HCH and DDT are the main organochlorine pesticides used in China. Western countries have cyclopentadiene compounds such as aldrin, dieldrin and endrin. These compounds are stable in nature, and it takes several years or even more than ten years to degrade half of them in soil. They can enter the water body with runoff, drift around the world with the atmosphere, and then fall to the ground with rain and snow. Therefore, organochlorine pesticides can also be detected in Antarctica and Greenland. Some organometallic pesticides, such as organomercury fungicides, have stable properties and the residual toxicity of degradation products is quite serious, so most countries have banned their use. Not all kinds of pesticides have the problem of residual toxicity (see pesticide residues), and the harm of the same kind of pesticides to the environment is different. Different processing forms of pesticides will affect the spreading and covering ability of pesticides on the surface of crops, whether the sprayed liquid (or powder) can be stably attached to the surface of crops, and whether the pesticides can penetrate into the cuticle of the surface of plants without rapid loss, so that the pollution degree of pesticides to crops will be different. In addition, the physical properties of loss, leakage and adsorption of different pesticide formulations in soil are different, so their residual capacity in soil is also different.
Pesticide pollution mainly includes organochlorine pesticide pollution, organophosphorus pesticide pollution and organic nitrogen pesticide pollution. People mainly take pesticides from the environment through diet. There are two reasons for the presence of pesticides in plant foods, one is the direct pollution of pesticides, and the other is that crops absorb pesticides from the surrounding environment. Pesticides contained in animal foods are ingested by animals through the food chain or directly from water. The residual concentration of pesticides in the environment is generally low, but the concentration of pesticides in organisms can be increased to thousands or even tens of thousands of times through food chain and biological concentration (see the impact of pesticide pollution on health). Due to the extensive use, improper abuse and non-degradability of pesticides, it has caused serious pollution to the earth, and then threatened the safety of human beings.
1962 ~ 197 1 year, during the Vietnam war, the United States sprayed 6,434 liters of defoliants-2,4-d (2,4-dichlorophenoxyacetic acid) and 2,4,5-t (2,4,5-trichlorophenoxy) to Vietnam. 2,4-D and 2,4,5-T also contain highly toxic by-products dioxin. As a result, a large number of Vietnamese suffer from liver cancer, miscarriage of pregnant women and neonatal malformation. This proves that organochlorine pesticides have serious toxic effects. Since then, the United States and other western countries have banned the use of organochlorine pesticides in their own countries, and China has also banned the production and use of organochlorine pesticides in 1983.
According to statistics, the annual use area of pesticides in China reaches 65.438+0.8 billion hectares. Since the 1950s, 6.66 has reached 4 million tons, DDT has exceeded 500,000 tons, and contaminated farmland is 6.5438+0.33 million hectares. The residues of 666 and DDT in farmland topsoil were 0.72× 10-6 and 0.42× 10-6 respectively. The total amount of DDT accumulated in soil is about 80 thousand tons. The detection rate of organochlorine in grain is 100%, and the over-standard rate of 666 in wheat is 95%.
After the production and use of organochlorine pesticides were banned in 1980s, they were replaced by organophosphorus and carbamate pesticides, but the toxicity of some pesticides was 10 times or even 100 times that of organochlorine, and the detoxification coefficient of pesticides to the environment was higher than 1983. In addition, although the residues of these pesticides are very low, some of them will form combined residues with soil, although they can temporarily avoid decomposition or mineralization. Because pesticides are generally applied by spraying, organic solvents and some pesticides in pesticides will float in the air and pollute the atmosphere; Farmland is washed away by rain, and pesticides enter rivers, thus polluting the ocean. In this way, pesticides are carried around the world by airflow and water flow, and pesticides in residual soil can reach the depths of strata through infiltration, thus polluting groundwater.
According to the report of the World Health Organization, the air above London 1 ton contains about 10 microgram of DDT, and the rain contains about 7×10-12 ~ 400×10/2, which is produced all over the world. From 1994 to 1998 in a southern province of China, the polluted area of fishery waters reached more than 450,000 hectares, and more than 800 pollution accidents occurred. Pesticides in water are transmitted and concentrated through the food chain of phytoplankton-zooplankton-small fish-big fish, and finally reach human beings and accumulate in human bodies. Improper pesticide abuse leads to drug resistance of pests and bacteria. According to statistics, the number of pests with drug resistance has increased from 1 and 99 1 to more than 800, and at least 50 species of pests in China have developed drug resistance. The emergence of drug resistance led to the increase of dose. The dilution concentration of dimethoate, dichlorvos and other common pesticides was increased from the conventional11000 to 1/500, and the dilution multiple of some pyrethroid pesticides was also increased from 3000 to 5000 times to1000 times.
In the early 1980s, the control of cotton bollworm and cotton aphid in China only needed pyrethrum insecticide for 2-3 times, with the dosage of 450ml/ha each time, and the damage could be controlled throughout the growing season. In 1990s, the resistance of cotton aphid to this kind of insecticide has exceeded 1000 times, and the control effect has been ineffective. Helicoverpa armigera has also produced several hundred times to several thousand times of resistance to it, and has been controlled for 8 ~ 65,438+00 times, or even more than 20 times, and the control effect is still far lower than that in the early 1980s.
When pesticides and fungicides are used in large quantities and in high concentrations, many natural enemies of pests are killed, the ecological balance of nature is destroyed, and a large number of pests and diseases that have not caused serious harm in the past occur, such as red spiders, scale insects, leafhoppers and various soil-borne diseases. In addition, pesticides will directly lead to the rapid reproduction of pests. In the late 1980s, rice planthoppers were treated with methamidophos and triazophos in Hubei, which stimulated them to lay eggs by more than 50%. After 7 ~ 10 days, rice planthoppers became rampant again. This vicious cycle of using pesticides not only increases the cost of prevention and control, but also reduces the benefit, which is more serious, leading to an increase in human and animal poisoning accidents.
Long-term and large-scale use of chemical pesticides has not only killed the natural enemies of pests, but also killed insects that are harmless to human beings, affecting insects-eating creatures such as birds, fish and frogs; In areas where pesticides are produced and applied in large quantities, casualties of non-target organisms such as birds, animals, fish and silkworms also occur from time to time. According to the report published by the World Wildlife Fund 1998, if the biological index of the earth was 100 in 1970, it had dropped to 68 in 1995. In a short period of 25 years, 32% of the living things on the earth have been extinct. During this period, the marine life index decreased by 30%.