Aging and phytoavailability of newly introduced and legacy cadmium in paddy soil and their bioaccessibility in rice grain distinguished by enriched isotope tracing

Abstract

Phytoavailability of Cadmium (Cd) plays a critical role in its accumulation in soil-rice systems. However, differential aging and phytoavailability of newly introduced Cd (CdN) and legacy Cd (CdL) in the soil-rice system remains unknown. Moreover, distinguishing their aging and phytoavailability is challenging. Enriched 112Cd isotope was introduced into a series of pot experiments, combined with sequential extraction and isotope dilution (110Cd isotopic spike), to investigate the aging and distribution of CdN and CdL under different treatments. The treatments included simulated acid rain, slaked lime, and biochar. CdN aged quickly than CdL in flooded soil and its availability was similar to that of CdL 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 CdN and CdL in rice plants under slaked lime and biochar treatments suggested their different in vivo complexations and translocations. Analysis of bioaccessibility of CdN and CdL in rice grains provided valuable insights regarding human Cd exposure.