1, industrial sewage and domestic irrigation water
In some areas of China, a large number of untreated or substandard industrial sewage and urban domestic water will be directly discharged into vegetable fields, resulting in excessive heavy metals in vegetable fields.
2. Abuse of chemical pesticides and organic fertilizers.
Phosphate fertilizer contains many trace elements, some of which are harmful elements, and Cd is a more serious one.
No production process can completely eliminate heavy metals, so long-term application of phosphate fertilizer will make toxic heavy metals enter the soil.
3. Application of mining, smelting, papermaking and municipal waste.
Wastes from mining, smelting, papermaking and other activities will eventually flow into the market if they are not treated or discharged up to standard.
Soil and water, and cause the heavy metal content in soil or water to exceed the standard.
4. Livestock manure
With the development of modern animal husbandry, feed additives are widely used, which often contain a certain amount of heavy metals such as copper and zinc. These heavy metals pollute the environment with the discharge of livestock manure, and the heavy metals in these fertilizers will also accumulate in the soil and become pollution sources.
5. Air pollution
On the one hand, heavy metals discharged into the atmosphere by industrial and mining activities and transportation can enter the soil through sedimentation and accumulate in the corresponding areas, resulting in heavy metal pollution in the soil.
How to distinguish contaminated vegetables?
1. Vegetables with abnormal shapes and colors
Because vegetables with normal shape and color are generally cultivated routinely and have not been treated with chemicals such as hormones, they can be safely eaten. Abnormal vegetables may be treated with hormones, and some vegetables may be treated with hormones during cultivation; However, leek leaves without hormones are narrow and have a strong fragrance.
But some vegetables are not normal in color, so we should also pay attention. It may be that ammonium phosphate pesticide was sprayed or soaked before harvesting. I suggest you not buy it.
2. "Multi-insect" and "multi-drug" vegetables
Among many vegetables, some vegetables are especially favored by pests and can be called "multi-insect vegetables"; Some vegetables are disliked by pests and can be called "insect-free vegetables". This is determined by the different components and odor specificity of vegetables.
Because there are many pests in insect-infested vegetables, they have to be sprayed frequently to prevent and control them, which is bound to become heavily polluted "multi-drug vegetables". Usually, we should try to choose vegetables with fewer pests. If insects hibernate and overwinter in low temperature season and pesticide spraying stops, it is no harm to eat a small amount of insect-damaged vegetables at this time. ____
3. Don't eat greasy vegetables.
Due to the extensive use of chemical fertilizers, especially the excessive use of nitrogen fertilizers, the nitrate pollution of vegetables will be more serious. Nitrate itself is not very toxic to people, but vegetables will be reduced to nitrous acid after entering the gastrointestinal tract, and will combine with secondary amines in the gastrointestinal tract to form ammonium nitrite, which is a carcinogen.