China is a big agricultural country, and the sustainable development of agriculture is related to the overall situation of national economic construction and social stability. Crop diseases, insects, and grass diseases are important biological disasters for agricultural production. According to the data, there are more than 2,300 kinds of harmful organisms in China. These pests are not only many types, but also widely distributed, and the disaster conditions are complex and frequent. If not controlled, the annual total grain output will be 15%, cotton 20%-25%, and vegetables 25%. The actual annual output of pesticides in China is about 400,000 tons, second only to the United States, which is the second in the world, with an annual consumption of about 270,000 tons, ranking first in the world. According to statistics, in the 1990s, the average annual incidence of pests and diseases in China was 4.4 billion mu, and the area of ​​prevention and control was 4.9 billion mu. The amount of food lost annually was only 65 million tons, equivalent to 325 million. Human rations (calculated at 200 kg per person per year). In the comprehensive management of biological disasters, according to the current level of development of plant protection disciplines, chemical control is still the most convenient, stable, effective, reliable and cheapest means of prevention. Especially when encountering sudden and invasive biological disasters, there is no control method that can replace chemical pesticides. Only chemical control can be effective. In 2000, 2001 and 2002, a large disaster relief occurred, and the effective and rapid control effect of pesticides was a strong evidence. Agricultural production is inseparable from pesticides, now or in the future.
With the development of agricultural industrialization, the production of agricultural products is increasingly dependent on foreign substances such as pesticides, antibiotics and hormones. The use of pesticides in food, vegetables, fruits and tea is high in China, and the unreasonable use of these substances will lead to excessive pesticide residues in agricultural products, affecting the safety of consumers, and causing illness and development of consumers in severe cases. Not normal, even directly lead to poisoning death. Excessive pesticide residues will also affect the trade of agricultural products.
One of the key aspects of controlling pesticide residues in agricultural products is the timely and accurate analysis and detection of pesticide residues in agricultural products to monitor the rational use of pesticides and prevent the listing of products with excessive pesticide residues. At present, there are two main types of pesticide residue detection methods in China: rapid detection of pesticide residues and chromatographic detection methods. The rapid detection method of pesticide residues is mainly used to prevent vegetables and fruits with serious excess of organophosphorus and carbamate pesticide residues from entering the market. Chromatographic detection is the basis for the enforcement of pesticide residues.
1. Pesticide residue laws and regulations
In 1997 and 1999, China promulgated the "People's Republic of China Pesticide Management Regulations" and "People's Republic of China Pesticide Management Regulations Implementation Measures." Article 27 of the Regulations on the Administration of Pesticides as amended on November 29, 2001 stipulates that “the use of pesticides shall comply with the provisions of the State on the safe and reasonable use of pesticides, in accordance with the prescribed dosage, number of medications, methods of administration and safe intervals. Medicine to prevent pollution of agricultural and sideline products. Highly toxic and highly toxic pesticides shall not be used to control sanitary pests, and shall not be used for vegetables, fruits, teas and Chinese herbal medicines." Article 37 provides for "the relevant departments of the people's governments at or above the county level." The detection of pesticide residues in agricultural and sideline products should be done and the test results should be announced." Article 38 stipulates that it is prohibited to sell agricultural and sideline products with pesticide residues exceeding the standard.
Second, pesticide residue rapid detection method
There are many kinds of rapid detection methods for pesticide residues in the world. The principle is divided into two major categories: biochemical assay and chromatographic rapid assay. The biochemical test method uses the biochemical reaction of a certain biochemical substance extracted from the living body to judge whether the pesticide residue exists and the pesticide contamination. The sample does not need to be purified during the measurement, or the purification is relatively simple, and the detection speed is fast. In the biochemical assay, enzyme inhibition and enzyme-linked immunoassay are the most widely used. The chromatographic rapid detection method directly extracts the organophosphorus pesticide residues in vegetables and fruits by simplifying the sample purification step as much as possible. The above rapid detection method can be selected and used according to the actual situation and the respective applicable scope and advantages and disadvantages of the method in a specific application.
(1) Rapid test method for pesticide residues
The rapid detection method of pesticide residues is limited to the detection of organophosphorus and carbamate pesticide residues in vegetables and fruits. It is based on the principle that organophosphorus and carbamate pesticides inhibit the activity of acetylcholinesterase in living organisms to detect the above two types of pesticide residues. .
In recent years, acute poisoning accidents have occurred frequently due to severely excessive consumption of agricultural products. In particular, vegetables and fruits that are highly toxic with organophosphorus pesticides and carbamate pesticides are extremely susceptible to acute poisoning, and even cause consumers. death. Due to the relatively short storage time of vegetables and fruit fresh produce, the market is in urgent need of organophosphorus and carbamate pesticides (the two pesticides have a high proportion of highly toxic pesticides, such as methamidophos, parathion, omethoate, Quick test method for residual toxicity of phorate, carbofuran, aldicarb, etc. The rapid detection method of pesticide residue can quickly detect the above-mentioned two kinds of vegetables and fruits with serious pesticides exceeding the standard. By allowing some vegetables containing pesticide residues to be not allowed to enter the market, the problem of acute poisoning caused by eating prevention can be achieved. At the same time, the method has the characteristics of low-time detection of a large number of samples, low detection cost, low technical requirements for the inspectors, and easy promotion at the grassroots level (such as vegetables, fruit production bases and wholesale markets). An effective method for toxic pesticide residues is also the most widely used rapid detection method for pesticide residues in China. However, the rapid detection method of pesticide residue has its own limitations. For example, the detection of pesticides is limited to organophosphorus and carbamate pesticides, and qualitative and quantitative test results cannot be given. The detection limit is generally high. The international and domestic standards for residue limits are generally high. Therefore, it cannot be used as a basis for legal arbitration. According to the principle of enzyme inhibition method, the Ministry of Agriculture's pesticide testing institute has developed 8 kinds of organophosphorus pesticides such as methamidophos and omethoate, and 10 kinds of carbamate pesticides such as carbofuran and aldicarb. standard. Although the pesticide rapid detection method still has certain defects, it is still widely used in some countries in Southeast Asia such as South Korea, Thailand, Vietnam, and Taiwan and Hong Kong in China. Especially in Taiwan, it has been used since 1985 and has been continued for 16 years. Development has formed a complete set of management systems. The rapid detection method covers 27 kinds of carbamate pesticides such as 27 kinds of organic phosphorus such as fenthion and butyl thiocarbamate. Recently, a variety of speed measuring instruments based on the principle of enzyme inhibition method have appeared in the market in China. The sources of cholinesterase are different, and the discriminating standards are not uniform, resulting in poor comparability of the speed measurement results.
(B), enzyme-linked immunoassay and rapid chromatographic detection
The enzyme-linked immunosorbent assay is a pesticide residue detection method based on the specific and reversible binding of antigen and antibody. The main detection method is the use of a kit. Enzyme-linked immunosorbent assay has the advantages of high specificity, high sensitivity, rapidity and simple operation. Due to the wide variety of pesticides, the preparation of antibodies is difficult (about 50 kinds). When it is not certain that there are certain pesticide residues in the sample, the detection is blind and the antibody is dependent on foreign imports. The application range of enzyme-linked immunosorbent assay is more affected. Big restrictions. At present, the kits for enzyme-linked immunosorbent assays on the market in China rely on foreign imports. There are 15 pesticides , 16 herbicides and 4 fungicides.
The main steps of the chromatographic detection method are: after the sample is extracted, it is subjected to a strict purification step, and qualitatively and quantitatively determined by using techniques such as chromatography or chromatography and mass spectrometry. Conventional Instrumentation In order to maintain high recovery and sensitivity, pre-treatment must be enhanced accordingly, making sample extraction and purification steps more and more time consuming. The gas chromatography rapid detection method greatly improves the detection speed by directly simplifying the purification step and directly analyzing the organophosphorus pesticides in vegetables and fruits after extraction. The biggest advantage of this method is that it can give qualitative and quantitative results of organophosphorus pesticides in vegetables and fruits, and provide arbitration basis. The method covers the detection of residual residues of 74 organophosphorus pesticides in fruits or vegetables, and can include almost all organophosphorus pesticides registered in China. However, the technical requirements of the inspectors are relatively high, and a large investment in testing equipment is required.
Third, pesticide residue chromatography detection method
(1) Extraction and purification of pesticide residues
Peptide residue chromatography is the most complex area of ​​analytical chemistry, mainly for:
1. The amount of residual pesticide to be separated and measured is often in the range of ng (10-9g), pg (10-12g) or even fg (10-15g). A successful analysis requires the correct combination and selection of many operating conditions. Especially the successful application of extraction and purification methods.
2. Analyze the unknown history of sample medication, ie the unknown of the source of contamination and the diversity of sample types.
3. A single sample determination can analyze multiple pesticide residues, ie the requirements for multi-residue analysis.
The extraction and purification technology of pesticide residues is the key to the analysis of pesticide residues. At present, the extraction and separation technology commonly used in pesticide residue analysis in China is still a traditional technique developed in the 1970s, such as Soxhlet extraction, oscillation extraction, variable speed mashing extraction and ultrasonic extraction. There are many shortcomings such as large sample size and extraction. Long time, consume a lot of organic solvents, some are toxic solvents, resulting in a large amount of solvent waste. Residual extraction technology is the bottleneck restricting the analysis speed and analytical efficiency of pesticide residues. Traditional extraction techniques cannot meet the requirements of fast and accurate food safety analysis. In the mid-to-late 1980s, solid phase extraction (SPE) technology and supercritical fluid extraction (SFE) were developed internationally for the lack of traditional extraction techniques.
Based on these technologies, a new generation of extraction technology has emerged since the 1990s, in view of the limitations of its application range or cost. Solid phase microextraction (SPME) has been widely used in pesticide residue testing. It overcomes the shortcomings of liquid-liquid distribution and general column chromatography, and is characterized by high efficiency, simplicity, fastness, safety, reproducibility and easy pre-processing automation. Supercritical Fluid Extraction (SFE): One of the fastest growing analytical techniques available today, and many foreign laboratories have been used as pretreatment techniques for liquid and solid samples. The utility model has the advantages that the organic solvent is basically avoided, the simple and rapid, the selective extraction of the component to be tested and the interference component are minimized, the glass instrument and the laboratory occupied by the general extraction method are reduced, and the operation automation is realized. Matrix solid phase dispersion extraction (MSPDE): first proposed by StarenBarker, with the advantage of no need for tissue homogenization, precipitation, centrifugation, pH adjustment and sample transfer steps. Principle of MSPDE: The solid phase extraction material coated with various polymer supports such as C18 is ground together with the animal tissue sample to obtain a mixture in a semi-dry state and packed as a packing, and then the column is rinsed with a different solvent. Various analytes were eluted.
MSPDE is suitable for multi-residue analysis of pesticides and is particularly suitable for the separation of a class of compounds or the separation of individual compounds, either endogenous or exogenous. In addition to animal tissue, it is also suitable for plant samples. The salient features of these technologies are:
1. Efficient, fast, time-saving, one-step extraction, no need to purify.
2. It consumes little or no solvent.
3. The technical equipment has low cost, simple operation and easy application. It fully meets the three requirements of modern people's environmental friendliness, health and safety and high efficiency in the analysis of pesticide residues. These pre-treatment methods can quickly and efficiently complete the extraction, separation and purification process of multiple or multiple pesticides in the sample in a short period of time, with high degree of automation, greatly shortening the sample preparation time and improving the sample. The extraction rate of pesticides ensures the accuracy of the test data.
(2) Pesticide residue detection method
Developed countries mainly rely on chromatographic detection methods for qualitative and quantitative detection of pesticide residues. At present, common residue detection methods can be divided into multi-type multi-residue detection methods, selective multi-residue detection methods and single-residue detection methods.
For the monitoring of pesticide residues in agricultural products, the multi-residue test method is preferred, and the number of pesticides covered by the selection method is required to be as many as possible. At present, there are many kinds of multi-residue methods in the world, including: German DFG method (detectable 325 kinds of pesticides) and S19 method (detectable 220 kinds of pesticides), US FDA multi-residue detection method (detectable of more than 360 kinds of pesticides) ), the Dutch Ministry of Health multi-residue test method (200 kinds of pesticides can be detected), Canada multi-residue test method (detectable 251 kinds of pesticides). With the introduction of high-tech analytical techniques into pesticide residue detection, developed countries often use advanced pesticide residue detection technology to enhance pesticide residue monitoring. The detection technologies used include gas chromatography and mass spectrometry, liquid chromatography and mass spectrometry, and capillary. Electrophoresis and mass spectrometry, as well as gas phase, liquid chromatography and multi-stage mass spectrometry. The application of these techniques has greatly improved the qualitative capabilities of pesticide residue detection and the sensitivity, detection limits and detection coverage of detection.
Compared with the residue detection methods in developed countries, the current pesticide residue detection technology in China has the following shortcomings:
1) The pesticide residue detection method has a narrow coverage. China has formulated 38 national standards for pesticide residue detection methods (26 single residue detection methods, 9 single pesticide residue detection methods, 2 pesticide residue detection methods 2, and 3 pesticide residue detection methods 1) A total of 72 pesticides were covered; 33 industry standards were established by relevant departments (24 single-residue testing methods, 8 single-agent pesticide multi-residue testing methods, and 2 types of pesticide multi-residue testing methods), covering only 55 pesticide types. Kind. The national standard and the standard mark cover 95 kinds of pesticides, including 72 kinds of insecticides, 8 kinds of fungicides and 15 kinds of herbicides. Among them, the national standard GB/T5009.20-1996 covers 20 kinds of organophosphorus pesticides, GB/T 17331-1998 covers 20 kinds of organophosphorus and carbamic acid pesticides, and the industry standard SN0334-95 covers 22 kinds of pesticides, which is China. At present, the standard methods for pesticide residue detection cover several methods of pesticides. In addition, there are still many pesticide types in national standards and industry standards, which are far from the effective ingredients of more than 400 pesticides currently registered in China.
2) The test method standard has not been updated in time with the development of detection technology. For example, the current international pesticide residue detection methods generally use capillary separation separation technology, and many of the existing detection method standards in China still use packed column separation technology; gas chromatography and mass spectrometry combined with high performance liquid chromatography detection technology are commonly used in the world. Pesticide residues in agricultural products, and the two types of testing standards in China are still blank.
3) Pesticide residue detection technology does not match the limit standard. Among the 197 limit standards of 79 kinds of pesticides that have been formulated in China, 33 kinds of pesticides have matching testing methods, and 46 kinds of pesticides have no supporting testing methods. There are considerable problems in the actual implementation process.
In summary, the research and development of pesticide residue detection method standards in China lags far behind the current monitoring work, but it is not a question of providing technical reserves for pesticide residue testing in the future.
Fourth, the maximum residue limit of pesticides
There are two basic conditions for the monitoring of pesticide residues in agricultural products: one is that there must be a standard for pesticide residue testing methods, and the other is that there must be a pesticide residue identification standard, that is, a pesticide residue limit standard. The maximum residue limit for pesticides refers to the requirements of the prevention and control of various pests and diseases in accordance with the good agricultural practices promulgated by the state or the safe and rational use of pesticides. Under strict technical supervision, under the premise of effective prevention and control of pests and diseases, a series of residual data is obtained. A representative higher value is obtained, which is defined as the maximum residue limit. The residue limit can be used to test whether the farmers strictly abide by the state's regulations on the rational use of pesticides. If the farmers do not comply with the national regulations on the rational use of pesticides, the pesticide residues in the final harvested agricultural products are likely to exceed the maximum residue limit set by the state. The agricultural products are unqualified products. It should not be allowed to sell or export, so the establishment of the maximum pesticide residue limit is conducive to improving the quality of agricultural products in the country and promoting international trade in agricultural products, as well as the protection of domestic agricultural products and pesticide products by means of technical barriers.
The pollution of pesticides in agricultural products has become an increasingly important issue in the world. All countries have made the formulation of pesticide residue standards an important task. Due to the strict requirements for pesticide residues in the importing countries of agricultural products and the looser requirements of exporting countries, and the different dietary patterns of the people of different countries, the residue limit systems developed by countries are often different. In order to reduce disputes between international trades and to be compatible with each other, the FAO/WHO Codex Alimentarius Commission has two organizations dedicated to the development and coordination of pesticide residue regulations and maximum residue limits for pesticides in food: Joint Meeting of Expert Committees on Pesticide Residues (JMPR: Joint FAO/WHO Meeting on Pesticide Residues and CCPR: Codex Committee on Pesticide Residues. JMPR is responsible for the academic evaluation of pesticide safety toxicology, and only modifies the daily allowable intake of pesticides (ADI: Acceptable Daily Intake). It only academically evaluates the pesticide residue test data submitted by governments, pesticide companies and companies, and market monitoring data. , propose the maximum residue limit recommended value. The CCPR is responsible for submitting priority lists for pesticides for pesticide residue and toxicological evaluation, reviewing the draft maximum residue limits for pesticides submitted by JMPR, and establishing the Code of Maximum Residue Limits for Pesticides in Food (and Feed). As of 2002, FAO/WHO has officially promulgated 155 kinds of 2,322 pesticides with the highest residue limit. The United States has developed nearly 10,000 standards for maximum pesticide residue limits. Germany has established more than 3,400 pesticide residue limits for 200 pesticides. By 2002, the Japanese Ministry of Health had developed more than 9,000 MRLs for 218 pesticides. So far, China has formulated 79 national pesticide standards for the maximum residue limit of 197 pesticides in 32 kinds of agricultural and sideline products. Compared with the international advanced countries, the formulation of the current pesticide residue limit standards in China has yet to be further strengthened. In particular, there are prominent problems in the current standards such as the inaccurate classification of crops and the small number of standards.
V. Foreign monitoring of pesticide residues in agricultural products
1. Analysis of pesticide residues in food by EU and UK governments
Under the situation of accelerating global economic integration, the inclusion of technical norms in the scope of laws and regulations has become an effective basis for economically developed countries to develop their economies and protect their own interests. More stringent residue limits are regulated by the European Union 2000/24/EC and 2000/42/EC. The inspection of pesticide residues in agricultural products is also highly valued, such as the UK Government's Special Committee on Pesticide Residues (WPPR), and the establishment of an expert committee formed by a chairperson who can independently exercise administrative powers. Monitoring project for pesticide residues in food. Special investigations and follow-up tests are carried out on all foods, especially those with obvious pesticide residues; 40% of the samples are from imported food. The government spends an annual fee of 1,700,000 pounds, or about 23,460,000 yuan; it tests about 4,000 samples per year and gets more than 80,000 data. Pesticide residues were detected in approximately 34% of the 1996 test results, the amount of which was within the maximum residue limit (MRL), and 1% of the samples had pesticide residues exceeding the specified maximum residue limit. To this end, the British government has strengthened the inspection of pesticide residues and conducted direct sampling tests on domestic agricultural products at the place of production. Advance warnings for agricultural products that exceed the standard before listing, and are not allowed to enter the market. The imported agricultural products are directly tested at the port for pesticide residue. Once the pesticide residue is found to exceed the standard, the import of the entire batch is strictly prohibited.
2. Detection of pesticide residues in tea exported to Europe
As of August 19, 2002, the EU imposed a maximum residue limit of 118 pesticides on tea. The new regulations have a maximum residue limit of 0.1 mg/kg for organophosphorus pesticides and a maximum residue limit of 0.05 mg/kg for triazophos. On August 19, 2002, the EU Directive 2002/71/EC stipulated that the maximum residue limit for dimethoate should be reduced from 0.2 mg/kg to 0.05 mg/kg, which must also be brought to our attention. The problem of organochlorine pesticide residues, due to the significant decline in the amount of BHC in tea since the ban on 666, is no longer the main problem of excessive pesticide residues in exported tea. However, the excess rate of DDT residues in exported tea is still high. The new regulations also add some new pesticides. For example, the maximum residue limit for buprofezin is tentatively set at 0.02 mg/kg. In this pesticide residue limit, a large number of residue limits for herbicides are also added.
Europe is one of the major export markets for tea in China, and it is also a region with high tea prices. The EU and some countries in the world will impose new restrictions on pesticide residues on tea, which will have a major negative impact on China's tea exports, such as not seriously studying. The solution will seriously affect the export volume of China's tea, which will reduce the share of China's tea market in Europe. In the future, it is necessary to strengthen the inspection of pesticide residues in exported tea, especially for the testing of pyrethroids, organophosphorus pesticides, DDT, and dicofol.
The EU proposes to test at least the residues of the following 25 pesticides (including isomers) for tea exported to Europe, such as acephate, dimethoate, methamidophos, triazophos, cyhalothrin, cyfluthrin, Fenmethrin, bifenthrin, fenvalerate, permethrin, fluvalinate, cypermethrin, hexachlorocyclohexane, DDT, dicofol, dicofuron, hexachlorobenzene, endosulfan, thiazine ketone.
3. Provisions, standards and analysis of pesticide residue limits in Japan
The Japanese Ministry of Health and Welfare stipulates that foods must not contain harmful or toxic substances; strictly control the amount of pesticide residues in food. This work is increasingly valued by the Japanese government and nationals. In 1999, the Japanese government conducted 160,000 inspections of pesticide residues in food and drinking water, and 22 of them were found to be exceeding the standard. The government stipulates that all foods with excessive pesticide residues will be destroyed and are not allowed to be imported.
In 1968, Japan established the first maximum residue limit (MRL) for pesticides. At that time, only the maximum residue limit was set for five pesticides. In 1978, the maximum residue limit for 26 pesticides was added. In 1997, 161 pesticides were set. There are 8,000 maximum residue limits. By 2002, the Japanese Ministry of Health had developed more than 9,000 MRLs for 218 pesticides. Among them, the residue limit for vegetable agricultural products is the most complete, and 3,728 maximum residue limits have been formulated for cruciferae, potato, cucurbitaceae, Compositae, mushrooms, Umbelliferae, Solanaceae, Liliaceae, and single-row vegetables. The maximum residue limit was established for vegetable categories such as varieties, such as the MRL for 77 pesticides for Chinese cabbage and the maximum residue limit for 141 pesticides for mushroom products. A maximum residue limit of 122 pesticides was established for rice. Japan is a major exporter of vegetables and rice in China. Taking vegetables as an example, the export volume to Japan in 1999 was 882,200 tons, and the export volume in 2000 was 1.141 million tons. The export volume accounts for more than 40% of China's vegetable export trade. In order to stabilize and expand this major international market for rice and vegetables, we must carefully study the food hygiene and safety standards of Japan.
6. Accelerate the detection of pesticide residues, the study of limited standards and the construction of monitoring systems
1. Faced with a wide variety of rapid measurement methods for pesticide residues in China's market, the test data lacks comparability. It is recommended to quickly standardize the rapid measurement technology of pesticide residues and its supporting reagents, and strengthen the supervision and management of the speedometer market.
2. Intensify the research and standard setting of pesticide residue detection technology. The government should give certain support to the research and development of international standards and foreign advanced testing methods, and the research and development of domestic testing methods. Focus on the development of residual detection methods for agricultural products that are frequently used in agricultural production and affect the import and export trade. Develop long-term plans for standards for residue testing methods based on the needs of the agricultural development phase.
3. Accelerate the research and formulation of pesticide residue limit standards. In the face of the formulation of China's pesticide residue standards, we must first actively carry out research work on international standards, especially the research on the limited standards of China's major agricultural products exporting countries. Second, there are too general and small number of pesticide limit standards in China. It is necessary to carry out combing and speed up the work of supplementing and revising the limited standards. The key point is to formulate the development of limited standards for pesticides that have a great impact on human health and import and export trade. Third, timely understand the rules and latest developments of the standards for standards, and do timely The corresponding policy adjustments are made to protect the interests of producers and consumers of agricultural products in China.
4. Establish and improve the pesticide residue monitoring system for agricultural products as soon as possible. In view of the current problems of unsound system, scattered power and lack of monitoring funds in China's pesticide residues, the government should increase investment in the construction of pesticide residue monitoring system and establish a multi-level system at the central, provincial (district, city), prefecture and county levels as soon as possible. The function clearly covers the pesticide residue monitoring system of production and sales, and realizes the residue monitoring of imported and exported agricultural products. The monitoring of pesticide residues is a social welfare undertaking and requires the support of government investment. The relevant government should set up a pesticide residue monitoring fund every year to ensure that the residue management work is carried out normally.
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