In recent years, MPs have been widely found in different environments, including oceans, rivers and Lakes, sediments, groundwater, the atmosphere, polar regions, sea salt, fish, shellfish, birds, etc. (Waller et al., 2017; Chae and An, 2017; Chen et al., 2020; Mishra et al., 2021; Parvin et al., 2022; Ren et al., 2021; Sultan et al., 2023; Tokunaga et al., 2023). The sources of MPs are extremely extensive, mainly including primary microplastics (PMPs) (cotton fabrics, care products, tire wear, industrial and agricultural film fishing products, etc.) and secondary microplastics (SMPs) are affected by wave action, temperature changes, biological processes and UV-B radiation in the environment (Andrady, 2011; Browne et al., 2007; Dong et al., 2021). In our previous study, the development of the economy, tourism, industry, agriculture, and fishery were positively related to the abundance and distribution of MPs (Sun et al., 2021). This study has shown that the MPs in the HRR and PER have similar occurrence characteristics, which are significantly higher than those of the SMY. These may be closely related to the surrounding environment and human factors.
The sewage discharged from hospitals and hotels results in the HRR having a high level of MPs abundance. The high frequency of leisure and entertainment also results in the PER having a high MPs abundance. Research has confirmed that the MPs present in hospital wastewater and surgical environment (Field et al., 2022; Tuvo et al., 2023). When analyzing MPs in PMFC samples (n = 354) collected from different restaurants in 28 cities, MPs were detected in all PMFC samples, with an abundance of 5–173 items per container (Zhu et al., 2023). These MPs may easily flow into surrounding lakes. Meanwhile, the PER involves fishing and children's plastic toy products, this may be one of the important reasons for the high abundance of MPs in this area. Studies have shown that tourism activities may be one of the direct sources of MPs (Krishnakumar et al., 2018; Bayo et al., 2019). Yin et al. (2019) selected eight major lakes from every district as sampling sites in Changsha. The maximum concentration of MPs appeared in the tourist spots in the city center. Wang et al. (2017) investigated the levels of MPs in the surface water of 20 urban lakes and the reaches of the Hanjiang River and the Yangtze River in Wuhan, which recommended that MPs abundance in lakes varied markedly in space, and negatively correlated with the distance from the city center. As campus lakes in Guangzhou, which is one of the most developed cities in China, the MPs abundance in three different functional lakes also presented similar trends. The SMY MPs abundance was lower than the HRR and PER, with (2. 93 ± 1.3)-(11. 4 ± 1. 8) items/L. This was because the SMY had less disturbance from human activities and no outfall. Christopher et al. (2014) found that Lake Hovsgol is more heavily polluted with MPs than the more developed Lakes Huron and Superior in the Laurentian Great Lakes, with MPs density decreasing with distance from the park's most populated and accessible southwest coast. The SMY had higher MPs abundance in April relative to other periods due to the rainfall, which showed a significant improvement from January (1.5 mm) to April (63.6 mm) (Guangzhou statistical yearbook, 2022) (Fig. 6), as the rainwater runoff is considered to be an important way to transport and enrich the MPs into the freshwater (Sang et al., 2021), and significant changes in the concentration of MPs in inland waters during rainfall (Xia et al., 2020). As a whole, the discharge of hospital and restaurant wastewater and the discard of their appliances, the fishing activities and children's plastic toy products in the play and entertainment region, the erosion of rainwater have become important sources of MPs in freshwater, and the management and prevention should be strengthened.
According to the average particle size ratio of MPs in each lake, whether the HRR, PER, or SMY, MPs less than 1mm in size account for the majority of the proportion. Studies have shown that small MPs are more likely to migrate, either to lakes through surface runoff caused by precipitation, or dispersed by atmospheric deposition (Barnes et al., 2009). Therefore, the particle size of MPs measured in the lakes was mostly small. The HRR and PER have high a similarity in particle size ratio composition. PYH lakes had a higher proportion of small MPs than the SMY, which also reflected the fact that human activities may accelerate the accumulation of small MPs. The surface water MPs detected in lakes and rivers are mainly small-size MPs, which is related to the fact that small MPs can be formed from large MPs through physical weathering, ultraviolet decomposition, water impact, and wave action (Yan et al., 2019). Small MPs are even more harmful because they can absorb more pollutants and are more easily consumed by microorganisms, and are concentrated among high-end consumers.
Blue MPs accounted for nearly half of the total MPs in the HRR, PER, and SMY. Previous studies have shown that the blue or transparent MPs were the most common in the river estuary and the urban area of Guangzhou, and a large proportion of blue MPs were found in the rivers and lakes in Guangzhou (Yan et al., 2020, Wang et al., 2023). In this present study, the proportion of blue MPs in the HRR and PER was relatively close, which were 41.42% and 43.97%, respectively, but in the SMY, the blue MPs accounted for nearly 61.13%. These indicated that the blue MPs may have higher homology in the campus lakes and Pearl River of Guangzhou. Compared to the lakes of HRR and PER, there are fewer types of colors in the SMY, and purple and yellow were not found, respectively. This also indicated that human activities have a positive contribution to increasing the variety and quantity of MP colors.
By analyzing and comparing the shapes of MPs in different functional lakes, we determined that the MPs in each lake were mainly fibers, that the fragments of MPs in the PER were larger than those in other lakes, while the fiber MPs were less than those in other lakes. The HRR, PER, and SMY accounted for 97.98%, 71.54%, and 90.73% respectively. Yan et al. (2019) discovered that the main shapes of microplastics were film, fragment, and fiber. Wang (2020) found that fiber MPs accounted for 80.4% of the Filip Bay watershed, and the shape of surface water MPs observed in the Changjiang Estuary was mainly fiber. Fiber is mainly sourced from offshore aquaculture, fishing, and clothing. On the other hand, it has been shown that the fibers in the wastewater from washing clothes can reach more than 100 items/L (Ajith et al., 2020), and the wastewater from textile factories also contains many fiber MPs. It can be seen that the MPs in the environment are mainly MPs fibers, and less of other MPs shapes. It can also be inferred that the shape of MPs in environmental water bodies is closely related to human lifestyle and habits.