Quantifying microplastic stocks and flows in the urban agglomeration based on the mass balance model and source-pathway-receptor framework: Revealing the role of pollution sources, weather patterns, and environmental management practices

Are we underestimating the driving factors and potential risks of freshwater microplastics from in situ and in silico perspective?

The high loads of heterogeneous microplastics (MPs) in water system sparked the exploration of MPs source and impact in the environment. However, the contributions of driving factors to MPs contamination and the potential risks posed by multidimensional characteristics are still poorly understood. By incorporating in situ investigation with machine learning predictions, this study reported widespread MPs contamination in both textile upstream and receiving watershed in the Yangtze River Delta. The dominant MPs categories were fibers (0.1-0.5 mm in size), transparent in color, and composed of polyethylene terephthalate. These morphological characteristics indicated a conditional fragmentation process, suggesting that larger MPs are more prone to fragmentation. Multivariable analysis revealed significant correlations between MPs occurrence and factors of metal concentrations, geographic locations, and water qualities, highlighting the roles of textile production and automotive tire wear in determining MPs abundance. Among five machine learning models, Random Forest outperformed others in predicting MPs abundance. The interpretable analysis indicated that longitude (35.3 %), TN (13.8 %) and Sb (13.4 %) were pivotal nodes in shaping the MPs abundance. Emission point sources from express, autotire and textile yield feature importance from 6.60 % to 7.88 %. A total 12.39 % of the predicted variability can be further explained by interaction effects. Besides, MPERI and MultiMP indices based on abundance, size, color, shape, and polymer distributions suggested that most sampling sites fell within moderate to high-risk categories. Artificial neural network-based assessment results are suitable for explaining the MPs induced risks and polymer type was the most influential variable in determining the risk values. These quantitative insights into the driving factors and potential risks behind MPs occurrence improve our knowledge to manage MPs pollution in large-scale watersheds, providing crucial information for the development of effective mitigation strategies.

Implementing differential recovery corrections enhances accuracy of mass balances on microplastics in wastewater treatment

This study examined the impact of using different analytical recovery practices to correct MP concentrations on the performance of count and mass balances of primary wastewater settling. Spiking tests using standard MPs were conducted to evaluate the influence of MP size and sample type on recovery. The derived recovery values were then used to correct MP concentrations and loads in a full-scale primary treatment facility. The results reveal substantial differences in recovery that were dependent upon MP size and sample type, underlining the necessity of incorporating these discrepancies when estimating MP concentrations. Omitting recovery considerations during MP concentration reporting led to underestimations of approximately 40 %. In contrast, incorporating MP size and sample type during recovery calculations fostered a more accurate representation of MP concentrations, thereby enhancing the closure of balance models. While a count balance model was not apparently improved through the use differential recovery, the mass balance model showed a significant improvement in closure, reducing the lack of balance from 30.2 % to 17.2 %. This discrepancy was primarily attributed to the differing proportions of the primary sludge stream load in each model. These findings highlight the importance of incorporating differential recovery into mass balance models and demonstrate the complementary nature of count and mass balance approaches in understanding the fate and transport of MPs in WWTPs. The results of this study have significant implications for improving environmental assessments, policies and engineering design of wastewater treatment processes.

Microplastics: an often-overlooked issue in the transition from chronic inflammation to cancer

The presence of microplastics within the human body has raised significant concerns about their potential health implications. Numerous studies have supported the hypothesis that the accumulation of microplastics can trigger inflammatory responses, disrupt the microbiome, and provoke immune reactions due to their physicochemical properties. Chronic inflammation, characterized by tissue damage, angiogenesis, and fibrosis, plays a crucial role in cancer development. It influences cancer progression by altering the tumor microenvironment and impairing immune surveillance, thus promoting tumorigenesis and metastasis. This review explores the fundamental properties and bioaccumulation of microplastics, as well as their potential role in the transition from chronic inflammation to carcinogenesis. Additionally, it provides a comprehensive overview of the associated alterations in signaling pathways, microbiota disturbances, and immune responses. Despite this, the current understanding of the toxicity and biological impacts of microplastics remains limited. To mitigate their harmful effects on human health, there is an urgent need to improve the detection and removal methods for microplastics, necessitating further research and elucidation.

Occurrence and emission characteristics of microplastics in agricultural surface runoff under different natural rainfall and short-term fertilizer application

Land-based microplastics (MPs) are considered the primary source of MPs in aquatic environments, with runoff being a major pathway for their transfer from soil to surface water. However, the transportation characteristics of MPs via agricultural surface runoff remain unclear. In this study, we investigated the occurrence and emission characteristics of MPs in agricultural surface runoff under various short-term fertilizer applications and natural rainfall events using laser direct infrared imaging analysis (LDIR). MPs from fertilizers and soils co-migrated with the agricultural runoff. The abundance and concentration of MPs in runoff were 145.90 ± 22.48-2043.38 ± 89.51 items·L-1 and 39.17 ± 21.94-523.04 ± 47.85 µg·L-1, respectively. Small and low-density MPs, such as polyethylene (PE), chlorinated polyethylene (CPE), and polyurethane (PU) in film/fragment form with 20-50 µm exhibited a higher mobility. No statistical differences were observed in the distribution of runoff MPs with the application of different fertilizers. There was a significant positive relationship between runoff MP abundance and rainfall intensity. The annual emission load in this study area was 116.73 g·hm-2, indicating that the transportation of MPs via agricultural surface runoff cannot be ignored. This study is conducive to understanding the migration behavior of MPs in soil-water environments in a better manner.

Microplastic pollution differences in freshwater river according to stream order: Insights from spatial distribution, annual load, and ecological assessment

Microplastic (MP) pollution has become a pressing concern in global freshwater ecosystems because rivers serve as essential channels for the transport of terrestrial debris to the ocean. The current researches mostly focus on the large catchments, but the impact on the small catchments remains underexplored. In this study, we employed Strahler's stream order classification to delineate the catchment structure of the Beijiang River in South China. The distribution pattern of MP contamination and the factors influencing the distribution pattern, were assessed across the streams at different orders. We found that the Beijiang River was moderately polluted compare to other rivers in China, with an average MP abundance of 2.15 ± 1.65 items/L. MP abundance ranged from 3.17 to 1.45 items/L in the streams at different orders, and significantly decreased with increasing stream order (R2 = 0.93). This highlights the key role of small rivers as the channels for the transport of MPs from watersheds to main streams. The high abundance of PP and PE fibers, the high correlation between the stream order and the resin proportion (R2 = 0.89), and the significant correlation between MP abundance and proximity to urban centers (P = 0.02), indicated that MP pollution across the streams at different orders was predominantly influenced by anthropogenic activities, rather than natural environmental factors. By integrating MP data with hydrographic information, the annual MP loads for the streams at Orders 1 to Order 5 were estimated to be 4.63, 39.38, 204.63, 503.06, and 1137.88 tons/yr, respectively. Additionally, an ecological risk assessment indicates that MP pollution led to a low risk in the Beijiang River. Our findings deepen the understanding of MP pollution within freshwater river networks, and emphasize the crucial role of tributary systems in transporting MPs to main river channels.

Effect of tire wear particle accumulation on nitrogen removal and greenhouse gases abatement in bioretention systems: Soil characteristics, microbial community, and functional genes

Tire wear particles (TWPs), as predominant microplastics (MPs) in road runoff, can be captured and retained by bioretention systems (BRS). This study aimed to investigate the effect of TWPs accumulation on nitrogen processes, focusing on soil characteristics, microbial community, and functional genes. Two groups of lab-scale bioretention columns containing TWPs (0 and 100 mg g-1) were established. The removal efficiencies of NH4+-N and TN in BRS significantly decreased by 7.60%-24.79% and 1.98%-11.09%, respectively, during the 101 days of TWPs exposure. Interestingly, the emission fluxes of N2O and CO2 were significantly decreased, while the emission flux of CH4 was substantially increased. Furthermore, prolonged TWPs exposure significantly influenced the contents of soil organic matter (increased by 27.07%) and NH4+-N (decreased by 42.15%) in the planting layer. TWPs exposure also significantly increased dehydrogenase activity and substrate-induced respiration rate, thereby promoting microbial metabolism. Microbial sequencing results revealed that TWPs decreased the relative abundance of nitrifying bacteria (Nitrospira and Nitrosomonas) and denitrifying bacteria (Dechloromonas and Thauera), reducing the nitrification rate by 42.24%. PICRUSt2 analysis further indicated that TWPs changed the relative abundance of functional genes related to nitrogen and enzyme-coding genes.

Quantifying annual microplastic emissions of an urban catchment: Surface runoff vs wastewater sources

Urban clusters are recognized as hotspots of microplastic pollution, and the associated urban rivers convey microplastics into the global oceans. Despite this knowledge, the relative contributions of various sources to the annual microplastic emissions from urban catchments remain scarcely quantified. Here, we quantified microplastic emissions from a riverine urban catchment in Japan. The total microplastics (size range: 10-5000 μm) released from the catchment amounted to 269.1 tons/annum, of which 78.1% is contributed by surface runoff and other uncontrolled emissions (UCE), and 21.1% emerges from the regulated wastewater (controlled emissions; CE), implying that approximately one-fifth is intercepted and removed by the wastewater treatment plants (WWTPs). This further indicated higher microplastic pollution by unmanaged surface runoff compared to untreated wastewater. In the dry season, WWTPs contributed significantly to the reduction of total microplastic emissions (95%) compared to wet periods (8%). On an annual scale, the treated effluent occupies only 0.1% of the total microplastics released to the river network (212.4 tons/annum), while the remaining portion is dominated by UCE, i.e., primarily surface runoff emissions (98.9%), and trivially by the background microplastic inputs that are potentially derived through atmospheric depositions in dry days (1.0%). It was shown that moderate and heavy rainfall events which occur during 18% of the year (within the context of Japan), leading to 95% of the annual microplastic emissions, are crucial for pollution control of urban rivers. Furthermore, our study demonstrated that surface area-normalized microplastic emissions from an urban catchment (∼0.8 tons/km2/annum) is globally relevant, especially for planning microplastic interventions for developed cities.

Microplastics in water: Occurrence, fate and removal

A global study on tap water samples has found that up to 83% of these contained microplastic fibres. These findings raise concerns about their potential health risks. Ingested microplastic particles have already been associated with harmful effects in animals, which raise concerns about similar outcomes in humans. Microplastics are ubiquitous in the environment, commonly found disposed in landfills and waste sites. Within indoor environments, the common sources are synthetic textiles, plastic bottles, and packaging. From the various point sources, they are globally distributed through air and water and can enter humans through various pathways. The finding of microplastics in fresh snow in the Antarctic highlights just how widely they are dispersed. The behaviour and health risks from microplastic particles are strongly influenced by their physicochemical properties, which is why their surfaces are important. Surface interactions are also important in pollutant transport via adsorption onto the microplastic particles. Our review covers the latest findings in microplastics research including the latest statistics in their abundance, their occurrence and fate in the environment, the methods of reducing microplastics exposure and their removal. We conclude by proposing future research directions into more effective remediation methods including new technologies and sustainable green remediation methods that need to be explored to achieve success in microplastics removal from waters at large scale.

An overview of microplastic pollution in the environment over the megacity of Shanghai during 2013-2022

Microplastics (MPs) are emerging pollutants that have been globally found in the environment, and have become a focus of intensive management for the Shanghai government in China. Although there are several studies reporting the abundance of microplastics (MPs) in different matrices in Shanghai city, the general data are still limited. This work comprehensively reviews microplastic (MP) pollution in the water, sediment, atmosphere, and soil of Shanghai during 2013-2022. A summary of characteristics such as the abundance, shape, and polymer composition of MPs is presented. Additionally, the pollution trends, traceability, and ecological risks of MPs are analyzed and evaluated. Based on the analytical results, we find that the inland water in Shanghai city is the most contaminated with the highest abundance of MPs at 14.76 × 103 particles/m3 on average, while the abundances of MPs in the external water, inland sediment, external sediment, indoor atmosphere, outdoor atmosphere, inland soil, and external soil are 2.78 × 103 particles/m3, 0.80 × 103 particles/kg, 1.37 × 103 particles/kg, 0.03 × 103 particles/m3, 0.08 × 103 particles/m3, 0.27 × 103 particles/kg, and 0.18 × 103 particles/kg, respectively. Polyethylene and polypropylene are the top two detected polymer compositions of MPs. Results of ecological risk assessment using risk index and pollution load index models indicate that the risks of MPs in the water and sediment of the Yangtze Estuary are high. It is noteworthy that the abundances of MPs at the junction site of Suzhou Creek and the Huangpu River as well as in the Yangtze Estuary exhibited an increasing trend between 2017 and 2019. This work contributes to a comprehensive overview of MPs in the environment of Shanghai city during 2013-2022 and provides important data for local governments to develop urgent strategies for the management of MP pollution. However, more investigations are increasingly needed for better understand the production, migration, ecological risk, and management of MPs in the environment of Shanghai city.

High-throughput absolute quantification sequencing reveals the adaptive succession and assembly pattern of plastisphere communities in municipal sewer systems: Influence of environmental factors and microplastic polymer types

Municipal sewer systems have received increasing attention due to the magnitude of the microplastic stock and its potential ecological impacts. However, as a critical aspect of the adverse impacts, little is known about the plastisphere that forms in these engineered environments. Using high-throughput absolute quantification sequencing, we conducted a systemic study combining field survey and laboratory batch test to explain the general plastisphere pattern and the role of environmental and polymeric factors in driving plastisphere succession and assembly there. We demonstrated the capacity of microplastics to support high levels of microbial colonization, increasing by 8.7-56.0 and 1.26-5.62 times at field and laboratory scales, respectively, despite the less diverse communities hosted in the resulting plastisphere. Sediment communities exhibited higher diversity but greater loss of specific operational taxonomic units in their plastisphere than in the wastewater. The former plastisphere had primarily an enhanced methanogenesis-oriented metabolic network linked to hydrolysis fermentation, hydrogen-producing acetogenesis, and denitrification, while the latter had a pronounced niche partitioning and competitive interaction network. Exogenous substrate flux and composition were key in stimulating plastisphere community growth and succession. Furthermore, the high nitrogen baseline facilitated alternative niche formation for plastisphere nitrifiers and denitrifiers, and the plastisphere pathogens associated with denitrification and plastic biodegradation functions increased significantly. The aerobic state also promoted a 1.71 times higher colonizer load and a denser interaction pattern than the anaerobic state. Selective filtering by polymers was evident: polyethylene supported higher plastisphere diversity than polypropylene. This study provides new insights into the mechanisms driving colonizer loads and the adaptive succession and assembly of the plastisphere in such a typically hydrodynamic and highly contaminated environment. The results help to fill the knowledge gap in understanding the potential role of microplastics in shaping the microecology of sewers and increasing health risks and substrate loss during sewer transfer.

Are wastewater treatment plants as the source of microplastics in surface water and soil?

Microplastics (MPs) are widely detected in wastewater treatment plants (WWTPs) and natural environment, while the relationship of MPs pollution in both media is not fully understood. In this study, the occurrence of MPs in WWTPs and in surface water and soil was investigated, and their relationship was critically formulated. Results showed although wastewater treatment could effectively remove MPs (58.2%), the effluent was still the important source of MPs in the river, while sludge was not as important as the effluent of MPs in the soil. Specifically, the dominant size ranges of MPs were 0-200 µm, with main type of PE in all wastewater, sludge, river and soil. The dominant shape of MPs in wastewater and river was film. However, the shapes were different between sludge (52.1% of fibers) and soil (40.6% of fragment). Overall, WWTP input and surface runoff were the main source of MPs pollution in surface water, and the abrasion of agricultural films accounted for the MPs pollution in soil. The findings revealed the distribution and interconnection of MPs in WWTPs and environmental media, which could help to trace the sources of MPs pollution and assess the ecological risks in the environment.

Microplastics discharged from urban drainage system: Prominent contribution of sewer overflow pollution

Urban drainage system is an important channel for terrigenous microplastics (<5 mm in size) to migrate to urban water bodies, especially the input load caused by overflow pollution in wet weather. Investigating how they transport and discharge is essential to better understand the occurrence and variability of microplastics in different water ecosystems. This study evaluated the abundance and distribution characteristics of microplastics in the drainage systems of typical coastal cities in China. The impacts of meteorological conditions and land use were explored. In particular, the prominent contribution of drainage sewer overflow pollution during storm events were investigated. The results showed that the microplastics abundance in daily sewage discharge from different drainage plots ranged between 13.6 and 30.8 items/L, with fibers as the dominant type of microplastics. Sewer overflow discharge can greatly aggravate microplastic abundance to 83.1 ± 40.2 items/L. Road runoff and sewer sediment scouring were the main pollution sources. Systematic estimates based on detailed data showed that the average microplastics emitted per capita per day in household wastewater was 3461.5 items. A quantitative estimation method was proposed to show that the annual emissions load of microplastics via urban drainage system in this research area was 5.83×10¹⁰ items/km², of which the proportion of emissions in wet weather accounted for about 60%. This research provides the first full-process of assessment and source apportionment of the microplastic distribution characteristics in old drainage system. The occurrence of storm events is an important marker of increased microplastic abundance in urban rivers, with a view to urgent need for interception of surface runoff and purification of sewer overflow pollution.