Research On Heavy Metal And Its Main Pollution Sources In The Whole Country And Typical Northern Agricultural Soils In China

Heavy metals could enter agricultural soils via sources such as atmospheric deposition,livestock manures,fertilizers,sewage irrigation,sewage sludge,causing potential hazards to human health.Therefore,in order to control the heavy metal contents in agricultural soils and to maintain the food safety,it is urgent to find out the main sources of heavy metal pollution in China.With the continuous development of economic and industrial structures and agricultural planting habits as well as the differences in geographical conditions and climates in different regions,it is of great significance to renew the main sources of heavy metals in time in China,North and South China,and to explore the initial sources of heavy metals in atmospheric deposition.In this study,the main sources of heavy metals in agricultural soils in China and different input amounts of various pollution sources between North and South China were obtained by using the input-output inventory method.Meanwhile,Wuqing district in Tianjin City was selected as a typical farmland in northern China to explore the contents,chemical forms and morphological changes of heavy metals in atmospheric particulate matter as the main carriers of heavy metals in the atmosphere.In addition,further source identification of heavy metals in Wuqing District were studied to control the accumulation of heavy metals in the soil.The main research results are as follows:?1?Atmospheric deposition was the main pollution source of the total As,Cd,Cr,Hg,Ni,and Pb inputs,with livestock manures was the main source of total Cu inputs.However,due to industrial structure,geographical condition and the characteristics of economic development,the contribution of different sources to heavy metal pollution varies in different regions.For example,atmospheric deposition was the most important contributor in North China with its highly developed heavy industry and more coal combustion,while the contribution of livestock manures was obviously higher in South China due to its flourishing agricultural production and animal husbandry.?2?The mass concentrations of PM_2.5 and PM₁₀ in the agricultural areas in Wuqing District of Tianjin City is higher than that of National Secondary Air Quality Standard.The mass concentration and bioavailability of PM_2.5 are higher than that of PM₁₀,which indicates that the smaller particle size,the stronger ability to carry heavy metals and the greater environmental hazard.In addition,heavy metals in PM₁₀ mainly from natural sources?such as soil,dust,etc.?,while heavy metals in PM_2.5 mainly from industrial activities,such as exhaust emissions from coal combustion in winter,in the study area.?3?The accumulation of heavy metals in surface soils in Wuqing District of Tianjin City decreased in the order of Cd>Cr>Cu>Zn>Pb>Ni,and 26.7%of Cd exceeded the Second Standards of Soil Environment?GB15618-2018?.Relatively higher proportion of exchangeable Cd,Cu and Zn in the surface soil might increase the potential risk of heavy metal in agricultural soils.The principal component analysis showed that Cr and Ni may derive from soil parent material,Zn may from agricultural activities?such as livestock manures?,Cd,Pb and Partial Cu may derive from exhaust emission in the process of industrial activities through atmospheric deposition.In Wuqing District of Tianjin,industrial activities and exhaust gas emissions such as coal burning in winter could cause the accumulation and relatively high bioavailability of heavy metals in PM_2.5.Ultimately,the heavy metals could be accumulated in the agricultural soils through atmospheric deposition.Therefore,more attention should be paid to controlling the effects of industrial activities on the accumulation of heavy metals in agricultural soils in Wuqing.