Interactions and quantification of multiple influencing factors on cadmium accumulation in soil-rice systems at a large region

The accumulation of Cd in soil-rice systems at a large region is often extremely complicated due to environmental heterogeneity and the interactions of multiple influencing factors. However, the interactive effects and quantification of the contributions of influencing factors on Cd accumulation in large regions remain unclear. In this study, conditional inference trees and random forest analysis were used to identify the interactions of various factors (soil properties, topography and demographic-economic), and quantify their contributions to Cd accumulation in soil-rice systems of Sichuan-Chongqing region, China. The results showed that Cd content in the soil was the most significant influencing factor on Cd accumulation in soil-rice systems, especially bioavailable Cd in soil contributed to 35.73 % and 54.78 % for soil total Cd (Cdsoil) and brown rice Cd (Cdrice), respectively. Population density (PD) and elevation contributed 31.16 % and 27.40 % to Cdsoil content, respectively, and their interaction promoted the increase in Cdsoil content. Moreover, PD played a leading role in Cdsoil content when the elevation exceeded 324 m. The relative importances of slope and elevation for Cdrice content were 16.81 % and 8.49 %, respectively, and their interaction facilitated the increment of Cdrice content. As soil pH, gross domestic product (GDP) and slope decreased, the interaction of soil pH with GDP led to the increase of bioavailability factor (BAF), and that with slope enhanced the bioaccumulation factor (BCF). In addition, soil pH, PD and elevation were of considerable importance for the migration and transformation of Cd, with contributions of 22.11 %, 12.90 % and 12.52 % to BAF, and 5.05 %, 5.62 % and 5.50 % to BCF, respectively. This study is hopeful to provide a scientific insight into the prevention and control of Cd contamination in soil-rice systems at a large region. [Display omitted] •The synergistic interaction of soil pH and GDP enhanced the bioavailability of Cd.•The interaction of slope with elevation facilitated the increase of Cd content in brown rice.•Quantified contributions to Cd accumulation: soil properties > economy > topography.•More attention should be paid to the effects of population density and elevation on Cd accumulation.