In 2018, the total global plastic production reached 360 million tons, and the wide use of plastic products is accompanied by the generation of large amounts of plastic waste. From 1950 to 2015, the world's plastic waste amounted to about 6.3 billion tons (Chae & An, 2018; Bradney et al., 2019; Ju et al., 2021). Although most plastics are durable and recyclable materials, only 6–26% of plastic waste is recycled. Most of the rest ends up in landfills or is directly discarded into the environment (de Souza Machado et al., 2018; Windsor et al., 2019). Under ultraviolet radiation, weathering, and biological activities, large pieces of plastic garbage are gradually decomposed to form plastic fragments, particles, or fibers with particle sizes lower than 5 mm, i.e., microplastics (Qi et al., 2018; Jebe, 2020).
As an emerging pollutant, microplastics have attracted the attention of scholars and the general public in recent years (Browne et al., 2011; Cole et al., 2013). Due to their light weight, small particle size, large quantity, and difficult degradation, microplastics are found in rivers, lakes, oceans, and even in drinking water and salt (Yan et al., 2019; Malankowska et al., 2021). Microplastics can exhibit diverse forms and complex chemical compositions. At present, common chemical types of microplastics include polyethylene (PE), polyvinyl chloride (PVC), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), polyamide (PA), and polyester (PES) (Free et al., 2014; Oni et al., 2020; Qi et al., 2020; Zhang et al., 2020). Microplastics have a certain hydrophobicity, which can cause the enrichment of microorganisms and pollutants on their surface. They can also accumulate in microorganisms through feeding, change the biological metabolism of organisms, and produce biological effects such as immune responses, neurotoxicity, genotoxicity, and inflammatory reactions (Eerkes-Medrano et al., 2015; Xiong et al., 2019; Hernández-Sánchez et al., 2021). They can be transferred from low to high trophic levels in food webs, thus affecting biodiversity, ecosystem services, and human health (Yang et al., 2015; Shen et al., 2020; Wong et al., 2020).
To date, the microplastic pollution of aquatic ecosystems, especially marine environments, has been widely studied. Global research on microplastic has mainly focused on the oceans (Costa and Barretta, 2015; Kooi et al., 2016; Taylor et al., 2016), polar glaciers (Obbard et al., 2014), and coastlines of continents (Browne, 2015). Microplastics have been found even in aquatic organisms far away from human settlements, such as deep-sea corals (Woodall et al., 2014). Compared with ocean studies, there are many reports on freshwater microplastics globally (Zhang et al., 2018; Xiong et al., 2018; Lahive et al., 2019; Zhang et al., 2020). Among those, most studies on microplastics in rivers and lakes are from Europe, followed by North America and Asia. For example, Fischer et al. (2016) analyzed the contents of microplastics in 36 lakeshore sediment samples from Italy and found contents ranging from 268 to 3360 particles/kg. Vaughan et al. (2017) evaluated the concentration of microplastics in the sediments of small lakes and urban lakes in the UK for the first time. Maximum concentration reached 25–30 particles per 100 grams of dry sediments, and fibers and films were the most common microplastic types. Sruthy & Ramasamy (2017) studied microplastics in Vembanad Lake in India. The abundance of microplastics in sediments ranged from 96 to 496 particles/m2, with an average abundance of 252.80 ± 25.76 particles/m2. Low-density polyethylene was the main polymer component of microplastics.
Soil is one of the most valuable resources on earth and provides a series of important ecosystem functions and services to humans and other organisms. It provides the medium for plant growth, participates in biogeochemical cycles and carbon sequestration, and maintains soil biodiversity (Hü-Tsch et al., 2002; Waldrop et al., 2010; Mohanty et al., 2013). Due to increasing human activities, the soil suffers from erosion, heavy metal pollution, compaction, and salinization (Arias-Estévez et al., 2008; Rosowiecka & Nawrocki, 2010). As an emerging pollutant, microplastics also threaten soil health and may lead to land degradation. The pollution of soil with microplastics has attracted much attention in recent years (Andrady, 2011; Obbarb et al., 2014; Law & Thompson, 2014). It is estimated that the total amount of microplastics entering the soil environment every year is about 4–23 times that of the marine environment. In Europe and North America, more than 700,000 t of microplastics accumulate in the soil every year, which greatly exceeds the total weight of microplastics in the global ocean and surface water (93,000–236,000 t) (Andrady, 2017; Zhang et al., 2020). Soil has become a huge microplastic sink and considering its core role in terrestrial ecosystems, it is imperative to study the impact of microplastics on terrestrial systems, especially the soil environment. At present, the main contents of researches include (i) the sources and migration of soil plastics and the basic characteristics of long-term storage in soil, (ii) the impacts of soil microorganisms on plastics, and (III) the impacts of plastic pollution on the soil microbial community and enzyme activity, soil animals, crop production, and global terrestrial ecosystem function (He et al., 2018; Scheurer & Bigalke, 2018; Ju et al., 2021).
Here, we studied the Ebinur Lake basin, an oasis in Xinjiang with rapid industrial and agricultural development, and investigated occurrence characteristics, the pollution status, occurrence relationships, and sources of microplastics in the soil and heavy metal pollutants. Our results may provide a scientific basis and reference for preventing and controlling microplastic pollutants in oasis soils in the Ebinur Lake Basin and other arid areas in Central Asia.