Factors Affecting the Translocation and Accumulation of Cadmium in a Soil-Crop System in a Typical Karst Area of Guangxi Province, China

Abstract

To understand the main factors influencing the translocation and accumulation of cadmium (Cd) in soil-crop systems in typical karst areas, 68 sets of paddy soil and rice grain samples were collected in Guangxi Province. These were used to analyze Cd concentrations and soil properties (pH, organic matter (OM) content, oxide content, and texture). Spearman's correlation coefficients and principal component analysis (PCA) were used to examine the effects of soil properties on Cd concentrations and identify the main influencing factors. The studied soils were highly enriched in iron oxide (TFe2O3), aluminum oxide (Al2O3), and manganese oxide (MnO) compared to background levels, with average concentrations of 20.2%, 19.0%, and 0.2%, respectively. However, the soils are relatively depleted in silica (SiO2), with an average concentration of 41.0%. The soils are strongly weathered and leached in study area, giving rise to rich occurrences of Fe-Mn nodules. The concentrations of TFe2O3 and MnO in the study soils were significantly correlated with soil Cd, rice seed Cd, and the Cd bioconcentration factor (BCF). The PCA analysis further showed that TFe2O3 and MnO in soils were the main factors affecting the migration and enrichment of Cd while soil pH, OM, and Al2O3 had less of an influence. Furthermore, SiO2 and soil texture indirectly affected the migration and enrichment of Cd. It is suggested that the Fe-Mn nodules effectively adsorb and immobilize Cd in the study area soils, acting as a heavy metal scavenger that reduced the biological accessibility of Cd.