Spatial distribution, morphology, and risk assessment of microplastics in sediment from the Pearl River Estuary, China

Microplastics (MPs) (< 5 mm) are a growing environmental problem and have garnered significant global interest by scientists and policy makers. Coastal ecosystems are vulnerable to MP pollution, and assessing their sources, fate, and transport in the environment is imperative for marine ecosystem health. Data for marine sediment are still limited, particularly in the Pearl River Estuary (PRE) ecosystem in China. Here, we assessed the abundance, characteristics, and risks of MPs in marine sediments from PRE. MPs abundance ranged from 2.05 × 103 items ·kg-1 to 7.75 × 103 items ·kg-1 (dry weight), and white and black MPs were the dominant colors. The majority (> 64.12%) of detected MPs were <0.85mm and primarily consisted of pellets (36.84%) and fragments (29.65%). Three polymer types of MPs were identified by Fourier Transform Infrared Spectroscopy (FT-IR) including polyethylene (PE), polyethylene terephthalate (PET), and polypropylene (PP). Meanwhile, polyurethane (PU) sponge was reported for the first time in this study area. Observations of the surface morphology of typical MPs using Scanning Electron Microscopy (SEM) showed that all MPs exhibited varying degrees of erosion, characterized by cracks, folds, and bumpy structures. Furthermore, different concentrations of heavy metal elements were found on the surfaces of some MPs, potentially adsorbed from the surrounding environment. Based on type and quantity of MPs and the polymers identified, we assessed and classified the risk of MP contamination in PRE sediment as category III, indicating a severe ecosystem contamination. Results of this investigation may serve as an effective model for other estuaries facing similar pollution regimes and provides valuable information for marine sediment risk assessment.