Heavy Metal(loids) in typical Chinese tobacco-growing soils: Concentrations, influence factors and potential health risks.

The level of concentration of heavy metal (loids) in tobacco-growing soils is detrimental to soil quality. In this study, 256 topsoil samples were collected from Zunyi city to understand the concentration, spatial distribution characteristics, sources and health risks of heavy metal (loids) by using mathematical statistics, geostatistical analyst, and conditional inference tree (CIT). The results showed that the average contents of Hg, Pb, Zn, and Cd in tobacco-growing soils were high with 1.7, 1.2, 1.1 and 1 times the background value, respectively. While, Ni, Cr, Cu and As were temporarily within the permissible limits. Concentrations of Hg, Cd, Pb, and Zn in the soils of Wuchuan, Tongzi, Daozhen, and Yuqing were much higher than the other regions due to human activities. According to the CIT, the main nodes were 1) distance from sampling to the main road, 2) organic matter, 3) factories, and 4) soil types. The results indicated that for Pb and Zn, the sources of pollution might be transportation; for Cu, As, and Cd, the sources were utilization of phosphate, tobacco-specific fertilizers, and organic fertilizers; and the sources of Hg were coal combustion and metals smelting. In addition, high background values of heavy metal (loids) in karst landforms were responsible for the accumulation of Cd. With respect to Hazard Quotient and Lifelong Carcinogenic Risk, the exposed individual was unlikely to experience obvious adverse health effect due to the heavy metal (loids) pollution, except Cr, which should be particularly considered in further risk control.