Elevated CO2 may increase the health risks of consuming leafy vegetables cultivated in flooded soils contaminated with Cd and Pb

Elevated CO2 levels threat the crop quality by altering the environmental behavior of heavy metals (HMs) in soils. In reality, multiple HMs often co-exist in field, while details regarding coexisting HMs migration in flooded soil at elevated CO2 levels remain unclear. A pot experiment in open-top chambers (CO2 at 400 and 600 mu mol mol(-1)) was conducted to explore the uptake and transfer of cadmium (Cd) and lead (Pb) in water dropwort (Oenanthe javanica DC.) grown in flooded soils contaminated with Cd and Pb. Results showed that elevated CO2 significantly reduced soil pH, promoting the release of Cd and Pb (by 63.64-106.90% and 10.66-30.99%, respectively) into soil porewater. In the harvested O. javanica, elevated CO2 decreased the root uptake of Cd but promoted that of Pb. Further mechanism analysis showed that elevated CO2 promoted the formation of iron plaque on root surface by 44.60-139.57%, with lower adsorption capacity to HMs (0-34.93% and 63.61-67.69% for Cd and Pb, respectively). Meanwhile, Pb showed lower adsorbability in iron plaque but higher transfer capacity when compared with Cd. Ultimately, elevated CO2 increased the target hazard quotient values of Pb in O. javanica. These findings provide new insights on the effects of elevated CO2 on the transfer of coexisting HMs in soil-plant system, and the risk of HMs pollution under climate changes needs to be more fully assessed.