[Analysis of Influencing Factors and Sources of Soil Heavy Metals Based on Classification Regression Tree and PMF Model].

To explore the sources and influencing factors of heavy metals in soil at the township scale， 280 surface soil samples were collected from a town in southeastern Chongqing， which served as the research area， and indicators such as As， Cd， Cr， Cu， Hg， Ni， Pb， Zn， pH， and C_org were analyzed and tested. The regional soil heavy metals were evaluated using the land accumulation index method， and the sources of eight heavy metals were analyzed using correlation analysis， cold and hot spot analysis， the classification regression tree model， and the positive matrix factorization （PMF） model. The results showed that the average contents of eight heavy metals， i.e.， As， Cd， Cr， Cu， Hg， Ni， Pb， and Zn， in the study area were higher than the soil background values in Chongqing. The main soil risk factors were Cd， As， and Hg. Distance from residential areas was the most critical factor affecting soil Hg， distance from highways was the most critical factor affecting soil Cd， and distance from industrial and mining enterprises was the most critical factor affecting As and Pb. There are four main sources of heavy metals in the research area， namely， agricultural production sources， traffic pollution and natural parent material composite sources， mining activity sources， and natural parent material sources， which account for 16%， 23%， 31%， and 30% of the heavy metals， respectively. Hg is mainly affected by agricultural production sources， Cd is mainly affected by traffic pollution and natural parent material composite sources， As and Pb are mainly affected by mining activity sources， and Cu， Ni， Zn， and Cr are mainly affected by natural parent material sources.