Current Levels, Composition Profiles, and Potential Risks of Microplastics in Irrigation Water

Abstract

Microplastic pollution is an increasing global concern due to its extent and the potential risk it poses. Land-based sources are considered to be the most important sources of microplastic pollution to the coastal and marine environment. The number of research studies examining microplastic pollution in freshwater and inland water systems is increasing, but most research focus is on rivers, reservoirs, and lakes. This study investigates the spatial–temporal distribution, characteristics, sources, and risks of microplastics in irrigation water in Taiwan. The results show that microplastics are widely and unevenly distributed along the irrigation system and are abundant at sites surrounded by a dense population and sites that receive lateral canal and urban runoff input. The abundance of microplastics ranges from 1.88 items/L to 141 items/L, and samples collected in May have the highest microplastic concentrations. Polypropylene, polyethylene, and polystyrene are identified as the predominant polymers. Fibers (36–64%) are the most typical and abundant shape, and a small size (333–1000 µm) (49–63%) and white/transparent (45–51%) are the dominant size and color among all samples. Principal component analysis and hierarchical cluster analysis are used to assess the impact of the rainy season and typhoons and address the dramatic changes in distinct population densities. The polymer risk index is calculated to evaluate the environmental risk of microplastics in irrigation water, and the results reveal a high microplastic risk throughout the year except in November and January. This study provides a valuable reference and impetus for a better understanding of the profile and source apportionment of microplastics in irrigation water, which are important for environmental management.

Keywords: Microplastics, Irrigation water, Spatial-temporal distribution, Source apportionment, Pollution characteristics