Export of microplastics from land to sea. A modelling approach

Impact of microplastics on microbial community structure in the Qiantang river: A potential source of N2O emissions

This study aimed to investigate the spatial distribution of microplastics (MPs) and the features of the bacterial community in the Qiantang River urban river. Surface water samples from the Qiantang River were analyzed for this purpose. The results of the 16S high-throughput sequencing indicated that the microbial community diversity of MPs was significantly lower than in natural water but higher than in natural substrates. The biofilm of MPs was mainly composed of Enterobacteriaceae (28.00%), Bacillaceae (16.25%), and Phormidiaceae (6.75%). The biodiversity on MPs, natural water, and natural substrates varied significantly and was influenced by seasonal factors. In addition, the presence of MPs hindered the denitrification process in the aquatic environment and intensified N2O emission when the nitrate concentration was higher than normal. In particular, polyethylene terephthalate (PET) exhibited a 12% residue of NO3--N and a 4.2% accumulation of N2O after a duration of 48 h. Further findings on gene abundance and cell viability provided further confirmation that PET had a considerable impact on reducing the expression of nirS (by 0.34-fold) and nosZ (by 0.53-fold), hence impeding the generation of nicotinamide adenine dinucleotide (NADH) (by 0.79-fold). Notably, all MPs demonstrated higher the nirK gene abundances than the nirS gene, which could account for the significant accumulation of N2O. The results suggest that MPs can serve as a novel carrier substrate for microbial communities and as a potential promoter of N2O emission in aquatic environments.

Characteristics of soil microplastics and ecological risks in the Qilian Mountains region, Northeast Tibetan Plateau

Microplastics (MPs) pollution has become a vital global environmental issue. However, comprehensive understanding of the ecological risks of MPs in soils of Northeast Tibetan Plateau still requires further study. In this study, we used laser diffuse reflectance infrared (LDIR) spectroscopy to analyze the characteristics of 10-1000 μm MPs in soils of different vegetation types throughout the Qilian Mountains basin, and to comprehensively explore the ecological risks of MPs in various ecological environments. The results indicate that MPs abundance is highest in soil of shrub areas (26,369 ± 32,147 items kg-1-dry weight (dw)), followed by woodland (22,215 ± 22,544 items kg-1-dw), desert (17,769 ± 9,040 items kg-1-dw), grassland (16,462 ± 12,872 items kg-1-dw), and forest (15,662 ± 13,857 items kg-1-dw). MPs in soils of different vegetation types show similar physical and chemical characteristics, with the shape dominated by fragments (93% - 96%), followed by fibers and a few beads, with dominant sizes of 10 - 30 μm (63% - 76%), and polymers dominated by polyamide and polyethylene terephthalate. Additionally, the environmental risks posed by the fundamental characteristics of MPs have been quantified through the Pollution Load Index (PLI), Pollution Hazard Index (PHI), and Potential Ecological Risk Index (PERI) models. According to the PLI assessment, the current levels of MPs in the environment have not yet imposed significant burdens on the ecosystem. However, the results of PHI and PERI indicate a higher risk of MPs pollution in the Qilian Mountains. This study offers vital information for MPs pollution in the whole Qilian Mountain regions and their potential environmental risks in remote areas' soil.

Global microplastic fiber pollution from domestic laundry

The rapid expansion of fast fashion has significantly increased microplastic fiber (MPF) release during laundry practices, accounting for approximately one-third of primary microplastics entering the ocean. Currently, a significant gap exists in global-scale research on the release of MPFs from washing textiles. This study introduces an innovative empirical model to assess the spatial distribution of MPF emissions. The model estimates an annual global emission of 5.69 million tons of MPFs from laundry. Of this total, machine washing accounts for the majority (93.7 %), with hand washing contributing the remaining 6.3 %. As the primary source of MPF pollution, Asia's emissions reach 3.71 million tons, far exceeding those of North America (1.18 million tons) and Europe (0.45 million tons). The primary issue is that wastewater management efficiency varies significantly worldwide. In Asia, there is persistently high discharge of MPFs into natural waters, and the removal efficiency of wastewater treatment plants is still comparatively low. In contrast, the United States and many European countries exhibit better MPF retention. The global nature of this challenge mandates international collaboration for comprehensive environmental conservation. Our study provides the first high-resolution global distribution map of MPF emissions and discharge into natural waters, establishing a data foundation for global and regional management of microplastics originating from household laundry sources.

Microplastics monitoring in freshwater systems: A review of global efforts, knowledge gaps, and research priorities

The escalating production of synthetic plastics and inadequate waste management have led to pervasive microplastic (MP) contamination in aquatic ecosystems. MPs, typically defined as particles smaller than 5 mm, have become an emerging pollutant in freshwater environments. While significant concern about MPs has risen since 2014, research has predominantly concentrated on marine settings, there is an urgent need for a more in-depth critical review to systematically summarize the current global efforts, knowledge gaps, and research priorities for MP monitoring in freshwater systems. This review evaluates the current understanding of MP monitoring in freshwater environments by examining the distribution, characteristics, and sources of MPs, alongside the progression of analytical methods with quantitative evidence. Our findings suggest that MPs are widely distributed in global freshwater systems, with higher abundances found in areas with intense human economic activities, such as the United States, Europe, and China. MP abundance distributions vary across different water bodies (e.g., rivers, lakes, estuaries, and wetlands), with sampling methods and size range selections significantly influencing reported MP abundances. Despite great global efforts, there is still a lack of harmonized analyzing framework and understanding of MP pollution in specific regions and facilities. Future research should prioritize the development of standardized analysis protocols and open-source MP datasets to facilitate data comparison. Additionally, exploring the potential of state-of-the-art artificial intelligence for rapid, accurate, and large-scale modeling and characterization of MPs is crucial to inform effective strategies for managing MP pollution in freshwater ecosystems.

From riverbank to the sea: An initial assessment of plastic pollution along the Ciliwung River, Indonesia

This study presents the first comprehensive analysis of anthropogenic debris on the riverbanks of the Ciliwung River, covering upstream to downstream areas. The mean of debris found in each measurement was 32.79 ± 15.38 items/m2 with a weight of 106.00 ± 50.23 g/m2. Plastic debris accounted for over 50 % of all litter items identified and represents 55 % by weight, signifying a significantly high prevalence compared to global studies examining litter along riverbanks. The majority of the plastics found originated from Single-use applications and were predominantly made from Styrofoam. This investigation demonstrated the importance of actions to reduce single use applications and to improve waste management strategies. This can be achieved through proactive initiatives coupled with adaptable approaches, such as implementing effective urban planning and enhancing waste collection capacity.

Tire and road wear particles in the aquatic organisms - A review of source, properties, exposure routes, and biological effects

With the continuous development of the modern social economy, rubber has been widely used in our daily life. Tire and road wear particles (TRWPs) are generated by friction between tires and the road surface during the processes of driving, acceleration, and braking. TRWPs can be divided into three main components according to their source: tire tread, brake wear, and road wear. Due to urban runoff, TRWPs flow with rainwater into the aquatic environment and influence the surrounding aquatic organisms. As an emerging contaminant, TRWPs with the characteristics of small particles and strong toxicity have been given more attention recently. Here, we summarized the existing knowledge of the physical and chemical properties of TRWPs, the pathways of TRWPs into the water body, and the exposure routes of TRWPs. Furthermore, we introduced the biological effects of TRWPs involved in size, concentration, and shape, as well as key toxic compounds involved in heavy metals, polycyclic aromatic hydrocarbons (PAHs), N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), and benzothiazole on aquatic organisms, and attempted to find the relevant factors influencing the toxic effects of TRWPs. In the context of existing policies that ignore pollution from TRWPs emissions in the aquatic environment, we also proposed measures to mitigate the impact of TRWPs in the future, as well as an outlook for TRWPs research.

The seasonal variation and ecological risk of microplastics in the Lower Ganges River, Bangladesh

Microplastic (MP) pollution has gained considerable attention in various ecosystems; however, it has received relatively less attention in freshwater-riverine environments than in other ecosystems. The Ganges River Delta, one of the world's most densely populated areas, is a potential source of MP pollution in the freshwater ecosystem. MPs were identified throughout the year in the lower Ganges River water. Seasonally, the highest abundance was observed during the monsoon (14.66 ± 2.06 MPs/L), followed by the pre-monsoon (13.46 ± 1.75 MPs/L) and post-monsoon (11.50 ± 0.40 MPs/L). Throughout the year, MP discharge was estimated at 4.12 × 1012 to 2.17 × 1013 MPs/year. Fourier transformed infrared spectroscopy identified plastic polymers in the water, like ethylene vinyl acetate, polystyrene, polypropylene, polyethylene, and nylon. Moderate contamination by MPs was assessed throughout the year. Significant correlations between MP abundance and both rainfall and discharge were observed. It is essential to implement preventative measures in the Ganges River Basin to mitigate MP pollution before the situation worsens. PRACTITIONER POINTS: Throughout the year, MP concentration ranged from 10.67 to 20.33 MPs/L The highest MP occurrence was observed in the monsoon season (14.66 ± 2.06 MPs/L) The lowest abundance was detected in the post-monsoon period (11.50 ± 0.40 MPs/L) There was a moderate level of MP contamination in the lower Ganges River water It was shown that discharge and rainfall were correlated with MP abundance.

Microplastic abundance in the semi-enclosed Osaka Bay, Japan

Anthropogenic particles in sea surface water of the semi-enclosed Osaka Bay were identified using stereomicroscopy, classified according to polymer type using Fourier-transform infrared spectroscopy (FTIR), and categorized according to their physical characteristics. A total of 565.1 particles were detected in the water samples. However, plastic particles accounted for only 22.4% of the particles. Microplastic abundance in Osaka Bay showed seasonal variance from 8.9 ± 1.4 (in May) to 22.8 ± 6.5 particles/L (in July), which is consistent with previous reports in other semi-enclosed bays. Microplastics were mainly fragmented and fiber shaped, with gray and colorless/white coloration. The dominant polymer types were polypropylene, poly(methylmethacrylate), polyester, polyethylene, and polyethylene terephthalate. Generally, there were considerably higher abundances of microplastics at offshore sites compared with nearshore sites. The results of this study suggest that local river effluents and marine-related activities are probable sources of microplastics in Osaka Bay.

Rapid Mass Conversion for Environmental Microplastics of Diverse Shapes

Rivers have been recognized as the primary conveyors of microplastics to the oceans, and seaward transport flux of riverine microplastics is an issue of global attention. However, there is a significant discrepancy in how microplastic concentration is expressed in field occurrence investigations (number concentration) and in mass flux (mass concentration). Of urgent need is to establish efficient conversion models to correlate these two important paradigms. Here, we first established an abundant environmental microplastic dataset and then employed a deep neural residual network (ResNet50) to successfully separate microplastics into fiber, fragment, and pellet shapes with 92.67% accuracy. We also used the circularity (C) parameter to represent the surface shape alteration of pellet-shaped microplastics, which always have a more uneven surface than other shapes. Furthermore, we added thickness information to two-dimensional images, which has been ignored by most prior research because labor-intensive processes were required. Eventually, a set of accurate models for microplastic mass conversion was developed, with absolute estimation errors of 7.1, 3.1, 0.2, and 0.9% for pellet (0.50 ≤ C < 0.75), pellet (0.75 ≤ C ≤ 1.00), fiber, and fragment microplastics, respectively; environmental samples have validated that this set is significantly faster (saves ∼2 h/100 MPs) and less biased (7-fold lower estimation errors) compared to previous empirical models.

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.

Emerging pollutant in surface water bodies: a review on monitoring, analysis, mitigation measures and removal technologies of micro-plastics

Water bodies play a crucial role in supporting life, maintaining the environment, and preserving the ecology for the people of India. However, in recent decades, human activities have led to various alterations in aquatic environments, resulting in environmental degradation through pollution. The safety of utilizing surface water sources for drinking and other purposes has come under intense scrutiny due to rapid population growth and industrial expansion. Surface water pollution due to micro-plastics (MPs) (plastics < 5 mm in size) is one of the emerging pollutants in metropolitan cities of developing countries because of its utmost resilience and synthetic nature. Recent studies on the surface water bodies (river, pond, Lake etc.) portrait the correlation between the MPs level with different parameters of pollution such as specific conductivity, total phosphate, and biological oxygen demand. Fibers represent the predominant form of MPs discovered in surface water bodies, exhibiting fluctuations across seasons. Consequently, present study prioritizes understanding the adaptation, prevalence, attributes, fluctuations, and spatial dispersion of MPs in both sediment and surface water environments. Furthermore, the study aims to identify existing gaps in the current understanding and underscore opportunities for future investigation. From the present study, it has been reported that, the concentration of MPs in the range of 0.2-45.2 items/L at the Xisha Islands in the south China sea, whereas in India it was found in the range of 96 items/L in water samples and 259 items/kg in sediment samples. This would certainly assist the urban planners in achieving sustainable development goals to mitigate the increasing amount of emergent pollutant load.

Microplastics pollution in the Asian water tower: Source, environmental distribution and proposed mitigation strategy

Microplastics generated from fragmentation of leftover plastics and industrial waste has reached in the remotely located Asian water tower (AWT) region, the 3rd pole of earth and origin site of several freshwater rivers. The accumulation of microplastics in AWT ecosystem has potential to alter the climatic condition contributing in global warming and disturbing the biodiversity structural dynamics. The present paper provides a comprehensive critical discussion over quantitative assessment of microplastics in different ecosystems (i.e. river, lakes, sediment and snow or glacier) of AWT. The hydrodynamic fate and transport of microplastics and their ecological impact on hydromorphology and biodiversity of AWT has been exemplified. Furthermore, key challenges, perspectives and research directions are identified to mitigate microplastics associated problems. During survey, the coloured polyethylene and polyurethane fibers are the predominant microplastics found in most areas of AWT. These bio-accumulated MPs alter the rhizospheric community structure and deteriorate nitrogen fixation process in plants. Significance in climate change, MPs pollution is enhancing the emissions of greenhouse gases (NH3 by ∼34% and CH4 by ∼9%), contributing in global warming. Considering the seriousness of MPs pollution, this review study can enlighten the pathways to investigate the effect of MPs and to develop monitoring tools and sustainable remediation technologies with feasible regulatory strategies maintaining the natural significance of AWT region.

Understanding the Dynamics of Microplastics Transport in Urban Stormwater Runoff: Implications for Pollution Control and Management

The transport of microplastics (MPs) from urban environments to water resources via stormwater runoff poses significant concerns due to its adverse impacts on water safety and aquatic ecosystems. This study presents a modeling approach aimed at understanding the transport mechanisms of MPs in an urban residential setting, considering settling and buoyant MPs. To consider the effect of MP shapes, the settling velocity of various settling MPs in shapes of fibers, films, and fragments was calculated. Using an analogy of sediment transport, a Rouse number criterion was used to analyze the transport of MPs. For buoyant MPs, it was assumed that they transport as wash-load as soon as they float in the water and the travel time for them to reach the storm drain was determined. The calculation of settling velocity revealed the influence of shape on the settling velocity of MPs was particularly pronounced as the equivalent diameter of the MPs increased. The transport mechanism for the smallest settling MPs, irrespective of their shapes, density, and depth of flow, was wash-load. However, for larger MPs, the shape and size distribution of settling MPs, along with the depth of flow and slope significantly influenced their transport mechanisms compared to sediment particles. The influence of weathering on the MPs' transport mechanisms depended on their sizes and shapes. The site-specific characteristics, including slope and surface friction, significantly influenced the velocity of stormwater runoff and, consequently, the extent of MP transport during rain events. Moreover, an evaluation of the transport mechanism of settling MPs was conducted using the reported field data on MP abundance in road dust collected from residential and traffic sites. This study underscores the complexity of MP transport dynamics and provides a foundation for developing targeted strategies to mitigate MP pollution in urban environments.

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.

Transport and retention of sinking microplastics in a well-mixed estuary

Estuaries have been shown to be potential hotspots of microplastic accumulation, but the hydrodynamic conditions and particle properties that control this process need further investigation. We have designed a series of numerical particle-tracking experiments to examine the sensitivity of retention in estuaries to particle size, particle density and varying tides and freshwater flow. At the end of the simulation, over 90 % of sinking particles are retained in the estuary, and the retention rate is further increased by high river runoff. In contrast, increased river discharge increases the number of marginally-buoyant (i.e. density close to estuarine water) particles that escape the estuary. Larger particle size tends to limit the downstream transport of sinking particles but can facilitate the transport of marginally-buoyant particles. Tidal asymmetry, vertical turbulent mixing and the vertical structure of the subtidal circulation are proposed as the underlying mechanisms controlling the fate of particles.

Identification and quantification of microplastics in salts by complementary approaches using pyrolysis-gas chromatography/quadrupole-time of flight mass spectrometry (Py-GC/QTOFMS) and laser direct infrared (LDIR) chemical imaging analysis

Microplastics (MPs) and nanoplastics (NPs) have been suspected as contaminants in various foodstuffs, including salts, all over the world. Regarding the different sizes and polymer types, the mass concentrations of actual plastic particles in salt are not very clear. The purpose of this study is to develop a scalable method for qualitative and quantitative analysis of MPs and NPs by using Pyrolysis Gas Chromatography Quadrupole-Time of Flight mass spectrometry (Py-GC/QTOFMS) to detect their mass concentrations in salt samples. The targeted and suspected lists of polymers in salts were compiled based on the combined results of the high-resolution mass spectrometry (HRMS) full scanning with auxiliary MS dataset and the laser direct infrared (LDIR) chemical imaging analysis. The seven targeted MPs with polymer standards, i.e., polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), polypropylene (PP), polystyrene (PS), polyethylene (PE), polyethylene terephthalate (PET), and polycarbonate (PC), were first subjected to a full MS scanning mode of the Py-GC/QTOFMS analysis. Subsequently, the parental masses of their pyrolysis compounds were used as the seeds to generate the related daughter masses. This process established both retention time and mass-pairs matching for the target MS/MS mode for enabling the identification and quantification of the particles. The suspected MPs with a matching degree >0.65 in the LDIR list were explored either by the full scan MS. Only PVC was identified, and PET was suspected. The Py-GC/QTOFMS result is complementary and comparable to the LDIR detection with the matching degree >0.85. We identified that PVC and PET (suspected) can be measured in both commercial and bulk sea salts, and their concentrations in sea salts are much higher than in rock salts, implying heavy contamination of the seawater.

Microplastics and 17α Ethinylestradiol: How Do Different Aquatic Invertebrates Respond to This Combination of Contaminants?

The synthetic hormone 17α ethinyl estradiol (EE2) is a molecule widely used in female contraceptives and recognized as a contaminant of attention (Watch List) in the European Union due to its high consumption, endocrine effects and occurrence in aquatic environments. Its main source of introduction is domestic sewage where it can be associated with other contaminants such as microplastics (MPs). Due to their characteristics, they can combine with each other and exacerbate their isolated effects on biota. This study evaluated the combined effects of microplastics (MPs) and 17α ethinylestradiol (EE2) on two tropical estuarine invertebrate species: Crassostrea gasar and Ucides cordatus. Polyethylene particles were spiked with EE2 and organisms were exposed to three treatments, categorized into three groups: control group (C), virgin microplastics (MPs), and spiked microplastics with EE2 (MPEs). All treatments were evaluated after 3 and 7 days of exposure. Oysters exhibited changes in phase 2 enzymes and the antioxidant system, oxidative stress in the gills, and reduced lysosomal membrane stability after exposure to MPs and MPEs. Crabs exposed to MPs and MPEs after seven days showed changes in phase 1 enzymes in the gills and changes in phases 1 and 2 enzymes in the hepatopancreas, such as disturbed cellular health. The combined effects of microplastics and EE2 increased the toxicity experienced by organisms, which may trigger effects at higher levels of biological organization, leading to ecological disturbances in tropical coastal ecosystems.

Enzyme_Metal-Organic Framework Composites as Novel Approach for Microplastic Degradation

Plastic pollution is one of the main worldwide environmental concerns. Our lifestyle involves persistent plastic consumption, aggravating the low efficiency of wastewater treatment plants in its removal. Nano/microplastics are accumulated in living beings, pushing to identify new water remediation strategies to avoid their harmful effects. Enzymes (e. g., Candida rugosa-CrL) are known natural plastic degraders as catalysts in depolymerization reactions. However, their practical use is limited by their stability, recyclability, and economical concerns. Here, enzyme immobilization in metal-organic frameworks (CrL_MOFs) is originally presented as a new plastic degradation approach to achieve a boosted plastic decomposition in aqueous systems while allowing the catalyst cyclability. Bis-(hydroxyethyl)terephthalate (BHET) was selected as model substrate for decontamination experiments for being the main polyethylene terephthalate (PET) degradation product. Once in contaminated water, CrL_MOFs can eliminate BHET (37 %, 24 h), following two complementary mechanisms: enzymatic degradation (CrL action) and byproducts adsorption (MOF effect). As a proof-of-concept, the capacity of a selected CrL_MOF composite to eliminate the BHET degradation products and its reusability are also investigated. The potential of these systems is envisioned in terms of improving enzyme cyclability, reducing costs along with feasible co-adsorption of plastic byproducts and other harmful contaminants, to successfully remove them in a single step.

Removal and release of microplastics and other environmental pollutants during the start-up of bioretention filters treating stormwater

Untreated stormwater is a major source of microplastics, organic pollutants, metals, and nutrients in urban water courses. The aim of this study was to improve the knowledge about the start-up periods of bioretention filters. A rain garden pilot facility with 13 bioretention filters was constructed and stormwater from a highway and adjacent impervious surfaces was used for irrigation for ∼12 weeks. Selected plants (Armeria maritima, Hippophae rhamnoides, Juncus effusus, and Festuca rubra) was planted in ten filters. Stormwater percolated through the filters containing waste-to-energy bottom ash, biochar, or Sphagnum peat, mixed with sandy loam. Influent and effluent samples were taken to evaluate removal of the above-mentioned pollutants. All filters efficiently removed microplastics >10 µm, organic pollutants, and most metals. Copper leached from all filters initially but was significantly reduced in the biochar filters at the end of the period, while the other filters showed a declining trend. All filters leached nutrients initially, but concentrations decreased over time, and the biochar filters had efficiently reduced nitrogen after a few weeks. To conclude, all the filters effectively removed pollutants during the start-up period. Before being recommended for full-scale applications, the functionality of the filters after a longer period of operation should be evaluated.

Are vehicle tires major contributors to microplastic emissions into the China seas? A simple model perspective

Microplastics pose a substantial threat to our environment. Given China's large population and rapid economic growth, it is urgent to estimate the annual emissions of microplastics into its marine environment. The microplastics show a significant variation in their source emissions as well as in their physical and chemical properties, leading to differences in their transport and fate in aquatic environments. To account for these variations, we developed a process-oriented model that considers microplastics from different sources and the inter-provincial variation in their retention rate to assess annual microplastic emissions into the China seas. On a national scale, of the microplastics emitted, 36.05 % are from household laundry activities, 27.26 % are from the wear and tear of vehicle tires, and 24.04 % are from the abrasion of plastic household items. After emission, 60.21 % are removed by wastewater treatment plants. The overall proportion of microplastics that end up in the marine environment highly depends on the specific riverine retention rate of microplastics from vehicle tires. Including the high settling rate of these microplastics, this proportion drops from 9.96 % to 3.29 %, rendering vehicle tires a minor contributor to microplastic emissions into the China seas compared to other sources. Moreover, when using the density-dependent approach and considering the east/west dimension of each province, the microplastic emissions from vehicle tires into the China seas decrease from 71 % to 5.27 %. This underscores the urgent need for global and regional models to account for the detailed riverine transport process of microplastics from vehicle tires in order to enhance the accuracy of their emission estimates into coastal waters.

Effects of ocean acidification and polystyrene microplastics on the oysters Crassostrea gigas: An integrated biomarker and metabolomic approach

The adverse impacts of microplastics (MPs) or ocean acidification (OA) on mollusks have been widely reported, however, little is known about their combined effects on mollusks. The oysters Crassostrea gigas were exposed to two sizes of polystyrene MPs with 1 × 104 particles/L (small polystyrene MPs (SPS-MPs): 6 μm, large polystyrene MPs (LPS-MPs): 50-60 μm) at two pH levels (7.7 and 8.1) for 14 days. The antagonistic effects between MPs and OA on oysters were mainly observed. Single SPS-MPs exposure can induce CAT enzyme activity and LPO level in gills, while LPS-MPs exposure alone can increase PGK and PEPCK gene expression in digestive glands. Ocean acidification can increase clearance rate and inhibit antioxidant enzyme activity, whereas combined exposure of OA and SPS-MPs can affect the metabolomic profile of digestive glands. This study emphasized that the potential toxic effects of MPs under the scene of climate change should be concerned.

Effects of tire-road wear particles on the adsorption of tetracycline by aquatic sediments

Tire-road wear particles (TRWPs) are formed by friction between the tire and the road. TRWPs are ubiquitous across the globe, especially in sediments. However, the possible effects of TRWPs on tetracycline (TC) in aquatic sediments are unknown. To investigate the potential role of TRWPs as carriers of co-pollutants, this study investigated the pore surface properties and TC adsorption behavior of TRWP-contaminated sediments and explored the TC behavior in water sediments, as well as the role of aging processes and TRWPs abundance. The results showed that the surface morphology of TRWP-contaminated sediments changed and the adsorption capacity of sediments to TC increased. The TC adsorption capacity of sediments contaminated by 2% TRWPs increased from 3.15 to 3.48 mg/g. Moreover, the surface physical and chemical properties of TRWPs after UV aging changed, which further increased the TC adsorption capacity. The TC adsorption capacity of the sediments contaminated by aged TRWPs increased from 3.48 to 3.65 mg/g. Changing the proportion of aged TRWPs, we found that the adsorption capacity of sediments contaminated by different proportions of TRWPs for TC was 2% > 1% > 0.5% > 4% > blank sediment. These results may contribute to predicting the potential environmental risks of TRWPs in aquatic sediments.

Microbial hitchhikers on microplastics: The exchange of aquatic microbes across distinct aquatic habitats

Microplastics (MPs) have the potential to modify aquatic microbial communities and distribute microorganisms, including pathogens. This poses a potential risk to aquatic life and human health. Despite this, the fate of 'hitchhiking' microbes on MPs that traverse different aquatic habitats remains largely unknown. To address this, we conducted a 50-day microcosm experiment, manipulating estuarine conditions to study the exchange of bacteria and microeukaryotes between river, sea and plastisphere using a long-read metabarcoding approach. Our findings revealed a significant increase in bacteria on the plastisphere, including Pseudomonas, Sphingomonas, Hyphomonas, Brevundimonas, Aquabacterium and Thalassolituus, all of which are known for their pollutant degradation capabilities, specifically polycyclic aromatic hydrocarbons. We also observed a strong association of plastic-degrading fungi (i.e., Cladosporium and Plectosphaerella) and early-diverging fungi (Cryptomycota, also known as Rozellomycota) with the plastisphere. Sea MPs were primarily colonised by fungi (70%), with a small proportion of river-transported microbes (1%-4%). The mere presence of MPs in seawater increased the relative abundance of planktonic fungi from 2% to 25%, suggesting significant exchanges between planktonic and plastisphere communities. Using microbial source tracking, we discovered that MPs only dispersed 3.5% and 5.5% of river bacterial and microeukaryotic communities into the sea, respectively. Hence, although MPs select and facilitate the dispersal of ecologically significant microorganisms, drastic compositional changes across distinct aquatic habitats are unlikely.

Distribution and risk assessment of microplastic pollution in a rural river system near a wastewater treatment plant, hydro-dam, and river confluence

Rivers are the natural drainage system, transporting anthropogenic wastes and pollution, including microplastics (plastic < 5 mm). In a riverine system, microplastics can enter from different sources, and have spatial variance in concentration, physical and chemical properties, and imposed risk to the ecosystem. This pilot study presents an examination of microplastics in water and sediment samples using a single sample collection from the rural Raquette River, NY to evaluate a hypothesis that distinct locations of the river, such as downstream of a wastewater treatment plant, upstream of a hydro-dam, and river confluence, may be locations of higher microplastics concentration. In general, our results revealed the presence of high microplastic concentrations downstream of the wastewater treatment plant (in sediments), upstream of the hydro dam (both water and sediment), and in the river confluence (water sample), compared to other study sites. Moreover, the risk assessment indicates that even in a rural river with most of its drainage basin comprising forested and agricultural land, water, and sediment samples at all three locations are polluted with microplastics (pollution load index, PLI > 1; PLIzone = 1.87 and 1.68 for water and sediment samples respectively), with risk categories between Levels I and IV ("minor" to "danger"). Overall, the river stands in a "considerable" risk category (PRIzone = 134 and 113 for water and sediment samples respectively). The overall objective of this pilot study was to evaluate our hypothesis and advance our understanding of microplastic dynamics in rural river systems, elucidating their introduction from a point source (wastewater treatment plant), transit through an impediment (hydro-dam), and release into a vital transboundary river (confluence of Raquette-St. Lawrence Rivers).

Are we underestimating stormwater? Stormwater as a significant source of microplastics in surface waters

Stormwater represent a critical pathway for transporting microplastics (MPs) to surface waters. Due to complex dynamics of MPs in stormwater, its dispersion, weathering, risk, and transport are poorly understood. This review bridges those gaps by summarizing the latest findings on sources, abundance, characteristics, and dynamics involved in stormwater MP pollution. Weathering starts before or after MPs enter stormwater and is more pronounced on land due to continuous heat and mechanical stress. Land use patterns, rainfall intensity, MPs size and density, and drainage characteristics influence the transport of MPs in stormwater. Tire and road wear particles (TRWPs), littering, and road dust are major sources of MPs in stormwater. The concentrations of MPs varies from 0.38-197,000 particles/L globally. Further MP concentrations showed regional variations, highlighting the importance of local monitoring efforts needed to understand local pollution sources. We observed unique signatures associated with the shape and color of MPs. Fibers and fragments were widely reported, with transparent and black being the predominant colors. We conclude that the contribution of stormwater to MP pollution in surface waters is significantly greater than wastewater treatment plant effluents and demands immediate attention. Field and lab scale studies are needed to understand its behavior in stormwater and the risk posed to the downstream water bodies.

Common types of microdebris affect the physiology of reef-building corals

Marine debris, particularly microdebris (< 1 mm) poses a potential threat to marine life, including reef-building corals. While previous research has mainly focused on the impact of single polymer microplastics, the effects of natural microdebris, composed of a mixture of materials, have not been explored. Therefore, this study aimed to assess the effects of different microdebris, originating from major sources of pollution, on reef-building corals. For this, we exposed two scleractinian coral species, Pocillopora verrucosa and Stylophora pistillata, known to frequently ingest microplastics, to four types of microdebris in an 8-week laboratory experiment: fragmented environmental plastic debris, artificial fibers from clothing, residues from the automobile sector consisting of tire wear, brake abrasion, and varnish flakes, a single polymer microplastic treatment consisting of polyethylene particles, and a microdebris-free control treatment. Specifically, we (I) compared the effects of the different microdebris on coral growth, necrosis, and photosynthesis, (II) investigated the difference between the microdebris mixtures and the exposure to the single polymer treatment, and (III) identified potential mechanisms causing species-specific effects by contrasting the feeding responses of the two coral species on microdebris and natural food. We show that the fibers and tire wear had the strongest effects on coral physiology, with P. verrucosa being more affected than S. pistillata. Both species showed increased volume growth in response to the microdebris treatments, accompanied by decreased calcification in P. verrucosa. Photosynthetic efficiency of the symbionts was enhanced in both species. The species-specific physiological responses might be attributed to feeding reactions, with P. verrucosa responding significantly more often to microdebris than S. pistillata. These findings highlight the effect of different microdebris on coral physiology and the need for future studies to use particle mixtures to better mimic naturally occurring microdebris and assess its effect on corals in more detail.

Retention efficiency for microplastic in a landscape estimated from empirically validated dynamic model predictions

Soils are recipients of microplastic that can be subsequently transferred to the sea. Land sources dominate inputs to the ocean, but knowledge gaps about microplastic retention by land hinder assessments of input rates. Here we present the first empirical evaluation of a dynamic microplastic fate model operating at landscape level. This mechanistic model accounts for hydrology, soil and sediment erosion, particle characteristics and behavior. We predict microplastic concentrations in water and sediments of the Henares river (Spain) within the measurement uncertainty boundaries (error factors below 2 and 10, respectively). Microplastic export from land and discharge by river fluctuates in a non-linear manner with precipitation and runoff variability. This indicates the need of accurate dynamic descriptions of soil and stream hydrology even when modeling microplastic fate and transport in generic scenarios and at low spatio-temporal resolution. A time-averaged landscape retention efficiency was calculated showing 20-50% of the microplastics added to the catchment over a multiannual period were retained. While the analysis reveals persistent uncertainties and knowledge gaps on microplastic sources to the catchment, these results contribute to the quantitative understanding of the role of terrestrial environments in accumulating microplastics, delaying their transport to the sea.

Modeling the transport of microplastics along river networks

The excessive use of plastics in modern life has led to a significant increase in production and a corresponding rise in plastic waste generation. The slow degradation of plastics results in the introduction and accumulation of microplastics (MP) in the environment, posing environmental and health risks. River networks, acting as conduits between terrestrial and marine environments, play a crucial role in controlling the transport of MP. Predicting the complex processes of MP pathways in these environments is an ongoing challenge. To address this issue, we propose a model that integrates the advection-dispersion equation with anthropogenic MP loads and hydraulic river network characteristics. The validity of the model was assessed using literature data from three river networks worldwide. Model results show a good agreement between predictions and field observations (R2=0.72). Consequently, predicted MP data was used to perform a potential pollution assessment through the pollution load index, revealing in most cases higher MP contamination in headwaters stream and a dilution effect along the river network. The structure of the proposed model allows its further implementation to account for other transport mechanisms, interactions with other emerging contaminants (i.e., pharmaceuticals), and connections with other riverine environments, making it a valuable tool for understanding and mitigating MP pollution.

Aggregation behavior of polystyrene nanoplastics: Role of surface functional groups and protein and electrolyte variation

Aggregation kinetics of plastics are affected by the surface functional groups and exposure orders (electrolyte and protein) with kinds of mechanisms in aquatic environment. This study investigates the aggregation of polystyrene nanoplastics (PSNPs) with varying surface functional groups in the presence of common electrolytes (NaCl, CaCl2, Na2SO4) and bovine serum albumin (BSA). It also examines the impact of different exposure orders, namely BSA + NaCl (adding them together), BSA → NaCl (adding BSA firstly and then NaCl), and NaCl → BSA (adding NaCl firstly and then BSA), on PSNPs aggregation. The presence of BSA decreased the critical coagulation concentration in NaCl (CCCNa+) of the non-modified PS-Bare from 222.17 to 142.81 mM (35.72%), but increased that of the carboxyl-modified PS-COOH from 157.34 to 160.03 mM (1.71%). This might be ascribed to the thicker absorbed layer of BSA onto the PS-Bare surface, known from Ohshima's soft particle theory. Their aggregation in CaCl2 was both increased because of Ca2+ bridging. Different from the monotonous effects of BSA on PS-Bare and PS-COOH, BSA initially facilitated PS-NH2 aggregation via patch-charge attraction, then inhibited it at higher salt levels through steric repulsion. Furthermore, exposure orders had no significant effect on PS-Bare and PS-COOH, but had a NaCl concentration-dependent impact on PS-NH2. At the low NaCl concentrations (10 and 100 mM), no obvious influence could be observed. While, at 300 mM NaCl, the high concentrations of BSA could not totally stabilize the salt-induced aggregates in NaCl → BSA, but could achieve it in the other two orders. These might be attributed to the electrical double layer compression by NaCl, "patch-charge" force and steric hindrance by BSA. These experimental findings shed light on the potential fate and transport of nanoparticles in aquatic environments.

The processes and transport fluxes of land-based macroplastics and microplastics entering the ocean via rivers

Approximately 80% of marine plastic waste originates from land-based sources and enters oceans through rivers. Hence, to create effective regulations, it is crucial to thoroughly examine the processes by which land-based plastic waste flows into marine environments. To this end, this review covers the complete journey of macro- and microplastics from their initial input into rivers to their ultimate release into oceans. Here, we also discuss the primary influencing factors and current popular research topics. Additionally, the principles, applicability, accuracy, uncertainty, and potential improvement of the standard methods used for flux estimation at each stage are outlined. Emission estimates of land-based macro- and microplastics are typically assessed using the emission factor approach, coefficient accounting approach, or material flow analysis. Accurately estimating mismanaged plastic waste is crucial for reducing uncertainty in the macroplastic emission inventory. In our review of the processes by which land-originating plastics enter rivers, we categorized them into two major types: point-source and diffuse-source pollution. Land surface hydrological models simulate transport from diffuse sources to rivers, necessitating further research. Riverine (micro)plastic flux to the ocean is often estimated using monitoring statistics and watershed hydrological models at the watershed scale; however, standardized monitoring methods have not yet been established. At the global scale, algorithms based on river datasets are often used, which require further improvements in river data selection and microplastic number-mass conversion factors. Furthermore, the article summarizes the accuracy and sources of uncertainty of various methods. Future research efforts should focus on quantifying and mitigating uncertainties in resultant projections. Overall, this review deepens our understanding of the processes by which land-based plastic waste enters the ocean and helps scholars efficiently select or improve relevant methods when studying land-ocean transport fluxes.

A catchment-wide microplastic pollution investigation of the Yangtze River: The pollution and ecological risk of tributaries are non-negligible

The Yangtze River is an important global channel for plastics and microplastics (MPs) to enter the sea. However, the existing research on MPs in the Yangtze River has primarily focused on the mainstream region, without regarding the occurrence, spatial distribution, and ecological risks associated with tributaries, as well as their relationship with the mainstream. To address this knowledge gap, we conducted a large-scale catchment-wide investigation of the surface water in the Yangtze River, encompassing MPs (48 µm-5 mm) of the mainstream and 15 important tributaries. Tributaries and upstream regions exhibited relatively higher levels of MPs compared with the mainstream and different sections of the river. The distribution of MPs is primarily influenced by the emission of arable land and the pH of water. Notably, the upstream tributary areas demonstrated the highest ecological risks associated with MPs. Further analysis highlighted that the tributaries accounted for a contribution ranging from 16% to 67% in quantity and from 14% to 90% in mass of the microplastics observed in the mainstream. Our results suggest that the pollution of tributaries and their associated ecological risk migration must be effectively regulated.

Analysis of Flow Characteristics between Tandem Flexible Structures Based on PIV: Substantial Applications for the Removal of Microplastics

This study emphasizes the potential risk posed by microplastics, particularly in tap water. Numerous studies have reported the removal of microplastics, but the limitations in addressing this issue remain challenging. To tackle this problem, a new method is introduced using tandem flexible structures (FSs) for microplastic removal. The present study focused on understanding the hydrodynamic characteristics between FSs to utilize microplastic removal. This comprehension of fluid flow and FSs offers valuable insights for improving the efficiency of microplastic removal methods. Therefore, the optimal conditions for removing microplastics were experimentally investigated inside the FSs gap region. Based on the gap distance and height, the flow structures between FSs were investigated. A small secondary vortex structure that could trap particles from upstream was continuously maintained behind the upstream FSs under certain geometric conditions. It is shown that this vortex structure has an effective way of confining the particles from upstream. The persistency of a small secondary vortex was also evaluated. This study may be helpful to researchers working on microplastic removal and FSs with a tandem arrangement.

Causes of coastal waters pollution with nutrients, chemicals and plastics worldwide

Worldwide, coastal waters contain pollutants such as nutrients, plastics, and chemicals. Rivers export those pollutants, but their sources are not well studied. Our study aims to quantify river exports of nutrients, chemicals, and plastics to coastal waters by source and sub-basin worldwide. We developed a new MARINA-Multi model for 10,226 sub-basins. The global modelled river export to seas is approximately 40,000 kton of nitrogen, 1,800 kton of phosphorous, 45 kton of microplastics, 490 kton of macroplastics, 400 ton of triclosan and 220 ton of diclofenac. Around three-quarters of these pollutants are transported to the Atlantic and Pacific oceans. Diffuse sources contribute by 95-100 % to nitrogen (agriculture) and macroplastics (mismanaged waste) in seas. Point sources (sewage) contribute by 40-95 % to phosphorus and microplastics in seas. Almost 45 % of global sub-basin areas are multi-pollutant hotspots hosting 89 % of the global population. Our findings could support strategies for reducing multiple pollutants in seas.

Distribution and characteristics of microplastics in an urban river: The response to urban waste management

The rivers have been proven to be potential sources and the major transport pathways of microplastic (MP) in natural aquatic eco-systems, yet there is an absence of understanding the provenances and distribution dynamics of MP in fluvial water body of urban regions. The present investigation aimed to characterize the distribution and accumulation of MPs in both surface water and riverine bed sediments in a typical urban river (Nanming River, southwest China), during the dry and wet seasons of 2021. MP were detected throughout the entire sample set, with average surface water abundances of 750 ± 53 n/m3 and 693.3 ± 40 n/m3 in dry and wet seasons, respectively, and 2250 ± 496.7 n/kg (dw) in surface sediments. Furthermore, the composition of 25 polymer types MPs were analyzed. The sediment of the Nanming River is a sink for MPs, recording their long-term accumulation. Multivariate statistical analysis-based results indicated that urban littering and agricultural input were the major contributors of non-point MP in the Nanming River, while the discharged effluent was another factor influencing the distribution of MPs in urban fluvial system. The average abundance of MPs was negatively correlated with purchase power parity (PPP), demonstrating that the poorly waste management results in a higher abundance of MPs in municipal river systems. The present study systematically characterized the distribution of MPs in medium-sized urban rivers systems in Southwest China. These findings can inform policy and management decisions to reduce MPs pollution in urban rivers and protect aquatic ecosystems.

Review: Mitigation measures to reduce tire and road wear particles

The generation of tire wear is an inevitable outcome of the friction between the road and the tire which is necessary for the safe operation of vehicles on roadways. Tire wear particles form agglomerates with road surface material. These agglomerates are called tire and road wear particles (TRWP). Due to their persistence in the environmental compartments and their potentially harmful effects, research on preventative and end-of-pipe mitigation strategies for TRWP is essential. The major goal of this study is to summarize and assess the state of the art in science and technology of mitigation measures for TRWP as the basis for further research activities. Approximately 500 literature sources were found and analyzed in terms of the efficiency, maturity, implementation, and impact of the mitigation measures. Generally, technological and management mitigation measures to reduce the generation of TRWP are beneficial since they prevent TRWP from entering the environment. Once released into environmental compartments, their mobility and dispersion would increase, making removing the particles more challenging. Technological and management mitigation measures after the release of TRWP into the environment are mainly well established in industrialized countries. Street cleaning and wastewater technologies show good removal efficiencies for TRWP and microplastics. In any case, no individual measure can solely solve the TRWP issue, but a set of combined measures could potentially be more effective. The absence of fully-developed and standardized methods for tire abrasion testing and measuring TRWP in the environment makes it impossible to reliably compare the tire abrasion behavior of different tire types, determine thresholds, and control mitigation actions. Field tests and pilot studies are highly needed to demonstrate the effectiveness of the abatement measures under real conditions.

Incidence and exposure to microplastics in table salt present in the Iran market

Plastics and microplastics (MPs) are toxic, pervasive and threatening the biotic and abiotic components of the earth, and they threaten food safety and food security by moving in the food chain. In this study, the amounts and characteristics of 40 table salt samples with different brands, including sea salt (No = 13), rock (No = 13), bulk (No = 8) and non-standard (No = 6), were investigated with a combination of sieving, filtration, observation and FTIR, Micro-Raman and SEM techniques. The results showed that all the salts were contaminated with MPs. In general, the abundance range of detected particles was 700-5470 MPs/kg. The abundance of MPs was higher in counterfeit and non-standard salts (1825 ± 1808 MPs/kg). Investigating the relationship between the effect of the purification process (Kruskal-Wallis Test, P = 0.841), the type of packaging (Kruskal-Wallis Test, P = 0.609), and the type of salt (Kruskal-Wallis Test, P = 0.942), on the abundance of MPs using a comparison test Kruskal-Wallis was not significant. However, the numerical difference was recognizable. The most identified polymer in the salts was cellulose acetate, which probably causes by unmanaged plastic litter in the environment (especially cigarette butts). The dominant form of particles was fragment-shaped, which is the most abundant form of identified MPs in the environment. Both environmental pollution and secondary pollution (during production and packaging), respectively, contribute to the contamination of salts with MPs. The estimated human dietary intake (EDI) and the amount of estimated annual intake (EAI) for different ages in Iran were obtained EDI = 5-59 MPs/capita/day and EAI = 1967-21563 MPs/capita/year. The surface morphology of the particles showed that the MPs were affected by continuous weathering, mechanical fracture and oxidation. MPs are a threat to human health due to the absorption and transmission of dangerous pollutants and their inherent toxicity. Therefore, a solution must be thought of to prevent the contamination of the food chain through salts by MPs, (with protective measures at the salt source, and by improving its production processes.

Impact of flooding on microplastic abundance and distribution in freshwater environment: a review

Due to smaller particle size (0.1 µm-5 mm), non-biodegradable or slowly degradable nature, and high accumulation capacity in the environment, microplastics are becoming a cause of concern throughout the globe. The abundance and distribution of microplastics in aquatic compartments are strongly influenced by various natural and anthropogenic variables. Hydrodynamic conditions like flood events, caused due to extreme precipitation, accelerate the transport and settlement of microplastics in freshwater bodies. This review highlights the current literature which focuses on the effect of flooding on microplastic abundance, characterization, and distribution in freshwater environments worldwide. However, only limited research papers are identified through focused literature search, as this area of research is relatively new. Most of the studies reported increased and decreased abundance of microplastics in water and sediment samples, respectively, during post-flooding period with the exception of few studies. We also evaluate the post-flooding abundances of different morphological shape and polymer type of microplastics. Fragments, fibers, beads, and film were the most frequently reported microplastic shape and polystyrene, and polyethylene was the dominant polymer type found in freshwater environments. Future research should focus on more advanced techniques to understand microplastic fluxes under flood condition and the dominance of various natural and human-induced factors over one another in determining microplastic abundance. This will further enhance to mitigate microplastic pollution in freshwater environments.

Water, Water Everywhere, but Every Drop Unique: Challenges in the Science to Understand the Role of Contaminants of Emerging Concern in the Management of Drinking Water Supplies

The protection and management of water resources continues to be challenged by multiple and ongoing factors such as shifts in demographic, social, economic, and public health requirements. Physical limitations placed on access to potable supplies include natural and human-caused factors such as aquifer depletion, aging infrastructure, saltwater intrusion, floods, and drought. These factors, although varying in magnitude, spatial extent, and timing, can exacerbate the potential for contaminants of concern (CECs) to be present in sources of drinking water, infrastructure, premise plumbing and associated tap water. This monograph examines how current and emerging scientific efforts and technologies increase our understanding of the range of CECs and drinking water issues facing current and future populations. It is not intended to be read in one sitting, but is instead a starting point for scientists wanting to learn more about the issues surrounding CECs. This text discusses the topical evolution CECs over time (Section 1), improvements in measuring chemical and microbial CECs, through both analysis of concentration and toxicity (Section 2) and modeling CEC exposure and fate (Section 3), forms of treatment effective at removing chemical and microbial CECs (Section 4), and potential for human health impacts from exposure to CECs (Section 5). The paper concludes with how changes to water quantity, both scarcity and surpluses, could affect water quality (Section 6). Taken together, these sections document the past 25 years of CEC research and the regulatory response to these contaminants, the current work to identify and monitor CECs and mitigate exposure, and the challenges facing the future.

The distribution and characterisation of microplastics in air, surface water and sediment within a major river system

Rivers are key pathways for the transfer of microplastics (MP) to marine environments. However, there are considerable uncertainties about the amount of microplastics transported by rivers to the ocean; this results in inaccuracies in our understanding of microplastic quantity and transport by freshwater systems. Additionally, it has been suggested that rivers may represent long-term sinks, with microplastics accumulating in sediment due to their high density or other biological, chemical, and physical factors. The atmosphere is also an important pathway by which airborne microplastics may enter aquatic habitats. Here, we compare for first time microplastics type and concentration in these key environmental mediums (air, water and sediment) along a major river (Ganges), from sea to source to understand 1) the abundance, 2) the spatial distribution, and 3) characteristics. Mean microplastic abundance settling from the atmosphere was 41.12 MP m2 day-1; while concentrations in sediment were 57.00 MP kg-1 and in water were 0.05 MP L-1. Across all sites and environmental mediums, rayon (synthetically altered cellulose) was the dominant polymer (54-82 %), followed by acrylic (6-23 %) and polyester (9-17 %). Fibres were the dominant shape (95-99 %) and blue was the most common colour (48-79 %). Across water and sediment environmental mediums, the number of microplastics per sample increased from the source of the Ganges to the sea. Additionally, higher population densities correlated with increased microplastic abundance for air and water samples. We suggest that clothing is likely to be the prominent source of microplastics to the river system, influenced by atmospheric deposition, wastewater and direct input (e.g. handwashing of clothes in the Ganges), especially in high density population areas. However, we suggest that subsequent microplastic release to the marine environment is strongly influenced by polymer type and shape, with a large proportion of denser microplastics settling in sediment prior to the river discharging to the ocean.

Quantifying microplastics pollution in the Red Sea and Gulfs of Suez and Aqaba: Insights from chemical analysis and pollution load assessment

Microplastics (MPs) constitute the majority of marine plastic litter. The pollution caused by MPs has been categorized as a gradual and persistent crisis, but little is known about its extent along the shores of the Red Sea, particularly on the Egyptian side. The Red Sea is a rapidly developing region and home to critical ecosystems with high levels of endemism. This study represents the first comprehensive survey investigating the extent of MP pollution along the Egyptian shores of the Red Sea, including the Gulf of Suez and Aqaba. Mean concentrations ranged from 23.3 ± 15.28 to 930.0 ± 181.9 MPs/kg DW. Out of 17 beaches surveyed, 12 had mean concentrations of <200 items/kg, indicating a low occurrence of MPs compared to the shores of the Mediterranean Coast of Egypt. The pollution load index varied from low to medium levels in most locations. Ras Mohamed, a marine protected area, showed high vulnerability to MP pollution. All the investigated particles were fragments of secondary MPs. The sources of pollution mainly come from maritime activities, including cargo shipping and intense recreational activities. Fourier Transform Infrared Spectroscopy identified four plastic polymers, with polyethylene and polypropylene being the most common. The surface morphology of plastic particles was examined using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy. All the particles exhibited signs of degradation, which could generate countless plastic pieces with possible deleterious impacts. This work has highlighted the importance of conducting region-specific assessments of mismanaged plastic waste, focusing on the role of tourism and recreational navigation as contributors to plastic litter, to estimate plastic waste inputs into the waters of the Red Sea Coast of Egypt. Efforts are needed to develop strategic plans to reduce the disposal of plastic waste in the region.

Modeling impacts of river hydrodynamics on fate and transport of microplastics in riverine environments

Microplastics pose a significant and growing threat to marine ecosystems and human health. Rivers serve as critical pathways for the entry of inland-produced microplastics into marine environments. In this paper, we developed a numerical modeling scheme using OpenFOAM to investigate the fate and transport of microplastics in a river system. Our simulation results show that microplastics undergo significant aggregation and breakage as they are transported downstream by river flows. This significantly alters the particle size distribution of microplastics. The aggregation-breakage process is mainly controlled by river hydrodynamics and pollution scale. Our findings suggest that a significant extent of particle aggregation occurs at an early stage of the release of microplastics in the river, while the aggregation-breakage process becomes limited as the microplastic plume is gradually dispersed and diluted downstream. Eddy diffusivity drives the dispersion of the microplastic plume in the river, and its spatial patterns affect the aggregation-breakage process.

Unraveling the Marine Microplastic Cycle: The First Simultaneous Data Set for Air, Sea Surface Microlayer, and Underlying Water

Microplastics (MP) including tire wear particles (TWP) are ubiquitous. However, their mass loads, transport, and vertical behavior in water bodies and overlying air are never studied simultaneously before. Particularly, the sea surface microlayer (SML), a ubiquitous, predominantly organic, and gelatinous film (<1 mm), is interesting since it may favor MP enrichment. In this study, a remote-controlled research catamaran simultaneously sampled air, SML, and underlying water (ULW) in Swedish fjords of variable anthropogenic impacts (urban, industrial, and rural) to fill these knowledge gaps in the marine-atmospheric MP cycle. Polymer clusters and TWP were identified and quantified with pyrolysis-gas chromatography-mass spectrometry. Air samples contained clusters of polyethylene terephthalate, polycarbonate, and polystyrene (max 50 ng MP m-3). In water samples (max. 10.8 μg MP L-1), mainly TWP and clusters of poly(methyl methacrylate) and polyethylene terephthalate occurred. Here, TWP prevailed in the SML, while the poly(methyl methacrylate) cluster dominated the ULW. However, no general MP enrichment was observed in the SML. Elevated anthropogenic influences in urban and industrial compared to the rural fjord areas were reflected by enhanced MP levels in these areas. Vertical MP movement behavior and distribution were not only linked to polymer characteristics but also to polymer sources and environmental conditions.

Toxicity of co-exposure of microplastics and lead in African catfish (Clarias gariepinus)

Microplastics (MPs) are an emerging threat to freshwater ecosystems with several ecotoxicological ramifications for fish. Microplastics (MPs) can adsorb heavy metals on their surfaces and increase their availability to aquatic organisms. The combined impact of lead and microplastics on fish has only been studied seldom utilizing a variety of markers. The present study aimed to evaluate the hematological, biochemical, and inflammatory signals (cytokines), as well as antioxidant enzymes in African catfish (Clarias gariepinus) exposed to lead (Pb) and MPs individually and combined for 15 days (acute toxicity experiment). The fish were split into four groups, the first of which was the control group. The second group received exposure to 1 mg/L of lead nitrate [Pb(NO3)2]. The third group was given 100 mg/L of MPs. A solution containing 100 mg/L of MPs and 1 mg/L of lead nitrate [Pb(NO3)2] was administered to the fourth group (the combination group). According to the findings, when MPs and Pb were combined for 15 days, the red blood cells (RBCs), thrombocytes, and lymphocytes were significantly reduced in comparison to the control fish. When compared to the control fish, the fish exposed to MPs and Pb alone or together showed a significant rise in blood interleukin-1β (IL-1β) and interleukin-6 (IL-6) cytokines. Both MPs and Pb exposure in catfish resulted in significant changes in the plasma electrolytes. The fish treated with MPs and Pb individually or in combination showed significant reduction in superoxide dismutase (SOD) and total antioxidant capacity (TAC) levels compared to the control group. The fish exposed to the combined action of MPs and Pb showed a considerable modification in all biochemical markers. The difference in the mean concentration of Pb (mg/L) between the fish exposed to Pb alone and the fish subjected to Pb and MPs combination was not statistically significant. In conclusion, according to this investigation, exposure to Pb caused an insignificant increase in Pb accumulation when MPs were present. However, co-exposure may result in anemia, cellular harm, extremely high levels of oxidative stress, and an inflammatory reaction.

Microplastics in water from the confluence of tropical rivers: Overall review and a case study in Paraiba do Sul River basin

Rivers are known for carrying out a fundamental role in the transportation of human debris from continental areas to the marine environment and have been identified as hotspots for plastic pollution. We characterized microplastics (MPs) along confluence areas in the Paraíba do Sul River basin, the biggest river in southeastern Brazil. This water body crosses highly industrialized areas, with the highest population density, and the major water demand in South America. Considering the important ecological function of this extensive watershed and the implications of MP pollution, we evaluate the spatial variation of MP concentration in the confluence areas and upstream from the confluence. Samples were taken from the superficial layer of the water column in February and June 2022, using manta net with 300 μm mesh size. A total of 19 categories and 2870 plastic particles were determined. The confluences areas of rivers showed the highest concentration of MPs, highlighting the confluences of the Paraiba do Sul and Muriaé rivers (0.71 ± 0.25 MP/m3), followed by Paraíba do Sul and Dois Rios rivers (0.42 ± 0.23 MP/m3) and Paraíba do Sul and Pomba rivers (0.38 ± 0.14 MP/m3). Black fibers were the main category, followed by blue fibers and blue fragments. The MPs in the surface waters of Paraíba do Sul River is significantly influenced by the sampling points spatiality. This result corroborates other studies around the world and reinforces the argument that affluents are important sources for the introduction of MPs in larger rivers. Nevertheless, our results provide a better understanding of the different contributing factors and occurrence of MPs in river basins.

Lethal effect of leachates from tyre wear particles on marine copepods

With thousands of tons of Tyre Wear Particles (TWP) entering the aquatic environment every year, TWP are considered a major contributor to microplastic pollution. TWP leach organic compounds and metals in water, potentially affecting the marine food web. However, little is known about the toxicity of TWP leachates on marine copepods, a major food web constituent, and a key group to determine the environmental risk of pollution in marine ecosystems. In this study, we determined the lethal effect of TWP leachates on marine copepods after 24, 48, and 72-h of exposure to 0.05-100% leachate solutions prepared using a concentration of 5 g TWP L-1. The calanoids Acartia tonsa, Temora longicornis and Centropages hamatus, the cyclopoid Oithona davisae and the harpacticoid Amonardia normanni were used as experimental species. TWP leachates were toxic to all the studied species, with toxicity increasing as leachate solution and exposure time increased. Median lethal concentration (LC50, 72-h) ranged from 0.22 to 3.43 g L-1 and calanoid copepods were more sensitive to TWP leachates than the cyclopoid O. davisae and the harpacticoid A. normanni. Toxicity of TWP leachates was not related to the copepod body size, which suggests that other traits such as foraging behaviour or adaptation to contaminants could explain the higher tolerance of cyclopoid and harpacticoid to TWP leachates compared to calanoid copepods. Although field data on the concentration of TWP and their chemical additives are still limited, our results suggest that TWP leachates can negatively impact planktonic food webs in coastal areas after road runoff events.

Potential transmission of SARS-CoV-2 through microplastics in sewage: A wastewater-based epidemiological review

In light of the current COVID-19 pandemic caused by the virus SARS-CoV-2, there is an urgent need to identify and investigate the various pathways of transmission. In addition to contact and aerosol transmission of the virus, this review investigated the possibility of its transmission via microplastics found in sewage. Wastewater-based epidemiological studies on the virus have confirmed its presence and persistence in both influent sewage as well as treated ones. The hypothesis behind the study is that the huge amount of microplastics, especially Polyvinyl Chloride and Polyethylene particles released into the open waters from sewage can become a good substrate and vector for microbes, especially Polyvinyl Chloride and Polyethylene particles, imparting stability to microbes and aiding the "plastisphere" formation. A bibliometric analysis highlights the negligence of research toward plastispheres and their presence in sewage. The ubiquity of microplastics and their release along with the virus into the open waters increases the risk of viral plastispheres. These plastispheres may be ingested by aquatic organisms facilitating reverse zoonosis and the commercial organisms already reported with accumulating microplastics through the food chain poses a risk to human populations as well. Reliance of high population density areas on open waters served by untreated sewage in economically less developed countries might bring back viral transmission.

Quantification of microplastic by particle size down to 1.1 μm in surface road dust in an urban city, Japan

The impact of microplastics (MPs, plastic particles ≤5 mm) on ecosystems is of great concern. Road surfaces represent a significant source of MPs where plastic fragments are physically and chemically reduced to MPs. However, the literature lacks information on fragmentation tendencies below 11 μm. This study aimed to characterize the occurrence of MPs in road dust in different size fractions down to 1.1 μm. Road dust was collected at five sites near a major road in Kusatsu city, Japan, and partitioned by size into 13 fractions (1.1-850 μm). The coarser fractions accounted for a greater proportion of the dust. The percentage of organic matter, determined by loss on ignition, increased as the fractions became finer. Pyrolysis-gas chromatography-mass spectrometry was used to quantify 12 types of polymers in each fraction. The dust was found to contain nine types of MP, namely, polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC), polystyrene (PS), styrene/butadiene rubber (SBR), acrylonitrile/butadiene/styrene resin (ABS), polycarbonate (PC), polymethylmethacrylate (PMMA), and polyamide 66 (PA66). The total MP concentration in road dust particles by particle size fraction (concentrationf) began to increase from the 125-250 μm fraction and remained elevated in finer fractions down to 1.1 μm, indicating that MPs in the road dust micronized to at least 1.1 μm. However, for individual polymer types, the tendency for concentrationf to increase or decrease with particle size fraction varied: the concentrationf of some polymers, such as PE and PVC, remained elevated in fractions down to 1.1 μm; the concentrationf of SBR, a rubber-MP, showed a stable or decreasing trend in fractions of 7.0-11 μm and finer. Particles of PE, PVC, and some other plastics might become increasingly finer, even down to 1.1 μm. Further research is needed to understand the comminution limits of these polymers under pertinent environmental conditions.

Microplastic ingestion by invasive Prussian carp (Carassius gibelio) used in fishmeal production in Türkiye

MP contamination in the gastrointestinal tract (GIT) of Prussian carp (Carassius gibelio) used in fishmeal production was examined. The samples were collected from Balık Lake, Karaboğaz Lake, and Liman Lake located in Kızılırmak Delta, Türkiye. The overall average abundance was 3.20±0.18 MP per fish and 0.036±0.002 MP per g. No significant correlation was determined between the MP abundance in the fish, fish length, and fish weight. The polymers were composed of 56.91% PET, 25.20% PP, 9.76% PE, and 8.13% PA. The determined shapes were fiber (78.0%), fragment (13.46%), and film (8.54%). The size ranged between 112 and 4775 μm with an average of 1341.41±66.07 μm. Depending on the occurrence frequency and abundance, it can be concluded that Carassius gibelio can be considered a MP vector in fishmeal. The results provide an essential baseline for future MP studies on the potential effects of MPs on aquatic organisms, fate, and impact on the fishmeal production process, aquaculture practices, and human health.

Integrated numerical modeling to quantify transport and fate of microplastics in the hyporheic zone

Despite the significance of rivers and streams as pathways for microplastics (MP) entering the marine environment, limited research has been conducted on the behavior of MP within fluvial systems. Specifically, there is a lack of understanding regarding the infiltration and transport dynamics of MP across the streambed interface and within the hyporheic sediments. In this study, transport and retention of MP are investigated using a new numerical modeling approach. The model is built as a digital twin of accompanying flume experiments, which are used to validate the simulation results. The model accurately represents particle transport in turbulent water flow and within the hyporheic zone (HZ). Simulations for transport and infiltration of 1 µm MP particles into a sandy streambed demonstrate that the advection-dispersion equation can be used to adequately represent particle transport for pore-scale sized MP within the HZ. To assess the applicability of the modeling framework for larger MP, the experiment was repeated using 10 µm particles. The larger particles exhibited delayed infiltration and transport behavior, and while the model successfully represented the spatial extent of particle transport through the HZ, it was unable to fully replicate hyporheic transit times. This study is the first to combine explicit validation against experimental data, encompassing qualitative observations of MP concentration patterns and quantification of fluxes. By that, it significantly contributes to our understanding of MP transport processes in fluvial systems. The study also highlights the advantages and limitations of employing a fully integrated modeling approach to investigate the transport and retention behavior of MP in rivers and streams.

Hydrostatic pressure drives microbe-mediated biodegradation of microplastics in surface sediments of deep reservoirs: Novel findings from hydrostatic pressure simulation experiments

Microplastics originate from the physical, chemical, or biological degradation of plastics in the environment. Once ingested by organisms at the bottom of the food chain, microplastics are passed on to organisms at higher trophic levels, posing a threat to human health. The distribution of microplastics and the metabolic pathways involved in their microbial degradation in surface sediments of drinking water reservoirs are still poorly understood. This study analyzed the occurrence patterns of microplastics and microbial community structure associated with microplastic biodegradation in surface sediments from a deep reservoir at various hydrostatic pressures. Based on the results of Fourier-transform and laser direct infrared spectroscopy, elevating the pressure resulted in altered sizes and shapes of microplastics in sediment samples with the presence of microorganisms. The influence of hydrostatic pressure on small-sized microplastics (20-500 μm) was pronounced. For instance, high pressure accelerated the breakdown of fibers, pellets, and fragments into smaller-sized microplastics. In particular, the mean size of polyethylene terephthalate microplastics decreased from 425.78 μm at atmospheric pressure to 366.62 μm at 0.7 Mpa. Metagenomic analysis revealed an increase in the relative abundances of plastic-degrading genera, such as Rhodococcus, Flavobacterium, and Aspergillus, in response to elevated pressures. Eight functional genes for biodegradation of polystyrene, polyethylene, and polyethylene terephthalate microplastics were annotated, including paaK, ladA, tphA3. Of these, tphA3 gene abundance was negatively influenced by hydrostatic pressure, providing direct evidence for the pathway by which microbial metabolism of polyethylene terephthalate led to decreased microplastic size under high pressure conditions. This study presents novel insights into hydrostatic pressure-driven microbial community structure, functional gene abundance, and key metabolic pathways associated with biodegradation of microplastics in reservoir sediments.