Occurrence and distribution of microplastics in an urban river: A case study in the Pearl River along Guangzhou City, China

Occurrence and distribution of microplastics in peatland areas: A case study in Long An province of the Mekong Delta, Vietnam

Vietnam is known as one of the high plastic consumption countries in Southeast Asia. This study initially determined characteristics of microplastics (MPs) including morphology, polymer type, and abundance at peatland areas in Mekong Delta in Vietnam. The MPs level was found with an average abundance of 192.3 ± 261.3 items kg^-1. In details, those values at Thanh Hoa, Duc Hue, and Tan Thanh were observed at 57.0 ± 110.4 items kg^-1, 7.0 ± 10.6 items kg^-1, and 513.0 ± 186.9 items kg^-1, respectively. The results indicated that MP particle contaminations in peatland sediments are significant among sampling sites (p < 0.001). Also, FT-IR analysis indicated that polyvinyl chloride is the primary polymer (46.2 %), followed by polyethylene (20.9 %), and polypropylene (9.2 %) in peatland samples and their composition varies in different regions significantly. The fragments (67.0 %) and films (24.6 %) were the most common shapes, followed by fibers (7.6 %) and foams (0.9 %). Small MPs with particle size (300-1000 μm) was the most abundant in sediment samples. Moreover, the most popular colors observed in peatland sediments were aqua (26.6 %), white (25.6 %), blue (25.4 %), and green (12.7 %). Our findings indicated that anthropogenic factors and environmental processes that caused the transformation/transportation and accumulation, leading to rising MP contaminant concerns in peatland areas in Mekong Delta in Vietnam, mainly in terms of the spatial distribution of MPs. In summary, this study provided an in-depth knowledge of microplastic pollution in peatland areas, which is crucial for the building sustainable development strategies in these areas.

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

Microplastics are widely present in global ecosystems, threatening both marine and freshwater species. Given this problem, it is vital to research where land-based microplastics originate and how they are transmitted to receiving waters in urban agglomerations. Research results should inform systemic mitigation efforts to prevent future contamination. This study established the multi-directional transmission network of a microplastic mass balance system using a source-pathway-receptor framework, and involving annual source stocks and pathway flows with considerable variations under dry and wet weather patterns. Details of a baseline scenario quantifying the occurrence and spread of microplastics in an urban agglomeration were also determined in the context of current environmental management practices. We demonstrated that the total stock of the six major pollution sources amounted to 5317.7 ± 2175.3 and 3320.1 ± 953.6 tons/a in dry and wet weather, respectively; and 2347.8 ± 766.9 and 1991.8 ± 701.8 tons/a flows directly entered the sewer system and receiving water in Shanghai, China, respectively. Prominent microplastic stocks were found in atmospheric fallout, industrial wastewater, and domestic sewage. These stocks were much higher compared to crop farming wastewater, aquacultural wastewater, and livestock and poultry breeding wastewater. Total microplastic flows entering receiving water reached 3207.4 ± 1071.6 tons/a; the largest contributions were from wet weather overflow (23.7%), direct atmospheric fallout (21.7%), wastewater treatment plant effluent (14.2%), industrial wastewater (14.1%), and surface runoff (10.4%). Weather patterns led to divergent microplastic transmission pathways and mass flows, revealing a lagging timeline mode and illustrating the basic spatiotemporal features of microplastic contamination in urban agglomerations. Terminal disposal practices retained about two-fifths of the microplastic flows that would have otherwise been transmitted into receiving water. Of these, land surface sweep contributed half of the retained flow. Improvements in WWTP removal efficiency, storm sewage interception rate, industrial wastewater collection rate, and sewer sediment dredge rate could further enhance the systemic benefits.

Microplastics contamination in bivalves from the Daya Bay: Species variability and spatio-temporal distribution and human health risks

Microplastic contamination is an emerging global threat for various marine organisms. Marine invertebrates such as bivalve mollusks are more susceptible to the widespread presence of microplastics due to their limited abilities to escape from pollution exposure and they can readily ingest environmental pollutants like microplastics through their filter-feeding behaviors. In this study, microplastic contamination in bivalves related to species, spatial, and temporal variability were conducted. Results showed that the frequency of microplastic occurrence varied from 86.7 % to 93.3 % in six species of bivalves, and the average abundance of microplastics ranged from 3.5 to 8.6 items per individual or from 0.2 to 3.1 items per gram tissues wet weight. No significant difference was observed in microplastic abundances of bivalves collected from different research regions and sampling seasons. However, the sediment-dwelling bivalves had higher microplastics abundances than the water-dwelling bivalves. Microplastic features with various shapes, colors, sizes, and polymer types detected in bivalves were similar with those in seawater and sediment environments that they are living in. The potential risk assessment of microplastics in bivalves basing on polymer hazard index (PHI) was in the risk levels of II-III, implying that microplastic contamination in bivalves may pose health risk to human via seafood consumption.

Differences, links, and roles of microbial and stoichiometric factors in microplastic distribution: A case study of five typical rice cropping regions in China

Microplastics (MPs), as new pollutants in agroecosystems, have already attracted widespread attention from scientists. However, our understanding of MP geographic distribution and its influencing factors across spatial scales remains poor. Here, a regional-scale field investigation was conducted to assess the distribution characteristic of MPs in five major rice-growing regions of China, and we explored the roles of biological and abiotic factors, especially stoichiometry and microbial influences on MP distribution. MPs were observed in all sampling sites, averaging 6,390 ± 2,031 items⋅kg^–1. Sizes less than 0.5 mm and black and transparent MPs dominated. Fiber, classified as one of the MP shapes, occurred most frequently. MP community analysis, firstly used in paddy soil, revealed more black MPs abundance in Henan (HE), more rayon, blue, and other colors MPs in Hunan (HN), more transparent MPs in Tianjing (TJ), and more PE MPs in Heilongjiang (DB). Higher MP community diversity was found in most south paddy soils of this study, due to a broader range of sources. C/N showed a positive relationship with pellet-shaped MP abundance and MPs of size between 2 and 5 mm (P < 0.05). Chao1 index of soil microbial communities was positively correlated with the MP abundance, MPs of size less than 0.5 mm, and fiber abundance. The minimum temperature was positively correlated with MP abundance (P < 0.05), implying the potential effects of the freeze-thaw process might exist. The regression analysis highlighted the important role of population quantity in determining MP abundance (R = 0.421, P = 0.02). This study confirmed the wide distribution of MPs in different soil depths of paddy lands in China and demonstrated that its distribution was influenced by population quantity and environmental variables, such as microbiology. These findings could provide a basis for the toxicological behavior of MPs and the potential risk to human health.

Occurrence, characterization, and source delineation of microplastics in the coastal waters and shelf sediments of the central east coast of India, Bay of Bengal

The present study investigates the abundance, distribution, and characterization (shape, size, colour, chemical composition) of microplastics (MPs) in surface water and sediment from the shelf region of the central east coast of India. The surface water and sediment samples were collected at varying depths (12.8-63 m) from 21 locations covering ∼1200 km. The mean abundance of MPs in surface water and sediments were 5.3 × 10⁴ particles. km^-2, 209 ± 99 particles. kg^-1 of dry weight, respectively. Stereomicroscopy, Raman spectroscopy, and micro Fourier Transform Infra-red Spectroscopy (FTIR) were employed for the quantification and characterization of the polymers. Polyolefin (polyethylene and polypropylene) were the dominant polymers in both surface water and sediments indicating their source primarily land based. Surface water and sediment MPs were mostly blue coloured. Fibre (77%) and fragment (38%) were the dominant morphotypes in surface water and sediments, respectively. Surface characteristics studies using Scanning Electron Microscope (SEM) highlight the breakdown progress of the particles; Small MPs (<1 mm) account for >50% of the whole and dominant in the offshore region (10 km). The results reveal that the primary sources of MPs are most likely to be originating from riverine fluxes and fishing-based activities.

Distribution of microplastics in benthic sediments of Qinghai Lake on the Tibetan Plateau, China

Although several studies of microplastics (MPs) with size <5 mm in lake sediments focused on lakeshore areas, there have been no studies of distributions of MPs from lakeshores to the center of a lake. To test our hypothesis that MPs decrease from lakeshore to the center, a study was conducted on the largest brackish lake on the remote and high-altitude Tibetan Plateau, China. Abundances and characteristics of MPs in 14 samples of surface sediment collected from a river bay, a lake bay, and a lake central area were investigated. Distributions were influenced by river inflow, tourism, and minimal activity of humans, respectively around Qinghai Lake. The mean abundance of MPs in sediments of Qinghai Lake was 393 ± 457 items/kg, dry mass (dm). Based on the range of MP abundances in surface sediments of lakes worldwide, Qinghai Lake was classified as being moderately polluted with MPs. The dominant color, shape, size, and polymer type of MPs in sediments were transparent, fiber, 0.05-1 mm, and polypropylene, respectively. The river bay had a mean abundance of MPs two-fold greater than either the bay or central area of the lake. This indicates that the river catchment caused more pollution with MPs, while the central area of the lake was not a sink for MPs. Spatial trends of MPs in sediments from the shore to the center of the lake differed among areas, and were significantly related to wind, lake current, sedimentation rate, water- and sediment-properties, water depth, and proximity to land sources of MPs.

Slower antibiotics degradation and higher resistance genes enrichment in plastisphere

Microplastics (MPs) are increasingly entering the urban aquatic ecosystems, and the environmental significance and health risks of plastisphere, a special biofilm on MPs, have received widespread attention. In this study, MPs of polylactic acid (PLA) and polyvinyl chloride (PVC) and quartzite were incubated in an urban water environment, and the tetracycline (TC) degradation ability was compared. Approximatedly 24% of TC biodegraded in 28 d in the water-quartzite system, which is significantly higher than that in the water-PLA (17.3%) and water-PVC systems (16.7%). Re-incubation of microorganisms in biofilms affirmed that quartzite biofilm has a higher TC degradation capacity than the plastisphere. According to high-throughput sequencing of 16S rRNA and metagenomic analysis, quartzite biofilm contained more abundant potential TC degrading bacteria, genes related to TC degradation (eutG, aceE, and DLAT), and metabolic pathways related to TC degradation. An oligotrophic environment on the quartzite surface might lead to the higher metabolic capacity of quartzite biofilm for unconventional carbons, e.g., TC. It is also found that, compared with quartzite biofilm, the distinct microbes in the plastisphere carried more antibiotic resistance genes (ARGs). Higher affinity of MPs surface to antibiotics may lead to higher antibiotics stress on the plastisphere, which further amplify the carrying capacity for ARGs of microorganisms in the plastisphere. Compared to the nondegradable PVC MPs, surface of the biodegradable PLA plastics harbored significantly higher amounts of biomass and ARGs. Compared to the mineral particles, the capability of plastisphere has lower ability to degrade unconventional carbon sources such as the refractory organic pollutants, due to the abundance of carbon sources (adsorbed organic carbon and endogenous organic carbon) on the MPs surface. Meanwhile, the stronger adsorption capacity for pollutants also leads to higher pollutant stress (such as antibiotic stress) in plastisphere, which in turn affects the microbiological characteristics of the plastisphere itself, such as carrying more ARGs.

Spatio-vertical distribution of riverine microplastics: Impact of the textile industry

Microplastics (MPs) contamination in rivers and lakes is of paramount environmental importance as freshwater systems transport MPs from land to ocean. However, information regarding the spatio-vertical distributions of MPs in rivers, and their associations with surrounding industrial activities, is scarce and unclear. This study investigated MPs in the Taipu River, where there is a highly developed textile industry in Yangtze River Delta, China. Results showed a widespread occurrence of MPs particles with concentrations in the range of 0.65-6.07 items/L and 0.30-3.63 items/L in surface and bottom waters. A higher abundance of MPs was observed in surface waters than in bottom waters (t = 5.423, p = 0.024). The MPs distributions varied markedly in space, with the highest abundances being found in textile manufacturing zones as a consequence of industrial release (F = 14.642, p < 0.001). Transparent fibers were the major MPs compositions with 100-500 μm in size. Polyethylene terephthalate (PET) accounted for 71.4% and 59.73% of the total MPs identified in surface and bottom water, respectively. These PET polymers were predominantly presented in "fibrous" shapes, further reflecting the point sources of textile wastewater. Moreover, polyvinyl acetate (PVAC), used as fabric coating and resin matrix to form nonwoven fabrics, was firstly highlighted at a watershed scale. Although risk assessments revealed a light to moderate risks of MPs in the Taipu River, textile wastewater appears to cause a high "grey water" footprint and increase the risks of MPs pollution from textile life-cycle production. This study bridged gaps between field data and policy-making for MPs control and shed insight into the cleaner production of the textile industry.

A review on microplastics and nanoplastics in the environment: Their occurrence, exposure routes, toxic studies, and potential effects on human health

Microplastics (MPs) and nanoplastics (NPs) are emerging environmental pollutants, having a major ecotoxicological concern to humans and many other biotas, especially aquatic animals. The physical and chemical compositions of MPs majorly determine their ecotoxicological risks. However, comprehensive knowledge about the exposure routes and toxic effects of MPs/NPs on animals and human health is not fully known. Here this review focuses on the potential exposure routes, human health impacts, and toxicity response of MPs/NPs on human health, through reviewing the literature on studies conducted in different in vitro and in vivo experiments on organisms, human cells, and the human experimental exposure models. The current literature review has highlighted ingestion, inhalation, and dermal contacts as major exposure routes of MPs/NPs. Further, oxidative stress, cytotoxicity, DNA damage, inflammation, immune response, neurotoxicity, metabolic disruption, and ultimately affecting digestive systems, immunology, respiratory systems, reproductive systems, and nervous systems, as serious health consequences.

Distribution Patterns of Microplastics Pollution in Urban Fresh Waters: A Case Study of Rivers in Chengdu, China

Microplastics are widely found in oceans and rivers. In China, the research on microplastic pollution in inland urban fresh waters of China is insufficient. We studied microplastics in the surface waters of urban rivers in Chengdu, which is the largest city in western China. The concentration of microplastics in the analysis environment ranged from 5.00 to 10.5 items/L, and the average quantity was 8.82 items/L. The majority of the microplastics were transparent and took the form of fragments, particles, and fibers. Polyethylene terephthalate (PET) and polyamide (PA) were the dominant polymer types of the microplastics analyzed. Plastic particles ≤ 500 μm accounted for 69.8% of the total. This large proportion of small transparent microplastics in urban rivers in Chengdu is a potential threat to the growth of aquatic organisms and birds foraging from the river and may pose hazards to human health. Additionally, the correlation of microplastic content with population quantity and economic level was calculated by the Pearson coefficient method (p < 0.05), and the results showed that both have an important effect on the number of microplastics in rivers. This research provides a reference for understanding the level of microplastics in urban rivers in Chengdu and pollution control.

Riverine Plastic Pollution in Asia: Results from a Bibliometric Assessment

Rivers are important ecosystems, vital to the livelihoods of hundreds of millions of humans and other species. Despite their environmental, social, and economic importance, current use of rivers is unsustainable, due to a combination of solid waste and high levels of pollutants. Plastic materials are among the most predominant of such pollutants. Based on the need for additional research in this area, this study examines pressures put to rivers and explores trends related to riverine plastic pollution, with a focus on Asia. Apart from the bibliometric analysis, and relying on the collected information, examples describing the drivers of riverine plastic pollution in a sample of Asian countries are described, outlining the specific problem and its scope. Among some of the results obtained from it, mention can be made to the fact that much of the literature focuses on plastic pollution as a whole and less on one of its most significant ramifications, namely microplastics. Additionally, there is a need related to data availability on riverine plastic data and improving the understanding of transport mechanisms in relation to riverine plastic emission into the ocean. The results from this study illustrate the significance of the problems posed by plastic waste to Asian rivers and point out the fact that there are still significant gaps in respect of regulations and standards, which prevent improvements that are highlighted in this study. Based on the results of this bibliometric assessment, specific measures via which levels of riverine plastic pollution may be reduced are presented, bringing relevant new insights on this topic beyond the existing reviews.

Effect of land use on microplastic pollution in a major boundary waterway: The Arvand River

The occurrence of microplastics (MPs) was investigated in the Arvand River (Iran). The Arvand River (200 Km) is a major water body that flows through land with diverse use and it meets the Persian Gulf. This study constitutes the first assessment of MP pollution (prevalence and physico-chemical characteristics) in the Arvand river, both in the sediment and in the water. MP monitoring has been carried out in 24 stations located along the river. The MP pollution found ranged between 1 and 291 items·L^-1 and 70 to 15,620 items·kg^-1 (dw), in water and sediment, respectively. The majority of MPs were fibres, black/grey and yellow/orange in colour, and mainly 250-500 μm and >1000 μm in size. Polyethylene terephthalate (PET), polypropylene (PP), nylon (NYL), high-density polyethylene (HDPE), and polystyrene (PS) were found in sediment samples. All these polymers, except HDPE, were also identified in the water samples. PET and PP were dominant in the water samples; whereas PET and PS were the most abundant in the sediments. The vicinity of urban wastewater effluents could be behind MP pollution in both water and sediments. Significant differences (p < 0.05) of MP concentrations were affected by different land uses when comparing MP levels in undisturbed natural area with urban areas. A strong correlation between MP fibres and fragments found with PCA biplots revealed their similar distribution in water. In the sediment samples, fibre and fragment MP particles were significantly correlated with colloidal particles (e.g., clay and organic matter) suggesting a relevant role of colloidal particles in the aquatic ecosystem of the Arvand River in transporting MPs. This study contributes to the better understanding of the presence of MP in major rivers, which are systems that have been scarcely investigated for this type of pollution, and it can inform interventions to reduce MP inputs to the river and sea.

CH4 and CO2 Emissions from the Decomposition of Microplastics in the Bottom Sediment—Preliminary Studies

In recent years, a significant new threat to the environment has emerged, namely contamination with microplastics and their degradation products. The decomposition products of microplastics include, among others, greenhouse gases that are responsible for climate change. The article analyzes the emission of carbon dioxide and methane during the decomposition of various types of plastics in the form of microplastics in the bottom sediments in the presence of water. The research covers plastic materials made of polyvinyl chloride with a high and low content of plasticizers, polypropylene, and rubber. All analyzed microplastics generated the tested greenhouse gases. However, the quantity of gases generated depended on the type of polymer used. The highest concentration of methane, at 25,253 ppm after 180 days of incubation, was characterized by high plasticizer polyvinyl chloride, i.e., di (2-ethylhexyl) phthalate. In the case of carbon dioxide emissions, the values were comparable. The maximum value was obtained at 65,662 ppm for polypropylene microplastics. The influence of particle size on the amount of the emissions of these gases was also investigated. During the decomposition of microplastics in the bottom sediments in the presence of water, it was observed that the smaller the microplastic particles are, the greater the production of methane and carbon dioxide.

Urban natural wetland as a sink for microplastics: A case from Lalu Wetland in Tibet, China

Microplastics have been reported in a wide range of aquatic habitats. The wetlands are considered to be important roles in microplastic migration in water bodies. Nevertheless, knowledge about the occurrence and fate of microplastics in urban natural wetland is still limited for us to better understand how they become a sink of microplastics. In this study, the distribution and characteristics of microplastics in surface water, surface sediments, and sediment cores of the Lalu Wetland watershed, China's highest urban wetland, were investigated in August 2020 and January 2021. The abundances of microplastics in the surface water were 0.06-3.05 MPs/L. Microplastic abundance in the surface sediment and sediment core was 0.01-1.10 MPs/g and 0-16.23 MPs/g, respectively. The abundance of microplastics in the water was significantly lower in the wetland than that in the channel in the watershed. Comparing the wetland inlet and outlet water, the microplastic interception rates were 53% in January and 95% in August. The characteristics and seasonal variation of microplastics in the Lalu Wetland implied that urban natural wetlands were good at intercepting microplastics, and vegetation growth might play an important role on the interception of microplastics by the wetland. The increasing of microplastics from bottom to top in the sediment cores of Lalu Wetland also indicated that the ecological risks of microplastics accumulation in sediments of urban natural wetland required further attention.

Surface water, sediment, and biota: The first multi-compartment analysis of microplastics in the Karnafully river, Bangladesh

The Karnafullly River, which flows through Chattogram and falls into the Bay of Bengal, Bangladesh, is vulnerable to microplastic contamination. In this study, we looked at microplastics in the Karnafully River's surface water (5 sites), sediment (9 sites), and biota (4 species). Microplastic concentrations ranged from 0.57 ± 0.07 to 6.63 ± 0.52 items/L in surface water, 143.33 ± 3.33 to 1240 ± 5.77 items/kg dry weight in sediment, and 5.93 ± 0.62 to 13.17 ± 0.76 items/species in biota. A significant difference (P < 0.05) was found in the concentration of MPs in the Karnafully River's sediment, biota, and surface water. High percentage of fiber-shaped and small-sized MPs (<1 mm) were detected throughout the samples. Water and sediment MPs were often transparent/white and blue, whereas biota MPs were mostly black and red, indicating a color preference during biological uptake. The Bay of Bengal received 61.3 × 10⁹ microplastic items per day. The feeding zone of biota influenced the level of microplastics, with a trend of pelagic > demersal > benthic > benthopelagic. Polyethylene and polyethylene terephthalate were the most abundant polymer. Using the average fish intake rate in Bangladesh, we computed a possible consumption of 4015-7665 items of MPs/person/year.

Wastewater treatment plant effluent and microfiber pollution: focus on industry-specific wastewater

The production, use, and disposal of synthetic textiles potentially release a significant amount of microfibers into the environment. Studies performed on municipal wastewater treatment plants (WWTPs) effluent reported a higher presence of microfibers due to the mix of domestic laundry effluent through sewage. As municipal WWTPs receive influents from households and industries, it serves as a sink for the microfibers. However, research on textile industry WWTPs that primarily treat the textile fabric processing wastewater was not explored with the concern of microfibers. Hence, the review aims to analyze the existing literature and enlighten the impact of WWTPs on microplastic emission into the environment by specifically addressing textile industry WWTPs. The results of the review confirmed that even after 95-99% removal, municipal WWTPs can emit around 160 million microplastics per day into the environment. Microfiber was the dominant shape identified by the review. The average microfiber contamination in the WWTP sludge was estimated as 200 microfibers per gram of sludge. As far as the industry-specific effluents are analyzed, textile wet processing industries effluents contained > 1000 times higher microfibers than municipal WWTP. Despite few existing studies on textile industry effluent, the review demonstrates that, so far, no studies were performed on the sludge obtained from WWTPs that handle textile industry effluents alone. Review results pointed out that more attention should be needed to the textile wastewater research which is addressing the textile wet processing industry WWTPs. Moreover, the sludge released from these WWTPs should be considered as an important source of microfiber as they contain more quantity of microfibers than the effluent, and also, their routes to the environment are huge and easy.

Identification, classification and quantification of microplastics in road dust and stormwater

Microplastics (MP) have become a major emerging class of pollutants representing significant eco-toxicological risks for ecosystems and marine environments. The aim of this study was to identify, classify and quantify MP present in both road dust and stormwater samples. A significantly higher level of MPs within road dust samples was detected from industrial area (1130 particles/kg of dust) than from residential area (520 particles/kg of dust), while stormwater samples from industrial and residential sites yielded 26 particles/L and 17 particles/L, respectively. Fiber-like shape accounted for 53% and 74% in road dust and stormwater samples, respectively. The main polymeric materials collected for both road dust and stormwater samples were, in order of occurrence (i) low-density polyethylene, (ii) high-density polyethylene, (iii) polypropylene, (iv) polyethylene terephthalate, (v) polystyrene, (vi) polyester and (vii) poly (amide). Most of the MP had an average maximum dimension smaller than 2 mm for both road dust and stormwater samples. The results from this study demonstrates that road dust is a significant contributor to MP pollution through direct polymeric materials wear off and transfer through stormwater, which eventually will end up in open water ways and broader ecological niches.

Characteristics and distribution of microplastics in shoreline sediments of the Yangtze River, main tributaries and lakes in China-From upper reaches to the estuary

Microplastics (MPs) pervade the environment and increasingly threaten both natural ecosystems and human health. In this study, we investigated MP particle concentrations in sediment samples collected from 54 sites along the banks of the Yangtze River and its major tributaries and on lakeshores. The main polymer types found in the samples were polypropylene (PP), polystyrene (PS) and polyethylene (PE). MP particle abundance in the various types of locations was 35-51,968 particles/kg dry weight (d.w.) on the banks of the main river, 52-1463 particles/kg (d.w.) on the banks of tributaries and 2574-23,685 particles/kg (d.w.) on lakeshores. Correlation between MP abundance and mean annual runoff of each upstream tributary was significant, which suggests that increased runoff brings more microplastic waste to streambank sediments. The most common shape of MP particles in all upstream samples was flake, and in downstream samples it was foam. Small microplastic particles (< 0.50 mm) were predominant at all sites in this study, and the minimum particle size in samples from the Yangtze river banks was 0.065 mm. Average abundance of MP particles on the shores of the source lake was 9069 particles/kg around the inlet but only 866 particles/kg around the outlet; the difference was due to interception associated with sedimentation and precipitation in the lake. Our study represents the large-scale study of MPs contamination in sediment along the Yangtze River and provides important data regarding the accumulation and distribution of MPs in shoreline sediments of the upper, middle and lower reaches of the Yangtze River, main tributaries and lakes in China.

Comparative analysis of microplastic organization and pollution risk before and after thawing in an urban river in Beijing, China

Urban rivers are potential sinks for microplastic (MP) contamination in the environment. However, the footprint of MPs in urban rivers is not well understood because it is influenced by natural and anthropogenic factors. This study focused on the occurrence, pollution risk, and potential sources of MPs in surface water and sediments before and after thawing in Shahe River, Beijing. The size distribution, morphological characteristics and polymer types of MPs were analyzed using a micro-Raman spectroscopy. The results showed that the average abundance of MP obviously increased after river thawing, from 1772 ± 1668 items·m^-3 to 3877 ± 2517 items·m^-3 in surface water and 4776 ± 4817 items·kg^-1 to 14,004 ± 5371 items·kg^-1 in sediments. The MP polymer types were more diverse after thawing. The main MP type in surface water changed from polyethylene terephthalate (PET) to polypropylene (PP). Moreover, PP was the most common type in sediments. Small-sized MPs (SMPs, 10-300 μm) were dominant in Shahe River, with the proportion increasing from 48.5% to 83.3% in surface water and from 84.3% to 94.4% in sediments after thawing. Although the MP pollution risk increased after thawing, it was still low in the Shahe River. Unfortunately, changes in polymer types caused by thawing and the emergence of toxic polymers increased the ecological risk in the urban river. These results revealed the information of MP contamination before and after thawing, and highlighted the barrier influence of river icing on the migration of MPs. Overall, the results presented a new perspective on the environmental behavior of microplastics in urban rivers, suggesting that the occurrence and dominance of SMPs and the emergence of toxic polymers in urban environmental media require close attention in the future.

Plastic Interactions with Pollutants and Consequences to Aquatic Ecosystems: What We Know and What We Do Not Know

Plastics are a group of synthetic materials made of organic polymers and some additives with special characteristics. Plastics have become part of our daily life due to their many applications and uses. However, inappropriately managed plastic waste has raised concern regarding their ecotoxicological and human health risks in the long term. Due to the non-biodegradable nature of plastics, their waste may take several thousands of years to partially degrade in natural environments. Plastic fragments/particles can be very minute in size and are mistaken easily for prey or food by aquatic organisms (e.g., invertebrates, fishes). The surface properties of plastic particles, including large surface area, functional groups, surface topography, point zero charge, influence the sorption of various contaminants, including heavy metals, oil spills, PAHs, PCBs and DDT. Despite the fact that the number of studies on the biological effects of plastic particles on biota and humans has been increasing in recent years, studies on mixtures of plastics and other chemical contaminants in the aquatic environment are still limited. This review aims to gather information about the main characteristics of plastic particles that allow different types of contaminants to adsorb on their surfaces, the consequences of this adsorption, and the interactions of plastic particles with aquatic biota. Additionally, some missing links and potential solutions are presented to boost more research on this topic and achieve a holistic view on the effects of micro- and nanoplastics to biological systems in aquatic environments. It is urgent to implement measures to deal with plastic pollution that include improving waste management, monitoring key plastic particles, their hotspots, and developing their assessment techniques, using alternative products, determining concentrations of micro- and nanoplastics and the contaminants in freshwater and marine food-species consumed by humans, applying clean-up and remediation strategies, and biodegradation strategies.

Coral-inspired environmental durability aerogels for micron-size plastic particles removal in the aquatic environment

Removing microplastics (MPs) from water has been a huge challenge due to their inherent features including small size and high stability. In this research, inspired by the active adsorption and passive adhesion mechanisms of corals to MPs, a new strategy to fabricate polydopamine enhanced magnetic chitosan (PDA-MCS) aerogels was developed with a target to match the surface properties of MPs, achieving high MPs removal efficiency. PDA-MCS aerogels were highly efficient in adsorbing polyethylene terephthalate (PET) microplastics in water at pH values of 6-9, with a removal efficiency of up to 91.6%. Even after three recycles, PDA-MCS aerogels still displayed comparatively high removal efficiency (83.4%). Kinetic and isothermal experiments showed that the adsorption process was the result of electrostatic interactions and physical adhesion between aerogels and microplastics. Moreover, PDA-MCS aerogels maintained high removal efficiency under simulated environmental conditions, and the removal efficiency of PET, polyethylene (PE) and polystyrene (PS) microplastics in waters reached 97.3%, 94.6%, and 92.3%, respectively. Therefore, high-efficiency environmentally durable aerogels adsorbent materials have the potential for the removal of MPs from the aquatic environment.

Spatial and temporal distributions of microplastics and their macroscopic relationship with algal blooms in Chaohu Lake, China

Microplastics are emerging pollutants with sizes less than 5 mm, and they are ubiquitous. The occurrence of algal blooms has become a major problem affecting water quality in Chaohu Lake. To understand the relationship between the microplastic distribution and algal bloom density from a macroscopic point of view in Chaohu Lake, we collected microplastic samples from water and sediments during the wet and dry seasons and collected satellite remote sensing images of the algae density in recent years. The research results showed that the spatial and temporal distributions of microplastics were uneven and varied greatly. The average abundances of microplastics in the water samples were 2133 ± 1534 n•m^-3 in the dry season and 1679 ± 1577 n•m^-3 in the wet season, and the average abundance of microplastics in sediments was 308 ± 231 n•kg^-1. The abundance of microplastics in the estuaries was higher than those in other locations, and it was higher in the western part of the lake than in the eastern part. The microplastics in water and sediments presented different sizes, colors, shapes and compositions. The abundance, distribution and migration of microplastics were mainly affected by population density, rainfall, runoff, hydrodynamic force and wind direction. At a more macroscopic level, the distribution of microplastics was similar to that of algal blooms, TN and TP to some extent, especially in the early stage of algal bloom outbreaks, and the algal density was significantly positively correlated with the flux of microplastics into the lake. Microplastics, as carriers of algae, could promote the growth of algae blooms in the early stage, while in the later stage, microplastics and algal blooms could aggregate and coprecipitate through adsorption or adhesion and then inhibit the growth of algae.

Microplastic concentration, distribution and dynamics along one of the largest Mediterranean-climate rivers: A whole watershed approach

Microplastics (MPs) have been recognized as one of the most ubiquitous environmental pollutants globally. They have been found in all ecosystems studied to date, threatening biological diversity, ecosystem functioning and human health. The present study aimed to elucidate the environmental and anthropogenic drivers of MP dynamics in the whole catchment of the Biobío river, one of the largest rivers in South America. MP concentration and characteristics were analysed in 18 sites subjected to different sources of pollution and other human-related impacts. The sampling sites were classified in relation to altitudinal zones (highland, midland and lowland) and ecosystem types (fluvial and reservoir), and different water and territorial environmental variables were further collated and considered for analysis. Seven types of microplastic polymers were identified in the samples analysed, with a catchment mean (±SE) MP concentration of 22 ± 0.4 particles m^-3, and MP presence being significantly higher in lowlands (26 ± 2 particle m^-3) and in reservoirs (42 ± 14 particle m^-3). The most abundant type of MP was fragments (84%), with a mean concentration of 37 ± 6 particles m^-3. Overall, MP concentrations were low compared to those found in other studies, with a strong influence of human population size.

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.

Optimization of polypropylene microplastics removal using conventional coagulants in drinking water treatment plants via response surface methodology

Background and purpose

The ubiquitous presence of microplastics (MPs) in aquatic environments has been studied widely. Due to toxicological impacts of MPs and associated contaminants, it is crucial to understand the performance of MPs removal in drinking water treatment plants (DWTPs). Few studies have investigated removal characteristics of MPs via coagulation/flocculation processes, yet removal characterization of polypropylene microplastics (PPMPs) in this process is poorly understood. This study aims to optimize coagulation of virgin PPMPs in conventional DWTPs.

Methods

In this study, samples were synthesized through response surface methodology (RSM), polyaluminium chloride (PACl) was applied as a conventional coagulant to remove PPMPs in the coagulation/flocculation process, which has the least density among common polymers and is one of the most abundant manufactured polymers worldwide. A particle size analyzer (PSA) was used to measure floc size at different pH levels. Additionally, a zeta potential analyzer was used to measure stability of the flocs at different pH.

Results

Base on the experimental range in Design-Expert, results revealed that the optimum removal rate was predicted to be at pH 9, PACl concentration of 200 ppm, polyacrylamide (PAM) concentration of 21 ppm, and PPMPs size of d < 0.25 mm. According to the predicted optimum condition, actual and predicted removal rates were 18.00 ± 1.43% and 19.69%, respectively.

Conclusion

According to this study, PACl is not capable of efficiently removing virgin PPMPs in DWTPs, thereby exposing humans to eco-toxicological impacts of PPMPs through tap water.

Following the fate of microplastic in four abiotic and biotic matrices along the Ticino River (North Italy)

Microplastics (MPs) are emerging contaminants in freshwater systems that have already attracted much scientific interest, but little attention has been paid to a multi-matrix analysis of MP occurrences along the length of a river. The present research provides the first record of MP contamination of four abiotic and biotic matrices from a river ecosystem simultaneously analysed. MPs were isolated and identified by micro-Fourier Transform Infrared (μ-FTIR) spectroscopy from samples collected along the Ticino River in North Italy during spring 2019. Abiotic samples were surface water (n = 18, 33 MPs m^-3) and sediment (n = 18, 11 MPs kg^-1), while biological samples consisted of stomach and gut content of fish (n = 18, wels catfish, Silurus glanis, 0.032 MPs g^-1) and macroinvertebrates (n = 90, caddisfly larvae, Hydropsychidae, 0.03 MPs mg^-1). MPs were found in biota from all stations; 44% of fish and 61% of macroinvertebrate samples contained MPs. The calculated unit-consistent concentration ratios indicate that both S. glanis and Hydropsychidae larvae had a consistent higher amount of MPs than their respective medium (sediment and water), strongly suggesting an efficient uptake pathway into organisms. MP levels in surface water, sediment, fish and macroinvertebrates were not correlated and did not increase with the river's length. From our mass balance calculations, the Ticino River transports a consistent amount of MP (yearly load of 3.40 × 10¹¹ ± 1.1 × 10¹¹ MPs) to the Po River. This MP load was almost half than an estimated MP load from wastewater treatment plants (WWTPs). On that basis and supported by the finding that MP concentration in sediment was mostly opposed to that in surface water but was on average 750-fold higher compared to the water matrix, we surmise that the complex hydrological network of the Ticino River retains a consistent amount of MPs which might build up over time.

Microplastic pollution in the surface seawater in Zhongsha Atoll, South China Sea

The prevalence of microplastics in the marine environment has attracted extensive attention. So far, no information is known regarding the temporal and spatial variations of microplastics in Zhongsha Atoll. This study, for the first time, comprehensively investigated the occurrence and distribution of microplastics in the surface seawater in Zhongsha Atoll based on two ocean cruises. The abundances of microplastics measured in the surface seawater of Zhongsha Atoll were in the ranges of not detected (ND) to 67 items/m³, and ND to 160 items/m³ in 2019 and 2020, respectively. All microplastics detected in Zhongsha Atoll were fibers, most of which were transparent and less than 2 mm. Polyethylene terephthalate was the dominating composition of microplastics. These results suggested that sewage, surface runoff, atmospheric deposition by neighboring land, and fishing activities may be the primary pollution sources. This study provides critical information on microplastic pollution in Zhongsha Atoll for the first time, calling for more research in the management of marine plastic debris in the future.

Polyethylene microplastics interfere with the nutrient cycle in water-plant-sediment systems

Increasing microplastic (MP) pollution and its effects on aquatic systems have become a global issue; however, the impact of MPs on biogeochemical cycles is poorly understood. A simulation study was performed to analyse the influence of polyethylene (PE) microplastics on the morphological, physiological, and stoichiometric (C, N, P) characteristics of submerged plants, and to investigate their effects on the nutrient cycle and microbial community in freshwater sediment. The results showed that PE-MPs treatments significantly decreased leaf nitrogen and carbon contents. Exposure to 1% PE-MPs suppressed the plant height, total biomass, root activity, and relative growth rate of Vallisneria natans. Decrease in dissolved oxygen (DO) concentrations (19.93-40.26%) were observed in the 1% PE-MPs treatment group compared to that in the control between 1 and 6 days. The activities of enzymes (ammonia monooxygenase and nitrate reductase) related to the nitrogen cycle were significantly altered by the addition of PE-MPs. We found that PE-MPs acted as obstacle disruptors, resulting in a reduction in the release of nitrogen and phosphorus from the sediment to the overlying water. This is because PE-MPs significantly alter the composition and metabolic properties of the microbial communities in sediments, the plant growth, and the nutrient cycle. These findings helped evaluate the impacts of PE-MPs on the water-plant-sediment system and on the biogeochemical cycles of the freshwater ecosystems.

Interactions effects of nano-microplastics and heavy metals in hybrid snakehead (Channa maculata ♀ × Channa argus ♂)

The interaction between microplastics and contaminants has potentially generated new undefined risks on animals and ecosystems, and nano-microplastics are considered to be more harmful than microplastics. This experiment investigated the interactions and effects of nano-microplastics with heavy metals cadmium in hybrid snakehead. Different concentrations of nano-microplastics 80 nm (50 μg/L and 500 μg/L) and Cd (50 μg/L) were used for exposure, and four sampling points were set for 24 h, 48 h, 96 h and clear-48 h. Results indicated that the morphology of gill was altered under the influence of nano-microplastics and cadmium, and the damage was aggravated with time. Nano-microplastics and Cd can cause oxidative damage to fish liver partly by effect the activities of antioxidant enzyme, and significantly suppressed the expressions of genes related to the inflammation (IL-1β and TNF-α) and as well as significantly up-regulated the expression of genes HSP70 and SOD. Additionally, the mRNA levels of MT gene can be speculated that the heavy metal cadmium may accumulated in the body over time. And the concentration of heavy metals will also affect their accumulation in the body. Our study elucidated the nano-microplastics and Cd will increase the impact on environmental and organisms that the nano-microplastics contribute to the bioaccumulation of metals, which served as a new support for study the interaction between environmental contaminants.

A comprehensive review of the circulation of microplastics in aquatic ecosystem using scientometric method

Nowadays, the extensive application of microplastics (MPs) has led to the gradual accumulation of toxicity in aquatic environment and caused potential harm to aquatic organisms and human life, which has become a hot issue of worldwide concern. Although MPs show inert or sublethal toxicity in many cases, its long-term existence can still cause harmful ecological effects. However, to our knowledge, there is a lack of comprehensive literature on the current research hotspots, circulation process, and future development trend of MPs in aquatic ecosystem. This study aims to comprehend the current research hotspots and future development trend in the field of the MPs in aquatic ecosystem using scientometric method. And the circulation process of MPs in aquatic ecosystem is also investigated. The results indicate the most of the current publications on MPs in aquatic ecosystems focus on the formation and harmful properties of MPs. The current research hotspots mainly include the causes of the formation of MPs, the extent of contamination, deposition phenomena, and the toxicity and harm caused to aquatic organisms and humans after ingestion. And the future trends in the researches related to MPs mainly include the study of microplastic cycling processes in aquatic and terrestrial ecosystems, as well as the effective collection of microplastics and their conversion into valuable carbon sources. This review has filled in the knowledge gap in the field of MPs research in aquatic ecosystem to some extent and plays a guiding role in the future researches.

An enhanced risk assessment framework for microplastics occurring in the Westerscheldt estuary

Microplastics (MPs) pollution in the aquatic environment raises considerable concerns. Freshwater system is generally considered as an important source for MPs transformation into the marine environment, however, only limited data on the MPs pollution in global freshwater systems is available at this time. In this study, we explored the abundance, characteristics and distribution of microplastics in the Scheldt River. The investigation results indicated that the abundance of microplastics in sediments (15-413 items/kg dry weight (DW)) was much higher than that in surface water (0-113 items/m³), and small size MPs (less than 500 μm) frequently appeared in sediments. Industrial activities were regarded as the major cause of MP discharging. Risk assessment models with using data of the concentration of MPs, polymer types and toxicity of MPs exposure were developed to assess the risk of MPs pollution in both surface water and sediment of the Westerscheldt estuary. Risk assessment results revealed that MPs exposure have potentially adverse effects on the aquatic ecosystem and human health. MPs tend to be transported from "Hotspots", such as urban or industries area, to remote areas. The risk assessment of MPs serves as a baseline for better understanding the distribution and characteristics of MPs and highlights the need of intensively monitoring to limit MPs release by intensively monitoring. This research provides a perspective on the risk of MPs that could be used in future studies.

Spatiotemporal dynamics of microplastics in an urban river network area

Microplastics contamination in the environment is a global problem, but little is known about their dynamics in urban river networks, an important site of microplastics occurrence and harboring complex transport pathways. In this study, we investigated the spatiotemporal dynamic of microplastics in a typical urban river network in eastern China from December 2018 to September 2019. microplastics abundance (mean ± standard deviation) in the river network ranged from 2.3 ± 1.2 to 104.6 ± 5.6 particles/L and was significantly higher during the wet than during the dry season. The distribution of microplastics in the upper, middle, and lower reaches of the river network did not significantly differ, nor did the abundance of microplastics in the surface water vs. the bottom water. However, high abundances were determined in commercial and industrial areas, at a wastewater treatment plant outlet, in an urban canal, and in an urban-rural fringe area. The seasonal dynamics of the overall abundance of microplastics could be explained by the hysteresis effect of urban plastic production and the variation in regional precipitation. 78.2% of the microplastics were < 330 µm in size; the most common colors were blue and black, and the most common shapes were fragments and fibers. The polymer types of the microplastics were assessed using laser direct infrared (LDIR), a novel chemical imaging system that identified silicone, rubber, polytetrafluoroethylene, and polypropylene as the main components of the microplastics. A non-metric multidimensional scaling analysis (NMDS) based on the abundance of the polymer components across samples showed aggregations of sampling sites, that indicated the possible sources of the microplastics. Our study provides insights into the spatiotemporal dynamics of microplastics in an urban river network and suggests the potential of LDIR in the accurate quantitative analysis of microplastics in the environment.

Occurrence, spatial distribution, and main source identification of ten bisphenol analogues in the dry season of the Pearl River, South China

Bisphenol analogues (BPs) including bisphenol a (BPA) have been broadly utilized as industrial feedstocks and unavoidably discharged into water bodies. However, there is little published data on the occurrence, distribution, and environmental risks of other BPs in surface water. In this study, ten BPs besides BPA were analyzed in surface water from the Pearl River, South China. Among these detected BPs, BPA, bisphenol F (BPF), bisphenol AF (BPAF), and bisphenol S (BPS) were the most frequently detected compounds. The median concentrations of the measured BPs were ranked in the order of BPA (34.9 ng/L) > BPS (24.8 ng/L) > BPAF (10.1 ng/L) > bisphenol F (BPF) (9.0 ng/L) > bisphenol B (BPB) (7.6 ng/L) > bisphenol C (BPC) (1.2 ng/L). Among them, BPA and BPS were predominant BPs, contributing 68% of the total ten BPs in surface water of the Pearl River. These results demonstrated that BPA and BPS were the most extensively utilized and manufactured BPs in this region. The source analysis of BPs suggested that the BPs may be originated from domestic wastewater, wastewater treatment plant (WWTP) effluent, and the leaching of microplastic in surface water of the Pearl River. The calculated BP-derived estrogenic activity exhibited low to medium risks in surface water, but their combined estrogenic effects with other endocrine disrupting compounds should not be ignored.

Pollution characteristics and source analysis of microplastics in the Qiantang River in southeastern China

Microplastic pollution resulting from industrialization and urbanization is increasingly serious. Hangzhou is a city with high industrial/urban growth in Southeast China. Focusing on the microplastic pollution in the Hangzhou section Qiantang River, six samples were collected and analyzed during different hydrological periods (normal, wet, and dry periods) and the relationship between microplastic pollution and economic development was investigated. Results showed that more microplastics were found during the dry period than that of the wet period (49.8 vs. 13.2%). Microplastic abundance was 1.5-9.4 items L^-1, showing significant spatial differences in sampling sites. Among the collecting microplastics, debris and fibers accounted for 36.4 and 30.9%. Polyethylene terephthalate and polyvinyl chloride were the main polymers, accounting for 48.3 and 31.8%, respectively. Microplastics with size <1 mm accounted for 60% of the microplastics in surface water samples. Spatially, microplastic abundance was the highest in the middle of the river. Redundant analysis revealed that the per capita GDP (p = 0.002), high-end equipment industry (p = 0.028) and fashion manufacturing (p = 0.006) influenced microplastic abundance. Urbanization coupled with rapid economic development led to increase in local microplastic pollution. Our results provide insight into microplastic distribution patterns in urban river systems in China.

Distribution Characteristics and Source Analysis of Microplastics in Urban Freshwater Lakes: A Case Study in Songshan Lake of Dongguan, China

Current studies on microplastic pollution mainly focus on marine systems. However, few studies have investigated microplastics in an urban lake. This research intends to use an urban lake (Songshan Lake) as an example to explore the pollution characteristics of microplastics and use the principal component as well as the heat map analysis to discuss the relationships between different shapes of microplastics. According to this study, the average abundance of microplastics in the surface water and surface sediments of Songshan Lake were, respectively, 2.29 ± 0.98 items/m3 and 244 ± 121 items/kg; thin films were the major microplastics in both media; transparent this type of color has the most microplastic content. The particle size of microplastics was mainly 0.18–0.6 mm (43.3%) in surface water and 1–2 mm (48.3%) in surface sediments. The composition included five polymers: polyethylene (PE), polypropylene (PP), polypropylene–polyethylene copolymer (PP–PE copolymer), polystyrene (PS), and polyvinyl chloride (PVC), among which PE (47%) and PP (36%) were the main components. Principal component analysis (PCA) showed that there was a positive correlation among the four shapes of microplastics: films, fragments, foams, and fibers. The heat map analysis showed that the same category of shape distribution features may be similar for each sampling site.

Microplastics in the sediments of small-scale Japanese rivers: Abundance and distribution, characterization, sources-to-sink, and ecological risks

Microplastic pollution in small-scale river sediments remains mostly unknown. This study explored microplastics in the sediments of four small-scale Japanese rivers in Yamaguchi Prefecture: the Awano, Ayaragi, Asa, and Majime. Sediment samples (n = 23) were collected from the selected stations. Density separation and wet peroxidation methods were applied to extract microplastics. Polymers were detected through attenuated total reflectance-Fourier transform infrared spectroscopy. Microplastic abundance indicated relatively moderate values in the small-scale Japanese rivers compared to other rivers around the world. Large microplastics (1-5 mm) in size, fragments in shape, and high-density particles of diverse polymers dominated. Polyvinyl chloride, polyethylene, and polypropylene were the major polymers. The polymers-polyvinyl chloride, polymethylmethacrylate, polyurethane, fluorinated ethylene propylene, and polybutylene in sediments were distinct from those detected in surface water, as were the predominance of large-size (1-5 mm) and fragment-shape microplastics. In contrast to surface water, sediments preserved both common and distinctive microplastics. Thus, the riverine sediment compartment acted as microplastic sink. Scanning electron microscopic (SEM) analysis suggested the presence of weathered microplastics in sediments. Energy dispersive X-ray spectroscopic analysis (EDX) revealed metal contaminants on the microplastic surfaces, indicating synergistic hazard potentials in the riverine ecosystems. Ecological risk assessment results suggested low to very high risks of microplastic pollution for the rivers. The higher abundances of microplastics and highly toxic polymers contributed to the elevated ecological risks. Polyvinyl chloride, acrylonitrile butadiene styrene, polyurethane, and polymethylmethacrylate were the detected highly toxic polymers. The urban and residential areas affected stations ranked high to very high ecological risks. The sites posing very high ecological risks were regarded as pollution hotspots. Overall, this study developed new insights into microplastic pollution in the small-scale rivers and ecological risks for riverine environments, as well as providing a baseline for more comprehensive risk assessments and developing pollution control and management strategies.

The contamination of microplastics in China's aquatic environment: Occurrence, detection and implications for ecological risk

The widespread occurrence of microplastics in aquatic ecosystems that resulted in environmental contamination has attracted worldwide attention. Microplastics pose a potential threat to the growth and health of aquatic organisms, thereby affecting the function of the ecosystems. As one of the top ten countries producing and consuming plastic products globally, China's aquatic ecosystems have been profoundly affected by microplastics. In this review, we have summarized the microplastics contamination in three typical water environments (marine environment, freshwater environment, and wastewater treatment plants) in China, elaborated on the adverse impacts of microplastics on the ecological environment, and evaluated the potential ecological risks exposed to the ecosystem. In addition, the progress of microplastics extraction methods, as the important basis of microplastics related research, in aquatic ecosystems was introduced, especially the difference between the extraction of microplastics from wastewater and sludge samples. At present, most of the research on microplastics focuses on "one point", such as a certain river or wastewater treatment plant. Research on the mitigation and transfer of microplastics among different connected water environments is still lacking. Also, the microscale ecotoxicity caused by microplastics is poorly understood. In the end, we proposed suggestions and perspectives for future research regarding microplastics in the aquatic ecosystems in China.

Microplastics in Asian freshwater ecosystems: Current knowledge and perspectives

Plastic pollution in freshwater ecosystems, including microplastics (MPs) smaller than 5 mm, has become an emerging global concern. Asia is considered a "hot spot" for plastic pollution due to rapid economic and demographic growth, together with rapid urbanization. Here, we provide an overview of the current knowledge on MP abundance, sources, fate, and transfer in Asian freshwater ecosystems based on publications from January 2014 to May 2021. MP contamination in freshwater compartments, including water, sediment, and biota, was found to vary strongly. In water, it ranged from 0.004 items m^-3 in a moderately urbanized region to more than 500,000 items m^-3 in a dumping river in a highly populated watershed. In the sediment, MP abundance ranged from 1 to more than 30,000 items kg^-1 dry weight. Polyethylene (PE) and polypropylene (PP) were predominant in both water and sediment compartments. MP was detected in biota samples from all the studied species, but their abundance depended on the locations and species studied. Overall, MP characteristics (form, size, color, and polymer type) depended on sources and natural constraints (mainly hydrodynamics). This study also revealed that MP in Asian freshwater ecosystems mainly originated from domestic wastewater/runoff, followed by industrial emissions, fisheries and aquaculture wastewater. Plastic waste is not efficiently recycled or incinerated in Asia, leading to MP transfer and accumulation in the aquatic environment, and, more importantly, to ingestion by low to high trophic level organisms. This work highlights several knowledge gaps to guides future research to improve MP pollution management for the sustainable development of highly populated regions such as Asia.

Long-Term Occurrence and Fate of Microplastics in WWTPs: A Case Study in Southwest Europe

Microplastic (MP) water pollution is a major problem that the world is currently facing, and wastewater treatment plants (WWTPs) represent one of the main alternatives to reduce the MP release to the environment. Several studies have analysed punctual samples taken throughout the wastewater treatment line. However, there are few long-term studies on the evolution of MPs over time in WWTPs. This work analyses the performance of a WWTP sited in Southwest Europe in relation with annual occurrence and fate of MPs. Samples were monthly taken at different points of the facility (influent, secondary effluent, final effluent, and sludge) and MPs were quantified and characterised by means of stereomicroscopy and FTIR spectrophotometry. The majority of MPs found in wastewater and sludge samples were fragments and fibres. Regarding to the chemical composition, in the water samples, polyethylene (PE), polyethylene terephthalate (PET) and polypropylene (PP) stood out, whereas, in the sludge samples, the main polymers were PET, polyamide (PA) and polystyrene (PS). The MPs more easily removed during the wastewater treatment processes were those with sizes greater than 500 µm. Results showed that the MPs removal was very high during all the period analysed with removal efficiencies between 89% and 95%, so no great variations were found between months. MP concentrations in dry sludge samples ranged between 12 and 39 MPs/g, which represented around 79% of the total MPs removed during the wastewater treatment processes. It is noticeable that a trend between temperature and MPs entrapped in sewage sludge was observed, i.e., higher temperatures entailed higher percentage of retention.

Polystyrene microplastics induced female reproductive toxicity in mice

Plastics have caused serious environmental pollution. In recent years, microplastics (MPs) have caused widespread concern about their potential toxicity on animals and humans, especially on organ and tissue deposition. However, there is little known about the reproductive toxic effects of MPs in female mammals. In this study, the reproductive toxicity of polystyrene MPs (PS-MPs) in female mice was evaluated after continued exposure for 35 days. Results showed that PS-MPs could accumulate in heart, liver, spleen, lung, kidney, brain, large intestine, small intestine, uterus, ovary and blood of exposed mice. Moreover, PS-MPs exposure increased the IL-6 level and decreased malondialdehyde (MDA) level in mouse ovaries. The results also showed that PS-MPs exposure decreased the first polar body extrusion rate and the survival rate of superovulated oocytes. Meanwhile, PS-MPs reduced the level of glutathione (GSH), mitochondrial membrane potential (MMP), endoplasmic reticulum calcium ([Ca²⁺]_ER) and increased reactive oxygen species (ROS) in oocytes. In conclusion, our study illustrated that PS-MPs exposure induced the inflammation of ovaries and reduced the quality of oocytes in mice, which provided a basis for studying the reproductive toxic mechanism of PS-MPs in female mammals.

Urban drainage channels as microplastics pollution hotspots in developing areas: A case study in Da Nang, Vietnam

This study provides information on the current situation of microplastics contamination in inland freshwater bodies in Vietnam. An urban drainage channel in Da Nang City was selected as a case study. Receiving mainly domestic wastewater and landfill leachate, the channel itself is becoming a microplastic pollution hotspot with a microplastic concentration of 1482.0 ± 1060.4 items m^-3 in waters and 6120.0 ± 2145.7 items kg^-1 in sediments. The dominant shapes of microplastics were fibers and fragments, in which the polymer types were mainly polyethylene, polypropylene, and polyethylene terephthalate. Microplastics with sizes ranging from 1000 to 5000 μm tended to be distributed primarily in surface waters, whereas particles from 300 to 1000 μm accumulated in sediments. The channel places Da Nang Bay at a high risk for microplastic pollution, with an estimated pollution load of approximately 623 × 10⁶ items d^-1 in dry weather.

Occurrence and spatial distribution of microplastics, and their correlation with petroleum in coastal waters of Hainan Island, China

In this study, the distribution, abundance, morphology, and composition of microplastics (MPs) in surface seawater and sediment of Hainan Island were systematically investigated. Seawater and sediment samples were collected from six functional zones, including harbor, industrial district, sparsely populated area, tourist area, residential area, and aquaculture area. The abundance of MPs in seawater was 0.46-19.32 items/L, with an average of 2.59 ± 0.43 items/L, which were similar to those detected in the South China Sea (e.g., Nansha (1.25-3.20 items/L) and Xisha (2.57 ± 1.78 items/L)). The highest level was detected in Qinglan Bay Estuary, and the lowest was in Sanya West Island. The abundance of MPs in sediment was 41.18-750.63 items/kg, with an average of 372.47 ± 62.10 items/kg; the highest concentration was detected at Tanmen Port, and the lowest was in Lingao sea area. It was detected that the MPs with smaller size exhibited a higher concentration in seawater. MPs were commonly black and white, and predominantly linear and fragmented in shape. Polyethylene terephthalate (PET) was the dominant polymer, which might be derived from laundry wastewater. The petroleum concentration was 0.02-0.21 mg/L in the investigated area, with harbors being the most severely polluted areas. Furthermore, this study also found that MPs pollution was positively correlated with petroleum in seawater, indicating similarities between MPs and petroleum-based sources of pollution. This study identifies the contamination and characteristics of MPs and their correlation with petroleum in Hainan Island, the biggest island in the South China Sea, providing important data for further research on protecting marine ecosystems.

Microplastic pollution in coastal ecosystem off Mumbai coast, India

Microplastics (MPs) are anthropogenic pollutants which can adsorb toxic substances from surrounding water and absorb into the fish body. During the present study, MPs were observed in water, sediment, and gastrointestinal tracts of marine biota samples collected from the coastal waters of Mumbai, India. The mean abundances of MPs recorded in water samples 372 ± 143 items/liter and 9630 ± 2947 items/kg dry weight (DW) in sediment samples. The mean abundance of MPs in pelagic fish species varied from 6.74 ± 2.74 to 9.12 ± 3.57 items/individual and in the demersal species the values ranged from 5.62 ± 2.27 to 6.6 ± 2.98 items/individual. Shape-wise, four type of MPs were observed in the surface waters, sediments and all studied species, predominantly fibers, followed by fragments, pellets/beads, and films. Seven different colors of MPs (red, blue, black, translucent, brown, green, and yellow) were observed from studied samples. MPs of size below 250 μm formed the dominant size in the surface water, sediments, and biota samples except Bombay duck and Malabar sole fish. Based on Raman spectroscopy analysis, eleven types of plastic polymers identified from all studied samples. Thus, presence of MPs in studied biota indicates the transfer of MPs through interlinked food chain/web to higher trophic levels and the occurrence of MPs in the fish gut underlines the necessity of more studies on processing interventions for reducing the microplastic contamination in fish for human consumption.

Abundance and characteristics of microplastics in the surface water and sediment of parks in Xi'an city, Northwest China

Microplastics (MPs), as a new type of pollutants, have attracted wide attention especially in recent years, but there was insufficient research on the distribution and characteristics of MPs in urban park water body. In this study, the pollution of MPs in water and sediment of Xi'an, the largest city in northwest China, was investigated. The MPs concentration in the surface water and sediment was 2900-6970 items/m³ and 940-3560 items/kg, respectively. According to the urban functions, the parks were divided into residential areas, commercial areas, tourism areas and industrial areas, and the highest abundance of MPs was observed in the tourism and residential areas, suggesting the impacts of human activities. MPs in these parks were mainly in four kinds of shapes, namely fiber, pellet, fragment and film, and dominated by fibers and fragments. Most of the extracted MPs were small in size, and 63-92% of them were smaller than 0.5 mm. Polypropylene and polyethylene terephthalate were the main polymer types in surface water and sediments, respectively. This study showed that the park water and sediment can be used as an important "sink" in MPs, which is of great significance for monitoring and alleviating the pollution of urban MPs. This study provided important reference for better understanding MPs levels in inland freshwaters.

Release of tens of thousands of microfibers from discarded face masks under simulated environmental conditions

While mechanical abrasion by water and sediment is a primary and critical step in weathering process, the upsurge of discarded face masks will undoubtedly become a potential source of micro-/nanofibers owing to the spread of novel coronavirus (COVID-19) pneumonia. However, effects of mechanical abrasion on discarded face masks have neither been seriously addressed nor understood. Therefore, we conducted a simulated experiment to explore abundance, size distribution and morphology of microfibers released from common, surgical and face filtering piece (FFP) masks after mechanical abrasion. Technologies such as Fourier transform infrared spectrometry, fluorescence microscopy, scanning electron microscopy, and confocal laser scanning microscopy were used. Results showed that the abundance of released microfibers followed order of surgical > common > FFP in both water and sediment environments, and the maximum abundance reached 272 ± 12.49 items per square centimeter of mask (items·cm^-2) after sediment abrasion. Taking surgical mask for further investigation, the length of released fiber was observed to vary from 47.78 μm to 3.93 mm, and 72.41-89.58% of the total number of released microfibers fell in the range of 0.1-1 mm. However, microfibers with a very small length (1-100 μm) can occupy 0.09-13.59% of the total number of released fibers in sediment environment. The roughness of fiber surface after sediment abrasion was successively increased. Furthermore, the morphology analysis showed significant changes with countless cracks and many prominent protrusions on fiber surface after sediment abrasion. The cracks and protrusions may further accelerate mask decomposition, thereby potentially resulting in the adsorption of other contaminants and the release of self-containing chemicals. This study provides a valuable database of microfibers released from discarded face masks at the primary but critical stage, and further contributes knowledge on environmental impact of discarded personal protective equipment due to COVID-19.

Prevalence of microplastic fibers in the marginal sea water column off southeast China

Microplastic (MP) fibers are present in all environmental media, yet little is known about their distribution, sources, and transport in the water column of marginal seas. In this study, we conducted an intensive sampling campaign in the marginal sea water column off southeast China, which is an area that is greatly influenced by high MP emissions. We found that hydrological effects largely regulated the spatial variations of MP fiber distribution and that MP fibers likely were not entering the South China Sea through terrestrial input from southeast China during the summer monsoon. Polyethylene terephthalate (PET) fibers were pervasive in the surface water (SW) (89.47%), subsurface chlorophyll maximum layer (SCML) (92.65%), and bottom water (BW) (94.29%) of the water column during the sampling period. Approximately 32% of MP fibers in the samples were smaller than 330 μm. The abundance of MP fibers in SW was significantly lower than that in the SCML and BW. Based on this observation, we estimated the inventory of MP fibers in the SW, SCML, and BW of the sampling area to be 1.377-1.378, 2.820-2.825, and 2.627-2.629 metric tons, respectively. These results improved our understanding of the source-to-sink process of MP fiber contamination in the water column of marginal seas.

An ignored potential microplastic contamination of a typical waste glass recycling base

The service life of glass is limited, leading to a large amount of waste glass generated. The waste glass recycling base, as an essential municipal supporting facility of a sustainable city, has a significant impact on the surrounding ecological environment. This study conducted a comprehensive investigation and analysis of the potential pollutants in a large waste glass terminal recycling base. It was found that the waste glass treatment process may produce various pollutants such as particulate matter, heavy metals and so on, which might cause pollution to surrounding areas. Microplastics (MPs) of particulate matter, which were widely distribute in the study area, had high abundance and interact with heavy metals. Its release is related with different treatment processes. MPs were found in all sampling sites, a total of 59 polymer types were identified. The relationship between MPs and process characteristics is mainly reflected on the polymer types. The crushing and screening process are more likely to produce Acrylic, while the label-eliminate process is more likely to produce PMMA. It was estimated that the annual load of MPs in the waste glass recycling site is about 3.211 tons.

Selection of a density separation solution to study microplastics in tropical riverine sediment

Microplastics (MPs) are small (< 5 mm) plastic particles that are widely found in marine, freshwater, terrestrial and atmospheric environments. Due to their prevalence and persistence, MPs are considered an emerging contaminant of environmental concern. The separation and quantitation of MPs from freshwater sediments is a challenging and critical issue. It is necessary to identify the fate and sources of MPs in the environment, minimise their release and adverse effects. Compared to marine sediments, standardised methods for extracting and estimating the amount of MPs in freshwater sediments are relatively limited. The present study focuses on MP recovery efficiency of four commonly used salt solutions (NaCl, NaI, CaCl₂ and ZnCl₂) for isolating MPs during the density separation step from freshwater sediment. Known combinations of artificial MP particles (PS, PE, PVC, PET, PP and HDPE) were spiked into standard river sediment. Extraction using NaI, ZnCl₂ and NaCl solutions resulted in higher recovery rates from 37 to 97% compared to the CaCl₂ solution (28-83%) and varied between polymer types. Low-density MPs (PE, HDPE, PP and PS) were more effectively recovered (> 87%) than the denser polymers (PET and PVC: 37 to 88.8%) using NaCl, NaI and ZnCl₂ solutions. However, the effective flotation of ZnCl₂ and NaI solutions is relatively expensive and unsafe to the environment, especially in the context of developing countries. Therefore, considering the efficiency, cost and environmental criteria, NaCl solution was selected. The protocol was then tested by extracting MPs from nine riverine sediment samples from the Red River Delta. Sediments collected from urban rivers were highly polluted by MPs (26,000 MPs items·kg^-1 DW) compared to sediments located downstream. Using a NaCl solution was found to be effective in this case study and might also be used in long-term and large-scale MP monitoring programmes in Vietnam.

Controlling Factors of Microplastic Riverine Flux and Implications for Reliable Monitoring Strategy

A significant proportion of marine plastic debris and microplastics is assumed to be derived from river systems. In order to effectively manage plastic contamination of the marine environment, an accurate quantification of riverine flux of land-based plastics and microplastics is imperative. Rivers not only represent pathways to the ocean, but are also complex ecosystems that support many life processes and ecosystem services. Yet riverine microplastics research is still in its infancy, and many uncertainties still remain. Major barriers exist in two aspects. First, nonharmonized sampling methodologies make it problematic for compiling data across studies to better estimate riverine fluxes of microplastics globally; Second, the significant spatiotemporal variation of microplastics in rivers which was affected by the river characteristics, MPs properties, etc. also have important influence on the estimation of riverine MPs fluxes. In this study, we made a comprehensive review from the above two aspects based on published peer-reviewed studies and provide recommendations and suggestions for a reliable monitoring strategy of riverine MPs, which is beneficial to the further establish sampling methods for rivers in different geographical locations. Besides, methods for achieving a high level of comparability across studies in different geographical contexts are highlighted. Riverine microplastic flux monitoring is another important part of this manuscript. The influential factors and calculation methods of microplastic flux in rivers are also discussed in this paper.