Chemical fertilizers are composed of various salts, so long-term and large-scale application of these fertilizers composed of salts will increase the concentration of the soil solution and produce different sizes when the fertilizer enters the soil. Due to osmotic pressure, crop root cells not only cannot absorb water from the soil solution, but instead flow the water in the cytoplasm back into the soil solution, causing crop damage. A typical example is crop "seedling burning"
After a large amount of pesticides are applied, pesticide residues may be caused or penetrate deep into the groundwater, causing pollution to water sources. The price of garlic has been low in recent years because of excessive pesticide residues and foreign purchasers canceling their purchases. The food we eat may also fail the test, but the awareness of the domestic people is not that high, and the cost of testing ourselves is too high. Ordinary people cannot afford it.
The main environmental problems caused by chemical fertilizer pollution are:
① Eutrophication of rivers, lakes and inland seas. The main cause of eutrophication in waters is the increase in nitrogen and phosphorus content in the water, which causes excessive growth of algae and other aquatic plants.
② The soil is contaminated and the physical properties of the soil deteriorate. Excessive application of chemical fertilizers over a long period of time will cause acidification of the soil. The amount of ammonium ions in the organic and inorganic complexes in the soil solution and on the soil micelles increases, and replaces Ca2+, Mg2+, etc., causing the soil colloids to disperse, destroying the soil structure, and hardening the soil, and directly affects agricultural production costs and crop yields. quality.
③ Toxic components in food, feed and drinking water have increased. Nitrite is 5 to 10 times more biologically toxic than nitrate, and N-nitroso compounds formed by combining nitrite with amines are strong carcinogens (see N-nitroso compounds and cancer). The content of nitrogen compounds in well water or river water in areas where chemical fertilizers are used can increase and even exceed drinking water standards. Soils that are heavily fertilized can increase nitrate levels in crops such as vegetables and pastures. Excessive nitrite content in food and feed has caused poisoning accidents in children and livestock.
Chemical fertilizers also contain other impurities, such as phosphate rock containing 1 to 100 ppm of cadmium and 5 to 10 ppm of lead. These impurities can also cause environmental pollution.
④ The content of nitrogen oxides in the atmosphere increases. A considerable amount of nitrogen fertilizer applied to farmland evaporates directly from the soil surface into gas and enters the atmosphere. A considerable part also enters the soil in the form of organic or inorganic nitrogen. Under the action of soil microorganisms, it is converted from insoluble, adsorbed and water-soluble nitrogen compounds into nitrogen and nitrogen oxides, and enters the atmosphere.
In order to prevent environmental pollution, the chemical fertilizers applied should be controlled and managed.
Organic pesticides Organic pesticides can be divided into organophosphorus pesticides, organochlorine pesticides, organic nitrogen pesticides, organosulfur pesticides, organometallic pesticides, and groups containing nitro, amide, nitrile, mesitylene, etc. Group of organic pesticides. Among the above categories of organic pesticides, organochlorine pesticides have the longest application history; organophosphorus pesticides have the most varieties.
The main organochlorine pesticides used in China are HCH and DDT. Western countries still have cyclopentadiene compounds such as aldrin, dieldrin, and endrin. These compounds are stable in nature, and the time required for half of their degradation in soil is several years or even ten years. They can enter water bodies 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, are stable in nature and have serious residual toxicity in their degradation products, and their use has been banned in most countries.
Inorganic pesticides There are very few varieties of inorganic pesticides used. Inorganic pesticides used in some areas are mainly mercury-containing fungicides and arsenic-containing pesticides. Mercury-containing fungicides such as mercury chloride (mercuric chloride), calomel (mercurous chloride), etc., can harm crops, so they are generally only used for seed disinfection and soil disinfection. Mercury preparations are generally stable in nature, highly toxic, and have serious residue problems in soil and living organisms. Many countries such as China, the United States, Japan, and Sweden have banned their use. Arsenic pesticides include arsenic acid (arsenic), sodium arsenite and other arsenic acid compounds, and arsenic acid compounds such as lead arsenate and calcium arsenate. Arsenous acid compounds are highly toxic to plants and have been used as poison baits to control underground pests. Arsenic acid compounds were once widely used to control chewing mouthparts pests, but they have also been replaced by organic pesticides due to their narrow control coverage and low efficacy.
Pesticide Residues and Pollution Not all types of pesticides have residual toxicity problems (see Pesticide Residues), and different types of pesticides of the same type have different environmental hazards. Different processing forms of pesticides affect the ability of the pesticide to spread and cover the crop surface, whether the sprayed liquid (or powder) can stably stick to the crop surface, and whether the pesticide can penetrate the cuticle of the plant surface without causing damage. Quick dissipation and other effects will have an impact, thereby making a difference in the degree of pesticide contamination of crops. In addition, the physical properties of different formulations of pesticides in terms of loss, leakage and adsorption in the soil are different, so their residual capabilities in the soil are also different.
Pesticide pollution is mainly organochlorine pesticide pollution, organophosphorus pesticide pollution and organic nitrogen pesticide pollution. Humans' intake of pesticides from the environment is mainly through diet. The reasons why plant foods contain pesticides are, firstly, direct contamination of pesticides, and secondly, crops absorb pesticides from the surrounding environment. Pesticides contained in animal foods are ingested by animals through the food chain or directly from water bodies. The concentration of pesticide residues in the environment is generally very low, but through the food chain and bioconcentration, the concentration of pesticides in organisms can increase to thousands or even tens of thousands of times (see the impact of pesticide pollution on health).
Degradation of pesticides Pesticides can be degraded in the natural environment. Organophosphorus pesticides degrade easily. Organochlorine pesticides that are difficult to degrade can also be slowly degraded under the action of microorganisms, ultraviolet rays and other factors. Pesticides also undergo metabolism and degradation in living organisms. Generally speaking, the degradation or metabolites of pesticides are less toxic than their parent substances. However, there are several situations that should be noted: First, some degradation or metabolite products are more toxic than the parent drug. For example, 4-chloro-o-toluidine, the degradation product of chlorpyrichloride, is much more carcinogenic to mice than the chlorpyrichloride parent drug. Second, although the degradation products are less toxic, their properties have changed. For example, the solubility of the degradation products of some pesticides has increased, and the hazards have also increased. Third, some pesticide parents are non-toxic, but their metabolites are toxic. For example, ethylene thiourea, a degradation product formed by dithiocarbamate fungicides, has teratogenic and mutagenic effects on test animals, while parent compounds It won't have this effect. Fourth, the residual toxicity of some pesticides after use is caused by impurities contained in the drugs. For example, the herbicide 2,4,5-T has a teratogenic effect on animals because the product contains the impurity tetrachlorodioxin. Therefore, in what natural environment and in what way pesticides degrade, it is a subject that must be further studied.
Toxicity As for the chronic toxicity of pesticides, except for organic mercury, 2,4,5-T, dipyrmid, etc., there is no definite conclusion yet for most pesticides, including those currently used in large quantities. in conclusion. When evaluating the chronic toxicity of pesticides, in addition to the impact on human health, the impact on organisms should also be considered.
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① Organophosphorus pesticides, as neurotoxicants, can cause neurological disorders, tremors, insanity, speech disorders and other manifestations.
② Pyrethroid pesticides are generally highly toxic and have accumulation properties. Symptoms of poisoning include neurological symptoms and skin irritation symptoms.
③ 666, DDT and other organochlorine pesticides. After organochlorine pesticides enter the human body through food, they are mainly accumulated in fat, followed by liver, kidney, spleen and brain. Passed to the fetus through human milk, causing pathological changes in the next generation