Study On Heavy Metals Pollution In Agricultural Soil Of Important Oasis Cities In Hexi Region

Hexi Region is located in a key part of the Silk Road Economic Zone,it is also the most important agricultural zone in Gansu Province,China.Known as "Gold Zhangye,Silver Wuwei",the two important oasis cities in Hexi Corridor are in unique natural conditions and have rich mineral resources.With the rapid development of industry and agriculture,the agricultural soil of these two major grain production bases is currently threatened by natural pollutants and anthropogenic pollutants including industrial wastes,organic and inorganic fertilizers and pesticides.Due to the variety of human activity,it is difficult for researchers to determine the potential sources of pollutants in agricultural soil.Heavy metals in agricultural soil can be absorbed into ecosystem by crops,but it is difficult to be degraded by microorganisms or chemicals,so they can stay in soil for a long time,deteriorate the soil environment and debase the environment quality.Therefore,it is necessary for controlling the discharge of heavy metal and ensuring the safety of agricultural products to conduct heavy metal source apportionment and pollution and health risk assessment based on source contribution in agricultural soil in the study areas.By studying in Wuwei and Zhangye,sources of pollutants,results of pollution assessment and health risk assessment can be collected,which are very meaningful for us to make plans from the perspective of source.To get the information of heavy metals in Wuwei and Zhangye agricultural soil,92 and 80 sampling sites were posited in agricultural soil of Wuwei and Zhangye.All the samples in this study were used to get concentration of heavy metals by Olympus Delta Professional Handheld X-ray Fluorescence Analyzer.Receptor models are always used in identifying pollutant sources and quantifying source contribution,so they can help preventing environmental pollution and controlling pollution,but their application in agricultural soil is relatively few.In this study,the agricultural soil of oasis in northwest China was studied.Three receptor models,namely Grouped Principal Component Analysis/Absolute Principal Component Scores(GPCA/APCS),Positive Matrix Factorization(PMF),and UNMIX,were used tentatively.Results of sources,source contribution and model performance by three models were compared.It can be concluded that these three models supplemented each other,and GPCA/APCS was outstanding.In Wuwei,results from GPCA/APCS and UNMIX suggested that agricultural activities were the prime anthropogenic source(51.06%–61.56%),followed by the combustion of fossil fuels(coal and oil)(27.92%–28.66%)and building materials-related activities source(10.52%–20.29%).Fertilizers and pesticides(67.88%–74.81%)contributed more than traffic emissions(25.19%–32.12%)in agricultural activities.Similar results were acquired via positive matrix factorization(PMF),while industrial activity was the highest individual contributor(29.91%).In Zhangye,atmospheric sediment source(steel industry and traffic source and leather and metal processing industry source)by GPCA/APCS and PMF is the greatest contributor,which account for 62.70% and 53.13%,respectively.While the contribution of mining activities is the lowest,which account for 15.85% and 19.18%,respectively.Therefore,combining these models was the most effective approach.Based on the source contribution by GPCA/APCS,heavy metals from different sources were evaluated by fuzzy synthetic evaluation model and health risk assessment model.The results of source apportionment showed that traffic emissions of Lead(Pb)and the use of chemical fertilizers,pesticides produced by the process of Copper(Cu)in Wuwei agricultural soil were in high level of fuzzy synthetic evaluation.In Zhangye,the pollution levels of Chromium(Cr)derived by leather industry and metal processing industry and Nickel(Ni)derived by steel industry and traffic source were higher.Based on source contribution,health risk assessment revealed that the non-carcinogenic and carcinogenic risks of Cr derived by combustion of fossil fuels(coal and oil)in Wuwei,Cr derived by leather industry and metal processing industry and Lead(Pb)derived by steel industry and traffic source in Zhangye were higher.