Phytoavailability of Cadmium (Cd) plays a critical role in its accumulation in soil-rice systems. However, differential aging and phytoavailability of newly introduced Cd (Cd) and legacy Cd (Cd) in the soil-rice system remains unknown. Moreover, distinguishing their aging and phytoavailability is challenging. Enriched Cd isotope was introduced into a series of pot experiments, combined with sequential extraction and isotope dilution (Cd isotopic spike), to investigate the aging and distribution of Cd and Cd under different treatments. The treatments included simulated acid rain, slaked lime, and biochar. Cd aged quickly than Cd in flooded soil and its availability was similar to that of Cd after tillering stage. The grain Cd contents were positively correlated to Cd concentrations in the overlying water. Acid rain reduced the soil pH, increasing the grain Cd, while slaked lime reduced grain Cd content. The acidic biochar used in this study increased grain Cd, possibly through soil acidification-induced Cd release. The differences in bioaccumulation and translocation factors between Cd and Cd in rice plants under slaked lime and biochar treatments suggested their different in vivo complexations and translocations. Analysis of bioaccessibility of Cd and Cd in rice grains provided valuable insights regarding human Cd exposure.
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