new toxins in food. Losey, J.E. et al. (1999) reported that after spraying transgenic Bt corn pollen on the leaves of a plant milkweed, Papilio Papilio had few edible leaves and slow growth, and the mortality rate of larvae was 44% in 4 days. However, none of the control group (leaves fed with Bt corn pollen) died. Insecticidal toxins produced by genetically modified crops can penetrate from the roots to the surrounding areas, but it is not clear what effect they will have.
(3) Allergy or allergic reaction: Genetic technology will produce unpredictable and unknown allergens in food. It is reported that subjects who are allergic to Brazil nuts are also allergic to soybeans genetically modified with this nut. Scientists transplanted the characteristics of Brazilian walnuts to soybeans, but as a result, some people who are allergic to walnuts may be allergic when eating soybeans. Phytocoagulants are toxic to some pests, and genetically modified foods must not contain such toxic substances.
(4) Reducing the nutritional value of food or degrading important ingredients in food: The purpose of genetics is to remove or inactivate substances that people think are unnecessary. These substances may be unknown, but they are basic. For example, it has a natural ability to inhibit cancer (Pariza, M.W., 1990). American research data show that in soybeans with herbicide-resistant genes, anti-cancer components such as isoflavones are reduced. The false freshness of genetically modified foods confuses consumers. Red tomatoes with fragrance and luster can be preserved for several weeks, but their nutritional value is low. When consumers buy fruits or vegetables, they can't accurately judge the true quality of the products only by appearance and texture. Transgenic microorganisms disturb the natural circulation of nutrients in the environment.
(5) Antibiotic-resistant bacteria: Gene technology uses antibiotic-resistant genes (such as kanamycin, ampicillin, neomycin, streptomycin, etc.). ) to identify transgenic crops, that is, crops have antibiotic resistance genes. These genes affect us through bacteria. British research shows that mutant genes in genetically modified crops may enter organisms. If the mutant gene crosses the population and is transferred to bacteria, the result may lead to new diseases. Although this probability is very small, if there is an incurable and widely spread disease that poses a serious threat to life, the consequences will be unimaginable. According to the experimental results published by Dutch scientists in New Scientist magazine, an artificial stomach was designed to simulate the process of human digestion of genetically modified food. It was found that DNA remained in the intestine, and some genetically modified bacteria could transfer their antibiotic resistance genes to the bacteria in the artificial stomach. If similar results happen to humans and animals, it is possible to cultivate the most powerful superbacteria that antibiotics cannot kill. The British New Food and Technology Advisory Committee has banned the trend of feeding a genetically modified corn with ampicillin resistance gene to cattle, because the DNA contained in it remains intact and may accelerate the resistance to antibiotics.
(6) The problem cannot be traced back: if it is not marked, our public health authorities will not be able to find the source of the problem, and the potential harm is doubtful.
(7) Side effects can be fatal: Mayeno, A.N. et al. (1994) reported a new disease of unknown cause, mainly manifested as eosinophilic myalgia. Clinical manifestations include paralysis, neurological problems, pain and swelling, itchy skin, heart problems, memory loss, headache, light sensitivity and emaciation (Brenneman, D.E. et al.,1993; Love, L.A., etc., 1993). It was later discovered that tryptophan was produced by genetically engineered bacteria born in a Japanese company. Three months later, the eater fell ill, resulting in 37 deaths, 1, 500 people were partially paralyzed, and more than 5,000 people were occasionally weak. According to the determination, the content of 0. 1% can kill people.
3. Direct harm
The Lancet magazine199910 June16 reported that Puztai, A. (1998) of Rowett Institute in Scotland first fed mice with potatoes with the gene of snowdrop lectin (GNA). After 10 days, it was found that the mucosa of colon, jejunum and some small intestine in the feeding group was thickened. He thinks it may be the result of introducing genes to activate or prevent other genes in plants. In addition, it was observed that the kidney, thymus and spleen of experimental rats grew abnormally or atrophied or grew improperly, and many important organs were also destroyed, the brain shrank and the immune system weakened. Although the Royal British Medical Association has conducted an investigation on this special organization of scientists, it believes that the experiment has many defects in design, implementation, analysis and so on, and it should not be premature to draw conclusions. Although there are differences between the two groups, these differences can not explain the problem because of the limitation of experimental technology and the incorrect use of statistical methods. But it still can't dispel people's doubts about genetically modified food. After the recombinant cow production hormone (rbGH) was put into commercial use in the United States, users quickly found that this kind of drug led to an increase in the incidence of mastitis in dairy cows and a low reproductive rate. Due to the effect of drugs, the metabolism of dairy cows is accelerated, resulting in increased energy consumption and death. The nutritional value of milk has also decreased. Scientists have conducted targeted research on genetically modified corn and cotton that have been approved for commercial cultivation in Spain and the United States, and believe that genetically modified crops may cause meningitis and other new diseases. It is also confirmed that genetically modified food may induce cancer and pass it on to the next generation, which may take 30 years or more.
Whether transgenic therapeutic drugs and human tissues and organs have an impact on human health. We can't test for confirmation yet.
4. Environmental impact
(1), the use of herbicides has increased: scientists estimate that transgenic crops are resistant to herbicides, and the actual use is three times higher than normal. Farmers know that their crops are resistant to herbicides and will use a lot of herbicides.
(2) Increased use of pesticides: Genetically modified crops often use their own unique pesticides, which are classified as pesticides by the US Environmental Protection Agency, which means that more pesticides enter our food and fields than before. It has been reported that implanting excellent specific genes (such as pesticide resistance) into crops may improve the surrounding wild plants and make them show the characteristics of pesticide resistance.
(3) Ecological destruction: GEO affects the local ecological environment through the food chain, and new microorganisms compete effectively with related organisms, causing intangible damage to the environment. As an artificial genetically modified crop, it may become an exotic variety that does not exist in nature. After several years, it may cause damage to soil, wild relatives, ordinary crops, adjacent plants and the environment.
(4) Genetic pollution is difficult to eliminate: genetically modified organisms, bacteria and viruses cannot be preserved or recovered after entering the environment. Unlike chemical or nuclear pollution, the side effects are irreversible.
(5) Transgenic crops can turn wild relatives into weeds and become "super weeds" through gene flow. It has been proved that 93% of the germinated offspring seeds are proved to be interspecific weeds when there are related weeds nearby after the release of transgenic rapeseed.
(6) Harmful to non-target organisms and threatening biodiversity: Hilbeck( 1998) fed the European corn borer (ECB) with transgenic Bt corn as the feed for lacewings, while GN fed ordinary corn as the control. The experimental results showed that the mortality rate of transgenic Bt corn group was above 60%, while that of control group was below 40%. It is considered that the factors related to Bt are related, and the maturity time of surviving Chrysopa in Bt corn group is 3 days later than that in control group on average. The experimental results of Birch, A. et al. (1996/7) showed that feeding aphids with transgenic potatoes reduced the number of eggs laid by females 1/3. When male aphids fed with transgenic potatoes mated with aphids in the control group, the number of unfertilized eggs was four times higher, and the mortality rate of fertilized eggs before hatching was nearly three times higher than that in the control group. The survival time of female mosquitoes fed with transgenic potato aphids is better than that of the control group
In fact, our knowledge of DNA is limited. 97% of human genes are called "junk" because we don't know many of its functions. The metabolism of a single cell is quite complicated, and their whole process is even more difficult to understand.
Second, the detection progress of genetically modified organisms
Although the public is paying more and more attention to the safety of genetically modified food, the cost of separating genetically modified crops from non-genetically modified crops is quite high. Food goes through many links from the farm to the table, and there are many participants in each link. It is difficult to distinguish between genetic crops and non-genetic crops.
At present, the detection of genetically modified crops has made progress. The detection of genetically modified ingredients must be rapid, accurate, sensitive and reliable. At the same time, there are many varieties and quantities of agricultural products containing genetically modified ingredients, especially foods containing genetically modified ingredients. The components to be detected (nucleic acid or protein) are often degraded or destroyed, or contain only a small proportion of transgenic components, so it is very difficult to detect.
The unique DNA sequence of transgenic components implies the gene expression profile. One is manual detection, which is carried out manually in traditional biological laboratories, but it takes at least one working day to determine the sequence of more than a dozen DNA fragments (about 4000 base pairs). Second, instrument detection, PE3700-DNA sequence analyzer and other similar instruments can detect nearly 2,000 DNA sequences (about 700,000 base pairs) in one working day. 1in March, 1999, British RHM technology company announced that it had invented a new method, which can accurately detect whether the deep-processed food contains trace amounts of genetically modified soybeans or corn and the specific proportion of genetically modified ingredients in the ingredients. According to the researchers, they studied a piece of bread and found that it contained 0.67% soybean flour. After further accurate analysis by the new method, they successfully found that 2% of these trace soybean powders were genetically modified. The third is biochip. Shanghai Institute of Cell Biology (1999) has successfully developed the primary form "cDNA array" of biochip, which is used to detect the changes of gene expression profile in biological samples. An immature biochip completed the determination of 16000 base pairs in 15 minutes, and 96 such biochips worked in parallel, which was equivalent to the analysis capacity of1470,000 base pairs per day. 1996, a company in California successfully manufactured the first DNA chip and made a "gene chip" system. In addition, a Russian institute of molecular biology and other companies in the United States have also invested in similar research and are committed to expanding the scope of application.
According to the report of China Guomen Times, the entry-exit inspection and quarantine department of China applied new detection methods to detect some imported agricultural products, and found genetically modified ingredients. Based on the principle of biochip technology, the Plant Quarantine Laboratory of the State Administration of Inspection and Quarantine (2000) explored the detection method of "affinity adsorption -PCRHyb-ELISA". Compared with similar PCR methods known in the world, this method solves the problem of sample nucleic acid preparation in transgenic detection, reduces the detection cost and time, improves the detection sensitivity and stability, and improves the automation degree of sample detection, which is suitable for the detection of large samples at ports. This detection method can specifically detect the nucleic acid sequences of 35S promoter and Nos terminator, which exist in most known transgenic components.
The Agricultural and Livestock Food Laboratory of Jiangsu Inspection and Quarantine Bureau scientifically determined to extract DNA by CTAB method, thus mastering the detection method of PCR amplification technology to determine whether there are genetically modified components, and the genetically modified components in the test samples can be accurately detected when they reach 2%.
Shanghai Inspection and Quarantine Bureau and Shanghai Institute of Plant Physiology, China Academy of Sciences (2000) used PCR technology and CTAB method to extract total DNA from transgenic rice. GUS, a reporter gene widely used to identify the expression of the target gene, can detect transgenic rice with the content exceeding 1% in mixed rice samples.
The molecular marker technology based on PCR will be widely used in the detection of genetically modified organisms and foods (Kary, B. et al.,1994; Boyce, O. et al.,1998; Nobuaki, S. et al.,1998; Hoef van A.M.A et al.,1998; Hupfer, C. et al., 1998). It can be qualitative and quantitative, and it is more sensitive than protein immunoassay 100 times. But the test results of this technology may be different. Its reliability and sensitivity are affected by three factors: DNA extraction and purification, DNA PCR analysis technology and electrophoresis analysis of PCR reaction products, among which DNA purification and extraction are the key. If DNA is degraded and contaminated, the test results will not reach the expected test results. If DNA degradation and pollutants coexist, there may be false negative results, that is, the test substance itself contains genetically modified substances, but it is not detected. When pollutants exist, false positive results may occur, that is, there is no genetically modified substance, but genetically modified components are detected. All these results may lead to economic disaster for food sellers or buyers.
Robert, M.( 1999) reported that it is worth noting that the transformation of genetically modified organisms into food requires heavy processing, which can effectively remove DNA components, and most of the foods that people eventually eat do not contain new genes at all. In this sense, genetically modified foods have lost the memory of all the genes they added. For example, genetically modified soybean contains herbicide gene, but refined soybean oil does not contain any genetically modified DNA residue, and a trace of protein can be found in unrefined soybean oil, which can be completely removed during refining. Thus increasing the difficulty of detecting genetically modified ingredients in food. The key problem in the detection of genetically modified ingredients in food is that food contains protein such as salt, oil and sugar. In the process of extracting DNA from processed food, it is necessary to ensure the purity of its DNA and not to be polluted and degraded.
The 1998 loop test method proposed by JRC of the European Union almost 44% of laboratories can't completely analyze the genetically modified DNA.
John B. Fagan (2000) introduced a new method. Gene ID method can avoid the above results, while guanidine isothiocyanate extraction method can avoid DNA degradation and pollution. This method is time-consuming and very expensive. Other laws of water solubility cannot be avoided. Gene ID method has the following advantages: 1, which can detect transgenes entering the market; 2. It has a three-level detection system, and only when all three transgenic specific primers are positive can it be judged that there are transgenic components; 3. The sample size is large, which is 10 times larger than the conventional method. Many laboratories only use the sample size that can meet the statistical analysis; 4, rapid and accurate quantification, and qualitative or quantitative results can be obtained within 3 days; 5, widely used in food detection, not only for raw materials, but also for different processed foods; 6, fast, 36-24 hours or 3 working days to get the results. Because of its accuracy and credibility, it is considered to be at the international leading level.
This method has been applied to beans, corn and its derivatives, such as plastic corn, soybean meal, corn germ, tofu (with or without fat removal), corn flour, non-baked soybean meal, fried corn by-product powder, processed and full-fat non-baked soybean meal, fat-removed baked soybean meal, corn gluten pills (electrophoresis technology is improving), concentrated soybean protein, corn paste products, soybean protein isolate, soybean hull and soybean milk (soy milk).
All detection methods are reported as samples containing less than XX% genetically modified ingredients. The genetically modified ingredients in the whole batch of goods or production lines cannot be accurately quantified.
ADM Group of the United States said that it has established a crop identification system to ensure that agricultural products supplied to foreign countries do not contain genetically modified crops.
Three. assess
The safety of genetically modified food is a very important and complicated issue, which should be treated with caution and not be rushed to conclusions.
1, Necessity of food safety assessment: Traditional breeding has a history of 100 years, which is limited to sexual hybridization within species or related species, and no one has ever raised the issue of biosafety assessment. However, genetically modified food is designed according to human intentions and purposes through genetic engineering, which is obviously different from traditional breeding methods. The genes used in genetic engineering come from any organism, and the boundaries between biological species are completely disrupted. The performance of new combinations and traits in different genetic backgrounds still has insufficient impact on the environment and human beings, and some of them are even ignorant, so it is absolutely necessary to evaluate the safety of genetically modified organisms and food.
2. Several problems that should be paid attention to in food safety evaluation: (1), safety is a relative and dynamic concept, and with the passage of time and the improvement of scientific level, the understanding of food safety may change; (2) At any time, food supply cannot be 100% safe. Contaminated foods such as aflatoxin and shellfish toxin still occur today; (3), 100% is never possible without evidence of harmful effects. No one has found that lecithin, soybean oil or soybean starch in transgenic plants have any potential health hazards after eating. Without any assumptions, it is impossible to design a sensitive experiment. The main problem of food safety testing is to ask relevant scientific questions and answer them. If the safety analysis includes all possible variables, it will be too complicated and difficult to deal with. On the contrary, if only a few variables are observed, some important factors may be ignored.
3. The Organization for Economic Development and Cooperation (OECD)( 1993) put forward the principle of food safety analysis-the principle of substantial equivalence, that is, whether the food and food ingredients produced by biotechnology are substantially equivalent to the food currently on the market (WHO,1995; FAO/WHO 1996). The contents of the evaluation include natural toxic substances, nutritional components and anti-nutritional factors, allergens, process characteristics, etc. Who (1995) divides it into three categories, and 1 is "substantially equivalent" to traditional commodities on the market; Second, except for some specific differences, it is "substantially equivalent" to traditional commodities on the market; 3. There is no "substantial equivalence" with traditional food. Considering the diversity of genetically modified organisms, the principle of case analysis should be adopted, that is, genetically modified foods cannot be said to be safe or unsafe. The safety evaluation of genetically modified food mainly includes the safety of marker genes such as toxicity, allergy and antibiotic resistance. However, FDA scientists are worried that genetically modified foods may bring new toxins and allergens, and these new problems cannot be discovered by simple "substantial equivalence" principle. WHO experts also suggested that the safety assessment of genetically modified foods should consider the types of consumers, exposure levels, the impact of food processing on food safety, and potential changes in food nutrition and composition.
At present, the challenge is the difficulty of allergy evaluation in protein, where the allergen source is unknown. It is recommended not to carry out gene transfer on common allergic foods.
4. Safety detection of transgenic plants: To detect acute poisoning, most scientists think that short-term animal feeding experiments can be used. Testing of other harmful substances must be carried out among volunteers. If its substance is not fatal, it can only cause headaches, and animal experiments are impossible to get results. Rabbits can't tell researchers that they have headaches. Allergy can't get results in animals. WHO suggests strengthening the research on detection methods and animal testing methods.
Fourth, look ahead.
At present, governments, social organizations and biological companies represented by the United States, Japan, the European Union and other countries are arguing endlessly about the safety of genetically modified organisms and food, and each has its own views. At the same time, corresponding strict management measures have been formulated. The debate on the safety of genetically modified food has risen from a technical issue to a trade and political issue.
We should not only fully understand the advantages of genetically modified organisms, but also attach great importance to their potential safety problems. So far, the safety of genetically modified food has not been confirmed at home and abroad, and the potential harm caused by genetic and technical instability of genetically modified organisms can not be ignored. The impact on ecology and the prevention of gene transfer between transgenic plants and wild species and weeds need to be controlled more carefully and effectively. Most commercial crops lack information about genetic stability. We should vigorously carry out toxicity and allergy analysis of genetically modified organisms and foods, speed up the research on identification and detection methods of genetically modified organisms and foods, establish a system of "safety monitoring of genetically modified organisms", formulate scientific management regulations, implement effective supervision, widely carry out scientific publicity of genetically modified organisms, and correctly guide public opinion. The author believes that under the premise of legal research, after removing a few unsafe factors, organisms with the advantages of stress resistance, insect resistance, weed resistance, Fusarium wilt resistance, high quality, high yield, drought resistance, frost resistance, added value and renewable energy will be widely used to solve the problem of human food shortage. Genetically modified food is not only accepted by people, but also brings more benefits to human beings.
American scientists are studying a new technology called "chimera transplantation", which can modify genes without implanting foreign genes. Just take a DNA gene fragment and combine it with RNA, just like giving a cell a chemical instruction to change its gene in the required way. Recently developed technology allows other marker genes not to use antibiotic resistance genes. The success of these methods will largely dispel people's doubts about the "genetic pollution" caused by genetically modified foods.