Heavy Metal Accumulation in Maize and Wheat in Acidic Soil: A Comparative Study

Maize and wheat grains are at significant risk of accumulating excessive heavy metals in acidic soils, but relatively few comparative studies have been conducted on the two. This study employed Spearman correlation analysis, random forest modeling, and structural equation modeling to systematically investigate the interdependences between soil properties and heavy metal accumulation (Cd, Cr, As, Pb, Hg) in cereal grains. The results revealed distinct patterns in heavy metal content sequences between wheat and maize grains: maize exhibited Cr > Pb > As > Cd > Hg, while wheat followed Cr > Pb > Cd > As > Hg. Bioconcentration factor (BCF) sequences differed significantly, showing Hg > Cd > As > Cr > Pb in maize versus Cd > Hg > As > Cr > Pb in wheat. Soil cation exchange capacity demonstrated the strongest influence on Cd accumulation in both crops. Arsenic accumulation mechanisms displayed species-specific dependencies, with wheat primarily regulated by soil organic matter and maize by clay content. Notably, a significant positive correlation (p ≤ 0.05) between As and Pb concentrations was observed in both crops, suggesting potential homologous pollution sources. These findings elucidate crop-specific heavy metal accumulation mechanisms governed by soil physicochemical properties. This study demonstrates that under similar growing conditions, maize (BCF = 0.068) exhibits a weaker ability to accumulate heavy metals compared to wheat (BCF = 0.467). Moreover, maize and wheat showed distinct responses to soil properties, particularly in their accumulation of As and Cd. By addressing heavy metal contamination in acidic soils, this work supports the development of safer agricultural practices and improved crop quality control.