Using cadmium bioavailability to simultaneously predict its accumulation in crop grains and the bioaccessibility in soils

Highlights: • Both Cd-Bav and Cd-Bac vary remarkably with extraction methods and soils. • The Cd-Bav based on chelators is higher in low-Cd soils but lower in high-Cd soils compared to that based on acid solutions. • All four Cd-Bav predict well Cd levels in wheat grains, but not in rice grains. • Specifically, the HCl method also has great potential to predict Cd-Bac in soils. -- Abstract: Single extraction procedures (SEPs) have been extensively conducted to determine Cd bioavailability (Cd-Bav) in soils. However, whether SEPs can simultaneously predict Cd accumulation in crop grains and bioaccessibility (Cd-Bac) in soils remains unclear. To assess their suitability, the Cd-Bav in 20 contaminated soils (containing 0.27–56.59 mg/kg Cd) determined by four SEPs (including DTPA, EDTA, HOAc and HCl) was compared with Cd concentrations in crop grains (wheat and rice) and Cd-Bac in soils (based on SBET and PBET assays). The results indicated that both Cd-Bav (0–103.2%) and Cd-Bac (0–110.4%) in soils varied greatly with the methods used. The Cd-Bav obtained from chelators (DTPA and EDTA) was generally greater in low-Cd soils but lower in high-Cd soils as compared to those obtained from acid solutions (HOAc and HCl). Regression analysis revealed that bioavailable Cd concentrations in soils were linearly correlated with Cd concentrations in wheat grains (R² = 0.88–0.91); however, no significant correlation was found for rice grains. The Cd-Bac in soils was significantly correlated with Cd-Bav obtained from HOAc (R² = 0.55–0.59) or HCl (R² = 0.60–0.68), but not with those obtained from chelators (DTPA and EDTA). Our data suggest that SEPs, particularly the HCl method, have great potential to simultaneously predict Cd accumulation in wheat grains and Cd-Bac in contaminated soils.