Study On Heavy Metal (Loids) Pollution Characteristics,Sources Identification And Risk Assessment Of Tobacco-Growing Soil In Zunyi City,Guizhou Province

Tobacco is a plant that more easily absorbs and enriched heavy metal（loids）from soils,Importantly,the reactivity and toxicity of these heavy metal（loids）can be much higher via tobacco smoking than via food ingestion.There are numbers of productions and needing of tobacco in China.The condition of tobacco-growing soil has been the key to the quality of tobacco.Meanwhile,the tobacco-growing soil environment is the main factor affecting the heavy metal（loids）content in tobacco leaves.Thus,in order to comprehensively analysis the concentration,sources and pollution level of heavy metal（loids）in the tobacco-growing soil,256 samples were collected of the main farmland in Zunyi city.The content of Cd、Hg、Zn、Pb、Ni and As were measured.Heavy metal（loid）s were analyzed using geostatistical,PCA,CA,Conditional Decision Tree（CIT）,ecological risk and human health risk.The study tends to provide local government with reliable foundation for the comprehensive prevention and control of heavy metal（loids）pollution,and the scientific guidance for efficient utilization of agricultural soil.The main conclusions are as followed:（1）The whole soil of the study area was acidic,with the mean pH value of 6.51,and the organic matter content was between 0.55%and 8.31%,which fertility was low.The mean values of As and Ni were 19.77 mg/kg and 38.43 mg/kg respectively,which were close to the corresponding background values.Besides,the concentrations of Hg,Pb and Zn were0.03～2.21,17.56～118.57and 47.72～315.74 mg/kg,respectively.The super percentage background value was 83.98%,69.92%and 58.20%,respectively.There was the most obvious accumulation of Hg and Pb.As for Cd,the content was from 0.18 to 3.81 mg/kg,with the mean value of 0.66 mg/kg,which was close to its local background value.Compared with GB15618-2018,about 88.3%of Cd were exceeded the risk screening value,the rest of five did not.（2）According to Person correlation analysis,the possibility of homology between Pb and Zn was high.The correlation between Ni and Cd was higher,while the correlation between other heavy metal（loids）was opposite.Besides,from the results of PCA and CA,Pb,As and Zn were mainly from traffic and agricultural sources,and Hg from industrial sources.while Cd and Ni are mainly affected by natural sources.From the CIT’s results,the key nodes of sources were the distance from samples to roads,numbers of factories,continuation situation,soil type,pH and OM.（3）From the perspective of concentration spatial variation,the high value area of Pb and Zn were located in the northeast and central regions with dense traffic.The concentration of Hg decreased from east to west,which was consistent with the east-west decreasing trend of industrial and mining distribution.The distribution of As was obvious in spot,and the influence of intensive agricultural activities was more significant.The trend of Cd and Ni was obviously decreasing from north to south,which was influenced by the mature karst geomorphology and geology in the study area.（4）According to₉),Cd,Hg,Pb,Ni and Zn were slightly polluted,while As was in safety level.According to RI,Cd、As、Pb、Ni and Zn were in the low risk,and Hg was in moderate risk.Because the HI of adult and children were lower than 1,presenting little non-carcinogenic risk to the surrounding population.Meanwhile,the LCR of As and Cd was lower than 10^-6,which was within a safe range.