The Survey Of Heavy Metal Content In Cultivation Layer Soil Of The Main Vegetable Production Areas In Lanzhou City

The specific gravity of heavy mentals including approximately forty-five categories is above four or five. Most heavy metals are toxic to human beings, so in the environment they are contaminants.Soil is the offspring of weathering of rocks and volcano eruption. Although the most heavy metals in soil are derived from the environment itself, with the increasing human activities, the pollution by human beings cannot be neglected. The heavy metals in soil are absorded by plants and then enter the food chain. The most concerned problem is that those heavy metals in soil will make harm to human's health.Vegetables are necessary food in human daily life. The quality of vegetables is directly affected by the heavy metal content in the environment of vegetable production area. Lanzhou city has a long history of cultivating vegetables, and the vegetable production plays a key role in rural economic development. To analyze the heavy metal content of vegetables plays a significant part in improving the quality of vegetables, safeguarding the food security and people's heath, and developing the rural economy of the city.In the survey, we collected 570 soil samples from the top soil layer in almost 60 thousands hm~2 of the main vegetable production areas in Lanzhou city, including 308 villages of 60 towns of 6 counties, and analyzed the contents of Pb, Cd, As, Hg, Cr, Ni, Cu and Zn accounting to 3700 data. The results indicate that compared to the average level of Gansu province, the heavy metal content in Lanzhou city's soil for vegetables has an abundance in the order: Hg>Cd>Pb>Zn>Cu>Cr>As>Ni; compared to nationwide level, the order is Cd>Zn>Ni>Cu>Cr>Hg>Pb>As. From the orders, it is very obvious that the pollution level of Cd is significantly higher, so we conclude that the vegetable soil in Lanzhou city is severely polluted by Cd. The reason for that will need a further research. Also, from the total content of eight heavy metals, Honggu district, Yuzhong county, and Yongdeng county are much more polluted than other regions.As a whole, the regions of the survey on the environmental conditions for vegetable production in Lanzhou city are relatively better than other regions, and the contents of eight familiar heavy metals Pb, Cd, As, Cr, Ni, Cu and Zn are relatively normal and without much pollution made by human beings. But with the development of economy and extension of city, it is inevitable for further pollution. We should follow the nationwide implement of the plan for pollution-free vegetables, extend the production of harmless vegetables. We should focus on the production area, protecting the as-yet-unpolluted region, and handling the little polluted area. The aim is to protect the production area from pollution and benefit everyone to take the real pollution-free food.