Home >> News
Stored grain fumigants developments and prospects
From :2004-11-9 "food storage"

     Stored-grain pests by fumigation fumigant can not move in the case of food to the elimination and control of pests of purpose, its economic and other operational measures are second to none. As early as the 11th century BC during the Western Zhou Dynasty, China has used Vitex Ju, Kerry grass, plants, etc.food pesticides to kill pests smoked. From France in 1854 the first combat use of carbon disulfide fumigation, the gradual rise to nearly 40 kinds of chemical fumigants. Many fumigants in use or after use, are a result of such or such a bad performance, has been canceled or Restrictions on the Use. Some countries are allowed to use the main fumigant phosphine, methyl bromide, carbon dioxide, nitrogen, dichlorvos, and hydrocyanic acid, such as chloropicrin. In 1987, China's "grain and oil storage technical specifications" (for trial implementation) provided fumigants include: phosphine (its made for the aluminum phosphide biological tablet, pill, powder and zinc phosphide), chloropicrin, methyl bromide, dichlorvos and so on. However, the application of the above-mentioned several fumigants not optimistic about the prospects.

1. Out of methyl bromide

     Methyl bromide, methyl bromide, also known in Chinese, from the perspective of fumigation insecticide that is an excellent fumigant, applied since the 1950s has been widely used in agriculture, including soil, planting insecticide products and sterilization products, plant products in international trade, as well as immigration and quarantine processing, all types of buildings, such as history, old buildings, warehouses, boat, vehicles, aircraft cabin, food processing plants and so on. However, methyl bromide is a material damage to the environment, can damage the ozone layer in the atmosphere. Deplete the Ozone Layer was substantial, the ability to absorb ultraviolet radiation weakened, leading to ultra-violet rays reaching the earth's surface a marked increase in B, to human health and the ecological environment has brought about many of the hazards, the current widespread concern has been mainly on human health, terrestrial plants, aquatic ecosystems, biochemical cycles, materials, and tropospheric composition and air quality impact. On human health, including potentially dangerous and lead to increased eye diseases, skin cancer and infectious diseases. Experimental proof of ultraviolet damage the cornea and eye lens, such as caused by cataract and other eye lens deformation. According to analysis, the atmosphere of stratospheric ozone by 1% each, the global incidence of cataract will increase by 0.6% ~ 0.8%, the whole world blind due to cataracts caused by the number of people will increase to 15,000 people 10,000; if no measures are taken, From now to 2075, the increase in UV-B radiation will lead to approximately 18 million cases of the occurrence of cataract cases. The increase in UV-B can be clearly induced by regular human beings suffering from three kinds of skin diseases, including the Basel squamous skin tumors and non-malignant skin tumor, a malignant melanoma of the skin is very dangerous, the hazards of light color people especially children is particularly serious. At present, "Montreal Protocol" have been classified as controlled substances environment, environmental assessment of the use of controlled substances of the ozone depletion potential (Ozone depletion potential, referred to as ODP) concept. Provisions, including 95 kinds of controlled substances: CFC, halons, carbon tetrachloride, 1,1,1 - trichloroethane, fluorine bromine hydrocarbons, such as HCFCs and methyl bromide. Ozone depletion substances (Ozone depletion substance, ODS) in the atmosphere the greenhouse effect will have to surface and near-surface air temperature increased, resulting in global warming, environmental issues. With CFCs damage the ozone capacity of 1 compared to methyl bromide to ozone destruction capacity of 0.7. For this reason, international organizations (United Nations Development Program, United Nations Industrial and Development Organization and the World Bank) on the substitution and the abolition of the use of methyl bromide set out a program. Time-out of methyl bromide in developed countries for the 25 percent cut in 1999, 50 percent cut in 2001, 70 percent cut in 2003, all-out in 2005. Developing countries out of time for the 2002 freeze in 1995 and 1998 the average level of 20 percent cut in 2005, all-out in 2015.
     At present, the developed countries have successfully achieved the goal of ODS phase-out. Around the new objectives and the problems faced by the Chinese government began to formulate in 1993 "China's ODS phase-out of national programs" to make amendments. 1999 freeze in 2005 and 50 percent out of 2010 out of 100% of three-phase-out targets in the re-analysis and careful consideration, and to develop a detailed plan of action. From the production, supply, consumption, import and export control, etc. At the same time, the production and consumption of ODS. The Chinese government has approved in April 2003 "Montreal Protocol" and "Copenhagen amendment." In accordance with the protocol, China will be the year 2005 to reduce methyl bromide consumption from 1995 to 1998 the average consumption of 80% by 2015 in addition to quarantine things completely out of methyl bromide fumigation. State Grain Administration of China's grain storage management industry, is determined to implement the Chinese government's decision to work closely with the State Environmental Protection Administration and other departments to implement positive action should be international obligations.

2. But they still face severe challenges for long-term use of phosphine

     Phosphine as a fumigant has been the history of 70 years, for a long time to make some use of unscientific its resistance to insect pests is becoming increasingly serious, at the same time also in the production there were a lot of the failure of fumigation. Phosphine unscientific application of some of the main performance: ① many fumigation building structure from the warehouse on the existence of a congenital lack of the seal, in the late fumigation treatment alone can not meet the simple sealed fumigation requirements, resulting in after application in the absence of a large number of gas distribution to the grain heap of disease of internal parts, especially before the leak, or uneven distribution of grain pile can not be completely killed in various parts of the heap of grain pests, or fumigation with gas in the grain heap maintain an effective concentration, such as lack of time; ② some places using the old method and dose of insecticide can not achieve the desired effect, mistakenly believe that dosage may be too little, in order to kill pests, fumigation again when over - increase the dosage, the result is a pest in the phosphine or a high concentration of high-dose under the protection of coma, which caused the failure of fumigation; ③ There are circumstances that are conducive to low-concentration phosphine fumigation to enhance the effect, without taking into account some resistance to pests is also needed due to the high concentration of the killing, the lack of practice in the fumigation confrontational insect pest population and resistance of the targeted state is considering or dealing with fumigation led to an important cause of failure; ④ In some hydrogen phosphide (AlP) product application note, the proposal after administration sealed 3 to 5 days, was developed to seal 7 or 10 days, these proposals in time for phosphine fumigation seal now appears in many cases far far. Phosphine fumigation in sealed affected by many factors of time, such as grain stack temperature, drug concentration, drug resistance or resistance to pests and so on, can not be generalized; ⑤ many fumigation is carried out under the guidance of dose, in the fumigation only consider unit volume of food or medication dose and the total amount of these agents were applied in the warehouse or grain pile can quickly achieve an effective concentration of insecticide, when the concentration of insecticide to achieve, whether the concentration is too high may lead to pest coma appears to protect, whether there is any fumigation or in part, the low concentration of dead zones exist, the effective concentration is maintained sufficiently long time, this series is basically to use their experience to judge by the feeling, there is no concentration of detection, it is inevitable that fumigation of blindness.
     The use of phosphine fumigation of grain at a reasonable grasp of the gas concentration is essential in practical applications, for different warehouse, at different times, different insect species, different state insect, the degree of resistance to different pests and so on, there will be differences in effective concentration. In general, the concentration of phosphine to kill pests because of confined conditions, ambient temperature, such as the occurrence of pests vary. In order to ensure the insecticide effect, should be prepared to detect the concentration of phosphine gas to various parts of the reactor to ensure that food is always to maintain the effective concentration of phosphine insecticide. This is to avoid the failure of fumigation, and further said that to prevent pest resistance to phosphine in the development of a more important significance. In other words, should the concentration of phosphine fumigation and insecticidal effect of the guidance. Published in 2002 the implementation of LS/T1201-2002 "Technical Specification phosphine fumigation circulation" in the case of different pests in different conditions of temperature, food recommended concentration of 100 ~ 350mL/m3, sealing time 14-28 days in the light of the above value. From the application of the last few years, these basic parameters can guide the successful fumigation, but for some drug-resistant or highly resistant pests, such as Tribolium castaneum rust red flat, the actual fumigation concentration should be on high or higher.
     Phosphine fumigation process to ensure the effective concentration, uniform distribution is related to application technology, methods and means are inseparable. Domestic technology in the application to make a lot of useful to explore more practical and viable technological major release of application method, application generator phosphine positions outside the law, positions outside the cylinder mixture sprayed law. To promote uniformity in the rapid distribution of phosphine, the technology is used for large-scale circulation in the deep grain of the effective ways to stack fumigation. Phosphine circulation of our technology applications in the rapid development in recent years, the level of living in the world's leading from the warehouse outside the mobile and fixed positions outside the loop devices, the development of subendocardial circulation fumigation warehouse, general warehouse from the large-scale applications, the development of to small and medium-sized warehouse, and even open-air grain storage, apart from the position of application development to the natural gas combined circulation of application, such as deliquescence. Loop Fumigation abroad also have a certain development, combined with the use of mixed gas cylinders loaded fumigation of airflow, air recycling law has been recognized, such as the 1980s, developed by BOC Australia ECO2Fume (environmentally friendly fumigant), countries have been registered in South Africa, New Zealand, Cyprus and the United States. Recently, the Australian experts are to promote application of the phosphine generator technology, more of the gas cylinders loaded more economical. Phosphine applications in research and theoretical basis, there are some progress, mainly on the effective concentration of the more detailed exploration, the study of pest-resistant and more and more, such as by the College of Engineering, Zhengzhou, Chengdu Institute of Science and grain storage Guangdong Food Research Institute and Australia's international cooperation projects; Schilpalius (2000) found that more than 200 DNA markers, combined with each other in the genome, described in the Valley valens chromosome 9 gene, including six with the resistance. DNA technology can be used to determine the resistance genes, can be used for rapid detection of synergist, such as resistance and research.

3. Fumigation or face out of the limited capacity of the fumigant

3.1 Dichlorvos

     Dichlorvos to the grain of sand in the proliferation of poor and vulnerable to food absorption, it fumigation warehouses for grain surface, but also to their short positions, processing, packaging equipment, paving the way the insecticide-treated materials. Dichlorvos is toxic to mammals, cholinesterase inhibition, and its toxicity to lift soon, but the pests Dichlorvos cholinesterase inhibition is not easy to revive, so the pest can not be lifted poisoning. Dichlorvos insecticide used for short positions, in particular tall warehouse, after application of the stratified gas will affect the insecticidal effect, care should be taken to maintain high effective concentration.
    The British Government's recent decision to ban the sale of about 50 kinds of pesticides, because they contain could cause human cancer and neurological disorders of dichlorvos. It is reported that this decision is based on the UK Advisory Board of pesticides made. The Commission takes the view does not rule out the long-term exposure to dichlorvos cause skin cancer, liver cancer and the possibility of breast cancer. The decision involving about 50 families are often used to kill flies, moths, wasps and cockroaches and other insects of pesticides. The enterprise has introduced a substitute product does not contain dichlorvos. Scientific research personnel of the carcinogenic properties of dichlorvos will do further study.

Chloropicrin 3.2

     Chloropicrin in accordance with the existing norms can be used to handle grain and plant products, but not fumigate grain products, peanut, sesame, cottonseed, grain seeds (the beans within the safety exception of water) and germinated barley. Not easy to loose as a result of gas, not to use the underground bunkers. Fumigation temperature, preferably above 20 ℃. Chloropicrin is a highly provocative agents tear, can be very small proportion of police to join other agents to act as fumigants. Chloropicrin also has bactericidal and fungicide, and the role of metal corrosion, should pay attention to metal surfaces and equipment protection. Chloropicrin can be strongly irritates the eyes, resulting in lung injury. Articles by fumigation of the reaction product contains residual inorganic nitrates and nitrosamines. The first to use French in 1917, Japan in 1934 banned the valley for rice, the reason for this is that its chemical structure in the nitroso may have carcinogenic effects. 

3.3 hydrocyanic acid

     Hydrocyanic acid in water and high solubility, high water will damage the material. It is a water soluble acid. This acid will not only deal with these items become unpalatable, after human consumption may also be dangerous, and it was also caused by burns, such as the role of wilt or fade. Of higher animals and is a potent poison available, may cause injury to plants for seed security, but not recommended for fresh fruit and vegetables. Hydrocyanic acid adsorption capacity under the strong pressure of some items do not have a strong penetration. Hydrocyanic acid on the human body affect the performance of chronic neurasthenia syndrome, such as dizziness, headache, fatigue, chest pressure, muscle pain, abdominal pain and can cause eye and upper respiratory tract irritation. Long-term exposure to skin may lead to rash, manifested as rash, papules, itching and other great.
     Used as a fumigant to start in 1877, California in 1886 invented in the United States under a tent fumigation with hydrocyanic acid to combat scale insects trees. The 1950s was the main fumigant used in China due to excessive toxicity and economic reasons, such as the convenience of alternative phosphine. Hydrocyanic acid fumigation has been widely used in building structures such as the flour mill warehouse, was more convenient for the use of methyl bromide alternatives. At present in France, Germany, Sweden and Singapore are still allowed to deal with vehicle or building.