The environmental pollution caused by intensive pig raising has received global attention. A large amount of inorganic trace elements such as copper (Cu), zinc (Zn), and iron (Fe) are used in pig feed due to low absorption and utilization rate, and trace elements are excreted in large amounts in the feces, causing serious pollution to the environment (soil, water system, etc.). In the production of pigs, the use of high copper as a growth promoting additive is quite common. The amount of trace elements such as zinc and iron is also higher than the recommended amount. Therefore, people are paying more and more attention to the technical improvement and pollution control of large-scale pig farms.
1 Hazard of high-dose trace elements
In the pollution of the environment caused by modern animal husbandry production, trace elements such as copper and zinc account for the majority. Although high-dose inorganic trace elements can improve pig performance and prevent certain intestinal diseases, pigs have to digest and absorb inorganic mineral elements with low utilization rate, so they must be added in excess to play the role of application. . This not only leads to over-nutrition and economic waste of trace elements in animals, but also causes serious pollution to the ecological environment. According to reports, the amount of trace elements used in China is 15-18 million tons per year. However, due to its low utilization rate, about 100,000 tons of minerals not used by animals are polluted by excreta and urine.
Generally, the amount of inorganic trace elements such as copper in the feed is 20-40 times of the normal requirement of the body. 90% of the copper in the feed is excreted by feces, and copper is a non-degradable substance, which will inevitably cause serious pollution of soil, water and vegetation. Impede the development of environmentally friendly agriculture.
1.1 Impact on soil ecological environment
Taking copper as an example, the copper content in the soil is generally between 1-20 mg/kg. When the copper content in the soil is higher than this value, it will affect the soil. Soil microbes are an important part of the soil. When the copper content reaches 100ppm, the protein structure can be destroyed, the microbial protein can be denatured and die, resulting in soil compaction and soil fertility decline.
In Japan, copper is a hazardous substance in laws that prevent soil pollution in agricultural land. According to the report of the Japan Soil and Fertilizer Society, the copper content in the soil should not exceed 80 ppm. According to Japanese reports, if copper in the pig manure is left in the soil, the copper content in the soil will exceed the above limit within 23 years. According to Japanese experts, if zinc in all pig manures stays in the soil, the zinc content will exceed the standard (120mg/kg) in 17 years, and the contaminated land will not be arable.
1.2 Impact on plants and aquatic ecological environment
Copper contamination of the soil can also cause plant growth to be hindered, resulting in reduced crop yields and crop nutrient content. It also affects the amount of other nutrients in the plant. Excess copper can also lead to changes in plant populations, plants that can adapt to high copper, and those that cannot adapt will be eliminated, causing the extinction of certain plant species. Plant organic matter is consumed by herbivores, and herbivores are eaten by parasites, carnivores, scavengers, and soil invertebrates and microorganisms. Therefore, the curvature of plants will undoubtedly affect the entire food chain.
When the amount of copper in the water is excessive, some algae will be seriously affected, and most of them will die, which will lead to the extinction of some aquatic organisms, causing the fish to die in large quantities due to lack of food. In addition, if trace elements such as copper and zinc in the feces enter the water in a large amount, the water quality may deteriorate, resulting in fish poisoning and death, and damage to the ecological environment.
Zinc is more toxic to fish and aquatic organisms. Therefore, the fishery water quality requires zinc content within 0.1 mg/L. When the zinc concentration in water is 10 mg/L, the water becomes turbid, and at 4 mg/L, odor is generated. Significantly inhibit the biological oxidation of water.
1.3 Harm to the pig industry and human health
High copper can not only cause copper poisoning in pigs, but also cause some nutrients (such as VA, VD, VE, VB2) in pigs. When the copper content in the feed is as high as 250ppm, it has a bad influence on pork quality, which leads to food safety problems. . In view of the hazards of high-dose trace elements, at present, the United States, Britain, Germany and other developed countries no longer advocate the addition of high-copper and high-zinc feed; the United States does not allow the use of high-copper preparations in feed; the Canadian National Feed Association will use copper in the diet. The maximum limit of zinc and zinc is specified as 125mg/kg and 500mg/kg respectively; in the Netherlands, high copper and high zinc are no longer allowed to be used as growth promoters in the diet; Japan uses strict amounts of copper and zinc. limit.
China's limited food hygiene standard for meat products (GB 15199-94) stipulates that the copper content in pork does not exceed 10ppm. High-copper diets can increase the copper content of pig liver by 10-15 times. People who eat copper-containing animal products can cause copper to accumulate in liver, brain and kidney tissues, increase the level of free radicals in the body, and change lipids. Metabolism causes atherosclerosis and accelerates cell aging and death. At the same time, the food safety and hygiene of pig products will also limit the export of pig products in China and restrict the development of pig industry in China.
After long-term exposure to arsenic (As) by feed production personnel, skin damage or even skin cancer can occur, and a small number of workers can develop lung cancer. Inhalation of a large amount of zinc oxide (ZnO) dust can cause zinc poisoning. Generally, zinc poisoning can occur when inhaling 40 mg of zinc, and zinc poisoning symptoms are observed after inhalation of 80 mg.
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