Translocation coefficients of heavy metals in the soil-rice system and their environmental implication

Background, aims and methods

Investigating and quantifying the transfer of heavy metals from soil to rice plants under different environmental conditions is crucial. This study explores the characteristics of heavy metals transfer within soil-rice system and the environmental implications of translocation coefficients (TCs) through analysis of data from major rice-growing regions in Asia.

Results

The translocation patterns of different heavy metals demonstrate variability, varying across geographical areas. For instance, As and Cd show high transfer propensity from soil to roots (average TCs: 3.71 for As and 3.63 for Cd), but their subsequent retranslocation to straw is substantially constrained, with average TC_straw/root and TC_grain/straw values dramatically decreasing (0.18 for As and ≤ 0.45 for Cd). Rice plants effectively regulate the transport Cu and Zn from roots to aerial tissues: TC of Cu decreases from 0.87 (TC_root/soil) to 0.27 (TC_straw/root), then increased to 0.78 (TC_grain/straw); for Zn, TC_root/soil, TC_straw/root and TC_grain/straw are 0.74, 0.65 and 0.63, respectively. Cluster analysis reveals distinct translocation patterns, with elements like Pb in the Yangtze River Delta showing a “parabola” transfer pattern, characterized by anomalously high TC_straw/root, along with Cr, Ni and Hg.

Conclusion

The sketched pattern generated by TCs exhibits available implication for environment condition. The abnormal translocation patterns observed for Pb, Cr, Ni and Hg suggest that these elements in rice aerial tissues may originate from atmospheric sources, influenced possibly by historical Pb-containing petrol use or non-ferrous mining activities.