Atmospheric deposition of cadmium in an urbanized region and the effect of simulated wet precipitation on the uptake performance of rice

Abstract

Excessive inputs of potentially toxic elements (PTEs) into the surface environment as a consequence of atmospheric deposition, imposes long-term burdens on agricultural ecosystems. Studying the spatial and temporal variation in PTEs in atmospheric deposition and their effects on plant shoot accumulation are important in understanding the sources and contributions of PTEs in soils and agricultural products. Here, the spatial and temporal variations in cadmium (Cd) concentration and atmospheric deposition fluxes were investigated in five rice-producing areas of the urbanized Chang-Zhu-Tan region over two years. Then, the effects of simulated wet precipitation on the uptake of Cd in rice seedlings in hydroponic culture was explored. The results showed substantial spatial variability in Cd concentrations and atmospheric deposition fluxes in this region. The Cd concentration of atmospheric deposition ranged from 0.07 to 114 μg L−1, and the annual Cd fluxes in the industrial area reached 61.0 g ha−1 but all were <10.0 g ha−1 in the rural areas. Rice seedling growth became significantly inhibited with increasing concentrations of Cd. Cadmium content in the shoots and white roots and dithionite-citrate-bicarbonate (DCB) extractable Cd on root surfaces were significantly and positively correlated with the concentration of Cd in the nutrient solution. Shoot Cd concentrations increased significantly (p < 0.05) when the annual Cd precipitation flux was ≥50 g ha−1 compared to the control with no Cd precipitation, and the concentration in the shoot was higher than that in roots of rice cultivar A159, when the annual simulated wet precipitation flux of Cd was 400 g ha−1. Thus, shoot Cd was directly related to the simulated wet precipitation when the flux exceeded 50 g ha−1a−1, indicating that air pollution is an important source factor affecting crop Cd uptake.