Migration of Heavy Metals from Soil to Rice Plant

Characteristics of the migration of 5 heavy metals (i.e., Cd, Pb, Cr, As, and Hg) in a soil-rice system were investigated. Field samples of soil and the rice grown on it were collected from typical rice production areas in western Fujian for the study. Contents and enrichment/migration capabilities of the heavy metals in the system were determined for a correlation analysis. To varying extents, the metal contents in rice grain samples exceeded the national food safety limits. The severities of the heavy metal pollution in rice were in the order of Pb > Cd > As > Cr > Hg; whereas, in soil, Hg > Cd > Pb > Cr > As. The enrichment capabilities of rice on heavy metals from the soil were in the order of Cd > As > Cr > Hg > Pb.The heavy metal migrations from soil to organs of a rice plant decreased in the order of root > stem leaf > grain. Among the 5 heavy metals, Cd had the highest migration rate, while Pb the lowest. The physiochemical properties of soil also affected the metal transfer. For instance, pH contributed more to the movement of heavy metals in a soil-rice system than others. At low pHs, the heavy metal transfer to and absorption by the plant tended to increase.