Next Article in Journal
Dynamic Responses in a Pipe Surrounded by Compacted Soil Suffering from Water Hammer with Fluid–Structure–Soil Interactions
Previous Article in Journal
Ichthyoplankton Assemblages from the Coasts of Hamsilos Nature Park, Sinop, Southern Black Sea: Biodiversity, Abundance, and Relationships with Environmental Variables
Previous Article in Special Issue
Water Quality of Lake Erhai in Southwest China and Its Projected Status in the near Future
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Water
Volume 16
Issue 18
10.3390/w16182672
water-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

The Occurrence of Microplastics Pollution in the Surface Water and Sediment of Lake Chenghai in Southwestern China

by
Lizeng Duan
1,
Liancong Luo
1,*,
Longwu Zhang
1,
Donglin Li
2,
Huayu Li
1,
Tianbao Xu
1,
Jing Xu
1 and
Hucai Zhang
1,3,*
1
Institute for Ecological Research and Pollution Control of Plateau Lakes, School of Ecology and Environmental Science, Yunnan University, Kunming 650500, China
2
Institute of Culture and Tourism, Qujing Normal University, Qujing 655011, China
3
Southwest United Graduate School, Kunming 650500, China
*
Authors to whom correspondence should be addressed.
Water 2024, 16(18), 2672; https://doi.org/10.3390/w16182672
Submission received: 25 July 2024 / Revised: 9 September 2024 / Accepted: 17 September 2024 / Published: 19 September 2024
(This article belongs to the Special Issue Plateau Lake Water Quality and Biodiversity: Impacts of Human Activity and Trans-regional Water Diversion)
Browse Figures
Versions Notes

Abstract

:
Microplastics (MPs) in freshwater environments, such as lakes, have become a significant issue in recent years. However, studies on the lakes of the Yunnan Plateau have been limited. To understand the pollution status and sources of MPs in Lake Chenghai (LCH), 36 sampling sites were selected for the surface water and sediment samples. Morphological identification, compositional analysis, abundance measurement, and spatial distribution mapping of the MPs were carried out. We also performed correlation analyses with hydrological parameters and physicochemical indexes of water and sediments. We aimed to uncover the spatial distribution patterns of the MPs in LCH, along with potential sources. Our findings revealed that all samples contained MPs and all of them were fibers. The abundance of MPs ranged from 90 to 770 n/m3 (329.44 rms) in the water and from 10 to 115 n/kg (43.19 rms) in the sediments, with particle sizes of 1-3 mm and less than 1 mm, respectively. Transparent MPs were prevalent, comprising 68% of the MPs found in the water and 63% in the sediments. The primary components of the MPs were polypropylene (PP), polyethylene terephthalate (PET), and man-made fibers (rayon). The spatial distribution showed an increasing concentration of MPs from south to north in the surface water, whereas the opposite trend was found in the sediments. Human activities, prevailing winds, and the river flowing into the lake influenced the spatial distribution pattern of the MPs. The abundance and assemblage characteristics of the MPs were directly correlated with the factors of nitrogen, phosphorus, and particle size in the water and sediments, but the correlation was not significant. The main source of MPs was the production and livelihoods of the neighboring residents, especially the use of fishing gears and nets. Since LCH shows significant pollution from MPs, there is an urgent need to control and manage the watershed in order to reduce the input of MPs in the future.

1. Introduction

As human activities increase, more pollutants enter the environmental system via point or non-point sources, causing water pollution and eutrophication, and triggering changes in the structure and function of the ecosystem [1]. Microplastics (MPs), as a new type of environmental pollutant, are widely distributed, have a multisource mechanism, are of extremely high ecological risk, and can ultimately jeopardize human health through transmission into the food chain [2]. Studies have shown that plastic waste has spread throughout freshwater ecosystems globally, but there is a lack of knowledge regarding the presence of MPs in freshwater systems [3]. The occurrence of MPs in freshwater system, especially in drinking water, poses a serious threat to human health [4,5]. However, previous studies have focused on marine ecosystems and neglected the important channels for the transfer of MPs from land-based sources to the ocean, such as lakes [6]. Since the freshwater system was more closely linked to human activities, the potential for and extent of MP contamination grows with increased human activity [7]. In recent years, research on freshwater has increased rapidly, becoming a hotspot in the field of environmental pollution research [8,9]. Conducting research on MPs pollution in lakes and other freshwater systems, with the aim of reducing exogenous inputs, may be an effective way to realize the prevention and control of MPs in the environment [10]. Despite the uncertainty of the effects of microplastic contamination on ecosystem health and function, it is critical to understand, monitor, and prevent further microplastic contamination of lakes [11].
As the main source of inland freshwater storage, lakes act as sinks for regional land-sourced detrital materials, and can be used to record the processes and mechanisms of material inputs [12]. These water bodies are relatively closed, with stable hydrological conditions, which is conducive to the deposition and retention of MPs [13]. The average abundance of MPs in the water bodies and sediments of lakes in China has been found to be 0.34–8.9 items/L and 3–14,700 items/kg, respectively [10]. The study area was mainly concentrated in the Yangtze and Pearl River Basins and some intra-urban waters, where MPs pollution has become more serious with the increase in human activities and the population density [14]. MP pollution has been found to be directly related to human activities, such as the use of agricultural plastic mulching film, plastic landfill waste, and wastewater discharge [15]. Furthermore, without proper waste management systems, the consumption of plastics by low-density populations can also pose a serious hazard to freshwater systems [16]. Overall, the abundance of MPs in most lakes in China is higher than that in developed countries and regions due to China’s high population density and lack of regulatory disposal measures [17]. Subsequent studies have also detected MPs in several lakes on the Tibetan Plateau, and in remote alpine mountainous areas with extremely low population densities, such as Lake Trash in Hoh Xil [18,19]. MPs now have been found in instead of contaminated remote lakes located far away from direct human interference [6]. Reports of MPs in Yunnan Plateau lakes have mainly focused on Lake Dian (the maximum surface water area in the Yunnan-Guizhou plateau). The average abundance levels of MPs in the water and sediment of Lake Dian were 91.2 n/m3 and 338.48 n/kg, respectively. The spatial distribution of the MPs was highest in the center and northern parts of the lake, and the main sources were the discharge of tail water from the sewage treatment plant, textiles, and the use of fishing nets [20,21,22]. Furthermore, the abundance of MPs in Lake Dian was significantly positively correlated with the total nitrogen (TN) (p < 0.01) and negatively correlated with chlorophyll a (Chl-a). The topography of the lakebed and the water (flow) direction were also noted as important factors influencing the spatial distribution of the MPs in the sediments of Lake Dian [23]. There was no correlation between the abundance, the physical assemblage characteristics of the MPs and the selected environmental parameters of the surface sediments of lake Qilu, located in Central Yunnan [24]. As the main organisms in the cyanobacterial blooms, Microcystis presents with a similar spatial distribution as MPs, and both are affected by wind in the lake Taihu [25]. Thus, the natural environment, both directly and indirectly, influences the pollution levels of MPs. Investigating the correlation between MPs and environmental factors is crucial to understanding the mechanisms of their presence and distribution characteristics.
There are numerous lakes on the Yunnan Plateau, most of which are typical tectonic fault-trapped shallow lakes. These lakes have unique natural characteristics, including high altitude, high pH levels, small watershed areas, long water replacement cycles, distinctive lake bottom topographies, and perennial prevailing winds. Additionally, they are subject to significant anthropogenic disturbances. These factors have drawn considerable attention from researchers, with most existing studies focusing on the lake sediments in terms of environmental evolution, eutrophication, and heavy metal contamination. However, research on emerging environmental pollution issues, such as microplastics (MPs), remains relatively rare.
Lake Chenghai (LCH) combines natural and human characteristics such as a north–south orientation, east–west narrowness, perennial prevailing winds, and differences in the intensity of human activities along the north and south lake shore. Studies on the sources of materials in its watershed, the hydrodynamic process of the lake, the sedimentation process, and the process of pollutant transport are required [26]. Furthermore, under the dual influence of climate change and human activities, LCH is faced with accelerated eutrophication and cyanobacteria outbreaks, as well as the ecological risks of new environmental pollutants [27]. Therefore, this study was conducted on LCH, a typical plateau lake, to identify the morphological features, microstructure, and elements enriched on the surface of the MPs in the water body and sediments, to clarify their abundance and spatial distribution characteristics, and to determine the correlation between the MPs and environmental factors so as to identify the potential sources of the MPs. The results of this study will help us to better understand the characteristics and distribution of MPs in plateau lakes under the dual influence of human activities and special natural environments and provide a reference for the analysis of multiple sources of MPs pollution in freshwater systems.

2. Materials and Methods

2.1. Study Area and Sample Collection

LCH is located at 26°27′ to 26°38′ N, 100°38′ to 100°41′ E, in Yongsheng County, Lijiang City, Yunnan Province. As a typical tectonic depression and deep-water type plateau lake, the water level continues to decline due to a combination of climate change and anthropogenic disturbances, and is now in the shrinking phase. Due to the small watershed area with seasonal inflow of rivers into the lake, and the surface evaporation being approximately three times greater than the watershed precipitation, the recharge is mainly from groundwater, neighboring basins, and recharge from water transfer projects [28]. As a typical alkaline lake, LCH is also one of three lakes in the world in which Spirulina can grow naturally [29]. With the rapid socio-economic development of the basin, the environmental conditions of LCH have deteriorated, and it is progressing from a mesotrophic level to eutrophication. Therefore, the lake is facing a series of environmental problems, such as water level decline, water pollution, and eutrophication. Based on the morphology, water depth, and distribution of inflowing rivers, 36 sample sites were established by means of the satellite-based global positioning system (GPS) for surface water and sediment samples (Figure 1).
Surface water and sediment samples were collected in the field using glass water collectors (5 L) and stainless-steel grabs. Specifically, 20 L of surface water (~20 cm) was collected, then sequentially filtered using stainless-steel mesh sieves (<5 mm) and plankton mesh (<0.112 mm), before being stored in glass bottles. Additionally, 1 L water samples were collected in brown polyethylene bottles and stored at a low temperature and in the dark for the measurement of other hydrochemical indicators. Surface sediment (~2 cm) was collected using a grapple and stored in glass bottles. It was crucial that sufficient quantities of samples were obtained for the determination of the different hydration parameters, and the correct transportation and storage conditions were considered for each indoor analytical parameter.

2.2. Flotation and Observation of the MPs

The field-filtered water samples were shaken well and then fixed at 500 mL and divided into three portions. One sample was randomly selected and sieved through a 150-mesh sieve. The samples were rinsed into a beaker with 50 mL of hydrogen peroxide (H2O2) solution at a concentration of 30%, then shaken at a rotational speed of 100 r/min−1 and a constant temperature of 60 °C for 24 h to remove organic matter. Subsequently, saturated sodium chloride (NaCl) solution was added to the MPs, and the supernatant was collected after standing at room temperature for 24 h. The flotation was repeated three times. The supernatant was pumped and filtered using a mixed cellulose microporous filter membrane (<0.45 μm) using a vacuum pump, and the beaker containing the samples was rinsed three times with pure water. The solutions were all vacuum pumped and filtered. Finally, the membrane was placed in a glass Petri dish and closed for drying [30].
A stereo microscope was used to observe the morphological features of the MPs and record their morphology, color, and size. The microstructural features of the MPs were observed by means of scanning electron microscopy (SEM-EDS, AeroSurf 1500, Hitachi High-Technologies Corporation, Tokyo, Japan), and an energy spectrometer (S-3400N, Tokyo, Japan) was used to determine the elements attached to the surfaces of the MPs and their percentage contents. A Fourier infrared spectrometer was utilized to compare the MPs with standard maps of known plastics to determine the chemical composition [31].

2.3. Water Quality Parameters and Physicochemical Indexes Testing

Multi-parameter water quality monitoring instruments (YSI EXO2 series, Ohio, USA) were used in the field to measure pH, water temperature (T), dissolved oxygen (DO), nephelometric turbidity (NTU), salinity (Sal), and conductivity (CD). The concentrations and levels of total nitrogen (TN), total phosphorus (TP), Chl-a, dissolved total nitrogen (DTN), nitrate–nitrogen (NO3−-N), dissolved total phosphorus (DTP), and orthophosphate (PO43−-P) in the water body were determined using an ultraviolet (UV) spectrophotometer under different wavelength coverages [32].
The concentrations of sediments TN, DTN, NO3−-N, TP, and DTP were determined via UV (the alkaline potassium persulfate oxidation method). A Mastersizer 2000 laser particle sizer (Malvern, UK, measuring range 0.02–2500 μm), total organic carbon (TOC) analyzer, and gas isotope ratio mass spectrometer (MAT253, Thermo Fisher Scientific, Waltham, MA, USA, error range within 0.2%) were used to measure the grain size, TOC, and stable isotopes (δ13Corg and δ15N) of the surface sediments, respectively. The average value of each index was taken after two repeated measurements.

2.4. Quality Control and Data Analysis

In order to minimize systematic errors, cotton clothing was worn during field sampling and the indoor experiments, and plastic utensils were avoided during sampling, transportation, and the experiments. The containers involved in the experiment were washed in deionized water, dried, and used. Beakers were closed with tinfoil to ensure that the glass Petri dishes were always enclosed. In addition, doors and windows were kept closed during the experiment to avoid exposure to MPs in the outdoor dust and air [33].
The abundance of MPs was expressed as the number of particles per m3 (n∙m−3) and per kg (n∙kg−1) of water and sediment, respectively. Excel 2021 was used to count the different colors, particle sizes, and shapes of the MPs. ArcGIS 10.4.1 was used to plot the sample points and the spatial distribution of the MPs. Origin 2018 was used to plot the morphology composition and the abundance of the MPs. Correlation analyses were performed using R language 4.2.2, and the level of significance was set to 0.05.

3. Results

3.1. Microstructural Characterization and Elemental Attachment

Under the stereo microscope, all the MPs analyzed in the surface water and sediments of LCH were fibrous MPs, predominantly appearing as long threads. Some of these fibers were curved spirals, exhibiting transparent, blue, and red colors, with most particle sizes being less than 1 mm (Figure 2a). High-resolution scanning electron microscopy (SEM-EDS) was used to capture the microstructural features of the MPs. The overall structure revealed a long tubular shape, with surface-aging phenomena such as roughness, porousness, cracks, folds, depressions, or bumps (Figure 2b).
The MP surfaces were detected using an energy spectrometer (S-3400N) and found to be enriched in elements such as aluminum (Al) and iron (Fe) and halogens such as fluorine (F), chlorine (Cl), bromine (Br), and iodine (I), as well as metalloids and transition metals such as tellurium (Te) and silver (Ag), and the basic constituent elements of the material, such as carbon (C), oxygen (O), nitrogen (N), and silicon (Si) (Figure 3). Fluorine is a key element in special plastics, rubber, and other highly oxidizable products. Bromine and its compounds can be used as insecticides and dyes, while chlorinated compounds are chemically active and toxic. Various elements enriched on the surface of microplastics (MPs) participate in different environmental processes within water bodies and sediments.

3.2. Morphological Composition Characteristics

MPs are generally classified on the basis of factors such as shape, color, and particle size [34]. Based on the above classification criteria, the morphological compositions of the MPs in the surface water and sediment of LCH are shown in Figure 4. According to the classification criteria of <1 mm, 1–3 mm, 3–5 mm, and >5 mm, the detection rate of MPs of sizes <1 mm and 1–3 mm in the surface water of LCH was 100%, accounting for 34.8% and 51.5%, respectively, and the detection rate of MPs of sizes 3–5 mm and >5 mm was relatively low, accounting for 8.9% and 4.8%, respectively (Figure 4a). For sediments, the percentages of MPs of the four grain sizes were 52.4%, 39.5%, 6.8%, and 1.3%, respectively. The proportion of MPs of a size >5 mm was the lowest (Figure 4b). There was no sample site containing all four types of MPs in the whole lake.
In terms of the color composition of the MPs, the colors of the MPs in the surface water and sediment in LCH consisted of transparent, blue, red, black, pink, yellow, and green. The colors of the MPs in the surface water body were mainly transparent, blue, red, and black, accounting for 68%, 15.7%, 10.1%, and 5%, respectively, and pink, yellow, and green MPs accounted for a total of only 1.2% (Figure 4c). The variety of MP colors in the sediment was roughly the same as in the water column. The main color components were transparent and blue, with 63% and 26%, respectively, and the other three colors together accounted for 11% (Figure 4d).
The main components of the detected fibrous MPs were polypropylene (polypropylene, PP), polyethylene terephthalate (PET), and rayon. In addition, some of the suspected polymers were found to be non-plastics after testing; these may have been substances such as carbon, cotton, and digestive fibers.

3.3. Abundance and Spatial Distribution of MPs

The statistical results showed that MPs were detected in the surface water and sediment at all sites in LCH, with a detection rate as high as 100%. The abundance of MPs in the surface water ranged from 90 to 770 n∙m−3, with an average value of 329.44 n∙m−3, and the abundance of MPs in the sediment ranged from 10 to 115 n∙kg−1, with an average value of 43.19 n∙kg−1. Overall, the abundance of MPs was higher in the surface water than in the sediment.
In terms of the spatial distribution, the abundance of MPs in the surface water and sediment in LCH did not exhibit obvious regular changes. However, higher concentrations of MPs in the surface water were found in the northeastern part of the lake, and the southern lake area also showed higher MP levels compared to other regions (Figure 5a). The abundance of MPs in the sediment displayed a general increasing trend of increasing from north to south, with the highest concentrations located in the southern lake area (Figure 5b).

3.4. Environmental Parameters in the Surface Water and Sediment

The experimental results showed that the concentration of TN in the surface water of LCH was 0.7–1.4 μg/mL, with an average concentration of 1.15 μg/mL, and the sample points with higher concentrations were located in the northeastern and eastern parts of the lake (Figure 6a). The TP concentrations ranged from 0.03 to 0.13 μg/mL, with an average of 0.06 μg/mL. In contrast to the spatial distribution of the TP, which was highest in the surface waters of the southwestern part of the lake, the southern and central parts of the lake had relatively low concentrations of TP (Figure 6b). The Chl-a concentration ranged from 4.4 to 9.9 μg/L, with an average of 6.16 μg/L. The highest Chl-a was in the northernmost part of the lake, followed by the northern and the southern lake area, forming a distribution pattern of high in the north and south and low in the center of the lake (Figure 6c). The DO concentration in the water body was 0.21–3.52 mg/L, with an average concentration of 0.7 mg/L. The spatial distribution of the DO was consistent with the changes in the Chl-a concentration, showing higher concentrations in the northern and southern parts of the lake and significantly lower concentrations in the center (Figure 6d).
The spatial distribution trends of the organic matter and the carbonate percentage in the surface sediment were basically consistent, with the highest values located at the western lake shore and an overall trend of decreasing variation from the western and northwestern lake shore to the eastern and southeastern parts of the lake. The variation of the organic matter (OM) ranged from 2.36 to 12.17%, with a mean value of 8.25% (Figure 7a). The variation of the carbonate (CaCO3) ranged from 8.5 to 16.65%, with a mean value of 13.01% (Figure 7b). The spatial variability of the stable isotope (δ13Corg and δ15N) ratios (C/N) was large, with a range of 2.38–25.62. In terms of the spatial distribution of other lakes in the eastern lake’s region, the highest values were located in the southern area with more inlet rivers (Figure 7c). The median grain size is a crucial parameter in the composition of sediment grain size, reflecting changes in the overall sediment grain size content of the lake. In LCH, the median grain size of the surface sediment ranged from 3.61 to 30.16 μm, with an average value of 6.42 μm. Spatially, the median grain size exhibited a decreasing trend from south to north (Figure 7d).

4. Discussion

4.1. Pollution Characteristics of MPs in LCH

Fibrous MPs, as the most common type of MP contamination, dominate freshwater systems such as lakes and rivers [35]. The predominance of fibrous MPs in the surface water and sediment of LCH was in agreement with the findings of previous studies, such as the surface water of Lake Dianshan (88.04%) [15], surface water of Lake Dian (83.49%) [21], sediment of Lake Anchar, India (91%) [36], surface sediments of Lake Yangzong (72.68%) [37], and surface water and sediment of Lake Taihu (96.11% and 52.02%, respectively) [25]. In terms of color composition, a total of seven colors were detected in the surface water and sediment of LCH, suggesting the diversity of their sources. In addition, compared with the rapid changes of MP contamination in the water body, MPs in the sediment are the result of the accumulation of pollutants from the watershed environment after input [38]. MPs in the water body are partially decomposed during the sedimentation process, resulting in less kinds of color compositions in the MPs in the sediments compared to the water body. The results of the particle size combination characterization showed that small-sized MPs dominated in both the water body and sediment in the surface layer of LCH. The water body was dominated by a 1–3 mm particle size, and the sediment was dominated by a <1 mm particle size. This result was consistent with the statistical results of other investigations such as at Lake Dian (64.7%) [21], Lake Yangzong (72.82%) [37], and typical lakes in the Wuhan area (91.94% of MPs < 1 mm) [39]. MPs with a small particle size have a greater ability to migrate and carry pollutants. Fibrous MPs are more harmful to organisms than MPs with other properties [21,40]. With more fibrous and small particle size MPs in the surface water and sediment of LCH, the ecological risk is higher.
The surface structure of the MPs in the surface waters and sediment of LCH was mostly rough, porous, and cracked because of the combined effects of UV radiation, mechanical abrasion, and chemical weathering [41]. In addition, MPs undergo photo-oxidation, thermal oxidation, and chemical aging after long-term exposure to the external environment, as well as an increase in their specific surface area, which affects the functional groups and adsorption behavior of the MPs [42]. Due to their small size, large specific surface area, and hydrophobicity, MPs facilitate the transport of pollutants [43]. A large number of elements are attached to the surface of MPs, which also contain toxic and harmful elements such as F, Cl, and Br. Therefore, MPs in freshwater environments may form new complex pollution and then may impact ecosystems [44].
The nature of MPs themselves (shape, density, size, etc.) alters their sedimentation rate and migration capacity, and affects their spatial distribution pattern [45,46]. Furthermore, a number of aspects, such as the distribution of inlet rivers and the basin-scale differences in the intensity of human activities, dominate the spatial distribution patterns of MPs in lakes. In addition, the perennial prevailing winds and the intensity and flow direction of lake currents are important factors influencing the spatial re-differentiation of MPs. As the main input channel of MPs into the LCH water body, its inlet rivers and populated areas, are mainly concentrated in the southern part of the lake, the MPs transfer rapidly in the surface water body to the northeastern lake. For sediment, the direction of the bottom lake current was opposite to that of the surface water body, and the MPs were transferred from the northeastern lake area to the southern lake area with the lake current, resulting in a spatial distribution pattern in which the abundance of MPs in the surface sediments of LCH was higher in the south than in the north.
Due to the relatively low intensity of human activities around LCH, the industrial layout is predominantly agricultural, resulting in a relatively singular source of microplastics (MPs). Consequently, the abundance of MPs is relatively low compared to lakes such as Lake Taihu, Lake Dian, and the urban lakes in Wuhan (Table 1). However, during periods when the water level is lower than the outlet, it is difficult for pollutants to discharge from LCH, as a closed lake, causing the MPs to remain in the lake for extended periods. As a result, the abundance of MPs in the surface water and sediment of LCH is relatively high compared to Lake Dian, Lake Yangzong, and Lake Qinghai (Table 1). LCH is at risk of MPs pollution, warranting increased attention and more in-depth research.

4.2. Occurrence Mechanism and Potential Source of MPs in LCH

For freshwater systems such as lakes, environmental factors are closely related to the fate of microplastic particles in the lakes and tracing the interrelationship between their abundance and environmental conditions is an important method of determining the source of MPs [47]. The NTU, DO, and CD in the water body can reflect, to a certain extent, the accumulation and migration of MPs in localized spots, while turbidity, WT, and pH cannot accurately reflect the accumulation characteristics and migration of MPs [48]. The spatial distribution of microplastic abundance and TN mass concentration in Lake Dian was consistent, with a significant positive correlation between the two (p < 0.01). There was a negative correlation between microplastic abundance and Chl-a in the water body [49].
The abundance of MPs showed a positive correlation with total dissolved nitrogen and total phosphorus in the surface water in LCH, suggesting a common source. Dissolved organic nitrogen and total phosphorus were likely to originate from agricultural activities, such as fertilizer use and mulching processes, which contributed to this correlation. As these substances enter the lake via water currents, they form significant positive correlations with DO, pH, and Chl-a. Additionally, the abundance of MPs was relatively lower at higher levels of ammonia and nitrogen in the water column, indicating that MPs may be more likely to undergo re-mobility in anaerobic environments (Figure 8a). Conversely, in the sediment, because of the significantly lower dissolved oxygen, the microbial decomposition of organic matter was enhanced, accompanied by biodegradation, which converted organic nitrogen into inorganic nitrogen, thus significantly increasing the nutrient salt concentration in the sediment, while MPs degradation led to a relative decrease in their concentration, resulting in a significantly different distribution from that of the surface water column. The MPs of 3-5 mm in the sediment showed a significant positive correlation with the median particle size, indicating an area of higher MPs abundance in the sediment, which was inferred to the near-source deposition (Figure 8b).
The results indicated that the abundance of MPs in the surface water and sediments of LCH, as well as the correlation between the MPs of different colors and grain sizes with various environmental factors, were not significant. Although there was some correlation between the MPs and environmental factors, it was not strong. This suggests that human activities, land use patterns and intensity, and the location and flow rate of rivers entering the lake are the primary factors determining the spatial distribution pattern of the MPs. MPs are indirectly influenced by various environmental factors during their migration and transformation processes.
The classification characteristics of MPs are often an important basis for identifying their sources. As far as particle size is concerned, waste plastics under natural conditions are continuously weathered into smaller MPs under various physical and chemical effects, and the smaller the particle size, the easier it is for the MPs to enter tributary channels with rainfall and then converge into lakes, and ultimately accumulate in the sediment. Color provides information for the traceability of MPs and affects the feeding preference of animals [6]. The surface waters and sediments of LCH were dominated by transparent-colored MPs, which are similar to the colors of fishing lines and nets used by fishermen. The detected polymer components such as PP and PET are also commonly used for making fishing nets [50]. Fibrous MPs are mostly used in items of daily living, such as clothing washing, fishing gear use, and product packaging bags [51].
Combining the above source identification bases, small particle size, fibrous, transparent-colored MPs were the dominant components in the surface water and sediment of LCH. It can be hypothesized that their sources are clothing washing, plastic packaging bags, tail water discharge from sewage treatment plants, and the use of fishing gear and agricultural films. In addition, atmospheric deposition of MPs from long-range transport is another non-negligible source. However, only MPs of dominant components can be detected in the water body of each locus. Therefore, it is necessary to synthesize the detection results from multiple sites to objectively reflect the pollution status of MPs in the water.

5. Conclusions

At catchment areas for a watershed, such as LCH, plastic debris accumulates from different environmental carriers in the watershed, which eventually become MP particles after a long period of transport and transformation. This study showed that the abundance of MPs in the surface water and sediment of all sampling sites (36) covering the whole lake was not as high as that of the lakes in densely populated and developed areas, but MPs were detected at each sampling site, and their abundance was higher than that of lakes in sparsely populated and remote areas. The physical assemblage of the MPs did not show regular characteristics, which was consistent with other rivers and lakes. These results indicate that there is no geographical difference in the distribution characteristics of MPs in freshwater systems.
Based on the physical combination of the MPs and the compositional characteristics of the MPs, it was determined that the MPs mainly originated from the daily life of the residents in the flow area, such as from the washing of clothes and the use of plastic products like agricultural films and fishing nets, as well as MPs carried by the atmospheric long-distance transmission process. Human activities are the primary factor determining the spatial distribution of MPs in lakes, and natural environmental factors are involved in the migration and conversion process, affecting the secondary distribution pattern of MPs. The spatial distribution of microplastics in LCH did not show obvious regularity characteristics, and it exhibited an opposite pattern in the surface water and sediment. The findings indicated that the final distribution of MPs in the environment was influenced by a comprehensive range of factors, and the correlation between the environmental factors and the abundance of MPs was due to the large specific surface area of the MPs and the substances attached to their surface. This may have also been a coincidence. Therefore, the influence of the natural environment on MPs is a complex issue that needs further in-depth study.
LCH is a perennial closed lake, and the continuous input of watershed substances has led to unsatisfactory water quality. Compared to traditional environmental issues, the detection of new pollutants such as MPs in the water body and sediment and the toxic and harmful elements enriched on their surfaces, means that LCH is facing greater environmental stress. In addition, the introduction of biological factors will be an indispensable part of research work to recognize the potential ecological risk of MPs in freshwater systems.

Author Contributions

Conceptualization, methodology, supervision, resources, foundation acquisition, writing—review and editing, H.Z.; formal analysis, writing—original draft preparation, L.D.; investigation and data curation, L.L., D.L., L.Z., H.L., T.X. and J.X. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by Yunnan Fundamental Research Projects (grant NO. 202301AT070362; 202101AT070049), the NSFC (Grant No. U2202207), and the Special Project for Social Development of Yunnan Province (Grant No. 202103AC100001).

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Acknowledgments

We are grateful to the teachers and students who participated in the field collection of the data.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Li, Y.; Fang, L.; Wang, Y.; Mi, W.; Li, J.; Zhang, G.; Yang, P.; Chen, Z.; Bi, Y. Anthropogenic activities accelerated the evolution of river trophic status. Ecol. Indic. 2022, 136, 108584. [Google Scholar] [CrossRef]
  2. Vethaak, A.D.; Legler, J. Microplastics and human health. Science 2021, 371, 672–674. [Google Scholar] [CrossRef]
  3. Wang, W.; Yuan, W.; Chen, Y.; Wang, J. Microplastics in surface waters of Dongting Lake and Hong Lake, China. Sci. Total Environ. 2018, 633, 539–545. [Google Scholar] [CrossRef] [PubMed]
  4. Rochman, C.M.; Hoellein, T. The global odyssey of plastic pollution. Science 2020, 368, 1184–1185. [Google Scholar] [CrossRef]
  5. Sun, C.; Li, W.; Zhang, Y. Pollution status and toxicological characteristics of microplastics in freshwater environment. Envrionmental Polution Control 2023, 45, 384–392, (In Chinese with English Abstract). [Google Scholar]
  6. Nava, V.; Chandra, S.; Aherne, J.; Alfonso, M.B.; Antao-Geraldes, A.M.; Attermeyer, K.; Bao, R.; Bartrons, M.; Berger, S.A.; Biernaczyk, M.; et al. Plastic debris in lakes and reservoirs. Nature 2023, 619, 317–322. [Google Scholar] [CrossRef]
  7. Wang, Z.Q.; Zhang, Y.L.; Kang, S. Research progresses of microplastics pollution in freshwater systems. Sci. Total Environ. 2021, 795, 148888. [Google Scholar] [CrossRef]
  8. Cao, Y.; Lin, L.; Pang, X.; Dong, L. CiteSpace-based visual bibliometric analysis of research status and emerging trends of microplastics in freshwater environment. J. Yangtez River Sci. Res. Inst. 2023, 40, 153–160, (In Chinese with English Abstract). [Google Scholar]
  9. Yuan, W.; Liu, X.; Wang, W.; Di, M.; Wang, J. Microplastic abundance, distribution and composition in water, sediments, and wild fish from Poyang Lake, China. Ecotoxicol. Environ. Saf. 2019, 170, 180–187. [Google Scholar] [CrossRef]
  10. Sun, X.; Chen, H.; Jia, Q.; Zhu, Y.; Ma, C.; Ye, J. Ecological risk assessment of microplastics occurring in surface water of terrestrial water systems across China. Environ. Sci. 2022, 43, 5040–5052, (In Chinese with English Abstract). [Google Scholar]
  11. Ballent, A.; Corcoran, P.L.; Madden, O.; Helm, P.A.; Longstaffe, F.J. Sources and sinks of microplastics in Canadian Lake Ontario nearshore, tributary and beach sediments. Mar. Pollut. Bull. 2016, 110, 383–395. [Google Scholar] [CrossRef] [PubMed]
  12. Zhang, G.; Ren, H.; Zhou, T.; Shen, H.; Wu, F. Research progress on the distribution and biotoxicity of microplastics in freswater environment. Water Wastewater Eng. 2022, 48, 162–171, (In Chinese with English Abstract). [Google Scholar]
  13. Wang, H.; Wang, W.; Liu, H.; Cao, J.; Zhang, X.; Chen, J.; Qi, Z.; Jiao, X.; Zhu, J. Spatial and temporal distribution characteristics of microplastics in the surface water of typical shallow lakes. J. Lake Sci. 2024, 36, 731–740, (In Chinese with English Abstract). [Google Scholar]
  14. Zhang, S.; You, X.; Gao, L.; Cai, J.; Chai, W. Research progress on detection methods, distribution and hazards of microplastics in freshwater environment. City Town Water Supply 2022, 6, 67–72, (In Chinese with English Abstract). [Google Scholar]
  15. Zhou, G.; Xu, C.; Shen, C.; Liu, S.; Liu, Y.; Li, F. Distribution, composition and ecological risks of microplastics in surface water of the Dianshan Lake. Acta Sci. Circumstantiae 2022, 42, 214–224, (In Chinese with English Abstract). [Google Scholar]
  16. Free, C.M.; Jensen, O.P.; Mason, S.A.; Eriksen, M.; Williamson, N.J.; Bazartseren, B. High-levels of microplastic pollution in a large, remote, mountain lake. Mar. Pollut. Bull. 2014, 85, 156–163. [Google Scholar] [CrossRef]
  17. Wang, Z.; Chen, L. Research progress on microplastics in terrestrial water systems. Appl. Chem. Ind. 2019, 48, 677–680, (In Chinese with English Abstract). [Google Scholar]
  18. Feng, S.; Lu, H.; Yao, T.; Xue, Y.; Yin, C.; Tang, M. Spatial characteristics of microplastics in the high-altitude area on the Tibetan Plateau. J. Hazard. Mater. 2021, 417, 126034. [Google Scholar] [CrossRef]
  19. Sun, X.; Hou, S.; Huang, R.; Zhang, W.; Zou, X.; Liu, K. Characteristics, sources and ecological risks of microplastics in Telashi Lake in Hoh Xil. Acta Sci. Circumstantiae 2023, 43, 231–240, (In Chinese with English Abstract). [Google Scholar]
  20. Zhang, F.; Guo, X.; Zhang, J.; Zhang, Z. Microplastics in Qinghai-Tibet Plateau and Yunnan-Guizhou Plateau lakes, China. Sci. Total Environ. 2024, 915, 169978. [Google Scholar] [CrossRef]
  21. Li, D.; Deng, C.; Zhang, Q.; Zhang, H.; Li, H.; Yuan, Z.; Duan, L. Pollution characteristics and source analysis of fibrous microplastics in the water body of Dianchi Lake. Wetl. Sci. 2022, 20, 529–536, (In Chinese with English Abstract). [Google Scholar]
  22. Yuan, Z.; Li, J.; Deng, C.; Li, D.; Zhang, Q.; Zhang, H.; Li, H. Spatial distribution and source analysis of microplastics in surface sediments of Dianchi Lake. J. Yunnan Agric. Univ. (Nat. Sci.) 2023, 38, 503–510, (In Chinese with English Abstract). [Google Scholar]
  23. Deng, C.; Li, D.; Li, J.; Guo, J.; Yang, F.; Zhu, A.; Li, H.; Zhang, H.; Yuan, Z.; Xie, M. Impacts of underwater topography on the distribution of microplastics in lakes: A case from Dianchi Lake, China. Sci. Total Environ. 2022, 837, 155708. [Google Scholar] [CrossRef]
  24. Duan, L.; Zhang, H.; Li, D.; Xu, W.; Li, H.; Xu, J.; Xu, T.; Deng, C. Pollution Characteristics of Microplastics in Surface Sediments from Lake Qilu. Environ. Sci. Technol. 2024, 47, 140–149, (In Chinese with English Abstract). [Google Scholar]
  25. Wang, B.; Zhu, W.; Wu, S.; Hou, H.; Cheng, L.; Xu, X.; Li, Y.; Lin, X.; Xue, Z. Distribution and changes in microplastics in Taihu Lake and cyanobacterial blooms formed by the aggregation of Microcystis colonies. Environ. Sci. Pollut. Res. 2023, 30, 107331–107340. [Google Scholar] [CrossRef]
  26. Hu, J.; Zhang, H.; Chang, F.; Li, T.; Cai, M.; Duan, L.; Zhang, L.; Zhang, Y. Spatial distribution of grain size composition of surface sediments in Lake Cheng (Chenghai) and their influential factors. Acta Sedimentol. Sin. 2020, 38, 340–348, (In Chinese with English Abstract). [Google Scholar]
  27. Hou, P.; Chang, F.; Duan, L.; Zhang, Y.; Zhang, H. Seasonal variation and spatial heterogeneity of water quality parameters in lake Chenghai in southwestern China. Water 2022, 14, 1640. [Google Scholar] [CrossRef]
  28. Wang, Y.; Tang, Y.; Xu, Y.; Yu, H.; Cao, X.; Duan, G.; Bi, L.; Peng, J. Isotopic dynamics of precipitation and its regional and local drivers in a plateau inland lake basin, Southwest China. Sci. Total Environ. 2020, 763, 143043. [Google Scholar] [CrossRef] [PubMed]
  29. Yu, H.; Qi, W.; Liu, C.; Yang, L.; Peng, J. Different stages of aquatic vegetation succession driven by environmental disturbance in the last 38 years. Water 2019, 11, 1412. [Google Scholar] [CrossRef]
  30. Xiong, X.; Zhang, K.; Chen, X.; Shi, H.; Wu, C. Sources and distribution of microplastics in China’s largest inland lake-Qinghai Lake. Environ. Pollut. 2018, 235, 899–906. [Google Scholar] [CrossRef]
  31. Hidalgo-Ruz, V.; Gutow, L.; Thompson, R.; Thiel, M. Microplastics in the marine environment: A review of the methods used for identification and quantification. Environ. Sci. Technol. 2012, 46, 3060–3075. [Google Scholar] [CrossRef] [PubMed]
  32. Wang, S. Sediment-Water Interface Process of Lakes: Theories and Methods; Science Press: Beijing, China, 2017. [Google Scholar]
  33. Bai, M.; Zhao, S.; Peng, G.; Gao, L.; Li, D. Occurrence, characteristics of microplastic during urban sewage treatment process. China Environ. Sci. 2018, 38, 1734–1743, (In Chinese with English Abstract). [Google Scholar]
  34. Di, M.; Wang, J. Microplastics in surface waters and sediments of the Three Gorges Reservoir, China. Sci. Total Environ. 2017, 616, 1620–1627. [Google Scholar] [CrossRef] [PubMed]
  35. Ding, L.; Mao, R.; Guo, X.; Zhang, Q.; Chen, Y. Microplastics in surface waters and sediments of the Wei River, in the northwest of China. Sci. Total Environ. 2019, 667, 427–434. [Google Scholar] [CrossRef] [PubMed]
  36. Neelavannan, K.; Sen, I.S.; Lone, A.M.; Gopinath, K. Microplastics in the high-altitude Himalayas: Assessment of microplastic contamination in freshwater lake sediments, Northwest Himalaya (India). Chemosphere 2022, 290, 133354. [Google Scholar] [CrossRef] [PubMed]
  37. Yuan, Z.; Li, J.; Chen, D.; Wang, X.; Deng, C. Occurrence differences and sources of microplastics in surface sediments and farmland soil in Yangzong Lake. Environ. Sci. Technol. 2023, 46, 151–159, (In Chinese with English Abstract). [Google Scholar]
  38. Zhao, X.; Chen, H.; Jia, Q.; Shen, C.; Zhu, Y.; Li, L.; Nie, Y.; Ye, J. Pollution Status and pollution behavior of microplastics in surface water and sediments of Urban Rivers. Environ. Sci. 2020, 41, 3612–3620, (In Chinese with English Abstract). [Google Scholar]
  39. Wang, F.; Bao, K.; Qi, X. Occurrence characteristics and ecological risk assessment of microplastics in surface water of Wuhan lakes in Yangtze River Basin. Chin. J. Environ. Eng. 2023, 17, 3953–3959, (In Chinese with English Abstract). [Google Scholar]
  40. Devriese, L.I.; Witte, B.D.; Vethaak, A.D.; Hostens, K.; Leslie, H.A. Bioaccumulation of PCBs from microplastics in Norway lobster bioaccumulation of PCBs from microplastics in Norway lobster (Nephrops norvegicus): An experimental study. Chemosphere 2017, 186, 10–16. [Google Scholar] [CrossRef]
  41. Xu, Z.; Chen, A.; Zhao, Y.; Zhang, Z.; Ban, Y.; Wang, J.; Huang, S.; Liu, H. Separation, identification and microscopic characteristics analysis of microplastics in Wuhan Municipal Sewage. Res. Environ. Sci. 2021, 34, 637–645, (In Chinese with English Abstract). [Google Scholar]
  42. Wei, J.; Wang, L.; Shen, J.; Luo, X.; Deng, L.; He, M. Effects of aging of microplastics in the environment on their physicochemical properties and ecotoxicity. J. Green Sci. Technol. 2022, 24, 195–199, (In Chinese with English Abstract). [Google Scholar]
  43. Zhang, G.; Zhou, Y.; Xu, Q.; Wang, Y.; Liu, C.; Li, F. Proceedings of joint effect of microplastics and pollutants in water. Trans. Oceanol. Limnol. 2019, 2, 59–69, (In Chinese with English Abstract). [Google Scholar]
  44. Ho, W.K.; Leung, K.S.Y. The crucial role of heavy metals on the interaction of engineered nanoparticles with polystyrene microplastics. Water Res. 2021, 201, 117317. [Google Scholar] [CrossRef] [PubMed]
  45. Hu, J.; Zuo, J.; Li, D.; Xie, Z.; Chen, L. Composition and distribution of microplastics in the water and sediments of urban rivers in Beijing. Environ. Sci. 2021, 42, 5275–5283, (In Chinese with English Abstract). [Google Scholar]
  46. Van Emmerik, T.; Schwarz, A. Plastic debris in rivers. WIREs Water 2020, 7, e1398. [Google Scholar] [CrossRef]
  47. Xu, S.; Ma, J.; Ji, R.; Pan, K.; Miao, A. Microplastics in aquatic environments: Occurrence, accumulation, and biological effects. Sci. Total Environ. 2020, 703, 134699. [Google Scholar] [CrossRef]
  48. Li, Y. Occurrence Characteristics, Source Apportionment and Environmental Influencing Factors of Microplastics in the Urban Rivers of Harbin. Master’s Thesis, Harbin Normal University, Harbin, China, 2022. [Google Scholar]
  49. Yuan, H.; Hou, L.; Liang, Q.; Li, J.; Ren, J. Correlation between microplastics pollution and eutrophication in the near shore waters of Dianchi Lake. Environ. Sci. 2021, 42, 3166–3175, (In Chinese with English Abstract). [Google Scholar]
  50. Irfan, T.; Khalid, S.; Taneez, M.; Hashmi, M.Z. Plastic driven pollution in Pakistan: The first evidence of environmental exposure to microplastic in sediments and water of Rawal Lake. Environ. Sci. Pollut. Res. 2020, 27, 15083–15092. [Google Scholar] [CrossRef]
  51. Men, C.; Li, D.; Zuo, J.; Xing, W.; Liu, M.; Wei, F.; Hu, J.; Xie, Z.; Xing, X.; Shen, Y. Spatial variation and potential sources of microplastics in rivers in Tongzhou District, Beijing. Environ. Sci. 2022, 43, 3656–3663, (In Chinese with English Abstract). [Google Scholar]
Water 16 02672 g001
Figure 1. Sampling sites of Lake Chenghai.
Figure 1. Sampling sites of Lake Chenghai.
Water 16 02672 g001
Water 16 02672 g002
Figure 2. The morphological (a) and microstructure (b) characterization of the MPs under the microscope.
Figure 2. The morphological (a) and microstructure (b) characterization of the MPs under the microscope.
Water 16 02672 g002
Water 16 02672 g003
Figure 3. Microstructure and surface attachment elements of MPs using SEM-EDS.
Figure 3. Microstructure and surface attachment elements of MPs using SEM-EDS.
Water 16 02672 g003
Water 16 02672 g004
Figure 4. Particle size and color composition of MPs in surface water (a,c) and sediment (b,d) of LCH.
Figure 4. Particle size and color composition of MPs in surface water (a,c) and sediment (b,d) of LCH.
Water 16 02672 g004
Water 16 02672 g005
Figure 5. The abundance and spatial distribution of the MPs in LCH; (a) surface water; (b) sediment.
Figure 5. The abundance and spatial distribution of the MPs in LCH; (a) surface water; (b) sediment.
Water 16 02672 g005
Water 16 02672 g006
Figure 6. The water quality parameters of the surface water in LCH; (a) total nitrogen (TN); (b) total phosphorus; (c) chlorophyll a (Chl-a); and (d) dissolved oxygen (DO).
Figure 6. The water quality parameters of the surface water in LCH; (a) total nitrogen (TN); (b) total phosphorus; (c) chlorophyll a (Chl-a); and (d) dissolved oxygen (DO).
Water 16 02672 g006
Water 16 02672 g007
Figure 7. The physicochemical parameters in the surface sediment of LCH; (a) organic matter (OM); (b) carbonate (CaCO3); (c) ratio of carbon to nitrogen; and (d) median size (d).
Figure 7. The physicochemical parameters in the surface sediment of LCH; (a) organic matter (OM); (b) carbonate (CaCO3); (c) ratio of carbon to nitrogen; and (d) median size (d).
Water 16 02672 g007
Water 16 02672 g008
Figure 8. Relationship between environmental factors and MPs in LCH; (a) water quality parameters with MPs in surface water; (b) physicochemical indexes with MPs in surface sediment.
Figure 8. Relationship between environmental factors and MPs in LCH; (a) water quality parameters with MPs in surface water; (b) physicochemical indexes with MPs in surface sediment.
Water 16 02672 g008
Table 1. Abundance and composition of MPs in other lakes.
Table 1. Abundance and composition of MPs in other lakes.
LakeAbundanceTypeSizeColorReference
Dianshan575–5375 n/kg bFiber<0.5 mmBlack[15]
Dian91.2 n/m3 aFiber<1 mmTransparent[21]
609.6 ± 206.1 n/kg bBlue[22]
Qilu157.66 n/kg bFiber<1 mmTransparent[24]
Taihu0–3.7 n/L aFiber1–5 mmBlack[25]
44.42–417.56 n/kg b0.3–1 mmWhite
Qinghai0.05–7.58 * 105 n/kg aSheet0.1–0.5 mm [30]
50–1292 n/m2 bFiber
Yangzong323.7 ± 115.6 n/kg bFiber<1 mmBlue[37]
LCH329.44 n/m3 aFiber<1 mmTransparentthis study
43.19 n/kg b
Note(s): a means the water, b indicates the sediment.
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Duan, L.; Luo, L.; Zhang, L.; Li, D.; Li, H.; Xu, T.; Xu, J.; Zhang, H. The Occurrence of Microplastics Pollution in the Surface Water and Sediment of Lake Chenghai in Southwestern China. Water 2024, 16, 2672. https://doi.org/10.3390/w16182672

AMA Style

Duan L, Luo L, Zhang L, Li D, Li H, Xu T, Xu J, Zhang H. The Occurrence of Microplastics Pollution in the Surface Water and Sediment of Lake Chenghai in Southwestern China. Water. 2024; 16(18):2672. https://doi.org/10.3390/w16182672

Chicago/Turabian Style

Duan, Lizeng, Liancong Luo, Longwu Zhang, Donglin Li, Huayu Li, Tianbao Xu, Jing Xu, and Hucai Zhang. 2024. "The Occurrence of Microplastics Pollution in the Surface Water and Sediment of Lake Chenghai in Southwestern China" Water 16, no. 18: 2672. https://doi.org/10.3390/w16182672

APA Style

Duan, L., Luo, L., Zhang, L., Li, D., Li, H., Xu, T., Xu, J., & Zhang, H. (2024). The Occurrence of Microplastics Pollution in the Surface Water and Sediment of Lake Chenghai in Southwestern China. Water, 16(18), 2672. https://doi.org/10.3390/w16182672

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop