Elevated CO2 enhances health risk of heavy metals in different paddy-rice species growing in Cu/Cd contaminated soils

There is a growing concern over elevated CO 2 levels and increased metal contamination in soils. Elevated atmospheric CO 2 usually increases plant productivity and alters nutrient elements mobility. However, it is still not clear whether rising CO 2 can result in changes incontaminating elements in crops, for example in different rice cultivars. Therefore, in this study, a pot experiment was conducted to investigate the combined effects of CO 2 elevation levels and metals (Cu and Cd) on rice growth. The study showed that elevated CO 2 led to higher tiller number, root length and grain yield when compared to ambient CO 2 .Average Cu concentrations in the tissues of four rice cultivars with elevated CO 2 levelswere significantly lower than those with ambient CO 2 . The Cd concentrations in three parts of rice cultivars subjected to elevated CO 2 levels were higher than thosein plants subjected toambient CO 2 levels. In addition, CO 2 elevation significantly reduced the pH values of soils and changed the fractionation of Cu and Cd in soils.The associated risk was assessed using the hazard quotient (HQ), which was found to be high for Cd and Cu in all tested varieties of rice, with Cd posing a more severe threat than Cu.