Fate and mass budget of microplastic in the Beibu Gulf, the northern South China sea Zuhao Zhu a,b,**,1 , Kazi Belayet Hossain c,d,e,f ,1 , Huihua Wei a,b , Jie Chen b , Renming Jia a,b , Xiaofeng Gao g,i , Haiyan Jin a,b,h , Minggang Cai a,b,c,d,e,f ,* a Guangxi Key Laboratory of Beibu Gulf Marine Resources, Environment and Sustainable Development, Fourth Institute of Oceanography, Ministry of Natural Resources, Beihai 536000, PR China b Key Laboratory of Tropical Marine Ecosystem and Bioresource, Fourth Institute of Oceanography, Ministry of Natural Resources, Beihai 536000, PR China c State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361102, PR China d College of Ocean and Earth Science, Xiamen University, Xiamen 361102, PR China e Coastal and Ocean Management Institute, Xiamen University, Xiamen 361102, PR China f College of Environment and Ecology, Xiamen University, Xiamen 361102, PR China g Key Laboratory of the Three Georges Reservoir Region’s Eco-Environment, Ministry Education, PR China h Key Laboratory of Marine Ecosystem Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310000, PR China i College of Environment and Ecology, Chongqing University, Chongqing 400045, PR China A R T I C L E INFO Keywords: Microplastic Inventory Mass budget Beibu gulf ABSTRACT This study investigated the distribution, abundance, and mass budget of microplastics (MPs) in the Beibu Gulf, Northern South China Sea, focusing on their ecological significance and anthropogenic influence. Microplastics were found in all water and sediment samples, with concentrations in surface water ranging from 0.10 to 0.89 items/m 3 , and in bottom water from 0 to 0.85 items/m 3 . Sediment samples exhibited higher levels, ranging from 13.12 to 155.59 items/kg. The spatial distribution revealed higher concentrations along the northern Gulf and Guangxi Province, suggesting significant human influence from coastal activities, such as mariculture and in- dustrial discharges. The study utilized both field data and a mass balance box model to estimate the MPs mass budget, revealing that oceanic flow and riverine discharge are major contributors, accounting for 49% and 52% of MPs, while Atmospheric deposition and sedimentation represents 8% and 1%, respectively. The inventory estimation calculated that 0.24 tons of MPs exist in the water column, and 137 tons in the sediment, emphasizing the substantial environmental burden posed by these pollutants. The significance of this research lies in its comprehensive assessment of MPs in a semi-enclosed gulf, providing critical insight into the role of coastal and hydrodynamic processes in MP distribution. This study highlights the urgent need for better waste management practices in coastal regions to mitigate microplastic pollution and its detrimental effects on marine ecosystems. 1. Introduction At present, plastic waste has become an unavoidable threat to our world. Vast quantities of plastic have accumulated in landfills and the natural world. It makes up about 10% of the weight of municipal garbage (Barnes et al., 2009). Plastics are widely utilized today (Geyer et al., 2017; Peng et al., 2022), and by 2060, the output of plastic waste is predicted to increase to 155–265 MT annually (Geyer et al., 2017; Plastics Europe, 2018). Microplastics (MPs) with a size between 0.1 μm and 5 mm, have emerged as a contaminant over the decades (Cai et al., 2018; Chen et al., 2020; Liu et al., 2020; Zhu et al., 2022) as it is the byproduct of plastic waste, degrades or becomes exposed to wave action, wind abrasion, and UV sunlight radiation. Over 260 species of organisms in the ecosystem, including invertebrates, turtles, fish, seabirds, and mammals, have been reported to consume or become entangled in plastic debris (Omidi et al., 2012; Xia et al., 2021; Zhao et al., 2018), which impairs their ability to move and feed and reduces their repro- ductive output. They also suffer lacerations and ulcers and even die as a * Corresponding author. College of Ocean and Earth Science, Xiamen University, Xiamen 361102, PR China. ** Corresponding author. Fourth Institute of Oceanography, Ministry of Natural Resources, Beihai 536000, PR China. E-mail addresses: zhuzuhao@4io.org.cn (Z. Zhu), mgcai@xmu.edu.cn (M. Cai). 1 Dual First authors because of equal contributions to this paper. Contents lists available at ScienceDirect Marine Environmental Research journal homepage: www.elsevier.com/locate/marenvrev https://doi.org/10.1016/j.marenvres.2024.106797 Received 6 July 2024; Received in revised form 26 September 2024; Accepted 14 October 2024 Marine Environmental Research 202 (2024) 106797 Available online 18 October 2024 0141-1136/© 2024 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.