Fate of nano/microplastics and associated toxic pollutants in paddy ecosystems: Current knowledge and future perspectives

Abstract: The contamination of nano/micro-plastics (NPs/MPs) has now been found in all environments and food supply chains. Rice is the staple food for half of the world's population but knowledge on the impact of NPs/MPs and their associated pollutants on rice plants and paddy soils is limited. The NPs/MPs enter paddy soils through the application of biosolids, organic amendments, flooding and irrigation, plastic mulching, and atmospheric deposition. Introduced particles have varying impacts on the physical (increasing aggregation and water content while decreasing bulk density), chemical (enhancing soil carbon, greenhouse gas emission and bioavailability of pollutants), and biological properties (providing habitats for pathogens and decreasing microbe diversity) of paddy soils. Ultimately, they hinder the growth (reducing root growth, photosynthesis and nutrient uptake) and physiology (increasing oxidative damage and reducing antioxidant activity) of rice plants. Soils can be further contaminated with different pollutants such as toxic elements, antibiotics, pathogenic microbes and pesticides which adhere to the surfaces of NPs/MPs, affecting their bioavailability, which further harm the growth and metabolisms of rice plants. Many factors such as type, size and dose of NPs/MPs, as well as paddy soil properties and cultivation history, environmental factors such as drought, and rice cultivar can affect the impact of contamination. We have found that there is limited research on the interaction between paddy soil systems and NPs/MPs, as well as their associated toxic pollutants. Future studies should focus on minimizing the current research gap in actual field conditions in order to protect the health of over 3 billion human consumers.