Simultaneous reduction of arsenic (As) and cadmium (Cd) accumulation in rice by zinc oxide nanoparticles

Accumulation of arsenic (As) and cadmium (Cd) in rice grains is a serious food safety concern for populations consuming rice as a staple food worldwide. Some agricultural practices such as water and nutrient management strategies can exhibit significant impact on their fate and bioavailability in rice paddies due to the profound impact of these activities on paddy soil properties. However, due to the unique biogeochemistry of As and Cd in rice paddies, their bioavailability often goes opposite directions and thus simultaneous control of both As and Cd in rice grains has not been achieved. Several previous studies have showed that some engineered nanoparticles (ENPs) can substantially lower the accumulation of either As or Cd in rice grains. The primary goal of this study was to evaluate whether zinc oxide nanoparticles, a popular nanofertilizer, can simultaneous lower both As and Cd in rice tissues using a greenhouse setup. The results suggested that both zinc oxide nanoparticles (ZnONPs) and zinc ions (Zn2+) significantly reduced the total As in rice roots (−39.5% and −83.3%) and shoots (−60.2% and −80.0%) and the reduction was primarily due to the lowered inorganic As(III) and organic As species. However, only ZnONPs reduced the Cd accumulation in rice shoots. Zn2+ significantly increased Cd content in rice shoot by 26.8%, suggesting the differential impact of ZnONPs and Zn2+ on As and Cd accumulation in rice tissues. Only ZnONPs holds the potential to simultaneously reduce both As and Cd in rice grains in As and Cd co-contaminated rice paddies. The results provide new insights into the sustainable applications of nanotechnology in agriculture.