Distribution and sedimentation of microplastics in Taihu Lake
Graphical abstract
Introduction
The wide production and use of plastics has generated many environmental problems. There has been growing concern in recent years about microplastics, which are generally defined as plastic debris <5 mm. The physical and chemical properties of microplastics make them more likely to combine with contaminants and act as vectors to organisms (Carbery et al., 2018; C. Li et al., 2019; Y. Li et al., 2019). Microplastics have been found to be injurious to the digestive tracts of zooplankton (Besseling et al., 2017; Nasser and Lynch, 2016; Rehse et al., 2016), and their accumulation can cause liver glycogen depletion and fat vacuolation in fish (Rochman et al., 2013). Food chain transmission of microplastics has effects on inflammation of the gut and on the human immune system (Bouwmeester et al., 2015).
There has been less research focus on freshwater systems compared with that examining ocean systems. Preliminary research shows that microplastics are common in freshwaters worldwide, including rivers (Ding et al., 2019; Eo et al., 2019), lakes (Su et al., 2016; Eriksen et al., 2013; W. Wang et al., 2018; Z. Wang et al., 2018), ponds (Bordós et al., 2019) and estuaries (Vendel et al., 2017; Gallagher et al., 2016). Freshwater systems in a close relationship with human activities face a greater threat. The United States has enacted the Microbead-Free Waters Act to ban cosmetics containing plastic beads (McDevitt et al., 2017), and Canada's Plastic Beads in Cosmetics Act came into force on January 1, 2018 (Xanthos and Walker, 2017). China is the greatest producer of plastics (Yin et al., 2020), resin and polypropylene fiber production in China accounts for 28% and 68%, respectively, of global totals (Yao et al., 2019; Geyer et al., 2017). In 2017, 1.5 million tonnes of packaging waste was generated from food delivery in China's megacities (Yao et al., 2019; G. Song et al., 2018; Y. Song et al., 2018).
As major parts of the freshwater system, lakes play an important role in water supply, aquaculture and other aspects of the hydrological cycle. In recent years, research into microplastics in lakes gradually increased, but most researchers have only performed preliminary analyses of microplastics in lake areas, and have not taken inflow and outflow rivers into account. This may explain our lack of knowledge about the different spatial distributions in lakes and the fluxes of microplastics into lakes. Water quality between lakes and rivers is highly correlated. The water quality of inflow rivers can have a direct impact on lakes, and the water quality of lakes also certainly impacts the water quality of outflow rivers and adjacent areas (Zhong et al., 2014; Yan et al., 2011). At the same time, the flux of microplastics into lakes is key to lake management and needs to be studied further.
The combination of microplastics and suspended solids, algae or colloids leads to variable mobility and density (C. Li et al., 2019; Y. Li et al., 2019). These changes may cause microplastics to settle or float. Sediment is an important destination for microplastics in freshwater systems, and resuspension of sediment is also a source of pollution. Settling characteristics determine the different destinations of different microplastics. Nevertheless, there is little research focusing on the settling characteristics of microplastics of different sizes and types.
Taihu Lake connects Jiangsu, Zhejiang and Shanghai, and is located in one of the most industrialized and densely populated regions in China. Since the 1980s rapid economic development in the Yangtze River Delta has led to increasingly serious pollution of Taihu Lake, causing considerable environmental problems including eutrophication, which has attracted many researchers. The interaction between microplastics and the aquatic ecosystem may change the distribution of toxic cyanobacteria and increase the ecological risk to drinking water sources. The most recent study of microplastics distribution in Taihu Lake was carried out several years ago, and the basin is subject to disturbance from human activities. For this reason, our study mainly focused on: (1) recent levels of microplastics spatial distribution and pollution in Taihu Lake; (2) the settling characteristics of microplastics of different shapes and sizes; (3) identifying which inflow rivers are the main sources of microplastics and determining if microplastics have a common source with conventional pollutants.
Section snippets
Survey area and sample collection
Taihu Lake, the third biggest freshwater lake in China, has a surface area of 2338 km2. It is a typical subtropical shallow lake and has an average depth of 1.9 m. There are about 100 million people living around the lake, contributing over USD5 trillion to gross domestic product (GDP) in 2018 (Wang et al., 2019). Taihu Lake is a critical source of drinking water for the local population, and so plays an important role in the regional economy and social development (Su et al., 2016). In recent
Microplastics pollution levels in the Taihu Basin
The abundance of microplastics varied from 1.65 ± 0.18 to 8.48 ± 0.55 items/L in the surface water of the lake and from 1.81 ± 0.09 to 18.26 ± 4.44 items/L in the rivers. The lake waters and river waters contained average (median) microplastic concentrations of 5.67 ± 1.92 (5.99) items/L and 5.68 ± 3.04 (4.87) items/L, respectively. The abundance of microplastics in sediment varied from 464.26 ± 44.51 to 1380.69 ± 328.92 items/kg. The average (median) microplastics concentration was 893.48 ±
Conclusions
We detected microplastics in the sediment and surface water of Taihu Lake and in the 30 major rivers around it. We then studied the distribution patterns of microplastics in the lake, comparing inflow and outflow rivers, and researching the settlement features of microplastics.
Compared with other studies, the levels of microplastics pollution in Taihu Lake basin (1.7–8.5 items/L in lake water, 1.8–18.2 items/L in river water and 460–1380 items/kg in sediment) were regarded as moderate.
Inflow
CRediT authorship contribution statement
Qiji Zhang: Conceptualization, Methodology, Formal analysis, Investigation, Data curation, Writing – original draft, Visualization. Tong Liu: Writing – review & editing, Supervision. Liu Liu: Investigation. Yifan Fan: Resources. Wenxin Rao: Resources. Jinglan Zheng: Resources. Xin Qian: Conceptualization, Writing – review & editing, Funding acquisition, Supervision.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This study was supported by National Natural Science Foundation of China (No. 41907388).
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