Occurrences and characteristics of full-size microplastics derived from mulch films in major exorheic rivers of Hainan, China

Abstract Mulch film residues in farmland take risk of being transported to the wider environment, which may cause greater plastic pollution. Discharge of various sewage, as well as the releases from tourism, shipping, and aquaculture, was confirmed to important sources of microplastics (MPs) in rivers. However, the occurrences, characteristics and contribution of microplastics derived from mulch films (MMF) in rivers were still largely unknown. In this study, UV-Vis Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were sequentially used to identify the full-size MMF (1-5000 µm) in field samples. Studies confirmed that MMF, as a polyethylene-matrix composite doped with additives, is an important contributor of MPs in upstream farmland soil and riparian sediments, and even exists in a small amount in estuarine sediments. Specifically, the value of MMF in estuarine sediments ranged from 38 ± 8 to 82 ± 17 items/kg (including 54.9–74.2% small size (1-5 µm )), accounting for 9.0–13.7% of total MPs. Moreover, black and fragment were the dominant color and shape of these MMF, respectively. Our work first demonstrated that MMF was a neglected part of MPs in estuaries, especially in the drainage areas with high agricultural activity.