Microplastic pollution in sediments of urban rainwater drainage system

The sink of microplastics (MPs) in sediments of urban rainwater drainage system (RDS) is of great concern, because the MPs deposited can be resuspended by flow disturbance. Previous research has confirmed the significant accumulation of MPs in sediments of urban RDS, but it remains poorly elucidated, such as pollution sources and influencing factors. In this study, we investigated the MPs in sediments from RDS of a university campus. MPs were detected from all sediment samples, showing the ubiquity of microplastic pollution. Among 11 samples MPs' abundance ranged from 80 to 2610 particles/kg (dry weight), with highly spatial variability, depending on land type and environmental management practice within the catchment. Sites from office & teaching area had the averaged abundance of 335.00 ± 196.85 particles/kg, while 270.00 ± 89.09 particles/kg for staff residential area, and 795.00 ± 1050.65 particles/kg for student living area, indicating that the sediments of RDS from student living area had the highest abundance of MPs. However, independent sample t-test analysis suggests there is no statistically significant difference between land types, because of effective environmental management practices in the catchment. The surfaces of MPs were much rough, which implies that the fragmentation of larger plastic particles resulted in the production of MPs. Although the MPs of <1000 μm were the most, 1000-2000 μm MPs also accounted for a significant proportion in this study, showing a slight difference from the previous study in which MPs over 1 mm were quite low. Polypropylene (PP) and polyester (PET) found to be dominant with 49.75 ± 18.69 % and 49.75 ± 18.69 % of the total number, respectively. As to shapes, the proportion of fiber and fragment MPs exceeded 80 %. The color of MPs diversified greatly, and the MPs with bright colors occupied over 80 %. Fabric fibers, food packaging and courier packaging materials were figured out to be the considerable contributors of MPs.