Research On The Method Of Source Analysis Of Heavy Metals In Different Spatio-temporal Regions

Heavy metal pollution in farmland in China is serious,and the safe production of agricultural products has been threatened,which has become a topic of concern all over the world.Because of the complex source of heavy metal emission,the tracing of heavy metal source in farmland seriously hinders the development of source reduction technology.Yangtze River Delta is a typical industrial and agricultural production area in China.The highly developed industry and transportation industry has exported a large number of heavy metals,which leads to the serious deterioration of ecological environment in some areas and has a great impact on human health.However,most studies are devoted to the remediation of heavy metal pollution,but the identification and blocking of pollution sources are not perfect.Therefore,this study will take heavy metal pollution in Yangtze River Delta as the research object,and use different pollution source analysis methods to analyze heavy metal pollution on field scale and regional scale.In order to construct a set of heavy metal source analysis method system with different regional scales,provide theoretical basis for source prevention and control.On the field scale,this study analyzed the current situation of heavy metal pollution in farmland of Shaoxing City by investigating the survey data of soil heavy metal pollution,and predicted the ecological health risk of rice and human body by modeling.On this basis,combined with LCA、PMF（positive matrix decomposition）and CA clustering analysis method,the pollution sources of heavy metals in farmland in small and medium-sized areas of Shaoxing City were studied.The results showed that the content of heavy metals in Shaoxing soil changed greatly.The content of heavy metals in Yuecheng area is higher,followed by Zhuji City,mainly polluted by Cd;third,Keqiao area,except Cr,is higher;Shengzhou City ranks fourth,the Cr and Pb content is higher;Shangyu area soil heavy metal pollution in other counties is relatively small;Xinchang heavy metal pollution load is the lowest,but some areas soil Cr content is still high.Rice throughout the study area is hardly contaminated with arsenic or lead.There is a risk of mercury pollution in Yuecheng District,and cadmium pollution in rice in Zhuji City is serious,especially in Northwest China.Chromium pollution in rice is mainly distributed in the southeast of Zhuji City,central Shengzhou City and central Xinchang County.The predicted concentrations of all metals in the human body are within the range of other research observations,where the Cd and Cr levels in human blood in the study area are greater than the health risks associated with other metals.Therefore,there is a need to identify pollution sources and develop mitigation plans.With regard to small areas（taking six districts and counties of Shaoxing City as an example）,using LCA and PMF to analyze the source of farmland soil at the county level in Shaoxing City,it is found that the pollution sources of each district and county are quite different,and each metal may have different sources of pollution in different districts,counties and cities.The heavy metal pollution sources in Shaoxing city were analyzed by LCA and CA in medium area.The results show that the spatial differentiation of heavy metal pollution types in Shaoxing City can be divided into six major pollution types,but the distribution areas of each pollution type are different,and their different regions show different characteristics of heavy metal pollution.Its pollution sources are also different.On the large regional scale,this study constructed the agricultural emission factor list of artificial cadmium in Zhejiang Province,and estimated the source and sink of artificial cadmium emission in Zhejiang Province by inventory accounting method.The results showed that the anthropogenic cadmium emissions in Zhejiang Province increased from 39 t in 1995to 141 in 2007 t,After 2007,the total Cd emission reached a certain peak with around 140t·a^-1。The majored sink was solid waste which counted more than 75%of total emission.The sinks of atmosphere and water were only about 15%and 10%of total emission.Regarding Cd emission sources,raw coal combustion was the largest contribution with over 50%of total emission.And it followed by iron and steel production,non-ferrous metal smelting,paper production,cement production,plastic production,non-ferrous metal mining,oil consumption,phosphate fertilizer,battery production,flat glass production and ceramic production.For the spatial distribution,the northern area was much higher than southern area.Hangzhou and Ningbo showed very high Cd emission during the study period of 1995—2017 and it was up to over 20 t·a^-1in 2015.To mitigation Cd pollution in Zhejiang,it suggested that focus on reducing raw coal combustion,iron and steel production,nonferrous metal smelting,paper production,cement production,especially in the northern region.It can be seen that this study developed different heavy metal source identification methods for different regional and temporal scales,which can provide better pollution source analysis for field scale and regional scale farmland heavy metals,and provide better suggestions for farmland heavy metal source reduction.