Leaving a plastic legacy: Current and future scenarios for mismanaged plastic waste in rivers

Increased assimilation efficiency and mortality rate in Gammarus fossarum exposed to PVC microplastics

Shredder organisms play a key role in rivers by feeding and fragmenting coarse organic matter that will then be exploited by other consumers. The effects of microplastics (MPs) on Gammarus sp., an ubiquitous genus of freshwater amphipods, and its shredding activity have been broadly investigated. However, the potential behavioral and physiological effects of different sizes of MPs on Gammarus sp. remain overlooked despite the recognized influence of MP size on MP toxicity. This study investigated the effects of a 28-day exposure to four different concentrations of two size fractions of PVC-microplastics (PVC-MPs), on Gammarus fossarum mortality rate, feeding rate, assimilation efficiency, and expression of proteins involved in key processes. Increased mortality was observed for all treatments exposed to PVC-MPs, with higher mortality in the presence of smaller PVC-MPs at the highest concentration. No protein biomarker modulation was observed in presence of PVC-MPs, suggesting that no metabolic stress but direct physical damages of PVC-MPs might have led to the observed mortalities. No difference was observed for feeding rates, but a higher assimilation efficiency was measured for individuals exposed to PVC-MPs, regardless of the concentration. This could be due to energy reallocation towards defense mechanisms or indicate a potential shift in digestive microbiota. This study highlighted the toxicity of PVC-MPs, particularly of smaller sizes and even at relatively low concentration, for Gammarus fossarum. PVC-MP pollution may therefore alter the functional integrity of river ecosystems by reducing the abundance of shredder organisms and, subsequently, the process of leaf litter decomposition.

Assessment of environmental and socioeconomic drivers of urban stormwater microplastics using machine learning

Microplastics (MPs) are ubiquitous environmental contaminants with urban landscapes as major source areas of MPs and stormwater runoff as an important transport pathway to receiving aquatic environments. To better delineate the drivers of urban stormwater MP loads, we created a global dataset of stormwater MP concentrations extracted from 107 stormwater catchments (SWCs). Using this dataset, we trained and tested three optimized gradient boosting Machine Learning (ML) models. Twenty hydrometeorological and socioeconomic variables, as well as the MP size definitions considered in the individual SWCs, were included as potential predictors of the observed MP concentrations. CatBoost emerged as the best-performing ML model. Shapley additive explanations revealed that features related to hydrometeorological conditions, watershed characteristics and human activity, and plastic waste management practices contributed 34, 25, and 4.8%, respectively, to the model's predictive performance. The MP size definition, that is, the lower size limit and the width of the size range, accounted for the remaining 36% variability in the predicted MP concentrations. The lack of a consistent definition of the MP size range among studies therefore represents a major source of uncertainty in the comparative analysis of urban stormwater MP concentrations. The proposed ML modeling approach can generate first estimates of MP concentrations in urban stormwater when data are sparse and serve as a quantitative tool for benchmarking the added value of including further data layers and applying uniform definitions of size classes of environmental MPs.

Micro- and mesoplastic pollution in the surface water and nekton from the eastern Indian ocean: Spatiotemporal variation, correlation and risk assessment

The pollution of micro- and mesoplastic (MMP) in the Eastern Indian Ocean (EIO) remains poorly understood. The present study revealed that MMP abundance in nekton from EIO in 2022 (mean: 2.30 ± 0.39 items individual-1 and 1.81 ± 0.54 items g-1) was significantly higher than that in 2021 (mean: 1.60 ± 0.22 items individual-1 and 0.80 ± 0.13 items g-1). In contrast, MMP abundance in surface water varied insignificantly between 2021 (mean: 0.04 ± 0.01 items m-3) and 2022 (mean: 0.05 ± 0.02 items m-3). The rise in predominant polymers-polypropylene (PP), rayon (RA), and polyester (PES)-in nekton from 2021 to 2022 may suggest increased pollution from face masks and home textiles along coastal regions. Notable spatial variation in PP and RA between the northeastern and southeastern regions was observed only in nekton, suggesting they are better indicators of MMP spatiotemporal variation than surface water. Shadow driftfish ingested more MMPs than purpleback flying squid and mackerel scad, likely due to its deeper habitat. By simultaneously considering color, composition, and shape, integrated MMP analysis showed insignificant correlation between MMP pollution in surface water and nekton, suggesting that nekton may ingest MMPs through multiple pathways beyond surface water. Risk indices for surface water and nekton reached moderate to upper levels globally, emphasizing the need for continued monitoring in the EIO. Epoxy resin, rubber, and PP + acrylic were identified as the most hazardous polymers, providing a valuable basis for developing effective strategies to mitigate plastic pollution.

Elbay A, El-Maghrabi N, Fawzy M. From Waste to Worth: Upcycling Plastic into High-Value Carbon-Based Nanomaterials

Plastic waste (PW) presents a significant environmental challenge due to its persistent accumulation and harmful effects on ecosystems. According to the United Nations Environment Program (UNEP), global plastic production in 2024 is estimated to reach approximately 500 million tons. Without effective intervention, most of this plastic is expected to become waste, potentially resulting in billions of tons of accumulated PW by 2060. This study explores innovative approaches to convert PW into high-value carbon nanomaterials (CNMs) such as graphene, carbon nanotubes (CNTs), and other advanced carbon structures. Various methods including pyrolysis, arc discharge, catalytic degradation, and laser ablation have been investigated in transforming PW into CNMs. However, four primary methodologies are discussed herein: thermal decomposition, chemical vapor deposition (CVD), flash joule heating (FJH), and stepwise conversion. The scalability of the pathways discussed for industrial applications varies significantly. Thermal decomposition, particularly pyrolysis, is highly scalable due to its straightforward setup and cost-effective operation, making it suitable for large-scale waste processing plants. It also produces fuel byproducts that can be used as an alternative energy source, promoting the concept of energy recovery and circular economy. CVD, while producing high-quality carbon materials, is less scalable due to the high cost and required complex equipment, catalyst, high temperature, and pressure, which limits its use to specialized applications. FJH offers rapid synthesis of high-quality graphene using an economically viable technique that can also generate valuable products such as green hydrogen, carbon oligomers, and light hydrocarbons. However, it still requires optimization for industrial throughput. Stepwise conversion, involving multiple stages, can be challenging to scale due to higher operational complexity and cost, but it offers precise control over material properties for niche applications. This research demonstrates the growing potential of upcycling PW into valuable materials that align with global sustainability goals including industry, innovation, and infrastructure (Goal 9), sustainable cities and communities (Goal 11), and responsible consumption and production (Goal 12). The findings underscore the need for enhanced recycling infrastructure and policy frameworks to support the shift toward a circular economy and mitigate the global plastic crisis.

Pathways to reduce global plastic waste mismanagement and greenhouse gas emissions by 2050

Plastic production and plastic pollution have a negative effect on our environment, environmental justice, and climate change. Using detailed global and regional plastics datasets coupled with socioeconomic data, we employ machine learning to predict that, without intervention, annual mismanaged plastic waste will nearly double to 121 million metric tonnes (Mt) [100 to 139 Mt 95% confidence interval] by 2050. Annual greenhouse gas emissions from the plastic system are projected to grow by 37% to 3.35 billion tonnes CO2 equivalent (3.09 to 3.54) over the same period. The United Nations plastic pollution treaty presents an opportunity to reshape these outcomes. We simulate eight candidate treaty policies and find that just four could together reduce mismanaged plastic waste by 91% (86 to 98%) and gross plastic-related greenhouse gas emissions by one-third.

Plastic pollution and human pathogens: Towards a conceptual shift in risk management at bathing water and beach environments

Emerging evidence indicates that micro- and macro-plastics present in water can support a diverse microbial community, including potential human pathogens (e.g., bacteria, viruses). This interaction raises important concerns surrounding the role and suitability of current bathing water regulations and associated pathogen exposure risk within beach environments. In response to this, we critically evaluated the available evidence on plastic-pathogen interactions and identified major gaps in knowledge. This review highlighted the need for a conceptual shift in risk management at public beaches recognising: (i) interconnected environmental risks, e.g., associations between microbial compliance parameters, potential pathogens and both contemporary and legacy plastic pollution; and (ii) an appreciation of risk of exposure to plastic co-pollutants for both water and waterside users. We present a decision-making framework to identify options to manage plastic-associated pathogen risks alongside short- and longer-term research priorities. This advance will help deliver improvements in managing plastic-associated pathogen risk, acknowledging that human exposure potential is not limited to only those who engage in water-based activity. We argue that adopting these recommendations will help create an integrated approach to managing and reducing human exposure to pathogens at bathing, recreational water and beach environments.

Ceratophyllum demersum alleviates microplastics uptake and physiological stress responses in aquatic organisms, an overlooked ability

It has been demonstrated that microplastics (MPs) may be inadvertently ingested by aquatic animals, causing harm to their physiological functions and potentially entering the food chain, thereby posing risks to human food safety. To achieve an environmentally friendly and efficient reduction of MPs in freshwater environments, this experiment investigates the depuration effect of C. demersum on MPs using three common aquatic animals: Macrobrachium nipponense, Corbicula fluminea, and Bellamya aeruginosa as research subjects. The amounts of MPs, digestive enzyme activity, oxidative stress index, and energy metabolism enzyme activity in the digestive and non-digestive systems of three aquatic animals were measured on exposure days 1, 3, and 7 and on depuration days 1 and 3. The results indicated that the depuration effect of C. demersum and the species interaction were significant for the whole individual. Concerning digestive tissue, C. demersum was the most effective in purifying B. aeruginosa. When subjected to short-term exposure to MPs, C. demersum displayed a superior depuration effect. Among non-digestive tissues, C. demersum exhibited the earliest purifying effect on C. fluminea. Additionally, C. demersum alleviated physiological responses caused by MPs. In conclusion, this study underscores C. demersum as a promising new method for removing MPs from aquatic organisms.

Snapshot Sampling May Not Be Enough to Obtain Robust Estimates for Riverine Microplastic Loads

Wastewater treatment plants (WWTPs) have been described as key contributors of microplastics (MPs) to aquatic systems, yet temporal fluctuations in MP concentrations and loads downstream are underexplored. This study investigated how different sampling frequencies (hourly, weekly, and monthly) affect MP estimates in a stream linked to a single WWTP. Utilizing fluorescence microscopy and Raman spectroscopy, considerable hourly variations in MP concentrations were discovered, while the polymer composition remained consistent. This temporal variability in MP loads was influenced by MP concentration, discharge rates, or a mix of both. These results show a high uncertainty, as relying on sparse snapshot samples combined with annual discharge data led to significant uncertainties in MP load estimates (over- and/or underestimation of emissions by 3.8 billion MPs annually at this site). Our findings stress the necessity of higher-frequency sampling for better comprehending the hydrodynamic factors influencing MP transport. This improved understanding enables a more accurate quantification of MP dynamics, crucial for downstream impact assessments. Therefore, preliminary reconnaissance campaigns are essential for designing extended, representative site-monitoring programs and ensuring more precise trend predictions on a larger scale.

Time-varying microplastic contributions of a large urban and industrial area to river sediments

The quantification of microplastic (MP) pollution in rivers is often constrained by a lack of historical data on a multi-decadal scale, which hinders the evaluation of public policies. In this study, MP contents and trends were analyzed in dated sediment cores sampled upstream and downstream of a large metropolis, in environmental deposits that exhibited consistent sedimentation patterns from the 1980s to 2021. After a thorough sedimentological analysis, MPs were quantified in samples by micro Fourier Transform InfraRed spectroscopy (μFTIR imaging) and a density separation and organic matter digestion procedure. Microplastics recorded in the upstream core are relatively ubiquitous all along the dated sequence. The results also confirmed a sever increase of microplastics levels in the downstream core, by one order of magnitude, and an increase of polymer types. Polypropylene, polyethylene, and polystyrene represent ubiquitous contamination and were predominant at the two stations, whereas polyvinyl chloride and polytetrafluoroethylene were suspected to be abundant at the downstream station, but were not detected at the upstream station. Their presence could be linked to local contamination from specific industrial sources that manufactured and utilized these polymers. Surprisingly, in the downstream station sediment has recorded a relative improvement in polymers associated with industrial sources since the 2000s and, to a lesser extent, for ubiquitous ones since the 2010s. This trend of mitigation diverges from that of global assessments, that assume uncontrolled MP pollution, and suggest that European Union wastewater policy and regulation on industrial discharges have positively influenced water quality, and certainly also on MPs. However, the accumulation of microplastics remains high in recent deposits and raises the emerging concern of the long-term management of these reservoirs.

Microplastics in packaged water, community stored water, groundwater, and surface water in rivers of Tamil Nadu after the COVID-19 pandemic outbreak

The increased load of plastic in waste streams after the COVID-19 pandemic outbreak has increased the possibility of microplastics (MPs) contamination channelling through the rivers and infiltrating the aquatic ecosystems. MPs in packaged water, community-stored water, groundwater, and surface water of Kaveri River (KR), Thamirabarani River (TR), Adyar River (AR), and Cooum River (CR) in Tamil Nadu were therefore investigated about 2 years after the COVID-19 pandemic outbreak. Using μFTIR and μRaman spectroscopy, polyamide, polypropylene, polyethylene, ethylene vinyl alcohol copolymer resin, and polyvinyl chloride were identified as the primary polymer types. The average number of MPs was 2.15 ± 1.9 MP/L, 1.1 ± 0.99 MP/L, 5.25 ± 1.15 MP/L, and 4 ± 2.65 MP/L in KR, TR, AR, and CR, respectively, and 1.75 ± 1.26 MP/L in groundwater, and 2.33 ± 1.52 MP/L in community stored water. Only LDPE was detected in recycled plastic-made drinking water bottles. More than 50% of MPs were found to be of size less than 1 mm, with fibrous MPs being the prevalent type, and a notable prevalence of blue-coloured microplastics in all the sample types. The Pollution Load Index (PLI) was >1 in all the rivers. Toxicity rating based on the polymer risk index (PORI) categorized AR and TR at medium risk (category II), compared to KR and CR at considerable risk (category III). Overall pollution risk index (PRI) followed a decreasing trend with CR > AR > KR > TR of considerable to low-risk category. Ecological risk assessment indicates a negligible risk to freshwater biota, except for four sites in the middle and lower stretches of Adyar River (AR - 2, AR - 4) and upper and lower stretches of Cooum River (CR - 1, CR - 3), located adjacent to direct sewer outlets, and one location in the lower stretch of Kaveri River (KR - 9), known for fishing and tourist activities.

Plastic litter colonization in a brackish water environment

Transitional waters, including coastal ponds, represent unique environments. These distinct ecosystems are often among the most severely polluted systems due to intensive human activities. Our study marks the first evaluation of aquatic invertebrates associated with plastic litter in two brackish ponds. We collected 43 items of plastic litter (including bottles and disposable plastics) during the winter and spring of 2022. Most of plastic litter (76.8 %) was colonized by aquatic invertebrates. A total of 495 individuals were observed on the plastic litter, with the number of individuals ranging from 1 to 54 (average = 13.4). The most abundant taxa were from the families Gammaridae, Serpulidae, and Sphaeromatidae. Invertebrates colonized both the external and internal surfaces of the plastic bottles. Plastic bottles trapped 25 % of the total biota. The internal entrapped taxa were mainly represented by gammarids, molluscs egg mass, and sphaeromatids. Open bottles could potentially serve as temporary or permanent traps for invertebrates colonizing their internal surfaces. We argue that the dispersal of species driven by plastics is possible but limited, just as water exchanges with the seas are limited. These brackish lakes could be transit areas, but more importantly, they could be hotspots for plastic litter.

Inter-event and intra-event dynamics of microplastic emissions in an urban river during rainfall episodes

Urban rivers represent the major conduits for land-sourced microplastics in the global oceans, yet the real-time dynamics of their emissions in rivers during rainfall (and runoff) events are poorly understood. Herein, we report the results of high-frequency sampling of microplastic particles (MPs) and fibers (MPFs) in the surface water of an urban river in Japan over the course of three rainfall events (i.e., light, moderate, and heavy rainfalls). The event mean concentrations (EMCs) of MPs amounted to 35,000 items/m3, 929,000 items/m3, and 331,000 items/m3; and the corresponding total loads were 0.5 kg, 19.8 kg, and 35.0 kg for light, moderate and heavy rainfalls, respectively. The inter-event total loads of MPs correlate well with the total rainfall, while the concentrations were linked with the number of antecedent dry days. The dynamic trends show that <2000 μm MPs displayed first flush effects during light to moderate rainfall events (>50% mass discharged with the initial 20-40% of flow). Small-sized MPs (10-40 μm) mobilized rapidly at lower rainfall intensities, whereas MPs over 2000 μm discharged immediately after the peak rainfall intensity. Moreover, <70 μm MPs depicted a surge following heavy rainfall events due to turbulent flow conditions reverting the deposited MPs into suspension. Overall, the three events increased the loads by 4-110 folds, and EMCs by 10-350 folds compared to the concentrations during dry weather while portraying a significant impact on 300-1000 μm MPs. The dynamics of MPs were correlated with those of suspended solids in river water, and the characteristics were comparable to the same of road dust sampled in Japan. Although the dynamic trends between MPs and MPFs in river water were comparable, MPFs were relatively less impacted by rain, likely due to the intervention of separate sewer systems in the study area.

A recipe for plastic: Expert insights on plastic additives in the marine environment

The production and consumption of plastic products had been steadily increasing over the years, leading to more plastic waste entering the environment. Plastic pollution is ubiquitous and comes in many types and forms. To enhance or modify their properties, chemical additives are added to plastic items during manufacturing. The presence and leakage of these additives, from managed and mismanaged plastic waste, into the environment are of growing concern. In this study, we gauged, via an online questionnaire, expert knowledge on the use, characteristics, monitoring and risks of plastic additives to the marine environment. We analysed the survey results against actual data to identify and prioritise risks and gaps. Participants also highlighted key factors for future consideration, including gaining a deeper understanding of the use and types of plastic additives, how they leach throughout the entire lifecycle, their toxicity, and the safety of alternative options. More extensive chemical regulation and an evaluation of the essentiality of their use should also be considered.