Analysis Of Sources Of Heavy Metal Contamination Using Receptor-based Modelling And Cd Isotope Tracing In Arable Soils

Industrial activity is an important source of heavy metal pollution in soil.Chongqing,as an old industrial base in southwest China,has undergone rapid industrialisation and urbanisation since its direct administration,which has brought about increasingly serious problems of heavy metal pollution in soil,and analyzing the sources of heavy metals in contaminated arable soils is an important prerequisite for implementing pollution source control and safe utilization of arable soils.Therefore,in this study,the content and spatial distribution characteristics of eight heavy metals(Cd,Hg,As,Pb,Cr,Cu,Ni and Zn)in soil and crops were analyzed in a concentrated contaminated arable land in Chongqing,and the Nemero integrated pollution index,ground accumulation index,potential ecological risk index and health risk model were used to evaluate the characteristics,environmental risk and health risk of heavy metal contamination in soil and crops.The study combined geostatistics,multivariate statistical analysis,receptor modeling,input fluxes and isotope tracing to analyze the sources of soil heavy metal pollution and provide a scientific basis for precise prevention and control in arable soils.The main results are as follows:(1)The mean contents of soil Cd,Hg,As and Pb in the study area were higher than the background values of soils in Chongqing,among which the mean contents of Cd and Hg were 4.1 and 2.1 times higher than the background values,respectively,with 11.8%of the samples showing that the soil Cd contents exceeded the risk screening values of the Soil Environmental Quality Risk Control Standards for Soil Pollution on Agricultural Land(Trial)(GB 15618-2018).The Cd and Hg contents of surface soil were significantly higher than those of the lower and middle layers(P<0.05),showing that they were more accumulated in the surface soil and were greatly influenced by anthropogenic activities,which needs to be paid more attention to.(2)The results of the the Nemero integrated contamination index indicated that the soil in the study area was contaminated with heavy metals,with Cd as the primary contaminant.The results of the potential ecological risk assessment also showed that the ecological risk of soil Cd was relatively high,which has reached an intense ecological risk level,and should be treated as a priority contaminant for pollution control and risk management.(3)The results of the soil and crop health risk assessment indicated that hand-tomouth intake is the main exposure route for soil heavy metals.The non-carcinogenic and carcinogenic risks of soil heavy metals for both adults and children were within acceptable limits,but children are more sensitive to heavy metals and it still requires attention.Cd and As are the main non-carcinogenic risk elements for crops,while Cd is the main carcinogenic risk element for crops,and rice consumption is the main risk exposure pathway to human.Cd should be included as the priority pollutant in pollution control and risk management.(4)The positive definite matrix factor model identified three sources of pollution,namely natural sources,industrial sources and mixed traffic and agricultural sources.The contributions of natural sources to As,Ni,Zn and Pb pollution were 56.98%,48.42%,39.34% and 34.42%,respectively,the contributions of industrial sources to Cd,Cu and Cr were 73.38%,66.25% and 54.07%,respectively,while the contributions of mixed traffic and agricultural sources to Hg was 49.00%.The contribution of these three sources(industrial sources,traffic and agricultural sources and natural sources)contributed73.38%,19.58% and 7.04%,respectively,to Cd pollution in soils.(5)Soil Cd input flux analysis showed that atmospheric deposition contributed89.17% to the total Cd input,followed by irrigation water(10.44%,with other input factors contributing less than 0.39%.Cd isotope analysis further indicated that Cd accumulation in surface soils which were far away from industrial enterprises was mainly influenced by concentrated emissions of smoke and fly ash released from the enterprises,while Cd accumulation in surface soils which were closer to the enterprises was mainly influenced by unorganised emissions of the transportation and depositon of raw and auxiliary materials as well as slag.