The contribution of atmospheric deposition to cadmium and lead accumulation in rice grains

Purpose: Over-accumulation of cadmium and lead in rice grain is a global concern as it has adverse health impacts. Atmospheric deposition is an important source of heavy metal accumulation in soil, but contribution to crops has not been quantified and the mechanisms of foliar Cd and Pb uptake via the stomata of rice leaves exposed to atmospheric fallout are unclear. Methods: To quantify the contribution of atmospheric deposition on Cd and Pb accumulation in rice grains, a rice pot experiment with three exposure treatments (T1, all day exposure without geotextile membranes; T2, all day exposure with geotextile membranes; T3, daytime exposure with geotextile membranes; and T4, night exposure with geotextile membranes) using severely (ZZ) and moderately (XT) polluted soils was conducted. Results: Cd content in shoots and roots was T1 > T2, T3 > T4 in XT soils, and T1 > T2, T4 > T3 in ZZ soils, while Pb content in both soils was T1 > T2, and T4 > T3. Cd and Pb contents in rice grains showed the same trend. Using the tracer of isotope tracer ratios ( 114/111 Cd, 112/111 Cd, and 207/206 Pb, 208/206 Pb) the contribution of atmospheric deposition to rice grains was quantified as 63.55% and 18.01% for Cd, and 27.69% and 41.13% for Pb in XT and ZZ soils, respectively. Conclusions: Foliar uptake atmospheric deposition had substantial effect on Cd and Pb accumulation in rice grains and the control of heavy metal foliar uptake should be paid more attention in to maintain rice safety production.