Heavy metals that enter the soil as the atmosphere subsides
Heavy metals in the atmosphere mainly come from gases and dust generated by energy, transportation, metallurgy and construction material production. Except for mercury, heavy metals basically enter the atmosphere in the form of aerosols and enter the soil through natural sedimentation and precipitation.
Heavy metals entering the soil with sewage
Due to the shortage of water resources and increased pollution, many farmers use sewage as an irrigation water source. According to the source and quantity, sewage can be divided into urban domestic sewage, petrochemical sewage, industrial mine sewage and urban mixed sewage.
Heavy metals that enter the soil with solid waste
There are many types of solid wastes and complex components. Different types have different hazards and pollution levels. Among them, mining and industrial solid waste pollution is the most serious. During the stacking or treatment of this type of waste, heavy metals are easily moved due to sunlight, rain, and washing, and spread to the surrounding soil and water in a radial or funnel shape. Some solid waste is directly or through processing applied as fertilizer into the soil, causing heavy metal pollution in the soil. Some solid waste comes from sewage treatment.
Heavy metals that enter the soil with agricultural materials
Pesticides, chemical fertilizers and plastic film are important agricultural materials, which play a major role in promoting the development of agricultural production, but long-term unreasonable application can also lead to heavy metal pollution in the soil. The content of heavy metals in fertilizers is generally phosphate fertilizer> composite fertilizer> potassium fertilizer> nitrogen fertilizer.