Current levels and composition profiles of microplastics in irrigation water

Land-based sources have been considered 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 focuses on rivers, reservoirs, and lakes. This study investigated the spatial-temporal distribution, characteristics, sources, and risks of microplastics in irrigation water in Taiwan. The results showed that microplastics were widely and unevenly distributed along the irrigation system and were abundant at sites surrounded by a dense population and sites that received lateral canal and urban runoff input. The abundance of microplastics ranged from 1.88 items/L to 141 items/L, and samples collected in May had the highest microplastic concentrations. Polypropylene, polyethylene, and polystyrene were identified as the predominant polymers. Fibers (36-64%) were the most typical and abundant shape, and 333-1000 μm size (49-63%) and white/transparent (45-51%) were the dominant size and colors among all samples. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were used to assess the impact of the rainy season and typhoons and addressed the dramatic changes in distinct population densities. The polymer risk index was calculated to evaluate the environmental risk of microplastics in irrigation water, and the results revealed a high microplastic risk throughout the year except in November and January. This study provided a valuable reference and impetus for a better understanding of the microplastic profile and source apportionment in irrigation water, which was important for environmental management.