Global meta-analysis of microplastic contamination in reservoirs with a novel framework

Vertical Differentiation of Microplastics Influenced by Thermal Stratification in a Deep Reservoir

Microplastics (MPs) are an emerging environmental concern. However, vertical transport of MPs remains unclear, particularly in deep reservoirs with thermal stratification (TS). In this study, the vertical variation in MP organization, stability, migration, and the driving factors of the profile in a deep reservoir were comprehensively explored. This is the first observation that TS interfaces in a deep reservoir act as a buffer area to retard MP subsidence, especially at the interface between the epilimnion and the metalimnion. Interestingly, there was a size-selection phenomenon for MP sinking. In particular, the high accumulation of large-sized MPs (LMPs; >300 μm) indicated that LMPs were more susceptible to dramatic changes in water density at the TS interfaces. Furthermore, simultaneous analysis of water parameters and MP surface characteristics showed that the drivers of MP deposition were biological to abiotic transitions during different layers, which were influenced by algae and metals. Specifically, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and microscopic Fourier transform infrared analyses implied that the occurrence of metals on the MP surface can promote MP deposition in the hypolimnion. Our findings demonstrated that TS significantly influenced the MP fate in deep reservoirs, and the hotspot of MP exposure risk for vulnerable benthic organisms on the reservoir floor deserves more attention.

Multidecadal heavy metals and microplastic deposition records in an urban lake: the ecological risk assessments and influencing factors

With the development of urbanization and economic growth, the urban lake ecosystem faces many challenges derived from external factors. As pollutants in the aquatic environment, heavy metals and microplastics negatively influence the urban lake ecosystem due to their intrinsic properties. To understand the distribution patterns and multidecadal deposition characteristics of heavy metals and microplastics, six sediment cores were collected in March 2021 from a Chinese urban lake, Xinghu Lake, and the isotopic composition of cesium-137 and lead-210 was analyzed for the chronology of the sediment core. Here, the classifications of comprehensive ecological risk evaluation methods for heavy metals and microplastics were adjusted further. Meanwhile, the correlations among heavy metals, microplastics, sediment grains, and natural and social factors were further analyzed. The results showed that the sediments of Xinghu Lake were mainly fine silt (39%), and the average surface area of sediment was 1.82 ± 0.60 m²/g. The average concentrations of cadmium, chromium, copper, nickel, lead, vanadium, and zinc were 0.268 ± 0.077, 59.91 ± 16.98, 23.29 ± 6.48, 52.16 ± 13.11, 36.83 ± 11.78, 119.57 ± 26.91, and 88.44 ± 29.68 mg/kg, respectively. The average comprehensive potential ecological risk indexes of heavy metals and microplastics in sediment cores were 46.59 ± 9.98 and 105.78 ± 23.32 in Xinghu Lake, and their risks were projected to reach high and very high levels by 2030 and 2050. The annual average temperature was the key natural factor for the abundances of heavy metals and microplastics, and the small sediment grain had a significant correlation with these. Agricultural activities were major pollution sources of heavy metals and microplastics, while the chemical fibers and plastic products were closely related to the abundance of microplastics.

Size dependent effects of nanoplastics and microplastics on the nitrogen cycle of microbial flocs

NANO: and microplastics (NPs/MPs) are a new type of persistent environmental pollutant. Microbial flocs are a type of microbial aggregate commonly used in aquaculture. To investigate the impact of NPs/MPs on microbial flocs with different particle sizes: NPs/MPs-80 nm (M 0.08), NPs/MPs-800 nm (M 0.8), and NPs/MPs-8 μm (M 8), NPs/MPs exposure tests (28 days) and ammonia nitrogen conversion tests (24 h) were conducted. The results showed that the particle size was significantly higher in the M 0.08 group when compared with the control group (C group). The TAN (total ammonia nitrogen) content of each group maintained the order of M 0.08 > M 0.8 > M 8 > C from days 12-20. The nitrite content in the M 0.08 group was significantly higher on day 28 than that in the other groups. In the ammonia nitrogen conversion test, the nitrite content of the C group was significantly lower than that of the NPs/MPs exposure groups. The results suggested that NPs contributed to microbial aggregation and affected microbial colonization. In addition, NPs/MPs exposure could reduce microbial nitrogen cycling capacity, with a size-dependent toxicity difference of NPs > MPs. The findings of this study are expected to fill the research gap on the mechanisms of NPs/MPs' impact on microorganisms and the nitrogen cycle in aquatic ecosystems.

Source or sink role of an urban lake for microplastics from Guangdong-Hong Kong-Macao greater bay area, China

Plastic production and consumption in China are larger than others in the world, and the challenge of microplastic pollution is widespread. With the development of urbanization in the Guangdong-Hong Kong-Macao Greater Bay Area, China, the environmental pollution of microplastics is becoming an increasingly prominent issue. Here, the spatial and temporal distribution characteristics, sources, and ecological risks of microplastics were analyzed in water from an urban lake, Xinghu Lake, as well as the contribution of rivers. Importantly, the roles of urban lakes for microplastics were demonstrated through the investigations of contributions and fluxes for microplastic in rivers. The results showed that the average abundances of microplastics in water of Xinghu Lake were 4.8 ± 2.2 and 10.1 ± 7.6 particles/m³ in wet and dry seasons, and the average contribution degree of the inflow rivers was 75%. The size of microplastics in water from Xinghu Lake and its tributaries was concentrated in the range of 200-1000 μm. In general, the average comprehensive potential ecological risk indexes of microplastics in water were 247 ± 120.6 and 273.1 ± 353.7 in wet and dry seasons, which the high ecological risks of them were found through the adjusted evaluation method. There were also mutual effects among microplastic abundance, the concentrations of total nitrogen and organic carbon. Finally, Xinghu Lake has been a sink for microplastics both in wet and dry seasons, and it would be a source of microplastics under the influence of extreme weather and anthropogenic factors.

Recent trends on microplastics abundance and risk assessment in coastal Antarctica: Regional meta-analysis

We investigated sources, abundance and risk of microplastics (MPs) in water, sediments and biota around Antarctica. The concentration of MPs in Southern Ocean (SO) ranged from 0 to 0.56 items/m³ (mean = 0.01 items/m³) and 0-1.96 items/m³ (mean = 0.13 items/m³) in surface and sub-surface water. The distribution of fibers in water was 50%, sediments were 61%, and biota had 43%, which were followed by fragments in the water (42%), sediments (26%), and biota (28%). Shapes of film had lowest concentrations in water (2%), sediments 13%), and biota (3%). Ship traffic, drift of MPs by currents, and untreated waste water discharge contributed to the variety of MPs. The degree of pollution in all matrices was evaluated using the pollution load index (PLI), polymer hazard index (PHI), and potential ecological risk index (PERI). PLI at about 90.3% of locations were at category I followed by 5.9% at category II, 1.6% at category III, and 2.2% at category IV. Average PLI for water (3.14), sediments (6.6), and biota (2.72) had low pollution load (<10). Mean PHI for water, sediments, and biota showed hazards level V with a higher percentage of 84.6% (>1000) and 63.9% (PHI:0-1) in sediments and water, respectively. PERI for water showed 63.9% minor risk, and 36.1% extreme risk. Around 84.6% of sediments were at extreme risk, 7.7% faced minor risk, and 7.7% were at high risk. While 20% of marine organisms living in cold environments experienced minor risk, 20% were in high risk, and 60% were in extreme risk. Highest PERI was found in the water, sediments, and biota in Ross Sea, due to high hazardous polymer composition of polyvinylchloride (PVC) in the water and sediments due to human activity, particularly use of personnel care products and waste water discharge from research stations.

Distribution and risk assessment of microplastics in Liujiaxia Reservoir on the upper Yellow River

Microplastics (MPSs) distribution in global freshwater systems is extensively reported, but the distribution of MPSs in reservoirs of the Yellow River has rarely been studied. To fill in this gap, we systematically investigated the distribution of MPSs in surface water and bank sediments gleaned from Liujiaxia Reservoir of the upper Yellow River for the first time and conducted an ecological risk assessment in succession in this work. The results showed that the main polymer types of MPSs in the surface water and bank sediments of Liujiaxia Reservoir were polyethylene terephthalate (PET), polystyrene (PS), and polypropylene (PP), and the abundance of MPSs in the reservoir surface water and bank sediments ranged from 4.48 to 12.09 item/L and 447.27 to 1543.80 item/kg (dry weight), respectively. Further physical morphology analysis of MPSs in the samples revealed that MPSs in the surface water and bank sediments of Liujiaxia Reservoir were predominantly fibrous with small particle sizes (<1 mm), and there was abundant color, mainly exhibiting transparent, black, and blue. The results of the MPS pollution load index (PLI>1) and the hazard ranking of MPSs (H_Zone = 10.20 for surface water and H_Zone = 14.06 for bank sediments) yielded a hazard class II for MPS pollution in Liujiaxia Reservoir, the combined pollution risk index (PRI_Zone = 17.05 for surface water and PRI_Zone = 31.25 for bank sediments) stated clearly the potential ecological risk in the Liujiaxia Reservoir. Briefly, this study supplemented and enriched the data on the distribution of MPSs in the reservoirs of the Yellow River basin, and provide a benchmark for future pollution control and management in the reservoir area.

Tracing the Century-Long Evolution of Microplastics Deposition in a Cold Seep

Microplastic (MP) pollution is one of the greatest threats to marine ecosystems. Cold seeps are characterized by methane-rich fluid seepage fueling one of the richest ecosystems on the seafloor, and there are approximately more than 900 cold seeps globally. While the long-term evolution of MPs in cold seeps remains unclear. Here, how MPs have been deposited in the Haima cold seep since the invention of plastics is demonstrated. It is found that the burial rates of MPs in the non-seepage areas significantly increased since the massive global use of plastics in the 1930s, nevertheless, the burial rates and abundance of MPs in the methane seepage areas are much lower than the non-seepage area of the cold seep, suggesting the degradation potential of MPs in cold seeps. More MP-degrading microorganism populations and functional genes are discovered in methane seepage areas to support this discovery. It is further investigated that the upwelling fluid seepage facilitated the fragmentation and degradation behaviors of MPs. Risk assessment indicated that long-term transport and transformation of MPs in the deeper sediments can reduce the potential environmental and ecological risks. The findings illuminated the need to determine fundamental strategies for sustainable marine plastic pollution mitigation in the natural deep-sea environments.

Global occurrence, drivers, and environmental risks of microplastics in marine environments

With an increasing quantity of plastic waste being discharged into the oceans, marine microplastic (MP) pollution has received widespread attention. However, the global occurrence characteristics, environmental risks, driving factors, and source-sink relationships remain unclear. In this study, we conducted a meta-analysis based on 165 articles about marine MP pollution. It was found that the global marine MP abundance displayed a significant spatial heterogeneity, and the distribution pattern was influenced by offshore distance, population density, and economic development. The morphological characteristics of MPs showed a significant difference between seawater and marine sediment, and small-size MPs (<1 mm) accounted for the majority of all MPs in the marine environment. The environmental risk assessment revealed that most of the marine MP pollution still remains at low concentrations in the global context, with the Polyurethane (PU), Polyacrylonitrile (PAN), and Polyvinyl chloride (PVC) types of MPs showing high environmental-risk contributions. In addition, land-based waste and marine operations, which were considered to be the dominant sources of marine MPs, primarily aggregated at nearshore submarine areas, in the water column, and in the deep-sea bottom environment. This study suggested that the combination of a meta-analysis and Monte Carlo simulation can provide much valuable information regarding the global occurrence characteristics and environmental risks of marine MPs.

A novel framework-based meta-analysis for in-depth characterization of microplastic pollution and associated ecological risks in Chinese Bays

Among aquatic ecosystems, bays are ubiquitously contaminated with microplastics (MPs, size <5 mm), but a comprehensive understanding of their pollution characterization in Chinese Bays is largely elusive. The current study aims to systematically highlight factors intricating MP contamination as well as their geographic distribution, interactions, risk evaluation, and abundance prediction in bays. MPs' abundance was varied in different bays, at concentrations ranging between 0.26 ± 0.14-89, 500 ± 20, 600 items/m³ in water, 15 ± 6-6433.5 items/kg dry weight in sediment and 0.21 ± 0.10-103.5 items/individual in biota. Redundancy analysis, Permannova, and GeoDetector model revealed that the sampling and extraction/identification methods, and geographical locations were the major drivers affecting MP distribution and characteristics. The Mantel test highlighted that the MP characteristics changed with geographic distance, higher in water than that in sediment and biota. ANOSIM results showed that the different environmental media exhibit significant differences in MP characteristics (e.g., color, shape, and polymer). The ARIMA model predicted that Sanggou Bay and Hangzhou Bay have a higher potential for significantly increasing MP contamination in the future. The highest hazard index (HI) values for water, sediment, and biota were respectively reported at Jiaozhou Bay (18,844.16), Bohai Bay (11,485.37), and Dongshan Bay (48,485.11). The highest values for the ecological risk index (RI) in water, sediment, and biota were detected at Beibu Gulf (6,129,559.02), Haikou Bay (2229.14), and Dongshan Bay (561,563.05), respectively. Overall, this framework can be used at different scales and in different environments, which makes it useful for understanding and controlling MP pollution in the ecosystem.

The pollution of microplastics in sediments: The ecological risk assessment and pollution source analysis

The occurrence of microplastics (MPs) pollution in sediments has brought huge challenges to the development of society. Pollution control of MPs in sediments has become an inevitable requirement for current society. This requires implementing targeted pollution control measures in high MPs ecological risk areas and controls MPs discharge in pollution source. Existing studies lack in-depth understanding in MPs ecological risk assessment and MPs pollution source analysis, this limits the pollution control of MPs in sediments. In this study, the studies of MPs pollution in sediments from 2013 to 2022 were reviewed. The results showed that the environmental problems caused by MPs pollution in marine sediments have been widely discussed over the past decade. And the occurrence of MPs pollution in sediments brought potential threat to marine ecology and human food supply. Furthermore, pollution load index, polymer risk index and potential ecological risk index of MPs were frequently used in the existing ecological risk assessment of MPs in sediments. A large amount of monitoring data and simulation data is conducive to improving these MPs ecological risk assessment indicators. This can provide a useful reference for managers to formulate MPs pollution control measures. And MPs types and land-use types can provide basis to analyze the pollution source of MPs in sediments. Developing more accurate MPs detection and analysis technologies can further improve current MPs pollution source analysis system. This is conducive to control the discharge of MPs in the pollution source. In future studies, more complete MPs ecological risk assessment system and MPs pollution source analysis system should be established to control the pollution of MPs in sediments.

Damming has changed the migration process of microplastics and increased the pollution risk in the reservoirs in the Shaying River Basin

The impact of damming on river ecosystems has received increasing attention, but a comprehensive understanding of the occurrence, drivers and exposure risks of microplastic (MP) pollution in multigate dam-type rivers is lacking. We investigated the characteristics and abundance of MPs in water, sediment and biological tissues from samples collected in the vicinity of ten dams in the Shaying River basin and analyzed the effect of environmental and food web structural changes on MP accumulation in freshwater animals under the influence of dams. Dam construction affects the transportation, suspension, and deposition of MPs at different dam locations (upstream, reservoir, and downstream) by altering hydrodynamihas changed the migration process of MPs. The dams intercepted a large amount of MPs from upstream sediments in the reservoir but had no significant capturing effect on MPs in water. The structure of the food web in the reservoir was simplified and the animals in the reservoir had the highest risk of MP contamination. A high MP abundance (or high microplastic diversity integrated index (MDII) values) in the environment or simplification of the food web may have led to higher MP accumulation in animals. More effort is needed to monitor MP pollution in reservoirs and control it sources.

Data-driven discoveries on widespread contamination of freshwater reservoirs by dominant antibiotic resistance genes

The propagation of antibiotic resistance genes (ARGs) in freshwater reservoirs threatens ecosystem security and human health, and has attracted increasing attention. A series of recent research articles on ARGs provides a unique opportunity for data-driven discoveries in this emerging field. Here, we mined data from a total of 290 samples from 60 reservoirs worldwide with a data-driven framework (DD) developed to discover geographical distribution, influencing factors and pollution hotspots of ARGs in freshwater reservoirs. Most data came from Asia and Europe where nine classes of ARGs were most frequently detected in reservoirs with multi-drug resistance and sulfonamide resistance genes prevailing. Factors driving distribution of reservoir ARGs differed between reservoir waters and sediments, and interactions among these factors had linear or nonlinear enhancement effects on the explanatory power of ARG distribution. During the cold season, small-sized reservoir waters rich in organic carbon, mobile genetic elements (MGEs) and antibiotics had a higher pollution potential of ARGs; during the spring drought, sediments in large reservoirs located in densely populated areas were more conducive to dissemination of ARGs due to their richness in antibiotics and MGEs. Thus, distribution pattern of ARG pollution hotspots in reservoir waters and sediments varies greatly depending on the differences of internal and external factors. From the "One Health" perspective, this widespread contamination of freshwater reservoirs by ARGs we discovered through the DD framework should be a push to promote integrated research across regions and disciplines. Especially the human - food-chain - ecosystem interface needs an improved understanding of ARG contamination mechanisms and targeted monitoring and evaluation systems should be developed to maintain all ecosystem services in freshwater reservoirs as well as to safeguard human health.

New Perspective on the Mobilization of Microplastics through Capillary Fringe Fluctuation in a Tidal Aquifer Environment

The presence of plastic fragments in the environment is a growing global concern. In this study, we explored the effects of dynamic fluctuations of capillary fringe on the transport of microplastics (MPs) in the substrate combining various environmental and MP properties. Both experimental and Hydrus-2D modeling results confirmed that increasing cycles of water table fluctuation led to the rise of capillary fringe. An increase in the cycles of water table fluctuations did not significantly change the overall MP retention percentages in 0.5 mm substrate but altered the MP distribution along the column. In 1 and 2 mm substrate, the increase in cycle numbers enhanced the MP transport from substrate to the water below. In terms of the size of the MPs, more 20-25 μm polyethylene (PE2) were retained in the substrate compared to 4-6 μm polyethylene (PE1) under the same number of fluctuation cycles. High-density polytetrafluoroethylene (PTFE, 5-6 μm) exhibited higher retention percentages compared to PE1 particles. Ultraviolet aging for 60 days enhanced PE1 transport along the column, while 60 days of seawater aging did not affect PE1 transport greatly. For PTFE, ultraviolet and seawater aging enhanced its retention in the substrate. The retention percentages of both PE1 and PTFE in the column increased with the elevated ionic strength and the decrease of fluctuation velocity. This work highlights that capillary fringe fluctuation can serve as a pathway to relocate MPs to the tidal aquifer.

Long-term deposition records of microplastics in a plateau lake under the influence of multiple natural and anthropogenic factors

Microplastic accumulation in the lake aquatic environment has attracted worldwide attention, but the long-term deposition characteristics and influencing factors of microplastics are not clear. Hence, we attempted to analyze the factors that influence the accumulation of microplastics during the process of natural environmental change and social development through the method of the sedimentological approach. In this investigation, the chronological sequence of sediment core was set up based on lead-210 composition to study microplastic accumulation rates in a plateau lake, Jianhu Lake. For the first time, the records of microplastic deposition were analyzed combined with multiple anthropogenic and natural factors, including 4 natural and 17 social factors to reveal the influence of natural processes and social development on microplastic abundances. The results showed that sediments were highly contaminated by microplastics, and the mean abundance of microplastics in the sediment cores of Jianhu Lake was 924 ± 427 particles/kg, and showed a gradually increasing trend from the bottom (25 to 30 cm) to surface layer (0 to 5 cm). Blue and black were the main colors of microplastics, and the average proportion of wirelike microplastics was 63 %. Additionally, the polymer type of microplastic was mainly rayon, the surface morphology of different polymer types was disparate, and various elements enriched on the surface of microplastics were also detected. In the past 70 years, the deposition rate of microplastics in Jianhu Lake maintained the trend of continuous growth, and the abundance of microplastics is projected to be 448 to 3017 and 513 to 3670 particles/kg by 2035 and 2050, respectively. What is more, there are significant correlations among multiple natural and anthropogenic factors and microplastic deposition, as well as microplastic polymer species.

The sustainable management of microplastics pollution in sediments from China: Promulgating relevant laws and implementing targeted management

Microplastics (MPs) pollution in sediments brings a huge challenge to the sustainable development of society. China is one of the countries with the largest production and application of plastic products in the world. The sustainable management of MPs pollution in sediments from China has important implications for achieving the United Nations Sustainable Development Goals. There is a lack of targeted management measures for the sustainable management of MPs pollution in sediments from China. In this study, 74 study areas were collected to analyze the pollution status of MPs in sediments from China. The results showed that the study on MPs pollution in sediments from China was concentrated in the Bohai Rim Economic Circle (n = 12), the Yangtze River Delta Economic Circle (n = 16) and the Pearl River Delta Economic Circle (n = 13). And the average abundance of MPs in sediments from China showed a decreasing trend from coastal to inland. Fiber had the highest centrality degree in the correlation network of MPs types. The reduction of fiber in sediments can reduce the diversity of MPs in sediments from China. Population density, economic level, urbanization level and industrial structure were significantly correlated with MPs types in sediments from China. The targeted management measures can be formulated based on the contribution of different human activities to MPs types. Managing pollution sources and cutting off transmission pathways are effective means for the targeted management of MPs in sediments. In addition, legislation can effectively restrict the application of plastic products. Promulgating relevant laws and implementing targeted management are conducive to the sustainable management of MPs pollution in sediments from China. In future studies, a big data platform for MPs pollution should be established to obtain a comprehensive understanding in the pollution status of MPs in sediments from China.

Prevalence and risk assessment of microplastics in the Nile Delta estuaries: "The Plastic Nile" revisited

Recent research is directed toward studying plastic pollution in rivers, and estuaries due to the importance of freshwater bodies in all aspects of life. The river deltas and estuaries are interesting for studying the flux of plastics into the oceans. The Nile River has been identified as a hot spot of plastic litter flux in the eastern Mediterranean basin. In addition, it was nicknamed "Plastic Nile", yet this major river is largely unexplored with a lack of field measurements and adequate surveys. The current study was based on bridging this scientific gap. Three trips were conducted, covering 30 km in the Rosetta branch and 23 km in the Damietta branch, during the high water level in summer 2021, and 10 km off the inlet of Lake Burullus, in spring 2021. Microplastics in surface water ranged from 761 ± 319 to 1718 ± 1008 MPs/m³, and from 167 ± 137 to 1630 ± 1303 MPs/kg of dry sediments. Land use/ land cover mapping using Sentinel-2 images showed several sources of pollution that contribute to plastic contamination in the study area. Thermal analysis indicated seven plastic polymers; including, PE, PP, PET, PEVA, and PTFE, using discarded plastic products as reference materials. Microplastics were composed of colored and glossy fragments of sizes <500 μm, originating from land-based sources. Pollution load, polymer risk assessment, and ecological risk indices were calculated. Based on field observations macro-plastics were retained within the extensive network of infrastructure and dam systems. 80-106 billion MPs/year were estimated to flux from the Nile estuaries into the Mediterranean Sea. The current situation urges the development of binding plans to reduce plastic waste in the Nile Delta, as well as setting environmental monitoring points along the Deltaic coast.

A review of sources, status, and risks of microplastics in the largest semi-enclosed sea of China, the Bohai Sea

The largest semi-enclosed sea of China, the Bohai Sea, serves as an important sink of microplastics (MPs) originated from terrestrial and marine sources. This study summarized potential sources and migration pathways of MPs in the Bohai Sea and reviewed the abundance and characteristics of MPs in water, sediments, and organisms. Coastal anthropogenic activities (i.e., plastic production, agricultural activities, and industrial and domestic sewage discharge) and marine origins (i.e., aquaculture, marine litters, and transportation) might accelerate the MPs enrichment in the Bohai Sea. The abundance of MPs ranged from 0.07 to 5200 items/m³ in the seawater, mainly influenced by the application of different trawl nets/sieves with different sizes (0.005-0.33 mm). Sediments of coastal rivers contained the MPs ranging from 56.7 to 1795 items/kg, significantly higher than that of the Bohai Sea (6.24-461.6 items/kg). Among organisms, the average abundance of MPs was the lowest in zooplanktons (0.03 items/animal), significantly lower than that in invertebrates (1.39 items/animal) and fish (2.12 items/animal), but no biomagnification of MPs was observed. The preliminary risk assessment indicated that seawater in the Liaodong Bay had medium ecological risk of MPs while other bays of the Bohai Sea had minor risks. To make the ecological risk of MPs quantifiable and comparable, future research priorities are recommended to focus on more frequent field surveys, standardization of sampling methods, and establishment of toxicity database of common polymer types of MPs in the Bohai Sea.

Widespread occurrence of microplastics in marine bays with diverse drivers and environmental risk

Microplastic contamination in the sediment of marine bays has attracted widespread attention, whereas the distribution, sedimentation, morphology and risk of microplastics at regional scale remain poorly understood. By introducing a data mining framework into microplastic research, we compiled a microplastic dataset of 649 samples from 24 bays to enhance the understanding of geographical difference and drivers, transfer, composition profile and environmental risk of sedimental microplastics. Microplastic abundance varied from 0.72 to 1963.96 items/kg dry weight, with higher concentrations mainly occurring in East Asian bays. The spatial pattern in abundance was driven by the river plastic emissions, aquaculture production and hydrodynamic condition. A significantly positive correlation between microplastic abundance in water and sediment was found, and microplastic sedimentation was related to polymer density, hydrodynamic conditions and sediment properties. The dominant shape and polymer of sedimental microplastics were fiber and polypropylene, respectively, and the similarity of microplastic composition decreased with increasing geographical distance. The environmental risks of microplastics were partitioned into three classes (Rank II-Rank IV) with a two-dimensional assessment system considering the bioavailability and toxicity of microplastics, and Asian bays were identified as potential high-risk areas. To reduce the environmental risk of sedimental microplastics in bays, priority should be given to the removal of microfibers, and control measures depend on the risk classes and dominant polymers. Microplastic abundance and composition were significantly affected by methodological choices regarding sampling, pretreatment and identification, suggesting a unified methodology is essential to further enhance our knowledge on the distribution and risk of microplastics in marine bays.

Microplastics shift macrobenthic community structures near a coastal nuclear power plant under construction in North East China

Coastal sediments are considered to be a potential sink for microplastics, which mainly derived from the land-based sources. This study investigated microplastic pollution in the sediments of 20 stations near a nuclear power plant under construction in North East China and analyzed its impacts on macrobenthic communities. The average abundance of microplastics in three stations close to the nuclear power plant was 0.33 items/g, which was approximately 10 times higher than those in the distant stations. The clustering of microplastic characteristics (sizes, shapes, and colors) showed that the three stations near the plant were in one group, and the distant stations were in another group. A total of 105 macroinvertebrate species belonging to 7 phyla were identified in all stations, and the dominant phyla were Annelida and Arthropoda. Spearman rank correlation showed that rare taxa (83 species with a contribution <1 %) were positively correlated with microplastics and As, and redundancy analysis demonstrated that the distribution patterns of macrobenthic communities were similar to those of microplastics. Moreover, co-occurrence networks showed that the rare taxa were positively correlated with microplastics. Therefore, microplastics released from the nuclear power plant under construction might shift the structure of macrobenthic communities, especially the rare taxa.

Transport of Microplastics in Shore Substrates over Tidal Cycles: Roles of Polymer Characteristics and Environmental Factors

Tidal zones providing habitats are particularly vulnerable to microplastic (MP) pollution. In this study, the effects of tidal cycles on the transport of MPs (4-6 μm polyethylene, PE1; 125 μm polyethylene, PE2; and 5-6 μm polytetrafluoroethylene, PFTE) in porous media combined with various environmental and MPs properties were systemically investigated. The results indicated that smaller substrate sizes exhibited higher retention percentages compared to those of larger substrate sizes under different tidal cycles. In terms of the size of MPs, a larger size (same density) was found to result in enhanced retention of MPs in the column. As the number of tidal cycles increased, although the transport of MPs from the substrate to the water phase was enhanced, PE1 was washed out more with the change in water level, compared to PTFE. Additionally, more MPs were retained in the column with the increase of salinity and the decrease of flow velocity under the same tidal cycles. Ultraviolet and seawater aged PE1 showed enhanced transport, while aged PTFE showed enhanced retention under the same tidal cycles. These results can help understand the MP behaviors in the shoreline environment and provide support for future cleanup and sampling in tidal zones.

Characteristics and source-pathway of microplastics in freshwater system of China: A review

China plays a key role in global plastic production, consumption and disposal, which arouses growing concern about microplastics (MPs) contamination in Chinese freshwater systems. However, few reviews have discussed the characteristics of MP pollution in whole freshwater systems at a national scale. In this review, we summarized the characteristics, sources and transport pathways of MPs in Chinese freshwater systems including surface water and sediment. Results showed that current research mainly focused on the middle and lower reaches of the Yangtze River and its tributaries, as well as lakes and reservoirs along the Yangtze River. Large-scale reservoirs, rivers and lakes located in densely populated areas usually showed higher abundances of MPs. The majority of MPs in Chinese surface water and sediment mainly consisted of polyethylene and polypropylene, and the most common morphologies were fibers and fragments. To identify the sources and pathways, we introduced the source-sink-pathway model, and found that sewage system, farmland and aquaculture area were the three most prevalent sinks in freshwater systems in China. The source-sink-pathway model will help to further identify the migration of MPs from sources to freshwater systems.