Macroplastic fragmentation in rivers

A Quantitative Relationship between Settling and Wettability for Weathered Microplastics in Aquatic Systems

Settling plays a crucial role in determining the residence time, distribution, transport, and ultimate fate of microplastics (MPs) in aquatic environments. The settling dynamics of particles are influenced by their macroscale shape, mesoscale roundness, and microscale surface properties, along with ambient fluid flow conditions. Variations in the wettability of submillimeter MPs affect molecular interactions at the particle-water interface, altering the microscopic flow field and subsequently modifying drag forces during settling. This study examines the impact of wettability on the settling behavior of aged acrylonitrile butadiene styrene MPs by measuring their settling velocities and contact angles. It was shown that increased wettability promotes the settlement of the MPs. A drag model incorporating the Eötvös number─a dimensionless ratio of buoyancy energy to contact angle-derived surface energy─is developed to quantify the relationship between interfacial chemistry and hydrodynamic resistance. Unlike the conventional models, our model considers wettability as a key factor controlling the settling of MP particles. The model was validated using independently measured data and four sets of published data for the MPs. Results demonstrate that the model significantly improves the accuracy of the settling predictions for weathering spherical MPs. Additionally, by integrating the shape factor, it effectively accounts for the settling behavior of irregularly shaped MPs using published data sets. This improvement enhances predictability for MP transport pathways, helping assess MP accumulation zones and potential ecological risks in marine and freshwater systems.

Evaluating the environmental impact of cleaning the North Pacific Garbage Patch

Cleanup of existing plastic pollution is crucial to mitigate its impact on marine ecosystems, but such efforts must ensure benefits outweigh potential environmental damage caused by the cleanup. Here, we present an impact assessment framework and apply it to evaluate whether cleaning the North Pacific Garbage Patch (NPGP) benefits marine life and carbon cycling, using The Ocean Cleanup as a case study. Our findings indicate that marine life is more vulnerable to plastic pollution than to macroplastic cleanup, with average vulnerability scores (1 = low, 3 = high) of 2.3 for macroplastics, 1.9 for microplastics, and 1.8 for cleanup, suggesting a net positive impact. An 80% cleanup could reduce macroplastic concentrations to within reported safe levels for marine mammals and sea turtles. Estimated cleanup-related carbon emissions [0.4-2.9 million metric tons (Mt) in total] are significantly lower than potential long-term microplastics impacts on ocean carbon sequestration (15-30 Mt C per year). However, uncertainties remain regarding effects on air-sea carbon exchange. Our framework serves as a critical tool for assessing trade-offs between plastic pollution and remediation impacts. It demonstrates the environmental net benefits of the proposed NPGP cleanup and can be adapted to similarly evaluate other remediation plans.

Low-dose exposure to microplastics retards meiotic maturation via HDAC3 insufficiency

Microplastics (MPs) are considered one of the main causes of male and female infertility. However, the reproductive toxicity and its related mechanisms are currently understood primarily through animal models with acute exposure to MPs. In this study, we demonstrate that low-dose exposure to polystyrene microplastics (PSMPs) leads to severely abnormal reproduction in females, manifested by oocyte meiotic maturation defect. Mechanistically, PSMPs exposure induce the overactivation of cell metabolism pathways, insufficient HDACs, and H4K16 hyperacetylation in oocytes both in vivo and in vitro. When an HDAC3 inhibitor is added, the oocyte maturation defect, overactivation of cell metabolism pathways, and H4K16 hyperacetylation are recapitulated. Conversely, the overexpression of HDAC3 can rescue the defects in meiotic maturation induced by PSMPs. Our observations suggest a direct link between the maturation defects caused by PSMPs and HDAC3 insufficiency. Thus, we propose potential treatments to address the meiotic maturation defect of oocytes in women highly exposed to MPs by activating or supplying HDAC3.

Reefs of Brachidontes exustus and Petaloconchus spp. as traps and sink for microplastics in tropical coastal areas

Microplastics (MPs) are emerging contaminants in marine environments. This study quantified, chemically identified, and described MPs in reefs of Brachidontes exustus and Petaloconchus spp. on the tropical coast of Brazil. Samples were collected in reefs of northeastern Brazil in the dry (February) and rainy (July) seasons of 2023. MPs were classified (shape and color), measured, and counted. MPs were present in all samples. Most MPs were transparent fibers, with more particles in Brachidontes reefs and during the rainy season. MPs were mainly polystyrene, polypropylene, polyester, and polyamide. The characteristics of reefs and seasonal changes in rainfall are the main drivers of the accumulation of MPs, and the shape and chemical composition of particles reveal that their principal source is probably the textile and apparel industry. The trapping of MPs in Petaloconhus spp. and Brachidontes exustus reefs reveals that biogenic reefs may be a sink for microplastics in tropical coastal areas.

Notable ecological risks of microplastics to Minjiang River ecosystem over headwater to upstream in Eastern Qinghai-Tibetan Plateau

Microplastics (MPs) in aquatic environments has been observed globally. However, the ecological risks of MP pollution in riverhead prior to highly urbanized region remain poorly understood. This study investigated MP pollution related to microbiome in sediments, and ecological risks of MPs in riverhead prior to urbanized area over 291 km of Minjiang River (MJR) in Qinghai-Tibetan Plateau (QTP). MPs in river water and sediments were averagely 245±128 items/L and 124±67 items/kg, respectively, over the investigated river range. The MP distribution indicated that MP abundance is low in headwater section and elevated in middle section and down section with increase of urbanized area. The MPs were found mainly in film, fragments, and fiber morphotypes, with size < 500 μm in both river water and sediments. The polymers of MPs were contributed by polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyvinyl chloride (PVC), and polycarbonate (PC) at 41.7 %, 22.7 %, 17.9 %, 1.8 %, and 1.2 % in river water, and 32.6 %, 15.0 %, 29.3 %, 3.1 %, and 0.8 % in sediments, respectively. Microbiome analyses of sediments revealed that the majority of microorganisms were aerobic bacteria, which contained potential plastic-degrading bacterial genes. Ecological risk assessment indexes of pollution load, polymeric risk assessment and pollution risk indicated that MPs in MJR river water and sediments displayed noticeable pollution levels, i.e., river water exhibited medium to very high pollution risk levels, and sediments showed from low to very high pollution risk levels in riverhead. Monte Carlo simulation revealed that PVC and PC MPs were considered as priority control pollutants although they were not the most abundant polymers identified due to their intrinsic chemical toxicity. Compared with risk levels of global rivers, the results indicate prominent ecological risks caused by MPs in MJR riverhead areas, and thus raise a warning sign.

Meso and macroplastics present on the surface and soil of a stream bank in the Pampas Region of Argentina

The presence of meso and macroplastics extracted from the surface and the soil of the banks of the most polluted point of the Langueyú stream, located in the Pampas Region of Argentina, was studied. The plastic waste extracted from the surface occupies 19.4% of the total area and 70.7% corresponded to single-use plastics, with a predominance of Bags. 331 plastic wastes were extracted from the soil, 93.7% were macroplastics, with a predominance of Threads, Others, Wrappers and Bags. The most abundant categories of mesoplastics were Bags, then Threads and Coarse plastics. 73.6% of the plastics extracted from the surface and the macroplastics extracted from the soil were white or transparent, and these occupied a total area of 8090 cm2, with a greater quantity of plastics with areas less than 100 cm2. The meso/macroplastics ratio was 0.07 on the surface and 14.76 in the soil. Macroplastics on the surface would come mainly from flooding of the stream and from inappropriately deposited waste. There would also be an influence of the wind, which could move macroplastics from their entrapment in vegetation towards the water or away from the banks of the stream. Another important process in this case is the burial of plastics in the banks of the stream and their degradation and fragmentation into mesoplastics. The results were analyzed within the framework of local and national regulations, and current legislation regarding the use of single-use plastics in other countries in the region and abroad was presented.

Numerical plastic transport modelling in fluvial systems: Review and formulation of boundary conditions

In recent years, it has become clear that plastic pollution poses a significant threat to aquatic environments and human health. Rivers act as entry points for land-based plastic waste, while a certain fraction of entrained plastics is carried into marine environments. As such, the accurate modelling of plastic transport processes in riverine systems plays a crucial role in developing adequate remediation strategies. In this paper, we review the two main multiphase flow numerical approaches used in plastic transport modelling, comprising Lagrangian Transport Models (LTMs) and Eulerian Transport Models (ETMs). Although LTMs and ETMs can be regarded as complementary and equivalent approaches, LTMs focus on the transport trajectories of individual particles, whereas ETMs represent the behaviour of particles in terms of their mass or volume concentrations. Similar results of the two approaches are expected, while our review shows that plastic transport models are yet to be improved, specifically with respect to the formulation and implementation of boundary conditions, comprising plastic interactions with the channel bed, river bank, and the free surface, as well as interactions with biota. We anticipate that an implementation of these boundary conditions will allow for a better representation of different plastic transport modes, including bed load, suspended load, and surface load. Finally, we provide suggestions for future research directions, including a novel threshold formulation for free surface detachment of plastics, and we hope that this review will inspire the plastic research community, thereby triggering new developments in the rapidly advancing field of numerical plastic transport modelling.

Plastic transport in rivers: Bridging the gap between surface and water column

Rivers act as an important transportation pathway for land-based plastic litter to the ocean. Recently, rivers have also been identified as potential sinks and reservoirs for plastics. Knowledge of plastic transport over different depth profiles in rivers remains limited. In this study, we evaluated the vertical distribution of macro- and mesoplastics, using a larvae net and a trawl net in the river Rhine and its two major branches, i.e. Waal and IJssel. Subsequently, to estimate the relationship between the surface transport of plastic items, i.e., floating items, compared to the transport in deeper layers in the water column, including suspended and bed-transported plastic, an extrapolation factor was derived per day for the middle and bottom nets divided by those found in the surface net. The observed macro- and mesoplastic OSPAR categories collected in different layers in the water column were rather consistent between different sampling techniques. Fragments of soft mesoplastic falling under the category "Plastic film plastics 0-2.5 cm (soft)" were recorded most frequently in the investigated rivers with our monitoring techniques. During larvae net monitoring, hard plastics were more frequently found at the river surface than at the middle or bottom of the river for both macroplastic and mesoplastics, while soft plastics were more frequently detected near the bottom. For larvae net monitoring, the extrapolation factor, reflecting the concentration ratio of macroplastic items transport at different depths, i.e., from the surface downwards to the middle and the bottom ranged between 0.38 to 2.2 and 0.36 to 5.7, respectively. The extrapolation factor of mesoplastic transport from the surface downwards to the middle and the bottom ranged between 0.70 to 1.84 and 0.69 to 2.57. During trawl net monitoring, the extrapolation factor, reflecting the concentration ratio, for macroplastic ranged between 0.82 and 1.30, and for mesoplastic between 0.52 and 1.40. Overall, the findings of this study show that estimates of plastic concentrations solely based on surface transport could result in an under- or overestimation of riverine plastic transport.

Toxicological effects and molecular metabolic of polystyrene nanoplastics on soybean (Glycine max L.): Strengthening defense ability by enhancing secondary metabolisms

Nanoplastics, as emerging pollutants, have attracted worldwide concern for their possible environmental dangers. The ingestion and accumulation of nanoplastics in crops can contaminate the food chain and have unintended consequences for human health. In this study, we revealed the effects of polystyrene nanoplastics (PS-NPs; 80 nm) at different concentrations (0, 10, 100 mg L-1) on soybean (Glycine max L.) seedling growth, antioxidant enzyme system and secondary metabolism. Using laser confocal microscopy, we demonstrated that the absorption and translocation of PS-NPs in soybean. Plant growth inhibition was observed by changes in plant height, root length, and leaf area after 7 days of exposure to PS-NPs. The effect of PS-NPs on photosynthetic characteristics was reflected by a significant reduction in total chlorophyll content at 10 mg L-1. Activation of the antioxidant system was observed with increased malondialdehyde (MDA) content, and elevated activities of superoxide dismutase (SOD) and catalase (CAT). Non-targeted metabolomics analysis identified a total of 159 secondary metabolites, and exposure to 10 and 100 mg L-1 PS-NPs resulted in the production of 61 and 62 differential secondary metabolites. Metabolomics analysis showed that PS-NPs treatment altered the secondary metabolic profile of soybean leaves through the biosynthesis pathways of flavonoid, flavone flavonol, and isoflavones, which is expected to provide new insights into the tolerance mechanisms of plants to nanoplastics. Overall, the results of this study deepen our understanding of the negative impacts of nanoplastics in agricultural systems, which is crucial for assessing the risks of nanoplastics to ecological security.

Field experiment confirms high macroplastic trapping efficiency of wood jams in a mountain river channel

Identifying macroplastic deposition hotspots in rivers is essential for planning cleanup efforts and assessing the risks to aquatic life and the aesthetic value of river landscapes. Recent fieldwork in mountain rivers has shown that wood jams retain significantly more macroplastic than other emergent surfaces within river channels. Here, we experimentally verify these findings by tracking the deposition of 64 PET bottles after 52-65 days of transport in the mid-mountain Skawa River (Polish Carpathians) under low to medium flow conditions. Despite variations in river channel management and the resulting morphological patterns along the study reach, the majority (71.9%, n = 46) of tracked bottles were trapped by wood jams near the low-flow channel. The trapping efficiency was three times higher in the straight, regulated reach (14.8% per km) than in the highly sinuous, unregulated reach (4.5% per km). In the regulated reach, water inundations and wood jams are confined to a narrow zone near the low-flow channel, which may explain the high macroplastic trapping efficiency under low to medium flow conditions. In contrast, in the unmanaged, seminatural reach, where wood jams and water inundation occur over broader areas formed by extensive gravel bars, the trapping potential is lower under similar flow conditions. Previous observations showed that macroplastic deposition hotspots associated with wood jams predominantly form in wide, unmanaged river sections, where numerous jams are inundated during high flows. Our results detail this understanding, suggesting that under low to medium flows, macroplastic hotspots can also form on wood jams in regulated, narrow reaches. These findings suggest that the occurrence of wood jams, channel morphology and past flow conditions are key predictors of macroplastic hotspots formation in mountain rivers.

Macroplastic pollution in riparian corridors of urban and pristine mountain streams in Patagonia (Argentina)

Plastic pollution has garnered much more attention in marine environments, while scientific research on freshwater and terrestrial ecosystems has been relatively overlooked. Numerous studies worldwide have highlighted the presence of macroplastics (>2.5 cm) in mountain riverine environments, revealing that even these seemingly pristine ecosystems are not invulnerable to plastic contamination. We investigated the composition and spatial variation of macroplastic debris in the riparian corridors of nine watercourses in Patagonia. Four types of river reaches were assessed: Reference (without urbanization), Upstream-Urban, Urban, and Downstream-Urban, each with varying degrees of urbanization. We analyzed the intrinsic characteristics of the plastics (manufacture and resin type) and environmental factors with possible incidence in plastic distribution (geomorphology, land use, riparian vegetation quality, and climate) during the Southern Hemisphere's spring season. The most abundant macroplastic debris originated from domestic sources, primarily bags (high- and low-density polyethylene), food wrappers (polypropylene), and beverage bottles (polyethylene terephthalate). The number of inhabitants and proximity to urban areas were the strongest drivers of riverside litter accumulation. Climatic variables such as wind speed and rainfall have incidence in macroplastic abundance, but other factors, such as river discharge possibly played a role in their mobilization. Macroplastics number positively correlated with urban area and negatively with non-woody vegetation. The quality of the riparian corridor, as measured by the QBRp index, had low explanatory power for litter accumulation. Lower QBRp scores were associated with a high number of macroplastic items suggesting that vegetation played a limited role in trapping litter, possibly because urban reaches were heavily anthropized. This study highlights the importance of identifying critical areas of litter accumulation on riverbanks. Our findings provide a foundation for developing strategies to mitigate plastic pollution, improve waste management, and raise public awareness about the challenges of macroplastic contamination and its proper disposal in Patagonia.

Aging of plastics and microplastics in the environment: a review on influencing factors, quantification methods, challenges, and future perspectives

The ubiquitous presence of fragmented plastic particles needs comprehensive understanding of its fate in the environment. The long-term persistence of microplastics (MPs) in the environment is a significant threat to the ecosystem. Even though various degradation mechanisms (physical, chemical, and biological) of commonly used plastics have been demonstrated, quantifying the degradation of MPs over time to predict the consequence of plastic littering and its persistence in the environment remains a challenge. Different advanced analytical techniques have been used to quantify the degradation of MPs by introducing various parameters such as bond indices, crystallinity, and carbon-oxygen ratio. However, a simple and widely accepted reliable methodology for comparing the environmental factors and their influence on the MP degradation has yet to be developed and validated. This paper reviews a section of relevant literature (n = 38) to synthesize an overview of methods implemented for the quantification of fragmentation and aging of MPs in natural and artificial environment. In addition, the inherent weakness and extrinsic factors affecting the degradation of MPs in the environment is discussed. Finally, it proposes challenges and future scope as guideline for research on MP degradation in the environment.

Quantification, characterization, and source identification of macro- and mesoplastics in the water column of Rivers Sabaki and Tana

Five sampling campaigns were conducted in the water columns of River Sabaki and Tana in Kenya, Between October 2021 and January 2023, covering a 1-year cycle, at four sites in River Sabaki (2.5 km, 3.05 km, 3.51 km, and 4.52 km) and River Tana (1.5 km, 1.8 km, 2.0 km, and 2.5 km) distant from the river mouth. The ebb and flood tides were sampled to calculate net plastic litter fluxes. Two 6350-µm seine nets were deployed in two replicates per sampling point. Factor and cluster analysis were used to investigate plastic litter sources for both rivers. The influences of rainfall on plastic abundance and mass were explored using permutational linear models. A total of 15,318 plastic litter items weighing 1.37 kg were recorded in River Sabaki, and 3741 plastic litter items weighing 0.95 kg in River Tana. The top ten captured plastic litter types sorted by abundance and mass were mostly plastic fragments. The annual net plastic litter flux to the ocean through River Sabaki amounted to 1,277,120.63 items year-1 by abundance and 22.30 kg year-1 by mass. For River Tana, the same fluxes were 207,550.76 items year-1, and 28.09 kg year-1, respectively. In River Sabaki, significant impacts of rainfall on plastic abundance and mass were found. River Sabaki's pollution sources included upstream reaches, fishing activities, and littering by locals and tourists. River Tana's major pollution sources were illegal dumpsites, littering, fishing, and recreational activities. This research can guide combat plastic pollution in the rivers and ultimately the ocean.

First attempt to measure macroplastic fragmentation in rivers

Direct field measurements of macroplastic fragmentation during its transport in rivers are currently unavailable, and there is no established method to perform them. Previous studies have showed that macroplastic fragmentation results in the production of harmful microplastics, and river channels can be hotspots for this process. Therefore, obtaining information about this process is crucial for quantifying the production of secondary microplastics in rivers and assessing the related risks for riverine biota and human health. Here, we propose a simple low-cost methodology for quantifying riverine macroplastic fragmentation by conducting repeated measurements of the mass of tagged macroplastic items before and after their transport in the river. As a proof-of-concept for this method, we conducted a 52-65 day experiment that allowed us to measure a median fragmentation rate of 0.044 ± 0.012 g for 1-liter PET bottles during their transport at low to medium flow in the middle mountain Skawa River in the Polish Carpathians. Using the obtained data (n = 42), we extrapolated that during low to medium flows, the median yearly mass loss of PET bottles in the study section is 0.26 ± 0.012 g/year (0.78 ± 0.036 % of bottle mass), and the median rate of bottle surface degradation is 3.13 ± 0.14 μm/year. These estimates suggest a relatively high fragmentation rate for a PET bottle in a mountain river even under low to medium flow conditions without high-energy transport. We discuss how our simple and relatively low-cost methodology can be flexibly adapted and future optimized to quantify macroplastic fragmentation in various types of rivers and their compartments, informing future mitigation efforts about the rates of formation and dispersion of secondary microplastics.

Effectiveness of Sampling Techniques in Collecting the Polyp Stage of the Invasive Freshwater Hydrozoan Craspedacusta sowerbii

Current sampling methods for detecting the presence of the invasive freshwater hydrozoan Craspedacusta sowerbii rely mainly on visual confirmation of the medusa stage. Confirming the presence of the polyp stage is equally important for observing medusae since typical late summer/early fall occurrences or observations of medusae are sporadic though are becoming more frequent. The polyp stage is important as it is the organism's primary stage and is present throughout the year depending on water temperatures. Therefore, sampling methods for the polyp stage are, commonly, the collection of substrates such as rocks, plants, or pieces of wood in a given body of water, and these can be cumbersome to examine. Polyps are also small, transparent, and difficult to see on natural substrates. Based on a preliminary culturing of the polyp stage on glass and plastic microscope slides in the laboratory, we designed a sampling methodology based on submerging four substrate types (glass and plastic microscope slides, Hester-Dendy discs, and small glass Petri dishes) to confirm the presence of C. sowerbii polyps in the field. We tested this method in three lakes in the Illinois-Indiana region (USA). Two of the lakes have recorded sightings of medusae but the third has no record of polyps or medusae. The sampling method we designed was effective in that C. sowerbii polyps were found on both plastic and glass slides. While this method can be sufficient for detection of the polyp stage, it also shows potential for improvement; we highlight abiotic and biotic ecological parameters as significant factors influencing the collection of C. sowerbii polyps to be considered for future methodologies.

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.